2015 was the best year ever for Marmorkrebs research

Back at the close of 2010, I made a prediction: that 2015 would see fourteen papers published on Marmorkrebs. How did I do? Here’s this blog’s traditional annual publication graph:

Coming into this last week of the year, I was worried, but a last minute publication helped me shame Nostradamus.

Being an academic, I must now add the caveats and qualifiers about my nailing it.

For this annual graph, I normally count peer reviewed journal articles and book chapters published during the year. But this year, there were a few new wrinkles. There were a bunch of book chapters in Freshwater Crayfish: A Global Overview that were published this year, but the book consistently gives its publication date as 2016 throughout. So I left those out, meaning we have a good head start on 2016 publications. I also left out a pre-print that came out later as a paper (no double dipping!) and some conference abstracts.

Not only were there more Marmorkrebs papers than ever, there was several notable ones.

We had two independent confirmations that Marmorkrebs were triploid organisms (one published, one in press), with one of the highest chromosome counts in the animal kingdom.

There was the first Marmorkrebs paper from a Japanese lab, with some interesting research on masculinizing Marmorkrebs.

There were several papers on the spread and risk assessment of Marmorkrebs and their prospects as disease vectors.

And there was the proposal that Marmorkrebs be given a new species name, Procambarus virginalis. I’ll be watching this one with interest to see if the community adopts the suggested new name. This is why I like “Marmorkrebs” as an informal name for these crayfish: it stays intact when formal taxonomic names change!

I’m feeling emboldened by this year’s successful prediction. But back in 2010, I also predicted there will be twenty papers in 2020. One should always revise predictions in the light of new data, however. Now that there are five more data points, the prediction machine (also known as a simple linear fit to the data) estimates that there will be sixteen Marmorkrebs papers published in 2020.

Place your bets, and I’ll meet you here in five years to find out.

Related posts

2008 was the best year ever for Marmorkrebs research
2009 was tied for the best year ever in Marmorkrebs research
2010 was the best year ever for Marmorkrebs research
2011 was not the best year ever for Marmorkrebs research
2012 was an average year for Marmorkrebs research
2013 was the second best year ever for Marmorkrebs research
2014 was a good year for Marmorkrebs research

Vogt, 2015b

Vogt G. 2015. Bimodal annual reproduction pattern in laboratory-reared marbled crayfish. Invertebrate Reproduction & Development 59(4): 218-223. http://dx.doi.org/10.1080/07924259.2015.1089329

Abstract

The marbled crayfish, Procambarus fallax f. virginalis, is a new research model and potent invader of aquatic ecosystems that reproduces by obligatory parthenogenesis. My data show that in captivity, it can reproduce throughout the year. However, when kept at constant 20 °C and natural photoperiod there were two prominent spawning maxima, one before the spring equinox and another one before the fall equinox. If temperature fluctuated between ~15 °C in winter and ~25 °C in summer, the first maximum was shifted beyond the spring equinox and the second maximum was shifted closer towards the fall equinox. These results indicate a bimodal annual rhythm for the reproduction in marbled crayfish that can be modulated by temperature. Comparison with P. fallax suggests that this rhythmicity was inherited from its sexually reproducing mother species. Potential consequences of my laboratory findings for wild populations of marbled crayfish in temperate and tropical regions are discussed. Since marbled crayfish can be kept in captivity for up to four years under a broad range of conditions, they offer the possibility to investigate endogenous circannual rhythms and their entrainment by environmental zeitgebers in decapod crustaceans.

Keywords: Marmorkrebs • Procambarus fallax • Decapoda • reproduction • circannual rhythm • zeitgeber

The gamete record holder?

In a fun new review paper on the extremes of crustacean reproduction, Vogt writes (lightly edited):

The record in chromosome number in animals is hold by the freshwater crayfish Pacifastacus leniusculus trowbridgii with a diploid set of 376 chromosomes, corresponding to a chromosome number of 188 in the gametes (Niiyama, 1962). The second highest chromosome number was recently found in the triploid crayfish Procambarus virginalis (3n=276) (Martin et al., 2015). ... It reproduces by apomictic parthenogenesis, i. e. without meiosis, and therefore, the eggs should include 276 chromosomes as well, making Procambarus virginalis the new animal world record holder with respect to chromosome number of gametes.

I am not sure whether I would call the new egg of a Marmorkrebs a “gamete” or not. A quick look through a few (admittedly non-technical) dictionaries usually define gametes as cells that must join with other cells to create a viable embryo. A Marmorkrebs egg doesn’t meet that definition. A first-stage Marmorkrebs egg is probably better compared to a zygote in most diploid organisms than a gamete.

Still, common parlance calls the Marmorkrebs egg... well... an egg. And eggs are gametes.

As so often happens, life overflows the dikes erected by the schools. – Mario Bunge, Intuition and Science

Still, the high chromosome numbers of these crayfish species are fascinating, quibbles over categories notwithstanding.

Reference

Vogt G. 2015. Structural specialities, curiosities and record-breaking features of crustacean reproduction. bioRxiv. http://dx.doi.org/10.1101/034223

Pic of the moment: 14 December 2015

Exactly five years ago, I posted some word clouds made up of abstracts of Marmorkrebs papers. It’s long past time for an update!

This word cloud was made of the abstracts of Marmorkrebs papers from 2011 to 2015. Perhaps the biggest change from the earlier word clouds is that the genus name Procambarus is now reasonably large, with the specific name virginalis also appearing, albeit a bit smaller than the genus.

And just for fun, here’s an alternate version:

Related posts

Pic of the moment: 14 December 2010

#Marmorkrebs #NoFilter

Here’s a collection of Marmorkrebs pics on popular social media site Instagram. I like scrolling through these pics, because it’s interesting to see the variation in colours or people’s crayfish. But as I’ve written before, make no mistake: if these are Marmorkrebs, their colour is diet and condition dependent. Their offspring won’t necessarily have that colour unless their conditions are similar.

