This study uses a hologenomic approach to elucidate the biology of two fish species found in the Mediterranean wetlands. Hologenomic insights into the biology of invasive and endangered fishes in Mediterranean wetlands

Freshwater habitats are under increasing pressure from numerous anthropogenic forces including the introduction of invasive species capable of altering ecosystems, resulting in an overall loss of genetic diversity as native and endemic populations disappear. Although alien species themself are likely to experience loss of genetic diversity when colonising novel environments, they manage to become invasive, suggesting that other factors might facilitate their adaptive capacity. Using a hologenomic approach, we elucidate population genomic trends, the gut microbiota and genome-environment-microbiota interaction in the endemic and endangered Spanish toothcarp (Aphanius iberus) and the highly invasive Eastern mosquitofish (Gambusia holbrooki). We find clear genetic signatures of captive breeding in the populations of A. iberus, and for G. holbrooki, we observe an overall low level of heterozygosity and potential signs of multiple introductions. Gut microbial communities of the two species differed significantly between locations and we find that the genetic profile of each fish is a better predictor of microbial composition than salinity. Using shotgun metagenomics, we observe an overall high functional capacity of the microbiota in both species, but identify no significant differences in the functional capacity between them. Overall, there were no signs of increased microbial plasticity in G. holbrooki, but as we were unable to make a direct comparison between the two species, we encourage future research to further explore the potential role of the microbiota in invasive species.