Shared and unique patterns of trait expression in a sulfide spring fish population in Guanacaste, Costa Rica

This is the authors' abstract. We don't add key points for this paper.

Organisms often exhibit similar traits when exposed to similar environmental pressures. In sulfide springs, which are rich in toxic hydrogen sulfide and severely hypoxic, members of the family Poeciliidae have repeatedly evolved similar life history, physiological, and morphological traits. Here, we quantified morphological and physiological traits related to hydrogen sulfide tolerance in a population of Poecilia gillii from a sulfide spring in Guanacaste, Costa Rica, and made comparisons with a nearby non-sulfidic population and with well-studied populations of P. mexicana from southern Mexico. While most differentially expressed genes found in P. gillii were not differentially regulated in the sulfidic P. mexicana populations, there were a number of differentially expressed genes associated with hydrogen sulfide detoxification, sulfur transport, and the cellular response to hypoxia shared with P. mexicana . Additionally, like sulfidic P. mexicana , P. gillii from sulfide spring habitats had longer heads, a more elongated abdomen, and reduced standard length compared to non-sulfidic fish. Previous studies in Southern Mexico indicated that standing genetic variation is an important driver of evolution in the sulfide spring fishes, but our study highlights how similar selection gradients can lead to similar traits even when ancestral standing genetic variation is unlikely due to large geographic separation. Future studies of P. gillii using common-garden rearing environments will need to investigate whether these results represent convergent adaptations to sulfide springs.