Related posts

The curious case of crustacean colours

Vogt, 2014

Vogt G. 2014. Life span, early life stage protection, mortality and senescence in freshwater Decapoda. In: Yeo DCJ, Cumberlidge N, Klaus S (eds.), Advances in Freshwater Decapod Systematics and Biology (Crustaceana Monographs 19), pp. 17-51. Brill: Leiden. http://www.brill.com/products/book/advances-freshwater-decapod-systematics-and-biology

Abstract

This article review the present knowledge on ageing and longevity in the freshwater Decapoda and examines the impact of abbreviated development and postembryonic brood care, two major adaptations to fresh water, on life expectancy. Life span data are available for only 4% of freshwater decapods. Reliably determined maximum life spans in freshwater shrimps, crayfish, crabs, and aeglids vary from 8 months to 38 years and may be underestimated in slow-growing species. Decapods that live at high latitudes and high altitudes tend to live longer, which may reflect life history adaptations to cool water temperatures. Particularly long-lived species are found among crayfish and in subterranean habitats. Abbreviated and direct development and postembryonic brood care reduce mortality of the early life stages of freshwater decapods and are associated with an increase of individual life expectancy but the longevity of freshwater decapod species is not extended when compared to marine decapods. Long-lived freshwater decapods maintain structural and functional integrity into old age and possess several effective anti-ageing mechanisms including life-long stem cell activity. The most obvious anti-ageing mechanisms are moulting and the regeneration of damaged appendages, both of which obviate mechanical senescence. Some species of freshwater decapods are suitable models for the investigation of general topics of biogerontology.

Keywords: None provided.

Veselý and colleagues, 2015

Veselý L, Buřič M, Kouba A. 2015. Hardy exotics species in temperate zone: can “warm water” crayfish invaders establish regardless of low temperatures? Scientific Reports 5: 16340. http://dx.doi.org/10.1038/srep16340

Abstract

The spreading of new crayfish species poses a serious risk for freshwater ecosystems; because they are omnivores they influence more than one level in the trophic chain and they represent a significant part of the benthic biomass. Both the environmental change through global warming and the expansion of the pet trade increase the possibilities of their spreading. We investigated the potential of four “warm water” highly invasive crayfish species to overwinter in the temperate zone, so as to predict whether these species pose a risk for European freshwaters. We used 15 specimens of each of the following species: the red swamp crayfish (Procambarus clarkii), the marbled crayfish (Procambarus fallax f. virginalis), the yabby (Cherax destructor), and the redclaw (Cherax quadricarinatus). Specimens were acclimatized and kept for 6.5 months at temperatures simulating the winter temperature regime of European temperate zone lentic ecosystems. We conclude that the red swamp crayfish, marbled crayfish and yabby have the ability to withstand low winter temperatures relevant for lentic habitats in the European temperate zone, making them a serious invasive threat to freshwater ecosystems.

Keywords: ecology • invasive species

Funkhauser, 2014

Funkhouser M. 2014. The toxicological effects of perfluorooctane sulfonate (PFOS) on a freshwater gastropod, Physa pomilia, and a parthenogenetic decapod, Procambarus fallax f. virginalis. Master's thesis, Environmental Toxicology, Texas Tech University. 102 pp. http://hdl.handle.net/2346/58533

Abstract

Perfluorinated compounds (PFCs) are a class of synthetic chemicals that have recently become of increased interest and concern due to their ability to biomagnify through food webs. Perfluorinated compounds, in general, are persistent in the environment and some are carcinogenic. One specific PFC, perflurooctane sulfonate (PFOS), has gained increased attention because it is slightly toxic to aquatic organisms and has been detected in tissues of a wide variety of animals from all over the world including remote species such as polar bears. Like other PFCs, PFOS is highly resistant to chemical, biological, and thermal breakdown, and has high water solubility and low volatility; all of which indicate that PFOS can be both mobile and persistent in the environment. Like many PFAAs, PFOS was a key ingredient in Aqueous Film Forming Foams (AFFF) to fight hydrocarbon-fueled fires on fire-fighting training facilities common to airports and air force bases. Despite the fact that PFCs like PFOS have been detected in many habitats, the fate, biotransport mechanism, and overall ecotoxicology of PFCs are highly uncertain. While there are some data on environmental concentrations and toxicity to organisms, there is a general lack of toxicity data for many aquatic taxa. Despite initial heavy use on U.S. Air Force Bases, there is now growing concern of PFCs as they emerge as important contaminants on a global scale, especially at Barksdale Air Force Base (BAFB) in Shreveport, Louisiana. Of particular concern is whether PFCs from BAFB have now entered surface water and, if so, whether concentrations are high enough to potentially cause human or ecological effects. The research presented here is part of a larger project to develop and implement a comprehensive approach for characterizing PFC contamination and estimating potential human and ecological risk focused on BAFB. The specific research presented here focused on further characterizing the toxicity of PFOS to several aquatic organisms, which represent taxa observed at BAFB. The goal was to determine dose-response relationships as well as species sensitivity to PFOS to ultimately support upcoming environmental risk assessments. Specifically, we conducted acute and chronic (full life cycle) toxicity tests to a model freshwater gastropod (Physa pomilia) and acute and sub-chronic toxicity tests to a new model organism, the marbled crayfish. Physa pomilia are excellent laboratory organisms and can make up a large portion of biomass in the aquatic ecosystem. Like many freshwater gastropods, this species can be readily collected from local habitats, has a short generation time, and is relatively easy to culture in the lab. We conducted several experiments to characterize toxicity of PFOS to P. pomilia including (1) a 96-hour acute toxicity study on adults, (2) a sub-chronic toxicity study on adults, (3) a full-life cycle study, and (4) a behavioral assay. Next, we characterized PFOS toxicity to the marbled crayfish, Procambarus fallax f. virginalis, which is a subspecies of Procambarus fallax. The marmorkreb (sic) is unique because it is the first known parthenogenetic decapod; offspring produced by individuals are genetically identical. To determine PFOS toxicity to the marmorkreb (sic) we conducted several studies that included (1) an acute juvenile study, (2) a sub-chronic juvenile study, and (3) a juvenile study in which animals were raised under two different densities. The last study was performed because the role of social interaction among crayfish is important due to their display of aggression toward conspecifics. The specific goals for this laboratory project on Physa pomilia and Procambarus fallax f. virginalis were to characterize the ecotoxicity of PFOS in two species that represent environmentally relevant taxa. Because the overall toxicity of PFOS varies considerably among taxa, our hope was to add toxicity data that could then be used to build an updated species sensitivity distribution (SSD) to inform future ecological risk assessments.

Keywords: None provided.

