Micropyle number is associated with elevated female promiscuity in Lepidoptera

In the majority of insects, sperm fertilize the egg via a narrow canal through the outer chorion called the micropyle. Despite having this one primary function, there is considerable unexplained variation in the location, arrangement and number of micropyles within and between species. Here, we examined the relationship between micropyle number and female mating pattern through a comparative analysis across Lepidoptera. Three functional hypotheses could explain profound micropylar variation: (i) increasing micropyle number reduces the risk of infertility through sperm limitation in species that mate infrequently; (ii) decreasing micropyle number reduces the risk of pathological polyspermy in species that mate more frequently; and (iii) increasing micropyle number allows females to exert greater control over fertilization within the context of post-copulatory sexual selection, which will be more intense in promiscuous species. Micropyle number was positively related to the degree of female promiscuity as measured by spermatophore count, regardless of phylogenetic signal, supporting the hypothesis that micropyle number is shaped by post-copulatory sexual selection. We discuss this finding in the context of cryptic female choice, sperm limitation and physiological polyspermy

Seed coat phytochemistry of both resistant and susceptible seeds affords some protection against the granivorous beetle Callosobruchus maculatus

The seed coat lies at the interface between the internal structures of the seed and the external environment and thus represents a key arena in the study of seed-herbivore interactions. Callosobruchus maculatus is a cosmopolitan pest of legume seeds, and under post-harvest conditions, females interact directly with the seed testa prior to laying their eggs. Here we investigate the effect of chemical extracts of the seed coat of the resistant Phaseolus vulgaris and the susceptible Vigna unguiculata beans on egg laying preferences and larval development of C. maculatus. Seed coat extracts contained phenolic, glycoside and alkaloid compounds. Upon re-incorporation of extracts into artificial host beans it was found that that several seed coat extracts from both the resistant and susceptible varieties reduced female oviposition and disrupted larval growth and development. However, none of the extracts assayed resulted in complete ovipositional or developmental failure suggesting that complete resistance in P. vulgaris is derived from other physical or chemical properties of the seed and/or seed coat that function either alone or synergistically. Further work is required to elucidate the importance of synergistic interactions between different physiological defence mechanisms on overall plant (seed) resistance

Effects of surgically implanted tags and translocation on the movements of common bream Abramis brama (L.)

Data collected from wildlife telemetry studies relies on tagging and attachment having minimal impactson behaviour. Though a widespread technique, relatively few studies evaluate the impacts of differingtagging methods on both welfare and behaviour. Here we use tracking data, collected for other aims, toinvestigate the impact of inter-peritoneal surgical implantation of acoustic transmitters on the healthand behaviour of common bream, Abramis brama (L.). In five separate capture events, the behaviour interms of distances moved and linear range of newly tagged fish (n = 61) were compared to previouslytagged fish (n = 55) present in the same river at the same time. In the first 5 days post-tagging, newlytagged fish moved significantly further than previously tagged fish. Despite this difference, the linearranges moved by the two groups of fish were equivalent. During 6–10 days post tagging there was nosignificant differences between the two groups. Thus, the tagging procedure had short term, but not longterm behavioural impacts. In addition, a number of tagged fish were recaptured between 51 and 461days post-surgery. Recaptured fish appeared to have clean, well-healed incisions and exhibited ‘normal’behaviour in that they were caught alongside a large number of conspecifics. Three recaptured taggedfish were translocated ∼35 km downstream, to ascertain how translocation would affect their behaviour.The translocated fish had a greater linear range than control fish, with all three fish returning to the siteof capture within 6 to 24 days, suggesting that common bream can exhibit site fidelity

Data from: Male–female interactions drive the (un)repeatability of copula duration in an insect

Across the animal kingdom the duration of copulation varies enormously from a few seconds to several days. Functional explanations for this variation are largely embedded within sperm competition theory in which males modulate the duration of copula in order to optimize their fitness. However, copulation is the union of two protagonists which are likely to have separate and often conflicting reproductive interests, yet few experimental designs specifically assess the effect of male–female interactions on the duration of copulation. This can result in inexact assertions over which sex controls copulatory behaviour. Here we analyse the repeatability of copulatory behaviour in the seed beetle Callosobruchus maculatus to determine which sex exerts primary influence over copulation duration. In C. maculatus, copulation follows two distinct phases: an initial quiescent phase followed by a period of vigorous female kicking behaviour that culminates in the termination of copulation. When males or females copulated with several novel mates, copulatory behaviour was not significantly repeatable. By contrast, when males or females mated repeatedly with the same mate, copula duration was repeatable. These data suggest copulatory behaviour in C. maculatus to be largely the product of male–female interactions rather than the consistent, sex-specific modulation of copula duration of one protagonist in response to the phenotypic variation presented by the other protagonist

repeatability data eady

treat: 1 = same male same female, 2 = diff male diff female. Femaleid = individual female identity, maleid = individual male identity, matenumber = mating sequence (1, 2, 3, 4), starttokick = raw data, starttokicks = time from start of copula to the female kicking phase (seconds), normstok = normalised start to kick time, ktoends = duration of kick to end phase (seconds), totals = total cop duration (seconds), normtotal = normalised total duration, femelytra = female elytra length (mm), maleelytra = male elytra length (mm)

Functional incompatability between the fertilization systems of two allopatric populations of Callosobruchus maculatus (Coleoptera: bruchidae)

