Effects of broken male intromittent organs on the sperm storage capacity of female earwigs, <Emphasis Type="Italic">Euborellia plebeja</Emphasis>

In earwigs of the family Anisolabididae, male intromittent organs (virgae) sometimes break off inside female sperm-storage organs (spermathecae) during mating. I examined the effects of this genital breakage on the sperm storage capacity of females using Euborellia plebeja as a representative species. When genital breakage was artificially induced in virgin females, subsequent males successfully inseminated these females. However the sperm-storage capacity of these females was limited by the presence of broken virgae in their spermathecae. In another experiment, genital breakage was experimentally induced in the spermathecae of inseminated females, and their reproductive performance was then monitored for 60 days. In all of four cases where the entire piece of the broken virga remained inside the spermatheca, females deposited fertile eggs (more than 60% hatchability). The average number of clutches, that of eggs laid, and that of hatchlings were similar to those of controls. On the other hand, females laid no eggs in the other two cases where the broken virgae protruded from the spermathecal opening. I discuss the relevance of the results to the mating system and possible removal of rival sperm, which has been reported for E. plebeja. Electronic Publication     

Mating frequency and reproductive success in an income breeding moth,Mnesampela privata

The frequency of mating in insects is often an important determinant of female reproductive output and male sperm competition. In Lepidoptera that provide male nutrients to the female when mating, it is hypothesized that polyandry may be more prevalent. This is thought to be especially so among species described as income breeders; that is, in species who do not derive all their nutrients for reproductive output entirely from the resources obtained during the larval stage. We selected the geometrid moth, Mnesampela privata (Guenée) (Lepidoptera: Geometridae), to examine this hypothesis further. We found this species was best characterized as an income breeder with female weight on emergence positively correlated with total egg load but not with the number of eggs laid. Further, in accord with income breeders, females emerged with a partially developed egg load and lifetime fecundity was positively correlated with the number of oviposition days. However, in the laboratory we found that incidence of repeated matings or polyandry was rare. When moths were paired singly over their lifetime, only 4% of mated females multiple mated. When females were paired with three males concurrently, female mating success increased from 60 to 81% with multiple mating among mated females increasing to just 15%. Dissection of wild caught M. privata found that polyandry levels were also low with a maximum of 16.4% of females collected at any one time being multiple mated. In accord with theory, mating significantly increased the longevity of females, but not of males, suggesting that females acquire essential resources from male ejaculates. Despite this, multiple mated females showed a trend toward decreasing rather than increasing female reproductive output. Spermatophore size, measured on death of the female, was not correlated with male or female forewing length but was negatively correlated with the number of fertile eggs laid and female longevity. Smaller spermatophore width may be related to uptake of more nutrients by the female from a spermatophore. We discuss our findings in relation to income breeding and its relationship to polyandry in Lepidoptera.     

Multiple paternity in egg clutches of hawksbill turtles (Eretmochelys imbricata)

We present the first data collected on the genetic mating system of the hawksbill turtle Eretmochelys imbricata, the only marine turtle not studied to date. We examined paternity within 12 egg clutches from ten female hawksbill turtles from Sabah Turtle Islands, Malaysia. A total of 375 hatchlings were analysed using five microsatellite markers. Results demonstrated that clutches from two out of ten females were sired by multiple males (maximum of two). Although at a low frequency, observation of multiple paternity indicates that hawksbill turtles exhibit the same genetic mating system (polyandry) as observed for other species of marine turtles. Consistent paternity across multiple clutches laid by individual females in one breeding season supports the hypothesis that sperm are stored from mating prior to nesting and are then used to fertilize all subsequent clutches of eggs that season.     

No material benefits, and a fertilization cost, for multiple mating by female leaf beetles

When females mate multiple times it presents an intriguing problem for evolutionary biologists due to the high costs and not very apparent benefits. Yet, this behaviour must have higher benefits than costs to be maintained by natural selection. We studied possible benefits for multiple mating by female leaf beetles, Leptinotarsa decemlineata, both with multiple males (polyandry) and multiple times with the same male (repeated matings). For polyandry, we tested the material benefits hypothesis, as well as fertility insurance, by mating females to varying numbers of males and looking at sperm received and fecundity. Although there was a relationship between amount of stored sperm and number of matings, we did not find the predicted positive relationship between fecundity and number of matings. Thus, the material benefits hypothesis was not supported. For repeated matings, we tested the sperm and nonsperm material benefit hypotheses by mating females to a single male varying numbers of times on one mount. For this set of tests neither sperm number nor fecundity was positively correlated with number of matings, therefore neither hypothesis was supported. Interestingly, in both experiments, there was a significant decrease in hatch rate with an increase in matings, demonstrating a cost of polyandry. These findings, along with previous research, suggest a cost of multiple mating with a possible role of seminal fluids in the reduction in female fecundity.     

