Variation in copulation duration in Mnais pruinosa pruinosa Selys (Odonata: Calopterygidae)

Summary Males of the damselfly Mnais pruinosa pruinosa were observed to use three different tactics to secure mates. The mean duration of copulation differed between the three observed tatics and resulted in varying degrees of sperm removal and insemination. It is shown that the last male to mate had almost 100% sperm precedence immediately after copulation regardless of the duration of copulation and therefore the quantity of sperm removed. In situations where less than 100% of rivals' sperm was removed the sperm from different males mixed within the female sperm storage organs over a period of about 6 days: sperm mixing produced variation in last male sperm precedence. The significance of sperm mixing in M. p. pruinosa is discussed in the context of the observed matesecuring tactics and the frequent female habit (37% of observations) of ovipositing without remating during an oviposition bout.     

Variation in copulation duration in Mnais pruinosa pruinosa Selys (Odonata: Calopterygidae)

Summary The Japanese calopterygid damselfly Mnais pruinosa pruinosa shows three distinct copulation durations (Siva-Jothy and Tsubaki 1989). A variety of factors which might influence copulation duration were investigated. Results indicate that the temperature in the vicinity of copulating pairs, the rate at which males encountered receptive females, territory quality, the rate of agonistic interactions between males, female gravidity and female willingness to oviposit have no effect on copulation duration. The most significant factor was the location of the site at which males captured their mates. We suggest that under natural conditions the location of the capture site provides males with reliable, indirect information about a female's intention to oviposit: it is important for males of this species to acquire such information since sperm precedence, and therefore reproductive success, is in part dependant on the interval experienced by females between copulation and subsequent oviposition. The results are discussed and it is suggested that the three observed mate-securing tactics of M.p. pruinosa are facultative and information-dependant.     

Copulation duration and sperm competition in white-faced dragonflies (Leucorrhinia intacta; Odonata: Libellulidae)

Summary In many odonates, females mate with more than one male while laying a single clutch of eggs. We studied paternity of eggs laid by remated females of Leucorrhinia intacta, a small libellulid dragonfly, at a pond near Syracuse, NY, USA. The probability of a female remating is a function of male density on the pond. The length of copulations differs considerably among males active on the study pond at the same time. Much of this variation was correlated with differences in mating tactics of the males; copulations by males that stayed on their territories during copulation were shorter than those by other males (Fig. 2). Eggs collected from females mated to irradiated, sterile males and to free-living, fertile males indicated that the average paternity expectation was higher for long than for short copulations, and that the variance in paternity expectation was lower for long than for short copulations. Some possible causes of the high variation in paternity at low copulation durations and possible reasons for differences in copulation duration between male mating tactics are discussed.     

Direct and indirect estimates of sperm precedence and displacement in the dragonfly Sympetrum danae (Odonata: Libellulidae)

Summary The non-territorial dragonfly Sympetrum danae shows a high degree of post-copulatory mate-guarding, which suggests precedence of the last male's sperm. Irradiated male techniques revealed that the last male that mates with a female fertilizes an average of 95% (100% in 28% of the cases) of the clutch laid immediately after copulation, irrespective of any previous matings. Sperm volume estimates in both sexes and sperm opacity changes in females at 7 stages of copulation and oviposition indicated that males remove 41–87% of previously deposited sperm from the female's storage organs during the first 5 min of the copulation. Ejaculation takes place during the remaining 10–15 min. We maintain that indirect estimates of precedence in libellulids, based on sperm volume changes, always understimate reality because of the supplementing effect of a first-in, last out mechanism. Because males are skilled at achieving sperm precedence, they are forced to be good guards as well, since a risk of take-overs exists. Females are believed to benefit from contact guarding because it results in a lowered risk of male harassment and predation as well as a lower energy expenditure during oviposition.     