Recent studies indicate that postcopulatory sexual selection may represent an important component of the speciation process by initiating reproductive isolation via the evolutionary divergence of fertilization systems. Using two geographically isolated populations of the polyandrous beetle Callosobruchus maculatus, we investigated divergence in fertilization systems by determining the extent of postcopulatory functional incompatibility. Through reciprocal, cross-population matings we were able to separately estimate the effects of male and female population origin and their interaction on the extent of last-male sperm precedence, female receptivity to further copulation and female oviposition. Our results indicate partial incompatibility between the fertilization systems of the two populations at all three functional levels. Males derived from the same population as females outcompete rival, allopatric males with respect to sperm preemption, sperm protection, and ability to stimulate female oviposition. This pattern is reciprocated in both populations indicating that postcopulatory, prezygotic events represent important mechanisms by which between-population gene flow is reduced. We suggest the partial gametic isolation observed is a by-product of the coevolution of male and female fertilization systems by a process of cryptic female choice. Our results are consistent with a mechanism akin to conventional mate choice models although they do not allow us to reject antagonistic sexual coevolution as the mechanism of cryptic female choice

Prior oviposition, female receptivity and last-male sperm precedence in the cosmopolitan pest Callosobruchus maculatus (Coleoptera: Bruchidae)

Sperm competition studies have shown that P2 (the proportion of ova fertilized by the last male to mate) increases as the interval between inseminations is experimentally increased. Variation in the number of sperm in storage is associated with sperm use (or loss) from the female's sperm stores between copulations (fewer sperm from previous mates at the time of the last copulation) and with the extent of prior oviposition and female receptivity to further copulation: females that lay many eggs tend to have few remaining sperm in storage and to be more receptive to further copulation. Using the bruchid beetle Callosobruchus maculatus, we examined the effect of prior oviposition and female receptivity to further copulation on the extent of last-male sperm precedence (measured as P2). Extent of prior oviposition was experimentally manipulated independently of the intermating interval by altering the availability of oviposition sites between inseminations. Females given few or no oviposition sites laid fewer eggs, were less receptive and had a lower P2 than females given abundant oviposition sites. To examine the effect of female receptivity on P2 independently of prior oviposition, we examined the outcome of sperm competition experiments using (1) females from lines that had been selected for different latencies to copulation and (2) natural variation in female latency to receptivity. Female receptivity to further copulation had no detectable effect on P2. When oviposition resource is abundant, female receptivity may be a poor predictor of current sperm load

Copulation, genital damage and early death in Callosobruchus maculatus

Antagonistic sexual coevolution stems from the notion that male and female interests over reproduction are in conflict. Such conflicts appear to be particularly obvious when male genital armature inflicts damage to the female reproductive tract resulting in reduced female longevity. However, studies of mating frequency, genital damage and female longevity are difficult to interpret because females not only sustain more genital damage, but also receive more seminal fluid when they engage in multiple copulations. Here, we attempt to disentangle the effects of genital damage and seminal fluid transfer on female longevity in the beetle Callosobruchus maculatus (Coleoptera: Bruchidae). Males copulating for the sixth time in succession inflicted greater levels of genital damage, but transferred smaller ejaculates in comparison with virgin males. The number of copulations performed by males was negatively related to female fecundity and positively related to female longevity, suggesting a trade-off between fecundity and longevity. However, inclusion of fecundity as a covariate revealed sperm and/or seminal fluid transfer to have a negative impact on female longevity above that caused by the fecundity–longevity trade-off. The consequences of multiple copulations on female longevity were examined. Females that mated twice laid more eggs and died sooner than those that mated once. However, incorporation of fecundity as a covariate into our statistical model removed the effect of female mating frequency on female longevity, indicating that double-mated females suffer greater mortality owing to the trade-off between fecundity and longevity. Males of this species are known to transfer very large ejaculates (up to 8% of their body weight), which may represent a significant nutritional benefit to females. However, the receipt of large ejaculates appears to carry costs. Thus, the interpretation of multiple mating experiments on female longevity and associated functional explanations of polyandry in this species are likely to be complex

Data from: Developmental temperature affects the expression of ejaculatory traits and the outcome of sperm competition in Callosobruchus maculatus

The outcome of post-copulatory sexual selection is determined by a complex set of interactions between the primary reproductive traits of two or more males and their interactions with the reproductive traits of the female. Recently a number of studies have shown the primary reproductive traits of both males and females express phenotypic plasticity in response to the thermal environment experienced during ontogeny. However, how plasticity in these traits affects the dynamics of sperm competition remains largely unknown. Here we demonstrate plasticity in testes size, sperm size and sperm number in response to developmental temperature in the bruchid beetle Callosobruchus maculatus. Males reared at the highest temperature eclosed at the smallest body size and had the smallest absolute and relative testes size. Males reared at both the high and low temperature extremes produced both fewer and smaller sperm than males reared at intermediate temperatures. In the absence of sperm competition developmental temperature had no effect on male fertility. However, under conditions of sperm competition, males reared at either temperature extreme were less competitive in terms of sperm offence (P2), whilst those reared at the lowest temperature were less competitive in terms of sperm defence (P1). This suggests the developmental pathways that regulate the phenotypic expression of these ejaculatory traits are subject to both natural and sexual selection: natural selection in the pre-ejaculatory environment and sexual selection in the post-ejaculatory environment. In nature, thermal heterogeneity during development is commonplace. Therefore, we suggest the interplay between ecology and development represents an important, yet hitherto underestimated component of male fitness via post-copulatory sexual selection