Paternity costs from polyandry compensated by increased fecundity in the hide beetle

Polyandry-induced sperm competition is assumed to impose costson males through reduced per capita paternity success. In contrast,studies focusing on the consequences of polyandry for femalesreport increased oviposition rates and fertility. For thesespecies, there is potential for the increased female fecundityassociated with polyandry to offset the costs to males of sharedpaternity. We tested this hypothesis by comparing the proportionand number of offspring sired by males mated with monandrousand polyandrous females in the hide beetle, Dermestes maculates,both for males mating with different females and for males rematingwith the same female. In 4 mating treatments, monandrous femalesmated either once or twice with the same male and polyandrousfemales mated either twice with 2 different males or thricewith 2 males (where 1 male mated twice). Polyandrous and twice-matingmonandrous females displayed greater fecundity and fertilitythan singly mating monandrous females. Moreover, males rematedto the same female had greater paternity regardless of whetherthat female mated with another male. In both polyandrous treatments,male mating order did not affect paternity success. Finally,although the proportion of eggs sired decreased if a male matedwith a polyandrous female, multiply mating females or femalesthat remated with a previous mate laid significantly more eggsand thus the actual number of eggs sired was comparable. Thus,males do not necessarily accrue a net fitness loss when matingwith polyandrous females. This may explain the absence of anyobvious defensive paternity-protection traits in hide beetlesand other species.     

Effect of multiple mating on the reproductive performance of the rice leaffolder moth,Cnaphalocrocis medinalis (Lepidoptera: Crambidae)

To clarify whether multiple mating of females and males affects the reproductive performance of the rice leaffolder moth, Cnaphalocrocis medinalis (Guenée), we examined the effect of the number of matings (once, twice, or three times) for females (female treatment) and males (male treatment) on the incidence of moth mating, number of eggs laid, egg hatchability, and adult longevity. We also compared the effect of multiple mating imposed on males or females separately with the effect of that imposed on both sexes simultaneously (both sexes treatment). The incidence of mating of females and males that mated three times (3-mated females and males) was significantly lower than for females and males that mated twice or once (2-mated or 1-mated females and males). The incidence of mating of 1-mated moths (both sexes) was significantly higher than for 2-mated or 3-mated moths (both sexes). Two-mated or 3-mated females laid significantly more eggs with significantly higher hatchability than 1-mated females. Females that mated with 1-mated males (second male mating) or 2-mated males (third male mating) laid significantly fewer eggs than those that mated with virgin males (first male mating). Females laid significantly more eggs after the second and third matings for moths of both sexes than after the first mating for moths of both sexes. The mechanisms of improvement and decline of female reproductive performance when multiple mating was imposed on males or females are also discussed in relation to the reproductive biology of C. medinalis.     

Sperm precedence in the dragonfly Erythemis simplicicollis

Females of the dragonfly Erythemis simplicicollis (Say) (Odonata, Libellulidae) store enough sperm to fertilize 6–13 clutches of eggs laid on consecutive days. Nonetheless, they usually mate one or more times per day. Males wait for females at ponds containing surface vegetation on which the females lay eggs. Some males defend vegetation while other act as satellites. After mating, both types of males attempt to guard females against takeover by other males. Sperm precedence by male E. simplicicollis was studied using sterility produced by gamma irradiation to label sperm. After a dose-response analysis, males receiving a dose of 25 kiloroentgens (>99.9% sterile) were returned to their home pond as territory residents and satellites. Both types of males fertilized an average of 99.5% (range 97.3–100%) of the female's remaining clutch. After mating with a sterile male, females were isolated in a large cage, and eggs collected for several consecutive days. These clutches revealed that sperm mixing in the bursa of the females is essentially complete after 24 to 48 h and that the last male to mate had replaced an average of more than 57–75% of the sperm stored by female from previous matings. Thus, the last sperm in is the first sperm out fertilizing essentially all of the eggs laid soon (5–6 min) after the mating. Sperm from the most recent mating competes for fertilizations with sperm stored from previous matings only if the female oviposits on the following day without remating.     

