23 November 2021

Captivity does not cause cloning

An article about Marmorkrebs by Paul Hetzler is showing up in a wide array of places, from New York state to India. It’s generally accurate, although I have to raise eyebrows as to the description of the origin of Marmorkrebs.

Sometime in the 1990s, a mutant crayfish able to conquer and degrade aquatic systems emerged as a result of secret German experiments gone awry. (What the what? - ZF) The marmorkreb (sic), a.k.a. marbled crayfish (Procambarus virginalis), is a destructive new species that first appeared aquariums in Germany. However, it’s more likely the result of too much inbreeding in captivity, rather than some mad-scientist scheme, that led to their mutation.


I think – I hope – Hetzzler meant the bit about “secret experiments” as a joke. I am willing to be that some people will take it as real and won’t make ti to the second part of the paragraph. But the second part of the paragraph is also pretty dubious. 


There is no evidence that inbreeding can cause triploidy. Inbreeding increases homozygosity. It doesn't create extra chromosomes, particularly a whole new set of chromosomes.

By weird coincidence, a technical paper in press also seems to think that just being in captivity is enough to make a species parthenogenetic.

The marbled crayfish Procambarus virginalis probably evolved clonal parthenogenetic reproduction while in the captive aquarium trade. ... With growth in human cultivation of invertebrates for food and other services, the potential for evolution and escape into the wild and subsequent rapid spread of other clonal species is increasing.


This stands in contrast to a recent paper by Gutekunst and colleagues that argues that there are triploid individuals in the natural slough crayfish population, from which Marmorkrebs ultimately emerged.

We need to stop with this narrative that somehow the origin of Marmorkrebs in humans’ fault. It’s not as though there is a shortage of crayfish guilt in the world. It’s our fault we spread them around the globe. That’s on us.


Hetzler also mentions a controversy that... I don’t think exists?

Perhaps the only amusing thing about these nasty aberrations of nature is the mild squabbling as to how one should describe them. Experts disagree on whether the new organisms are mottled, freckled, speckled, spotted, variegated, or something else.

I have never seen a single written comment arguing about what to call the pattern on Marmorkrebs.



Gutekunst J, Maiakovska O, Hanna K, Provataris P, Horn H, Wolf S, Skelton CE, Dorn NJ, Lyko F. 2021. Phylogeographic reconstruction of the marbled crayfish origin. Communications Biology 4(1): 1096. https://doi.org/10.1038/s42003-021-02609-w


Sutherland WJ, Atkinson PW, Butchart SHM, Capaja M, Dicks LV, Fleishman E, Gaston KJ, Hails RS, Hughes AC, Le Anstey B, Le Roux X, Lickorish FA, Maggs L, Noor N, Oldfield TEE, Palardy JE, Peck LS, Pettorelli N, Pretty J, Spalding MD, Tonneijck FH, Truelove G, Watson JEM, Wentworth J, Wilson JD, Thornton A. 2021. A horizon scan of global biological conservation issues for 2022. Trends in Ecology & Evolution: In press. https://doi.org/10.1016/j.tree.2021.10.014  


External links


Marbled Crayfish: The Mutants Have Landed

Help keep marbled crayfish from spreading

The Mutants Have Landed

05 November 2021

Chucholl and Chucholl 2021

Cover of Freshwater Biology, volume 66, issue 11.
Chucholl F, Chucholl C. 2021. Differences in the functional responses of four invasive and one native crayfish species suggest invader-specific ecological impacts. Freshwater Biology 66(11): 2051-2063. https://doi.org/10.1111/fwb.13813




  1. Invasive non-native species represent a leading threat to global freshwater biodiversity and non-native crayfish species frequently cause extensive ecological damage. However, the extent to which their impact: (1) depends on invader identity and (2) differs from the natural state with native crayfish remains unclear. Comparison of the functional responses of invasive and native species represents a promising approach in this regard.
  2. Here, we explored whether four invasive crayfish species (calico crayfish Faxonius immunis, spiny-cheek crayfish Faxonius limosus, signal crayfish Pacifastacus leniusculus, and marbled crayfish Procambarus virginalis) in European freshwaters and the most widespread native species (noble crayfish Astacus astacus) overlap in function in their potential effects on key resources of benthic food webs. First, the impact on gammarids and zebra mussels was assessed by means of comparative functional response analysis using the functional response ratio as impact metric; second, the consumption of macrophytes (Chara sp.) and detritus (leaf litter) was quantified and compared using feeding experiments.
  3. Both invader- and resource-specific effects were observed. Invasive calico crayfish and signal crayfish exhibited the strongest per capita effects on gammarids and zebra mussels, respectively, with functional response ratios being 2-fold higher than those of native noble crayfish. Marbled crayfish showed an intermediate effect on both prey species, whereas spiny-cheek crayfish had lower impacts than noble crayfish. In the feeding experiment, calico crayfish consumed the highest amount of detritus, while the consumption of macrophytes did not differ among the five crayfish species.
  4. Our work demonstrates as-yet unrecognised differences in functional responses among the four North American crayfish invaders and the European noble crayfish. The lack of congruence across the observed impacts suggests a mostly species-specific pattern and stresses the importance of species and resource identity when considering the ecological impact of crayfish. An initial assessment of invader-specific potential impacts positions calico crayfish and signal crayfish among the most impactful invaders.

