Male care,mate switching,and future reproductive success in a double-brooded passerine

Summary In species with male parental care, polygyny may reduce the parental effort provided by a male, and hence impose a cost on the fitness of his mates, because of decreased growth, survival or health of offspring. I examined a cost of polygyny in the green dart-poison frog, Dendrobates auratus, a species with male parental care in which both male polygyny and mate guarding by females occurs (Summers 1989). All D. auratus males seen carrying tadpoles in a marked area were followed and the pools where they deposited their tadpoles were recorded. Males frequently deposited more than one tadpole in the same pool (in 25% of the observed depositions a male deposited a tadpole in a pool where he had previously deposited at least one other tadpole). Experiments involving manipulation of tadpole densities in pools typically utilized by D. auratus (calabash husks and treeholes) showed that increasing tadpole number had a strong negative effect on both growth rate and survivorship, indicating that polygyny can impose a cost on the fitness of a male's offspring. Hence, females do face a potential cost, in terms of reduced offspring growth and survivorship, when their mates mate polygynously and care for the offspring of other females.     

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.     

Testing wetland features to increase amphibian reproductive success and species richness for mitigation and restoration

Aquatic habitat features can directly influence the abundance, species richness, and quality of juvenile amphibians recruited into adult populations. We examined the influences of within-wetland slope, vegetation, and stocked mosquito fish (Gambusia affinis) on amphibian metamorph production and species richness during the first two years post-construction at 18 experimental wetlands in northeast Missouri (U.S.A.) grasslands. We used an information theoretic approach (AICc) to rank regression models representing total amphibian metamorph production, individual amphibian species metamorph production, and larval amphibian species richness. Total amphibian metamorph production was greatest at shallow-sloped, fish-free wetlands during the first year, but shallow-sloped wetlands with high vegetation cover were best the second year. Species richness was negatively associated with fish and positively associated with vegetation in both survey years. Leopard frog (Rana blairi/sphenocephala complex) metamorph quality, based on average metamorph size, was influenced by slope and the number of cohorts in the wetland. However, the tested variables had little influence on the size of American toads (Bufo americanus) or boreal chorus frogs (Pseudacris maculata). Our results indicate that wetlands designed to act as functional reproductive habitat for amphibians should incorporate shallows, high amounts of planted or naturally established vegetation cover, and should be fish-free.     

Testing the priority-of-access model in a seasonally breeding primate species

In mammals, when females are clumped in space, male access to receptive females is usually determined by a dominance hierarchy based on fighting ability. In polygynandrous primates, as opposed to most mammalian species, the strength of the relationship between male social status and reproductive success varies greatly. It has been proposed that the degree to which paternity is determined by male rank decreases with increasing female reproductive synchrony. The priority-of-access model (PoA) predicts male reproductive success based on female synchrony and male dominance rank. To date, most tests of the PoA using paternity data involved nonseasonally breeding species. Here, we examine whether the PoA explains the relatively low reproductive skew in relation to dominance rank reported in the rhesus macaque, a strictly seasonal species. We collected behavioral, genetic, and hormonal data on one group of the free-ranging population on Cayo Santiago (Puerto Rico) for 2 years. The PoA correctly predicted the steepness of male reproductive skew, but not its relationship to male dominance: the most successful sire, fathering one third of the infants, was high but not top ranking. In contrast, mating success was not significantly skewed, suggesting that other mechanisms than social status contributed to male reproductive success. Dominance may be less important for paternity in rhesus macaques than in other primate species because it is reached through queuing rather than contest, leading to alpha males not necessarily being the strongest or most attractive male. More work is needed to fully elucidate the mechanisms determining paternity in rhesus macaques.     

Determinants of male reproductive success in wild long-tailed macaques (Macaca fascicularis)—male monopolisation, female mate choice or post-copulatory mechanisms?

One of the basic principles of sexual selection is that male reproductive success should be skewed towards strong males in species with anisogamous sex. Studies on primate multi-male groups, however, suggest that other factors than male fighting ability might also affect male reproductive success. The proximate mechanisms leading to paternity in multi-male primate groups still remain largely unknown since in most primate studies mating rather than reproductive success is measured. Furthermore, little research focuses on a female’s fertile phase. The aim of this study was to investigate the relative importance of male monopolisation and female direct mate choice for paternity determination. We also investigated the extent to which paternity was decided post-copulatory, i.e. within the female reproductive tract. We used a combined approach of behavioural observations with faecal hormone and genetic analysis for assessment of female cycle stage and paternity, respectively. The study was carried out on a group of wild long-tailed macaques living around the Ketambe Research Station, Gunung Leuser National Park, Indonesia. Our results suggest that both male monopolisation and post-copulatory mechanisms are the main determinants of male reproductive success, whereas female direct mate choice and alternative male reproductive strategies appear to be of little importance in this respect. Female cooperation may, however, have facilitated male monopolisation. Since paternity was restricted to alpha and beta males even when females mated with several males during the fertile phase, it seems that not only male monopolisation but also post-copulatory mechanisms may operate in favour of high-ranking males in long-tailed macaques, thus reinforcing the reproductive skew in this species.     

