Copulation Rate Research Articles

The beneficial sexually transmitted microbe hypothesis of avian copulation

Several hypotheses have been proposed to explain why female birds either copulate repeatedly with a single mate or copulate with multiple partners even though only a single copulation may be sufficient to fertilize an entire clutch. We hypothesize that females may directly benefit from high frequencies of copulation and multiple copulation partners if they receive a cloacal inoculation of beneficial sexually transmitted microbes (STMs) that can either protect them against future encounters with pathogens and/or serve as therapy against present infections. Experiments in domestic animal production, wildlife rehabilitation, and clinical medicine indicate that inoculations of beneficial microbes derived from the indigenous microflora of hosts can lead to nutritional benefits, resistance to colonization by pathogens, the elimination of infection, and improved immune system functioning in recipients. Our hypothesis predicts greater copulatory rates when the probability of the transmission of beneficial microbes exceeds that of pathogens and when the positive effects of beneficial microbes on host fitness exceed the negative effects of pathogens. Patterns of copulatory behavior in birds suggest the potential utility of our hypothesis. We discuss our hypothesis in the context of observed patterns of copulation in birds and propose some ways to directly test our hypothesis. Information on the probabilities of transmission during copulation of beneficial and pathogenic microbes and their relative potencies in birds are needed to directly test the predictions of our hypothesis.

Copulatory Behavior of the Bearded Vulture

We describe copulation activity by Bearded Vultures (Gypaetus barbatus) at nesting sites in the Pyrenees, northern Spain, between 1993 and 1995. Pairs copulated for an average period of 67 days (range: 50-90) prior to egg laying. Seventy-five percent of attempts ended in successful copulation. Pairs displayed a daily bimodal pattern of copulation, with copulations occurring most frequently in the evening. Low levels of opportunities for extra-pair encounters (0.02 intrusions hr-1) were obtained despite the high density of reproductive individuals present. The high copulation rate observed may be explained by the potential risk of extra-pair copulations occurring while a member of the pair is away foraging, an activity which takes up as much as 65% of time each day. This species also showed a pattern of pair attention similar to that of other species of raptors in which males guard their females during the fertile period.

Male rank and optimal lek size

Widemo and Owens presented a model that calculates the expected copulation rates of males on leks of a range of sizes. They claim that a negative relationship between lek size and male mating skew will result in low-ranking males having greater optimal lek sizes than higher ranking rivals. Widemo and Owens offered no proof of their claim, and their model assumes that the rank of a male does not change as lek size increases, whereas in reality, rank may change as more males arrive. We present a general model that allows rank to change as lek size increases. We show that the crucial determinant of whether optimal lek size increases with male rank is whether relative competitive differences increase with lek size. Contrary to the claim of Widemo and Owens, the relationship between skew and lek size has no direct bearing on the optimal levels of aggregation of males of different rank. We show that a negative relationship between skew and lek size can exist even when high-ranking males have the greatest optimal lek sizes.

Inter- and intra-sexual behaviour of free-ranging dogs ( Canis familiaris)

Inter- and intra-sexual behaviour of free-ranging dogs were studied in the natural environment. Both males and females differed in their degree of attractiveness to the opposite sex. There was a positive correlation between the number of males associated with a particular oestrous bitch and the duration of each association. The males preferred by the oestrous bitches enjoyed the highest rates of copulation, but the non-preferred dominant and powerful males occasionally mated forcibly. The young adults were more likely to copulate successfully than the old adults. There was a negative correlation between the number of males present in an association and the number of successful copulators. Occasionally, copulations were performed by opportunist males after being present only a short time. In spite of selective receptivity, a few bitches mated promiscuously. Sometimes the oestrous bitches showed different types of solicitations to their preferred males. In the courting places, aggressiveness of males to other males was higher than the aggressiveness of the females towards other females. Both male–male and female–female mountings from side or rear were observed in this study.

