MEPS 619:69-84 (2019)  -  DOI: https://doi.org/10.3354/meps12959

ABSTRACT: In marine invertebrates with planktotrophic larvae, modelling studies predict that water temperature and food availability are the primary factors influencing oocyte size, with large oocyte sizes being favoured by cold water and low food availability. We examined intraspecific variation in oocyte size in the polychaete Spirobranchus cariniferus in populations from the East and West Coasts of New Zealand’s North Island, which differ in temperature and food availability during the reproductive season: the East Coast has consistently warmer seawater temperatures throughout the summer and higher phytoplankton abundance in late summer than the West Coast. A cross-fertilization experiment and DNA sequencing confirmed that Spirobranchus populations on both coasts belong to the same species. Then, analyses of S. cariniferus oocytes from 5 sites per coast revealed that the West Coast population produces oocytes that are on average 14% larger and contain up to 41% more triacylglycerols (TAGs) than the East Coast population. West Coast S. cariniferus oocytes also developed into larger larvae that reached competence 22% sooner than East Coast oocytes and larvae. These intraspecific comparisons of East and West Coast S. cariniferus populations reveal oocyte size to differ substantially even among populations that are probably not fully isolated, consistent with predictions of life history models. We estimate that genetic divergence may be responsible for up to 58% of the difference in oocyte size between East and West Coast populations, and that oocyte size may be subject to local adaptation to temperature and, to a lesser extent, food availability differences between coasts.

KEY WORDS: Offspring size · Life history strategy · Maternal provisioning · Egg size · Biogeography · Phenotypic plasticity · Environmental effects · Genetic effects