Spatial connectivity in an adult-sedentary reef fish with extended pelagic larval phase.

Understanding the spatial scale of demographic connectivity in marine reef fishes dispersing pelagic larvae is a challenging task because of the technical difficulties associated with tagging and monitoring the movements of progeny at early life stages. Several studies highlighted a strong importance of local retention with levels of dispersal of ecological significance restricted to short distances. To date little information is available in species where pelagic dispersal lasts for long periods of time. In this work, population structure and connectivity were studied in the grey triggerfish, Balistes capriscus. Grey triggerfish larvae and juveniles remain associated with floating Sargassum sp. beds for an estimated period of 4-7 months before settling on benthic habitats where they remain sedentary as adults. Analysis of genetic variation among populations along the continental shelf of the northern Gulf of Mexico and U.S. east coast, encompassing over 3,100 km of coastline, revealed homogeneous allele frequencies and a weak isolation-by-distance pattern. Moment and maximum-likelihood estimates of dispersal parameters both indicated occurrence of large neighbourhoods with estimates of the dispersal distribution parameter σ of 914 and 780 km, respectively. Simulated distributions of dispersal distances using several distribution functions all featured substantial fractions of long-distance dispersal events with the 90% percentiles of travel distance prior to settlement averaging 1,809 km. These results suggest a high dependency of local recruitment on the output of nonlocal spawning stocks located hundreds of kilometres away and a reduced role of local retention in this species.

Spawning frequency of brood dams and sires in a marine fish stock-enhancement hatchery.

Parentage analysis, employing five hypervariable microsatellite markers, was used to follow spawning patterns of red drum Sciaenops ocellatus broodfish in two spawning tanks through most of a calendar year in a marine fish hatchery dedicated to stock enhancement. Five of six dams and all four sires spawned at least once during the year. Variation in dam and sire spawning incidence and in number of progeny produced per dam and per sire translated into reduced genetic effective size (N e) per spawn by 40·6% in one tank and 50·8% in the other.

Environmental effects on fish sex determination and differentiation.

Environmental factors affect the sex ratio of many gonochoristic fish species. They can either determine sex or influence sex differentiation. Temperature is the most common environmental cue affecting sex but density, pH and hypoxia have also been shown to influence the sex ratio of fish species from very divergent orders. Differential growth or developmental rate is suggested to influence sex differentiation in sea bass. Studies in most fish species used domestic strains reared under controlled conditions. In tilapia and sea bass, domestic stocks and field-collected populations showed similar patterns of thermosensitivity under controlled conditions. Genetic variability of thermosensitivity is seen between populations but also between families within the same population. Furthermore, in the Nile tilapia progeny testing of wild male breeders has strongly suggested the existence of XX males in 2 different natural populations. Tilapia and Atlantic silverside studies have shown that temperature sensitivity is a heritable trait which can respond to directional (tilapia) or frequency dependent selection. In tilapia, transitional forms within a genetic sex determination (GSD) and environmental sex determination (ESD) continuum seem to exist. Temperature regulates the expression of the ovarian-aromatase cyp19a1 which is consistently inhibited in temperature masculinized gonads. Foxl2 is suppressed before cyp19a1. Recent in vitro studies have shown that foxl2 activates cyp19a1, suggesting that temperature acts directly on foxl2 or further upstream. Dmrt1 up-regulation is correlated with temperature-induced male phenotypes. Temperature through apoptosis or germ cell proliferation could be a critical threshold for male or female sex differentiation.

Application of hypervariable genetic markers to forensic identification of 'wild' from hatchery-raised red drum, Sciaenops ocellatus.

Forensic identification of 'wild' versus hatchery-produced (cultured) red drum (Sciaenops ocellatus), an economically important marine fish in the southern United States, was assessed using hypervariable nuclear-encoded microsatellites and sequences of mitochondrial DNA. Both genotype exclusion and likelihood-ratio tests successfully identified 'wild' and 'cultured' individuals within requisite error bounds and within the context of complete parental sampling. Of the two, genotype exclusion was more effective, producing satisfactory results with fewer microsatellites and larger allowable error rates. Assignment tests proved ineffective, most likely because of the low level of genetic divergence between the sampled populations. An optimal, minimum set of ten markers that will reduce potential genotyping costs is identified. Results of the study should allay concerns regarding identification of 'wild'-caught fish sold illegally.

Conservation genetics and demographic history of the endangered Cape Fear shiner (Notropis mekistocholas).

We examined allelic variation at 22 nuclear-encoded markers (21 microsatellites and one anonymous locus) and mitochondrial (mt)DNA in two geographical samples of the endangered cyprinid fish Notropis mekistocholas (Cape Fear shiner). Genetic diversity was relatively high in comparison to other endangered vertebrates, and there was no evidence of small population effects despite the low abundance reported for the species. Significant heterogeneity (following Bonferroni correction) in allele distribution at three microsatellites and in haplotype distribution in mtDNA was detected between the two localities. This heterogeneity may be due to reduced gene flow caused by a dam built in the early 1900 s. Bayesian coalescent analysis of microsatellite variation indicated that effective population size of Cape Fear shiners has declined in recent times (11-25 435 years ago, with highest posterior probabilities between 126 and 2007 years ago) by one-two orders of magnitude, consistent with the observed decline in abundance of the species. A decline in effective size was not indicated by analysis of mtDNA, where sequence polymorphism appeared to carry the signature of an older expansion phase that dated to the Pleistocene ( approximately 12 700 > 1 million years ago). Cape Fear shiners thus appear to have undergone an expansion phase following a glacial cycle but to have declined significantly in more recent times. These results suggest that rapidly evolving markers such as microsatellites may constitute a suitable tool when inferring recent demographic dynamics of populations.