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     

Sperm precedence, mating interval, and a novel mechanism of paternity bias in a beetle (Tenebrio molitor L.)

When females mate with more than one male, the ensuing sperm competition leads to the evolution of male mechanisms that skew paternity. Males of the yellow mealworm beetle (Tenebrio molitor) transfer a spermatophore to females during copulation, but sperm release and storage occur later. We investigated how the interval between two matings with different males affects sperm precedence by varying the interval between the copulations so that the second mating was either: (1) before sperm release from the first spermatophore (<5 min); (2) after sperm release but before spermatophore ejection (15–20 min); (3) after spermatophore ejection but before sperm storage (4 h), or (4) after complete sperm storage (24 h). We collected offspring over a period of 2 weeks and determined paternity by protein electrophoresis. There was second-male sperm precedence in all treatments, but when the interval was <5 min, the second male usually (86% of cases) had complete sperm precedence (i.e., P ₂=1). Investigations into the mechanism of second-male sperm precedence during <5-min mating intervals indicate that sperm release from the first spermatophore is inhibited, a phenomenon which has not been previously documented. Received: 31 January 2000 / Revised: 9 June 2000 / Accepted: 26 August 2000     

Factors influencing paternity in multiply mated female red-sided garter snakes and the persistent use of sperm stored over winter

In some species, sperm is stored within the female reproductive tract for months to years, and yet remains viable to fertilize eggs and produce offspring. Female red-sided garter snakes store sperm for over 7 months of winter dormancy. In previous work, we demonstrated that these stored sperm account for an average of 25 % paternity of a litter when the female mates with a male at spring emergence. Here, we tested whether last-male sperm precedence was prevalent when a female mates with two males during the spring. On average, paternity was shared equally among the first (P₁ proportion of paternity of the first male to mate) and second males (P₂) to mate in the spring, and stored sperm (P_ss), but the variance in paternity was high. Thus, last male sperm precedence may diminish when a female has more than two mates. Male size did not affect paternity, but, as the interval between matings increased, P₁ increased at the expense of P_ss. Interestingly, as the second spring male’s copulation duration increased, P₁ also increased at the expense of P₂. This result suggests that female influence over sperm and/or copulatory plug transfer during matings may also affect which male fathers her offspring in response to coercive matings as we assisted females to mate for their second mating. Finally, all females were spring “virgins”; consequently, sperm stored from autumn matings (and/or previous spring matings) remain competitive even when faced with two rivals in sperm competition and is likely the driver of the evolution of sperm longevity.     

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

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

Male remating and female fitness in the wolf spider Pardosa astrigera: the role of male mating history

Although the effects of male mating history on female reproductive output and longevity have been studied in insects, few such studies have been carried out in spiders. In a mating system in which females are monandrous while males are polygynous, females may incur the risk by mating with successful males that have experienced consecutive matings and suffer from the possible depletion of sperm and/or associated ejaculates. Here, we examine the effects of male mating history on male courtship and copulation duration, female reproductive fitness, and female adult longevity of the wolf spider, Pardosa astrigera. Results indicated that male mating frequency had little effect on their subsequent copulation success, and of 35 males tested, about half of the males were able to copulate with five virgin females successively at an interval of 24 h. Male mating history had little effect on their courtship duration. However, male mating history significantly affected male copulation duration, female adult longevity, and reproductive output. Males that mated more frequently copulated longer and more likely failed to cause their mates to produce a clutch, although there was no significant difference in the number of eggs laid and the number of eggs hatched regardless of the first clutch or the second one. Multiple mating of male P. astrigera resulted in significant reduction in female adult longevity. Our results indicate that monandrous females mating with multiple-mated males may incur substantial fitness costs.     

Prolonged copulation: A male ‘postcopulatory’ strategy in a promiscuous species,Lygaeus equestris (Heteroptera: Lygaeidae)

