The role of male age, sperm age and mating history on fecundity and fertilization success in the hide beetle

Models of age-related mate choice predict female preference for older males as they have proven survival ability. However, these models rarely address differences in sperm age and male mating history when evaluating the potential benefits to females from older partners. We used a novel experimental design to assess simultaneously the relative importance of these three parameters in the hide beetle, Dermestes maculatus. In a two-part experiment we first explored age-related male mating success and subsequently examined the consequences of male age, sperm age and male mating history on female fecundity and fertilization success. In a competitive mating environment, intermediate-age males gained significantly higher mating success than younger or older males. To test the consequences for females of aged-related male mating success, a second set of females were mated to males varying in age (young, intermediate-age and old), in numbers of matings and in timing of the most recent mating. We found that male age had a significant impact on female fecundity and fertilization success. Females mated to intermediate-age males laid more eggs and attained consistently higher levels of fertilization success than females with young and old mates. A male's previous mating history determined his current reproductive effort; virgin males spent longer in copula than males with prior mating opportunities. However, differences in copulation duration did not translate into increased fecundity or fertilization success. There was also little evidence to suggest that fertilization success was dependent on the age of a male's sperm. The experiment highlights the potential direct benefits accrued by females through mating with particular aged males. Such benefits are largely ignored by traditional viability models of age-related male mating success.     

Age-related sperm transfer and sperm competitive ability in the male hide beetle

The influence of male age on reproductive success after a singlemating has been explored widely; however, few studies have investigatedwhether quantitative or qualitative differences in male spermare responsible for the observed patterns. Moreover, the roleof male age on sperm competitive ability has been largely ignored.We examined the importance of male age on the probability andamount of sperm transferred during a single mating and exploredwhether sperm competitive ability varies with male age in thehide beetle Dermestes maculatus, a species where sperm viabilitydoes not vary with male age. We also investigated whether spermtransfer rates varied with female age. We found that the probabilityof sperm transfer and the amount of sperm transferred variedwith male, but not female, age. All males performed behaviorallysuccessful copulations, but intermediate-age and old males weremore likely to transfer sperm successfully and also transferreda greater quantity of sperm than young males. Old males wereless likely to transfer sperm than intermediate-age males, butif they did transfer sperm successfully, they transferred comparableamounts. Sperm competitive ability varied with male age andreflected the quantity of sperm transferred. On average, intermediate-agemales achieved greater fertilization success when competingagainst young or old males than when competing against otherintermediate-age males. Old males were poor competitors againstintermediate-age males, but they achieved significantly higherrates of fertilization when competing against young males. Ourfindings suggest that quantitative differences in the amountof sperm transferred determine male success in sperm competitionin the hide beetle.     

Reproductive strategies of Aphidius ervi Haliday (Hymenoptera: Aphidiidae)

Hymenopteran parasitoids are usually arrhenotokous parthenogenetic, where females arise from fertilized and males from unfertilized eggs. Therefore, the reproductive fitness of females is a function of egg production and furthermore affected by mating, whereas that of males is mainly determined by the number of daughters they father. Aphidius ervi Haliday is a quasi-gregarious parasitoid of a number of aphid pests on economically important crops such as legumes and cereals. Females are monandrous whereas males are polygynous. Here, we tested how parental age at mating and male mating history affected mating success, fecundity and daughter production in this species. Once-mated males perform significantly better than naïve males with regard to mating success, suggesting that males learn from previous matings. The fecundity of virgin females is not significantly different from that of mated females regardless of parental age at mating and male mating history, indicating that mating does not stimulate egg production or contribute to female nutrient supply. Males can replenish sperm supply after mating, implying that they are at least moderately synspermatogenic. Preference for young over old mates for mating by both sexes may be explained by the fact that aging of both sexes contributes to the reduction of daughter production. Rather than sperm depletion, the reduced daughter production may be attributed to diminishing sperm viability and mobility in aging males and increasing constraints in fertilization process in aging females. Our results also show that female age has a stronger impact on the production of daughters, suggesting that fertilization process in females is more sensitive to aging than sperm vigor in males.     