Vogt and colleagues, 2015b

Vogt G, Falckenhayn C, Schrimpf A, Schmid K, Hanna K, Panteleit J, Helm M, Schulz R, Lyko F. 2015. The marbled crayfish as a paradigm for saltational speciation by autopolyploidy and parthenogenesis in animals. Biology Open 4(11): 1583-1594. http://dx.doi.org/10.1242/bio.014241

Abstract

The parthenogenetic all-female marbled crayfish is a novel research model and potent invader of freshwater ecosystems. It is a triploid descendant of the sexually reproducing slough crayfish, Procambarus fallax, but its taxonomic status has remained unsettled. By cross-breeding experiments and parentage analysis we show here that marbled crayfish and P. fallax are reproductively separated. Both crayfish copulate readily, suggesting that the reproductive barrier is set at the cytogenetic rather than the behavioural level. Analysis of complete mitochondrial genomes of marbled crayfish from laboratory lineages and wild populations demonstrates genetic identity and indicates a single origin. Flow cytometric comparison of DNA contents of haemocytes and analysis of nuclear microsatellite loci confirm triploidy and suggest autopolyploidisation as its cause. Global DNA methylation is significantly reduced in marbled crayfish implying the involvement of molecular epigenetic mechanisms in its origination. Morphologically, both crayfish are very similar but growth and fecundity are considerably larger in marbled crayfish, making it a different animal with superior fitness. These data and the high probability of a divergent future evolution of the marbled crayfish and P. fallax clusters suggest that marbled crayfish should be considered as an independent asexual species. Our findings also establish the P. fallax–marbled crayfish pair as a novel paradigm for rare chromosomal speciation by autopolyploidy and parthenogenesis in animals and for saltational evolution in general.

Keywords: marbled crayfish • autopolyploidy • parthenogenesis • epigenetics • chromosomal speciation • saltational evolution

Note: This is the final version of record of this paper, which was previously available as a pre-print.

“Millions of animals from a single specimen”

The forthcoming Biology Open paper on the speciation of Marmorkrebs continues to attract attention, with a very nice article on Medical XPress. It focuses on the prospects of using Marmorkrebs to study epigenetics, but includes the basic biology too:

Günter Vogt, a zoologist at Heidelberg University suggested that the DKFZ scientists take a look at the freshwater marbled crayfish which has now spread worldwide. In Madagascar, it reproduces so quickly that it poses a threat not just ecologically but also economically as the animals destroy rice crops. Marbled crayfish also occur in the lakes of southern Germany as well as in Sweden and Japan and are now even readily available in most aquarium and pet stores.

“As there are only females, I suspected that these crayfish might reproduce by cloning. If so, then these animals should all have identical DNA and the large variety in appearance and behaviour might be based entirely on epigenetic causes.”

Lyko was curious and started looking at these animals in the lab which confirmed the assumption. “We examined the DNA of 4 animals and found that they were completely identical, we did not detect a single genetic difference. The marbled crayfish is indeed a clone - millions of animals derive from a single original specimen.”

Cover girl

Look down in the lower left corner!

Marmorkrebs are featured on the cover, and will likely feature repeatedly in this forthcoming book. The table of contents lists a section titled, “Parthenogenesis. Obligatory and facultative. Cyclic. Geographic.”

Hat tip to Günter Vogt.

External links

Reproduction and Development of Crustacea

Pre-print power

Pre-prints are, of course, yesterday’s news in some circles. They are nothing new for the physics community, which has been using the arXiv pre-print server for more than two decades now. Several fields, including biology, have been reluctant to follow that trail. There is still a lot to talk about with pre-prints.

Pre-prints have been in the news a little more than usual lately, with a string of articles and editorials and blog posts about the potential benefits for pre-prints. (List of recent links at the bottom.) They’ve also been on my mind since a recent manuscript by Vogt and colleagues was the first in the Marmorkrebs research community to go up on a pre-print server, BioRxiv.

I asked two of the authors about what motivated their decision to post a pre-print, and how they thought this worked out for them.

Frank Lyko wrote:

We were a bit frustrated by the reviewing process. It takes time as it often takes some unexpected twists and turns. Also, it’s not uncommon that reviews or editorial decisions are completely off the mark. Posting provides you with an opportunity to let the community be the judge and not worry about the hidden agendas of reviewers or editors.

We wanted this story to be out in the open. Peer review can take an inordinate amount of time. BioRxiv promises to be fast, and indeed, 5 hours(!) after the initial submission, the screening process was completed. The paper was then instantly posted with a doi and thus became a citable reference.

And another point (even if it was not relevant in our case). The publication fees for some of the good journals now amass to several thousand euros. We are usually in the €5000 range if we want to include open access, which is egregious. BioRxiv posting is for free.

Günter Vogt wrote:

In the days after posting one of the staff writers of Science came across the paper and wrote a small article for the Science News. This small article was then discussed in the net and we have addressed some of the critical issues in our final paper in Biology Open, for example, the important question when a parthenogenetic lineage should be considered as an independent species and when not. The abstract of the BioRxiv version was clicked 1627 times already and the full paper was downloaded 666 times. This is a quite good distribution of knowledge in six weeks.

bioRxiv is still a developing resource. The site  recently started showing tweets about the paper. While more people are posting to the site (right), though, the number is a tiny fraction of biological publishing. This page indicates over 806,636 articles were added to PubMed in 2013, which works out to 67,000 papers a month. A couple of hundred bioRxiv papers per month pales in comparison.

As noted in the quotes above, the manuscript by Vogt and colleagues has been accepted for publication in a standard journal. I will be interested to see if interest in journal article tracks that of the pre-print. My own experience, with the PeerJ pre-print server, has been that while pre-prints are nice, the final journal article gets more attention.

References

Desjardins-Proulx P, White EP, Adamson JJ, Ram K, Poisot T, Gravel D. 2013. The case for open preprints in biology. PLOS Biology 11(5): e1001563. http://dx.doi.org/10.1371/journal.pbio.1001563

Pennisi E. 2015. Crayfish create a new species of female ‘superclones’. Science News ScienceShots. http://dx.doi.org/10.1126/science.aad1673

Shuai X, Pepe A, Bollen J. 2012. How the scientific community reacts to newly submitted preprints: article downloads, Twitter mentions, and citations. PLOS ONE 7(11): e47523. doi:10.1371/journal.pone.0047523

External links

Peer review, preprints and the speed of science
A PeerJ PrePrint – so just what is that exactly?
Preprints in paleontology: really that radical?
Preprints in science
Accelerating Scientific Publication in Biology
Four different reasons to post preprints
The science of asking

Kato and colleagues, 2015

Kato M, Hiruta C, Tochinai S. 2015. Androgenic gland implantation induces partial masculinization in Marmorkrebs Procambarus fallax f. virginalis. Zoological Science 32(5): 459-464. http://dx.doi.org/10.2108/zs150028

