Microsatellite identification of extrapair sires in a socially monogamous warbler

Few studies of avian mating systems have identified the siresof extrapair young, and hence it has been difficult to determinethe scale at which reproductive interactions occur. For instance,females may be free to copulate with any male in the population(a "global" scale of interactions), or females may be restrictedto copulating only with males on neighboring territories (a"local" scale). The scale of such interactions has importantconsequences for an understanding of the evolutionary causesand consequences of extrapair fertilizations. We used five hypervariable microsatellite loci and multilocus DNA fingerprintingto examine parentage of more than 400 nestling black-throatedblue warblers (Dendroica caerulescens). Extrapair fertilizationswere common, and the microsatellite markers allowed us to identifythe sires for 89% of the young analyzed. Most identified extrapairsires were males on neighboring or nearby territories, andmost nestlings for whom we could not identify a sire came fromterritories at the edge of the study plot. Thus, reproductive interactions appear to be more local than global in this population.Extrapair fertilizations contributed significantly to totalvariation in male reproductive success. However, the standardizedvariance in male reproductive success (0.68-0.74) was not substantiallygreater than that for females (0.53-0.60), and the contributionof extrapair fertilizations (9-14%) was much lower than thecontribution of within-pair fertilizations (75-77%). This suggeststhat the local scale of reproductive interactions may limitvariation in male reproductive success and hence the opportunityfor selection.     

Extra‐pair fertilizations contribute to selection on secondary male ornamentation in a socially monogamous passerine

Despite considerable research effort, it remains unclear whether extra‐pair fertilizations (EPF) drive the evolution of male secondary ornamentation in socially monogamous systems. In this study, we test the hypothesis that EPF contribute to the evolution or maintenance of male feather ornamentation in a sexually dichromatic passerine, the Scarlet Rosefinch, Carpodacus erythrinus. We show that the colouration of ornamental breast feathers is a good predictor of basic sources of variation in male annual reproductive output in rosefinches and that the annual realized reproductive success of males is positively associated with measures of ornamental colouration only when gains and losses because of EPF are considered. The results indicate that EPF in rosefinches may rely on absolute (good genes) rather than self referential (genetic complementarity) criteria of mate choice. Our study corroborates the potentially important role of EPF in the evolution and/or maintenance of elaborate male ornaments in socially monogamous taxa.     

Sexual selection and extrapair fertilization in a socially monogamous passerine, the zebra finch (Taeniopygia gullata)

We investigated paternal exclusion rate (the percentage of youngreared by a male that were not his genetic offspring), and behavioraland reproductive variables influencing this rate, in a freelybreeding laboratory population of zebra finches (Tae-niopygiaguttala castanotis), a socially monogamous grassfinch. Priorto the experiment, each male founder was fitted with eithertwo red bands (creating a phenotype previously demonstratedto be attractive to females) or two green bands (unattractiveto females) as part of a unique combination of four leg bands.The overall paternal exclusion rate was 28%, as determined bymultilocus, minisatellite DNA fingerprinting of 278 offspringreared by 26 males and their mates. Mean exclusion rates were16% and 40% for red- and green-banded males, respectively. Exclusionrates were directly proportional to rates of female participationin unforced extrapair copulations (UEPCs) with red-banded malesthat occurred when females were fertile. Rates of fertile, forcedextrapair copulations (FEPCs) and fertile UEPCs involving green-bandedmales either failed to influence exclusion rate or varied inverselywith exclusion rate, indicating that extrapair fertilization(EPF) is under female control. Effort devoted by males to seekingEPFs increased exclusion rate. Results suggest that males placegreater effort into seeking fertile versus infertile EPCs andthat unattractive males accrue fitness gains through high parentalinvestment (PI), whereas attractive males benefit through decreasedPI and increased allocation to EPF.     

The evolution of infidelity in socially monogamous passerines: neglected components of direct and indirect selection

A recent study by Goran Arnqvist and Mark Kirkpatrick in the American Naturalist (165:S26-S37) suggested that female polyandry in birds is not driven by females because quantitative genetic approximations of selection demonstrated that indirect selection for female infidelity is weaker than natural selection against it. Instead, it was argued that extrapair copulations are the result of antagonistic selection on male behavior driving female coercion. While the approach and framework of the study were very good, the conclusions of the study were premature because a number of potential adaptive components of polyandry were unaccounted for, and several critical assumptions are unsupported by the current empirical data. Our understanding of extrapair paternity in birds, and perhaps polyandry in general, will be improved by a better empirical understanding of the direct benefits of fertility assurance and postcopulatory cryptic female choice and the relationship between polyandry and male investment. In addition, we need to develop a greater awareness of the limitations of trying to study behavior by proxy in the molecular laboratory. Together, these challenges and the framework recently presented should improve our understanding of the true function of extrapair paternity in birds.     

