Matthieu Paquet

Maternal Effects in Relation to Helper Presence in the Cooperatively Breeding Sociable Weaver

In egg laying species, breeding females may adjust the allocation of nutrients or other substances into eggs in order to maximise offspring or maternal fitness. Cooperatively breeding species offer a particularly interesting context in which to study maternal allocation because helpers create predictably improved conditions during offspring development. Some recent studies on cooperative species showed that females assisted by helpers produced smaller eggs, as the additional food brought by the helpers appeared to compensate for this reduction in egg size. However, it remains unclear how common this effect might be. Also currently unknown is whether females change egg composition when assisted by helpers. This effect is predicted by current maternal allocation theory, but has not been previously investigated. We studied egg mass and contents in sociable weavers (Philetairus socius). We found that egg mass decreased with group size, while fledgling mass did not vary, suggesting that helpers may compensate for the reduced investment in eggs. We found no differences in eggs’ carotenoid contents, but females assisted by helpers produced eggs with lower hormonal content, specifically testosterone, androstenedione (A4) and corticosterone levels. Taken together, these results suggest that the environment created by helpers can influence maternal allocation and potentially offspring phenotypes.

A cross-fostering experiment reveals that prenatal environment affects begging behaviour in a cooperative breeder

Prenatal breeding conditions have broad influences on maternal allocation to reproduction which can strongly affect future begging behaviours of offspring. The social environment is part of the prenatal environment; however, its influence on maternal allocation has been poorly investigated and experimental tests linking prenatal conditions to begging behaviour have seldom been conducted. In cooperative breeders the presence of additional carers, the helpers, generally predicts an increase in provisioning during the nestling stage. Since begging is costly, in these species producing offspring that beg less in the presence of helpers may be a way of saving energy not only for the offspring but also for the future survival and reproduction of females. To date, whether mothers may manipulate begging behaviour in relation to helper presence is unstudied. We conducted a cross-fostering experiment in a cooperatively breeding bird, the sociable weaver, Philetairus socius, to disentangle the possible effects of prenatal and postnatal environments on begging behaviour. Pre- and postnatal environments correspond here to the number of carers in the nest of origin and the foster nest, respectively. As predicted, begging was influenced by the prenatal environment, with nestlings originally from larger groups begging less. In addition, chicks fed by more foster birds also begged at a lower rate. We conclude that the prenatal environment influences begging behaviour. This result has important implications for understanding cooperative breeding strategies since producing offspring that beg less with more helpers may allow energy savings for females and related offspring and helpers.

Females manipulate behavior of caring males via prenatal maternal effects

Significance In biparental species, sexual conflict arises as each parent attempts to minimize its personal effort. Most work has focused on how this conflict is resolved through symmetrical decisions between parents. We investigated whether females can influence male decisions by altering the offspring’s phenotype via the eggs. We manipulated the prenatal presence of the male, performed a cross-fostering experiment, and monitored the subsequent effects on offspring and parent performance. Offspring laid in presence of a male were smaller at hatching. In addition, males lost more weight when with larvae laid in presence of a male. Our results show that females can manipulate male behavior, suggesting that prenatal maternal effects can play an important role in the resolution of sexual conflict between parents. In species with biparental care, there is sexual conflict as each parent is under selection to minimize its personal effort by shifting as much as possible of the workload over to the other parent. Most theoretical and empirical work on the resolution of this conflict has focused on strategies used by both parents, such as negotiation. However, because females produce the eggs, this might afford females with an ability to manipulate male behavior via maternal effects that alter offspring phenotypes. To test this hypothesis, we manipulated the prenatal conditions (i.e., presence or absence of the male), performed a cross-fostering experiment, and monitored the subsequent effects of prenatal conditions on offspring and parental performance in the burying beetle Nicrophorus vespilloides. We found that offspring were smaller at hatching when females laid eggs in presence of a male, suggesting that females invest less in eggs when expecting male assistance. Furthermore, broods laid in the presence of a male gained more weight during parental care, and they did so at the expense of male weight gain. Contrary to our expectations, males cared less for broods laid in the presence of a male. Our results provide experimental evidence that females can alter male behavior during breeding by adjusting maternal effects according to prenatal conditions. However, rather than increasing the male’s parental effort, females appeared to suppress the male’s food consumption, thereby leaving more food for their brood.