Costs and benefits of polyandry in the egg parasitoid Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae)

Polyandry implies costs (i.e., time, energy, predation risk, etc.) especially in short-lived parasitoid species but females of several hymenopteran parasitoid species, mostly gregarious, do mate with multiple males. Several hypotheses have been proposed to explain the benefits of polyandry but controversy remains, especially in facultative gregarious species that bridge the gap between solitary and gregarious development. In this study, we investigated the possibility that polyandry may bring material benefits to Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae) females, a short-lived and facultative gregarious egg parasitoid. Females mated several times with different males both at emergence and throughout their life. No significant difference was found in the offspring sex ratio and the fecundity of multiple mated and single mated females and pre-mating duration increased with the female’s age. The longevity of females did vary significantly with the number of matings but only in the presence of hosts. Female T. evanescens received enough sperm from one mating to allocate an optimal offspring sex ratio and we found no evidence of either nutritional resources or convenience polyandry in this species. Polyandry in facultative gregarious parasitoids might be an adaptive strategy to minimize the risk of mating with males that have already emptied their sperm bank or to accumulate sperm from several partially sperm-depleted males. Polyandry may also increase the probability of non-sib mating in patches exploited by several females.     

Determinants of female fecundity in a simultaneous hermaphrodite: the role of polyandry and food availability

Classical sexual selection theory assumes that the reproductive success of females is primarily limited by the resources available for egg production rather than by the number of mating partners. However, there is now accumulating evidence that multiple mating can entail fitness costs or benefits for females. In this study we investigated the effect of polyandry (i.e., the mating with different mating partners) and food availability on the reproductive output of the female sex function in an outcrossing simultaneous hermaphrodite, the free-living flatworm Macrostomum lignano. We exposed virgin worms to different group sizes, a treatment that has previously been shown to affect the level of polyandry in this species. Moreover, we manipulated the food availability throughout the subsequent egg laying period, during which the worms were kept in isolation. The number of offspring produced was used as an estimate of female fecundity. We found that food availability, but not group size, had a significant effect on female fecundity. Additionally, female fecundity was positively correlated with the number of stored sperm in the female sperm-storage organ at the time of isolation, but it was not correlated with body or ovary size of the worms. Our results suggest that female fecundity in M. lignano is primarily determined by the resources available for egg production, and not by the level of polyandry, confirming classic sexual selection theory for simultaneous hermaphrodites.     

Cooperation and conflict among dunnocks, Prunella modularis, in a variable mating system

The mating system of a population of 90 breeding dunnocks (or hedge sparrow, Prunella modularis) included monogamy, polygyny, polyandry and polygynandry. Monogamous males guarded females during their fertile period to prevent neighbouring males from copulating. The most intense guarding occurred where two (unrelated) males shared a territory. Here, the alpha male tried to prevent the beta male from copulating with the female. Beta males were seen to copulate in only half the cases. They were more likely to succeed when the alpha male found it difficult to guard the female closely because her range was large, the vegetation was dense or there were other females breeding synchronously on the same territory. Close guarding and chasing by males reduced the female's feeding rate and was correlated with unhatched eggs in the nest. Females attempted to escape the alpha male's attentions and actively encouraged the beta male to mate. Beta males only helped to feed the young if they copulated with the female. Nestlings fed by two males and a female got more food and weighed more than those fed by just one male and a female. Indirect evidence suggested that when beta males failed to copulate, they destroyed eggs or young chicks. Females laid larger clutches when two males mated with them as opposed to one, thus adapting their clutch size to the amount of parental care they expected. The results of natural removal experiments and matched comparisons of the same female in different mating systems support these conclusions. For females, selection favours cooperative polyandry, whereas for males if favours polygyny; the variable mating system may reflect the different outcomes of this sexual conflict.     

