The evolution of benthic development in marine organisms: Constraints and consequences.

摘要

I carried out a number of studies aimed at describing constraints and consequences associated with the evolution of benthic development in marine organisms. I have tested hypotheses concerning constraints associated with the scaling of reproductive effort and body size in affecting the evolution of brooding in marine invertebrates using spirorbid polychaetes as study organisms; I found no evidence that scaling constraints limit brood size in spirorbids. Among marine invertebrates, brooding and simultaneous hermaphroditism are associated. To explore how the incidence of self-fertilization may affect brood size, I developed a mathematical model predicting the optimal levels of reproductive effort allocated to selfed and outcrossed broods in self-fertile organisms. This model shows that reductions in brood size upon selfing may represent an adaptive allocation decision by the parent, as opposed to arising solely as a consequence of inbreeding depression or self-incompatibility. The effects of brooding on other aspects of the reproductive biology of species, including developmental rates of embryos and mating systems, were studies in four species of jawfishes, a family in which males mouthbrood the embryos until hatching. The effects of physiological constraints on the evolution of benthic development, such as the demand for oxygen by developing embryos, and hydrodynamic factors affecting oxygen supply were explored using both comparative methods and laboratory experiments on benthic egg masses of fishes. These studies suggest that both flow regime at the oviposition site and characteristics of the egg mass, such as egg size and mass thickness, which influence flow through the mass, are important factors affecting mortality rates and developmental rates of embryos.