Copulation rate and sperm use by female bearded tits,Panurus biarmicus

We examined functional and mechanistic aspects of sperm competition in the bearded tit by determining (1) the variation in copulation rate between birds breeding alone or with other males present, and (2) the number of sperm present in the female reproductive tract estimated from the number of sperm trapped on the perivitelline layers of eggs. Females copulated at a higher rate with their partner when other males were present, but this did not translate into more sperm on eggs, possibly because insemination rates exceeded the female’s sperm storage capacity. The rate of sperm loss from the female’s reproductive tract, which is an important variable of sperm competition models, was obtained for the first time for a wild bird and was relatively high compared with other birds. This suggests that bearded tits copulate frequently because a single insemination is insufficient to fertilize the whole clutch, and females thus have to copulate during the egg-laying period to avoid infertile eggs. This finding is the first empirical support for the fertility insurance hypothesis. In line with this we discuss the significance of the interspecific variation in rate of sperm loss in relation to mating strategies in general, and the evolution of multiple mating rather than improved sperm storage in bearded tits with particular regard to the pronounced extrapair copulation behaviour of females.

Sperm competition and sexual selection: a meta-analysis of paternity studies of birds

Sperm competition (the competition among the sperm of different males for fertilization of the eggs of a female) has been suggested to be an important component of sexual selection, but no general assessment has been made of this proposition. We used a meta-analytic approach to assess the extensive literature on paternity (the proportion of offspring in a focal nest sired by an attending male) in birds based on allozyme and molecular techniques. The relative variance in male mating success was on average increased by a factor of 4.6 over the variance in apparent male success. Males with more extravagant secondary sexual characters had higher paternity in their own nests than less adorned males. There was a weak effect of male age being positively associated with paternity in own nests. Male body size measured as the length of wing and tarsus was weakly positively associated with paternity in own nests. Male survival prospect was positively associated with paternity in own nests. Polygynous males generally had decreased paternity of their broods compared to monogamous males. Paternity of the resident male decreased with increasing population density and breeding asynchrony. The intensity of paternity guards such as within-pair copulation rate and mate guarding were not significantly related to extra-pair paternity. Sperm competition was thus an important component of sexual selection by increasing the variance in male mating success, and by being associated with the expression of secondary sexual characters, in particular in dense and asynchronously breeding populations of birds.

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.

Patterns of courtship behavior and ejaculate characteristics in male red-winged blackbirds

Sperm competition in birds is likely to have important effects on the behavior and physiology of reproduction in both sexes. For males, such competition should select for large sperm reserves and behavioral adjustment of copulation when reserves are low. We investigated both these possibilities in free-living red-winged blackbirds (Agelaius phoeniceus), a highly polygynous species with apparently strong sperm competition. We found that the recent copulatory behavior of males did not affect the propensity to copulate with a model female. Ejaculates collected from individual males at 1-h intervals showed no evidence of sperm depletion, yet repeated ejaculates collected less than 10 min apart did. Male ejaculate size was significantly larger if it was the first one of the day (i.e., after an overnight rest). The average ejaculate size was 12.5 (±12.5 SD) million sperm. Males captured during the breeding season had an average of 111.7 (±52.8) million sperm stored in their seminal glomera. Because males average a peak copulation rate of six per female per day, in one day a male might utilize all the sperm in his seminal glomera if more than two females on his territory are fertilizable. We hypothesize that polygyny and sperm competition in this species have combined to select for rapid replenishment of the seminal glomera throughout the day, in contrast to other species that have been studied. Testis size and sperm reserves of male red-winged blackbirds are intermediate between monogamous species and species with intense sperm competition. Several possible explanations for this are discussed.