Dominions and site-fixed aggressive behavior in breeding male Leucorrhinia intacta (Odonata: Libellulidae)

Summary We report aggressive spacing behavior in male dragonflies, Leucorrhinia intacta, that is characterized by variations in the probability of chasing conspecific male intruders within a defined area around a male's perch. The chase probability depends on the total intruder pressure and the behavior and distance of the intruder from the perched male (Fig. 2). This nonexclusive, site-fixed area has been called a dominion.We also examined the distribution of intruders among the various behavior-distance categories. Chase rates (per 15 min) were correlated mostly with number of intruders that hovered (rather than flew) close to the territorial male. Finally, we examined the impact of the changing chase probabilities on the variation in aggressive interactions as a function of intruder pressure. We conclude that, to some extent, territorial males stabilized defense costs across a variety of intruder pressures by maintaining dominions.     

Copulation duration and sperm precedence in the stalk-eyed fly Cyrtodiopsis whitei (Diptera : Diopsidae)

Summary By means of field observations and laboratory experiments on the Malaysian stalk-eyed fly Cyrtodiopsis whitei we examined the consequences of variation in copulation duration for sperm competition. In this sexually dimorphic species over 90% of all copulations occur in nocturnal aggregations with from one to four males and up to 24 females. Copulation duration observed in both the field and the laboratory exhibited a bimodal distribution with peaks at 10 and 50 s. In the field short copulations less than 30 s long occurred frequently when more than one male was present in an aggregation but most were not the direct result of male interference. Sperm counts from female spermathecae after artificial interruptions indicated sperm are not transferred during the first 40 s of a copulation. When solitary males mated up to five times in succession to virgin females, short copulations did not occur, nor was the number of sperm transferred reduced. However, short copulations did occur when we mated isolated females within 6 min of a previous copulation. By mating irradiated and non-irradiated males in reciprocal pairs we discovered that C. whitei exhibits both first-male sperm precedence and sperm mixing. More than half of the females mated first to sterile and then to fertile males failed to produce offspring. Such variation in copulation duration and sperm precedence is consistent with male placement and detection of a spermatophore that acts as a temporary mating plug. Our data suggest that those male C. whitei which successfully defend large aggregations of females reduce sperm waste and competition by preferentially transferring sperm to females that have not mated recently. Correspondence to: G.S. Wilkinson     

Variation in sperm morphometry and sperm competition among barn swallow (Hirundo rustica) populations

Spermatozoa vary greatly in size and shape among species across the animal kingdom. Postcopulatory sexual selection is thought to be the major evolutionary force driving this diversity. In contrast, less is known about how sperm size varies among populations of the same species. Here, we investigate geographic variation in sperm size in barn swallows Hirundo rustica, a socially monogamous passerine with a wide Holarctic breeding distribution. We included samples from seven populations and three subspecies: five populations of ssp. rustica in Europe (Czech, Italy, Norway, Spain, and Ukraine), one population of ssp. transitiva in Israel, and one population of ssp. erythrogaster in Canada. All sperm traits (head length, midpiece length, tail length, and total length) varied significantly among populations. The variation among the European rustica populations was much lower than the differences among subspecies, indicating that sperm traits reflect phylogenetic distance. We also performed a test of the relationship between the coefficient of between-male variation in total sperm length and extrapair paternity levels across different populations within a species. Recent studies have found a strong negative relationship between sperm size variation and extrapair paternity among species. Here, we show a similar negative relationship among six barn swallow populations, which suggests that the variance in male sperm length in a population is shaped by the strength of stabilizing postcopulatory sexual selection.     

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

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

Females influence sperm storage and use in the yellow dung fly Scathophaga stercoraria (L.)

Summary The influence of the female on the process of sperm storage and use was examined. Copula duration, the condition of the female and whether or not a copula terminated naturally influenced the number of spermathecae (of three) in which once-mated females stored sperm. Females stored more sperm the larger their mate and the sperm from larger males were stored more unevenly amongst the spermathecae than were those from smaller males. Double-mated females had sperm in fewer spermathecae the larger the second of their mates and these spermathecae tended to be the ones which lay together within the female. The P2 values over three successive clutches were constant and sperm precedence was complete when the larger male was second to mate but began low and increased over subsequent clutches when the smaller male mated second. These results suggest females prefer, and are able, to use the sperm of larger males to fertilise their eggs. It is proposed that multiple spermathecae in Diptera have evolved to give females better control over offspring paternity.     