Keywords: ecological impact • ecological redundancy • functional response • invasive crayfish risk assessment

Open access.


Scholz and colleagues 2021

Zoomorphology journal cover
Scholz S, Göpel T, Richter S, Wirkner CS. 2021. High degree of non-genetic phenotypic variation in the vascular system of crayfish: a discussion of possible causes and implications. Zoomorphology 140: 317-329. https://doi.org/10.1007/s00435-021-00536-2




In this study, the hemolymph vascular system (HVS) in two cambarid crayfishes, i.e. the Marbled Crayfish, Procambarus virginalis Lyko, 2017 and the Spiny Cheek Crayfish, Faxonius limosus (Rafinesque, 1817), is investigated in regard of areas of non-genetic phenotypic variation. Despite their genetic identity, specimens of P. virginalis show variability in certain features of the HVS. Thus, we describe varying branching patterns, sporadic anastomoses, and different symmetry states in the vascular system of the marbled crayfish. We visualize our findings by application of classical and modern morphological methods, e.g. injection of casting resin, micro-computed tomography and scanning electron microscopy. By comparing our findings for P. virginalis to the vasculature in sexually reproducing crayfishes, i.e. F. limosus and Astacus astacus, we discuss phenotypic variation of the HVS in arthropods in general. We conclude that constant features of the HVS are hereditary, whereas varying states identified by study of the clonal P. virginalis must be caused by non-genetic factors and, that congruent variations in sexually reproducing F. limosus and A. astacus are likely also non-genetic phenotypic variations. Both common causal factors for non-genetic phenotypic variation, i.e., phenotypic plasticity and stochastic developmental variation are discussed along our findings regarding the vascular systems. Further aspects, such as the significance of non-genetic phenotypic variation for phylogenetic interpretations are discussed.


Keywords: Evolutionary morphology • phenotypic plasticity • circulatory system • heart • artery

Open access logo.


01 November 2021

Celbrate diversity: Charasmatic California condors can without consumation

California condor in flight


It’s been fascinating to watch species that have been well studied suddenly and unexpectedly show that they can reproduce by parthenogenesis. The latest entry to the club is perhaps the most surprising yet: the critically endangered California condor.

The story is making the rounds on science news, but the original technical article is here.

Two males were generated by parthenogenesis. This is in contrast to many other cases of parthenogenesis, where offspring are exclusively female. Birds have a ZW chromosome system, where the females have different sex chromosomes. The males have two of the same sex chromosome. I suppose that in theory, the condors could produce offspring of either sex by parthenogenesis?



Ryder OA, Thomas S, Judson JM, Romanov MN, Dandekar S, Papp JC, Sidak-Loftis LC, Walker K, Stalis IH, Mace M, Steiner CC, Chemnick LG. Facultative parthenogenesis in California condors. Journal of Heredity: In press. https://doi.org/10.1093/jhered/esab052


External links


After 30 Years of Breeding Condors, a Secret Comes Out

17 September 2021

Gutekunst and colleagues, 2021

Communications Biology
Gutekunst J, Maiakovska O, Hanna K, Provataris P, Horn H, Wolf S, Skelton CE, Dorn NJ, Lyko F. 2021. Phylogeographic reconstruction of the marbled crayfish origin. Communications Biology 4(1): 1096. https://doi.org/10.1038/s42003-021-02609-w




The marbled crayfish (Procambarus virginalis) is a triploid and parthenogenetic freshwater crayfish species that has colonized diverse habitats around the world. Previous studies suggested that the clonal marbled crayfish population descended as recently as 25 years ago from a single specimen of P. fallax, the sexually reproducing parent species. However, the genetic, phylogeographic, and mechanistic origins of the species have remained enigmatic. We have now constructed a new genome assembly for P. virginalis to support a detailed phylogeographic analysis of the diploid parent species, Procambarus fallax. Our results strongly suggest that both parental haplotypes of P. virginalis were inherited from the Everglades subpopulation of P. fallax. Comprehensive whole-genome sequencing also detected triploid specimens in the same subpopulation, which either represent evolutionarily important intermediate genotypes or independent parthenogenetic lineages arising among the sexual parent population. Our findings thus clarify the geographic origin of the marbled crayfish and identify potential mechanisms of parthenogenetic speciation.