Abstract

The androgenic gland in malacostracan crustacean species produces and secretes androgenic gland hormone, which is responsible for male sexual differentiation, such as the induction and development of male sexual traits, and in turn the suppression of female sexual traits. Marmorkrebs, Procambarus fallax forma virginalis, which was identified as the first parthenogenetic species in decapod crustaceans, produces only female offspring. In this study, in order to reveal whether the Marmorkrebs crayfish is sensitive to androgenic gland hormone, we transplanted an androgenic gland from a related congener, P. clarkii, to P. fallax f. virginalis. In androgenic gland-implanted specimens, partial masculinization was confirmed: the masculinization of several external sexual characteristics (i.e., thickening of the first and second pleopods; formation of reverse spines on the third and fourth pereopods) was detected, whereas that of internal sexual characteristics (e.g., the formation of ovotestes and male gonoducts) was not. Our results imply that P. fallax f. virginalis still has sensitivity to the androgenic gland hormone and, at least partly, the hormone should be able to induce male characteristics, even in parthenogenetic Marmorkrebs.

Keywords: androgenic gland • masculinization • parthenogenesis • implantation • Marmorkrebs

Shen and colleagues, 2015

Shen H, Braband A, Scholtz G. 2015. The complete mitogenomes of lobsters and crayfish (Crustacea: Decapoda: Astacidea) reveal surprising differences in closely related taxa and convergences to Priapulida. Journal of Zoological Systematics and Evolutionary Research 53(4): 273–281. http://dx.doi.org/10.1111/jzs.12106

Abstract

We sequenced the complete mitogenomes of three species of Decapoda, Astacidea, comprising Astacida (freshwater crayfish) and Homarida (marine clawed lobsters): 1. Procambarus fallax f. virginalis (Astacida, Astacoidea), 2. Homarus gammarus (Homarida, Nephropoidea) and 3. Enoplometopus occidentalis (Homarida, Enoplometopoidea). Together with the available species in GenBank, the taxon Astacidea is covered with at least one representative for each of the four main subtaxa. Astacidea show unexpectedly diverse genomic organizations. Ten different gene arrangements have been observed in the 28 investigated species. Compared with the decapod ground pattern, a huge inversion, involving more than half of the mitogenome, has been found in four freshwater crayfish species of Astacoidea and convergently in one lobster species. Surprisingly, this inversion can also be observed in the distantly related Priapulida. This multiple convergent evolution suggests a relative ease in the evolution of great similarities in mitochondrial gene order. In addition, a partial or complete loss of the protein-coding gene nad2 has been found in E. occidentalis and H. gammarus but not in Nephrops norvegicus, Homarus americanus and Enoplometopus debelius. A reversal of the strand asymmetry has been found in five astacideans which is supposed to be caused by the inversion of a replication origin in the control region.

Keywords: gene order • convergent evolution • gene inversion • nad2 • strand reversal

Vogt, 2016

Vogt G. 2016. Research on stem cells, aging, cancer resistance, and epigenetics in marbled crayfish and relatives: potential benefits for human biology and medicine. In: T Kawai, Z Faulkes, G Scholtz, eds. Freshwater Crayfish: A Global Overview, pp. 115-157. Boca Raton: CRC Press. https://www.crcpress.com/Freshwater-Crayfish-A-Global-Overview/Kawai-Faulkes-Scholtz/9781466586390

Excerpt

Freshwater crayfish and their relatives have not yet been taken into the focus of stem cell biology, biogerontology, cancer biology and epigenetics although research of the last decade suggests a promising potential. In this chapter, the state of the art in these emerging fields of astacology, emphasizing contributions made by the parthenogenetic marbled crayfish as an emerging model organism have been reviewed.

Keywords: None provided.

Related posts

Kawai and colleagues (editors), 2016

Chucholl, 2016

Chucholl C. 2016. Marbled crayfish gaining ground in Europe: the role of the pet trade as invasion pathway. In: T Kawai, Z Faulkes, G Scholtz, eds. Freshwater Crayfish: A Global Overview, pp. 83-114. Boca Raton: CRC Press. https://www.crcpress.com/Freshwater-Crayfish-A-Global-Overview/Kawai-Faulkes-Scholtz/9781466586390

Excerpt

In this chapter, knowledge on this novel and on-going pathway for alien crayfish species introductions will be reviewed. In line with the other chapters in this section, emphasis will be placed on the marbled crayfish (Procambarus fallax f. virginalis Martin et al. 2010). The history of the marbled crayfish is inseparably tied to the aquarium trade, which introduced this species to the scientific world and which, at the time of this writing, is still the only known ‘natural habitat’ of marbled crayfish.

Keywords: None provided.

Related posts

Kawai and colleagues (editors), 2016

Martin, 2016

Martin P. 2016. Parthenogenesis: mechanisms, evolution, and its relevance to the role of marbled crayfish as model organism and potential invader. In: T Kawai, Z Faulkes, G Scholtz, eds. Freshwater Crayfish: A Global Overview, pp. 63-82. Boca Raton: CRC Press. https://www.crcpress.com/Freshwater-Crayfish-A-Global-Overview/Kawai-Faulkes-Scholtz/9781466586390

Excerpt

This chapter deals with the question of what is behind the often misinterpreted term parthenogenesis and what effect it has on marbled crayfish. It starts with a general overview about the mechanisms and genetic consequences of sexual reproductive systems and several different asexual ones. This is followed by a section on the origin of parthenogenesis in animals, its short-term benefits and long-term disadvantages, from the perspective of the evolutionary theory of sex. Then, the current state of knowledge on the extraordinary reproduction mode of marbled crayfish and the presumed cause for its emergence is described. Finally, the possibilities for this crustacean as laboratory animal and its ecological impacts resulting from parthenogenesis are discussed.

Keywords: None provided.

