Polyandry and fecundity in the Lepidoptera: Can methodological and conceptual approaches bias outcomes?

Polyandry is a reproductive strategy whose occurrence has been explained in terms of both direct and indirect benefits to females. Among the direct benefits, a positive correlation between female remating and fecundity, mediated by receipt of nuptial gifts, is considered a major factor maintaining polyandry. However, a careful inspection of available studies reveals that such a correlation is not universal. In this comparative study of Lepidopterans we analysed two-way contingence tables based on 60 studies, and performed a meta-analysis of 39 studies to document associations between (1) the mating pattern (monandrous or polyandrous); (2) the methodological approach used (experimental or descriptive); and (3) the effect of female remating on fecundity. All three variables were significantly associated. Studies where remating increased fecundity were more often established in polyandrous species and when the experimental method was used. However, the experimental method also tended to be utilised more often for polyandrous species. Meta-analysis confirmed these 'vote-count'-based associations. We were also able to differentiate the relative effects of mating pattern and methodology on the remating-fecundity relationship. In polyandrous species, remating increased fecundity irrespective of the test method. In monandrous species, however, conclusions were method-dependent: fecundity did not increase with remating in descriptive studies. We discuss some biological and non-biological factors that may account for these heterogeneous results. We suggest that greater attention must be paid to variation among females in their propensity to mate multiply. The mating pattern of a species will influence the conclusions drawn from experimental and descriptive studies of the relationship between polyandry and fecundity because it covaries with the proportion of naturally monandrous females in that species.