Diversity and origin of freshwater amphipods of Mediterranean islands
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The Mediterranean islands are considered to be natural laboratories of evolution and places with extremely high level of endemism. Even though the fresh waters are among most diverse and also the most endangered ecosystems, still little is known about its biodiversity in the Mediterranean islands, as most of the studies on insular fauna focus mainly on terrestrial and marine biota. One of the most abundant organisms, being often keystone species in the freshwater macroinvertebrate communities are gammarid amphipods. In my PhD thesis, I investigated the diversity and origin of the freshwater gammarids of the Mediterranean islands. In the first part of my PhD, the available resources on the diversity of the freshwater malacostracan crustaceans from the Mediterranean islands were investigated and gathered together. Chapter I, is arguably the first such an extensive study on the freshwater fauna of the Mediterranean Islands, with valuable insight on its biogeographical affiliations. The findings indicate that amphipods are the most speciose group, being the most species-rich order on each of studied islands and archipelagos, with also one of the highest rate of endemism. In the main core of the PhD thesis, the diversity and origin of the freshwater gammarids from Aegean islands including Crete as well as Sicily were studied by gathering both morphological and molecular characteristics and by reconstructing the time-calibrated phylogenies using multimarket dataset. Chapter II provides the first evidence of the presence of freshwater populations of Gammarus on six Aegean islands with at least three endemic species, most probably new to science. The molecular methods were implemented to analyse their evolutionary history combining the information from the adjacent regions, including populations of recently described Gammarus plaitisi from Crete. Moreover, the divergence of these new species is strongly connected with the geological history of the Aegean region and its islands. In Chapter III, the substantial level of intraspecific diversity was detected within each of the Sicilian gammarid morphospecies. Moreover, these results support the different timescales and separate colonisation events of the gammarid fauna of Sicily. Altogether, these results indicate connectivity of the evolutionary history of the insular freshwater gammarids with the geological history of the islands as well as the entire Mediterranean region. Moreover, the level of overlooked diversity detected supports the importance of using molecular tools in the biodiversity assessments. The results of this thesis also highlight the need for future studies on the insular freshwater Mediterranean biota and deliver a valuable insight for better understanding of the mechanisms of the diversification of the freshwater organisms.
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