The Effect of Female Quality on Male Ejaculatory Expenditure and Reproductive Success in a Praying Mantid

Strategic ejaculation is a behavioural strategy shown by many animals as a response to sperm competition and/or as a potential mechanism of cryptic male choice. Males invest more mating resources when the risk of sperm competition increases or they invest more in high quality females to maximize their reproductive output. We tested this hypothesis in the false garden mantid Pseudomantis albofimbriata, where females are capable of multiply mating and body condition is an indicator of potential reproductive fitness. We predicted male mantids would ejaculate strategically by allocating more sperm to high quality females. To determine if and how males alter their ejaculate in response to mate quality, we manipulated female food quantity so that females were either in good condition with many eggs (i.e. high quality) or poor condition with few eggs (i.e. low quality). Half of the females from each treatment were used in mating trials in which transferred sperm was counted before fertilisation occurred and the other half of females were used in mating trials where fertilisation occurred and ootheca mass and total eggs in the ootheca were recorded. Opposed to our predictions, the total number of sperm and the proportion of viable sperm transferred did not vary significantly between female treatments. Male reproductive success was entirely dependent on female quality/fecundity, rather than on the number of sperm transferred. These results suggest that female quality is not a major factor influencing postcopulatory male mating strategies in P. albofimbriata, and that sperm number has little effect on male reproductive success in a single mating scenario.     

Differential sperm expenditure reveals a possible role for post‐copulatory sexual selection in a lekking moth

Male reproductive success in the lesser wax moth Achroia grisella is strongly determined by pre‐copulatory mate choice, during which females choose among males aggregated in small leks based on the attractiveness of ultrasonic songs. Nothing is known about the potential of post‐copulatory mechanisms to affect male reproductive success. However, there is evidence that females at least occasionally remate with a second male and that males are unable to produce ejaculates quickly after a previous copulation. Here we investigated the effects of mating history on ejaculate size and demonstrate that the number of transferred sperm significantly decreased from first (i.e., virgin) to second (i.e., nonvirgin) copulation within individual males. For males of identical age, the number of sperm transferred was higher in virgin than in nonvirgin copulations, too, demonstrating that mating history, is responsible for the decrease in sperm numbers transferred and not the concomitant age difference. Furthermore, the number of transferred sperm was significantly repeatable within males. The demonstrated variation in ejaculate size both between subsequent copulations as well as among individuals suggests that there is allocation of a possibly limited amount of sperm. Because female fecundity is not limited by sperm availability in this system, post‐copulatory mechanisms, in particular sperm competition, may play a previously underappreciated role in the lesser wax moth mating system.     

Impact of male condition on his spermatophore and consequences for female reproductive performance in the Glanville fritillary butterfly

In butterflies, male reproductive success is highly related to the quality and the size of the spermatophore transferred to the female. The spermatophore is a capsule produced by the male during copulation, which in many species contains sperm in addition to a nuptial gift, and which is digested by the female after copulation. The nuptial gift may contribute to egg production and offspring quality, and in some cases also to female body maintenance. The production of the spermatophore, however, represents a cost for the male and, in polyandrous species, ejaculates are sometimes allocated adaptively across matings. Nonetheless, although the ecological factors affecting the reproductive success of female butterflies have been the topic of numerous studies, little information exists on the factors affecting males’ contribution to reproduction, and the indirect impacts on female fecundity and fitness. We used the Glanville fritillary butterfly, Melitaea cinxia (Linnaeus, 1758) (Nymphalidae), in order to assess variation in male allocation to matings. In this species, smaller males produce smaller spermatophores, but variation in spermatophore size is not correlated with female reproductive success. We show that spermatophore size increases with male age at first mating, decreases with mating frequency and adult food‐deprivation, and is not influenced by developmental food‐limitation. The length of copulation period does not influence the spermatophore size nor influences the polyandrous mating behavior in this species. Male contribution to his spermatophore size is clearly influenced by his condition and adult‐resource at the time of mating. Despite this variation, spermatophore size does not seem to have a direct impact on female reproductive output or mating behavior.     

