Reproductive Effort of the Nudibranch Molluscs Adalaria proxima (Alder & Hancock) and Onchidoris muricata (Muller): An Evaluation of Techniques

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Abstract
Considerable controversy surrounds the validity and utility of measures of reproductive effort (RE) in analysing the evolution of given life history and, for marine invertebrates especially, larval strategies. Even more confusion has arisen from the wide array of measures of RE that have been variously employed. In assissing the reproductive strategies of two annual marine nudibranch molluscs (Adalaria proxima [Alder and Hancock] and Onchidoris muricata [Muller]) - both of which are semelparous hermaphrodites - we have evaluated the outcomes for five commonly used measures of RE, and developed a new statistic, the reproductive index (RI). When measures of reproductive production were used, higher REs were found for the species that has planktotrophic larvae (O. muricata). However, when measures of reproductive ''cost'' were employed the pattern was reversed - the higher ''cost'' were found for the species with lecithotropic larvae [A. (proxima). These results are contrasted with other published estimates for semelparous molluscs and the relative merits of the different measures are discussed. It is suggested that available data are not yet sufficiently comparable to enable conclusions to be drawn with regard to the association between reproductive allocation and the evolution of different larva types in marine invertebrates.

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