Sperm numbers,their storage and usage in the fly Dryomyza anilis

In the fly Dryomyza anilis females have two kinds of sperm storage organs: one bursa copulatrix and three spermathecae (two spermathecae with a common duct form the doublet, and the third is a singlet spermathecal unit). At the beginning of a mating the male deposits his sperm in the bursa copulatrix. After sperm transfer the male taps the female''s abdomen with his claspers. This behaviour has been shown to increase the male''s fertilization success. After mating, the female discharges large quantities of sperm before oviposition. To find out where the sperm remaining in the female are stored, I counted the number of sperm in the droplet and in the female''s sperm storage organs after different types of mating. I carried out three mating experiments. In experiment 1, virgin females were mated with one male and the matings were interrupted either immediately after sperm transfer or after several tapping sequences. The results show that during male tapping more sperm moved into the singlet spermatheca. In addition, the total number of sperm correlated with sperm numbers in all sperm storage organs, and male size was positively related to the number of sperm remaining in the bursa. In experiment 2, females mated with several males. The number of sperm increased with increasing number of matings only in the doublet spermatheca. No increase in the number of sperm in the singlet spermatheca during consecutive matings suggests that sperm were replaced or did not reach this sperm storage organ. In experiment 3, virgin females were mated with a single male and half of them were allowed to lay eggs. The experiment showed that during egglaying, females primarily used sperm from their singlet spermatheca. The results from the three experiments suggest that sperm stored in the singlet spermatheca is central for male fertilization success and male tapping is related to sperm storage in the singlet spermatheca. The different female''s sperm storage organs in D. anilis may have separate functions during sperm storage as well as during sperm usage.     

Selection of male traits during and after copulation in the seedbug Lygaeus simulans (Heteroptera, Lygaeidae)

In order to evaluate selection of male morphological traits during copulation, a laboratory experiment was performed with the promiscuous seedbug Lygaeus simulans. Three male traits suspected as putative targets of selection were measured: weight, fluctuating asymmetry of a measure on the forewings, and length of a conspicuous genital structure, the processus gonopori. As fitness measures we considered total fecundity (number of fertilized eggs), insemination and fertilization success (established if a female laid fertilized eggs after copulation), and the interval between copulation and oviposition. Eighty-four males were allowed a single copulation with one virgin female each. Out of 67 copulations, 27 (40.2%) resulted in fertilized eggs and the oviposition latency ranged from 6 to 26 days. Regressions of male traits on the fitness measures showed significant phenotypical selection of two male traits: (1) males of average weight are more likely to achieve fertilization and (2) the oviposition latency was shorter for males with lower asymmetry. The copulation-oviposition interval may be especially important for male fertilization success because Lygaeus males perform copulatory mate guarding and the last male copulating with a female fertilizes most of the eggs. No selection of the genitalic trait was detected.     

Repeated copulations benefit of the female inLethocerus deyrollei vuillefroy (Heteroptera: Belostomatidae)

TheLethocerus deyrollei male copulates repeatedly with the same female before and between ovipositions. Females stopped oviposition and waited for the next copulation when males were experimentally removed. This result suggests that females need to copulate before each oviposition bout. Since eggs fail to hatch without care of males, females have to detain males until the end of sequential ovipositions. Males assure their paternity with repeated copulations, and females can thus detain males.     

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 tactics and male wing dimorphism in the damselfly,Mnais pruinosa costalis selys (Odonata: Calopterygidae)

Males of the damselfly,Mnais pruinosa costalis, exhibit wing color dimorphism: one form has orange wings, and the other hyaline wings which resemble female wings. The former is usually territorial and the latter uses sneaky mate securing tactics. When orange-winged males failed to establish territory, they became floaters that day. Hyaline-winged males perched around their territories and often, formed in tandem without any apparent courtship behavior when they found females. Their copulation frequency was higher and copulation duration longer than those of territorial males. A few females oviposited without remating. Total oviposition duration of females with which a hyaline-winged male mated was more than 32 min per male on average in a day Females that copulated with hyaline-winged males often remated with orange-winged residents before oviposition. Total duration of oviposition bouts of females after mating with floaters was short (15 min), while that with territorial residents was long (66 min). As a result, total oviposition duration of females with which an orange-winged male mated was about 40 min in a day. The reproductive success of the hyaline-winged males may be similar to that of the orange-winged males.     

Reproductive behaviour of the white-tailed zygaenid moth,Elcysma westwoodii (Lepidoptera,Zygaenidae). II. Female mating strategy

Male white-tailed zygaenid moths.Elcysma westwoodii, often gather to a female to mate her. One of the factors that seems to cause male gathering is the females' tendency to refuse males. Field observations indicated that there was a relationship between the courtship duration, the copulation duration and egg fertilization: short courtship was followed by long copulation and oviposition of fertile eggs in the same day, while long courtship was followed by short copulation and failure of oviposition. This phenomenon may be the result of differences in male activity. More “fertile” males can reach copulation more quickly and continue it longer than males by limiting receptivity. This “passive female choice” seems to function in high male density. Long copulation usually continued until the female began oviposition.     