Postmating sexual selection: the effects of male body size and recovery period on paternity and egg production rate in a water strider

The role of male body size in postmating sexual selection wasexplored in a semiaquatic insect, the water strider Gerris lateralis.To separate effects of male size per se from those due to numericsperm competition, male recovery period (shown here to be proportionalto ejaculate size) was manipulated independently of body sizein a factorial experiment where virgin females were mated firstwith sterile males and then with focal males. Both relativemale fertilization success and female reproductive rate were measured.The number of sperm transferred increased with male recoveryperiod, an effect that was mediated by longer copulation duration,but there were no effects of body size on ejaculate size. Neithermale size nor recovery period had any significant direct effectson male fertilization success. However, copulation durationinfluenced relative fertilization success, suggesting that malesable to transfer more sperm also achieved higher fertilizationsuccess. Females exercised cryptic female choice by modulatingtheir reproductive rate in a manner favoring large males andmales that were successful in terms of achieving high relativefertilization success. Thus, successful males gained a twofoldadvantage in postmating sexual selection. This study has important implicationsfor previous estimates of sexual selection in this group of insectsbecause pre- and postmating sexual selection will be antagonisticdue to limitations in male sperm production: males mating frequently(high mating success) will on average transfer fewer sperm ineach mating and will hence tend to fertilize fewer eggs permating (low fertilization success).     

Mating Frequency, Fecundity and Fertilization Success in the Hide Beetle, Dermestes Maculatus

While the immediate benefits accrued to females through multiple mating are well documented, the effect of sperm depletion for multiply mating males is rarely considered. We show that, in small mixed-sex laboratory aggregations, both male and female hide beetles, Dermestes maculatus (De Geer) mated multiply. There was considerable variation in the mating frequency of both sexes; however the skew in mating success was comparable for males and females. Several individuals that mated multiply also re-mated with a previous partner, but in a competitive environment no male copulated more than seven times. Mating success was unrelated to an individual's size, but males that had the most inter-sexual matings also engaged in the most intra-sexual mating attempts. In a second experiment, we show that, even in the absence of rivals, only a small number of males mated with all available virgin females. Moreover, even though males were mated twice to each female, males that copulated more than eight times failed to fertilize any eggs. We suggest that under natural conditions male hide beetles may refrain from mating either prior to, or at the point of, sperm depletion thereby reducing the selection pressure for females to discriminate against sperm depleted males. However, fecundity and fertilization success varied considerably across females and even those mating with sperm-replete males were unable to fertilize 100% of their egg batch. Thus, direct fertilization benefits accrued by females through mating more than once with the same male may play a key role in the maintenance of polyandry in this species.     

Age‐Related Male Reproductive Investment in Courtship Display and Nuptial Gifts in a Moth,Ostrinia scapulalis

Due to a trade‐off between current and future reproduction, costly reproductive investments should be increased towards the end of a lifespan when the probability of reproduction becomes low (terminal investment hypothesis). We investigated age‐related changes in male reproductive investment towards courtship display and the spermatophore in three age classes (young, middle‐aged and old) of a monandrous moth, Ostrinia scapulalis. As predicted, old males had higher mating success than young and middle‐aged males in no‐choice tests. Moreover, two‐choice tests revealed that middle‐aged males had a higher success rate than young males because of their higher courtship frequency rather than any female preference for them. It was found that old males produced a larger spermatophore than young and middle‐aged males, suggesting greater reproductive effort. The protein content of spermatophores also tended to increase with male age. Despite the age‐related variation in spermatophore size and protein content, age did not affect female fecundity or longevity. A decrease in the number of sperm in the older males might counteract the nutritional benefit of larger spermatophores. Alternatively, fitness components other than longevity and fecundity may be influenced by male age.     