Summary Copulation in Lygaeus equestris L. (Heteroptera, Lygaeidae) is known to last 0.5–24 h. Variations in copula duration of field-collected insects were studied in the laboratory, and different hypotheses concerning the significance of prolonged copulations were tested.Through reciprocal matings with normal and sterile (irradiated) males, sperm displacement was estimated at about 90%. A male could thus increase his fitness by preventing subsequent matings of an inseminated female.Copulations with virgin insects, observed over 15 h, were classified in two categories: short (0.5–8.0 h) and long (> 15 h) duration (Fig. 1). No difference in the number of fertilized eggs was found between long and short copulations, and the insemination rate was highest during the first hour of a couplation (Fig. 2). Long-lasting couplations did not give rise to increased sperm displacement (Table 2). These results indicate that there is no difference in the amount of sperm transferred during short and long copulations and that no insemination takes place during the latter part of a prolonged copulation.Longer lasting copulations occurred when the sex ratio was male-biased than when it was female-biased (Fig. 1). The frequency of prolonged copulations was higher when the female was gravid than when she contained no eggs (virgin) (Figs. 3 and 4). Support is thus given to the hypothesis that prolonged copulation is a male postinsemination strategy to prevent subsequent matings of a female.Females subjected to male competition over a longer period, laid fewer eggs and died earlier than females that were mated but subsequently isolated from males (Fig. 5). Egg batches from females living with males were larger than batches from mated, isolated females (Table 3). This is probably due to a combination of many matings with short intermissions and prolonged copulations, both of which postpone oviposition.Comparisons between copulations of males with either gravid or virgin females during these experiments, led to the conclusion that short copulations with virgin females result from a male decision to terminate copulation after insemination is completed, whereas copula duration with gravid females is more likely to depend on a combination of male and female behavior.     

Determinants of paternity success in the spider Pholcus phalangioides (Pholcidae: Araneae): the role of male and female mating behaviour

In double mating experiments, we examined whether and to what extent various male and female behavioural traits influence the course of mating and fertilization success in the cellar spider. In males, we focussed on pre-copulatory behaviour and on the rhythmic twisting movements that the male performs with his pedipalps during copulation. In females, we investigated remating decisions and the effect of female termination of copulation. Second males fertilized a high proportion of the eggs (P ₂: median 89%) despite much shorter second matings, with high variation in relative paternity success. The number of pedipalp movements (PPMs) of either male was a better predictor of paternity than copulation duration. Our results suggest that in second matings, PPMs help to remove sperm from previous males, whereas in first matings a high number of PPMs enhances fertilization success, either due to numerical sperm competition or cryptic female choice. Furthermore, we found a negative male age effect on paternity in second matings, implying that age-related deterioration of spermatozoa may promote variation in fertilization success. Female receptivity decreased significantly in second matings; only 70% of the females remated. Females that accepted a second copulation were found to terminate these much earlier and with higher probability than first matings. This suggests that the intensity of conflict between the sexes is higher in second matings. Increased intensity of sexual conflict may be responsible for stronger selection on male traits, as pre-copulatory behaviour and age only affected male copulatory performance and paternity in second matings. Electronic Publication     

Multiple paternity and individual variation in sperm precedence in the simultaneously hermaphroditic land snail Arianta arbustorum

Intraspecific variation in the proportion of offspring sired by the second mate with a female (P₂) is an aspect of sperm competition that has received little attention. I examined the effects of delay between copulations (range 9–380 days) and size of sperm donor on sperm precedence in double-mated individuals of the simultaneously hermaphroditic land snail Arianta arbustorum. Using shell colour as a genetic marker, paternity was analysed in 132 broods produced by 35 snails that had mated with two partners of different genotype. Sperm precedence (P₂) was influenced by the time between the two matings when the mating delay exceeded 70 days (one reproductive season). P2 averaged 0.34 in the first brood of snails that mated twice within 70 days indicating first mate sperm precedence. In contrast, P₂ averaged 0.76 in broods of snails that remated in the following season, indicating a decreased viability of sperm from the first mate. The size of sperm-donating individuals had no effect on the fertilization success of their sperm in the first brood produced after the second copulation. Analysis of long-term sperm utilization in 23 snails that laid three to nine egg batches over 2 years revealed striking differences among individuals. Five snails (21.7%) exhibited first-mate sperm precedence throughout, eight snails (34.8%) showed second-mate sperm precedence throughout, whereas ten snails (43.5%) exhibited sperm mixing in successive batches. It is suggested that the individual variation in sperm precedence in A. arbustorum may partly be due to differences in the amount of sperm transferred. Paternity analysis in 34 batches laid by 19 wild-caught individuals of A. arbustorum indicated that at least 12 snails (63.2%) used sperm from two or more mates for the fertilization of their eggs. This suggests a high incidence of multiple paternity in broods of A. arbustorum under field conditions.     

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.     

Male genital length and mating status differentially affect mating behaviour in an earwig

Phenotypic variation in male genitalia may affect copulation behaviour, which can have important fitness consequences for males. Male genitalia commonly possess traits that increase male control over copulation, but in species where females control mating, a poor functional understanding often prevents insight into the processes responsible for such effects. Here, I investigate the effect of male genital length on copulation behaviour in the earwig Euborellia brunneri, where both sexes exhibit extremely elongated genitalia that correspond in shape. This model system is particularly suitable because pairs mate repeatedly and females can limit both the number and duration of copulations. I used both virgin and mated males and females in a double-mating design because longer male genitalia confer benefits in sperm competition. Consistent with a greater predicted male mating effort in mated females, the duration of individual copulations increased, but this traded off against mating frequency as cumulative mating duration remained unchanged. In contrast, male genital length increased both individual and cumulative mating duration, regardless of mating status. This difference suggests that, while males may modify copulation duration in response to mating status, females facultatively adjust mating frequency to prevent mating excessively or express preferences for increased male genital length. Notably, this study demonstrates that male genital phenotypes that are successful in sperm competition also enjoy female-mediated mating benefits.     

