THE REAL “FRAIL SEX”: PREVALENCE OF CARAPACE ABERRANCE IN MALE CYPRIDEIS AMERICANA (CRUSTACEA, OSTRACODA) DUE TO CLIMATE-DRIVEN SALINITY FLUCTUATION IN BAHAMIAN PONDS

How species respond to climate-driven salinity fluctuation in aquatic environments is a particularly important question for evolutionary studies, as it can be the difference between their adaptation or extinction. For ostracods specifically, male/female physiological differences influence this response, because the relative size of male reproductive organs seems to be related to the longevity of taxa in the fossil record. In the present study, we aim to determine how shape of the carapaces and valves of the Bahamian ostracod species Cyprideis americana varies as a result of salinity changes through space and time. Hypotheses of the present work include: 1) physiological response to environmental salinity variation in Recent specimens is detectable through eigenshape analysis; 2) it is possible to detect the same physiological response through time; and 3) male and female specimens of the same species change their carapaces and valves at different ratios in response to these variations. To test these hypotheses, samples containing C. americana specimens were taken from three ponds at San Salvador – the slightly brackish Blue Hole Five, the marine-like saline Clear Pond and the hypersaline French Pond – and from sediment cores from Duck Pond Blue Hole, Eleuthera. Principal component analysis and non-metric multidimensional scaling of specimens from San Salvador sites show male ostracods present greater eigenshape variation linked to salinity than females, ranging from overdevelopment in slightly brackish waters to underdevelopment in hypersaline conditions, in comparison to the control marine salinity groups. The same results are observed on Eleuthera, where in-depth morphometric and isotopic analyses data are strongly similar to those from Recent strata; additionally, they also indicate underdevelopment in excessively brackish intervals, especially of males, which are greatly reduced in number. Therefore, salinity-driven physiological change seems to be a real phenomenon that affects C. americana by causing detectable shape aberration in both geological and chronological scales, a quality that would make it a potential proxy for biological response to climate change. This holds especially true for male specimens, probably due to the metabolic cost involved in the development of their sexual organs.