Growth acceleration at sex change in the protogynous hermaphroditeChrysoblephus puniceus(Pisces: Sparidae)

Ecological and evolutionary consequences of alternative sex-change pathways in fish

Sequentially hermaphroditic fish change sex from male to female (protandry) or vice versa (protogyny), increasing their fitness by becoming highly fecund females or large dominant males, respectively. These life-history strategies present different social organizations and reproductive modes, from near-random mating in protandry, to aggregate- and harem-spawning in protogyny. Using a combination of theoretical and molecular approaches, we compared variance in reproductive success (V_k*) and effective population sizes (N_e) in several species of sex-changing fish. We observed that, regardless of the direction of sex change, individuals conform to the same overall strategy, producing more offspring and exhibiting greater V_k* in the second sex. However, protogynous species show greater V_k*, especially pronounced in haremic species, resulting in an overall reduction of N_e compared to protandrous species. Collectively and independently, our results demonstrate that the direction of sex change is a pivotal variable in predicting demographic changes and resilience in sex-changing fish, many of which sustain highly valued and vulnerable fisheries worldwide.

Sex change and effective population size: implications for population genetic studies in marine fish

Large variance in reproductive success is the primary factor that reduces effective population size (Ne) in natural populations. In sequentially hermaphroditic (sex-changing) fish, the sex ratio is typically skewed and biased towards the 'first' sex, while reproductive success increases considerably after sex change. Therefore, sex-changing fish populations are theoretically expected to have lower Ne than gonochorists (separate sexes), assuming all other parameters are essentially equal. In this study, we estimate Ne from genetic data collected from two ecologically similar species living along the eastern coast of South Africa: one gonochoristic, the 'santer' sea bream Cheimerius nufar, and one protogynous (female-first) sex changer, the 'slinger' sea bream Chrysoblephus puniceus. For both species, no evidence of genetic structuring, nor significant variation in genetic diversity, was found in the study area. Estimates of contemporary Ne were significantly lower in the protogynous species, but the same pattern was not apparent over historical timescales. Overall, our results show that sequential hermaphroditism may affect Ne differently over varying time frames, and that demographic signatures inferred from genetic markers with different inheritance modes also need to be interpreted cautiously, in relation to sex-changing life histories.

Life-history traits of the common snook Centropomus undecimalis in a Caribbean estuary and large-scale biogeographic patterns relevant to management

The ecology of common snook Centropomus undecimalis in Amatique Bay, a tropical estuary in eastern Guatemala, was investigated and life-history traits were used to conduct a meta-analysis of the species from Florida to Brazil. The reproduction cycle of C. undecimalis in Amatique was strongly related to the precipitation cycle, with a lag of 2 months. Spawning occurred from April to November with a peak spawning after the onset of the summer rains. Protandric sex reversal occurred early in the dry season (December) before somatic recovery from spawning. The growth cycle preceded that of body condition by c. 1 month, and was out of phase with the reproductive cycle. Growth was fast, as many individuals reached >70% of the maximum observed total length (LT , 102 cm) after 3 years. Sex transition occurred within a relatively narrow LT range (70-79 cm), but over a wide range of ages, indicating plasticity in this respect. The meta-analysis indicated a latitudinal-temperature gradient in life-history traits, as well as different seasonal patterns relative to temperature and hydrographical cycles. Centropomus undecimalis from cooler winter waters (e.g. Florida) reach larger maximum LT and LT at sex change, as well as greater gonado-somatic indices and longer life spans. Further, increased fishing mortality results in younger age at sex reversal and male predominance in the populations compared. Recognition of large-scale biogeographic patterns in this important, but little studied, fish species helps in the formulation of management advice in other areas of its occurrence.

Novel polymorphic microsatellite loci for the protogynous hermaphrodite slinger sea bream (Chrysoblephus puniceus, Sparidae)

As a result of the global decline of fish stocks, an increasing number of fish species are becoming targets of heavy exploitation, often concomitantly with a lack of biological knowledge on their structure and demographics. Here we present 11 new polymorphic microsatellite loci, isolated from the slinger sea bream (Chrysoblephus puniceus, Sparidae), a relatively recent target of coastal fisheries in eastern South Africa. Levels of genetic diversity were assessed in 39 individuals collected from the KwaZulu-Natal coast (Park Rynie, South Africa). Observed and expected heterozygosities varied between 0.39 and 0.97 and between 0.53 and 0.96, respectively. One locus (SL35) showed significant heterozygote deficiency and linkage disequilibrium was detected between SL35 and SL1. Importantly, five of these microsatellites cross-amplify in Cheimerius nufar, a sympatric species also subjected to exploitation.