Genital damage in the orb-web spider Argiope bruennichi (Araneae: Araneidae) increases paternity success

The morphology of male genitalia often suggests functions besidessperm transfer that may have evolved under natural or sexualselection. In several species of sexually cannibalistic spiders,males damage their paired genitalia during mating, limitingthem to one copulation per pedipalp. Using a triple-mating experiment,we tested if genital damage in the orb-web spider Argiope bruennichiincreases male fitness either through facilitating his escapefrom an aggressive female or by obstructing the female's inseminationducts against future copulation attempts from other males. Wefound no survival advantage for males damaging their pedipalps;however, copulations into a previously used insemination ductwere significantly shorter when the previous male had left partsof his genitalia inside the insemination duct. Because copulationduration determines paternity in this species, our result suggeststhat male genital damage in A. bruennichi is sexually selected.By breaking off parts of their intromittent organs inside avirgin female, males can reduce sperm competition and therebyincrease their paternity success.     

Male Performance and Body Size Affect Female Re-Mating Occurrence in the Orb-Web Spider Leucauge mariana (Araneae, Tetragnathidae)

Females can affect male probabilities of paternity success through behavioural, morphological and/or physiological processes occurring during or after copulation. These processes under female-control include the acceptance or rejection of mating attempts by subsequent males. Leucauge mariana is an orb weaving spider that shows male mate guarding of penultimate females, male–male competition on female webs and copulatory plugs, suggesting a polyandric mating system. The aim of the present study was to ascertain whether male behaviour during courtship and copulation in L. mariana relate with female re-mating decisions. Forty-three virgin females were exposed to up to three males until they mated. In 24 cases, the copulatory plug was absent after mating and females were exposed the next day to up to three other males. Eighteen females accepted a second mating. Relatively larger females were more receptive to second matings and were more likely to copulate if the second male was smaller. Longer duration of female tapping and abdominal bobbing during courtship, and first copulations with less short insertions and more flubs, were associated with increased female acceptance to second matings. The results indicate cryptic female choice on male courtship and copulatory performance and suggest female-control over the determination of male mating success in this spider species.     

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.     

FUNCTIONAL INCOMPATIBILITY BETWEEN THE FERTILIZATION SYSTEMS OF TWO ALLOPATRIC POPULATIONS OF CALLOSOBRUCHUS MACULATUS (COLEOPTERA: BRUCHIDAE)

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

The effect of differences in body size on the male territorial system of the fly Dryomyza anilis

Drymyza anilis nales defend carcasses, the oviposition sites for females. On carcasses less than 100 g in weight, a single male establishes a teriitory. Ther sex ratio at carcasses is male-biased. Territorial males are larger than other males on average, and move and attack other males more frequently than non-territorial males do. Large carcasses attract more males than smaller ones, but the female, but the advantage of territorial behaviour decreases with increasing density of males. Copulating males are significantly larger than average males, but smaller than territorial males, suggesting than some non-territorial males have access to females. Males seem to be albe to assess a female's egg load, and to adjust the duration of copulation accordingly.     

Value of male remating and functional sterility in redback spiders

In the Australian redback spider, Latrodectus hasselti, males typically use their paired copulatory organs (palps) to copulate twice with a single female then sacrifice themselves to their cannibalistic mates in a strategy that increases their paternity in that one mating, but leads to death. This type of terminal investment in one mating is predicted only if the expected value of future matings is low for males relative to the value of repeated mating with the same female. In this laboratory study, we quantified the reproductive value of mating more than once with the same female (repeated mating) and mating with more than one female (multiple mating) for male redback spiders. We tested two natural selection hypotheses for repeated mating, sperm limitation and reproductive insurance, but found no support for either hypothesis. We show that, in the absence of sperm competition or cannibalism, male lifetime reproductive output is the same whether a male copulates once, twice, or several times with a given female. Repeated mating does not increase the probability of successful fertilization, nor does it increase the number of offspring produced in successful matings. Although male repeated mating is not favoured because of increased fertility of mates, other studies suggest it may be important in sperm competition. Here we show that the relative reproductive value of the first two copulations is very high for redback males because they are functionally sterile after each palp has been used once; nonvirgin males are unable to father offspring. Functional sterility and repeated mating by male redbacks may be favoured by the same factors that lead to male sacrifice behaviour: ecological constraints on multiple mating combined with competitive benefits of maximal investment in the first mating. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Nuptial gifts and sexual selection in photinus fireflies

