CONSERVED LIFE HISTORY PHENOTYPES AMONG HISTORICALLY ISOLATED CLADES IN THE CHIRAL LIVEBEARER FISH OF LOWER CENTRAL AMERICA

Lower Central America contains some of the highest freshwater fish diversity on the planet. Yet, species by species, we still know remarkably little about factors that have created this diversity and the threats that could put it at risk. The chiral livebearer ( Xenophallus umbratilis ) exemplifies these deficits. This freshwater livebearing fish species primarily occupies habitats along the high-elevation fringes of large volcanoes in the central cordillera of Costa Rica.

Previous work suggests that current populations have been isolated by repeated marine incursions beginning around 5 mya. Genetic data point to four putative clades that could be considered evolutionarily distinct. Unfortunately, beyond this we know little about adaptive evolution of demographically relevant traits among these clades, making it difficult to determine the conservation status of this species overall. Moreover, a recent IUCN assessment of this species was limited to only a portion of its geographic range and lacked population level information from many locations where it occurs. To address these gaps, here we describe the life history of this species, taken from 23 collections made across its geographic range from locations where this fish is locally abundant. This allowed us to determine if life history traits differ among populations coincident with known population structure. Despite long periods of isolation among clades, we found only modest evidence for divergence in life history phenotypes, and this was limited to just two of the four clades. These data suggest that life history traits are mostly conserved among populations, data that are critical to future conservation planning.