No abstract

Fertilization success was measured in the bluehead wrasse, Thalassoma bifasciatum, a tropical reef fish with external fertilization of pelagic eggs. This species exhibits intraspecific variation in its spawning behavior; females either spawn with single males (pair spawning) or spawn with a group of at least three and often >20 males (group spawning). Fertilization success averaged °75% and did not differ between pair and group spawning, despite an estimated 80—fold increase in sperm release in group spawns. There was also no evidence that pair—spawning males suffered sperm depletion over the course of the spawning period. Thalassoma bifasciatum occurs in a variety of habitats and is exposed to varying levels of water turbulence. Fertilization success varied among days, and decreased with rougher water conditions. Within a reef, the calmer spawning sites behind the reef relative to the current had higher fertilization success than those along the side of the reef. These data suggest that while the type of spawning occurring at the site does not affect selection for fertilization success, females may gain fertilizations by selecting particular locations or periods of calmer water conditions to spawn. This is an alternative hypothesis to explain temporal and spatial patterns of mating. We provide detailed methods on how to accurately obtain data on fertilization success. Our technique can be used to study natural spawning in a wide variety of reef fishes and other marine organisms with pelagic eggs, external fertilization, and predictable spawning.

No abstract

Veliger larvae of mollusks were predicted to develop a larger velum relative to the larval shell when reared with scarce food. The functional consequences of such developmental plasticity would be (1) greater maximum capacity for capturing particles when food is scarce and (2) greater growth of structures retained in the postlarva when food is abundant. The hypothesis was tested by rearing veligers of the oyster Crassostrea gigas at high (near satiating) and low (growth limiting) concentrations of food. Veligers at the measured shell lengths (>200 {mu}m) had significantly larger velar lobes and longer prototrochal cilia than veligers reared in low concentrations of food. An analogous response to food levels (relatively longer ciliated band when food is scarce) has now been found for larvae as disparate as oyster veligers and sea urchin plutei. These observations suggest that functionally similar examples of developmental plasticity in the growth of larval parts have evolved more than once and may be widespread. An alternative interpretation is that differential mortality or growth in a genetically heterogeneous batch of oyster larvae results in advanced veligers of different forms at different concentrations of food. Both interpretations suggest an adaptive advantage to growing a larger apparatus for clearing particles from suspension when food is scarce and shifting materials to growth of postlarval structures (shell and associated structures) when food is abundant.