Reproductive variance in planar spawning Chromodoris species (Mollusca: Nudibranchia)

Abstract

Although variance in life history parameters is well known from comparisons among broad phylogenetic groups of marine invertebrates, there is still an outstanding need to increase empirical studies that compare closely related species. If the species under study share a recent common ancestor and developmental strategy, there is an opportunity to contrast maternal investment against interspecific variation while controlling for evolutionary distance. Furthermore, when these species co-occur, it allows for exploration of potential character displacement. We examined egg size and other factors related to reproduction in four closely related species, co-occurring nudibranchs belonging to the monophyletic Chromodoris planar spawning clade. The duration of oviposition appeared to be conserved and may be phylogenetically constrained in these four co-occurring species. In contrast, egg size differed significantly among species, but was not influenced by parental body length or position within the egg mass for any of the species. The number of egg mass whorls also varied, but did not correspond to the interspecific differences in parental body length. These results suggest that some significant differences exist among these sympatric Chromodoris species that may be candidate traits for character displacement. These characters would need to be re-measured in geographic areas where the studied Chromodoris species do not co-occur.

Keywords:

• nudibranchs
• egg size
• character displacement
• phylogenetic constraints

Acknowledgements

We thank the volunteers who assisted in collecting the specimens used in this study, with particular appreciation going to Lucy Turner and David Thompson. Operation Wallacea provided field support, and financial assistance was provided by the Hawaiian Malacological Society, the Lord Mayor's Trust, and the Hertfordshire Educational Foundation. Dr Tim Johnson kindly provided comments on an earlier version of this manuscript, and reviewers are thanked for providing constructive criticism.