The phenomenon of nuptial gift transfer during mating occursacross a remarkably wide range of taxa, and such male donationsare likely to influence both pre-copulatory and post-copulatorysexual selection. This paper reviews what is known about nuptialgifts in Photinus fireflies (Coleoptera: Lampyridae), and discussesthe adaptive significance of spermatophores in firefly matingsystems. During copulation Photinus males transfer a spiral,gelatinous spermatophore to the female: sperm are released intothe female's spermatheca for storage, while the remainder ofthe spermatophore disintegrates within a specialized gland.Radiolabelling studies indicate that male-derived protein isused to help provision the female's developing oocytes, andmultiply-mated females show increased fecundity. As most Photinusadults do not feed, these studies suggest that females shouldcontinue to forage for matings to supplement their diminishinglarval reserves, even after they have gained sufficient spermto fertilize their eggs. Male spermatophore mass declines acrosssequential matings, and smaller spermatophores are associatedwith lower paternity success in situations where males competefor fertilizations. Declining spermatophore size across sequentialmatings may thus lead to diminishing reproductive returns forfirefly males. Taken together, these results suggest that seasonalchanges in nuptial gift availability may contribute to reversalsof traditional courtship roles, with male choice and female-femalecompetition occurring as spermatophore availability declines.     

Reproductive behavior of the Japanese treefrog,Rhacophorus arboreus (Anura: Rhacophoridae)

Reproductive behavior of the foam-nesting treefrog,Rhacophorus arboreus, is described. Oviposition was made either by an amplectant pair (a female, and an amplectant male) alone or by an amplectant pair and other males (joiners). The snout-vent length of males and females was negatively correlated with the date of the first appearance in the pond. The period of staying in the pond in males was longer than that in females. Physical body contacts of other males, and encounter calls by ampletant males were frequently observed before oviposition with joiners. Snout-vent length of the female and an amplectant male were positively correlated. Encounter calls by amplectant males were likely to precede movement of females. There was no difference of snout-vent length between amplectant males and joiners. Females moved the hindlimbs more frequently than males during oviposition. Amplectant males made encounter cells more frequently in oviposition with joiners, than oviposition without joiners. The patterns of transitions between acts of females and amplectant males were similar between oviposition with and without joiners. Females more frequently responded to amplectant males than joiners. Both the duration of a bout of the movements of hindlimbs of females and the interval between the bouts were longer in oviposition without joiners than that with joiners. The number of the movements per bout in oviposition without joiners was smaller than that with joiners. Encounter calls by amplectant males during oviposition tended to precede the hindlimb movements of females.     

Females benefit from mating with different males in the scorpionfly Panorpa cognata

The adaptive significance of female polyandry has become a recurrentsubject of recent theoretical and empirical research. It hasbeen argued that in addition to direct benefits, such as nuptialgifts or an adequate sperm supply, females may gain geneticbenefits from mating with different males. Females of the scorpionflyPanorpa cognata mate with several males during their lifetime.In an experiment designed to rule out any direct nutritionalbenefit of multiple matings, I found that polyandrous femalesthat mated with two different males achieved a significantlyhigher egg-hatching success than monandrous females that matedtwice with the same male. However, individual males did nottrigger the same response in different females as the egg-hatchingsuccess of different females that mated with one and same maledid not correlate. The results, thus, do not conform to predictionsfrom hypotheses assuming that genetic benefits of polyandryare influenced by the intrinsic genetic quality of males. Theresults are, however, consistent with the genetic incompatibilityhypothesis. Nevertheless, substances from different males transferredduring copulation may synergistically affect zygote viability.Furthermore, I discuss why paternity studies can only explicitlytest the genetic incompatibility hypothesis if there are a prioriexpectations of female-male genome compatibilities.     

Sexual cannibalism and sperm competition in the golden orb-web spider Nephila plumipes (Araneoidea): female and male perspectives

Mating systems are frequently shaped by conflicts over reproductive interests between males and females. Sexual cannibalism canbe an especially dramatic manifestation of such conflicts.However, the resolutions of this conflict differ among sexuallycannibalistic spider species. Cannibalism may be in the interestof both sexes when females consume males as a foraging decisionto improve fecundity and/or males sacrifice their bodies toincrease fertilization success. In other species, females exertsequential choice of partner by selectively terminating copulationthrough cannibalism while males fail to obtain a paternityadvantage. Here, we investigate the adaptive value of cannibalismin the orb-web spider Nephila plumipes where 60% of males donot survive copulation. Virgin females in poor condition aremore frequently cannibalistic and more likely to kill largemales, but the frequency of cannibalism among mated femalesis not influenced by these factors. Instead, males that matewith mated females increase their fertilization success bybeing cannibalized. Cannibalized males generally mate for longer,but longer copulations correspond with increased paternity onlyin mated females. The amount of sperm from particular malesthat a female stored was not influenced by any of the measuredvariables. The number of sperm stored was not related to paternity,nor was there any detectable reduction in sperm number afterfemales had reproduced. Our data suggest that the conflict between the sexes differs between virgin and mated females.Females should always cannibalize a male, but males only gainfrom cannibalism when mating with mated females, not when matingwith virgin females. Interestingly, the frequencies of cannibalismare not different in matings with virgin or mated females.     