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     

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.     

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.     

Prolonged mating in the milkweed leaf beetle Labidomera clivicollis clivicollis (Coleoptera: Chrysomelidae): a test of the “sperm-loading” hypothesis

Summary Female milkweed leaf beetles (Labidomera clivicollis clivicollis) frequently mate with more than one male, and pairs form mating associations which last for up to 42 h in the field. I tested the hypothesis that males remaining with females for long periods of time benefit by numerically overwhelming the sperm of their competitors. Male L.c.clivicollis copulated intermittently with females throughout an 11 hour period in the laboratory. When virgin females were allowed a single copulation, 94.3% of the sperm they received were located in the spermatheca immediately afterward. Males were not sperm-depleted, for they had large numbers of sperm available after one copulation (mean=230,000±43,200); the maximal number of sperm a male transferred to a female in 24 h was 30,500. There was a positive linear relationship between the number of sperm transferred and time up to 24 h after mounting (r ²=0.178, P<0.003). These data suggest that males transfer increasing numbers of sperm throughout a 24-h-period. Mating duration was the most important determinant of paternity when females were placed with one male for 24 h and another male for 6 hours. Females whose first matings were longer showed first male sperm predominance (as determined by starch-gel electrophoresis), while females whose second matings were longer showed last male sperm predominance. In view of these data, it is puzzling that males do not inseminate with large numbers of sperm immediately after mounting the female. It is possible that female refractory behaviors make insemination difficult and favor prolonged mating by male milkweed leaf beetles.     

Male genital traits and mating interval affect male fertilization success in the water strider Gerris lacustris

Parker's seminal work brought attention to the possibility of postmating sexual selection by non-random fertilization success. Mechanisms for these processes are still only partly understood and there is clearly a need for more studies of intraspecific variation in sperm precedence. Here, we report results from an experimental study of the variation in fertilization success between males of the water strider Gerris lacustris. Genital morphology, male body size, and copulation duration were examined as possible correlates of paternity. The significance of guarding duration was also analysed. Only male genital morphology was correlated to fertilization success. This is one of the first studies showing a relationship between male genital traits and fertilization success, supporting the view that sexual selection may be responsible for the rapid and divergent evolution of genital structures in animals with internal fertilization. The fertilization success of last males varied considerably after double matings with a short mating interval (10 min). Last-male priority ranged from 0 to 100% and usually one of the males involved fertilized almost all the eggs. After double matings with a short mating interval, the proportion of eggs fertilized by the last male averaged 0.68 and was greater than 0.5. In contrast, the average fertilization success was biased towards the first male when the matings were more spread out over time (24 h). These results do not support earlier suggestions of a widespread last-male sperm priority in water striders. Received: 28 July 1998 / Received in revised form: 15 March 1999 / Accepted: 28 March 1999     

Mating behavior and sperm competition in the fly,Dryomyza anilis

Summary Mating behavior in D. andis was studied both in nature and in the laboratory. Each mating in nature consisted of several repeated copulation and oviposition bouts during which the male stayed mounted. One copulation bout included an intromission in the beginning followed by several tapping sequences. During one tapping sequence the male touched the external genitalia of the female with his claspers several times. The experimental matings with irradiated sterile males contained one copulation bout after which the female laid her eggs. In these matings the percentage fertilization for the last male to mate with the female increased with increasing number of tapping sequences. The percentage fertilization was affected positively also by the time between the end of the copulation bout and the start of oviposition, but the time spent in the copulation bout was not important. Furthermore, there was a negative correlation between the length of intromission and the percentage fertilization. After the copulation bout, the percentage fertilization was higher among the first eggs laid. This difference between the first and later eggs laid increased with the increasing number of tapping sequences, suggesting that copulating and ovipositing in several bouts further increase the male percentage fertilization. In matings recorded in nature, both the number of tapping sequences and the number of copulation and oviposition bouts varied greatly. Of the variables recorded during these matings, individual size and the number of eggs the female contained in the beginning of a mating affected the number of copulation bouts and the number of tapping sequences. Males also mated differently with females containing immature or mature eggs. The male behavior resulting in sperm precedence and the variability of matings in nature in relation to male sperm competition is discussed.     

