A popular notion in sexual selection is that females are polyandrous and their offspring are commonly sired by more than a single male. We now have large-scale evidence from natural populations to be able to verify this assumption. Although we concur that polyandry is a generally common and ubiquitous phenomenon, we emphasise that it remains variable. In particular, the persistence of single paternity, both within and between populations, requires more careful consideration. We also explore an intriguing relation of polyandry with latitude. Several recent large-scale analyses of the relations between key population fitness variables, such as heterozygosity, effective population size (Ne), and inbreeding coefficients, make it possible to examine the global effects of polyandry on population fitness for the first time.

Female receptivity in butterflies and moths is influenced by a multitude of factors that vary between virgin and mated females, and is often affected by the quality and persistence of courting males. Mated females of polyandrous species frequently display a period of non-receptivity following mating, often resulting from factors transferred by the male at mating. Some of these compounds have a transient effect (e.g. anti-aphrodisiacs and mating plugs), whereas others induce long-term suppression of receptivity (i.e. sperm and seminal factors). Sperm appear to generally induce long-term suppression of female receptivity in both butterflies and moths. In some species, production of non-fertile sperm may function to fill the female's sperm storage organ and switch off receptivity, although whether this is a general phenomenon across the Lepidoptera has not yet been examined. Examination of seminal fluids suppressing female receptivity in moths suggests that more than one factor is implicated, but frequently the transfer or stimulation of Juvenile Hormone production is involved. Surprisingly, potential seminal factors influencing female receptivity in butterflies remain largely unexplored. In this review, I summarize the various factors that are known to affect female receptivity in the Lepidoptera to date, and briefly compare the function and similarity of the Pheromone Suppressing Peptide (HezPSP) in moths to that of the Sex Peptide in Drosophila melanogaster (DrmSP). The exciting possibility that seminal peptides in the Lepidoptera and Diptera (e.g. Drosophila melanogaster) may have shared functionality is discussed.

The interaction between the Blue Moon butterfly, Hypolimnas bolina, and Wolbachia has attracted interest because of the high prevalence of male-killing achieved within the species, the ecological consequences of this high prevalence, the intensity of selection on the host to suppress the infection, and the presence of multiple Wolbachia infections inducing different phenotypes. We examined diversity in the co-inherited marker, mtDNA, and the partitioning of this between individuals of different infection status, as a means to investigate the population biology and evolutionary history of the Wolbachia infections.

Current theory postulates that the operational sex ratio (OSR) determines the relative degree of mating competition in the two sexes and is in turn influenced by a sexual difference in the potential reproductive rate (PRR) denned as 1/time out, where time out is the time an individual must spend recovering from a bout of mating activity and/or caring for offspring. In bushcricket mating systems where males provide females with a nuptial gift, relative energy expenditure in offspring influences the PRR of males and females and underlies a diet-mediated shift in the OSR. Here we investigated if there is a similar positive relationship between relative parental nutrient expenditure in offspring and PRR in the polyandrous butterfly Pieris napi, where female fecundity is strongly dependent on male nuptial gifts at mating. By varying the amount of nutrients females receive at mating and relating this to number of offspring produced, we show that male P. napi have, on average, a nutrient expenditure in offspring equaling that of females. In spite of this, the male reproductive rate is 8–13 times higher than that of females. Hence the relative degree of parental expenditure in offspring is largely decoupled from the degree of mating competition in P. napi. Two alternative explanations are advanced to account for the difference between the butterfly and the bushcricket mating systems.