Effects of prenatal exposure to 5-bromo-2′-deoxyuridine on the developing brain and reproductive function in male mouse offspring

The effect of prenatal exposure to 5-bromo-2′-deoxyuridine (BrdU) on the brain and reproduction in mice was studied. ICR mice were treated intraperitoneally (ip) with BrdU at 200 mg/kg on Day 10, 13, or 15 of gestation, or with BrdU at various doses (100 to 800 mg/kg) on Day 10 of gestation. In both experiments, dams were allowed to deliver, and male offspring were aged for 10 weeks and then cohabited with untreated females. In the phase-specificity study, the copulation rate was significantly decreased in the group treated on Day 10 of gestation, while the rate in the groups treated on Day 13 or 15 was comparable to the control level. In the dose-dependency study, copulation rates in the groups treated with BrdU at 200, 400, and 800 mg/kg were significantly lower than the control level, while the rate in the group treated with BrdU at 100 mg/kg was comparable to the control level. Masculine sexual behavior in the group treated with BrdU at 800 mg/kg was markedly impaired. Neither histopathologic changes of testis and sex-accessory glands nor alterations of sperm motility and concentration were observed in the offspring of the highest dose group. Dilatation of the third ventricles was observed in the highest dose group, whereas the relative brain weight in this group was comparable to that in the control group. In the subsequent study, ICR mice were treated ip with BrdU at various doses (25 to 800 mg/kg) on Day 10 of gestation, and the embryos were obtained 24 h after treatment. Histopathologic evaluation was performed in the ventricular zone of the telencephalon as well as ependymal and mantle layers of diencephalon (hypothalamus). The incidence of pyknotic cells in these areas was increased linearly with increasing BrdU dose and the incidence in the ependymal and mantle layers of the diencephalon was higher than that in the ventricular zone of the telencephalon. From these results, we conclude that damage to the central nervous system resulting from excessive cell death in the developing brain, particularly in the ependymal and mantle layers of the diencephalon (hypothalamus) may lead to reproductive dysfunction in postpubertal male offspring.

High Paternity without Paternity-Assurance Behavior in the Purple Sandpiper, a Species with High Paternal Investment

Among birds, males investing highly in paternal care should be under par- ticularly strong selection pressure to prevent extrapair paternity in their broods. Current literature implies that to obtain a high certainty of paternity, males should invest in pater- nity-assurance behaviors, and this makes them more likely to increase their investment in reproduction. The Purple Sandpiper (Calidris maritima) is a relatively long-lived arctic shor- ebird with a socially monogamous pair bond and strong mate and territory fidelity by both sexes. Paternal investment is high because males alone perform all of the brood care from hatching to fledging. We investigated the mating strategies of male and female Purple Sand- pipers through genetic analysis and examined the possibility that this species exhibits pa- ternity-assurance behaviors. We found no evidence that males exhibited behaviors such as frequent copulation or mate guarding during their mate's fertile period. Furthermore, high rates of copulation were not necessary for pairs to achieve complete fertility of the clutch. Multilocus DNA fingerprinting revealed little evidence for extrapair fertilizations: only 1 of 82 offspring was sired by an extrapair male. These results suggest that male and female Purple Sandpipers rarely seek extrapair copulations (EPCs). In contrast to several recent studies with similar findings, we believe that the apparent rarity of EPCs results because females have few genetic or other benefits to gain from seeking them. Thus, paternity-as- surance behaviors by male Purple Sandpipers were not necessary for achieving full paternity of the clutch, and such behaviors cannot be said to have led to the observed high level of paternal investment in reproduction. Uniparental brood care, however, is associated with a high certainty of paternity in this species. Received 3 June 1997, accepted 13 November 1997.

Normalization of reproductive function in germfree mice following bacterial contamination.

The capacity for reproduction in germfree mice remain inferior to their conventional counterparts even after improvement of feed and other such rearing conditions. The authors provide evidence of increased reproductive capacity in germfree mice following association with bacteria. Estrous cycles were normalized in female mice accidentally contaminated with bacteria, and in mice given fecal suspensions of the accidentally contaminated mice per os. Significant rises were seen in their copulation and implantation rates, reaching levels comparable to values in conventional mice. In male mice, bacterial contamination induced significant increase in sperm motility. Bacteria were identified in the feces of the contaminated mice, and reproductive capacity was examined in mice associated with the identified bacteria. As a result, normalization of the estrous cycle, and rises in copulation and implantation rates were noted in B. distasonis and C. perfringens di-associated mice. Values from B. subtilis mono-associated mice were comparable to those in germfree mice. These results from our accidental contamination indicate that B. distasonis and C. perfringens are capable of normalizing estrous cycles in female germfree mice, and in increasing their reproductive capacity by raising their rates of copulation and implantation.

