Ecomorphological diversification of the Cyprinodon species complex from Lake Chichankanab, Yucatan, Mexico

Chichankanab is a small, shallow, ⁓8,000-year-old, tropical lake where the adaptive radiation of seven sympatric Cyprinodon species have been described. Since the variation in size, morphology, and diet play a key role in facilitating niche partitioning, this study aims to determine if the sympatric species can be independently identified by their variation in size, morphology, and diet and to understand the role of those variables in the ongoing diversification. To fulfill our aim we gathered, from fish collections, an updated sample of the seven sympatric species and the sister species Cyprinodon artifrons from whom we took their size and photographs to develop geometric morphometric analyses, and collected information on their diet. According to our results, size range allows the separation of Cyprinodon beltrani as the largest species, geometric morphometric allows the segregation C. beltrani, Cyprinodon simus, Cyprinodon suavium, and Cyprinodon labiosus, and a morphotype of three species, Cyprinodon esconditus, Cyprinodon verecundus, and Cyprinodon maya, which can be segregated by body measurements and the size of the species. The diet can help to segregate C. beltrani herbivore, C. maya piscivore/omnivore, C. simus zooplanktivore/detritivore, C. suavium and C. verecundus carnivore/molluscivore, and C. esconditus and C. labiosus carnivores. The ongoing hybridization and the changes in the lake are driving the diversification and decrease of these species. According to our results, there is not one character that differentiated all the species, differentiation was only possible through their specific variation in one character or by a specific combination of characters. It is important to monitor and keep updating information on these evolving species since all seven are listed in the IUCN as vulnerable and near threatened, and according to official Mexican categories as in danger of extinction.