Développement hétérochroniquechez les Ostracodes: Stratégie d'adaptation à des environnements variables?

Abstract

The ontogenesis of Ruggieria lekkii and Chrysocythere ornata (Ostracoda, Crustacea) was investigated on thecontinental shelf of Congo. This study shows that the number or the length of development stages (progenesis or not) vary in different continental shelf areas. The architectural characters: costulation and reticulation for C. ornata, the spines for R. lekkii was observed and followed for each stage of development. Between two areas of the Congo shelf, the number of the spines doesn't increase at the same time in the development of R. lekkii. The first character to appear, for C. ornata's ontogenesis, is the costulation, the reticulation is later. But when the architectural characters have appeared during ontogenesis, their variation no more essentially depends on those of ontogenetic development, but also the variations of abiotic parameters. This phenomenon shows a heterochronic development between various characters of ontogenesis in diverse areas of the Congo shelf. The relationships between ecological parameters and variations of ontogenetic development explain the greater part of heterochronic development. The number of the stages or the length of the development of ostracods varies with environmental conditions (oxygenation, quantity of food) and population dynamics. When the ornamentation appeared, it varies essentially with bioprecipitation conditions (organic matter, carbonate equilibri). The study of heterochronic development highlights the adaptative capacities of ostracod faunas in different environmental conditions, and suggests the different strategies (colonization strategy, survival strategy) used for ostracods.