High degree of paternity loss in a species with alternative reproductive tactics

In many mating systems, males adopt alternative reproductive tactics (ARTs) to maximize reproductive success. In fishes, guarding males often invest more energy into courtship, defense, and paternal care, whereas cuckolding males forego such costs and steal fertilizations by releasing their sperm in the nest of a guarding male. These two tactics have been documented in the plainfin midshipman fish (Porichthys notatus), yet the relative reproductive success of the guarding and cuckolding male tactics remains unknown. In this study, we used microsatellite markers to determine the level of paternity of the guarding type I males. We explored how paternity varied with male phenotype and across the breeding season. Our results revealed the lowest documented levels of paternity in a species with obligate paternal care. Although paternity remained consistently low, it did increase as the breeding season progressed. Male body size did not significantly predict paternity. The low paternity in this species may be explained, in part, by aspects of their reproductive ecology including the duration of parental care period, limited nest availability and competition for nests, as well as the occurrence of nest takeovers. Overall, our findings contribute to the understanding of the ultimate factors underlying ARTs in this species and highlight the importance of investigating reproductive success across the entire breeding season.     

Parent-offspring resemblance in degree of sociality in a passerine bird

The tendency to aggregate with conspecifics is a common type of social behavior, and interspecific differences in degree of sociality may indicate that evolutionary changes in sociality have been shaped by past selection pressures. A pre-requisite for such evolutionary change is that the behavior in question has an additive genetic basis. I investigated parent-offspring resemblance in two characteristics of sociality (colony size and nearest neighbor distance) in the semi-colonial barn swallow Hirundo rustica. Heritability estimates of these phenotypic characters were statistically significant. Offspring that were transferred to foster nests as part of brood size manipulation or cross-fostering experiments resembled their original parents more than their foster parents with respect to sociality. There was little evidence of phenotypic characteristics of mothers being significantly related to colony size or nearest neighbor distance of their offspring. Maintenance of genetic variation in sociality in this species may be related to the facts that the relationship between reproductive success and colony size differs among years, and that individuals differing in phenotypic quality have different optimal colony sizes.     

The effect of perceived female parasite load on post-copulatory male choice in a sex-role-reversed pipefish

The last several decades of research in behavioral ecology have resulted in a deeper appreciation of post-mating processes and sexual conflict in sexual selection. One of the most controversial aspects of sexual selection is cryptic mate choice. Here, we take advantage of male pregnancy in a sex-role-reversed pipefish (Syngnathus typhle) to quantify cryptic choice based on perceived parasite load and other sources of variance in female fitness. Studies have shown that S. typhle males preferentially mate with females with lower parasite loads and that a male’s perception of female parasite load can be altered by tattooing females. We manipulated the apparent parasite load of females in controlled mating experiments to test the hypothesis that post-copulatory sexual selection is dependent on a male’s perception of female parasite load in pipefish. Our results provided no evidence for cryptic male choice based on perceived female parasite load. However, we found evidence that eggs from larger females were more likely to result in viable offspring than eggs from smaller females and that the first female to mate with a male transferred more eggs per copulation on average. Overall, our results show that potential for post-copulatory sexual selection does exist in pipefish, but the male’s perception of female parasite load does not play a major role in this process.     

Evidence of obligate female promiscuity in a socially monogamous passerine

Extrapair paternity in birds has been the focus of an increasing number of studies over the last decades. Nevertheless, there is little knowledge about extrapair copulation (EPC) behavior. In this study, we investigate whether female bluethroats (Luscinia s. svecica) with no extrapair offspring (EPO) in their broods really have been sexually monogamous or if they have copulated with extrapair males. We used an experimental approach to prevent transfer of sperm from the social male during copulation by fitting a rubber tube around the cloaca of randomly chosen males. If the females mated to these males do not participate in EPCs, they will produce infertile eggs, whereas females that copulate with extrapair males will only produce EPO. We found that 87% (n=15) of the experimental pairs compared to only 36% (n=51) of unmanipulated pairs produced EPO. Our result therefore suggests that females having no EPO may still have copulated with extrapair males and that promiscuity may be an obligate sexual strategy among bluethroat females.Communicated by S. Pruett-Jones     

