Speciation in the Central American Seaway: the importance of taxon sampling in the identification of trans-isthmian geminate pairs

Aim To create a molecular phylogenetic hypothesis for the closely related serranid genera Alphestes Bloch and Schneider and Dermatolepis Gill and assess the role of the Panamanian Isthmus in speciation within these reef fishes. Location Tropical eastern Pacific, Caribbean, and Indian Oceans. Methods Sequence data from one nuclear (TMO-4C4) and three mitochondrial genes (16S, 12S, and cytochrome b) were used in maximum parsimony and maximum likelihood analyses. Results Here we show that previously hypothesized trans-isthmian geminate species are not each other's closest living relatives. Species of Alphestes Bloch and Schneider in the eastern Pacific are sister taxa indicating post-closure speciation. Within Dermatolepis Gill, we identify a sister group relationship between the Caribbean and western Indian Ocean species, a rarely reported biogeographic pattern. Based on sequence divergence, speciation among the three species of Dermatolepis was, however, nearly simultaneous around the time of the isthmian closure event. Main conclusions Our molecular phylogenetic analysis of two closely related genera of reef fishes, each with presumed trans-isthmian geminates, cautions against the uncritical use of morphological similarity in identification of geminates, as well as the assumption that trans-isthmian sister groups date to the isthmian closure event. These findings suggest that in some instances incomplete sampling of species within a clade including putative geminates may lead to improper conclusions regarding the pattern and timing of speciation, as well as incorrect estimation of the rate at which evolution has proceeded

Estimating Abundance of Reef-Dwelling Sharks: A Case Study of the Epaulette Shark, Hemiscyllium ocellatum (Elasmobranchii: Hemiscyllidae).

v. ill. 23 cm.QuarterlyBenthic reef sharks play an important role in reef ecosystems, but little is known about their abundance or population dynamics. Abundance of the epaulette shark, Hemiscyllium ocellatum (Bonnaterre), on Heron Island Reef, Great Barrier Reef, Australia, was examined via a mark-recapture study. A total of 496 sharks was tagged between July 1994 and August 1997 in a 0.25-km2 area of reef flat, with 80 tagged sharks recaptured for a total of 102 recapture events. Captured individuals ranged in size from juveniles to adults (285–750 mm total length). Recaptured sharks were collected after 1–725 days at liberty and at distances of 0–329 m from their original capture point. The overall recapture rate was 20.6% with an estimated 17.5% tag loss. Population size was estimated using both closed and open population models. Closed population models produced various abundance estimates, with the Chao MðthÞ ranked best in model performance with an estimate of 2,224 sharks and 95% confidence intervals ranging from 1,730 to 2,916. Open population models produced lower estimates, with the Jolly D model producing an estimate of 559 individuals within the study site and confidence intervals ranging from 26 to 1,092. All models produced density estimations of 0.3 to 1.2 sharks per 100 m2. Based on thorough examination of model assumptions and results, open population models appear to provide the best population estimate within the study area