The effects of operational sex ratio and food deprivation on copulation duration in the water strider (Gerris remigis Say)

Summary A North American water strider, Gerris remigis (Hemiptera) copulates for prolonged periods of time, apparently beyond the time necessary for insemination (Rubenstein 1984; Wilcox 1984; Clark 1987), I tested predictions from two different hypotheses of the adaptive significance of this behavior. Manipulations of the operational sex ratio in artificial streams revealed that water striders copulate significantly longer when the sex ratio is male-biased. This result is consistent with the hypothesis that prolonged copulation functions as a type of contact mate guarding, which reduces sperm competition by preventing the female from remating prior to oviposition. The finding is also consistent with the hypothesis that copulation is prolonged to enhance female foraging efficiency. In a second experiment, sex ratio and total population density were held constant, and the period of food deprivation of females was manipulated. Contrary to the predictions of the female foraging hypothesis, starved females did not copulate longer than fed females. Of the two hypotheses considered, only the copulatory guarding hypothesis explains both results. This does not mean, however, that there is no selective benefit from the enhanced foraging efficiency resulting from prolonged copulation. Nor does it exclude the possibility that this benefit has been necessary for the evolution of prolonged copulation in water striders.     

Operational sex ratio versus gender density as determinants of copulation duration in the walnut fly,Rhagoletis juglandis (Diptera: Tephritidae)

In laboratory and field studies of the walnut fly, Rhagoletis juglandis Cresson (Diptera: Tephritidae), we assessed the effect of operational sex ratio on copulation duration and partitioned the sex ratio effect into component effects due to male density and female density. In our first laboratory experiment, results were clearly consistent with theoretical expectation: increases in male density were associated with significant increases in copulation duration while increases in female density were associated with significant decreases in copulation duration. These component effects yielded a striking composite effect of operational sex ratio (OSR) on copulation duration in which male-biased ratios were associated with low frequencies of short copulations and female-biased ratios were associated with high frequencies of short copulations. Consistent with a priori expectations concerning costs of territorial behavior, the effect of male density on copulation duration was stronger than that of female density. There was no significant interaction between the effects of gender density on copulation duration: each gender density contributed additively to the composite OSR effect on copulation duration. In contrast to the effect of OSR, overall density had little effect. Field data corroborated these findings fully and showed additionally that OSR in the vicinity of fruit tended in nature to be male-biased. In a second laboratory experiment, we measured copulation duration for individuals exposed alternately to male-biased and female-biased ratios. Individual flies consistently copulated for longer in male-biased environments than in female-biased ones. We propose that this plasticity permits individuals to track changes in local sex ratio over space and time and respond appropriately. Received: 15 November 1995/Accepted after revision: 27 April 1996     

Patterns of sperm use in the scorpionfly Panorpa germanica L. (Mecoptera: Panorpidae)

Sperm competition can be a powerful selective force in the evolution of reproductive strategies and mating systems. In studies on sperm competition, patterns of sperm use are typically reported as the mean species value of P ₂, determined as the proportion of offspring sired by the second male to copulate with a doubly mated female. However, the within-species variance in P ₂ has mostly been ignored, although taking this variance into account may be crucial for understanding the underlying mechanisms of sperm competition. Paternity analysis among the offspring of doubly mated females of Panorpa germanica (Mecoptera, Panorpidae) revealed a relationship between relative copulation durations of both males and the proportion of offspring each male will sire. This correlation between proportional copulation durations and paternity suggests mixing of sperm from different males inside the female’s spermatheca. Yet, sperm mixing appears to be incomplete, as paternity was overall slightly shifted towards the second male on average fathering a higher proportion of the offspring than its relative copulation duration would predict in case of complete sperm mixing. For individual males, however, the outcome of sperm competition is rather unpredictable as the intraspecific variance in P ₂ was found to be very high, irrespective of copulation durations. Possible causes of the observed variance in P ₂ and the partial last male sperm precedence are discussed.     