Fitness consequences of pre- and post-fledging timing decisions in a double-brooded passerine

The fitness consequences of a delayed timing of breeding are expected to affect the temporal characteristics of the whole annual breeding system. One major problem in quantifying the fitness relevance of timing is that individual differences between pairs may cause the seasonal trend. Differentials in juvenile survival due to pre-fledging timing decisions often only appear after fledging of the chicks. Therefore, timing decisions in the post-fledging period, i.e., the duration of parental care, might additionally influence juvenile survival. We tested the effects of timing and parental competence on the post-fledging survival of second-brood juvenile Barn Swallows (Hirundo rustica L.) by swapping earlier and later hatching clutches and radio-tracking the juvenile subjects. The mark-recapture models controlled for the effects of duration of post-fledging care and food availability. There was an annually varying negative seasonal trend in offspring survival that was associated with environmental conditions. Directional selection for early breeding occurred in the two years with scarce autumnal food supply. Furthermore, we found strong selection for long post-fledging parental care. The duration of care neither declined seasonally, nor did longer care compensate for the seasonal decline of juvenile survival. Hence, the reproductive output three weeks after fledging was determined by two parental timing decisions: the timing of breeding and the timing of family breakup. We suggest that differential survival of second-brood fledglings in relation to these decisions is an important part of the selective mechanisms shaping the reproductive system of Barn Swallows.     

Context-dependent genetic benefits of extra-pair mate choice in a socially monogamous passerine

Extra-pair paternity is common in socially monogamous passerines; however, despite considerable research attention, consistent differences in fitness between within-pair offspring (WPO) and extra-pair offspring (EPO) have not been demonstrated. Recent evidence indicates that differences between maternal half-siblings may depend on environmental conditions, but it is unclear whether the influence of paternal genetic contribution should be most apparent under comparatively poor or favourable conditions. We compared phenotypic characteristics of WPO and EPO in 30 mixed-paternity broods of the tree swallow (Tachycineta bicolor) in relation to experimentally increased nest temperature (n = 13 heated nests; 17 control nests) and natural abundance of haematophagous parasites (Protocalliphora spp.). This allowed us to test the hypothesis that genetic benefits of extra-pair mating are environment dependent. EPO grew their ninth primary feathers faster than WPO regardless of nest temperature or parasite load and had significantly longer ninth primary feathers at fledging when parasite abundance was low, and when they were positioned early in the hatching sequence relative to WPO. In contrast, WPO under similar conditions did not differ from EPO in any phenotypic trait measured. These results indicate that the fitness benefits of extra-pair mating are likely to be context dependent, and that genetic effects on some phenotypic traits may be more apparent when conditions are relatively favourable.     

Brooding behaviour and reproductive success in two species of free-living simultaneous hermaphrodites

Although polyclads are amongst the most structurally simple of the triploblastic metazoans, they adopt a wide range of reproductive strategies. Parental care behaviour in this group is yet to be quantified for any species. We assessed the significance of brooding behaviour to the reproductive success of two free-living marine flatworms. Echinoplana celerrima and Stylochus pygmaeus were collected from the field and placed in pairs in containers of filtered seawater where they laid batches of eggs. Both parents were then removed from half of the containers and the brooding behaviour and hatching success of eggs were quantified. There were interspecific differences in brooding behaviour. Egg masses were covered by one E. celerrima parent for 12 ± 2% of time, whereas egg masses of S. pygmaeus were covered by one or both parents simultaneously for 85 ± 8% of time. Egg batches were abandoned by both species immediately prior to the onset of hatching (10–12 days). Hatching success was generally high (~90%) and brooding did not enhance the hatching success of eggs. We assessed the significance of parental care to hatching success of E. celerrima egg masses in the presence of three potential egg predators; in the presence of other organisms. E. celerrima devoted less time to brooding; however, hatching success was not affected. The amount of time spent brooding eggs differed greatly between the two polyclad species but was not essential to their reproductive success under benign conditions. Parental care may be of adaptive value under more stressful environmental conditions commonly experienced in estuarine environments such as lowered salinity, increased hypoxia or turbidity. Covering egg batches may play an additional role of advertising sexual status and a willingness to care for eggs.     