Ecological, social, and genetic contingency of extrapair behavior in a socially monogamous bird

Extrapair mating strategies are common among socially monogamous birds, but vary widely across ecological and social contexts in which breeding occurs. This variation is thought to reflect a compromise between the direct costs of mates' extrapair behavior and indirect benefits of extrapair fertilizations (EPF) to offspring fitness. However, in most free-living populations, the complete spatial and temporal distribution of mating attempts, genetic characteristics of available mates, and their relative contribution to EPF strategies are difficult to assess. Here we examined prevalence of EPF in relation to breeding density, synchrony, and genetic variability of available mates in a wild population of house finches Carpodacus mexicanus where all breeding attempts are known and all offspring are genotyped. We found that 15% of 59 nests contained extra-pair offspring and 9% of 212 offspring were sired by extra-pair males. We show experimentally that paired males and females avoided EPF displays in the presence of their social partners, revealing direct selection against EPF behavior. However, at the population level, the occurrence of EPF did not vary with nests dispersion, initiation date, synchrony, or with distance between the nests of extrapair partners. Instead, the occurrence of EPF closely covaried with genetic relatedness of a pool of available mates and offspring of genetically dissimilar mating tended to be resistant to a novel pathogen. These results corroborate findings that, in this population, strong fitness benefits of EPF are specific to each individual, thus highlighting the ecological, social, and genetic contingency of costs and benefits of an individual's extrapair behaviors.     

Long-term fitness consequences of female extra-pair matings in a socially monogamous passerine

Whether female birds choose extra-pair mating partners to obtain genetic fitness benefits is intensely debated. The most straightforward and crucial test of 'good genes' models of female extra-pair mating is the comparison of naturally 'cross-fostered' maternal half-siblings sharing the same rearing environment as any systematic differences in performance between the two categories of offspring phenotype can be attributed to differential paternal genetic contribution. We analysed local recruitment and first-year reproductive performance of maternal half-siblings in the coal tit (Parus ater), a passerine bird with high levels of extra-pair paternity. We provide a highly comprehensive measure of the long-term fitness consequences of female extra-pair matings based on a large sample of 736 within-pair offspring (WPO) and 368 extra-pair offspring (EPO) from 91 first and 55 second broods, from which 132 breeders recruited into the study population. In contrast to predictions derived from 'good genes' models, we found no differences in local recruitment and seven parameters of first-year reproductive performance when comparing WPO and EPO. These results question the universal validity of findings in other bird species supporting 'good genes' models, particularly as they are based on the best approximation to female fitness obtained so far.     

Harvesting of males delays female breeding in a socially monogamous mammal; the beaver

Human exploitation may skew adult sex ratios in vertebrate populations to the extent that males become limiting for normal reproduction. In polygynous ungulates, females delay breeding in heavily harvested populations, but effects are often fairly small. We would expect a stronger effect of male harvesting in species with a monogamous mating system, but no such study has been performed. We analysed the effect of harvesting males on the timing of reproduction in the obligate monogamous beaver (Castor fiber). We found a negative impact of harvesting of adult males on the timing of parturition in female beavers. The proportion of normal breeders sank from over 80%, when no males had been shot in the territories of pregnant females, to under 20%, when three males had been shot. Harvesting of males in monogamous mammals can apparently affect their normal reproductive cycle.     

Size of ornament is negatively correlated with baseline corticosterone in males of a socially monogamous colonial seabird

The Goymann–Wingfield model predicts that glucocorticoid levels in social animals reflect the costs of acquiring and maintaining social status. The crested auklet is one of the few avian colonial species where a mutual ornament in males and females is used in both sexual and aggressive displays. Previous studies of the crested auklet support the notion that the crest ornament is a badge of status in this species. Here, we examined the relationship between the crest ornament size and the adrenocortical function in breeding crested auklets. Crest length was negatively correlated with corticosterone at baseline in males, but not in females. Baseline corticosterone in females (but not in males) was negatively correlated with body condition index. Although male and female crested auklets are monomorphic in their ornamental traits, our results suggest that the socially mediated physiological costs associated with status signaling may differ between the sexes.     

