Breeding synchrony and extra-pair mating in red-winged blackbirds

Using data from a 6-year paternity study of red-winged blackbirds, I tested the hypotheses that increased nesting synchrony should either promote extra-pair mating by increasing the advantage of extra-pair mating to females, or decrease extra-pair mating by constraining males from seeking extra-pair copulations. Contrary to these hypotheses, the occurrence of extra-pair paternity did not vary with nesting synchrony over the breeding season, or vary with the number of synchronous nests within territories or within marshes, or with nesting order on territories. However, for nearly all nests with extra-pair young, there were fewer females synchronous with that nest on the cuckolder's territory than on the territory of the cuckolded male. This “advantage” of a synchrony difference was less pronounced for older males that cuckolded younger males, particularly when the two males were not neighbors. Collectively, these results suggest that breeding synchrony affects extra-pair mating by affecting mate guarding, but that breeding synchrony alone can not be used to predict which females are more likely to engage in extra-pair mating, nor with which extra-pair males they will mate. Understanding why extra-pair mating by older males is less affected by breeding synchrony may explain much about both the proximate and ultimate causes of extra-pair mating in red-winged blackbirds. Received: 7 June 1996 / Accepted after revision: 25 November 1996     

Sexual coercion by male chimpanzees shows that female choice may be more apparent than real

The extent to which active female mating preferences influence male reproductive success in mammals is unclear, particularly for promiscuously breeding species like chimpanzees (Pan troglodytes). Previous studies from multiple long-term study sites have shown that female chimpanzees mate more restrictively around ovulation, and this has been taken as evidence for female choice. However, none of these studies rigorously evaluated the alternative hypothesis that restrictive mating results not from unconstrained choice, but in response to coercive mate guarding, in which males use punishment and intimidation to reduce female promiscuity and promote their own mating interests. Nor did they consider evidence for the potential genetic or phenotypic benefits that females might be choosing. Using 11 years of data from the Kanyawara community in Kibale National Park, Uganda, we previously demonstrated that males achieve elevated mating success with those females toward whom they direct high levels of aggression. Here we extend those findings to show that even female copulatory approaches, which have previously been attributed to female choice, are correlated with male aggression. Specifically, individual females at our site initiated periovulatory copulations most frequently with the males who were most aggressive toward them throughout their cycles. Those males showed high rates of aggression toward females throughout estrus, despite achieving high copulation rates, demonstrating a continuing conflict of interest over the exclusivity of mating access. Because sexual coercion is potentially widespread in primates and other mammals, our results stress the importance of considering the influence of male aggression in studies of female choice.     

Altered responses to female odors in parasitized male mice: neuromodulatory mechanisms and relations to female choice

There is accumulating evidence that females may preferentially select parasite-free or -resistant males. Minimal attention has, however, been paid to the mate preferences and responses of the parasitized male hosts themselves. Here, we considered the effects of parasitic infection on male host mate responses, the neuromodulatory correlates of these responses, and the relations of these responses to female mate choice. Using an odor “preference” test, we examined the effects of different stages of an acute, sub-clinical infection with the naturally occurring, enteric, single host, protozoan parasite, Eimeria vermiformis, on the responses of male mice, Mus musculus domesticus, to the odors of estrous females along with the responses of uninfected females to the parasitized males. At 4 days post-infection (non-infective, pre-patent stage) E. vermiformis-infected male mice showed a significantly decreased preference for the odors of estrous females, whereas at 10 days post-infection (infective, patent stage) infected males showed a significantly increased preference for the odors of estrous females. Parasitized males displayed no significant changes in their responses to the odors of non-estrous females, supporting effects on the reproductively related responses of the host. In parallel, estrous females displayed a reduced interest in the odors of infected males. Least interest was expressed in the odors of the patent, infective males, consistent with the avoidance of contagion. Using selective opioid peptide receptor agonists and antagonists we found evidence that enhanced kappa opioid peptide (e.g., dynorphin) activity was related to the decreased sexual interest of the pre-infective males, while augmented delta opioid peptide (e.g., enkephalin) activity was associated with the enhanced responses of the infective males to females. We further showed that acute kappa opiate administration reduced the responses of uninfected males to females and that uninfected females displayed modified responses to the odors of uninfected males subject to acute modifications of opioid activity. We suggest that these differential shifts in endogenous opioid activity in the parasitized males are associated with and, or related to alterations in neuro-immune and endocrine functions. These findings show that parasitic infection can have, depending on the stage of infection and associated neuromodulatory changes, either significant facilitatory or inhibitory effects on male host preferences for and responses to females. Received: 22 April 1996 / Accepted after revision: 15 March 1997     

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.     

