Catch rate and emergence of male and female spanner crabs (Ranina ranina) in Australia

Catches of the spanner crab, Ranina ranina (Linnaeus, 1788), in southern Queensland, Australia in 1982 and 1983 showed a seasonal cycle, with peak catches from August to September. In most catches, males outnumbered females. Catches of both male and female spanner crabs declined in November and December, when a high proportion of females caught were ovigerous. Fish, echinoderms and polychaetes were the main food items. Closed-circuit time-lapse video recording was used to study the emergence behaviour of R. ranina in a 6 m-diameter tank. Spanner crabs in this tank were buried most of the time, emerging on average for only 1.7 h d^-1. They emerged mainly between 16.00 and 24.00 hrs and, less often, between 01.00 and 15.00 hrs. Males remained emerged significantly longer than females. The duration of emergence of the females peaked before the spawning season, becoming shorter during the period when they were ovigerous. Temperature and emergence were negatively correlated. It is concluded that reproductive behaviour has a strong influence on catch composition of spanner crabs.     

Non-aggressive mate guarding by the blue-footed booby: a balance of female and male control

Thirteen pairs of blue-footed boobies (Sula nebouxii) were observed on their colony. Pairs courted frequently and, on average, copulated 24 times during the 30 days before laying, with 38% of those copulations occurring in the last 5 days (presumed fertile period). Males and females increased attendance at the nest site as laying approached. Seven females performed an average seven extra-pair copulations, with 1–2 paired male neighbors, but these were less concentrated in the presumed fertile period than within-pair copulations, and the last two copulations of all 7 females were with their social mates. Rates of female extra-pair copulations were six times lower when their social mate was present, and during the presumed fertile period, no female performed an extra-pair copulation in the presence of her mate. Males did not respond to infidelity of social mates with aggression, prompt copulation, retaliatory copulation, or increase in copulation. Seven of 13 males performed an average of five extra-pair copulations, with 1–3 paired female neighbors, before their own mates began egg-laying. The males' extra-pair copulations represented only 4% of their total copulations during their own mates' presumed fertile periods. Females, the larger sex, apparently control sexual access and copulate with extra males to achieve extra-pair fertilization. Males pursue a mixed strategy: they copulate with extra females, mostly outside their own mate's presumed fertile period, and they copulate increasingly with their social mate as laying approaches, probably assuring some paternity by mate guarding, involving attendance and courtship. Behavior of males and females is also consistent with other hypotheses for extensive joint nest site attendance: pairbonding, copulation access, and territory acquisition. Received: 14 November 1997 / Accepted after revision: 16 May 1998     

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.     

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.     

Inter-sexual conflicts over copulations in the European starling: evidence for the female mate-guarding hypothesis

Recent studies have suggested that conflicts of interests between the sexes may lead to variation in copulation behavior among pairs. We examined differences in the rate and timing of copulation solicitations and copulations among females of different mating status in the facultatively polygynous starling in an attempt to explain why females copulate repeatedly with their mate. All within-pair copulations were female-solicited indicating that females control copulations in the starling. Before egg laying, females solicited copulations at a high rate (usually more than 2 per hour). In contrast to most other species studied so far, females continued to solicit copulations throughout the egg laying period, and also solicited after egg laying (the latest solicitation occurred when the nestlings were 4 days old). Primary females solicited more copulations than monogamous females both during and after the fertile period. Many copulation solicitations of primary females occurred at the nestbox where their male was singing to obtain an extra female. Both primary and secondary females solicited more copulations after the egg-laying period than monogamous females. A large proportion of female copulation solicitations was refused by the male partner: female solicitation resulted in more male refusals in primary females than in monogamous females. Primary females were more likely to be chased aggressively when they solicited a copulation than monogamous females; most aggressive chases occurred when primary females flew towards their male to solicit copulation when he was singing at another nestbox. Overall, our results demonstrate that there is a conflict over copulation between males and females in polygynous pairs. The conflict presumably relates to the cost of sharing male parental investment: females use copulation solicitation behavior to interrupt their singing males apparently in an attempt to prevent them from becoming polygynous. We present the first empirical evidence that female songbirds use copulation solicitation behavior as a form of mate guarding, often in a non-reproductive context. We did not find a positive relationship between copulation rate during the fertile period and the amount of male parental care as is predicted by the paternity confidence hypothesis.     