Rapid assessment of female preference for male size predicts subsequent choice of spawning partner in a socially monogamous cichlid fish

Although size-assortative mating in convict cichlids, Amatitliana nigrofasciata, is supposed to result from mutual mating preference for larger individuals, female choice in relation to male size remains ambiguous. We revisited the evidence for directional preference for larger males in female convict cichlids using a classical two-way choice apparatus in which each female could decide to spend time in front of a small male or a large one. We found evidence for female preference for large males, as assessed from association preference during a 4-hour period following encounter. Furthermore, females decided to spawn in front of the initially preferred male more often than expected by chance. Our results thus confirm the existence of a directional preference for large males in female convict cichlids, and indicate that association preference measured over a short period of time can provide a quick and reliable proxy for reproductive preference in this species.     

High frequency of multiple paternity in broods of a socially monogamous cichlid fish with biparental nest defence

In several animal taxa, genetic analyses have demonstrated that social monogamy and biparental brood care do not preclude polygamous reproduction. Few studies have been conducted in fish, but in fish species without alternative reproductive phenotypes, social monogamy was largely congruent with genetic parentage. In contrast to these findings, we report an exceptionally high level of multiple paternity in a socially monogamous cichlid fish with biparental nest defence ( Variabilichromis moorii ), inferred from microsatellite and mitochondrial data of 10 broods. Whereas all offspring in a nest shared a common mother, each brood was sired by 2 to > 10 males. None of the inferred sires was assigned a large proportion of the brood. Paternity was estimated as the minimum number of sires required to explain multilocus offspring genotypes, and as the maximum-likelihood number of sires given population allele frequencies. Analysis of simulated brood genotypes suggested that, although these two methods tend to under- and overestimate, respectively, the true number of sires, primary sires with many offspring in a brood would have been detected. Hence, the genetic data indicate that the nest tending males suffer substantial cuckoldry and provide alloparental care for a large number of unrelated fry. We have no data on the social status of the cuckolding males, but due to synchronous spawning of pairs and commitment to brood care of paired males, it is possible that most of the parasitic spawners are solitary males.     

The role of sex steroids in courtship, pairing and pairing behaviors in the socially monogamous zebra finch

The purpose of this study was to test whether sex steroid actions are necessary for courtship and pairing in socially monogamous birds. We examined the effects of an aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD), combined with an anti-androgen, flutamide (F), on the behavior and pairing status of initially unpaired male and female zebra finches (Taeniopygia guttata). In the first experiment, 24 adult males were implanted with either a combination of ATD and flutamide or empty implants. Two weeks after implantation, birds were housed in aviaries containing 3 ATD + F males, 3 control males, and 3 females and allowed 2 weeks to pair, with observations 7 times during the 2-week period. A second experiment tested the effects of these same treatments in females. During the first 4 days of testing, ATD + F males were less likely to attack conspecifics than were control males. ATD + F males were also less likely to "greet," or approach, females than were control males, but other courtship behaviors, including directed singing, were unaffected. ATD + F females did not differ from control females on any courtship behavior measured. Furthermore, these treatments did not affect pairing behaviors (time spent clumping or in a nest box together) or the likelihood of pairing with a partner of the opposite sex. ATD + F treatments in females did, however, increase the likelihood of same-sex pairing. This suggests that, although sex steroids may regulate some courtship behaviors in males, they do not regulate pairing behaviors and have little effect on the likelihood that a male or female will be chosen as a mate by a bird of the opposite sex.     

CCAAT-enhancer-binding protein-beta expression in vivo is associated with muscle strength

Declining muscle strength is a core feature of aging. Several mechanisms have been postulated, including CCAAT/enhancer-binding protein-beta (C/EBP-β)-triggered macrophage-mediated muscle fiber regeneration after micro-injury, evidenced in a mouse model. We aimed to identify in vivo circulating leukocyte gene expression changes associated with muscle strength in the human adult population. We undertook a genome-wide expression microarray screen, using peripheral blood RNA samples from InCHIANTI study participants (aged 30 and 104). Logged expression intensities were regressed with muscle strength using models adjusted for multiple confounders. Key results were validated by real-time PCR. The Short Physical Performance Battery (SPPB) score tested walk speed, chair stand, and balance. CEBPB expression levels were associated with muscle strength (β coefficient = 0.20560, P = 1.03*10(-6), false discovery rate q = 0.014). The estimated handgrip strength in 70-year-old men in the lowest CEBPB expression tertile was 35.2 kg compared with 41.2 kg in the top tertile. CEBPB expression was also associated with hip, knee, ankle, and shoulder strength and the SPPB score (P = 0.018). Near-study-wide associations were also noted for TGF-β3 (P = 3.4*10(-5) , q = 0.12) and CEBPD expression (P = 9.7*10(-5) , q = 0.18) but not for CEBPA expression. We report here a novel finding that raised CEBPB expression in circulating leukocyte-derived RNA samples in vivo is associated with greater muscle strength and better physical performance in humans. This association may be consistent with mouse model evidence of CEBPB-triggered muscle repair: if this mechanism is confirmed, it may provide a target for intervention to protect and enhance aging muscle.     

