The genetic homogeneity of the Monterey Spanish mackerel Scomberomorus concolor population in the Gulf of California was confirmed using nine nuclear microsatellite loci in combination with mitochondrial cytochrome b gene sequences. Samples were collected from the upper and central Gulf areas, representing the two main biogeographical regions of the Gulf. The analyses support the existence of a single panmictic population of S. concolor inhabiting the Gulf of California which in terms of fishery management represents a single genetic stock. Additionally, the contemporary effective population size estimated for the S. concolor population (Ne = 3056.9) was high and similar to another pelagic species. The gene flow seems to be bidirectional between the upper and central Gulf, which coincides with the seasonal movements between both regions related to spawning and feeding activities. A population expansion event was detected, which agrees with a colonization-expansion hypothesis of the S. concolor population in the Gulf.
Spotted spiny lobsters, Panulirus guttatus, are small, obligate reef-dwellers that exhibit a highly sedentary lifestyle and a low tendency to aggregate with conspecifics, and that reproduce asynchronously year-round. Individual females can produce multiple clutches per year but have a short receptivity per clutch. As in most spiny lobsters, females of P. guttatus mate only once per clutch and resist further mating attempts, features that may favour development of female mate choice but limit the potential for sperm competition. We separately examined mate choice by large and small mature females through laboratory experiments that controlled for effects of male–male competition, quality of shelter, and mere social attraction. Only large females expressed preference for larger males relative to their own size, suggesting that only large females that mate with small males risk sperm limitation on fecundity success. In couples that mated, males deposited rather small, thinly spread spermatophores on the sterna of females. Spermatophore area (considered as a proxy measure of sperm content) increased with male size and showed no relationship with female size, suggesting that males of P. guttatus have a short sperm-recovery period or do not exhibit strategic sperm allocation in a non-competitive context. A comparison of average sperm allocation between P. guttatus and its sympatric species, P. argus (a much larger, highly mobile, and highly social species with more seasonal reproductive periods and a longer receptivity of females per clutch), suggests that males of P. guttatus allocate proportionally less sperm to females, on average, than males of P. argus do. According to predictions of across-species risk models, this result suggests that males of P. guttatus perceive lower average levels of sperm competition risk than males of P. argus do, implying that different Panulirus species may exhibit different mating strategies in accordance with their particular life-history and sociobiological traits.
The spiny lobster Panulirus guttatus is a highly sedentary, obligate reef-dweller that exhibits a low degree of gregariousness yet reproduces year-round. Previous laboratory studies revealed that these lobsters were significantly attracted to scents released by conspecifics during a 'high reproductive activity' period (HRA, Â60% of ovigerous females on average) but not during a 'low reproductive activity' period (LRA, Â20%), suggesting that becoming more closely distributed at the right time may increase reproductive opportunities for these lobsters. We tested this hypothesis in the field. We marked all crevices harbouring P. guttatus lobsters ('dens') on two isolated coral reef patches over six consecutive sampling periods (three during an LRA and three during the ensuing HRA) and recorded the number, sex and size of lobsters in each den. Dens marked at a given time were considered as harbouring zero lobsters at previous times. For each site, a model selection based on parameters of the negative binomial distribution showed that m (mean lobsters/den) varied little over time but that k (dispersion parameter) decreased across the LRA and remained low (indicating a more clumped distribution) across the HRA. These trends in aggregation were further confirmed by values of Lloyd's 'patchiness', supporting the hypothesis that seasonal aggregation increases reproductive opportunities for P. guttatus. However, the tendency to aggregate appeared to be modulated by density and mean size of lobsters, which differed with site. These findings have potential implications for exploited P. guttatus populations and invite further study of the complex behaviours that characterize sedentary lobsters.
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