The impact of Wolbachia,male age and mating history on cytoplasmic incompatibility and sperm transfer in Drosophila simulans

Most insects harbour a variety of maternally inherited endosymbionts, the most widespread being Wolbachia pipientis that commonly induce cytoplasmic incompatibility (CI) and reduced hatching success in crosses between infected males and uninfected females. High temperature and increasing male age are known to reduce the level of CI in a variety of insects. In Drosophila simulans, infected males have been shown to mate at a higher rate than uninfected males. By examining the impact of mating rate independent of age, this study investigates whether a high mating rate confers an advantage to infected males through restoring their compatibility with uninfected females over and above the effect of age. The impact of Wolbachia infection, male mating rate and age on the number of sperm transferred to females during copulation and how it relates to CI expression was also assessed. As predicted, we found that reproductive compatibility was restored faster in males that mate at higher rate than that of low mating and virgin males, and that the effect of mating history was over and above the effect of male age. Nonvirgin infected males transferred fewer sperm than uninfected males during copulation, and mating at a high rate resulted in the transfer of fewer sperm per mating irrespective of infection status. These results indicate that the advantage to infected males of mating at a high rate is through restoration of reproductive compatibility with uninfected females, whereas uninfected males appear to trade off the number of sperm transferred per mating with female encounter rate and success in sperm competition. This study highlights the importance Wolbachia may play in sexual selection by affecting male reproductive strategies.     

SPERMATOPHORE SIZE IN BUSHCRICKETS: COMPARATIVE EVIDENCE FOR NUPTIAL GIFTS AS A SPERM PROTECTION DEVICE

During courtship and copulation, males of many insect species provide the female with a nuptial gift of a prey item or synthesized material. These gifts may be explained as a form of paternal investment by increasing female reproductive output, or in terms of mating effort by increasing male fertilization success. These explanations, while not mutually exclusive, are controversial. While experimental studies examine the maintenance of nuptial gifts in single species, comparative studies are required to indicate more general evolutionary trends. Male bushcrickets provide females with a nuptial gift, a spermatophylax, which is transferred to females at mating along with the sperm-containing ampulla. Analysis of comparative data of 28 species of bushcrickets (Orthoptera: Tettigoniidae), reveals that male spermatophore size (spermatophylax and ampulla weight) is positively correlated with female refractory period, which, in turn, correlates with male fertilization success. Moreover, gift size (the spermatophylax) covaries with ejaculate size (the ampulla), which is consistent with the hypothesis that it serves as a sperm protection device. In contrast, there is no significant correlation between any measure of female fecundity and male spermatophylax size. This indicates that the variation in spermatophore size among bushcrickets is better explained by a mating-effort function than a paternal investment function.     

Heritable determinants of male fertilization success in the nematode Caenorhabditis elegans

Background  

Sperm competition is a driving force in the evolution of male sperm characteristics in many species. In the nematode Caenorhabditis elegans, larger male sperm evolve under experimentally increased sperm competition and larger male sperm outcompete smaller hermaphrodite sperm for fertilization within the hermaphrodite reproductive tract. To further elucidate the relative importance of sperm-related traits that contribute to differential reproductive success among males, we quantified within- and among-strain variation in sperm traits (size, rate of production, number transferred, competitive ability) for seven male genetic backgrounds known previously to differ with respect to some sperm traits. We also quantified male mating ability in assays for rates of courtship and successful copulation, and then assessed the roles of these pre- and post-mating traits in first- and second-male fertilization success.     