Cloacal erection promotes vent apposition during forced copulation in the New Zealand stitchbird (hihi): implications for copulation efficiency in other species

Cloacal protuberances (CP) in male birds result from spermatic engorgement of storage tubules around the cloaca during the breeding season. We examined seasonal changes in the volume and orientation of the CP in the New Zealand stitchbird Notiomystis cincta. The male stitchbird has one of the largest recorded CPs for any species (max = 1,570 mm³), with CP volume increasing by almost 400% between the non-breeding and breeding seasons. While sperm competition has been positively correlated with the magnitude of CP storage in other species, no evidence previously existed for the CP improving copulation efficiency. By measuring the relative orientation of the CP throughout the year, we show that not only does the CP increase in size as males become sexually active, it also changes its orientation by approximately 60°. This results in it shifting from facing posteriorly to becoming almost perpendicular to the abdomen. This cloacal erection improves the apposition of the male and female cloacal openings during face-to-face forced copulation in this species. This provides the first reported evidence supporting the copulation efficiency hypothesis of the avian CP. While the magnitude of seasonal changes in female cloacal volume was similar to males, female cloacal orientation remained virtually unchanged across seasons. This difference between the sexes is likely to reflect differing selection pressures for optimizing sperm transfer. In females, a posterior-facing cloaca is ideal for both waste evacuation and sperm reception, whereas, for the male, a posterior-facing cloaca is well suited for waste evacuation, but possibly hinders sperm delivery. Changes in male cloacal orientation from the non-breeding to the breeding season are a likely reflection of conflict in this dual function. Evidence of changes in CP orientation in another passerine species suggests this phenomenon is widespread and also important for understanding related fields such as sperm competition, forced copulation and constraints on the evolution of the avian intromittent organ.     

Occurrence of extra-pair copulation in the tree swallow (Tachycineta bicolor)

Summary A new method to mark sperm transfer events between birds, using microspheres inserted into males' cloacae, was employed to assess the frequency of extra-pair copulation (EPC) in a population of tree swallows (Tachycineta bicolor) in Ontario, Canada, during the summer of 1988. We inserted 25 males with microspheres; spheres from 8 (32%) of these males were found in extra-pair females, from which we infer that males pursue a mixed reproductive strategy of monogamy coupled with seeking EPCs. The cloacae of 10 of 41 (24.4%) females were found to contain microspheres from non-mates. EPCs occur more frequently between neighboring birds than between non-neighbors. Only two within-pair copulations were detected with this method, suggesting that it underestimates the occurrence of all copulations, extra-pair or within-pair. Copulation watches revealed that within-pair copulations occur very frequently. We propose that frequent pair copulations are used by males to ensure their paternity in their mate's offspring. Offprint requests to: R.J. Robertson     

Sperm transfer,displacement and precedence in Ischnura graellsii (Odonata : Coenagrionidae)

Summary Copulation in Ischnura graellsii may be divided into three stages, according to the movements and position of the male's abdomen. We measured sperm volumes in males and females interrupted at different phases of copulation in laboratory-reared and field specimens. The results showed that males remove sperm from the female during stage I, and do not transfer sperm until stage Il of the copulation. In the field females interrupted during stage I of copulation had less sperm than postcopula females, and the volume of sperm in laboratory females mated once or twice was similar. These results suggest that males can remove most of the sperm during stage I of copulation. Preparations of in-copula specimens showed the horns of the penis (used to remove sperm) inside the bursa copulatoox and the spermatheca. Therefore males can remove sperm from both organs, in contrast to the other Ischnura species so far studied, where males can empty only the bursa. The length of these horns is positively correlated with male body length, and there are significant differences in length between the left and right horns of individual males. This suggests great variability in the male's ability to remove sperm. On the other hand, ejaculate volume is positively related to male and female size, and negatively to male age. Males are likely to be able to detect the presence of sperm in females: if the effect of population density and time of start of copulation are taken into account, copulations are longer with mated than with virgin females. Using genetic markers, sperm precedence was studied by rearing the female offspring of 6 females mated with two males of different genotype. In 5 out of 6 crosses, the second male fertilized all the eggs laid by the female in her first clutch. On average, the following clutches were progressively more fertilized by the first male, but there were striking differences between crosses. These differences are probably due to the variability in the amount of sperm transferred and/or removed. Offprint requests to: A. Cordero     

Pre-mating sperm removal in the bushcricket Metaplastes ornatus Ramme 1931 (Orthoptera, Tettigonoidea, Phaneropteridae)

