High paternal investment in unrelated young: extra-pair paternity and male parental care in house martins

The response of males to reduced paternity has important consequences for the evolution and maintenance of a mixed reproductive strategy. Paternity is predicted to affect directly the level of male parental care in some cases but not in others. The response of males to reduced paternity will be influenced by their ability to assess their paternity, the predictability of cuckoldry and the costs and benefits of parental care. Although male house martins (Delichon urbica) provide among the highest levels of male parental care known in passerines (incubation, brooding and feeding nestlings), there was no evidence that cuckolded males substantially reduced their level of parental care, and, as a result, all young fledged successfully. Thus, extra-pair fertilizations enhanced the reproductive success of some males because they were able to parasitize the parental care of cuckolded males. We discuss several conditions which may favor extensive male parental care even when the male's paternity is very low.     

Testosterone-induced depression of male parental behavior in the barn swallow: female compensation and effects on seasonal fitness

In birds, many aspects of male socio-sexual and parental behavior are influenced by androgens, most notably testosterone (T). We report the effects of subcutaneous T-implants in male barn swallows (Hirundo rustica) on male and female parental behavior and on seasonal reproductive success. Males were assigned to one of three experimental groups: (i) implanted with a T-filled Silastic tube; (ii) implanted with an empty Silastic tube; and (iii) not implanted. T-implanted males provided a smaller proportion of feedings (number of feedings by the male/total number of feedings by both parents) and fed nestlings less frequently (number of feedings/h) than males of the other two groups. Females paired to T-implanted males fed nestlings significantly more often than females paired with unimplanted males. Females almost fully compensated for their mates' shortfall, and this resulted in similar combined feeding efforts among treatments. Reproductive success in their first broods or during the entire breeding season was unaffected by T- treatment. These results confirm earlier reports of the suppressive effects of T on male parental behavior. However, they are inconsistent with current ESS models that predict partial compensation as the optimal response by one individual to reduction of parental effort by its mate in monogamous, biparental systems.     

Mate compatibility,parental allocation and fitness consequences of mate choice in the sand goby <Emphasis Type="Italic">Pomatoschistus minutus</Emphasis>

Recent theory and empirical work suggests that there may be variation among females in mate preferences that is adaptive. One of the possible mechanisms maintaining variability in preferences and preferred traits is that the benefits of mate choice may depend on compatibility with potential mating partners. We examined fitness consequences of mate choice in a species of fish, the sand goby, Pomatoschistus minutus with a special focus on mate compatibility. Females were given the opportunity to establish their mate preferences in a dichotomous mate choice experiment. This information was then applied by mating the focal or control female with either the preferred or the non-preferred male. The parental performance of the males of these four mating combinations was then measured. In a separate experiment, we assessed the female differential allocation by determining the residual gonad weight of spawned females as a measure of the proportion of eggs spawned. We also estimated the amount of filial cannibalism separately for both sexes. Our results show that preferred males provided benefits in the form of an increased number of hatching eggs. This benefit was the same when the male was mated with a focal or a control female. Hence, we found no support for benefits that depend on mate compatibility. Neither did we find support for the hypothesis that females would lay a different number of eggs depending on the male status. The results also indicate that male filial cannibalism has a strong role in determining hatching success in this species.     

Non-adaptive adoptions of nestlings in the colonial lesser kestrel: proximate causes and fitness consequences

We examined the causes, costs and benefits of adoption in the altricial lesser kestrel Falco naumanni. Specifically, we tested the intergenerational conflict hypothesis, proposed to explain adoption in some birds. Adoptions involved 76% of the nests and 51% of the nestlings at a mean age of 25 days (12 days before fledging). Nest-switching nestlings were not in poorer body condition, more parasitized or younger than their siblings, and body condition and prey delivery rates of their parents did not differ from those of other parents. In the foster nest, adopted nestlings did not benefit from higher feeding rates or a prolongation of the nestling period. They did not have fewer nest-mates or achieve higher rank within the new brood. Thus, adopted nestlings did not improve their body condition and survival. Adult lesser kestrels seemed unable to finely discriminate beween their own and alien chicks. Foster parents bore the cost of an increase of prey delivery rates, although it did not affect their survival or subsequent reproductive performance. Therefore, our results do not support the intergenerational conflict hypothesis, and suggest that adoption in this species is non-adaptive. Traditionally, the lesser kestrel bred in cliffs where movement among nest-sites was restricted. Nowadays, about half of the colonies are in tiled roofs which facilitate nest-switching by nestlings. The high rate of adoptions may thus be explained as reproductive errors associated with the recent occupation of a new breeding habitat. Received: 3 May 1996 / Accepted after revision: 19 January 1997     