Mate guarding in the swallowHirundo rustica

Summary The importance of mate guarding by males in the monogamous swallowHirundo rustica was studied by temporarily detaining the males. Mate guarding reduced the frequency of extra-pair copulations and of sexual chases involving female mates. Males participated in sexual chases more frequently if they had a non-fertile female. Neighbouring males of ‘widowed’ females increased their own mate guarding presumably in response to the experimentally increased rate of sexual chases. Neighbouring males with a fertile female increased their mate guarding more than did males with a non-fertile female. Addition of eggs to swallow nests in the post-fledging period of the first brood induced mate guarding by male nest owners. These males also copulated more frequently with their mates than did control males. Neighbouring male swallows responded to the increased mate guarding by showing sexual interest in the guarded females. removal of eggs from swallow nests during the laying period, leaving only one egg in the nest, resulted in reduced nest attendance by females. Male mates responded by increasing their mate guarding intensity as compared to controls, and neighbouring males showed an increased sexual interest in these females.     

The efficacy of female choice in chimpanzees of the Taï Forest, Côte d’Ivoire

Male–male competition has historically been considered the major force driving sexual selection. However, female choice and inter-sexual conflict are increasingly recognized as important influences affecting differential mating and reproductive success. Many females exhibit preferences for particular males; however, male strategies may conflict with females’ ability to obtain their mate preferences. To influence paternity, females must affect both (1) whether or not sexual interactions occur, particularly during the periovulatory period (POP) and (2) the outcome of sexual interactions. This study focuses on the effectiveness of female choice in wild chimpanzees (Pan troglodytes verus). Over 2,600 h of data were collected on two habituated chimpanzee communities in the Taï National Park, Côte d’Ivoire. Female mate preferences were measured by quantifying proceptive and resistance behavior toward males in both the periovulatory period and non-POP phases of estrus. The efficacy of female preference was measured both (1) by measuring success rates of female proceptivity and resistance behaviors and (2) by determining how well measures of female mate preference (proceptivity and resistance rates) predict male mating success. Though male chimpanzees are clearly dominant to females, the results indicate that females could effectively resist male solicitations and, in most cases, unwanted copulations were averted. Both female proceptivity and resistance rates correlate (positively and inversely, respectively) with male mating success in POP. Outside POP, female proceptivity rates corresponded with male mating success, but resistance rates did not. Males (irrespective of rank) that were preferred by females obtained higher mating success compared to other males during the POP, suggesting that females were effective in their mate choice and that, despite clear male dominance, female choice influences paternity in wild chimpanzees.     

The relative roles of predation and sperm competition on the duration of the post-copulatory association between the sexes in the blue crab, Callinectes sapidus

In many species, post-copulatory mate guarding prevents other males from mating with the guarded female. In crabs, males stay with their mates to protect the female from predators because, in some species, mating occurs when she is soft and vulnerable after molting. I tested the relative roles of sperm competition and predation on the duration of the post-copulatory association in the blue crab, Callinectes sapidus. Unpaired females suffered greater predation mortality than paired females and males stayed with the female longer in the presence of predators than in their absence, suggesting that the post-copulatory association protects females during their vulnerable period. However, the association may also occur in blue crabs because of sperm competition since spermathecal contents of females in the field indicate that 12.4% mated twice. Females experimentally mated with two males contained both males ejaculates and each ejaculate had access to the unfertilized eggs, suggesting that the size of a male's ejaculate influences his fertilization rate in a multiply-mated female. Males stayed longest in response to a high risk of sperm competition. Longer post-copulatory associations allowed the first male's ejaculate to harden into a type of sperm plug, which limited the size of a second inseminator's ejaculate in a non-virgin female as compared with a virgin. Males passed larger ejaculates in the presence of rivals and when previous ejaculates were in the female spermathecae, another response to sperm competition. Larger ejaculates may need longer post-copulatory associations before a more effective sperm plug forms. Large males stayed with the female longer, which is consistent with their ability to pass larger ejaculates than small males and suggests that there may be costs to minimizing the duration of the post-copulatory association. In the field, associations last long enough to protect the female during her vulnerable phase and may ensure that the guarding male fertilizes the most eggs in the female, even if she remates. Thus, the post-copulatory association protects female blue crabs from additional inseminators as well as from predators. Received: 23 January 1996 / Accepted after revision: 9 November 1996     

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.     

