Where are the Procambarus clarkii clones?

Some years back, a paper came out purporting to have identified genetically identical red swamp crayfish (Procambarus clarkii) in China (Yue et al. 2008). At the time, this was a rather remarkable claim, given that there have been no shortage of labs looking at this species. You would have expected that if P. clarkii could reproduce by parthenogenesis, someone would have noticed by now.

The plausibility of that claim went up, in my mind, with the discovery of facultative parthenogensis in spinycheek crayfish (Orconectes limosus). If Marmorkrebs and spinycheek crayfish, two species in different genera, could be parthengenetic, it seemed plausible that there was more reproductive flexibility than we thought in crayfish. And we’ve been caught off guard with other well studied species being facultative parthenogens.

The likelihood of P. clarkii clones has, in my mind, gone back down again with the publication of a new paper by Li and colleagues. In a study looking at the genes of P. clarkii across China, they found no evidence of genetically identical organisms. In fact, they say the exact opposite:

All the P. clarkii populations in China showed relatively high genetic diversity(.)

In some ways, the papers are broadly comparable in their methods: both are using cytochrome oxidase (COI) genes and microsattelites. But it is fair to say that the new paper may not have found clones because that wasn’t what they had set up their experiment to find. This paper is very much interested in the red swamp crayfish as an invasive species, which meant sampling across a wide geographic range. The previous paper by Yue et al. (2008) sampled more individuals at fewer collection sites. Intensive sampling at a small number of locations would be much more likely to detect genetically identical individuals.

The claim of parthenogenetic P. clarkii still needs confirmation. The best way would be to have an identified, isolated parent in the lab and DNA genotyping of both parent and offspring.

And I’m still waiting for confirmation of whether there are Marmorkrebs in China!

Reference

Li Y, Guo X, Cao X, Deng W, Luo W, Wang W. 2012. Population genetic structure and post-establishment dispersal patterns of the red swamp crayfish Procambarus clarkii in China. PLoS ONE 7(7): e40652. 10.1371/journal.pone.0040652

Yue GH, Wang GL, Zhu BQ, Wang CM, Zhu ZY, Lo LC. 2008. Discovery of four natural clones in a crayfish species Procambarus clarkii. International Journal of Biological Sciences 4(5):279-282. http://www.biolsci.org/v04p0279.htm