Reproduction in four populations of brooding periwinkle (Littorina) at Ravenscar, North Yorkshire: adaptation to the local environment?

The current study examines the reproductive patterns found within four ovov iviparous, brooding periwinkle populations on one shore in the north-east c oast of England; the boulder dwelling populations Littorina saxatilis H (up per-shore form with thin shell and large aperture) and L. saxatilis M (mid- shore form with thick shell and small aperture), and the barnacle-dwelling L. saxatilis B (small form similar in morphology to L. saxatilis M) and L. neglecta. Littorina saxatilis H showed distinct seasonality in reproductive activity, unlike L. saxatilis M, and produced significantly larger eggs an d embryos than the latter population. Littorina saxatilis M maintained a si gnificantly higher weight-specific fecundity and reproductive activity thro ughout the year than L. saxatilis H and produced a larger number of small e mbryos. The two barnacle-dwelling populations also showed distinct seasonality in r eproductive activity and neither of the populations contained reproductivel y active females during the winter months. There was no significant differe nce in egg size between the two populations, but L. saxatilis B produced la rger crawlaways than did L. neglecta. Even though L. saxatilis B was signif icantly larger in body and shell size, L. neglecia had a higher weight-spec ific fecundity than the former population. The possibility that the observe d differences in egg and juvenile size, fecundity and seasonality between t he four populations can be attributed to microscale adaptation to the local environment is discussed.