Effects of prenatal exposure to 5-fluoro-2'-deoxyuridine on developing central nervous system and reproductive function in male offspring of mice.

The effect of 5-fluoro-2'-deoxyuridine (FrdU) on the developing brain and postpubertal reproductive function of male mouse offspring treated prenatally was investigated. FrdU was administered intraperitoneally to pregnant ICR mice at 1.5, 3, 6, 12.5, 25, and 50 mg/kg/day on days 8 through 13 of gestation or 12.5, 25, and 50 mg/kg/day on days 14 through 18 of gestation. Dams were allowed to deliver spontaneously. Dams treated with FrdU at 12.5, 25, and 50 mg/kg/day on days 8 through 13 of gestation did not deliver because of entire intrauterine death of embryos. Male offspring were aged for 10 or 15 weeks and then cohabited with untreated female mice for assessment of reproductive performance. Histological examination of the testis, epididymis, prostate, and seminal vesicle of offspring at 12 weeks of age, and sperm analysis of offspring at 12 or 17 weeks of age were performed. Dose-dependent decreases in body weight gain were noticed throughout the life of offspring. A marked decrease in the copulation rate was noted in the group treated with FrdU at 6 mg/kg/day on days 8 through 13 of gestation. However, neither histological examination of testes and sex-accessory glands nor sperm analysis revealed adverse effects of FrdU on the reproductive function in the male offspring of dams treated with FrdU at 6 mg/kg/day on days 8 through 13 of gestation. There were no significant differences in the relative weight of testes and epididymides between the group treated with FrdU at 6 mg/kg/day on days 8 through 13 of gestation and the control group. Absolute brain weight in the groups treated with FrdU on days 8 through 13 of gestation significantly decreased, while relative brain weight increased in the group treated at 6 mg/kg/day on days 8 through 13, and at 25 and 50 mg/kg/day on days 14 through 18 of gestation. Dilatation of the lateral and third ventricles was observed in all of the male offspring of dams treated with FrdU at 6 mg/kg/day on days 8 through 13 of gestation, when inspected at 12 and 17 weeks of age. In the subsequent study, ICR mice were treated intraperitoneally with FrdU at 6.25-100 mg/kg on day 12 of gestation, and the fetuses obtained 24 h after treatment. Histological observation was performed in the ventricular zone of telencephalon, and in the ependymal and mantle layers of diencephalon in the fetal brain. The incidence of pyknotic cells in these areas was increased linearly with increasing FrdU dose. From these results and our previous findings, we suggest that damage to the central nervous system, a substantial neuronal deficit, resulting from excessive cell death in the developing brain may lead to reproductive dysfunction after puberty.

Extra-pair paternity and tail ornamentation in the barn swallow Hirundo rustica

Females of socially monogamous species may copulate with attractive non-mates to obtain access to the genes of such males, and a preference for attractive copulation partners may result in sexual selection. Extra-pair copulations are common in the socially monogamous barn swallow Hirundorustica, and a 2-year study of paternity using multi-locus DNA fingerprinting demonstrated that 33% of 63 broods and 28% of 261 offspring were sired by extra-pair males. The frequency of extra-pair offspring within broods was highly skewed with the majority of all broods having either no extra-pair offspring or only extra-pair offspring. Individual pairs were consistent in their frequency of extra-pair paternity among broods, and the repeatability of extra-pair paternity of multiple broods of the same female was statistically significant. The proportion of extra-pair offspring was negatively related to the tail length of the male attending the nest. Behavioural observations showed that extra-pair fertilizations were more likely in broods raised by females that had been observed to engage in extra-pair copulations. The frequency of extra-pair offspring was unrelated to the intensity of two male paternity guards, mate guarding and the rate of intra-pair copulations. In an analysis of extra-pair paternity and male parental care in different broods of the same male, male barn swallows fed their offspring relatively less frequently if the brood contained more extra-pair offspring. Therefore, female barn swallows pursue extra-pair copulations with attractive males, which may result in sexual selection, even though extra-pair paternity is costly for females due to the reduction of paternal care by their social mates.

