No cost of male mating experience on female reproductive success in the almond moth, <Emphasis Type="BoldItalic">Cadra cautella</Emphasis> (Lepidoptera; Pyralidae)

Male copulation experience may have a profound impact on female reproductive success if male reproductive investment declines over consecutive copulations and if females are unlikely to re-mate. Male reproductive investment is particularly interesting in lepidopterans because males produce dimorphic sperm: a fertilizing (eupyrene) and a non-fertilising (apyrene) sperm. In two experiments, we explored the lifetime reproductive investment of male almond moths, Cadra cautella (also known as Ephestia cautella) and examined its influence on female reproductive success. In the almond moth, females re-mate infrequently and males transfer sperm in a spermatophore. Attached to the spermatophore is a large chitinous process, the function of which is unknown. One group of males were permitted consecutive copulations with virgin females and the amount of sperm and size of the spermatophore transferred were compared for all females. We found that the number of both eupyrene and apyrene sperm per ejaculate decreased with his increased mating frequency, while the size of the spermatophore process decreased dramatically after the male’s first copulation. In a second experiment, we allowed males to mate with females throughout their lives and then compared female fecundity and fertilisation success. We found no obvious decrease in female fecundity and fertilisation success with increased male copulation experience, despite the likely reduction in male gametic investment. We discuss potential explanations for the development of this enlarged and elaborate first spermatophore of male almond moths given that it confers no clear fitness advantage to females.     

Sperm allocation in relation to male traits, female size, and copulation behaviour in freshwater crayfish species

Sperm competition is a well-recognised agent in the evolution of sperm and ejaculate structure, as well as variation in female quality. Models of the evolution of ejaculate expenditure predict that male body condition, female fecundity and the risk and intensity of sperm competition may be the ultimate factors shaping optimal ejaculate size. We investigated sperm allocation in Austropotamobius italicus, a freshwater crayfish exhibiting a coercive mating system and external fertilisation, in relation to male and female traits and copulation behaviour under laboratory conditions. We found that mating males were sensitive to female size and produced larger ejaculates when mating with larger females, which were more fecund in terms of number of eggs produced. We found no evidence for female egg production being sperm-limited, as the number of eggs was not dependent on male sperm expenditure. Copulation duration and number of ejaculations reliably predicted the amount of sperm transferred, and both these behavioural measures positively covaried with female body size. These results indicate that male freshwater crayfish can modulate their sperm expenditure in accordance with cues that indicate female fecundity. In addition, a novel finding that emerged from this study is the decrease in sperm expenditure with male body size, which may either suggest that large, old male crayfish are better able than small males to economise sperm at a given mating to perform multiple matings during a reproductive season, or that they experience senescence of their reproductive performance.     

Mechanisms enabling sperm economy in blenniid fishes

Sperm competition, cost of spermatogenesis and spawning frequency are known to influence ejaculate expenditure. Accordingly, males, particularly those with high reproductive costs, are expected to have evolved mechanisms enabling them to prudently allocate sperm, such as the fractioning of ejaculate expenditure or the semi-cystic type of spermatogenesis, hypothesised to favour the production of small ejaculates. In this study, we investigate sperm competition risk, ejaculate size and mode of ejaculate release in seven polygynous blenniid fish where males provide sole paternal care of eggs. In addition, we estimated the relative size of the two parts composing the male gonad, the strictly testicular (testicular lobules or testis) and the glandular (testicular gland), as the development of the latter is indicative of the level of semi-cystic spermatogenesis. In all the examined species, eggs were laid one by one, and the sperm expenditure at mating, evaluated as the total number of sperm released per mating, was parcelled out in several successive ejaculations, allowing males to adjust the release of sperm to the duration of egg deposition. In accordance with sperm competition theory, species experiencing higher sperm competition risk allocated more in sperm, both considering ejaculate size and ejaculate expenditure per mating. An increase in sperm expenditure was paralleled by the development of the testis at the expense of the testicular gland. Smaller species, whose males do not face sperm competition risk and fecundity is low, produced smaller ejaculates and exhibited a more developed testicular gland, supporting the hypothesis that a semi-cystic type of spermatogenesis is a mechanism allowing sperm economy.     

