Congruence in annual energy input into reproduction in siphonariid limpets with planktonic and direct development

ABSTRACT Marine molluscs exhibit a wide range of developmental modes that can be explained by phylogenetic history but that can also be explained by ecological adaptation, involving trade-offs among fecundity, dispersal and offspring survival. We examined the energy apportioned to reproduction by two congeneric, co-existing species of the intertidal limpet Siphonaria that fall into different clades of the genus. Both species lay egg masses. Those of S. concinna contain thousands of eggs that hatch after a few days as planktotrophic larvae. The egg masses of S. serrata contain hundreds of eggs that develop for around 4 weeks and hatch as crawl-away juveniles. We measured each species’ annual reproductive output in terms of fecundity (number of egg masses per individual and estimated total number of eggs) and egg mass dry weight, to estimate an annual reproductive energy budget for a standard animal by measuring the calorific content of egg masses. Despite major differences in fecundity and development, both species apportioned similar amounts of energy into each egg mass (c. 0.17 J), with similar annual energetic investment into spawning (c. 1.06 and 1.04 J, respectively, for S. concinna and S. serrata). The life history attributes of the two species correspond with the classic r- and K-selected traits and the results suggest an evolutionarily stable value for reproductive investment where these two species co-exist.