Taxonomic, ecological and morphological diversity of Ponto-Caspian gammaroidean amphipods: a review

The dynamic geological history of the Ponto-Caspian region drove the evolution of a highly adaptable endemic fauna that gave rise to notorious aquatic invaders. Amphipod crustaceans of the superfamily Gammaroidea attained considerable diversity, becoming the world's second most speciose ancient lake amphipod radiation. Nonetheless, apart from a few species that became invasive, this group remains poorly studied. Herein, we review and quantify the taxonomic, morphological and ecological diversity, as well as the phylogenetic context of Ponto-Caspian gammaroids within the adaptive radiation framework. Molecular phylogenies indicate that this radiation has a likely monophyletic mid-Miocene Paratethyan origin and is nested within the morphologically conserved Atlanto-Mediterranean Echinogammarus clade. We find extensive disparity in body shape, size, ornamentation and appendage length, along a broad ecological gradient from mountain springs to depths exceeding 500 m, on virtually all substrate types (including symbiosis). We propose four putative ecomorphs that appear convergent with distantly related oceanic and Baikal Lake taxa. Thus, the identified patterns support the adaptive radiation hypothesis, although extensive further research is needed. A checklist and provisional key to all known endemic species are provided to facilitate taxonomic research. Ponto-Caspian gammaroids could be a potentially powerful model for studying adaptive radiations and invasive species evolution.

Automated summary

The dynamic geological history of the Ponto-Caspian region has led to the evolution of a highly adaptable endemic fauna, particularly the amphipod crustaceans of the superfamily Gammaroidea. This group has a diverse range of species and plays an important role in adaptive radiation. The molecular phylogenies suggest that this radiation originated in the mid-Miocene period and is nested within a morphologically conserved clade. The Ponto-Caspian gammaroids exhibit extensive disparity in body characteristics and ecological preferences, making them a potentially powerful model for studying adaptive radiations and invasive species evolution.