FOUNDATIONS OF GREGARIOUSNESS: A DISPERSAL POLYMORPHISM AMONG THE PLANKTONIC LARVAE OF A MARINE INVERTEBRATE

Current hypotheses to explain genetic chaos under the sea

Chaotic genetic patchiness (CGP) refers to surprising patterns of spatial and temporal genetic structure observed in some marine species at a scale where genetic variation should be efficiently homogenized by gene flow via larval dispersal. Here we review and discuss 4 mechanisms that could generate such unexpected patterns: selection, sweepstakes reproductive success, collective dispersal, and temporal shifts in local population dynamics. First, we review examples where genetic differentiation at specific loci was driven by diversifying selection, which was historically the first process invoked to explain CGP. Second, we turn to neutral demographic processes that may drive genome-wide effects, and whose effects on CGP may be enhanced when they act together. We discuss how sweepstakes reproductive success accelerates genetic drift and can thus generate genetic structure, provided that gene flow is not too strong. Collective dispersal is another mechanism whereby genetic structure can be maintained regardless of dispersal intensity, because it may prevent larval cohorts from becoming entirely mixed. Theoretical analyses of both the sweepstakes and the collective dispersal ideas are presented. Finally, we discuss an idea that has received less attention than the other ones just mentioned, namely temporal shifts in local population dynamics.

Laboratory culture and evaluation of the tubeworm Ficopomatus enigmaticus for biofouling studies

Ficopomatus enigmaticus, a euryhaline tube-building polychaete worm with a subtropical to temperate distribution, is an increasingly problematic fouling organism. In this study, laboratory protocols for maintaining adult broodstock, destructive spawning, larval culture and a settlement bioassay were developed. The method routinely yielded approximately 200 larvae per spawning adult. The mean number of eggs released by females was 1517 and the mean number of spermatozoids per male was 4.425 × 10(6). Fertilisation success, using an initial concentration of 2.5 × 10(6) spermatozoids and 45 eggs ml(-1), was 76% after a contact time of 60 min. The first cleavage occurred after 20 min and the trocophore larval stage was attained by 18 h. Metatrochophores were observed 4 d post-fertilisation and were competent to settle 1 day later. The proportion of larvae that settled after 48 h was surface-dependent: 10.24% on glass, 1.39% on polystyrene and 11.07% on a poly(dimethylsiloxane) elastomer. The presence of a biofilm on glass increased the rate of settlement 7-fold compared to clean glass.