BENEFITS OF MULTIPLE MATES IN THE CRICKET GRYLLUS BIMACULATUS

Despite the importance of polyandry for sexual selection, the reasons why females frequently mate with several males remain poorly understood. A number of genetic benefits have been proposed, based on the idea that by taking multiple mates, females increase the likelihood that their offspring will be sired by genetically more compatible or superior males. If certain males have intrinsically “good genes,” any female mating with them will produce superior offspring. Alternatively, if some males have genetic elements that are incompatible with a particular female, then she may benefit from polyandry if the sperm of such males are less likely to fertilize her eggs. We examined these hypotheses in the field cricket Gryllus bimaculatus (Orthoptera: Gryllidae). By allocating females identical numbers of matings but different numbers of mates we investigated the influence of number of mates on female fecundity, and both short- and long-term offspring fitness. This revealed no effect of number of mates on number of eggs laid. However, hatching success of eggs increased with number of mates. This effect could not be attributed to nongenetic effects such as the possibility that polyandry reduces variance in the quantity or fertilizing ability of sperm females receive, because a control group receiving half the number of copulations showed no drop in hatching success. Offspring did not differ in survival, adult mass, size, or development time with treatment. When males were mated to several different females there were no repeatable differences between individual males in the hatching success of their mate's eggs. This suggests that improved hatching success of polyandrous females is not due to certain males having genes that improve egg viability regardless of their mate. Instead, our results support the hypothesis that certain males are genetically more compatible with certain females, and that this drives polyandry through differential fertilization success of sperm from more compatible males.     

Seminal fluid reduces female longevity and stimulates egg production and sperm trigger oviposition in a moth

Previous studies suggest that a number of factors in relation to mating may reduce female longevity and stimulate egg production and oviposition. However, it is still not clear whether these factors act on these parameters independently or in a collective way. Here we carried out a series of experiments including mating trials and seminal fluid injection to determine the factors responsible for reducing female longevity and stimulating egg production and oviposition in relation to mating in the moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). Results show that seminal fluid and sperm work collectively to allow females to achieve maximum realized fecundity (number of eggs laid) in E. kuehniella but these factors play different roles in the process and their actions are independent. Seminal fluid signals females to allocate resources to ova, resulting in shorter longevity and greater egg production while eupyrene (not apyrene) sperm in the spermatheca trigger females to lay maximum number of eggs. We suggest that the receptors for seminal fluid signal may be located in the female reproductive tract and haemolymph, and those for sperm signal may be in the spermatheca. Hypotheses that females prolong their longevity by oosorption, physical injuries by males reduce female longevity, and mechanical stimulation by males triggers oviposition, are not substantiated in the present study.     

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.     

The leatherback turtle,Dermochelys coriacea,exhibits both polyandry and polygyny

The leatherback turtle (Dermochelys coriacea) is an endangered species, and world-wide populations are declining. To understand better the mating structure of this pelagic and fragile species, we investigated paternity in nearly 1000 hatchlings from Playa Grande in Parque Marino Nacional Las Baulas, Costa Rica. We collected DNA samples from 36 adult female leatherbacks and assessed allele frequency distributions for three microsatellite loci. For 20 of these 36 females, we examined DNA from hatchlings representing multiple clutches, and in some cases assessed up to four successive clutches from the same female. We inferred paternal alleles by comparing maternal and hatchling genotypes. We could not reject the null hypothesis of single paternity in 12 of 20 families (31 of 50 clutches), but we did reject the null hypothesis in two families (eight of 50 clutches). In the remaining six families, the null hypothesis could not be accepted or rejected with certainty because the number of hatchlings exhibiting extra nonmaternal alleles was small, and could thus be a result of mutation or sample error. Successive clutches laid by the same female had the same paternal allelic contribution, indicating sperm storage or possibly monogamy. None of 20 females shared the same three-locus genotype whereas there were two instances of shared genotypes among 17 inferred paternal three-locus genotypes. We conclude that both polyandry and polygyny are part of the mating structure of this leatherback sea turtle population.     

Repeated mating with the same male increases female longevity and fecundity in a polyandrous leaf beetle Galerucella birmanica (Coleoptera: Chrysomelidae)

Female multiple mating (polyandry) is widespread across Insecta, even if mating can be costly to females. To explain the evolution and maintenance of polyandry, several hypotheses, mainly focusing on the material (direct) and/or the genetic (indirect) benefits, have been proposed and empirically tested in many species. Considering only the direct benefits, repeatedly‐mated females are expected to exhibit the same fitness as multiply‐mated females under the same mating frequency. In the present study, we compare the fitness of females received monandrous repeated mating (MM) and polyandrous multiple mating (PM) in a polyandrous leaf beetle Galerucella birmanica and assess female mate preference with regard to polyandry or monandry. Our data indicate that the longevity and the egg‐laying duration of MM females are significantly longer than that of PM females. MM females produce significantly more hatched eggs than PM females over their lifetime under the same mating frequency, which results from the high hatching rate of eggs produced by MM females. PM females mated with novel virgin males in the second mating suffer decreased longevity and lifetime fecundity compared with PM females mated with novel mated males in the second mating. Once‐mated females are more likely to re‐mate with familiar males than novel males. By contrast to expectations, the results of the present study suggest that repeated mating provides females with more direct benefits than multiple mating in G. birmanica, and females prefer to re‐mate with familiar males. The possible causes of this finding are discussed.     

