Sex Ratio as a Function of Size in Marine Crustacea

Abstract

A deviation from the 1:1 sex ratio is apparently widespread in marine crustaceans, but the normal practice of calculating sex ratio for a population sample obscures this fact. An inspection of the field data in a number of different forms reveals that sex ratio is a function of size in all cases examined. A study of the original field data in different taxonomic categories further reveals that the male-female relationships fall into discrete patterns which have not been noticed earlier, apparently. Instead of calculating the overall sex ratio, one can calculate the different within-size-class sex ratios for each species or population. The composite set of ratios forms one of four (or perhaps more) probability curves. In this analysis of original data, it is evident that one sigmoid curve (at times two) accurately depicts the sex ratio-size class relationship in a population. Probability curves obtained thus far are clearly independent of animal groupings but are usually remarkably consistent within each species or population. Neither do these curves show much displacement with season or with variation in population structure. It might even develop that such curves will characterize the relationship between sexes in some species or populations. Although some investigators may have recognized a sex ratio deviation in the species they have studied and may have suggested an interpretation for that species, there does not seem to exist an overview of the situation. A study of the problem as a whole discloses that there are at least five conceivable interpretations for the patterns obtained. These different interpretations are discussed briefly, but it is evident that more comprehensive field and laboratory studies are necessary. Until these studies are done, it will not be possible to decide whether one interpretation will suffice for all patterns or whether a different interpretation is in order in each case.