Female benefit,male risk: Polyandry in the true armyworm Pseudaletia unipuncta

In Lepidoptera polyandry is common and females may increase their lifetime reproductive output through repeated matings if they acquire essential resources from male ejaculates. However, the paternity of males mating with previously-mated females is far from assured unless sperm precedence is absolute. In this study on the polyandrous armyworm, Pseudaletia unipuncta, we used two strains of male (the black-eyed wild type and a red-eyed homozygous, recessive mutant), mated with red-eyed females, to determine (i) whether male investment has any impact on female reproductive output, and (ii) if females do benefit from multiple matings, to what extent males fertilize the eggs to which they contributed. Multiple mating resulted in a significant increase in both the fecundity and longevity of females. However, the degree of sperm precedence (those eggs fertilized by the second male) varied from 0–100%, but was not affected by either male size or age, or by the duration of copulation. In cases where sperm precedence was <50% (x = 12%) females produced significantly more eggs (1384 versus 940) prior to the second mating than females where sperm precedence was >50% (x = 89%), indicating that the quality of the first mating influenced the fertilization success of the female's second mate.     

A female preference for experienced males in the almond moth, Cadra cautella

Male mating status can affect female reproductive output if male ejaculate investment declines over consecutive matings. Accordingly, females are predicted to mate preferentially with virgin males. In mildly polyandrous lepidopterans, female fitness is less affected by reduced male investment than in more polyandrous species, and so the predictions for female mating preferences are less clear. We examined female mating preferences in the mildly polyandrous almond moth, Cadra cautella, in which ejaculate size does not affect female reproductive output. First, we allowed females to mate with virgin or once-mated males, in which the males were presented individually or simultaneously. We recorded the latency to mating and, in the case of the simultaneously presented trials, the identity of the successful, copulating male. We found that females mated more frequently with mated males (when simultaneously presented with both males), yet females did not differ in the time taken to initiate copulation with any male. We further examined if this mated male advantage was due to differential mate detection or locomotory behaviour of the male treatments. We tested the ability of virgin and mated males to locate a receptive female within a wind tunnel using long-distance pheromone cues and recorded their activity budget. We found no difference in the ability of mated or virgin males to locate or approach a receptive female, or in their activity levels. These data suggest a female preference for mated males in this species, a preference that may minimise other potential costs of mating.     

Intraspecific variation of testis size and sperm length in the yellow-pine chipmunk (<Emphasis Type="Italic">Tamias amoenus</Emphasis>): implications for sperm competition and reproductive success

Comparative analyses have found that relative testis size is a strong predictor of the prevalence of sperm competition for many taxa, including mammals, yet underlying this pattern is the assumption that intraspecific variation in testis size is related to individual fitness. Because intraspecific variation in ejaculate investment underlies interspecific patterns, it is critical to understand the causes and consequences of intraspecific variation in ejaculate investment. We examined relationships between ejaculate investment (testis size and sperm length) and reproductive success, body size and condition in the yellow-pine chipmunk (Tamias amoenus), a small ground squirrel in which sperm competition occurs. We examined genetic estimates of male reproductive success from a wild population of yellow-pine chipmunks and determined that males with large testes had higher annual reproductive success than males with small testes. This result provides empirical support for the numerous comparative studies that indicate testis size is associated with the intensity of sperm competition. In addition, males in good condition had relatively larger testes than males in poor condition, but there was no evidence of sperm length being dependent on condition. Finally, contrary to many predictions, males that invested more in sperm production (relatively heavy testes) produced shorter sperm, not longer sperm, than males that invested less.Communicated by P.M. Kappeler     

Sperm removal and ejaculate size correlate with chelae asymmetry in a freshwater crayfish species

