Alternative reproductive tactics are characterized by the occurrence of discrete alternative morphs that differ in behavioural, morphological and physiological traits within the same sex. Although ...much effort has been made to describe the behaviour, morphology and physiology of such alternative morphs, less effort has been invested investigating how much overlap there is in the characteristics of such morphs in natural populations. We studied random population samples of the invasive Round Goby Neogobius melanostomus from five different localities in the river Rhine system in the Netherlands. We found two morphologically and physiologically distinct male morphs which likely represent alternative reproductive tactics. Almost all mature males under 9.35 cm total length had a gonadosomatic index > 3%, suggestive of a sneaker tactic, while nearly all males above 9.35 cm has a gonadosomatic index of < 3%, suggestive of a parental tactic. Cheek size and eye diameter alone were sufficient to distinguish the two morphs. Gonads had a different relationship with size in the two morphs, indicating separate growth trajectories. The gonad mass of sneaker morphs would be ca. 7.5 times as high as the gonad mass of parental morphs of the same total length after extrapolation. Few (9%) intermediates were found, suggesting that the expression of alternative reproductive tactics is determined before the first breeding season. This contrasts with studies on other goby species, which show evidence of plastic tactics that can be affected by social circumstances. We conclude that it is possible to distinguish two alternative male morphs in the Dutch Round Goby population using morphological measurements alone. Although behavioural observations are needed to provide conclusive evidence, the difference in GSI between these morphs indicates that these morphs reflect alternative reproductive tactics.
A nest of begging chicks invites an intuitive explanation: needy chicks want to be fed and parents want to feed them. Surprisingly, however, in a quarter of species studied, parents ignore begging ...chicks. Furthermore, parents in some species even neglect smaller chicks that beg more, and preferentially feed the biggest chicks that beg less. This extreme variation across species, which contradicts predictions from theory, represents a major outstanding problem for the study of animal signalling. We analyse parent-offspring communication across 143 bird species, and show that this variation correlates with ecological differences. In predictable and good environments, chicks in worse condition beg more, and parents preferentially feed those chicks. In unpredictable and poor environments, parents pay less attention to begging, and instead rely on size cues or structural signals of quality. Overall, these results show how ecological variation can lead to different signalling systems being evolutionarily stable in different species.
Conspicuous male signals often play an important role in both attracting mates and deterring rivals. In territorial species with extrapair mating, female and male forays to other territories may be ...an important component underlying female choice and male mating success and might be influenced by male advertisement signals. Yet, whether off-territory foraying is associated with male signals is still not well understood. Here, we tested how female and male forays are associated with short-range visual and long-range acoustic signals (dawn song). We used an automated radio tracking system to follow the movements of wild great tits (
) to other territories in relation to male dawn song, plumage ornaments, and extrapair paternity. We show that both sexes frequently forayed into others' territories throughout the breeding period. Movements of both males and females were associated with male song but not with plumage ornaments. Contrary to our expectations, females stayed away from territories where males sang elaborately, whereas males were attracted to those territories. Moreover, neither female nor male forays were associated with the occurrence of extrapair offspring. Our results, thus, suggest that, although forays into other territories are associated with male dawn song, females may not be attracted and males not repelled by dawn song. This sheds a different light on the sex-specific effects of male advertisement signals, expanding the view on the selection pressures shaping such communication systems.
When individuals invest in a common good, an efficient outcome is hard to achieve, because each can free ride on others' efforts. This problem can lead parents that raise their young together to ...reduce their investment in care, with negative consequences for offspring. Here, we present a mathematical model to show that a strategy of conditional cooperation, in which parents take turns feeding their young, can help to resolve this problem. To test this idea, we studied the behavior of great tit parents raising chicks together. We found that parents alternated visits to the nest more than would be expected by chance, speeding up their feeding rate after their partner had visited the chicks, but slowing down again once they had visited in turn. This effect was not mediated by visit-to-visit changes in offspring begging intensity, although females (but not males) were influenced by mean begging levels across broods. We conclude that conflict over parental investment in this species is partly ameliorated by a simple form of reciprocity.
Models of biparental care predict that parents should compensate incompletely for any change in their partner's investment. Experimental tests have, however, yielded results that range from full ...compensation, through a lack of any reaction, to a matching response. Here we suggest a new, adaptive explanation for such variation. Building on an approach developed by McNamara et al., we incorporate uncertainty regarding brood need or value into a game-theoretical model of biparental negotiation over offspring care. We show that when each parent has only partial information, greater effort invested by one serves as a signal to the other of brood need. This favors a matching response by the focal parent's mate, whereas the impact of increased effort on the marginal value of investment favors a compensatory response. The net outcome depends on the relative strength of these two effects. The greater the variation in brood need compared with parental state, the weaker the predicted level of compensation, and the more likely matching is to occur. Our model also suggests why males and females might respond differently to each other. If there is an informational asymmetry between them, then the parent that is better informed about brood need should work harder, respond more strongly to changes in brood need, be less sensitive to changes in the cost of feeding, and compensate more strongly for changes in partner effort. If the asymmetry is very great, the poorly informed parent may even match changes in its partner's work rate.
