No abstract

Pivotal temperature (the constant temperature giving 50% of each sex) for two clutches of loggerhead sea turtles (Caretta caretta) from Kyparissia Bay, Greece, was 29.3°C. Pivotal incubation duration (the time from laying to hatching giving 50% of each sex) was 52.6 days. These values are close to those obtained for this species in Brazil and the United States, providing further evidence that these characteristics are relatively conservative in different populations. Methodological differences between different experiments and limitations on accuracy of equipment make the detection of small differences problematic. Comparison of incubation durations in the field with the pivotal durations obtained here suggest that hatchling sex ratio on some Mediterranean beaches is female biased but probably varies considerably within this region.Résumé : La température charnière (la température constante d'incubation qui produit 50 % d'individus de chaque sexe) pour deux masses d'oeufs de caouanes (Caretta caretta) de la baie de Kyparissia en Grèce a été estimée à 29,3°C. La durée charnière de l'incubation (le temps entre la ponte et l'éclosion qui produit 50 % de tortues de chaque sexe) est de 52,6 jours. Ces valeurs se rapprochent de celles que l'on a obtenues chez cette espèce au Brésil et aux É.-U., ce qui est une indication supplémentaire que ces caractéristiques sont relativement conservatrices dans les diffé-rentes populations. Les différences méthodologiques entre les expériences et les limites de précision des appareils rendent problématiques la détection de petites différences. La comparaison des durées de l'incubation en nature avec les durées charnières obtenues ici laisse croire que le rapport mâles : femelles chez les nouveau-nés sur certaines plages méditerranéennes favorise les femelles, mais qu'il varie probablement beaucoup dans la région.[Traduit par la Rédaction] Mrosovsky et al. 2124

In multispecies assemblages, phylogenetic relatedness often predicts total community biomass. In assemblages dominated by a single species, increasing the number of genotypes increases total production, but the role of genetic relatedness is unknown. We used data from three published experiments and a field survey of eelgrass (Zostera marina), a habitat-forming marine angiosperm, to examine the strength and direction of the relationship between genetic relatedness and plant biomass. The genetic relatedness of an assemblage strongly predicted its biomass, more so than the number of genotypes. However, contrary to the pattern observed in multispecies assemblages, maximum biomass occurred in assemblages of more closely related individuals. The mechanisms underlying this pattern remain unclear; however, our data support a role for both trait differentiation and cooperation among kin. Many habitat-forming species interact intensely with conspecifics of varying relatedness; thus, genetic relatedness could influence the functioning of ecosystems dominated by such species.

No abstract

Phenotypic sex in sea turtles is determined by nest incubation temperatures, with warmer temperatures producing females and cooler temperatures producing males. The common finding of highly skewed female-biased hatchling sex ratios in sea turtle populations could have serious repercussions for the long-term survival of these species and prompted us to examine the thermal profile of a relatively pristine hawksbill nesting beach in Guadeloupe, French West Indies. Data loggers placed at nest depth revealed that temperatures in the forested areas were significantly cooler than temperatures in the more open, deforested areas. Using these temperatures as a predictor of sex ratio, we were able to assess the relative contributions of the different beach zones to the primary sex ratio: significantly more males were likely to be produced in the forested areas. Coastal forests are therefore important male-producing areas for the hawksbill sea turtle, and this has urgent conservation implications. On Guadeloupe, as on many Caribbean islands, deforestation rates are high and show few signs of slowing, as there is continual pressure to develop beachfront areas. The destruction of coastal forest could have serious consequences both in terms of local nesting behavior and of regional demography through the effects on population sex ratios. Human alterations to nesting habitat in other reptile taxa have been shown to modify the thermal properties of nest sites in ways that can disrupt their ecology by allowing parasite transmission, increasing vulnerability to climate change, or rendering existing habitat unsuitable.

The genetic composition of groups of individuals can significantly influence the productivity, resilience, and functioning of communities and ecosystems. For example, the relatedness of individuals within a group often dictates whether their interactions are competitive or cooperative. It is therefore necessary to characterize the genetic structure of populations at spatial scales relevant to these interactions and to determine the distribution of genetic diversity at those scales. Using microsatellite data, we assessed fine-scale population structure of Zostera marina, an important habitat-forming seagrass, within and between Bodega Harbor and Tomales Bay in northern California, USA. Despite the potential for long-range dispersal, we found significant population structure at all hierarchical scales (among bays, among sites, among tidal heights), corresponding to distances ranging from meters to tens of kilometers. The pattern of genetic differentiation that emerged at local scales differed between bays, with Tomales Bay being more structured even though the Euclidean distances among sites were similar in each bay. The relatedness of genets within a tidal height also differed among bays: in Bodega Harbor most genets occurred in proximity to unrelated individuals, whereas in Tomales Bay, genets were mixed with their close relatives, likely due to decreased dispersal. These contrasting kin structures, coupled with highly variable levels of clonal diversity, underscore the importance of examining variation at multiple scales, as this reveals genetic factors which might play an important role in many ecological processes.

All organisms face two fundamental trade-offs in the allocation of energetic resources: one between many small versus a few large offspring, and the second between present and future reproduction. Nowhere are these trade-offs more apparent than in the vast range of variation in the sizes of eggs and offspring exhibited among species of marine invertebrates. It has become increasingly clear that, in many taxa of marine organisms, there is also substantial intraspecific variation in the size of eggs and hatchings. This variation has largely been attributed to adaptive maternal effects. In theory, however, the inevitable conflicts of interest that arise in families of sexually reproducing organisms over the optimal distribution of parental resources among siblings could also account for much of this variation in egg and offspring size. Here, we explore the potential impacts of family conflict on offspring traits by comparing the life histories of two exemplar species of marine organisms, the polychaete Boccardia proboscidea and the gastropod Solenosteira macrospira, emphasizing how differences in modes of fertilization and parental care might influence the phenotype and, consequently, the fitness of offspring.

Within a single population of hawksbill sea turtles (Eretmochelys imbricata), we found a behavioral polymorphism for maternal nest site choice with respect to beach microhabitat characteristics. Some females preferred to nest in littoral forest and in places with overstory vegetation cover, and others preferred to nest in more open, deforested areas. Nest site choice was consistent within and between nesting seasons two years apart. This was not a result of females simply returning to the same location along the shoreline; beach sections used by individual turtles varied between seasons. Nest site choice was not influenced by changes in beach environment (e.g., beach width and foliage cover) or by changes in females' reproductive output (e.g., clutch size), suggesting that fidelity to particular microhabitats is a major determinant of the observed nesting patterns. Because hawksbills exhibit temperature-dependent sex determination, if the behavioral polymorphism in nest site choice has a genetic basis, as is plausible, then this would have implications for sex ratio evolution and offspring survival. By taking an individual-based approach to the study of maternal behavior we reveal previously overlooked individual variation and hope to provide some impetus for more detailed studies of nest site choice.