Asymmetry in traits of sexual relevance may impair copulation behaviour and sexual performance of males, ultimately resulting in a fitness cost. Freshwater crayfish males use chelae, a sexually selected trait, to secure and position the female prior to and during mating. Thus, a relatively large chelae asymmetry, resulting from accidental loss and regeneration of one cheliped after autotomy, could have great consequences for male sexual behaviour. We studied copulatory behaviour and sperm expenditure of males paired to a mated female in Austropotamobius italicus, a freshwater crayfish species where both male and female mate multiply and where last-mating males are able to actively remove previously deposited sperm. We aimed at assessing whether male sperm removal and expenditure varied according to sperm allocated by first-mating males, and according to copulation behaviour and phenotypic traits (carapace length, chelae length and relative chelae asymmetry) of second-mating males. Second-mating males did not adjust their ejaculate size in relation to first-mating male ejaculate, nor to the first-mating male’s sperm removed. Moreover, the amount of sperm removed by second-mating males increased with increasing first-mating males ejaculate size, and first-mating male sperm remaining after removal did not correlate with the original first-mating male ejaculate size. Interestingly, the amount of sperm removed by second-mating males decreased with increasing relative chelae asymmetry, while increasing with male body size. However, second-mating (but not first-mating) asymmetric-clawed males produced larger ejaculates than symmetric-clawed ones. Importantly, the proportion of second-mating male sperm remaining after the two matings did not vary with relative chelae asymmetry nor with body size of second-mating males. Thus, small, asymmetric-clawed crayfish males appear to adopt sperm allocation tactics that allow them to fully compensate for their inferior sperm removal ability.     

Elucidating the function of ejaculate expulsion and consumption after copulation by female Euxesta bilimeki

Postcopulatory processes can influence male reproductive success in several animal species. Females can use different mechanisms to bias male paternity after copulation. One of such mechanisms consists in expelling all or part of the ejaculate after copulation. Euxesta bilimeki is an Ulidiid fly whose females not only frequently expel ejaculates after mating but also consume the ejaculate after expulsion. In order to understand the significance of these behaviors we examined video recordings of courtship, copulatory, and postcopulatory behaviours. The presence of sperm in female storage organs was confirmed after mating with males of different sizes and was correlated with duration of courtship, copulation, and the period from the end of copulation to ejaculate expulsion. The effect of ejaculate consumption on female fitness (fecundity and longevity) was compared among females held under different dietary treatments: a rich diet consisting of protein, sugar and water, an intermediate diet composed of sugar and water, a poor diet of only water and females that were completely deprived of food and water. All of the observed females expelled ejaculates after mating. The probability of storing sperm in the two spermathecae and the ventral receptacle was correlated with interactions between the duration of all behaviours examined and male size. Except for starved females, who lived longer when allowed to consume ejaculates, ejaculate consumption had no effect on fitness. Results suggest that females can bias sperm storage according to male mating effort, while the consumed ejaculate had some nutritional value only evident when females were completely starved.     

Seasonal variation in ejaculate traits of male red-winged blackbirds (Agelaius phoeniceus)

Many reproductive traits, including ejaculate characteristics, usually show remarkable seasonal variation, but the potential for such dynamics in sperm morphology has been overlooked. Several studies have revealed high within-male repeatability in sperm morphology, but samples have typically been collected within a few hours or days, and the consistency of sperm morphology over longer periods remains unexplored. Here, we tested whether ejaculate traits, including sperm morphology, sperm number, and sperm velocity, exhibit seasonal phenotypic plasticity in a long-lived seasonal breeder, the red-winged blackbird (Agelaius phoeniceus). We found absolute and/or relative flagellum length and sperm velocity to increase across the season, whereas sperm numbers within ejaculates declined. Sperm morphological traits were further positively associated with harem size or the total number of offspring that fledged in each male’s territory, suggesting that sperm morphology is likely to be linked to male reproductive quality. The underlying mechanisms of these patterns of seasonal variation remain unresolved, but we discuss our results in the context of dynamics of reproductive hormones, testicular structures and function, and reproductive behavior.     

