28 April 2018

Allo or auto? Betting on Marmorkrebs origins

Picture of Bugatti car with text, 'Why not hybrid?'

In a new article in PNAS, James Mallet writes:

An extraordinary recent case is the marbled crayfish Procambarus virginalis, which seems to have originated via a hybrid between two North American Procambarus species and was likely spread via the pet trade. The marbled crayfish is a triploid hybrid, very likely created in captivity, and is entirely parthenogenetic. After escaping from captivity, it has since spread to become invasive in many European countries as well as in Madagascar.

Mallet cites Gutekunst and colleagues (2018) to support this. But they specifically said, “We do not think Marmorkrebs is a hybrid.”

Alternative hypotheses involving allopolyploid formation with P. alleni appear unlikely due to the lack of hybrid morphological features and the considerable genetic differences.

And it’s not just them. Vogt and colleagues (2016) wrote:

The morphological features and microsatellite patterns strongly suggest that marbled crayfish originated by autopolyploidisation and not by hybridisation with a closely related species, which is by far the most frequent cause of triploidy in animals.

There is some overlap in the author lists of Gutekunst et al. (2018) and Vogt et al. (2016). Having the some of the same authors makes it not surprising that the two papers reach the same conclusions. But they are not the only ones. Martin and colleagues (2016) reached the same conclusion:

Martin et al. (2010) suggested that the Marmorkrebs originated directly from sexual P. fallax without hybridization.

Our data tentatively support this conclusion. Based on the assumption of a hybridization between P. fallax and P. alleni, one would expect that the numerically different karyotypes of these two species would have led to a chromosome number higher than that counted in Marmorkrebs. Furthermore, a preliminary comparison of the nuclear protein coding histone H3 gene (H3) and the nuclear elongation factor 2 gene (EF-2) revealed at least seven polymorphic positions within the EF-2 intron that suggest a non-hybrid origin of the Marmorkrebs.

For a very long time, I would have bet money that Marmorkrebs was a hybrid, because so many cases of asexual reproduction trace back to hybridization events. All of the papers above go on to say that, strictly speaking, there is still a very slight possibility that Marmorkrebs is a hybrid. But hybridization isn’t the way to bet any more.


Gutekunst J, Andriantsoa R, Falckenhayn C, Hanna K, Stein W, Rasamy J, Lyko F. 2018. Clonal genome evolution and rapid invasive spread of the marbled crayfish. Nature Ecology & Evolution 2(3): 567–573. https://doi.org/10.1038/s41559-018-0467-9

Mallet J. 2018. Invasive insect hybridizes with local pests. Proceedings of the National Academy of Sciences: in press. https://doi.org/10.1073/pnas.1804081115

Martin P, Thonagel S, Scholtz G. 2016. The parthenogenetic Marmorkrebs (Malacostraca: Decapoda: Cambaridae) is a triploid organism. Journal of Zoological Systematics and Evolutionary Research 54(1): 13-21. http://dx.doi.org/10.1111/jzs.12114

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

10 April 2018

Maughan, 2018

Maughan M. 2018. Cyclical parthenogenesis in crustaceans. Poster presentation, Utah State University, 12 April 2018. https://digitalcommons.usu.edu/researchweek/ResearchWeek2018/All2018/283/


Apomixis is the replacement of sexual reproduction with asexual reproduction in plants. Some scientists hypothesize that apomixis is caused by genetics that evolved after sexual reproduction and apomixis mutated from sexual reproduction. However, we hypothesize that sexual reproduction and apomixis evolved simultaneously during eukaryogenesis, the evolution of eukaryotic life. We think that most organisms retain the capacity for apomixis and sexual reproduction in their genome. Many taxa, including plants and crustaceans, should have a single genome able to express both sexual and asexual reproduction as long as the correct metabolic signaling is provided to the germline cells. In Professor John Carman’s lab, researchers have successfully induced onset of apomixia in sexual plants. These successes support our hypothesis and suggest that some animals could also have the pathogenesis and sexual reproduction capabilities in their genome. The equivalent of plant apomixis in animals is apomictic parthenogenesis. We focus on cyclical parthenogenesis. In cyclical parthenogenesis animals alternate between sexual and asexual reproduction. Daphnia magna and Procambarus virginalis (marbled crayfish) are both cyclically parthenogenetic. The TOR (rapamycin complex 1) signaling pathway in plants and animals is a regulator of cell growth and it affects the pathway of reproduction. Oxidative stress turns off the TOR signaling pathway and turns SnRK1(SNF1-related kinase 1 in yeast and AMPK in animals) on. SnRK1 makes cells begin the process of sexual reproduction. To test this hypothesis, I will be researching how to switch asexual organisms to reproduce sexually. I will inject the ovaries of crayfish with chemicals designed to alter their glucose levels and place the Daphnia in a solution containing the appropriate chemicals. The presence of an egg sack from the Daphnia and the presence of male crayfish will show the success of the expirement (sic).

Keywords: None provided.

02 April 2018

Neff, 2018

Neff EP. 2018. The Marmorkrebs model. Lab Animal 47(4): 107-107. https://doi.org/10.1038/s41684-018-0030-y


Without abstract. First paragraph:

In his lab at the German Cancer Research Center in Heidelberg, Frank Lyko studies epigenetics, how the environment can change an organism’s phenotype without altering its underlying DNA. About 15 years ago, a colleague introduced him to the marbled crayfish, a triploid, clonal, parthenogenic, and only very recently speciated invertebrate that’s proven to be quite the invasive pest across the globe. At the time, the Marmorkrebs (as it’s known in German) didn’t register in Lyko’s research plans. But recently, he began thinking about alternative models. Classical laboratory animals, like mice, worms, and fruit flies, “always have the same phenotype, and if you induce a genetic mutation you get one aberrant phenotype normally,” he explains. “This is super helpful if you do genetic research but it’s not necessarily good for describing what’s going on in epigenetics.” He tried honeybees, but found them challenging to keep in the laboratory. His lab wasn’t fond of another potential epigenetic model, the African desert locust, either. “These were really big animals and they were always escaping and flying around, so that was a mess,” he recalls. “Then I remembered my old conversation with G√ľnter Vogt.”

Keywords: None provided.