Paternity analysis of two male mating tactics in the fiddler crab, Uca mjoebergi

The fiddler crab Uca mjoebergi mates both underground in male-defended burrows and on the surface near female-defended burrows. The reproductive tract of Uca species facilitates last-male precedence, suggesting that males that do not guard-mated females are likely to gain very little paternity if the female re-mates with another male. Here, we test the reproductive success of burrow and surface matings using paternity analysis. We found that 100?% of the females that mated in burrows extruded a clutch of eggs. Furthermore, we show conclusively, for the first time in a fiddler crab species, that last-male sperm precedence results in the majority of the female’s eggs being fertilised by the burrow-mated male. In contrast, surface matings resulted in significantly fewer females extruding eggs (5.6?%). Paternity analysis also revealed that more than half of the clutches from burrow-mated females showed low levels of extra-pair paternity from previous matings. Although multiple matings appear common in U. mjoebergi, burrow-mated males that guard females are guaranteed a successful mating with extremely high rates of assured paternity. Surface matings therefore appear to be an opportunistic tactic that may increase male reproductive success in a highly competitive environment.     

Determinants of paternity in the milkweed leaf beetle

Summary Males and females of the milkweed leaf beetle mate for up to 2.5 d in the field; copulation is interspersed with mounted courtship behavior and periods of passive riding on the female's back. In 1985, females mated with up to 10 different males in Bridgeport, New York, and matings averaged 0.75±0.04 (SE) d in duration. Sperm utilization patterns are complex in the milkweed leaf beetle. In the laboratory, mating duration, mating order and the duration of the gap between matings affected paternity. The second male's sperm predominated when a female's two consecutive matings were of equal duration (but were long: 45 h each) or when they were intermediate in duration (15 h each) with a 5 day gap between the two matings. The mechanism of sperm predominance appears to be one of time-dependent sperm removal and replacement. Neither relative nor absolute size of males affected the extent to which they superceded the sperm of rivals. Electrophoretic analysis of paternity at 6 polymorphic loci showed that offspring of at least eight out of 11 mating pairs pairs collected in the field at the end of the 1984 breeding season were sired by more than one male. At least seven of the 11 families produced some offspring that were sired by the female's most recent mate in the field and in no case was the collected male completely excluded from paternity. In a greenhouse plot, males climbed off females' backs a mean of 1.1±0.3 h before oviposition. Females did not oviposit with males on their backs and did not oviposit sooner when males were removed than when males were allowed to remain mounted, indicating that males don't keep females from ovipositing until they can achieve sperm predominance. The close concordance between male disembarkment and oviposition suggests that males remain with females beyond the time when they have superceded the sperm of their prior mates, possibly to guard them from rival males. Although the prolonged mating association of the milkweed leaf beetle cannot be separated into discrete copulatory and guarding phases, the results of this study suggest that prolonged mating enables males both to remove and replace the sperm of the females' prior mates with their own sperm and to prevent females from remating prior to oviposition.     

Copulatory tactics in relation to sperm competition in Rocky Mountain bighorn sheep

Summary Sperm competition arises in the bighorn mating system because receptive ewes are some-times defended and mated in sequence by a series of increasingly dominant rams and because subordinate (coursing) rams commonly succeed in forcing matings with defended ewes. To identify potential components in a male strategy of sperm competition, the social circumstances and schedule of copulation among free-ranging bighorns were investigated. Three such components emerged: (i) Defending and coursing rams copulated with estrous ewes at extraordinarily high rates, presumably to increase the proportion of their own versus rivals' sperm present at fertilization by simple numerical preponderance at insemination. (ii) Coursing but not defending rams concentrated copulations later in the period of estrus (sensu this study). Evidence from domestic sheep suggests that this may correspond to the period of maximum female fertility. A greater risk and/or reduced benefit associated with forced versus cooperative copulation may force coursing rams to restrict copulation to periods of highest fertility, whereas defending rams may gain even from copulations outside this period. (iii) Defending rams copulated at unusually high rates immediately after bouts of successful coursing. Such retaliatory copulations were associated with reduced amounts of courtship and were more likely to occur if the defending ram had copulated infrequently recently. The number of retaliatory copulations was independent of the number of preceding forced copulations, probably because defending rams rationed ejaculates in anticipation of future coursing. The function of retaliation is not clear, although the literature on domestic sheep suggests the possibility of some form of mechanical displacement of rival sperm. Unlike females of many ungulate species, bighorn ewes were typically receptive to cooperative copulation over a period of days. Although persistent courtship by defending rams may coerce such extended receptivity, it is also possible that ewes, facing unavoidable forced matings by coursing rams, gain genotypic benefits for offspring by providing prolonged copulatory access to relatively dominant defending rams.     

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.