Social monogamy and extra-pair fertilization in an Australian lizard, Tiliqua rugosa

This study investigates social monogamy in the Australian sleepy lizard, Tiliqua rugosa. At a 70-ha site near Mount Mary, South Australia, we radio tracked 55 adult female and 39 adult male lizards during their spring activity periods. Each lizard was observed in 1–5 years. Females were observed with a single male partner on an average of 10.8 days per year, although in 17.3% of cases, females were observed on 2 or fewer days with a male. The most intense pairing period each year was 15 September–15 November when females were with male partners on an average of 36% of observation days. Partnerships lasted an average of 43.3 days each year. After mating in early November, the pairs separated. Observations of females pairing with other males were rare. Most males (82%) were also consistently monogamous, although 7 were observed pairing with 2 females within one season. To investigate paternity, we allowed 21 gravid females to give birth to 42 offspring in the laboratory. We determined genotypes at five polymorphic microsatellite DNA loci for the females, their male partners and their offspring. Four litters (19%) and 6 of the offspring from those litters (14.3%) showed evidence of extra-pair fertilization (EPF). Although the sample sizes are small, females of polygynous males were more likely to experience EPF. Received: 22 February 1998 / Accepted after revision: 23 May 1998     

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.     

Estimating paternity with spatial behaviour and DNA fingerprinting in the striped plateau lizard, Sceloporus virgatus (Phrynosomatidae)

The association between spatial proximity and paternity was studied in a population of the striped plateau lizard, Sceloporus virgatus. The relationship between estimated mating success and male phenotypic traits was examined for a sample of 55 males. DNA samples were obtained from 13 female-offspring families. The males with the closest spatial proximity to each female were tested as possible sires within each family. Fingerprinting with two multilocus hypervariable minisatellite probes revealed a strong correspondence between male-female spatial proximity and actual paternity. Paternity could be assigned for 72 of the 100 hatchlings. Most hatchlings with identifiable sires were attributed to a male with the highest category of spatial proximity to the mother. However, there was a low to moderate level of multiple paternity within clutches, and for some clutches probable sires could not be identified even though the most likely behavioural candidates were tested. Thus, nonterritorial males or other males lacking strong social and spatial relationships with females may achieve some degree of reproductive success. Analysis of mating success revealed that male success increased with body size, up to a point beyond which larger size conferred no advantage. Received: 7 January 1997 / Accepted after revision: 16 June 1997     

A same-sex stepparent shortens a prebreeder's duration on the natal territory: tests of two hypotheses in Florida scrub-jays

Prebreeders of the Florida scrub-jay (Aphelocoma coerulescens) are less likely to be found on their natal territories with a same-sex stepparent than with parents or an opposite-sex stepparent. We tested two models that had been proposed to account for this sexual asymmetry. The dominance hypothesis states that stepparents perceive same-sex prebreeders as competitors, primarily for a mate, so behave aggressively toward them. The pair-formation hypothesis states that prebreeders remain home to pair eventually with the opposite-sex stepparent. Predictions from these two models were tested by analyses from a quarter-century of records on a study population at Archbold Biological Station and by new behavioral field observations at the Station. Results clearly rejected the latter and strongly supported the former hypothesis. No prediction from the pair-formation hypothesis was confirmed: no pairing by a prebreeder of either sex has ever occurred with a stepparent; remaining home was equally frequent in age-one males with stepmothers and genetic mothers, and in females with stepfathers and genetic fathers; and the same results were found in age-two prebreeders. By contrast, the data strongly supported the dominance hypothesis. Field data showed higher aggression rates by stepfathers to male prebreeders and stepmothers to female prebreeders than by parents to their same-sex genetic offspring. Fewer age-one males remained home with a stepfather than with the genetic father, and the same was found for age-one females with a stepmother and genetic mother; at age two, the effect occurred only in female prebreeders. The two hypotheses make different predictions about prebreeders with two stepparents versus with both parents, thus providing a critical test. The dominance hypothesis correctly predicted decreased duration at home by age-one males and females; data for age-two females were in the direction of predicted difference but not significant; and, as in other tests, no effect was found for age-two males. We propose that age-two male prebreeders remain home despite elevated aggression from stepfathers because these prebreeders retain the possibility of budding from or inheriting the natal territory. Received: 16 July 1997 / Accepted after revision: 26 June 1998     

