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