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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

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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.

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.