The marbled crayfish Procambarus virginalis is a unique freshwater crayfish characterized by very recent speciation and parthenogenetic reproduction. Marbled crayfish also represent an emerging invasive species and have formed wild populations in diverse freshwater habitats. However, our understanding of marbled crayfish biology, evolution and invasive spread has been hampered by the lack of freshwater crayfish genome sequences. We have now established a de novo draft assembly of the marbled crayfish genome. We determined the genome size at approximately 3.5 gigabase pairs and identified >21,000 genes. Further analysis confirmed the close relationship to the genome of the slough crayfish, Procambarusfallax, and also established a triploid AA’B genotype with a high level of heterozygosity. Systematic fieldwork and genotyping demonstrated the rapid expansion of marbled crayfish on Madagascar and established the marbled crayfish as a potent invader of freshwater ecosystems. Furthermore, comparative whole-genome sequencing demonstrated the clonality of the population and their genetic identity with the oldest known stock from the German aquarium trade. Our study closes an important gap in the phylogenetic analysis of animal genomes and uncovers the unique evolutionary history of an emerging invasive species.

In 2007 an unusual crayfish found in food markets in the capital of Madagascar was preliminarily identified as Procambarus 'Marmorkrebs': a new world taxa and the only decapod known to reproduce by parthenogenesis. We present information on the identity, distribution and ecology of this recent invader and attempt to evaluate the threat it poses to Madagascar's biodiversity and to livelihoods. The species appears to be currently limited to the area close to Antananarivo, but is being sold alive on major transport routes. We present molecular evidence of its taxonomic relationships and confirm that the Procambarus present in Madagascar is indeed the parthenogenic taxa. We investigate its reproductive ecology and find Procambarus 'Marmorkrebs' to have an extremely high fecundity; more than six times that of the native crayfish Astacoides. The limited evidence we have suggests that this species poses a serious threat to freshwater biodiversity and that it is likely to damage human livelihoods (through its impact on fishing and possibly rice agriculture). More research is urgently needed but in the meantime action is needed to reduce the rate of spread before it is too late.

BackgroundThe marbled crayfish (Procambarus virginalis) is a monoclonal, parthenogenetically reproducing freshwater crayfish species that has formed multiple stable populations worldwide. Madagascar hosts a particularly large and rapidly expanding colony of marbled crayfish in a unique environment characterized by a very high degree of ecological diversity.ResultsHere we provide a detailed characterization of five marbled crayfish populations in Madagascar and their habitats. Our data show that the animals can tolerate a wide range of ecological parameters, consistent with their invasive potential. While we detected marbled crayfish in sympatry with endemic crayfish species, we found no evidence for the transmission of the crayfish plague pathogen, a potentially devastating oomycete. Furthermore, our results also suggest that marbled crayfish are active predators of the freshwater snails that function as intermediate hosts for human schistosomiasis. Finally, we document fishing, farming and market sales of marbled crayfish in Madagascar.ConclusionsOur results provide a paradigm for the complex network of factors that promotes the invasive spread of marbled crayfish. The commercial value of the animals is likely to result in further anthropogenic distribution.Electronic supplementary materialThe online version of this article (10.1186/s12898-019-0224-1) contains supplementary material, which is available to authorized users.

The negative environmental and economic impacts of many invasive species are well known. However, given the increased homogenization of global biota, and the difficulty of eradicating species once established, a balanced approach to considering the impacts of invasive species is needed. The marbled crayfish (Procambarus virginalis) is a parthenogenetic freshwater crayfish that was first observed in Madagascar around 2005 and has spread rapidly. We present the results of a socio-economic survey (n = 385) in three regions of Madagascar that vary in terms of when the marbled crayfish first arrived. Respondents generally considered marbled crayfish to have a negative impact on rice agriculture and fishing, however the animals were seen as making a positive contribution to household economy and food security. Regression modeling showed that respondents in regions with longer experience of marbled crayfish have more positive perceptions. Unsurprisingly, considering the perception that crayfish negatively impact rice agriculture, those not involved in crayfish harvesting and trading had more negative views towards the crayfish than those involved in crayfish-related activities. Food preference ranking and market surveys revealed the acceptance of marbled crayfish as a cheap source of animal protein; a clear positive in a country with widespread malnutrition. While data on biodiversity impacts of the marbled crayfish invasion in Madagascar are still completely lacking, this study provides insight into the socio-economic impacts of the dramatic spread of this unique invasive species. "Biby kely tsy fantampiaviana, mahavelona fianakaviana" (a small animal coming from who knows where which supports the needs of the family). Government worker Analamanga, Madagascar. OPEN ACCESS Citation: Andriantsoa R, Jones JPG, Achimescu V, Randrianarison H, Raselimanana M, Andriatsitohaina M, et al. (2020) Perceived socioeconomic impacts of the marbled crayfish invasion in Madagascar. PLoS ONE 15(4): e0231773.