Related posts

Kawai and colleagues (editors), 2016

Vogt and colleagues, 2015

Vogt G, Falckenhayn C, Schrimpf A, Schmid K, Hanna K, Panteleit J, Helm M, Schulz R, Lyko F. 2015. The marbled crayfish as a paradigm for saltational speciation by autopolyploidy and parthenogenesis in animals. BioRxiv: 23 August 2015. http://dx.doi.org/10.1101/025254

Abstract

The parthenogenetic all-female marbled crayfish is a novel research model and potent invader of freshwater ecosystems. It is a triploid descendant of the sexually reproducing slough crayfish, Procambarus fallax, but its taxonomic status has remained unsettled. By cross-breeding experiments and parentage analysis we show here that marbled crayfish and P. fallax are reproductively separated. Both crayfish copulate readily, suggesting that the reproductive barrier is set at the cytogenetic rather than the behavioural level. Analysis of complete mitochondrial genomes of marbled crayfish from laboratory lineages and wild populations demonstrates genetic identity and indicates a single origin. Flow cytometric comparison of DNA contents of haemocytes and analysis of nuclear microsatellite loci confirm triploidy and suggest autopolyploidization as its cause. Global DNA methylation is significantly reduced in marbled crayfish implying the involvement of molecular epigenetic mechanisms in its origination. Morphologically, both crayfish are very similar but growth and fecundity are considerably larger in marbled crayfish, making it a different animal with superior fitness. These data and the high probability of a divergent future evolution of the marbled crayfish and P. fallax clusters suggest that marbled crayfish should be considered as an independent asexual species. Our findings also establish the P. fallax-marbled crayfish pair as a novel paradigm for rare chromosomal speciation by autopolyploidy and parthenogenesis in animals and for saltational evolution in general.

Keywords: None provided.

Kenning and colleagues, 2015

Kenning M, Lehmann P, Lindstrom M, Harzsch S. 2015. Heading which way? Y-maze chemical assays: not all crustaceans are alike. Helgoland Marine Research 69(3): 305-311. http://dx.doi.org/10.1007/s10152-015-0435-6

Abstract

In a world full of chemicals, many crustaceans rely on elaborate olfactory systems to guide behaviors related to finding food or to assess the presence of conspecifics and predators. We analyzed the responses of the isopod Saduria entomon to a range of stimuli by which the animal is likely to encounter in its natural habitat using a Y-maze bioassay. In order to document the efficiency of the experimental design, the same bioassay was used to test the behavior of the crayfish Procambarus fallax whose ability to track odors is well documented. The crayfish performed well in the Y-maze and were able to locate the source of a food-related odor with high fidelity. The isopod S. entomon reacted indifferently or with aversion to most of the stimuli applied. In 1800 trials, only four out of 15 different stimuli yielded statistically significant results, and only one odorant was found to be significantly attractive. The findings raise several questions whether the stimuli presented and/or the experimental setup used represents an ecologically relevant situation for S. entomon. In each instance, our experiments illustrate that established methods cannot be readily transferred from one species to another.

Keywords: Isopoda • Saduria entomon • Decapoda • crayfish • olfaction • behavior • flow channel

Harzsch and colleagues, 2015

Harzsch S, Krieger J, Faulkes Z. 2015. “Crustacea”: Decapoda – Astacida. In: A Wanninger (ed.), Evolutionary Developmental Biology of Invertebrates 4: Ecdysozoa II: Crustacea, pp. 101-151. Springer: New York. http://dx.doi.org/10.1007/978-3-7091-1853-5_4

Abstract

Thomas Henry Huxley, now often remembered as “Darwin’s bulldog”, wrote an entire book dedicated to crayfish, with no less a goal than showing how the study of crayfish could teach the reader all of zoology: “how the careful study of one of the commonest and most insignificant of animals, leads us, step by step, from every-day knowledge to the widest generalizations and the most difficult problems”. In retrospect, Huxley laid out the argument for model organisms several decades before another Thomas, namely, Thomas Hunt Morgan, started using fruit flies as model organisms, which became a wellspring of biological information in the twentieth century. While biology in the nineteenth century emphasised work on diverse species in the field, biology in the twentieth century was driven by a few model organisms in the lab, whether they were rats or fruit flies or Arabidopsis thaliana.

Keywords: None provided.

Kaldre and colleagues, 2016

Kaldre K, Meženin A, Paaver T, Kawai T. 2016. A preliminary study on the tolerance of marble crayfish Procambarus fallax f. virginalis to low temperature in Nordic climate. In: T Kawai, Z Faulkes, G Scholtz, eds. Freshwater Crayfish: A Global Overview, pp. 54-62. Boca Raton: CRC Press. https://www.crcpress.com/Freshwater-Crayfish-A-Global-Overview/Kawai-Faulkes-Scholtz/9781466586390

Excerpt

Temperatures in Nordic countries’ water bodies are much lower during winter, but there is no information about whether marble crayfish can survive temperatures as low as those experienced in Nordic countries, which is relevant to whether the marble crayfish can invade northern Europe. In this chapter we discuss the low temperature tolerance of marble crayfish as a factor in the potential invasion of marble crayfish in Nordic European countries.

Keywords: None provided.

Related posts

Kawai and colleagues (editors), 2016

Yazicioglu and Kozák, 2014

Yazicioglu B, Kozák P. 2014. What do we know about reproduction of crayfish? Poster presented at FABA 2014: International Symposium on Fisheries and Aquatic Sciences, Trabzon, Turkey, September 2014. https://www.researchgate.net/publication/280620396_What_do_we_know_about_reproduction_of_crayfish

Abstract

Study of the reproductive strategy of indigenous and non-indigenous crayfish species is of a great importance in the current astacological world. Crayfish are the largest aquatic invertebrates, and as a keystone species, they are capable of controlling the structure of the benthic fauna in the lake and stream ecosystems, demonstrating different ecological strategy and life span varying from Astacus leptodactylus, Austropotamobius torrentium, Austropotamobius pallipes, Procambarus clarkii and Pacifastacus leniusculus. However, the most recent information has revealed a few species that may have different models of reproduction, such as hermaphroditism, intersex (Cherax quadricarinatus, Samastacus spinifrons) and parthenogenesis (Procambarus fallax f. virginalis). In addition, there are many studies devoted to investigation of reproduction biology under various lab conditions. Present contribution covers all mentioned above topics, illustrates known among crayfish reproduction patterns, and summarizes published research articles from the past 20 years and until now.

Keywords: None provided.

Faulkes, 2016

Faulkes Z. 2016. Marble crayfish as a new model organism and a new threat to native crayfish conservation. In: T Kawai, Z Faulkes, G Scholtz, eds. Freshwater Crayfish: A Global Overview, pp. 31-53. Boca Raton: CRC Press. https://www.crcpress.com/Freshwater-Crayfish-A-Global-Overview/Kawai-Faulkes-Scholtz/9781466586390

Excerpt

In less than two decades, Marble crayfish have gone from a species completely unknown to science to a promising model organism for laboratory research and an increasingly problematic non-indigenous crayfish species. This series of events has been fortuitous in that it has created a framework for Marble crayfish research that unites basic, curiosity driven bench science and applied, pragmatic field science.

