Parent–Offspring Conflict in Primates

Parent–offspring conflict (POC) theory (Trivers, 1974) has stimulated controversy in evolutionary biology and behavioral ecology. The theory has been criticized by some primate behavioral researchers on both conceptual and empirical grounds. First, it has been argued that it would be more advantageous to mothers and offspring to agree over the allocation of parental investment and to cooperate rather than to disagree and engage in conflict. Second, some studies have provided data suggesting that primate mothers and offspring engage in behavioral conflict over the scheduling of their activities rather than parental investment. In reality, parent–offspring interactions are likely to involve both cooperation and conflict, and the hypothesis that mothers and infants squabble over the scheduling of their activities is not incompatible with POC theory. Furthermore, the predictions of POC theory are supported by a number of empirical studies of primates. POC theory has enhanced our understanding of the dynamics of parent–offspring relationships in many animal species, and it is very likely that future studies of primates will continue to benefit from using POC theory as an explanatory framework.     

Patient Parents: Do Offspring Decide on the Timing of Fledging in Zebra Finches?

Parent–offspring conflict over parental care is predicted to become most pronounced during offspring transition to independence when offspring are predicted to attempt to extend care for longer than parents are selected to provide it. However, on the proximate level, it is difficult to determine who plays the most important role in this process, parents or offspring. For several vertebrate taxa, it has been documented that parents end brood care by abandoning offspring after a fixed period or else show high flexibility in the duration of care, but teasing apart the role of offspring and parents underlying this flexibility has been difficult. Here, we studied the decision to fledge in captive zebra finches (Taeniopygia guttata), an altricial songbird. We experimentally delayed the time of fledging to determine who decides about the end of feeding inside the nest, parents or offspring. The experiment indicates that parents do not primarily rely on phenotypic offspring traits in their decision to feed offspring in the nest, but appear to adjust the duration of parental care as long as offspring are in the nest which parents may take as an indicator of offspring need and locomotor abilities. Delayed‐fledging offspring appeared not to suffer a disadvantage in terms of age at the onset of independent feeding. Our study suggests that, in zebra finches, offspring play a major role in determining the time of fledging and leave the nest on their own, possibly to reduce the risk of nest predation, or to evade sibling competition in the nest.     

Families on the spot: sexual signals influence parent–offspring interactions

In 1950, Tinbergen described the elicitation of offspring begging by the red spot on the bill of parent gulls, and this became a model system for behavioural studies. Current knowledge on colour traits suggests they can act as sexual signals revealing individual quality. However, sexual signals have never been studied simultaneously in relationship to parent–offspring and sexual conflicts. We manipulated the red-spot size in one member of yellow-legged gull pairs and observed their partners'' feeding efforts in relationship to offspring begging. In the enlarged-spot group, partners doubled their effort compared with the other groups. Furthermore, in the reduced-spot group, partners provided food in relationship to offspring begging, contrasting with the fixed effort of the partners of enlarged-spot gulls. Manipulated gulls, independently of treatment, provided food in relationship to chicks begging only when the partner''s investment was low, and performed a fixed effort when the partner''s contribution was high. Results demonstrate that the red spot in yellow-legged gulls functions as a sexual signal and indicate that parental rules are plastic, depending on the information on offer. Previous evidence and this study indicate that this signal is used by all family members to adjust decision rules. The incorporation of sexual signals in parent–offspring interactions can be crucial in understanding intra-familial conflicts.     

Coadaptation and conflict,misconception and muddle,in the evolution of genomic imprinting

Common misconceptions of the ‘parental conflict'' theory of genomic imprinting are addressed. Contrary to widespread belief, the theory defines conditions for cooperation as well as conflict in mother–offspring relations. Moreover, conflict between genes of maternal and paternal origin is not the same as conflict between mothers and fathers. In theory, imprinting can evolve either because genes of maternal and paternal origin have divergent interests or because offspring benefit from a phenotypic match, or mismatch, to one or other parent. The latter class of models usually require maintenance of polymorphism at imprinted loci for the maintenance of imprinted expression. The conflict hypothesis does not require maintenance of polymorphism and is therefore a more plausible explanation of evolutionarily conserved imprinting.     

Prenatal environmental effects match offspring begging to parental provisioning

The solicitation behaviours performed by dependent young are under selection from the environment created by their parents, as well as wider ecological conditions. Here we show how mechanisms acting before hatching enable canary offspring to adapt their begging behaviour to a variable post-hatching world. Cross-fostering experiments revealed that canary nestling begging intensity is positively correlated with the provisioning level of their own parents (to foster chicks). When we experimentally increased food quality before and during egg laying, mothers showed higher faecal androgen levels and so did their nestlings, even when they were cross-fostered before hatching to be reared by foster mothers that had been exposed to a standard regime of food quality. Higher parental androgen levels were correlated with greater levels of post-hatching parental provisioning and (we have previously shown) increased faecal androgens in chicks were associated with greater begging intensity. We conclude that androgens mediate environmentally induced plasticity in the expression of both parental and offspring traits, which remain correlated as a result of prenatal effects, probably acting within the egg. Offspring can thus adapt their begging intensity to variable family and ecological environments.     

Do parents play a role in the timing and process of fledging by nestling Mountain Bluebirds?

What causes young birds to leave nests remains unclear for almost all altricial species. For many years, the assumption was that parents often controlled the time of fledging by coaxing young from nests, e.g., by holding food within view, but out of reach, of nestlings. This assumption, though, was based solely on scattered anecdotal reports of such behavior. We used continuous video‐recording of nests to assess the role of parents, if any, in the timing and process of fledging of cavity‐nesting Mountain Bluebirds (Sialis currucoides). We placed perches ~50 cm in front of nest‐box entrances to give parents ample opportunity to display food to nestlings. We found no evidence that parents routinely initiated the fledging process. On the day of fledging, parents did not perch on supplemental perches with food more often, or for longer periods of time, than on the day before fledging. Also, after going to nest‐box entrances, parents never held food away from a nestling reaching for the food. Parents were usually absent (16 of 19 cases) when the first nestling fledged. In the remaining three cases, a parent perched with food in view of a nestling for 8, 15 and 65 s, respectively, just before that nestling fledged. Although these might have appeared to be attempts at coaxing, in each case, the parent was encountering, for the first time, a nestling partially emerging from the nest entrance. Parents may simply have hesitated to approach nests because the nestling's position prevented parents from delivering food in the normal manner. Finally, the rate at which parents fed nestlings on the day of fledging did not differ from the rate the day before, suggesting that parents do not try to use hunger to induce fledging. Our results are consistent with previous research suggesting that, in Mountain Bluebirds, it is a nestling that initiates fledging, typically when it reaches some threshold state of development.     

Provisioning control during maternal care by the earwig Anisolabis maritima (Dermaptera: Anisolabididae): Do mothers adjust provisioning according to offspring need?

Provisioning offspring is an important form of parental care for the improvement of offspring survival and growth. Because provisioning can be costly for parents, parents may change their investment levels in response to offspring need and begging signals. Anisolabis maritima is a cosmopolitan species of earwig that shows subsocial behavior. Females progressively provision their young in soil burrows. The present study investigated whether A. maritima mothers carry food to the nest for their offspring (nymphs) and whether the mothers adjust the amount of food carried to the burrow according to the degree of the nymphs’ hunger. Through laboratory experiments, I found that mothers carried food to sites where more nymphs were present, and more food to broods of more hungry nymphs. These results have revealed that mothers recognize the presence of offspring and the degree of their hunger. This study, therefore, indicates the presence of offspring begging signals in A. maritima.