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.     

Do male tree swallows guard their mates?

Summary We monitored the time spent at the nest and following behavior of mated tree swallows to determine if males were guarding their mates. The proportion of time spent together at the nest did not decrease significantly between fertile and postfertile periods, and the tendency of males to follow females was not significantly different from that of females to follow males. Following by either sex was infrequent. We suggest that the lack of mate guarding in tree swallows is related to an apparently low probability of extra-pair copulations, which in turn is likely to be due to two factors. Nesting opportunities are limited, perhaps more so for females than males. If the operational sex ratio is skewed towards females, this would not only reduce the risk of extra-pair copulations, but would also select against promiscuous females which would risk being abandoned by their mates. Secondly, under natural conditions, the limited availability of nest sites has selected for territorial defense by both males and females, which may decrease the occurrence of extra-pair copulation. Both factors would lead to relaxed selection for mate guarding behavior.     

Mixed reproductive strategy and mate guarding in a semi-colonial passerine,the swallow Hirundo rustica

Summary Both male and female swallows Hirundo rustica have a mixed reproductive strategy (parental care for offspring and extra-pair couplations). Mate guarding protects females from male harassment and male swallows from being cuckolded. Females hide their fertile period by copulating successfully with their mates for an extended period during first clutches. Males guard in the pre-fertile period, when many unpaired males are present. Early breeding swallows guard more than late breeders since more sexual chases of females by non-mate males take place in the early period. Solitarily breeding females experience few chases by strange males; copulation frequency, length of copulation period and mate guarding is adjusted to a lower level than among colonial birds. Male guarding activity is more intense in the fertile than in the pre-fertile period. Guarding reduces success of extra-pair copulation attempts.Three female swallows each paired and copulated with a single male and later changed to a new male before starting to breed. Extra-pair copulations most often take place between neighbouring swallows in the fertile period of the female. Many old, early breeding males and many young, late breeding females participate in extra-pair couplations. Successful extra-pair copulations peak in the fertile period contrary to success of pair copulations which does not change during the copulation period.     

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 copulation duration and the resultant degree of sperm removal inOrthetrum cancellatum (L.) (Libellulidae: Odonata)

Summary Orthetrum cancellatum showed two distinct copulation durations at a study site in the south of France. These different durations are correlated with different degrees of sperm displacement from the female sperm stores; long copulations (894±142 s) resulting in almost 100% sperm removal, and short copulations (21.0±13.5 s) resulting in 10–15% removal. The difference in copulation duration is also related to the site of copulation and to the relative age of the copulating males. At oviposition sites males who gained copulations were relatively young and copulated for long periods. The difference in the duration of copulation and the degree of sperm removal is discussed with reference to the female habit of ovipositing before remating during oviposition episodes, and the possibility of differences in the rate at which males encounter receptive females at the two sites.     

Blood corticosterone levels and intersexual selection games: best-of-bad-job strategies of male common lizards