Summary Mating in the bushcricket Metaplastes ornatus Ramme 1931 entails a number of peculiar genital couplings that precede the transfer of the large spermatophore. During these phase-I couplings, the male introduces his specially structured subgenital plate into the female's genital chamber, performs back-and-forth movements, and turns her genital chamber inside out when he withdraws, whereupon the female carefully cleans her everted genital chamber with her mouthparts. During the last coupling (phase II) the male's subgenital plate is not introduced but the large spermatophore, which averages 22% of a male's body weight, is transferred. Counts of sperm in the spermathecae of females suggested that the phase-I couplings, which occur prior to spermatophore transfer, function to remove, or at least to reduce, the sperm of a female's previous mates. The form of the keel of the male's subgenital plate, its position within the female's genital tract during phase-I couplings, and the back-and-forth movements suggest that the male may stimulate release of sperm from the female's spermatheca by a mechanism similar to fertilization as eggs pass through the genital chamber during oviposition.     

Copula duration and testes size in the yellow dung fly,Scathophaga stercoraria (L.) : the effects of diet,body size,and mating history

Summary Seasonal variation in mean hind tibia length and mean testes length is investigated in the yellow dung fly, Scathophaga stercoraria (L.). There is a cycle in mean hind tibia length and mean testes length over a season. The body size curve peaks later than the testes length curve, showing that there is no fixed relationship between the two variables. The causes of variation in testes size and its influence on copula duration are experimentally examined. Increasing the number of Drosophila eaten per day leads to increased mature testes length. Males with larger testes copulate for longer than males with smaller ones, and smaller males copulate for longer than do larger males. While testes shrivel with successive copulas, copula duration remains constant. The more females a male is prepared to copulate with in a day (up to five), the longer he copulates with each. The shrinkage of the testes of males collected throughout a day suggests that males copulate with an average of 4 females per day. The costs of sperm production are thus shown to have a significant influence on the copula duration.Offprint requests to: P.I. Ward at the second address     

Lifetime mating success in a natural population of the damselfly,Enallagma hageni (Walsh) (Odonata: Coenagrionidae)

Summary Variance in lifetime mating success was measured for individuals of a population of Enallagma hageni, a non-territorial damselfly in northern Michigan. E. hageni is an explosive breeder with scramble competition for mates. Highly skewed operational sex ratios resulted in intense male-male competition which took the form of interference with tandem pairs. 41% of the males failed to mate in their lifetime as opposed to only 3.6% mating failure in females. The effect on mating success of size, age, longevity, and time spent at the breeding site were investigated. Intermediate sized males obtained the most matings, and male lifetime mating success was highly correlated with longevity.     

Choice and utilization of oviposition sites by female Calopteryx maculata (Odonata: Calopterygidae)

Summary Females of the damselfly Calopteryx maculata (de Beauvois) initially choose the larger of a pair of adjacent oviposition sites, about 70% of the time (Table 1), or whichever of two equal sized sites had other ovipositing females on it (about 88% of the time-Table 2). These criteria for initial choice between a pair of sites also interact. Incoming females generally (57 to 74% of the time-Table 3) joined others on the small site rather than ovipositing alone at the adjacent, bigger site. When pairs of large and small sites were replicated across eight locations, there were nonsignificant trends towards greater utilization (eggs laid) of the larger of a pair of oviposition sites within locations (Table 4). The lack of agreement between initial choice and utilization shows that other factors besides size are important in the choice and use of oviposition sites. These include disturbance by males, the presence of other females and choice criteria that can only be assessed during oviposition. When all sites at the eight locations were equal in size, there was considerable day to day and location to location variation in eggs laid (Fig. 1). Viewed over periods of several days, some sites are obviously less attractive than others in terms of cumulative numbers of eggs laid at them. When the amount of vegetation was varied among locations, those with the bigger oviposition sites were used more often, somtimes significantly so, but there were also significant reversals (small sites used more often) (Table 5, Fig. 1). Thus, there is no simple effect of size on the utilization of oviposition sites by Calopteryx maculata females, despite a clear tendency for females to make initial choices based on this criterion. The considerable among and within location variation in number of eggs laid may reflect additional choice criteria or the interaction of size, the presence of other females, disturbance, and location.