Sperm competition and ejaculate investment in red squirrels (<Emphasis Type="Italic">Tamiasciurus hudsonicus</Emphasis>)

Sperm competition is widespread in mammals and occurs when ejaculates from two or more males compete within the female’s reproductive tract to fertilize the ova. Enlarged testes are associated with sperm competition because they produce sperm, but the accessory glands produce fluids and proteins that are also important for fertilization success. Sperm morphology can also have consequences for fertilization success because of its influence on sperm motility. Red squirrels engage in multiple mating, and thus sperm competition is likely. Here, we assess levels of multiple paternity in a natural population of red squirrels, test the prediction that testis size is correlated with size of the accessory glands and sperm morphometry, and test the prediction that ejaculate investment is condition-dependent. Five of six litters (83%) showed evidence of multiple paternity, indicating that sperm competition is likely to have occurred. Testis size was correlated with the size of all three accessory glands (prostate, seminal vesicle, epididymides), and there was a generally positive relationship between the size of the accessory glands and sperm length. Sperm morphology showed significant variation in size and shape among individual male squirrels. There was no evidence of condition dependence of testis size or the size of the accessory glands, but sperm midpiece length was negatively related to body condition. Further work should include determining the fitness consequence of variation in sperm morphometry, testis size, and accessory gland size, and determining the effects of variation in ejaculate investment on sperm motility.     

Male butterfly investment in successive ejaculates in relation to mating system

In Lepidoptera, female mating systems range from strict monandry to strong polyandry. Males transfer an ejaculate during copulation that contains both sperm and accessory gland substances. In butterflies the male ejaculate has at least three effects: it (1) contains sperm that can fertilize the eggs of the male’s mating partner, (2) influences the refractory period of the mated female, and (3) contains nutrients that can be used by the female to increase her reproductive output. A number of recent studies have shown that males in polyandrous mating systems are endowed with adaptations to increase mating capabilities. Relative to males in more monandrous species they transfer larger first ejaculates which contain relatively more protein, and allocate proportionally more resources to reproduction. The objective of this study was to compare male reproductive investment in successive ejaculates, in terms of both mass and quality, to determine if males of polyandrous species are capable of maintaining the production of larger and more nutritious ejaculates than males of more monandrous species. We used three species of pierid butterfly, with mating systems ranging from relative monandry to polyandry. The degree of polyandry had a substantial effect on the reproductive performance of males. The cumulative protein content of ejaculates increased with the degree of polyandry. Only males of the most polyandrous species, Pieris rapae, produced three successive ejaculates of similar mass and protein content. In the relatively monandrous species, Aporia crataegi and P. brassicae, males in subsequent matings never produced another ejaculate as large as that transferred by males mating for the first time, although the protein content (mg) of ejaculates did not differ in second and third ejaculates. Moreover, the ability to remate varied with the degree of polyandry. Given the opportunity to remate, the majority of P. rapae males mated three times, whereas relatively few A. crataegi and P. brassicae males were able to perform three matings. These results suggest that male capacity to produce large, nutritious ejaculates is limited in relatively monandrous species. In this study only males belonging to the most polyandrous species had the ability to recuperate quickly from a mating event and remate. Our results suggest that males in polyandrous systems are better adapted to mating more than once. Received: 3 November 1995/Accepted after revision: 13 July 1996     

Female fitness, sperm traits and patterns of paternity in an Australian polyandrous mouse

Multiple mating is a common reproductive strategy among mammals, and rodents living in communal, mixed sex social groups are predisposed to a polygamous existence. The sandy inland mouse is a naturally polyandrous species that occurs across most of Australia’s arid region. Females typically have greater reproductive restrictions compared with males and are therefore expected to acquire substantial fitness benefits from copulating with more than one male. Here, I show that the reproductive output of female sandy inland mice did not differ between females mated monandrously (single male) or polyandrously (two males). Paternity data obtained from the polyandrous litters revealed that in most cases, there was a first male-to-mate advantage. I discuss this result in relation to the chastity enforcement hypothesis for the evolution of the copulatory plug. Finally, I compared ejaculate traits of competing males and found that the paternity loss of males that mated first was attributable to their own sperm density and sperm quality, and not to that of their rivals. The sperm data also revealed that second males gained greater paternity representation when sperm velocities and motilities were higher in first-mated males. This investigation indicates that mating position is a critical determinant of male fitness in mammalian sperm competition.     

