|Consequences of brood protection in the diversity of Antarctic echinoids|
Poulin, E.; Féral, J.-P. (1998). Consequences of brood protection in the diversity of Antarctic echinoids. Océanis (Paris) 24(4): 159-188
In: Océanis (Paris). Institut Océanographique: Paris. ISSN 0182-0745, more
|Authors|| || Top |
- Poulin, E.
- Féral, J.-P., more
Marine invertebrates display a great variety of life-history traits and reproductive strategies. In echinoids, four patterns of larval development are generally recognized: planktotrophy, pelagic lecithotrophy, bottom dwelling and brood-protecting. Each broad type of free and protected development is found in all the oceans, but comparisons of the principal reproductive modes between different geographic regions have shown that they are not equally distributed. Frequency of pelagic development (planktotrophic and lecithotrophic) decreases from equator to Antarctic, where brood-protecting become dominant. Numerous theories have been proposed to explain the richness of non-pelagic development in most marine invertebrates within the Southern Ocean. These theories can be grouped into three categories: (1) larval survival, where selection acts on larvae, (2) energy allocation, (3) dispersal. All of them consider the adaptative significance of broodprotecting as the key to the success of this strategy in the Antarctic. However, the adaptative significance of brooding and the evolutionary success of this strategy in the Antarctic must be considered as two separate questions. To consider the problem at an evolutionary level, we have examined the consequences of different reproductive strategies on the genetic structure of species and on the longterm evolution of the clade. We examine this problem in the case of echinoids, a clade particularly well suited to addressing this question. In echinoids, the reduction of larval stage duration is associated with a decrease in gene flow and consequently of the geographical scale of genetic differentiation. This allows us to reconsider the high speciation rate model which leads to an increase in number of low dispersal species (isolation by distance). This model, previously tested by means of fossils is not satisfactory in living echinoids. Thus, the model is rebuilt with the addition of differential extinction rate between planktotrophic and brooding species in relation to the climatic history of the Antarctic.