The effect of female mating history on sperm precedence in the two-spot ladybird, Adalia bipunctata (Coleoptera, Coccinellidae)

Effects of two different mating regimes on sperm precedencein the two-spot ladybird, Adalia bipunctata, were studied usingthe polymorphic gene for melanism as a marker for paternity.Virgin nonmelanic females (homozygous recessive) were matedto nonmelanic male(s) and then, after laying fertilized eggs,were mated to a melanic male of known genotype. The resultsafter the two successive single matings showed a highly variabledegree of paternity of the second male. Initial multiple matingwith nonmelanic males did not alter the pattern of paternityafter the subsequent single mating with a melanic male, butit had two other effects: (1) the female showed an increasein rejection behavior, and (2) a longer copulation was requiredfor high success of the melanic male. Additional observationsin which families were reared from beetles collected in copulain the field demonstrated that sperm competition also occursunder natural conditions. The outcome of the competition wasvariable with frequent sperm mixing.     

A life-history perspective on strategic mating effort in male scorpionflies

In species with high male mating effort, there is a trade-offbetween mating effort spent in a current mating and resourcesleft for future matings. Consequently, to maximize their reproductivesuccess, males have to invest strategically, saving resourcesin matings with low reproductive gain for future, more valuablematings. However, as males age, the expected future reproductivesuccess constantly declines. Thus, the importance of resource rationing may drastically change during a lifetime. Males ofthe scorpionfly Panorpa cognata offer females a costly nuptialgift before copulation, which functions as male mating effort.Resources for the production of these salivary masses are severelylimited for males in poor condition. We found that males investedmore in copulations with high-quality females than in copulationswith low-quality females. However, males ceased to discriminateas they became older. Old males, with a relative small numberof expected future matings, did not invest differentially incopulations with high- versus low-quality females. In copulationswith low-quality females, males invested more in late thanin initial matings, whereas in matings with high-quality females,time of mating had no influence on mating effort. These resultsimply that males adaptively change their resource allocationstrategy during the course of the season. Initial matings seemto be characterized by male prudence; in later matings, malesseem to adopt a more opportunistic mating strategy.     

Why do females copulate repeatedly with one male?

For most animals, a small number of copulations is sufficient to fertilize all the eggs that a female will lay at any one time. However, in some species a very high frequency of mating occurs, indicating that individuals copulate many more times than are necessary for fertilization. If copulation behaviour carries costs, then the question arises as to how individuals of both sexes benefit from repeated matings with a single partner. For a male, a high frequency of copulation appears to be advantageous in securing or assuring paternity when his sperm is in competition with those of another male. Since copulation is likely to be as costly for females as it is for males, it is necessary to seek adaptive explanations from the female perspective. Attention is now being focused on why females should copulate repeatedly with a single male.     

Sperm competition experiments between lines of crickets producing different sperm lengths.

Sperm numbers can be important determinants of fertilization success in sperm competition. However, the importance of variation in sperm size is less well understood. Sperm size varies significantly both between and within species and comparative studies have suggested that some of this variance can be explained by sperm competition. In this study we examine whether variation in sperm length has consequences for fertilization precedence using controlled sperm competition experiments in the field cricket Gryllus bimaculatus. This species is an ideal model for such investigations because the mechanism of sperm competition generates complete mixing of different males' spermatozoa in the female (thereby allowing individual sperm to express their own competitive abilities). We successfully bred lines of crickets, the males of which produced short, medium and long sperm types with narrow and non-overlapping distributions. Males of different lines were then sequentially mated with control females in order to create two-male sperm competitions. The paternity outcomes of these competitions were measured after matings using an irradiated male technique (with a full reciprocal design that controls for natural fertility and any irradiation effects on gamete competitiveness) over a 12 day oviposition period. However, having successfully bred diverging sperm length lines and competing males that differed in sperm length, we found no evidence that a male's sperm size explained any of the variation in their relative fertilization success. Males from lines producing longer sperm showed no fertilization advantage over males producing shorter sperm across 97 double matings. There was also no advantage for males producing a sperm length close to the population mean over those competitors whose sperm length had been selectively diverged across 63 matings.