Copulation reduces male but not female longevity in Saltella sphondylli (Diptera: Sepsidae)

Mating more than once is extremely costly for females in many species, making the near ubiquity of polyandry difficult to understand. However, evidence of mating costs for males is much rarer. We investigated the effects of copulation on longevity of male and female flies (Saltella sphondylli). We also scrutinized potential fecundity and fertility benefits to females with differing mating history. Copulation per se was found to decrease the longevity of males but not that of females. However, when females were allowed to lay eggs, females that mated died earlier than virgin females, indicating costs of egg production and/or oviposition. Thus, although longevity costs of copulation are higher for males, reproduction is nevertheless costly for females. We also found no differences in fecundity or fertility relative to female mating history. Results suggest that polyandry may be driven by minor costs rather than by major benefits in this species.     

Effects of Single Versus Multiple Mates: Monogamy Results in Increased Fecundity for the Beetle <Emphasis Type="Italic">Phoracantha semipunctata</Emphasis>

Effects of polyandry versus monogamy were assessed for the beetle Phoracantha semipunctata (Coleoptera: Cerambycidae) by comparing measures of female reproductive success, including fecundity, egg viability, time until eclosion, and clutch size. The effect of intermittent presence or absence of a male was also evaluated. Polyandry was detrimental to female reproductive success in comparison to monogamy. Fecundity, egg viability, and clutch size were lower, and time to eclosion were increased for eggs from females with multiple mates compared with monogamous females. Intermittent presence of males had no effect on female reproductive success. Possible explanations for the decreased fecundity experienced by females with multiple mates include sperm competition intensity, costs of male harassment, and exceeding the optimal mating frequency. Females may reduce costs associated with polyandry by spending less time on host logs where mating occurs.     

The effect of mating frequency and mating pattern on female reproductive fitness in cabbage beetle,Colaphellus bowringi

It is generally thought that females can receive more of the material benefits from males by increasing mating frequency and polyandry can lead to greater reproductive success. The cabbage beetle, Colaphellus bowringi Baly (Coleoptera: Chrysomelidae), is a highly promiscuous species, in which females or males can readily mate repeatedly with a given partner or multiple partners at a very high frequency. In the present study, the effect of mating frequency (number of matings) and mating pattern (polyandry vs. monogamy) on female reproductive fitness was investigated by measuring fecundity, fertility, and female longevity. The results indicated that increased female mating frequency with the same male did not result in variation in lifetime fecundity, but significantly increased fertility and decreased female longevity. Moreover, five copulations were sufficient to acquire maximal reproductive potential. Female lifetime fecundity also did not differ between polyandrous and monogamous treatments. However, monogamous females exhibited a significant increase in fertility and significant prolongation of longevity compared with polyandrous females, further demonstrating that monogamy is superior to polyandry in this beetle.     

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.     

Polyandry in grain beetles, Tenebrio molitor, leads to greater reproductive success: material or genetic benefits?

Females that mate with more than one male may derive both materialand genetic benefits, and differentiating between the two benefitsis often difficult. We tested for both material and geneticeffects associated with multiple mating in the highly promiscuousyellow mealworm beetle, Tenebrio molitor. Females that matedfour times to the same male laid more eggs and produced morelarvae than females that mated only once. Whether copulationsoccurred on the same day or over several days, the result wasan immediate increase in the production of eggs by females.Some females were kept on a restricted diet to test whethernutrients in the spermatophore disproportionately benefittedfood-deprived females. Although females on poor diets producedfewer and smaller offspring, diet did not significantly affect the proportional benefit of mating treatment on female fecundity.By controlling for male mating history, we were able to separatethe effects of mating with different males from the effectsof receiving multiple spermatophores from the same male. Femalesthat mated with four different males achieved substantial gainsin numbers of eggs produced (32% increase) beyond those offemales that mated an identical number of times with the same male. We found no evidence that males allocate fewer sperm toprevious mates. Egg hatchability was unaffected by mating behavior,suggesting that genetic incompatibility at that stage is notresponsible for the low reproductive success of females matedwith a single male. These results suggest that females maydelay or reduce oviposition or may be incapable of achieving maximal fecundity until they have gained the material and/orgenetic benefits of mating with multiple males.