Divorce rate varies with fluidity of passerine social environment

Breaking family bonds: pair disruption alters female adolescent spatial neophobia but not other personality traits or corticosterone stress response in zebra finches (Taeniopygia guttata)

Adolescence is a sensitive period because it is associated with the ontogeny of key neurological, physiological and behavioural systems. These systems can be permanently altered by social disruption during adolescence and therefore impair an individual's ability to cope with its environment later in life. We tested whether pair disruption of captive zebra finches (Taeniopygia guttata) during emancipation affects the family social structure, with potential consequences for the nutritional status, personality and corticosterone stress response of juveniles. We experimentally manipulated the social environment of 22 families during emancipation by replacing fathers with unfamiliar males (experimental families) or leaving them unchanged (control families) and monitored the prevalence of affiliative, agonistic and sexual interactions between family members. We assessed offspring growth, timing of nutritional independence, body condition as well as five personality traits and the corticosterone stress response to isolation. While we observed more agonistic and sexual behaviours in experimental families, we also observed more affiliative behaviours between experimental siblings and more maternal provisioning of the experimental juveniles. Among all the traits we tested, we only found a sex-dependent effect of the experimental treatment on spatial neophobia, suggesting that pair disruption may have long-term consequences for females' ability to cope with new environments. However, our findings suggest overall that the emancipation phase is less sensitive to social environment in comparison to the prenatal and early postnatal periods and that nutritional and social buffers may mitigate the lasting impacts of pair disruption on adolescent behavioural and stress response profiles in altricial species such as the zebra finch.

Rainfall is associated with divorce in the socially monogamous Seychelles warbler

Divorce-terminating a pair bond whilst both members are alive-is a mating strategy observed in many socially monogamous species often linked to poor reproductive success. As environmental factors directly affect individual condition and reproductive performance, they can indirectly influence divorce. Given current climate change, understanding how environmental fluctuations affect partnership stability has important implications, including for conservation. Yet, the relationship between the environment and divorce remains largely unstudied. We examined the influence of temporal environmental variability on the prevalence of within- and between-season divorce and the possible underlying mechanisms in a socially monogamous passerine. Analysing 16 years of data from a longitudinal dataset, we investigated the relationship between rainfall and divorce in the Seychelles warbler (Acrocephalus sechellensis). First, we performed climate window analyses to identify the temporal windows of rainfall that best predict reproductive success and divorce. Then, we tested the effects of these temporal windows of rainfall on reproductive success and divorce and the influence of reproductive success on divorce whilst controlling for covariates. Annual divorce rates varied from 1% to 16%. The probability of divorce was significantly associated with the quadratic effect of 7 months of total rainfall before and during the breeding season, with divorce increasing in years with low and high rainfall. This quadratic relationship was driven by a heavy rainfall event in 1997, as excluding 1997 from our analyses left a significant negative linear relationship between rainfall and divorce. Although the same temporal window of rainfall predicting divorce significantly influenced reproductive success, we found no significant correlation between reproductive success and divorce. Our findings suggest that rainfall impacts divorce. Given that this effect is likely not directly mediated by reproductive success, we discuss other possible drivers. Although the 1997 super El Niño event shows how heavy rainfall may affect socially monogamous partnerships, more data are required to estimate the robustness of this effect. By adding to the growing body of literature showing that environmental conditions influence the stability of socially monogamous partnerships, we provide novel insights that may also be important for conservation efforts in times of climate change.

Early-Life Silver Spoon Improves Survival and Breeding Performance of Adult Zebra Finches

AbstractDevelopmental plasticity allows organisms to increase the fit between their phenotype and their early-life environment. The extent to which such plasticity also enhances adult fitness is not well understood, however, particularly when early-life and adult environments differ substantially. Using a cross-factorial design that manipulated diet at two life stages, we examined predictions of major hypotheses-silver spoon, environmental matching, and thrifty phenotype-concerning the joint impacts of early-life and adult diets on adult morphology/display traits, survival, and reproductive allocation. Overall, results aligned with the silver spoon hypothesis, which makes several predictions based on the premise that development in poor-quality environments constrains adult performance. Males reared and bred on a low-protein diet had lower adult survivorship than other male treatment groups; females' survivorship was higher than males' and not impacted by early diet. Measures of allocation to reproduction primarily reflected breeding diet, but where natal diet impacted reproduction, results supported the silver spoon. Both sexes showed reduced expression of display traits when reared on a low-protein diet. Results accord with other studies in supporting the relevance of the silver spoon hypothesis to birds and point to significant ramifications of sex differences in early-life viability selection on the applicability/strength of silver spoon effects.

Divorce rate in monogamous birds increases with male promiscuity and migration distance

Socially monogamous birds may break up their partnership by a so-called 'divorce' behaviour. Divorce rates vary immensely across avian taxa that have a predominantly monogamous social mating system. Although various factors associated with divorce have been tested, broad-scale drivers of divorce rate remain contentious. Moreover, the influence of sexual roles in divorce still needs further investigation because of the conflicting interests of males and females over mating and fertilization. Here, we applied phylogenetic comparative methods to analyse one of the largest datasets ever compiled that included divorce rates from published studies of 186 avian species from 25 orders and 61 families. We tested correlations between divorce rate and a group of factors: 'promiscuity' of both sexes (propensity to polygamy), migration distance and adult mortality. Our results showed that only male promiscuity, but not female promiscuity, had a positive relationship with divorce rate. Furthermore, migration distance was positively correlated with divorce rate, whereas adult mortality rate showed no direct relationship with divorce rate. These findings indicated that divorce might not be a simple adaptive (by sexual selection) or non-adaptive strategy (by accidental loss of a partner) in birds but it could be a mixed response to sexual conflict and stress from the ambient environment.

Male social niche conformance? Effects of manipulated opportunity for extra-pair mating on behavior and hormones of male zebra finches

Success in sperm competition is an important determinant of male fitness in mating systems with female multiple mating. Thus, sperm competition risk represents a key dimension of the male social environment to which individual males are expected to adaptively adjust their reproductive phenotype. Such adaptive phenotypic adjustment we here refer to as male social niche conformance. In this pre-registered study, we investigated how male zebra finches, Taeniopygia guttata, adjust their behavior to sperm competition risk. We experimentally manipulated the opportunity for extra-pair mating to create two levels of sperm competition risk: 1) Single-pair, no sperm competition risk; 2) Double-pair, sperm competition risk. We compared male courtship, mate guarding, copulation rates, and aggression between the treatment groups. To identify hormonal correlates of male behavioral adjustment, we measured plasma testosterone and corticosterone levels before and after the social treatment started. Contrary to our pre-registered predictions, males from the Double-pair treatment group decreased courtship rates compared to those from the Single-pair group, and Double-pair males responded less aggressively towards intruders than Single-pair males. Testosterone levels decreased over the breeding cycle, but social treatment had no effect on either testosterone or corticosterone levels. Our results indicate that male zebra finches do not intensify courtship or competitive reproductive behaviors, or upregulate key hormones when another breeding pair is present. Although we found no evidence for the predicted adaptive behavioral responses to sperm competition risk, we show that male zebra finches plastically adjust their behavior to their social environment.