Hormonal Activation of the Striatum and the Nucleus Accumbens Modulates Paced Mating Behavior in the Female Rat

Sexual behavior in the female rat has both sensorimotor and motivational components, which can be distinguished when the female rat is able to pace the rate of copulation. The experiments reported were conducted to determine whether estrogen application to the striatum and/or nucleus accumbens affects pacing behavior. In order to induce sexual receptivity, ovariectomized rats received sequential bilateral implants of 17β-estradiol followed by progesterone into the ventromedial nucleus of the hypothalamus. Then, bilateral implants of 17β-estradiol or cholesterol were administered into either the dorsolateral striatum or the nucleus accumbens. Pacing behavior was tested 4 hr later. It was found that intrastriatal application of estradiol significantly facilitated the percent exits exhibited after copulatory contact, whereas application of estradiol in the nucleus accumbens affected the return latency. To determine whether estrogen in the striatum or nucleus accumbens normally plays a role in pacing behavior, intrastriatal or intra-accumbens implants containing the steroidal antiestrogen ICI 182,780 or vehicle were given to ovariectomized female rats treated systemically with estrogen and progesterone. The antiestrogen treatment decreased the percent exits when delivered to the striatum and affected return latency when delivered to the nucleus accumbens. The results indicate that estrogen acts directly in the striatum and in the nucleus accumbens to differentially modulate specific components of pacing behavior.

Effects of prenatal exposure to 5-bromo-2′-deoxyuridine on reproductive function in male mouse offspring

The effect of the halogenated pyrimidine analog 5-bromo-2′-deoxyuridine (BrdU), on reproductive functions of male mouse offspring treated prenatally was studied. BrdU was administered intraperitoneally to pregnant ICR mice at 100 mg/kg/d on days 8 through 13 of gestation, and at 100 or 200 mg/kg/d on days 14 through 18 of gestation. Dams were allowed to deliver naturally. Male offspring were aged for 10 weeks and then cohabited with untreated female mice for assessment of reproductive performance. Histopathologic examination of the testes and pituitary, sperm analysis, and determination of plasma testosterone concentrations of offspring at 12 weeks of age were performed. In the subsequent study, pregnant ICR mice were treated with 200 mg BrdU/kg on day 10,13, or 15 of gestation. The embryos or fetuses were obtained from mothers from 6 to 48 h after treatment, and pyknotic cells in the ventricular zone of the telencephalon were counted. There was a significant decrease in body weight gain of offspring in all of the BrdU-treated groups. A marked decrease in copulation rate was noted in the male offspring of dams treated on days 8 through 13 of gestation, whereas no significant decreases in copulation and fertility rates were found in the male offspring of dams treated on days 14 through 18 of gestation. Neither histopathologic examination of testes nor sperm analyses revealed adverse effects of this compound, whereas cysts in the pars distalis of the pituitary were observed in the male offspring treated on days 8 through 13 of gestation. Dilatation of the lateral ventricles was also observed in male offspring at 12 weeks of age in the group treated on days 8 through 13 of gestation. The incidence of pyknotic cells in the ventricular zone of embryos was markedly increased 24 h after treatment on day 10 of gestation. These results indicate that the impaired fertility of the male offspring of dams treated with BrdU on days 8 through 13 of gestation may be due to the effects of BrdU exposure on central nervous system function that result in loss of libido rather than to the direct effects of this compound on the male reproductive organs.