Mating effort or paternal investment? Incorporation rate and cost of male donations in the wartbiter

Summary Provision of nuptial gifts and incorporation of male-derived substances occurs in several insects. There has been some discussion as to whether these gifts should be regarded as a form of paternal investment or part of mating effort. One assumption of the paternal investment hypothesis is that the donating male is expected to father all, or the majority of, the offspring. The rate of incorporation into developing eggs is therefore assumed to be rapid enough to assure the donating male of paternity of the offspring in which he is investing. Spermatophore production in a paternal investment system is also expected to be costly, since males are providing females with highly nutritious gifts during copulation, thereby increasing female fecundity. Therefore, under conditions of food limitation males are expected to alter either mating frequency or spermatophore size. Experiments on the wartbiter (Decticus verrucivorus), using radioactive isotopes, show that the incorporation rate of male-derived substances is so slow that females become sexually receptive before any material received from the last male have been incorporated into eggs laid by the female. Since sperm mixing occurs in this species and since the label is present in eggs laid up to more than 30 days after mating, males might potentially benefit another male's offspring. The nuptial gift (the spermatophylax) was found, regardless of mating frequency and diet, to have a low protein content. These findings coincide with previous results showing that consumption of the gift had no effect on female fecundity. Instead, wartbiter males keep mating frequency high, are capable of mating every day regardless of food availability, invest the same proportion of the body weight in spermatophore production regardless of size, and produce a spermatophylax that correlates with ampulla size. These results indicate that the nuptial gift mainly functions to increase fertilization success in the wartbiter.     

Effects of mating history on ejaculate size, fecundity, longevity, and copulation duration in the ant-tended lycaenid butterfly, Jalmenus evagoras

The mating system of the Australian lycaenid butterfly, Jalmenus evagoras, is highly unusual compared to most other Lepidoptera. Characteristics of this system, which has been termed an ’explosive mating strategy,’ include the formation of an intensely competitive mating aggregation of males, a highly male biased operational sex ratio, a lack of discrimination and mate choice by both sexes, a high variance in male mating success, and female monogamy. In this study, we tested the hypothesis that multiple mating by males imposes physiological costs resulting in smaller spermatophores, and that this results in a fitness cost to females. We found that male J. evagoras transferred only 2.2% of their eclosion weight during their first mating, consistent with the hypothesis that males of monandrous species produce a relatively small investment. The wet weight of the ejaculate declined by an average of 27% at the second mating and the dry weight by 29%, and an intermating interval of 5–9 days was needed for the ejaculate to return to the size at the first mating, regardless of male size or age. Wet ejaculate mass increased proportionally with male size, though dry mass was proportionally larger in smaller males. Ejaculate mass tended to increase with male age at both first and second matings. Female characteristics, in general, did not affect ejaculate mass, although the wet weight of the ejaculate was positively associated with female weight at the second mating. Copulation duration increased from 2.4 h to approximately 3 h at the second mating, and to over 4 h at the third and fourth matings. Fecundity was positively correlated with female size but not with mating history, copulation duration, or any other characteristics measured for either males or females. Female longevity declined significantly as the number of times the male partner had previously mated increased. We conclude that despite the small male investment in ejaculate, the costs of multiple mating may nonetheless be significant, as indicated by the reduction in ejaculate mass, an increase in copulation duration, and reduction in female lifespan with increasing mating number. Received: 22 January 1999 / Received in revised form: 28 July 1999 / Accepted: 18 September 1999     

Different ejaculate delivery strategies in first versus subsequent matings in the swallowtail butterfly Papilio machaon L.

