ABSTRACT
Ecological models suggest that individuals should not disperse in spatially varying but temporally constant environments. If such models are frequent in the literature, there are few studies that validates this assumption. In marine invertebrates, the larval stage is generally responsible for dispersal. One major way to reduce or avoid larval dispersal is to shorten or to lose the pelagic stage. The Antarctic and Subantarctic schizasterid echinoid species brood their offspring in dorsal pouches. The juvenile urchins are released directly onto the bottom around their mother. This situation correspond to an extreme strategy of non-dispersal.
Studies on spatial structure show that Abatus cordatas, a species endemic to the Kerguelen Islands, lives in dense isolated populations generally located at the bottom of sheltered bays, where the hydrodynamism is weak enough to permit the maintenance of populations. For this non-dispersal species, the spatial and temporal habitat structure fit the theoretical model predictions: spatial heterogeneity (difference of carrying capacities between sites) and persistence of the populations.
The consequences of such a strategy on the genetic structure of Abatus cordatas, as revealed allozyme polymorphism data, are that the populations are geographically differentiated as a result of the genetic drift and low migration rates between neighbouring populations. Moreover, genetic differentiation occurs over a scale of kilometers, contrary to the large scale differentiation generally reported for echinoid planktotrophic larvae species.
Considering a geological time scale, high differentiation rates leading to non-dispersal strategy as well as the extreme climatic and geographic position of Antarctica could explain the radiation of the echinoid brood protecting genus and contribute to the understanding of the high proportion of marine brood protecting invertebrates species in this area.