Glucocorticoids affect physiology and behaviour, reproduction and potentially sexual selection as well. Short-term and moderate glucocorticoid elevations are suggested to be adaptive, and prolonged and high elevations may be extremely harmful. This suggests that optimal reproductive strategies, and thus sexual selection, may be dose dependent. Here, we investigate effects of moderate and high elevations of blood corticosterone levels on intra- and intersexual behaviour and mating success of male common lizards Lacerta vivipara. Females showed less interest and more aggressive behaviour towards high corticosterone males and blood corticosterone levels affected male reproductive strategy. Males of moderate and high corticosterone elevations, compared with Control males, showed increased interest (i.e., higher number of chases, tongue extrusions, and approaches) towards females and high corticosterone males initiated more copulation attempts. However, neither increased male interest nor increased copulation attempts resulted in more copulations. This provides evidence for a best-of-a-bad-job strategy, where males with higher corticosterone levels compensated for reduced female interest and increased aggressive female behaviour directed towards them, by showing higher interest and by conducting more copulation attempts. Blood corticosterone levels affected intrasexual selection as well since moderate corticosterone levels positively affected male dominance, but dominance did not affect mating success. These findings underline the importance of female mate choice and are in line with adaptive compensatory behaviours of males. They further show that glucocorticoid effects on behaviour are dose dependent and that they have important implications for sexual selection and social interactions, and might potentially affect Darwinian fitness.     

Offshore spawning by the portunid crabScylla serrata (Crustacea: Decapoda)

The portunid crabScylla serrata (Forskål) is shown to migrate offshore to spawn. Records of 447S. serrata caught as bycatch by trawlers in the tropical waters of northern Australia were analysed with respect to area, depth, distance offshore and month of capture as well as the sex and size of the crabs and whether the females were ovigerous. The crabs were caught mainly in three areas that correspond to the tiger prawn trawl fishery, at between 10 and 60 m depth (mean 28.5 m), 3 to 95 km offshore (mean 17.9 km). Most (87%) of the crabs were captured in October and November, which suggests they move offshore in September and October. No crabs were reported from offshore by February. Over 97% of the crabs caught offshore were female, of these 61.5% were ovigerous. The size range of females (100–109 to 200–209 mm carapace-width size classes) and males (120–129 to 200–209 mm carapace-width size classes) caught was similar. The frequent occurrence in coastal waters of females that are larger than the modal size at spawning, as well as mature females with spent ovaries, suggests that many females return to the coast after spawning. Although some species of portunid crab are euryhaline, mature females of estuarine species migrate to the sea to spawn. The migration byS. serrata described here is far more extensive than would be required to reach sea water salinities; it probably provides a dispersal mechanism for larvae to enable the megalopa stage to recruit to habitats distant from those of the parents.     

Copulation behavior and paternity in the chaffinch

Summary We investigated two aspects of sperm competition in a wild population of chaffinches Fringilla coelebs: copulation behavior and genetic parentage determined by DNA fingerprinting. Pairs copulated at a high rate before laying, peaking at 4.4 copulation attempts per hour on day –3 relative to laying, with an average of 207 copulation attempts (83 behaviorally successful) per clutch. Extra-pair copulation attempts (n = 20) made up 7.8% of all copulation attempts that females were involved in. The rate at which pairs copulated was lower during egg-laying, but there was no evidence that this was due to the male of the pair timing copulations to coincide with an insemination window; it was more likely due to the fact that females solicited copulations at a lower rate. Both sexes solicited copulations but males solicited mainly extra-pair copulations. DNA fingerprinting showed that 17.0% of chicks (n = 47) in 23% of broods (n = 13) were fathered by a male other than the one paired to their mother. There was no evidence of intraspecific brood parasitism. In three cases where we were able to identify the father of extra-pair offspring it proved to be a neighboring male.Correspondence to: B.C. Sheldon     

Daring females,devoted males,and reversed sexual size dimorphism in the sand-dwelling spider <Emphasis Type="Italic">Allocosa brasiliensis</Emphasis> (Araneae,Lycosidae)