Duplex auditory distance assessment in a small passerine bird (Pipilo erythrophthalmus)

Eastern towhees, Pipilo erythrophthalmus, (Emberizidae, Passeriformes) in Florida estimate source sound-pressure level (SPL; i.e., sound amplitude) and often misjudge speaker distance in the field when vocalization source SPL is varied experimentally. Sound frequencies below ~3.5 kHz attenuate reliably with distance in comparison with higher sound frequencies in Florida scrub habitat. As a result, I predicted that towhees should use SPL as an auditory distance cue when they hear stimuli produced with sound frequencies below ~3.5 kHz but use another cue when they hear stimuli produced with sound frequencies above ~3.5 kHz. Subjects often misjudged speaker distance when approaching playbacks of SPL-altered stimuli produced with sound frequencies below ~3.5 kHz but rarely misjudged speaker distance when played SPL-altered stimuli produced with sound frequencies above ~3.5 kHz. I discuss the possibility that towhees employ a duplex sound localization strategy.     

Female-specific colouration, carotenoids and reproductive investment in a dichromatic species, the upland goose Chloephaga picta leucoptera

Although studies on the evolution and function of female ornaments have become more numerous in the last years, the majority of these studies were carried out in cases where female ornaments were a smaller and duller version of the ornaments found in males. There are substantially fewer studies on species with female-specific ornaments. However, no study so far investigated the potential of female-specific colouration as a quality signal in birds with conventional sex roles. We studied female-specific ornamentation in a strongly sexually dichromatic species, the upland goose Chloephaga picta leucoptera, in two consecutive years. Male upland geese have white head and breast feathers and black legs, whereas females have reddish-brown head and breast feathers and conspicuous yellow-orange legs. We found that female-specific colouration in upland geese can reliably indicate different aspects of female phenotypic quality. Females with more orange coloured legs and more red-like head colours had higher clutch and egg volumes than females with a paler leg and head colouration, and a more reddish plumage colouration was related to a higher body condition. These relationships provide the theoretic possibility for males to assess female phenotypic quality on the basis of colouration. Furthermore, the females with a more orange-like tarsus colouration had higher plasma carotenoid levels. Both tarsus colouration and carotenoid concentrations of individual females were highly correlated across years, indicating that tarsus colour is a stable signal. Despite this correlation, small individual differences in plasma carotenoid concentrations between the two study years were related to differences in tarsus colouration. We thus show for the first time in a wild bird and under natural conditions that carotenoid-based integument colouration remains consistent between individuals in consecutive years and is also a dynamic trait reflecting individual changes in carotenoid levels. In this species, where pairs form life-long bonds, the honesty of the carotenoid-based integument colouration suggests that it may be a sexually selected female ornament that has evolved through male mate choice.     

Patterns of brood division and an absence of behavioral plasticity in a neotropical passerine

Studies of parental behavior in various habitats provide an opportunity to gain insight into how different environments may mold strategies of parental care. Brood division by parents has been hypothesized to occur facultatively within and among species. Brood division occurs when each parent cares for specific offspring within a brood. We studied brood division in a neotropical passerine, the western slaty antshrike (Thamnophilus atrinucha). Our results present a unique picture of a highly specialized example of avian brood division. Division was a fixed behavioral pattern in the population studied: all broods divided by fledging and remained divided during the entire post-fledging period. Brood division before fledging, a previously unreported phenomenon, occurred in 40% of nests observed. Parents that preferentially fed a certain offspring (defined as their focal offspring) in the nest fed the same individual after fledging. Each parent fed only its focal offspring in broods of one and two. The male parent cared for the heavier offspring and the first offspring to leave the nest. Siblings were segregated spatially during the time of highest predation risk. These observations suggest that a consistently high risk of predation on offspring has favored initial spatial segregation and inflexibility of brood division behavior in this species. Factors other than predation risk alone may explain the observed patterns of long-term, perfect brood division. Because high predation is common and relatively predictable in the tropics, selection for fixed brood division may be stronger in tropical birds than in the temperate zone.     

Offspring sex ratios reflect lack of repayment by auxiliary males in a cooperatively breeding passerine

The repayment hypothesis posits that primary sex ratios in cooperative species should be biased towards the helping sex because these offspring “repay” a portion of their cost through helping behavior and therefore are less expensive to produce. However, many cooperatively breeding birds and mammals do not show the predicted bias in the primary sex ratio. Recent theoretical work has suggested that the repayment hypothesis should only hold when females gain a large fitness advantage from the presence of auxiliary adults in the group. When auxiliaries provide little or no fitness advantage, competition between relatives should lead to sex ratios biased towards the dispersing (non-helping) sex. We examined the benefits auxiliaries provide to females and corresponding offspring sex ratios in the red-backed fairy-wren (Malurus melanocephalus), a cooperatively breeding Australian bird with male auxiliary helpers. We found that auxiliaries provide little or no benefit to female reproductive success or survival. As predicted, the population primary sex ratio was biased towards daughters, the dispersing sex, and females with auxiliaries produced female-biased broods whereas females without auxiliaries produced unbiased broods. Moreover, offspring sex ratios were more strongly biased toward females in years when auxiliaries were more common in the population. These results suggest that offspring sex ratios are associated with competition among the non-dispersing sex in this species, and also that females may use cues to assess local breeding opportunities for their offspring.     