Copulation and mate-guarding patterns in polygynous European starlings

We recorded the timing and frequency of copulation and mate-guarding behaviour during the fertile period in relation to day of first ovulation and time of day in the facultatively polygynous European starling,Sturnus vulgarisAll within-pair copulations were female-solicited. Females solicited them at a high rate during both the pre-ovulatory and ovulatory period, but there were differences in solicitation rates between monogamous, primary and secondary females. Extra-pair copulation attempts were all male-initiated and females rarely engaged in them. Attempts by males were most frequent during the ovulatory period, when the probability of extra-pair fertilization was highest. Males intensively guarded their mate during both the pre-ovulatory and ovulatory period. In contrast to most other passerines, female starlings lay their eggs not at dawn but usually between 0900 and 1100 hours, implying that they may be most fertile in the late morning. During the ovulatory period, extra-pair copulation attempts were more frequent in the late morning than in the early morning, suggesting that males try to take advantage of this putative ‘insemination window’. Accordingly, there was some indication that mate guarding during the ovulatory period was more intense in the late than early morning. Females solicited within-pair copulations at a higher rate in the early morning than in the late morning, but copulation rate did not differ between early and late morning. The proportion of monogamous and polygynous males attempting extra-pair copulations did not differ significantly, but mate-guarding intensity differed significantly between female categories. Primary females were guarded less intensively than monogamous females suggesting that males trade mate guarding against mate attraction/courting additional females.

Male Competition, Mating Success and Female Choice in a Seasonally Breeding Primate (Erythrocebus patas)

AbstractMammals with restricted breeding seasons often show brief but intense bouts of male competition for mates and male reproductive success has been attributed to male competitive abilities, with the most aggressively successful males able to control access to fertile females, or with females choosing to mate with such males. We studied male competition, mating behaviour and female mate selection in patas monkeys, a primate with a restricted breeding period. We observed two habituated patas groups in Laikipia District, Kenya, during Jun.‐Aug. 1983. During the study, one group had a single resident male while the other group had multiple adult males. Within the multimale group, experienced adult males were no more successful than the subadult male. The sole resident male had a significantly higher rate of fights won (p < 0.02) although he did not differ from the multimale group males in rate of aggression or initiation of fights. We found no significant differences in either mating success or female preference based on males' experience or residency. The rates at which males copulated with and were solicited by females were not significantly correlated. We found no evidence of stable dominance ranks among males in the multimale group and aggressive success was not significantly correlated with copulation rate for males in the multimale group. Subadult males were responsible for the majority of copulations observed during the final third of the breeding season. Our observations of this patas population showed a fluid number of males in groups, with the same groups able to shift rapidly from single to multimale structure. This fluidity may result from the large fluctuations in numbers of breeding‐age males and females observed over 4 yr of studying this population.

Reproductive effects of prenatal exposure to 5-bromo-2′-deoxyuridine on male rats

5-Bromo-2′-deoxyuridine (BrdU) was administered intraperitoneally to Sprague-Dawley rats at doses of 12.5, 25, 50, or 100 mg/kg/d on days 9 through 15 of gestation, and at 50 or 100 mg/kg/d on days 16 through 20 of gestation. Dams were allowed to deliver naturally and the numbers of live and dead pups were recorded. Male offspring were allowed to mature and then cohabited with untreated female rats for assessment of reproductive performance. Dam body weight gain during pregnancy and lactation periods was not reduced by the treatment with BrdU. Dams treated with 50 and 100 mg BrdU/kg on days 9 through 15 of gestation had litters with decreased survival rates. The male offspring from dams treated with 25, 50, and 100 mg BrdU/kg on days 9 through 15 of gestation had reduced body weights over the course of the entire study. A dose-related decrease in copulation and fertility rates was found in the male offspring of dams treated on days 9 through 15 of gestation, while no significant decrease in those rates were found in the male offspring of dams treated on days 16 through 20 of gestation. Neither histopathologic examination of testes nor sperm examination indicated the cause of the impaired fertility in the male offspring from dams treated with BrdU on days 9 through 15 of gestation. All of the male offspring of dams treated with 100 mg BrdU/kg on days 9 through 15 of gestation failed to copulate, and some of the male offspring of dams treated with 50 mg BrdU/kg on days 9 through 15 of gestation did not form copulatory plugs or formed very small plugs. Dilatation of the lateral ventricles and cysts in the pars distalis of the pituitary were observed in all of the male offspring of dams treated with 100 mg BrdU/kg on days 9 through 15 of gestation. The impaired fertility of the male offspring of dams treated prenatally with BrdU may have resulted from BrdU exposure effects on central nervous system action such as loss of libido and from failure to form proper copulatory plugs, rather than the direct effects of BrdU on the male reproductive organs.