Sexual selection theory predicts that a higher investment in offspring will turn females into the selective sex, while males will compete for accessing and courting them. However, there are exceptions to the rule. When males present a high reproductive investment, sex roles can reverse from typical patterns, turning males into the choosy sex, while females locate males and initiate courtship. In many spiders, males are smaller than females, wandering in search of sedentary females and maximizing the number of copulations. In the present study, we present findings on the sand-dwelling wolf spider, Allocosa brasiliensis, evidencing a reversal in typical courtship roles reported for the first time in spiders. Males were bigger than females. Females located males and initiated courtship. Copulation always occurred in male burrows and took place mainly in long burrows. Males donated their burrows to the females after copulation, closing the entrance before leaving with female cooperation from inside. Males would provide females with a secure place for ovipositing, being exposed to predation and diminishing their future mating possibilities until constructing a new burrow. The cost of vacating the burrow and losing the refuge in an unpredictable habitat, such as sand dunes, would explain the courtship roles reversal in this spider species. Results turn A. brasiliensis as a promising model for discussing the determinants of sex roles and the pressures that drive their evolution and maintenance. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

No cost of male mating experience on female reproductive success in the almond moth, <Emphasis Type="BoldItalic">Cadra cautella</Emphasis> (Lepidoptera; Pyralidae)

Male copulation experience may have a profound impact on female reproductive success if male reproductive investment declines over consecutive copulations and if females are unlikely to re-mate. Male reproductive investment is particularly interesting in lepidopterans because males produce dimorphic sperm: a fertilizing (eupyrene) and a non-fertilising (apyrene) sperm. In two experiments, we explored the lifetime reproductive investment of male almond moths, Cadra cautella (also known as Ephestia cautella) and examined its influence on female reproductive success. In the almond moth, females re-mate infrequently and males transfer sperm in a spermatophore. Attached to the spermatophore is a large chitinous process, the function of which is unknown. One group of males were permitted consecutive copulations with virgin females and the amount of sperm and size of the spermatophore transferred were compared for all females. We found that the number of both eupyrene and apyrene sperm per ejaculate decreased with his increased mating frequency, while the size of the spermatophore process decreased dramatically after the male’s first copulation. In a second experiment, we allowed males to mate with females throughout their lives and then compared female fecundity and fertilisation success. We found no obvious decrease in female fecundity and fertilisation success with increased male copulation experience, despite the likely reduction in male gametic investment. We discuss potential explanations for the development of this enlarged and elaborate first spermatophore of male almond moths given that it confers no clear fitness advantage to females.     

Predation risk reduces male-male sexual competition in the Trinidadian guppy (Poecilia reticulata)

Because agonistic behaviour can increase an individual's risk of predation, natural selection should favour individuals that modify their behaviour in the face of predation hazard in ways that maximise fitness. We investigated experimentally the effects of an increase in the apparent risk of predation on male-male competition within mixed-sex shoals of the Trinidadian guppy (Poecilia reticulata). We show that males engaged in significantly fewer aggressive interactions with conspecific males in the presence of a fish predator. However, they continued to court and attempt copulations with females at the same rate irrespective of the level of predation risk. In comparison, under predation hazard, female guppies were less responsive sexually and avoided fewer male copulation attempts. Such predator-mediated changes in male-male agonistic interactions and female sexual responsiveness towards males have important implications for the mode and intensity of sexual selection within populations.     

Re-copulation and post-copulatory mate guarding increase immediate female reproductive output in the dragonfly Nannophya pygmaea Rambur

After copulation, male Nannophya pygmaea dragonflies mate guard by hovering over ovipositing females and repelling conspecific males. Copulation is not always a prerequisite for oviposition in the females of this species because females can store the sperm received during previous visits/copulations. An oviposition episode consists of several bouts of oviposition separated by periods of perching. We conducted two types of male-removal experiments to examine the effects of mating and post-copulatory mate guarding on the oviposition behaviour of females. In the first experiment, we removed all males from the habitat to eliminate the effect of re-copulation, mate-guarding and harassment by males. In the second experiment, we removed males immediately after copulation to eliminate the effects of guarding and other post-copulatory male-female interactions. We compared these experimental data with data obtained under natural conditions. The dipping rate in an oviposition bout was not influenced by copulation or guarding. However, guarded females made more dips per episode than did solitary females. The proportion of time actually spent ovipositing (total bout duration/oviposition episode duration) of guarded females was higher than that of solitary females. Solitary females often oviposited in more than one territorial site, while guarded females usually oviposited within a single territorial site during an oviposition episode. Because males tend to hold territories at sites where egg survival is high, guarded females (and the male guardian) benefit from guarding in terms of egg hatchability. The possible benefits for solitary females are discussed.     