Mating success of male guppy <Emphasis Type="Italic">Poecilia reticulata</Emphasis> in the wild

To understand how the diversity among male sexual traits is maintained despite directional female choice for attractive traits, it is important to study male reproductive success in each reproductive episode. Male reproductive success is indeed the comprehensive result of several processes such as mate choice, mating, and fertilization. In this study, male mating success was estimated in a wild guppy Poecilia reticulata population of Hiji River, Okinawa Island, in southern Japan. The mating success of males was estimated as the percentage of sperm transferred in relation to the total sperm reserve. In a preliminary experiment, it was confirmed that the sperm reserves of males were partly replenished after 12 h and fully replenished after 72 h, when all sperm were released. In addition, the results of investigation in the wild population revealed that approximately 20% of males had no sperm reserves at all, although their sperm reserves should have been replenished by sexual isolation. Male sexual traits such as body size or color pattern did not affect the percentage of sperm transferred. Results from this study provide important insights into male sperm transfer ability and sperm production in this population. However, the high frequency of male sperm-transfer success estimated in this study should to be taken with caution, and whether it is due to differences between wild and laboratory conditions, sex ratio or the rates of multiple matings by females in the wild population remain to be fully explored.     

Fitness advantage from nuptial gifts in female fireflies

Abstract 1. In many insects, males provide nuptial gifts to females in the form of spermatophores, sperm-containing structures produced by male accessory glands.
2. The work reported here examined the influence of both spermatophore number and spermatophore size on female reproductive output in two related firefly beetles, Photinus ignitus and Ellychnia corrusca (Coleoptera: Lampyridae). Based on differences in adult diet, male spermatophores were predicted to increase female reproductive output to a greater extent in P. ignitus than in E. corrusca .
3. Female fecundity was significantly higher in triply mated females than in singly mated females in both species, with no difference between mating treatments in female lifespan or egg hatching success. No effects of second male spermatophore size on fecundity, lifespan, or egg hatching success were detected in either species.
4. These results suggest a direct fitness advantage from multiple mating for females in both species, although enhanced fecundity may be due either to allocation of spermatophore nutrients to eggs or to other substances transferred within the spermatophore acting as oviposition stimulants.     

Resolving mechanisms of short-term competitive fertilization success in the red flour beetle

Postcopulatory sexual selection occurs when sperm from multiple males occupy a female’s reproductive tract at the same time and is expected to generate strong selection pressures on traits related to competitive fertilization success. However, knowledge of competitive fertilization success mechanisms and characters targeted by resulting selection is limited, partially due to the difficulty of discriminating among sperm from different males within the female reproductive tract. Here, we resolved mechanisms of competitive fertilization success in the promiscuous flour beetle Tribolium castaneum. Through creation of transgenic lines with fluorescent-tagged sperm heads, we followed the fate of focal male sperm in female reproductive tracts while tracking paternity across numerous rematings. Our results indicate that a given male’s sperm persist and fertilize eggs through at least seven rematings. Additionally, the proportion of a male’s sperm in the bursa (the site of spermatophore deposition), which is influenced by both timing of female’s ejecting excess sperm and male size, significantly predicted paternity share in the 24 h following a mating. Contrary to expectation, proportional representation of sperm within the female’s specialized sperm-storage organ did not significantly predict paternity, though spermathecal sperm may play a role in fertilization when females do not have access to mates for longer time periods. We address the adaptive significance of the identified reproductive mechanisms in the context of T. castaneum’s unique mating system and ecology.     

Sperm Numbers and Female Fertility in the Moth Plodia interpunctella (Hübner) (Lepidoptera; Pyralidae)

I investigated two possible reasons for remating in female Plodia interpunctella: i) females remate to obtain sufficient sperm to maintain fertility; and ii) male investment in non-sperm components increases female fecundity and longevity. The number of sperm and the mass of the spermatophore transferred by males decreases on successive matings. Sperm numbers and potential male investment were varied by allowing females to mate either once or twice with males either on their first or second mating. Females receiving a single small spermatophore containing few sperm (from a male on his second mating) had sufficient sperm to fertilize all their eggs. Females did not show increased fecundity or longevity as a result of obtaining more spermatophore material. I discuss why females remate when they already have sufficient sperm to fertilize all their eggs.     

