Subterranean Waters of Yucatán Peninsula, Mexico Reveal Epigean Species Dominance and Intraspecific Variability in Freshwater Ostracodes (Crustacea: Ostracoda)

The Yucatán Peninsula is a karstic region, rich in subterranean environments with diverse crustacean stygobiont fauna. In order to gain insights into the biological evolution of this we evaluated ostracode species composition caves and cenotes five independent sampling campaigns (2008, 2013, 2017–2019). Using morphometric analyses, inter-population morphological variability; using molecular analysis based on mitochondrial COI nuclear 18S rDNA, genetic differentiation selected species. observed fauna composed 20 (epigean) species, presenting lack strict stygobionts. Morphometric analyses discriminated up three morphotypes each most abundant species: Cytheridella ilosvayi, Alicenula sp. Cypridopsis vidua. High intraspecific variability was found either shape or size. Phylogenetic demonstrated existence lineages C. high support (>0.9). rDNA sequences were identical among individuals different populations. A congruence between markers precluded us from postulating speciation environments. It likely that Late Pleistocene—Early Holocene climate variation related sea level precipitation forcing agent for epigean dominance Peninsula.