Analysis of the causal components of assortative mating in water striders

Field studies demonstrate that natural populations of a group of water striders (Heteroptera: Gerridae) that share a common mating system are characterized by weak assortative mating by size and by large sizes of mating males and females relative to single individuals. This study presents an experimental assessment of the components of mating that may contribute to these mating patterns. The effects of male and female body size on each of three components of mating were studied in three water strider species in the laboratory. Large females of all three species mated more frequently, copulated for longer and were guarded longer than small females. Large males mated more frequently than small males in all three species, and also guarded females for longer in the two species where the average of mate guarding was long. However, we found an antagonistic effect of male size on copulation duration: small males copulated for longer than large males in all three species. We show that the combined effects of these size biases mimic the mating patterns found in the wild, e.g. weak and variable assortative mating, and stronger and less variable size ratios of mating versus non-mating females relative to males. We suggest that the antagonistic effects of male size on copulation and guarding duration may be a key source of interpopulational variation in assortative mating and sexual selection on male size. Further, neither spatial or temporal covariation in size, nor mechanical constraints, caused the assortative mating observed here in this group of water striders. Some combination of male and female choice (either active or passive forms) of large mates and male-male exploitation competition for mates play potentially important roles in producing population level assortative mating in water striders. Received: 17 March 1995/Accepted after revision: 28 October 1995     

Past reproductive success affects future habitat selection

Correlational studies have shown that an individual's past reproductive success often increases its breeding site fidelity (i.e., the tendency to return to a previously occupied location), suggesting that individuals use their reproductive experience to assess habitat quality. However, the causality of the relationship between reproductive success and site fidelity is still uncertain. In a field experiment, the effect of mating success on site fidelity was isolated from potential confounding variables in a territorial dragonfly, the eastern amberwing (Perithemis tenera). The experiment controlled for site quality, intrinsic characteristics of males, previous territorial experience at the site, arrival order, and territorial evictions. Males that were prevented from mating were much more likely to change sites the following day than control males that were allowed to mate. This result was not affected by age, the amount of time a male spent on the site, or mortality. These results imply that individuals use their own reproductive success to assess the quality of the habitat. The benefit to an individual of using its reproductive success to determine habitat quality is discussed relative to other sources of information. Received: 31 May 1996 / Accepted: 31 January 1997     

Post-copulatory aggression toward their mates by males of the rove beetle Leistotrophus versicolor (Coleoptera: Staphylinidae)

Summary Rove beetles (Leistotrophus versicolor) forage and mate at dung and carrion in the riparian forest of northwestern Costa Rica. After copulating, males often launch a post-copulatory attack against their recent partner. We test four hypotheses on the adaptive value of male behavior: (1) The sperm competition hypothesis proposes that the behavior may be the functional equivalent of mate-guarding, (2) the sperm-transfer signal hypothesis states that males bite their mates after copulating to signal that they have successfully passed sperm, (3) the feeding competition hypothesis argues that male aggression toward mates occurs to drive away competitors for fly prey, and (4) the redirected aggression hypothesis is that male attacks after mating occur when threatened males redirect their aggression onto their partners. Only the sperm competition hypothesis withstands testing. As required by this hypothesis, females are usually receptive while at dung, and will mate with more than one male in a morning. In addition, males are more likely to attack a mate when they have fought earlier in the day with other males, an indicator of the presence of rival males and the risk of sperm competition. Contrary to the sperm-transfer signal hypothesis (2), biting of mates does not occur after nearly 40% of all copulations; it seems unlikely that mating males so often fail to transfer sperm. Whether males have fed or not prior to mating has no effect on the probability of post-copulatory attack, a result that contradicts the food competition hypothesis (3). Finally, the occurrence of attacks by males on females in the absence of an immediate threat from a rival argues against the redirected aggression hypothesis (4).     

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.     

