Male reed buntings do not adjust parental effort in relation to extrapair paternity

Parental effort is considered to be costly; therefore, males are expected to provide less care to unrelated offspring. Theoretical models suggest that males should either reduce their care to the entire brood or alternatively distinguish between related and unrelated nestlings and direct provisioning to kin when paternity is in doubt. Reed buntings (Emberiza schoeniclus) have been found to have high levels of extrapair paternity (EPP, i.e., offspring of a male other than the male attending the nest; 55% of offspring), and males are therefore under strong selection pressure to adjust their parental effort according to the proportion of EPP in their brood. In this study, we investigated whether male reed buntings exhibit a reduction in paternal care (incubation and provisioning nestlings) in relation to decreased paternity. We also assess whether males bias their provisioning toward kin. We measured incubation time, provisioning rates, and food allocation to individual nestlings using video recordings at the nests. Microsatellite DNA analysis was used to analyze the paternity of offspring. In direct contrast to a previous study on the same species, our results provided no indication that males lowered their effort with decreased paternity. Furthermore, in nests of mixed paternity, males did not bias their provisioning behavior to kin. It remains to be investigated whether the absence of a relationship between paternity and paternal care can be ascribed to absence of reliable paternity cues or whether the benefits of reducing paternal care did not outweigh the costs in our study population. We found no evidence that the level of paternal care affected male survival or offspring mass, suggesting that both the benefits and costs of any reduction in paternal care would have been low. Copyright 2005.Emberiza schoeniclus; extrapair paternity; kin recognition; parental care

Individual benefits of nestling begging: experimental evidence for an immediate effect, but no evidence for a delayed effect

The evolutionary stability of honest signalling by offspring is thought to require that begging displays be costly, so the costs and benefits of begging—and whether they are experienced individually or by the whole brood—are crucial to understanding the evolution of begging behaviour. Begging is known to have immediate individual benefits (parents distribute more food to intensely begging individuals) and delayed brood benefits (parents increase provisioning rate to the brood), but the possibility of delayed individual benefits (previous begging affects the current distribution of food) has rarely, if ever, been researched. We did this using playback of great tit Parus major chick begging and a control sound from either side of the nest. Male parents fed chicks close to the speaker more when great tit chick begging, but not other stimuli, was played back. In contrast, there was no effect of playback at the previous visit on the chicks that male parents fed. We have thus demonstrated an immediate individual benefit to begging, but found no evidence of a delayed individual benefit in this species

Manipulative signals in family conflict? On the function of maternal yolk hormones in birds

The exciting discovery by Hubert Schwabl (Washington State University) in the early nineties that the yolk of bird eggs contains hormones originating from the mother opened up an extremely successful research area for endocrinologists and behavioral ecologists. Since then, knowledge of both the factors that influence the amount of hormones deposited in yolk by the female, and the consequences of exposure to these maternal hormones on offspring growth, physiology, and behaviour has accumulated rapidly. The field has been dominated by the idea that mothers use yolk hormones to adaptively adjust offspring development in their interest. However, this idea neglects that the (evolutionary) interests of mother and offspring may differ. Each offspring will try to maximize its share of parental investment while the mother wants to distribute her investment among all her offspring. When there is such parent-offspring conflict the offspring are selected to respond to the yolk hormones in a way that is b Parent-offspring conflict is not the only intra-familial strife that may shape the evolution of yolk hormone deposition. Parents disagree (evolutionarily) over the amount of care each of them is willing to provide to their young. Since yolk hormones affect offspring begging behavior, females may be able to use yolk hormone deposition to modify begging traits in a way that increases the amount of parental care provided by the male. The existence of sex differences in response to offspring begging The authors therefore suggest that for a full understanding of the evolution of hormone-mediated maternal effects it is essential to study both fitness consequences, and physiological mechanisms and constraints, from the perspective of all family members. Furthermore, the authors believe that the integration of evolutionary biology and endocrinology will lead to the most rapid advance in this field - from both an evolutionary and endocrinological point of view. It may therefore not be coincidenc

Neuroendocrine control of life histories: what do we need to know to understand the evolution of phenotypic plasticity?