Disruptive viability selection on a black plumage trait associated with dominance

Traits used in communication, such as colour signals, are expected to have positive consequences for reproductive success, but their associations with survival are little understood. Previous studies have mainly investigated linear relationships between signals and survival, but both hump‐shaped and U‐shaped relationships can also be predicted, depending on the main costs involved in trait expression. Furthermore, few studies have taken the plasticity of signals into account in viability selection analyses. The relationship between signal expression and survival is of particular interest in melanin‐based traits, because their main costs are still debated. Here, we first determined the main factors explaining variability in a melanin‐based trait linked to dominance: the bib size of a colonial bird, the sociable weaver Philetairus socius. We then used these analyses to obtain a measure representative of the individual mean expression of bib size. Finally, we used capture–recapture models to study how survival varied in relation to bib size. Variation in bib size was strongly affected by year and moderately affected by age, body condition and colony size. In addition, individuals bearing small and large bibs had higher survival than those with intermediate bibs, and this U‐shaped relationship between survival and bib size appeared to be more pronounced in some years than others. These results constitute a rare example of disruptive viability selection, and point towards the potential importance of social costs incurred by the dominance signalling function of badges of status.

Breeding decisions and output are correlated with both temperature and rainfall in an arid-region passerine, the sociable weaver

Animal reproductive cycles are commonly triggered by environmental cues of favourable breeding conditions. In arid environments, rainfall may be the most conspicuous cue, but the effects on reproduction of the high inter- and intra-annual variation in temperature remain poorly understood, despite being relevant to the current context of global warming. Here, we conducted a multiyear examination of the relationships between a suite of measures of temperature and rainfall, and the onset and length of the breeding season, the probability of breeding and reproductive output in an arid-region passerine, the sociable weaver (Philetairus socius). As expected, reproductive output increased with rainfall, yet specific relationships were conditional on the timing of rainfall: clutch production was correlated with rainfall throughout the season, whereas fledgling production was correlated with early summer rainfall. Moreover, we reveal novel correlations between aspects of breeding and temperature, indicative of earlier laying dates after warmer springs, and longer breeding seasons during cooler summers. These results have implications for understanding population trends under current climate change scenarios and call for more studies on the role of temperature in reproduction beyond those conducted on temperate-region species.

Sex differences in parental defence against conspecific intruders in the burying beetle Nicrophorus vespilloides

In species with biparental care, females often provide more care than males. Previous work has focused on sex differences in parental food provisioning and defence against predators. However, parents often also defend their offspring against conspecific intruders, which could be male or female. Thus, there is a need for studies examining sex differences in the behaviour of both caring parents and intruders, and whether sex differences in the behaviour of caring parents depend upon the intruders sex. We conducted an experiment on the burying beetle Nicrophorus vespilloides where a single female or male resident caring for a brood was confronted with a male or female intruder. Female residents were more successful in defending their brood and engaged in more fights against an intruder than males. Residents engaged in more fights against male intruders and, among those that successfully defended their brood, residents spent more time provisioning food to larvae when confronted with female intruders. There was no evidence that sex differences in the behaviour of caring parents depended upon the intruders sex. There were no sex differences in any measures of reproductive success among those residents that successfully defended their brood and no sex differences in the life span or mass gain of either residents or intruders. Our study extends the study of sex differences in parental care to the context of defence against conspecific intruders by demonstrating sex differences in the behaviour of both residents and intruders and sex differences in reproductive success in the presence of conspecific intruders.