Summary Evidence suggests that males incur costs in producing ejaculates. Therefore some discrimination should be expected with respect to their pattern of allocating ejaculates. In a laboratory study, males of the European swallowtail butterfly Papilio machaon were mated with conspecific virgin females up to six times. The weight of the spermatophore and of the accessory substances delivered by males, the duration of mating, and the number of sperm in ejaculates were measured. The weight of the first spermatophore was related to male weight but that of accessory substances was not. The weight of the spermatophore delivered by males upon remating was always less than that of the first spermatophore. Second spermatophores Produced by males were smallest when delivered on the day after the first mating and increased asymptotically to about half the initial size with time elapsed since the first mating. Copula duration was highest for males remating on the day after the first mating but decreased to the duration of the first mating for males that were remated on the third day after the first mating or later. The weight of accessory substances delivered by males and the number of sperm in ejaculates were also higher in first matings compared to all subsequent matings. Both of two males that were handpaired on three consecutive days after the first mating produced a cumulative ejaculate mass equalling that transferred at the first mating. Thus the fact that males delivered smaller ejaculates upon remating on the third day after the first mating or later requires explanation, especially in view of the fact that copulations were not prolonged. We argue that the male ejaculate delivery strategy in mildly polyandrous species should be to mate for the first time with virgin females, when a maximum size ejaculate should be delivered, and then to maximize the number of matings. The rationale behind the male shift towards smaller ejaculate sizes delivered at subsequent matings is that: (1) the size of the ejaculate that can be produced is dependent on the time elapsed since the last mating; (2) the abundance of virgin females decreases as the flight season proceeds; and (3) there is an inverse relationship between the size and number of ejaculates that a male can produce in his life-time.     

Male reproductive investment relative to age and flight behaviour in the monandrous butterfly Pararge aegeria

Male reproductive investment may signify a considerable cost to male insects that produce sperm packages or spermatophores. Male butterflies allocate much of their active time budget to mate location, and they may adopt different behavioural strategies to do so. In the speckled wood butterfly (Pararge aegeria L.), males adopt either a territorial wait-and-fight strategy (territorial perching) or a fly-and-search strategy in wider areas (patrolling). In this study, we analysed the impact of male age, male size and male behaviour (i.e. behavioural strategies and levels of activity) on spermatophore investment (i.e. spermatophore mass, number of eupyrene sperm bundles). As predicted, reproductive investment increased with male age and size. Nevertheless, the increase of spermatophore mass with age and the number of eupyrene sperm bundles (i.e. fertile sperm) was stronger in low-activity males compared to active flying males. This suggests that flight activity has a negative impact on male reproductive investment. However, males that were forced to fly in the laboratory produced more eupyrene sperm bundles than resting males. We discuss the potential effects of male–male competition and predation risk on current versus future male reproduction. Males adopting different mate-locating strategies (perching and patrolling) in outdoor cages did not differ in spermatophore traits as was predicted from their very different flight performances. Copulations of territorial perching males took somewhat longer than copulations with non-perching males. There was a significant family effect of spermatophore size and of the expression of male mate-locating strategies suggesting heritable variation. Female traits (i.e. age and size) did not strongly affect spermatophore production. We discuss the results relative to both ultimate and proximate explanations of the complex relationships between butterfly activity, behavioural strategies, age and spermatophore production.     

Patterns of sexual cohabitation and female ejaculate storage in the American lobster (<Emphasis Type="Italic">Homarus americanus</Emphasis>)

Little is known of the time and ejaculate allocation strategies during mating of American lobster, Homarus americanus. This study investigated sexual cohabitation and female ejaculate accumulation patterns in a laboratory mating experiment, as well as female seminal receptacle load in exploited populations in the waters of the Magdalen and Anticosti Islands, in eastern Canada. In the laboratory experiment, the length of sexual cohabitation was proportionate to female size for large but not for small males. Also, large males cohabited with pre- and postmolt females longer than small males. These different time investment strategies can be explained by different mutual benefits. In the field and laboratory, larger females accumulated more ejaculate than smaller ones. This suggests that male lobsters tailor ejaculate to female size, a reliable index of her reproductive potential. Moreover, similarly-sized females accumulated more ejaculate when mated with large compared to small males. Comparison of receptacle loads between wild-mated and laboratory-mated females suggests that the former were mating mainly with smaller males, although some evidence of positive size-assortative mating existed, especially at the less exploited Anticosti site. The results are discussed in the context of evolutionary theory and of proposed management measures to increase egg production in exploited populations.Communicated by T. Czeschlik     