Keywords: None provided.

Related posts

Kawai and colleagues (editors), 2016

Faulkes, 2015b

Faulkes Z. 2015. Marmorkrebs (Procambarus fallax f. virginalis) are the most popular crayfish in the North American pet trade. Knowledge and Management of Aquatic Ecosystems 416: 20. http://dx.doi.org/10.1051/kmae/2015016

Abstract

Introductions of non-native crayfish around the world are increasingly tied to the distribution, sale, and eventual release of pet crayfish. As part of risk assessment for the introduction of non-native crayfish in North America, I monitored the sale of crayfish on an auction website that specializes in aquatic pets and aquarium supplies for a year. Three species accounted for the majority of sales: the parthenogenetic crayfish, Marmorkrebs (Procambarus fallax f. virginalis), the Cajun dwarf crayfish (Cambarellus shufeldtii), and the orange morph of the endangered Mexican dwarf crayfish (Cambarellus patzcuarensis). Almost half of individual crayfish sold (48.5%) were Marmorkrebs, which is more than twice as many as C. shufeldtii, the second most commonly sold species. The Louisiana red swamp crayfish (Procambarus clarkii) was often offered for auction, but was bought much less often than the other three species. About 11% of P. clarkii auctions were successful, while more than 45% of auctions were successful for the other three. Four Cherax species were the only crayfish sold online whose native range was outside North America. Neither Marmorkrebs nor the orange morph of C. patzcuarensis can be collected regularly from natural habitats in North America, suggesting that most crayfish sold online in North America are obtained from existing stocks in the pet trade, rather than being collected from natural habitats.

Keywords: marbled crayfish • pet trade • Marmorkrebs • Cambarellus

Supplemental information: Faulkes Z. 2015. Crayfish pet trade in North America. figshare. http://dx.doi.org/10.6084/m9.figshare.1478015

Feria and Faulkes, 2016

Feria TP, Faulkes Z. 2016. Predicting the distribution of crayfish species: a case study using marble crayfish. In: T Kawai, Z Faulkes, G Scholtz, eds. Freshwater Crayfish: A Global Overview, pp. 13-30. Boca Raton: CRC Press. https://www.crcpress.com/Freshwater-Crayfish-A-Global-Overview/Kawai-Faulkes-Scholtz/9781466586390

Excerpt

Species Distribution Models (SDM) have been used in a variety of studies (e.g., Thuiller et al. 2005) to predict suitable areas for future invasions, including crayfish and similar freshwater decapods (Table 2.1). The parthenogenetic crayfish, Marble crayfish, provides an excellent example of the need for such predictive tools. Because Marble crayfish are parthenogenetic, the release of just one individual could establish a new population and they can compete and spread disease to native species. The aim of this chapter is to demonstrate the process of creating species distribution models, with particular reference to the challenges faced in modelling the potential distribution of crayfish species, using Marble crayfish as a case study.

Keywords: None provided.

Related posts

Kawai and colleagues (editors), 2016

Beard, 2012

Beard LS. 2012. Responses to predator recognition odors in Marmorkrebs. Master’s thesis, Department of Biology, The University of Texas-Pan American, ProQuest, UMI Dissertations Publishing. http://search.proquest.com/docview/1152525739?accountid=7116

Abstract

Marmorkrebs is a parthenogenetic crayfish with no indigenous populations. They have been introduced in several countries and could become an invasive species. Individuals introduced in Germany had longer, sharper spines, suggesting an adaptation to predators via developmental plasticity. This was tested by exposing juveniles to the odor of a predatory fish over their development and comparing them to controls. No difference in spine length or sharpness was found between the experimental and control groups.

Other crayfish detect predators via an alarm cue, hemolymph, and exhibit avoidant behavior in response. I hypothesized that Marmorkrebs would also treat hemolymph as an alarm cue. Adult crayfish were exposed to three conditions: food, fish odor, and hemolymph and recorded for behavioral measures. Results showed no difference across conditions indicating that Marmorkrebs do not use hemolymph or fish odor as cues.

Keywords: None provided.

Lyko, 2015

Lyko F. 2015. DNA methylation patterns of arthropod genomes. Presentation given at Ninth Annual Arthropod Genomics Symposium, Kansas State University, Manhattan, Kansas, 17-19 June 2015. Abstract and program book, p. 11. http://www.k-state.edu/agc/images/symposium/Abstracts-ProgramBook.pdf

Abstract

Eukaryotic species use (cytosine-5) DNA methylation to facilitate phenotypic adaptation to their environments, which can include both the modulation of developmental and adaptive gene expression programs. Variations in the complement of cytosine methyltransferase enzymes have been interpreted to reflect multiple versions of a toolkit for phenotypic adaptation. During evolution, specific parts of this toolkit could have been contracted or expanded to facilitate specific requirements for genome regulation. We are using whole-genome bisulfite sequencing to investigate this hypothesis and to establish genome methylation maps of various model systems at single-base resolution. Our results define three groups of arthropod methylomes with fundamental differences that will be discussed in detail: The first group is defined by Drosophila and is characterized by the complete absence of recognizable DNA methylation patterns. The second group is defined by the honeybee and is characterized by the highly selective methylation of specific CpG residues. The third group is characterized by pervasive genome-wide methylation and we will present the marbled crayfish (Procambarus virginalis) as a novel model system to understand the relevance of DNA methylation for phenotypic variation.

Keywords: None provided.

Gutekunst and colleagues, 2015

Gutekunst J, Falckenhayn C, Raddatz G, Lyko F. 2015. Assembly and annotation of the marbled crayfish genome. Poster presented Ninth Annual Arthropod Genomics Symposium, Kansas State University, Manhattan, Kansas, 17-19 June 2015. Abstract and program book, p. 23. http://www.k-state.edu/agc/images/symposium/Abstracts-ProgramBook.pdf

Abstract

Marbled crayfish are the only freshwater crayfish known to reproduce by cloning (apomictic parthenogenesis). Notably, among genetically identical offspring raised in the same environment phenotypic differences can be observed. Such non-genomic characteristics render the marbled crayfish an interesting laboratory model, especially for the field of epigenetics. We experimentally determined the genome size at approximately 3.8 Gbp by k-mer analysis and flow cytometry. Two individual females (Koelle, Steuerwald) were sequenced using shotgun sequencing with various insert sizes generating 350 Gbp and 196 Gbp of data respectively. High coverage sequencing data of Koelle was used to produce a first de novo draft assembly with a length weighted median contig size (N50) of 809 bp and scaffold N50 of 41 kb. To unambiguously demonstrate clonal reproduction in the marbled crayfish we are currently evaluating sequencing data from the second individual (Steuerwald). Transcriptome data provides additional information for quality control and assembly refinement. Genome wide comparisons to other arthropods will allow us to define characteristic features of decapods as ecologically and economically keystone species.

