Geometric Morphometric Analysis of the third epimeral plates of the genus Gammarus (Crustacea, Amphipoda) as a reliable character for identifying closely related species

Landmark-Based Geometric Morphometric Methods were used for the first time to quantitatively assess shape variations of the third epimeral plate (Ep3) of six Gammarus species (G. lordeganensis, G. parthicus, G. pretzmanni, G. pseudosyriacus, Gammarus sp1 and Gammarus sp2.) from five different localities in Iran. Two landmarks and 10 semi-landmarks on the posterior, anterior and inferior margins of the Ep3 were digitized on 78 adult male specimens. Shape diversity of samples and discrimination of all species were analyzed with Principal Components Analysis (PCA) and Canonical Variates Analysis (CVA). The results strongly supported the distinction in the posterior margin of Ep3 shape of the six species, while the inferior margin clearly showed similar morphological structure. A remarkable separation of G. lordeganensis as a distinct group from the rest of the species was found in both CVA and PCA analyses of anterior margin of Ep3 shape, while other species had overlaps with each other. Based on these findings, geometric morphometric data, could be used to identify diagnostic morphological traits. The shape of the Ep3 could be used as an appropriate character for separating closely related amphipod species of the genus Gammarus.