Adults provisioning dependent young are in conflict with their partners, who would prefer a greater level of effort, and with their offspring, who would prefer a greater supply of food. To what ...extent, then should adults negotiate their provisioning behaviour with other family members? We used experimental manipulations of brood size, and targeted playback of begging calls to determine the extent to which adult great tits Parus major adjust their provisioning rates in response to the behaviour of their partner and their brood. We found that males and females behaved similarly, both responding more to each other's behaviour than to chick calling. We also found that the degree to which adults negotiated their provisioning rates with each other varied between years. A review of the literature suggests that the extent of negotiation over provisioning is likely to vary not only between species of diverse taxa, but also between and within (this study) populations of the same species. We suggest that provisioning behaviour lies on a 'negotiation continuum', which describes the extent to which parents respond to the actions of other family members. We argue that an individual's location on the 'negotiation continuum' is determined partly by the extent to which it can physically respond to the behaviour shown by other members of the family and partly by the quality of information on offer.
Initial mate choice and re-mating strategies (infidelity and divorce) influence individual fitness. Both of these should be influenced by the social environment, which determines the number and ...availability of potential partners. While most studies looking at this relationship take a population-level approach, individual-level responses to variation in the social environment remain largely unstudied. Here, we explore carry-over effects on future mating decisions of the social environment in which the initial mating decision occurred. Using detailed data on the winter social networks of great tits, we tested whether the probability of subsequent divorce, a year later, could be predicted by measures of the social environment at the time of pairing. We found that males that had a lower proportion of female associates, and whose partner ranked lower among these, as well as inexperienced breeders, were more likely to divorce after breeding. We found no evidence that a female's social environment influenced the probability of divorce. Our findings highlight the importance of the social environment that individuals experience during initial pair formation on later pairing outcomes, and demonstrate that such effects can be delayed. Exploring these extended effects of the social environment can yield valuable insights into processes and selective pressures acting upon the mating strategies that individuals adopt.
Parent-Offspring Conflict and Coadaptation Hinde, Camilla A; Johnstone, Rufus A; Kilner, Rebecca M
Science (American Association for the Advancement of Science),
03/2010, Letnik:
327, Številka:
5971
Journal Article
Recenzirano
The evolution of family life has traditionally been studied in parallel by behavioral ecologists and quantitative geneticists. The former focus on parent-offspring conflict and whether parents or ...offspring control provisioning, whereas the latter concentrate on the coadaptation of parental supply and offspring demand. Here we show how prenatal effects on offspring begging can link the two different approaches. Using theoretical and experimental analyses, we show that when offspring control provisioning, prenatal effects primarily serve the parent's interests: Selection on parents drives coadaptation of parent and offspring traits. In contrast, when parents control provisioning, prenatal effects primarily serve the offspring's interests: Selection on the offspring drives coadaptation of parent and offspring traits. Parent-offspring conflict may thus be responsible for the selective forces that generate parent-offspring coadaptation.
In various animal species individuals differ consistently in their behaviour, often referred to as personality. In several species these personality differences also correlate with differences in ...social behaviour. This is important as the social environment is a key selection pressure in many animal populations, mediated, for example, via competition or access to social information. Using social network analysis, recent studies have furthered our understanding of the role of personality in the social environment, usually by focusing on swarming or flocking populations. However, social associations in such populations are fundamentally different from those in territorial populations, where individuals meet less frequently and where the costs and benefits of spatial associations differ from those for swarming or flocking species. In this study we therefore tested whether social network position is related to individual differences in exploration behaviour, an established measure of an avian personality trait, using a wild, territorial, personality-typed great tit, Parus major, population. By means of novel, large-scale, automated tracking (Encounternet) we show, while controlling for average territory distance, that slower exploring males had less central social network positions. Yet, slower explorers overall did not travel shorter distances than faster explorers, indicating that a less central social network position was not merely a consequence of lower activity. Finally, males with less central social network positions did not have reduced breeding success compared to males with more central positions. Our results suggest that territorial individuals influence the structuring of their own social environment in relation to their personality. This is relevant, because the establishment of social relations and familiarity with possible competitors is predicted to be important in many territorial populations.
•First study to analyse the role of personality in a territorial social network.•Novel use of automatized simultaneous radiotracking to identify the social network.•Exploration behaviour relates to social network position in territorial great tits.•There is no correlation between exploration behaviour and median distance moved.•We found no relationship between male social network position and breeding success.
Both social and ecological factors influence population process and structure, with resultant consequences for phenotypic selection on individuals. Understanding the scale and relative contribution ...of these two factors is thus a central aim in evolutionary ecology. In this study, we develop a framework using null models to identify the social and spatial patterns that contribute to phenotypic structure in a wild population of songbirds. We used automated technologies to track 1053 individuals that formed 73 737 groups from which we inferred a social network. Our framework identified that both social and spatial drivers contributed to assortment in the network. In particular, groups had a more even sex ratio than expected and exhibited a consistent age structure that suggested local association preferences, such as preferential attachment or avoidance. By contrast, recent immigrants were spatially partitioned from locally born individuals, suggesting differential dispersal strategies by phenotype. Our results highlight how different scales of social decision-making, ranging from post-natal dispersal settlement to fission–fusion dynamics, can interact to drive phenotypic structure in animal populations.
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