Effects of different male remating intervals on the reproductive success of Choristoneura rosaceana males and females

The mass of the spermatophore transferred by a previously mated Choristoneura rosaceana male increases with time elapsed since the last mating but, even after 4 days, it never reaches the mass of the spermatophore of a virgin male. However, spermatophore mass is clearly not a good indicator of the male reproductive investment as the quantity of sperm in the second ejaculate of a previously mated male is the same as that of his first, if he is allowed a 2 (eupyrene sperm) to 3 day (apyrene sperm) recovery period. The interval between the first two matings had no influence on female fecundity or longevity but significantly affected fertility if the male had only 1 day to recover. The length of the post-copulatory refractory period was also shorter in females mated with previously mated males than in those mated with virgins, regardless of the male's remating interval. Furthermore, a significant variation in the eupyrene sperm content of the spermatophore transferred by virgin males had no influence on the length of the female refractory period. Globally, these results support the hypothesis that a factor, other than sperm numbers in the spermatheca, is responsible for maintaining the inhibition of pheromone production in this species.     

Mating Effort and Cryptic Sperm Choice in Scorpionflies: Male Investment Strategy vs. Female Control

In this study, we examined which sex controls sperm transfer during copulation in scorpionflies. Therefore male scorpionflies were doubly mated to females of high and low fecundity to explore whether they allocate sperm according to female quality. While mating order had no effect males transferred sperm at higher rates when mating with low‐quality instead of high‐quality females. As there is no obvious benefit from providing low‐fecundity females with more sperm, we suggest a condition‐dependent female ability to counteract sperm transfer. Therefore, we disabled females at the beginning of copulations using the insecticide Propoxur which leads to total paralysis caused by tremors. While the provoked muscle contractions led to significantly smaller numbers of sperm transferred, Propoxur treatment had no effect on males. We suggest female counteracting of sperm transfer to be adaptive by decreasing the relative amount of sperm transferred by low‐quality males and increasing the proportion of offspring sired by high‐quality males.     

Reproductive biology and function of multiple mating in the mating system of a tree cricket,Truljalia hibinonis (Orthoptera: Podoscritinae)

A tree cricket,Truljalia hibinonis, is known to show a novel sperm removal during copulation. The pattern of copulations and ovipositions showed that the sperm removal functioned to increase reproductive success for sperm removing males. The sperm removal by males evolves under the system in which female accept multiple mating. The possible benefits of multiple mating for females are examined. Multiple mating did not seem to be necessary for avoiding sperm depletion, because females stored huge number of sperm in their sperm storage organ after finishing oviposition. The ingestion of metanotal secretion during copulation also had no effect on increasing fecundity and egg size. However, mating experience may have a positive effect on increasing fecundity slightly, though there were no differences between once- and twice-mated females. The other possible benefits for each male and female are discussed.     

The role of sperm numbers in sperm competition and female remating in Drosophila melanogaster

Single mating productivities (used as estimates of the relative number of sperm transferred) are highly correlated with several parameters used to quantify sperm competition in D. melanogster. Matings that result in the transferal of large numbers of sperm are associated with longer delay of female remating than are matings that transfer fewer sperm. Males that transfer larger numbers of sperm also suffer a smaller proportional reduction in reproductive success (smaller COST) than males transferring fewer sperm. The number of sperm transferred by a female's second mate is not related to the COST to the first male. However, there is a high positive correlation between the number of sperm transferred by the second male and P₂ (the proportion of second male progeny following female remating). Thus, large sperm numbers apparently increase the reproductive success of males whether they mate with virgin or non-virgin females. Because female receptivity mediates these events, there is no need to invoke sperm displacement to explain the reproductive outcome of female remating.The timing of female remating is evaluated in terms of a receptivity-threshold model. This model suggests that female receptivity returns when some small, relatively constant, number of sperm remain in storage.