Keywords: None provided.

29 August 2021

Tönges and colleagues 2021

Frontiers in Ecology and Evolution
Tönges S, Masagounder K, Lenich F, Gutekunst J, Tönges M, Lohbeck J, Miller AK, Böhl F, Lyko F. 2021. Evaluating invasive marbled crayfish as a potential livestock for sustainable aquaculture. Frontiers in Ecology and Evolution 9: 651981. https://www.frontiersin.org/article/10.3389/fevo.2021.651981



The marbled crayfish (Procambarus virginalis) is a recently discovered freshwater crayfish species, which reproduces by apomictic parthenogenesis, resulting in a monoclonal, and all-female population. The animals were widely distributed through the aquarium trade and have established numerous stable wild populations through anthropogenic releases. They are highly prevalent in Madagascar, where they have become a popular source of nutritional protein. As freshwater crayfish aquaculture in open systems is a thriving, but ecologically damaging global industry, alternatives are urgently needed. Although marbled crayfish are often branded by their invasive mode of reproduction, their overall invasiveness is not higher than for other cultured crayfish species. Furthermore, their resiliency and high adaptability provide a strong rationale for evaluating them for closed, and environmentally safe aquaculture approaches. Here we describe a novel population of marbled crayfish in a former German coal mining area that is characterized by acid and polluted water. Even under these adverse conditions, animals grew to sizes, and weights that are comparable to commercially farmed freshwater crayfish. Tailored feed development and laboratory testing demonstrated highly efficient feed conversion, suggesting a considerable capacity for sustainable production in closed systems. We further show that marbled crayfish meat can be readily introduced into European meals. Finally, chemical analysis of marbled crayfish exoskeletons revealed comparably high amounts of chitin, which is a valuable source for the synthesis of chitosan and bioplastics. Our results thus suggest that production of marbled crayfish in closed systems may represent a sustainable alternative for crayfish aquaculture.

Keywords: livestock • invasive species • feed conversion • chitin • sustainability • aquaculture • marbled crayfish • tailored feeds

Open access

Francesconi and colleagues 2021

Frontiers in Evology and Evolution.
Francesconi C, Makkonen J, Schrimpf A, Jussila J, Kokko H, Theissinger K. 2021. Controlled infection experiment with Aphanomyces astaci provides additional evidence for latent infections and resistance in freshwater crayfish. Frontiers in Ecology and Evolution 9: 647037. https://doi.org/10.3389/fevo.2021.647037




For 150 years the crayfish plague disease agent Aphanomyces astaci has been the cause of mass mortalities among native European crayfish populations. However, recently several studies have highlighted the great variability of A. astaci virulence and crayfish resistance toward the disease. The main aim of this study was to compare the response of two crayfish species, the European native noble crayfish (Astacus astacus) and the invasive alien marbled crayfish (Procambarus virginalis), to an A. astaci challenge with a highly virulent strain from haplogroup B and a lowly virulent strain from haplogroup A. In a controlled infection experiment we showed a high resistance of marbled crayfish against an A. astaci infection, with zoospores from the highly virulent haplogroup B strain being able to infect the crayfish, but unable to cause signs of disease. Furthermore, we demonstrated a reduced virulence in the A. astaci strain belonging to haplogroup A, as shown by the light symptoms and the lack of mortality in the generally susceptible noble crayfish. Interestingly, in both marbled crayfish and noble crayfish challenged with this strain, we observed a significant decrease of the detected amount of pathogen’s DNA during the experiment, suggesting that this A. astaci haplogroup A strain has a decreased ability of penetrating into the cuticle of the crayfish. Our results provide additional evidence of how drastically strains belonging to A. astaci haplogroup B and haplogroup A differ in their virulence. This study confirmed the adaptation of one specific A. astaci haplogroup A strain to their novel European hosts, supposedly due to reduced virulence. This feature might be the consequence of A. astaci’s reduced ability to penetrate into the crayfish. Finally, we experimentally showed that marbled crayfish are remarkably resistant against the crayfish plague disease and could potentially be latently infected, acting as carriers of highly virulent A. astaci strains.


Keywords: marbled crayfish • noble crayfish • host-pathogen co-evolution • crayfish plague • experimental infection

OPen access