Almost all life histories are phenotypically plastic: that is, life-history traits such as timing of breeding, family size or the investment in individual offspring vary with some aspect of the environment, such as temperature or food availability. One approach to understanding this phenotypic plasticity from an evolutionary point of view is to extend the optimality approach to the range of environments experienced by the organism. This approach attempts to understand the value of particular traits in terms of the selection pressures that act on them either directly or owing to trade-offs due to resource allocation and other factors such as predation risk. Because these selection pressures will between environments, the predicted optimal phenotype will too. The relationship expressing the optimal phenotype for different environments is the optimal reaction norm and describes the optimal phenotypic plasticity. However, this view of phenotypic plasticity ignores the fact that the reaction norm must be underlain by some sort of control system: cues about the environment must be collected by sense organs, integrated into a decision about the appropriate life history, and a message sent to the relevant organs to implement that decision. In multicellular animals, this control mechanism is the neuroendocrine system. The central question that this paper addresses is whether the control system affects the reaction norm that evolves. This might happen in two different ways: first, the control system will create constraints on the evolution of reaction norms if it cannot be configured to produce the optimal reaction norm and second, the control system will create additional selection pressures on reaction norms if the neuroendocrine system is costly. If either of these happens, a full understanding of the way in which selection shapes reaction norms must include details of the neuroendocrine control system. This paper presents the conceptual framework needed to explain what is meant by a constraint or cost being created by the neuroendocrine system and discusses the extent to which this occurs and some possible examples. The purpose of doing this is to encourage endocrinologists to take a fresh look at neuroendocrine mechanisms and help identify the properties of the system and situations in which these generate constraints and costs that impinge on the evolution of phenotypic plasticity

Female blue tits adjust parental effort to manipulated male UV attractiveness.

The differential allocation hypothesis predicts that parents should adjust their current investment in relation to perceived mate attractiveness if this affects offspring fitness. It should be selectively advantageous to risk more of their future reproductive success by investing heavily in current offspring of high reproductive value but to decrease investment if offspring value is low. If the benefits of mate attractiveness are limited to a particular offspring sex we would instead expect relative investment in male versus female offspring to vary with mate attractiveness, referred to as 'differential sex allocation'. We present strong evidence for differential allocation of parental feeding effort in the wild and show an immediate effect on a component of offspring fitness. By experimentally reducing male UV crown coloration, a trait known to indicate attractiveness and viability in wild-breeding blue tits (Parus caeruleus), we show that females, but not males, reduce parental feeding rates and that this reduces the skeletal growth of offspring. However, differential sex allocation does not occur. We conclude that blue tit females use male UV coloration as an indicator of expected offspring fitness and adjust their investment accordingly

The evolutionary outcome of sexual conflict

Inter-locus sexual conflict occurs by definition when there is sexually antagonistic selection on a trait so that the optimal trait value differs between the sexes. As a result, there is selection on each sex to manipulate the trait towards its own optimum and resist such manipulation by the other sex. Sexual conflict often leads additionally to the evolution of harmful behaviour and to self-reinforcing and even perpetual sexually antagonistic coevolution. In an attempt to understand the determinants of these different outcomes, I compare two groups of traits—those related to parental investment (PI) and to mating—over which there is sexual conflict, but which have to date been explored by largely separate research traditions. A brief review suggests that sexual conflict over PI, particularly over PI per offspring, leads less frequently to the evolution of manipulative behaviour, and rarely to the evolution of harmful behaviour or to the rapid evolutionary changes which may be symptomatic of sexually antagonistic coevolution. The chief determinants of the evolutionary outcome of sexual conflict are the benefits of manipulation and resistance, the costs of manipulation and resistance, and the feasibility of manipulation. All three of these appear to contribute to the differences in the evolutionary outcome of conflicts over PI and mating. A detailed dissection of the evolutionary changes following from sexual conflict exposes greater complexity than a simple adaptation–counter-adaptation cycle and clarifies the role of harm. Not all of the evolutionary changes that follow from sexual conflict are sexually antagonistic, and harm is not necessary for sexually antagonistic coevolution to occur. In particular, whereas selection on the trait over which there is conflict is by definition sexually antagonistic, collateral harm is usually in the interest of neither sex. This creates the opportunity for palliative adaptations which reduce collateral harm. Failure to recognize that such adaptations are in the interest of both sexes can hinder our understanding of the evolutionary outcome of sexual conflict