Defending young biparentally: female risk-taking with and without a male in the burying beetle, <Emphasis Type="Italic">Nicrophorus pustulatus</Emphasis>

A positive correlation between the parental effort of a male and female should promote stable biparental care. Risk-taking (as assessed by injuries) against infanticidal intruders by Nicrophorus pustulatus females was expected to be low when females had a low probability of successful defense of the young. I tested the hypothesis that when the presence of a male partner increased the probability of successful defense from low to moderate that female risk-taking would increase. Single females and pairs with first instar larvae were confronted by potentially infanticidal male and female conspecific intruders. Male intruders routinely took over nests from unpaired females (30 of 36 trials). Unpaired females and male intruders were injured infrequently, indicating less intense fights despite the high probability of infanticide. A resident female defending against a male intruder was injured more often when paired than unpaired, suggesting greater risk-taking. A male parent that delays desertion, therefore, receives fitness benefits not only from his own defense of the young, but from greater female defense against male intruders as well. It is hypothesized that the threat of infanticidal takeovers by males promotes extended biparental care in burying beetles. When the intruder was female, on the other hand, a female parent on her own had a moderate probability of successfully defending the brood (22 of 36 trials). The presence of a male partner against female intruders almost guaranteed successful defense (35 of 36 trials) and female intruders did not appear to contest pairs vigorously. Against female intruders the presence of a male partner did not significantly change injury rates of the defending female.     

Independent effects of male and female density on sexual harassment, female fitness, and male competition for mates in the western mosquitofish Gambusia affinis

Operational sex ratio (the ratio of sexually active males to fertilizable females) has a major influence on male competition for mates and male–female interactions. The contributions of male and female density per se to mating system dynamics, however, are rarely examined, and the fitness consequences are often inferred rather than quantified. Male mosquitofish (Gambusia affinis) compete aggressively and frequently harass females for copulations, a behavior thought to reduce female fitness. Female fitness can also be reduced by increases in female density, which may affect food availability, cannibalism rates, and chemical interactions between females. I manipulated male and female densities of G. affinis to measure their effects on male–male aggression, male harassment toward females, and female fitness. I found that males chased rivals more often and attempted fewer copulations when female density decreased, but surprisingly male density had no significant effect on the frequency of these male behaviors. In contrast, males’ agonistic displays toward other males increased with male density, but display behavior was unaffected by female density. These results suggest that male and female density do not always contribute equally or at all to the patterns of behavior we observe. Female fitness declined as female density increased, the opposite pattern expected if male harassment is costly to females. This suggests that a strong, negative effect of female density overwhelmed any potential costs of male harassment. Sources of female density dependence and the consequences of changes in male and female density to patterns of male behavior are discussed.     

Antipredator responses of California ground squirrels to rattlesnakes and rattling sounds: the roles of sex,reproductive parity,and offspring age in assessment and decision-making rules