Males on guard: paternity defences in violet-green swallows and tree swallows

Paternity-defence behaviour in two congeners, violet-green swallows, Tachycineta thalassina, and tree swallows, T. bicolor, was compared to identify ecological factors that influence how males avoid being cuckolded. Measurements of the proportion of time that mates spent together, their following behaviour and the rate of within-pair copulations revealed that male violet-green swallows allocated more time to guarding mates than nests and copulated with their mates relatively infrequently, while male tree swallows had opposite patterns. Males of each species were temporarily detained to test whether they faced different levels of competition for nest sites and female mates. Detained male violet-green swallows were more likely to be cuckolded than to lose their nests. Numerous non-territorial male floaters tried to gain access to each unguarded female violet-green swallow by following her, but they did not try to monopolize her nest. Detained male tree swallows suffered high risks of both nest loss and cuckoldry, because male intruders (usually territorial neighbours) tried to usurp the nest and copulate with the unguarded female when she was at the nest. Detained female violet-green swallows were not replaced by unmated female floaters, but detained female tree swallows were replaced. These results suggest that male violet-green swallows faced higher competition for females than for nest sites and benefited more by guarding mates than nests. The reverse was true for tree swallows. Paternity defence behaviour by males of the two species has diverged in response to these different challenges, at least in the populations studied.

INBREEDING DEPRESSION, NEUTRAL POLYMORPHISM, AND COPULATORY BEHAVIOR IN FRESHWATER SNAILS: A SELF-FERTILIZATION SYNDROME.

This paper examines the consequences of self-fertilization on life-history traits and neutral genetic polymorphism in natural populations of three species of hermaphrodite freshwater snails: Biomphalaria straminea, Bulinus globosus, and the aphallic species Bulinus truncatus. Life-history traits (fecundity, growth, hatching rate, and survival of offspring) are compared under laboratory conditions between isolated (obligatory selfing) and paired (outcrossing possible) snails in one population of B. straminea and B. globosus and two populations of B. truncatus. The genetic polymorphism of the same four populations is analyzed using electrophoretic markers in B. straminea and B. globosus and microsatellite markers in B. truncatus. In B. truncatus and B. straminea, isolated snails have a higher fecundity than paired snails, whereas the contrary is observed in B. globosus. For all populations, no difference in hatching rate and offspring survival is detected between the two treatments. Genetic analyses using microsatellite markers conducted in B. truncatus on progeny of paired snails reveal a high selfing rate in spite of high copulation rates, highlighting the difficulties of obtaining outcrossing in highly selfing snails. The high survival of selfed offspring in B. truncatus and B. straminea indicates that inbreeding depression is limited. The extent of inbreeding depression in B. globosus is less clear. Overall, fitness decrease in this species is limited to fecundity. The extent of allozyme polymorphism is very limited whereas a much higher variability is observed with microsatellites. Biomphalaria straminea and B. truncatus populations are also characterized by very low observed heterozygosities and large heterozygote deficiencies, whereas the B. globosus population does not exhibit such a deficiency. Overall these results allow the definition of a self-fertilization syndrome in hermaphrodite freshwater snails: selfing populations (such as those of B. straminea and B. truncatus studied here) are characterized by high selfing rates in spite of copulations, limited deleterious effects of selfing, limited neutral genetic polymorphism, and large heterozygote deficiencies.