The relationship between rates of HVc neuron addition and vocal plasticity in adult songbirds

In adulthood, songbird species vary considerably in the extent to which they rely on auditory feedback to maintain a stable song structure. The continued recruitment of new neurons into vocal motor circuitry may contribute to this lack of resiliency in song behavior insofar as new neurons that are not privy to auditory instruction could eventually corrupt established neural function. In a first step to explore this possibility, we used a comparative approach to determine if species differences in the rate of vocal change after deafening in adulthood correlate positively with the extent of HVc neuron addition. We confirmed previous reports that deafening in adulthood changes syllable phonology much more rapidly in bengalese finches than in zebra finches. Using [(3)H]thymidine autoradiography to identify neurons generated in adulthood, we found that the proportion of new neurons in the HVc one month after labeling was nearly twice as great in bengalese than in zebra finches. Moreover, among the subset of HVc vocal motor neurons that project to the robust nucleus of the archistriatum, the incidence of [(3)H]thymidine-labeled neurons was nearly three times as great in bengalese than in zebra finches. This correlation between the proportion of newly added neurons and the rate of song deterioration supports the hypothesis that HVc neuron addition may disrupt stable adult song production if new neurons cannot be "trained" via auditory feedback.     

Male red ornamentation is associated with female red sensitivity in sticklebacks

Sexual selection theory proposes correlated evolutionary changes in mating preferences and secondary sexual characters based on a positive genetic correlation between preference and the preferred trait. Empirical work has provided support for a genetic covariation between female preference and male attractiveness in several taxa. Here, we study parent and offspring visual traits in threespine sticklebacks, Gasterosteus aculeatus. While focusing on the proximate basis of mating preferences, we compare the red breeding coloration of males, which strongly contributes to female choice, with their daughters' red sensitivity measured by optomotor response thresholds. We show that the red color expression of fathers correlates well with their daughters' red sensitivity. Given that a within-population genetic correlation between signal and preference was experimentally confirmed for the red coloration in sticklebacks, our results indicate a proximate mechanism in terms of perceptual sensitivity being involved in the co-evolution of female preferences and male mating signals.     

The threshold trip duration for which recovery is no longer possible is associated with strength and reaction time

The recovery of young adults from trips of increasing severity was studied. Our null hypothesis was that lower extremity strength, and reaction time, step time, step distance and step velocity measured in a volitional stepping task would not explain a significant portion of the variance in the magnitude of the threshold trip duration for which recovery is no longer possible. Ten males and 11 females (average age 26.8 and 28.4 years old, respectively) were subjected to trips of increasing duration until recovery was no longer possible with a single step. The average threshold trip duration for which subjects were no longer able to recover with a single step was 681+/-169ms. The threshold trip duration significantly increased as lower extremity strength increased and volitional reaction time decreased (multiple stepwise linear regression: R(2)=0.52, p=0.001). The other volitional step parameters and the subject characteristics were not significantly associated with the magnitude of the threshold trip duration. These results suggest that some trip-related falls may be due to slower reaction times and/or reduced lower extremity strengths.     

Breeding rate is associated with pheomelanism in male and with eumelanism in female barn owls

Melanin-based coloration exists in 2 types: black eumelanismand reddish-brown pheomelanism, which both have a strong heritablecomponent. To test whether these 2 types of melanism are associatedwith alternative adaptations, we carried out a correlative studyover 8 years and an experiment in a Swiss population of barnowls, Tyto alba. This species varies in coloration from reddish-brownto white and from lightly to heavily marked with black spots.Based on the fact that plumage coloration and spottiness aremale- and female-specific secondary sexual characters, respectively,we examined whether the probability of breeding is associatedwith the degree of pheomelanism in males and of eumelanism infemales. In males, recruited nestlings were significantly lessreddish-brown than their nonrecruited nest mates. In females,individuals displaying larger black spots started to breed ata younger age and had a higher survival, and females with experimentallyreduced plumage spottiness bred less often than control females.Therefore, in the barn owl, the degree of male pheomelanismis associated with the probability of being recruited in thelocal population, whereas the degree of female eumelanism correlateswith age at sexual maturity, survival probability, and alsothe probability of skipping reproduction.