California ground squirrels (Spermophilus beecheyi) and northern Pacific rattlesnakes (Crotalus viridus oreganus) have an adversarial relationship. Adults are partially protected by venom resistance and harass rattlesnakes in part to defend their more vulnerable offspring. Larger, warmer snakes are more dangerous than smaller colder snakes, and in escalated conflict squirrels could benefit from risk assessment strategies. Rattlesnakes often rattle at harassing squirrels and rattling sounds produce cues related to body size and temperature. In study 1 we played back rattling sounds from snakes that varied in dangerousness and evaluated the roles of sex and parity in squirrel risk assessment strategies. In general, squirrels tail flagged and stood bipedally more, and were slower to reapproach the playback speaker following playbacks of rattling sounds from more dangerous snakes. In comparison with males and nonmothers, mothers were most responsive to rattling sounds and more sensitive to variation in snake dangerousness. Mothers tail flagged more than males and nonmothers, and this behavior tracked variation in snake dangerousness most closely, perhaps reflecting the effects of snake size and temperature on pup vulnerability. These findings suggest that many aspects of squirrel antisnake behavior are governed by their effects on descendant kin. In study 2 we tested the effects of offspring age on mothers responses to live rattlesnakes and rattling sounds. According to the offspring value hypothesis, mothers should take more risks in defense of older offspring because they are more likely to survive to reproductive age. By contrast, under the offspring vulnerability hypothesis, older offspring are less vulnerable to predators and thus mothers should take fewer risks. Risk-taking, as measured by behaviors that bring the squirrel close to the snakes strike range, was either unaffected by or negatively correlated with offspring age. Thus, our findings suggest that whereas offspring value is unimportant in squirrel antisnake behavior, offspring vulnerability may affect maternal defense. We suggest that offspring vulnerability in mammals, in comparison with birds, may play a larger role in parental defense against predators.Communicated by P.A. BednekoffAn erratum to this article can be found at     

Preference for male traits in female wolf spiders varies with the choice of available males,female age and reproductive state

Individual variation in female preference for male traits may influence mate choice, especially if benefits and costs of choosiness vary with the range of available males or reproductive timing. We examined variation in female preference for male leg tuft size in Schizocosa ocreata (Hentz) wolf spiders with video playback. Dichotomous (simultaneous) choice test experiments included all possible combinations of four stimuli (i.e., modified versions of the same video male stimulus): average tuft size (control), reduced (−25%), enlarged (+25%), and no tufts (removed). Females exhibited a directional preference for larger tuft size independent of the nature of the choice (except for reduced tufts vs no tufts where no difference was seen). Female preference in the short term (over a period of 4 days) was also highly repeatable for control vs reduced tufts, but not for control vs enlarged tufts. Responses of females in ‘no-choice’ presentations of a single (control) male stimulus varied with age post-maturity; females were less receptive in weeks 1 and 2, highly receptive at week 3, and less thereafter. Mated females were least receptive and most aggressive towards a male stimulus. Females offered choices repeatedly at different ages post-maturity consistently preferred the control male vs reduced tufts over all 3 weeks but varied in their preference for enlarged tufts vs control male. In the first 2 weeks, females preferred the enlarged tuft male stimulus, but showed no preference by the third week. Females tested in week 4 showed no preference in either choice. Results suggest that the potential interaction between female preference for male traits and female reproductive timing may be a critical consideration in mate choice.     

Sex in the dark: determinants and consequences of mixed male mating tactics in<Emphasis Type="Italic"> Microcebus murinus</Emphasis>, a small solitary nocturnal primate

In mammals with solitary females, the potential for males to monopolize matings is relatively low, and scramble competition polygyny is presumed to be the predominant mating system. However, combinations of male traits and mating tactics within this type of polygyny have been described. The main aim of our study was to identify the relative importance of, and interactions among, potential determinants of contrasting male reproductive tactics, and to determine their consequences for male reproductive success in a small solitary nocturnal Malagasy primate, the gray mouse lemur (Microcebus murinus). We studied their mating behavior over three consecutive annual mating seasons. In addition, we determined the genetic relationships among more than 300 study animals to quantify the reproductive success of individual males. We found that, with a given relatively low overall monopolization potential, successful male mouse lemurs roamed extensively in search of mates, had superior finding ability and mated as early as possible. However, contest competition was important too, as temporary monopolization was also possible. Males exhibited different mating tactics, and heavier males had a higher reproductive success, although most litters had mixed paternities. Switching between tactics depended on short-term local variation in monopolization potential determined by a pronounced dynamic in fertilization probability, number of alternative mating opportunities, and the operational sex ratio. This study also revealed that the dynamics of these determinants, as well as the mutual interactions between them, necessitate a detailed knowledge of the mating behavior of a species to infer the impact of determinants of alternative mating tactics.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by S. AlbertsThis revised version was published online in August 2004 with corrections to Figure 2.