Ontogenetic reaction norm for binary traits: the timing of phallus development in the snail Bulinus truncatus.

The ontogenetic trajectory of plastic binary traits may provide valuable insights into their evolutionary rate of change. In this paper, the timing of the plastic response of a temperature-dependent sexual polymorphism, aphally, is investigated in the freshwater snail Bulinus truncatus. Aphally is defined as the loss of the male copulatory organ in otherwise hermaphroditic animals. Individuals from two inbred lines were switched at various times during their early development between 25 and 30 degrees C, and their phally status ascertained, in order to evaluate the parameters characterising the ontogenetic reaction norm of aphally to temperature. A series of nested models including parameters for the onset, offset, and the intensity of the response to temperature were fitted to the data, allowing for a wide range of reaction norms. One genotype did not show any variation in aphally ratio with switching temperature, while a switch-point model (onset and offset corresponding to the same developmental point in time) best fitted the second genotype. The results suggest that the plasticity of aphally is expressed before eggs hatch. Their consequences on the evolution of aphally are discussed. More generally, the methodology proposed here can be used to analyse variation in ontogenetic parameters of discrete traits.

The metabolism of astaxanthin during the embryonic development of the crayfish Astacus leptodactylus Eschscholtz (Crustacea, Astacidea).

The developing eggs of the crayfish Astacus leptodactylus are found to contain important carotenoid amounts. Free astaxanthin, mainly associated with protein and lutein represent the main pigments occurring in the yolk at the end of the embryonic period. Esterification processes affecting astaxanthin appear concomitantly with the resorption of vitellin reserves, the activation of the digestive gland and the rapid decrease of lutein amounts. Esterified astaxanthin contents increase significantly within the interval between the juvenile stages I and II. Nevertheless, free astaxanthin levels appear insufficient to balance the amounts of the esterified form, scored at the end of the endotrophic period.