The assessment of female reproductive state during courtship and scramble competition in the fiddler crab, Uca paradussumieri

Male fiddler crabs, Uca paradussumieri, mate underground during a 4- to 7-day period each full and new moon. As soon as the tide recedes, males enter the burrows of females that will ovulate the following day ('pre-ovigerous' females). Males copulate with and guard these females until they ovulate. When interrupted by an intruding male, the first male to reach the female is usually able to defend her and successfully mate with her. In fiddler crabs, females mate multiply and there is last male sperm precedence. Before each semi-lunar mating period, male U. paradussumieri were more likely to court females with whom they would later mate than other nearby females with whom they did not mate. This suggests that males collect information on female reproductive state prior to the females becoming ovigerous. In this species, aggression was common between males that courted the same female. When previously courted females were approached by other males, the initial courter attempted to forcefully disrupt the courtship. This behavior may allow males the exclusive use of information on female reproductive condition. It also suggests a type of scramble competition between males over females. Furthermore, it indicates that males are able to locate receptive females prior to their becoming ovigerous. The shorter guarding period observed in this species, as compared with other fiddler crabs, is caused by females rejecting longer guarding periods. Male ability to assess female reproductive status may therefore be advantageous because it increases male mating success within a scramble type of competitive polygyny.     

Mate guarding behavior in clam shrimp: the influence of mating system on intersexual conflict

Mate guarding is a male strategy to gain access to receptive females but often results in antagonistic interactions between the sexes because of different costs/benefits of guarding. In addition to social, morphological, and physiological parameters, the type of mating system should also affect the strength of the conflict and thus the guarding duration. Specifically, when compared to females, self-compatible hermaphrodites might have reduced benefits of outcrossing. We investigated mate guarding in dioecious (co-presence of females and males) and androdioecious (co-presence of hermaphrodites and males) branchiopod crustaceans. Both sexes in androdioecious systems should shift their guarding times to lower values relative to dioecious systems because (1) androdioecious males are present in lower percentages than dioecious males and thus encounter rates with receptive mates are relatively greater for them; and (2) hermaphrodites should have low incentive to incur high costs of mate guarding, having the alternative of self-fertilization, and thus should be highly eager to resist. While females preferred short guarding times, when allowed to control the guarding duration (males tethered), dioecious males did not increase their guarding duration when females (treated with muscular relaxant) could not resist, in contrast to what has previously been found for androdioecious males. This indicates that hermaphrodites are more willing to resist mate guarding than females. The among-species comparisons supported our hypotheses: compromised guarding times were significantly lower in androdioecious than in dioecious species. The introduction of a parameter (mating system) not previously investigated in mate guarding models resulted in a powerful test of mate guarding theory, adding a valuable contribution to our understanding of intersexual conflict.     

Sex-biased dispersal in a long-lived polygynous reptile (Crocodylus johnstoni )

We compared natal dispersals of freshwater crocodiles (Crocodylus johnstoni) against the prediction of male dispersal bias for a polygynous mating system. The crocodiles inhabited a linear series of pools and we calculated the net distances from natal pools to recapture locations some 12–18 years later, at maturity. Philopatry was assessed in terms of adult social distances. A female social distance was 0.46 pools and a male social distance was 1.0 pool. By these criteria, both sexes showed low levels of philopatry (7–12%). However, individuals of both sexes dispersed from the natal site long before they were sexually mature. Divergence in dispersal patterns by sex occurred after the maturity threshold, as males dispersed two to three times farther than females. Intrasexual competition by males is resolved by a size-based hierarchy. The displacement of small males from local mating access is a probable cause of the longer dispersals undertaken by males. Competition, rather than inbreeding avoidance, is driving dispersal in this population of freshwater crocodiles. Received: 8 May 1998 / Accepted after revision: 26 June 1998     

Parentage and paternal care: consequences of intersexual selection in Savannah sparrows?

Empirical relationships between parentage and male parental care are commonly interpreted in the context of life-history models that consider increased offspring survivorship as the only benefit of paternal effort. However, indirect benefits associated with male care can also influence a male's response to cuckoldry: if females allocate paternity according to their prior experience with male parental care, it may pay for males to provision extra-pair young in early broods. Here, I assess the relationship between first-brood parentage and paternal care in a population of Savannah sparrows (Passerculussandwichensis) where a male's fertilization success in the second brood appears to be influenced by his prior parental performance. Based on the multi-locus DNA fingerprinting of 17 first broods, male feeding effort was influenced by parentage (percent of brood resulting from within-pair fertilizations) but not by brood size, male mating status (monogamous versus polygynous), timing of breeding (hatching date), structural size (wing length) or condition (mass). Males provided more care to broods that contained few within-pair young. This result supports the idea that males provision young to increase their future mating success, but alternative hypotheses involving male quality and timing of breeding cannot be excluded. Received: 13 August 1996 / Accepted after revision: 22 February 1997