Voices in the dark: predation risk by owls influences dusk singing in a diurnal passerine

Predation is an important cost of communication in animals and thus a potent selection pressure on the evolution of signaling behavior. Heterospecific eavesdropping by predators may increase the vulnerability of vocalizing prey, particularly during low light, such as at dusk when nocturnal predators are actively hunting. Despite the risk it entails, dawn and dusk chorusing is common in passerines. However, the dusk chorus has not been studied much, neglecting the opportunity for understanding how eavesdropping between predators and prey may shape communication in birds. Here, we report the first demonstration of simulated predation risk (playback of owl vocalizations) altering the dusk chorus of a diurnal passerine, the veery (Catharus fuscescens). Veeries have a pronounced dusk chorus, singing well after sunset and potentially exposing themselves to predation by owls. In response to brief playbacks of owl calls (~30 s of calls presented three times over 25 min), veeries sang fewer songs post-sunset and stopped singing earlier relative to control trials. These changes in singing remained evident 30 min after the last owl stimulus. Although the avian dusk chorus has received relatively little attention to date, our results suggest that the dusk chorus may pose a higher predation risk to singing males that may influence the evolution of singing behavior in diurnal birds.     

Testing hypotheses of exponential growth and size-dependent molting rate in two copepod species

Individual copepodids from nature of the lipidstoring, monocyclic, diapausing Calanus glacialis, and from nature and laboratory culture of the non-storing, polycyclic Eurytemora herdmani (both collected new Halifax, Nova Scotia in 1987 and 1988) were reared in excess food at ca. 3 and 10 °C. Soon after molts, prosome lengths and weights [total dry wt (TW) of E. herdmani; structural wt (SW) and estimated oil-sac wt (OSW) of C. glacialis] were measured. Stage durations were close to published temperature-dependent predictions; C. glacialis (almost all females) did not enter resting stages. Growth of body length was linear and of body weight (TW or SW) was exponential, with no sexual difference in E. herdmani. There were mixed effects of sizes on stage durations of individuals: weakly positive at 3 °C (but not significant at ca. 10°C) for length and SW of C. glacialis and generally weakly negative for E. herdmani, except for TW at 10 °C. Body condition (residuals of log SW vs log length) of C. glacialis at ca. 10°C, unlike length or SW, was negatively related to stage duration. There was no relationship between length-corrected SW and OSW in C. glacialis. The various results appear to suggest that health was more important than allometric constraints on growth rates of individuals. However, copepods reared at temperatures very different from those previously experienced may show long-term adjustments of size, whereas development rates respond immediately. If so, only the weakly positive effects on stage durations of length of C. glacialis at ca. 3 °C and of TW of E. herdmani at ca. 10 °C may illustrate expectations under stable temperatures and adequate food in nature.     

Long-term effects of yolk androgens on phenotype and parental feeding behavior in a wild passerine

Early growth conditions, such as exposure to maternally derived androgens in bird eggs, have been shown to shape offspring in ways that may have important long-term consequences for phenotype and behavior. Using an experimental approach, we studied the long-term effects of yolk androgens on several phenotypic traits and parental behavior in adult and female collared flycatchers (Ficedula albicollis). We elevated yolk androgen levels and monitored the experimental recruits the following breeding seasons. Androgen treatment had a sex-dependent effect on adult body condition, yolk androgen-treated males being heavier than control males when controlling for size, a result which may be caused potentially by selective mortality, physiological differences, or different life-history strategies. Androgen treatment did not however affect the expression of sexually selected plumage ornaments (forehead and wing patch size), UV coloration, or parental feeding rate in either sex. Our results suggest that yolk androgens are unlikely to affect sexual selection via plumage characteristics or contribute to breeding success via altered parental care. Yolk androgens do not seem to act as a means for female collared flycatchers to enhance the attractiveness of their sons. The lower return rate previously observed for androgen-treated male offspring compared to controls may therefore not be due to lower mating or breeding success, but may rather reflect lower survival or higher dispersal propensity of yolk androgen-treated males.