Eco-morphological diversity in Antarctic Epimeria (Crustacea, Amphipoda).

Supervisors: Bruno Frederich, Marie Verheye (University of Liège).
The amphipod genus Epimeria is very speciose in the Southern Ocean. Most of the studied species are classified as complexes of pseudocryptic species, presenting small and previously overlooked morphological differences. The present study aims to explore the possible evolutionary processes which generated the exceptional diversity within the Antarctic Epimeria clade. Enabling the evaluation of adaptation hypotheses and inform on the eco-evolutionary causes of phenotypic change between morphological and ecological traits in Antarctic Epimeria, to finally identify possible correlations between these two kind of data. The specimens were photographed in lateral and dorsal view, followed by size (linear) and shape (geometric) measurements of different body traits, and treated with image processing and morphometric softwares. To correlate this data with ecological data, stable isotope (13C and 15N) ratios were measured and used as variables to try and describe the trophic ecology of the species. To describe the morphological variation, principal components analysis (PCA) were produced in Past (Version 3.4) for the linear measurements, and in TpsRelw (Version 1.69) for geometric measurements. Scatter plots were produced for PCs that describes most of the variation (> 70%). Possible correlations between the principal components and ecological data were assessed by linear regression analyses. Additionally, the ecological data (δ13C and δ15N) was plotted against each ratio for the different morphospaces, and to reassure the strength of the relationships, a multivariate analysis of variance (MANOVA) was run to test the hypothesis of the correlation between morphological and ecological data. The results suggests that species E. cinderella, E. acanthochelon, E. amoentias, E. similis, E. amoenitas, E. anguloce and E. rubrieques represents the most extreme variations in the clade, regarding the traits explained by PC1 and PC2. Coxal plates morphometrics suggests phylogenetic similarities, and could be a valuable indicator of phenotypic adaptations, contributing to the understating of the processes that generated the diversity within the Antarctic Epimeria. Correlation between morphometric and ecological data showed little to no significance, therefore, indicating that the traits may not be ecologically variable and represent only a few aspects of the trophic ecology. Lastly, it was impossible to establish a connexion between the morphological and ecological diversity, and perhaps, the combination of different techniques could give a better overview of the ecological role of the species within the genus Epimeria.