Variation in larval life-history traits among reef fishes across the Isthmus of Panama

We tested the hypothesis that regional differences in oceanic productivity have led to the evolution of predictable patterns of regional variation in life-history traits of pelagic larvae of tropical reef fishes. To do so we compared larval traits (egg and hatchling size, larval growth rate and dura tion, and size at settlement) among closely related reef fishes from the At lantic and Pacific coasts of the Isthmus of Panama. This comparison provide s a control for phylogenetic effects because those regions shared a common fauna prior to the rise of the Isthmus similar to3.5 million years ago, sub sequent to which each fauna evolved independently under a very different pr oductivity regime. We measured larval traits of 12 benthic-spawning damself ishes (Pomacentridae: Abudeduf, Chromis and Stegastes) and 13 pelagic-spawn ing wrasses (Labridae: Bodianus, Halichoeres, and Thalassoma). These includ ed members of each genus on each side of the Isthmus and four sets of trans isthmian sister species of pomacentrids. Among the pomacentrids we found co nsistent transisthmian differences in hatchling size, but not in other larv al traits. Essentially the reverse pattern occurred among the labrids - lar val growth and duration differed consistently among congeners in the two re gions, but without consistent differences in hatchling size or size at sett lement. Neither relationship is predicted by the regional-productivity hypo thesis. Most of the differences were quite small. Stronger phylogenetic eff ects on larval traits (inter- and intrageneric variation within regions) oc cur in both families and evidently overwhelm any effect of regional variati on in productivity. Reassessment of data that takes into account such phylo genetic effects questions previous conclusions about the existence of regio nal differences in larval traits among damselfishes in the West Pacific and the Carribean.