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     

Mating behavior of <Emphasis Type="Italic">Abdopus aculeatus</Emphasis> (d’Orbigny 1834) (Cephalopoda: Octopodidae) in the wild

The mating system of Abdopus aculeatus incorporates sneaker matings, mate guarding, sex-specific body patterns, frequent copulations, and male–male competition for mates, making it more similar to that of aggregating decapod cephalopods than any previously known octopus social system. Large male–female A. aculeatus occupy ‘Adjacent’ (G_A) dens and copulate frequently in mate-guarding situations over successive days. Nearby individuals copulate in ‘Temporary guarding’ (G_T) and ‘Transient’ (T; non-guarding) situations, the latter of which can involve ‘Sneaker’ (S) mating. In a focal animal study of these octopuses in the wild (Sulawesi, Indonesia) we addressed the hypotheses that they demonstrate: (1) precopulatory mate choice, (2) differential copulation rates by individuals employing different mating tactics, and (3) distant sex identification. We quantified daily copulation rates of A. aculeatus of reproductive size as well as aspects of copulation duration, display, mate-competition, and mate rejection. Mating tactic correlated with daily copulation rates. ♂G_A spent significantly more time copulating than did ♂T, while ♀G_A spent more than twice as much time per day in copula than did other females. Sneaker copulations lasted longer than those by males adopting other tactics. Mate-guarding was an effective and important tactic used by males to temporarily monopolize mating with apparently non-selective females. Males demonstrated clear pre-copulatory mate choice by guarding and mating repeatedly with large females (typically ♀G_A). While foraging alone away from the den, ♂G procured ‘Transient’ copulations with unguarded females. However, mate-guarding reduced the amount of time ♂G were alone and may impede their ability to seek out new mates. Low-copulation rates by ♀T, the smallest female tactic on average, may reflect this trade-off between mate preference and mate-searching by males, or non-receptivity of some females. A male-typical body pattern (black and white stripes) appeared to facilitate distant sex identification. Although mating and aggression were often initiated before contact between individuals, same-sex copulations and intense male–female aggression were rare. By contrast frequent male–female copulations and intense male–male aggression were consistent behavioral components of mating in A. aculeatus at these sites. Because the behavioral and ecological characters conducive to this complex system are not exclusive to A. aculeatus, it is possible that other octopuses exhibit some or all of these behaviors. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Different tactics,one goal: initial reproductive investments of males and females in a small Arctic seabird

Despite a great number of studies on extra-pair paternity in birds, the actual roles of males and females in extra-pair contacts is poorly understood, as detailed behavioural studies comparing the reproductive performance of the two sexes prior to egg laying are relatively scarce. Here, we investigated mating behaviour (copulations and aggressive interactions), time budget and body condition (size-adjusted body mass and baseline corticosterone level) in the little auk (Alle alle), a monogamous and highly colonial, Arctic seabird. We performed the study in a large breeding colony of the little auk in Hornsund (Spitsbergen). We found that the males frequently attempted extra-pair copulations (EPCs), although these contacts were almost always unsuccessful, mostly because of the females’ rejection behaviour. These results clearly indicate that genetic monogamy is maintained through female control. Nevertheless, males tried to protect their paternity by staying in close proximity to their females and aggressively intervening when their mates became involved in EPCs. Compared to females, males also spent more time in the colony guarding nest sites. Despite the apparent sex differences in the time budget and frequency of aggressive interactions, body condition was similar in the two sexes, indicating comparable parental investments during the mating period.