Keywords: None provided

Scholtz, 2016

Scholtz G. 2016. Happy birthday! The first decade of Marmorkrebs research—results and perspectives. In: T Kawai, Z Faulkes, G Scholtz, eds. Freshwater Crayfish: A Global Overview, pp. 3-12. Boca Raton: CRC Press. https://www.crcpress.com/Freshwater-Crayfish-A-Global-Overview/Kawai-Faulkes-Scholtz/9781466586390

Excerpt

This brief review of the past 10 years of Marmorkrebs research reveals that we know a great deal more about many aspects of the biology of this very special crustacean. Both the similarity to other crayfish species and the unique aspects of Marmorkrebs biology offer excellent perspectives for the Marmorkrebs as a model system.

Keywords: None provided.

Related posts

Kawai and colleagues (editors), 2016

Award-winning crayfish

Marmorkrebs are an integral part of a new aquaponics project at Western Michigan University.

In March, five Western Michigan University students won a $15,000 Wege Prize—a national sustainability award—for their aquaponics system.

Marmorkrebs get used in this project because:

Instead of buying regular fish food, the team will raise spirulina algae and marbled crayfish—both of which are easy to raise.

You can tell from the bit about Marmorkrebs on the infographic that this is a university project run by academics.

Marbled crayfish
This recently-discovered crustacean species reproduces through parthenogenesis, an asexual process in which a single female creates genetically identical clones. As an all-female species, marbled crayfish reproduce exponentially and are less aggressive than other species, which makes them better suited for aquaculture. They are fed spirulina algae and BSFL frass. Being omnivorous scavengers, the crayfish can also process undigested waste as supplemental feed. In this system, they are used as a feed component, but could be raised for human consumption if demand exists.

How can I tell this was written by an academic? Not because of the fancy word “parthenogenesis,” but because only an academic would refer to a species that appeared in the scientific literature twelve years ago as “recently described.”

I’m also a doing a bit of an eyebrow raise over this statement, “As an all-female species, marbled crayfish reproduce exponentially and are less aggressive than other species...”. It’s worded in such a way that might suggest the alleged lower levels of aggression are due to them being female, which is absolutely not the case. Female crayfish fight just as hard as males, and study after study has repeatedly found no strong effects on sex on outcome of fights.

Finally, I think it’s a little unlikely that Marmorkrebs are likely to have much demand for food for people. They’re a small species, and you’ve not going to get much meat off them compare to, say, Louisiana red swamp crayfish or redclaw crayfish.

External links

WMU Students To Build Sustainable Aquaponics Farm
Local Loop Farms

Kawai and colleagues (editors), 2016

Kawai T, Faulkes Z, Scholz G (eds.). 2016. Freshwater Crayfish: A Global Overview. CRC Press: Boca Raton. http://www.crcpress.com/product/isbn/9781466586390

Table of contents

Preface

Section 1: Marbled Crayfish—A New Model Organism for Biology

• 1. Happy birthday! The first decade of Marmorkrebs research—results and perspectives — Gerhard Scholtz
• 2. Predicting the distribution of crayfish species: a case study using marble crayfish — Teresa Patricia Feria and Zen Faulkes
• 3. Marble crayfish as a new model organism and a new threat to native crayfish conservation — Zen Faulkes
• 4. A preliminary study on the tolerance of marble crayfish Procambarus fallax f. virginalis to low temperature in Nordic climate — Katrin Kaldre, Anton Meženin, Tiit Paaver and Tadashi Kawai
• 5. Reproductive biology: Parthenogenesis: mechanisms, evolution, and its relevance to the role of marbled crayfish as model organism and potential invader — Peer Martin
• 6. Aquarium: Marbled crayfish gaining ground in Europe: the role of the pet trade as invasion pathway — Christoph Chucholl
• 7. Cell biology research on stem cells, aging, cancer resistance, and epigenetics in marbled crayfish and relatives: potential benefits for human biology and medicine — Günter Vogt

Section 2: Crayfish: New Developments

• 8. Aquaculture: Developing markets for a new product: aquacultured redclaw in Mexico — Antonio Garza de Yta
• 9. The biology of crayfish plague pathogen Aphanomyces astaci: current answers to most frequent questions — Svetlana Rezinciuc, Jose V. Sandoval-Sierra, Birgit Oidtmann and Javier Diéguez-Uribeondo
• 10. A review of current techniques for sampling freshwater crayfish — Stephanie Parkyn
• 11. Behavior: Behavioral ecology of crayfish: its contribution to conservation and management — Elena Tricarico
• 12. Chaos and adaptation in the pathogen-host relationship in relation to the conservation: the case of the crayfish plague and the noble crayfish — Japo Jussila, Ivana Maguire, Harri Kokko and Jenny Makkonen
• 13. Crayfish as tools of water quality monitoring — Pavel Kozák and Iryna Kuklina
• 14. Phylogenetic estimate of the freshwater crayfish (Decapoda: Astacidea) using morphology and molecules — David Stern and Keith A. Crandall

Section 3: Global Overview of Freshwater Crayfish Biology

• 15. Asia — Tadashi Kawai, Gi-Sik Min, Evgeny Barabanshchikov, Vjacheslav Labay and Hyun Sook Ko
• 16. The crayfish fauna of Canada and the United States in North America — Roger Thoma
• 17. Historical biogeography of Pacifastacus crayfishes and their branchiobdellidan and entocytherid ectosymbionts in Western North America — Eric R. Larson and Bronwyn W. Williams
• 18. The crayfish of middle America — Fernando Alvarez and José Luis Villalobos
• 19. The native South American crayfish (Decapoda: Parastacidae) — Erich Harry Rudolph and Mauricio Pereira Almerão
• 20. Oceania: the freshwater crayfish of the Oceania Region — James M. Furse, Quinton F. Burnham, Kathryn L. Dawkins and Alastair M.M. Richardson
• 21. Crayfish of Africa — Christopher B. Boyko
• 22. Crayfish in Europe: Biogeography, Ecology and Conservation — Leopold Füreder
• 23. Global Overview of Branchiobdellida (Annelida: Clitellata) — Stuart R. Gelder and Bronwyn W. Williams

Index

Note: Although the release date of this book was released in 2015, the publication date within it is consistently given as 2016 throughout the book.