The ultimate function of nuptial feeding in the bushcricket Poecilimon veluchianus (Orthoptera : Tettigoniidae : Phaneropterinae)

Summary During mating the males of the bushcricket Poecilimon veluchianus transfer a large spermatophore of about a quarter of their body weight to the female. Such nuptial feeding is often thought to function as paternal investment by increasing the fitness of the male's offspring. According to an alternative, though not mutually exclusive, hypothesis, the size of the spermatophore is maintained because of its function as a sperm protection device. In this case the cost to the male should be classified as mating effort. To discriminate between these two hypotheses we measured the duration of sperm transfer into the female spermatheca and the time taken for spermatophore consumption. A comparison of durations revealed that spermatophore consumption interferes with the process of sperm transfer (Fig. 4). There was no significant effect of spermatophore consumption on number of eggs laid, weight of eggs or absolute weight of hatched larvae. The relative dry weight of hatched larvae, however, was increased as a result of spermatophore consumption (Table 1). Thus spermatophylax size is adjusted in accordance with a sperm protection function and the spermatophylax therefore represents mating effort. The increase in relative dry weight indicates that there may also be a paternal investment effect of the spermatophylax, if the offspring that benefit from spermatophylax materials are fathered by the donating male. Correspondence to: K. Reinhold     

Male mating history and female fecundity in the Lepidoptera: do male virgins make better partners?

In insects, large ejaculate and associated materials, including spermatophores, appear to have evolved via sexual selection acting on males to either delay female remating or to increase the rate of egg-laying. It is also possible, however, that females use nutrients transferred during mating to increase their lifetime fecundity. If so, male ejaculate size may also have evolved under natural selection as a form of paternal investment. In Lepidoptera, males with a greater number of prior matings tend to produce smaller spermatophores. However, the reported effects of male mating history on female fecundity vary widely among species. We therefore performed a meta-analysis using data from 29 studies of 25 species. Overall, the reproductive output of females mated to virgin males was significantly higher than that of females mated to sexually experienced males (Hedges d=0.33, P<0.01). A sample size of around 145 females per male mating type is required to detect an effect of this size with 80% statistical power at =0.05 (two-tailed). There was no difference in mean effect size between butterflies/skippers and moths. After controlling for any effect of taxonomic group, however, the mean effect size for polyandrous species was significantly greater than that for monandrous species (Hedges d=0.45 vs 0.25, P=0.01). We then discuss possible reasons why male mating history, presumably acting through its effect on spermatophore size, might have a stronger effect in polyandrous than monandrous species.Communicated by A. Cockburn     

Male dimorphism, sperm traits and immunology in the corkwing wrasse (Symphodus melops L.)

The evolution of alternative male mating phenotypes inevitably involves variation in risk or intensity of sperm competition. Males that typically mate in disfavoured roles (i.e. sneakers/parasitic males) are predicted to experience higher magnitudes of sperm competition than males mating in favoured roles (preferred by females/exhibiting mate monopolisation). Here, we investigated whether two distinct male phenotypes in corkwing wrasse (Symphodus melops) differ with respect to adaptations for sperm competition in terms of sperm quantity, sperm motility and fertilising capacity. We found that males exhibiting female mimicry (disfavoured role) had both absolutely and relatively larger gonads than males with typical secondary sexual characters (favoured role). Moreover, a higher proportion of sperm from female mimics was motile 5 min after activation compared to sperm of territorial males. There were, however, no differences in sperm concentration or in in vitro fertilisation ability between the two male morphs. We also examined whether the male phenotypes differed in some immune parameters and if any such variation is associated with sperm traits. Current theories predict that ejaculate quality should be negatively correlated with the level of immunocompetence. Territorial males had relatively heavier spleens than female mimics, but whether this reflects differing immunocompetence is uncertain, since the spleen is also an important organ for erythrocyte storage. Furthermore, there were no differences in the densities of circulating lymphocytes or granulocytes, and the immune parameters did not covary with the sperm traits. Differences in immunocompetence are therefore unlikely to provide a major proximate explanation for variations in sperm traits in corkwing wrasse.