The Francesca Gherardi Memorial Prize for 2016

The Francesca Gherardi Memorial Prize of €5,000 is awarded annually by the Department of Biology at the University of Florence to a young researcher who demonstrates outstanding ability in the fields of crustacean behaviour and/or invasion biology. The prize money is donated by the Gherardi family in memory of their beloved relative. The professors of zoology of the Department of Biology of University of Florence serve as the award committee.


The winner gives a lecture on the subject of his/her research and receives the award at the annual memorial honouring Francesca Gherardi at the Department of Biology, University of Florence, in May 2016.


Application Guidelines

Applications for the 2016 prize for research in crustacean behaviour are open to researchers under the age of 40, of all nationalities, lacking permanent positions. The deadline for submissions is 30 November 2015.

The application should be written in English, and include a CV, three articles published in peer-reviewed journals, a letter attesting that the applicant holds no permanent research or teaching position, and a copy of his/her identity card.

Send submissions in electronic format to Prof. Felicita Scapini, felicita.scapini@unifi.it.

More information at http://www.bio.unifi.it/vp-118-francesca-gherardi-prize.html.

Hanging out for a ride

Spotted here.

Support for doctoral students studying aquatic invaders

The project Marie Curie ITN Aquainvad-ED offers eight Ph.D. fellowships on early detection, control, and management of aquatic invasive species.

The main research goal of the project is to exploit novel molecular advances combined with the power of crowd data sourcing (citizen science) to develop innovative methods of early detection, control and management of aquatic invasive species. This will be achieved via a multi-disciplinary network of experts in invasion biology, ecology, marine and fresh-water biotechnology, citizen science and environmental policy working in three different countries: the United Kingdom (3 positions), Spain (3 positions), and Italy (2 positions).

Deadline for applications is 22 July 2015 for positions in Italy (ESR4, ESR7) and 14 August 2015 for positions in Spain (ESR5, ESR6, ESR8) and UK (ESR1, ESR2, ESR3). For more details on individual projects and how to apply, click on each one of the Fellow links (ESR1-8) in the following website: http://www.aquainvaded.com/individual-projects

For more information, contact Elena Tricarico (email: elena.tricarico@unifi.it).

Classical crays

I’m always fascinated by what music people think go with what animals. From here.

International Symposium on Conservation of Native European Freshwater Crayfish

the International Symposium on Conservation of Native European Freshwater Crayfish will be held in Olot, Girona (Spain) from 23-25 September 2015. Registration has been extended to 15 July 2015.

The conservation of native crayfish is one of the major challenges in European inland waters, since most species are endangered by many factors, but specifically by introduced species and pests. This symposium will focus on recent research advances, and also on management strategies and specific experiences focused to achieve a long-term conservation of our native freshwater decapods.

Wesbite: http://www.crayfishsymposiumlifepotamofauna.org/

Email: lifepotamofauna@consorcidelestany.org

Celebrate diversity: What the sawfish saw

Welcome the latest member of the parthenogenetic club, the smalltooth sawfish!

This case is interesting not only because it adds yet another case of facultative parthenogenesis to the list, but because it’s one of the few times facultative parthenogensis has been seen in wild populations. The bad news is that this might be because the sawfish is endangered: the population is so low that the fish are resorting to “last gasp” reproductive efforts.

A “boo” to this Miami Herald article, though, for confusing the religious doctrines of immaculate conception (conceived without original sin) with virgin birth (conceived without a father).

Hat tip to David Shiffman.

Reference

Fields AT, Feldheim KA, Poulakis GR, Chapman DD. 2015. Facultative parthenogenesis in a critically endangered wild vertebrate. Current Biology 25(11): R446-R447. http://dx.doi.org/10.1016/j.cub.2015.04.018

External links

Virgins gone wild
Father, son and holy sawfish! Researchers find ‘virgin birth’ in Florida endangered species 
Sawfish spawn without sex
Sawfish escape extinction through 'virgin births', scientists discover

Picture by Anna Pang on Flickr; used under a Creative Commons license.

Vogt, 2015

Vogt G. 2015. Stochastic developmental variation, an epigenetic source of phenotypic diversity with far-reaching biological consequences. Journal of Biosciences 40(1): 159-204. http://dx.doi.org/10.1007/s12038-015-9506-8

Abstract

This article reviews the production of different phenotypes from the same genotype in the same environment by stochastic cellular events, nonlinear mechanisms during patterning and morphogenesis, and probabilistic self-reinforcing circuitries in the adult life. These aspects of phenotypic variation are summarized under the term ‘stochastic developmental variation’ (SDV) in the following. In the past, SDV has been viewed primarily as a nuisance, impairing laboratory experiments, pharmaceutical testing, and true-to-type breeding. This article also emphasizes the positive biological effects of SDV and discusses implications for genotype-to-phenotype mapping, biological individuation, ecology, evolution, and applied biology. There is strong evidence from experiments with genetically identical organisms performed in narrowly standardized laboratory set-ups that SDV is a source of phenotypic variation in its own right aside from genetic variation and environmental variation. It is obviously mediated by molecular and higher-order epigenetic mechanisms. Comparison of SDV in animals, plants, fungi, protists, bacteria, archaeans, and viruses suggests that it is a ubiquitous and phylogenetically old phenomenon. In animals, it is usually smallest for morphometric traits and highest for life history traits and behaviour. SDV is thought to contribute to phenotypic diversity in all populations but is particularly relevant for asexually reproducing and genetically impoverished populations, where it generates individuality despite genetic uniformity. In each generation, SDV produces a range of phenotypes around a well-adapted target phenotype, which is interpreted as a bet-hedging strategy to cope with the unpredictability of dynamic environments. At least some manifestations of SDV are heritable, adaptable, selectable, and evolvable, and therefore, SDV may be seen as a hitherto overlooked evolution factor. SDV is also relevant for husbandry, agriculture, and medicine because most pathogens are asexuals that exploit this third source of phenotypic variation to modify infectivity and resistance to antibiotics. Since SDV affects all types of organisms and almost all aspects of life, it urgently requires more intense research and a better integration into biological thinking.

Keywords: clonal organisms • development • ecology • epigenetics • evolution • genotype-to-phenotype mapping • individuality • infectivity and resistance • phenotypic variation • stochasticity