Periodic Reporting for period 1 - Helping in Cyanopica (Why helping others? The role of direct fitness benefits within the social-networks in cooperatively breeding azure-winged magpies)
Período documentado: 2015-05-01 hasta 2017-04-30
"Cooperation is widespread in nature, including our own species, but in many cases it poses an evolutionary paradox with natural selection favouring own success in competition with alternative genetic forms. One main classic explanation is kin selection, i.e. the success of genes promoting copies of themselves not only by means of the reproduction of the bearer but also of its relatives. However, current literature on the evolution of cooperation agrees that kin selection cannot explain the benefits accrued by cooperators in many systems. One main gap is the type of direct benefits that helpers obtain in cooperative breeding systems and how they constitute an evolutionarily stable strategy, provided that natural selection favours defectors over cooperators in unstructured populations. Recent advances show that ""social viscosity"" could maintain benefits for cooperators. Thus, the study of social network structure could potentially explain why cooperation persists. This type of approach can only be tackled after a longterm study at individual level.
Birds are good model species for studying cooperation, in particular by investigating the helping behaviour in cooperatively breeding species. For more than 20 years, I have participated in a research team that monitored a population of cooperative breeding Iberian magpie (Cyanopica cooki). I have pedigree data, their reproductive behaviour in helper and breeder roles, and lifetime reproductive success for many birds. Yet, the reason why helpers contribute to rearing other birds' offspring has remained elusive.
The objective of this project was to use network approach to previous data plus new monitoring of breeding groups to study: the role of kinship, by using pedigree and genetic analyses; the structure of social networks based on cooperative relationships, to see whether interactions can explain the maintenance of cooperative behaviour from the point of view of reciprocity and generalized reciprocity predictions; potential paternity sharing between breeders and helpers; and the relative roles of different benefits in lifetime inclusive fitness.
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Birds are good model species for studying cooperation, in particular by investigating the helping behaviour in cooperatively breeding species. For more than 20 years, I have participated in a research team that monitored a population of cooperative breeding Iberian magpie (Cyanopica cooki). I have pedigree data, their reproductive behaviour in helper and breeder roles, and lifetime reproductive success for many birds. Yet, the reason why helpers contribute to rearing other birds' offspring has remained elusive.
The objective of this project was to use network approach to previous data plus new monitoring of breeding groups to study: the role of kinship, by using pedigree and genetic analyses; the structure of social networks based on cooperative relationships, to see whether interactions can explain the maintenance of cooperative behaviour from the point of view of reciprocity and generalized reciprocity predictions; potential paternity sharing between breeders and helpers; and the relative roles of different benefits in lifetime inclusive fitness.
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Project tasks included fieldwork, both observational and experimental, as well as laboratory and computational work. I worked with a natural population in the field, and hence many environmental hazards that escape the control of researchers may potentially affect the progress of the work. In our case, the breeding season in the spring of 2016 was unusually bad for the birds. Heavy rainfall during the nestling period and cold temperatures, along with an unusual strong predation by a Stone marten (Martes foina), that appeared photographed in our camera traps, drop the fledging success to only 10% of nests. As a consequence, I intensified data collection the next season in the spring of 2017 but this produced a delay in the timing for the laboratory results and analyses. Even so, the project arrived to interesting conclusions, with some of them also being subjected to revision with new laboratory results on genetic relatedness and increased sample size.
We already know from previous work that helping is beneficial to helped chicks (who increase survival and condition) and hence to parents (who gain reproductive success). But our results in this project have revealed an amazing finding: parents' survival is reduced when they receive help. We reached at this result by using capture-recapture data for individually marked birds. The result is paradoxical but it makes all sense when it is placed into the context of our previous knowledge on this species. We had already published that parents that count on helpers increase their effort to feed the chicks. This should entail survival costs. The interesting thing is that parents decide to increase their breeding effort when the opportunities to succeed in the current season are high because of the presence of helpers, since despite this decision may reduce survival, it increases lifetime reproductive success and hence it is favoured by selection. But why do this effect only happen in this species? Perhaps the highly unpredictable conditions that occur in these Mediterranean habitats, those that also affected our research in 2016, are responsible for the benefit balance between present and future, so that taking advance of a realized current good opportunity prevails against preserving for an uncertain future.
But our main question to tackle was why helpers help to unrelated birds. We have analysed two types of reciprocity, direct and indirect. By direct reciprocity we expect helped individuals to repay to their helpers individually. Indirect reciprocity, by contrast, is based on the idea that helping individuals may receive more help from any other birds in the group. To study direct reciprocity we considered the opportunities for paying back, i.e. whether the previously helped individual was available when the helper has laid its eggs and would need help. We found that although there were many opportunities for direct reciprocity it only happened very rarely, so we conclude that this should not be the main mechanism to maintain helping. Then we looked at indirect reciprocity, i.e. the help received by any members in the group. And yes, the results show that individuals that helped more received more help. Now we are deepen into the analysis of which individuals in particular give help to those that previously helped others, the possible role of spatial proximity between nests and the relationships within the social network.
We already know from previous work that helping is beneficial to helped chicks (who increase survival and condition) and hence to parents (who gain reproductive success). But our results in this project have revealed an amazing finding: parents' survival is reduced when they receive help. We reached at this result by using capture-recapture data for individually marked birds. The result is paradoxical but it makes all sense when it is placed into the context of our previous knowledge on this species. We had already published that parents that count on helpers increase their effort to feed the chicks. This should entail survival costs. The interesting thing is that parents decide to increase their breeding effort when the opportunities to succeed in the current season are high because of the presence of helpers, since despite this decision may reduce survival, it increases lifetime reproductive success and hence it is favoured by selection. But why do this effect only happen in this species? Perhaps the highly unpredictable conditions that occur in these Mediterranean habitats, those that also affected our research in 2016, are responsible for the benefit balance between present and future, so that taking advance of a realized current good opportunity prevails against preserving for an uncertain future.
But our main question to tackle was why helpers help to unrelated birds. We have analysed two types of reciprocity, direct and indirect. By direct reciprocity we expect helped individuals to repay to their helpers individually. Indirect reciprocity, by contrast, is based on the idea that helping individuals may receive more help from any other birds in the group. To study direct reciprocity we considered the opportunities for paying back, i.e. whether the previously helped individual was available when the helper has laid its eggs and would need help. We found that although there were many opportunities for direct reciprocity it only happened very rarely, so we conclude that this should not be the main mechanism to maintain helping. Then we looked at indirect reciprocity, i.e. the help received by any members in the group. And yes, the results show that individuals that helped more received more help. Now we are deepen into the analysis of which individuals in particular give help to those that previously helped others, the possible role of spatial proximity between nests and the relationships within the social network.
Our study birds show us that willingness to help others is a trait favoured by natural selection in unrelated social individuals because, even if there were not direct reciprocity by helped individuals repaying back to their helpers, helping others associated with being helped by any other unrelated birds in the social group. So far we have got evidences of what is happening but we are still working on modelling the evolutionary stability of the strategy within the social network, to fully understand how natural selection is favouring it.
The dissemination of the results has been done by two main kinds of actions. On one hand, directed to the scientific community through presentations at international conferences and publications in peer-reviewed scientific journals and book chapters. On the other hand, we intended to reach the audiences beyond the specialized scientific community, by participating in the European Researcher's Night (Marie Sklodowska-Curie actions) and giving open seminars at the CIBIO institute in Portugal and talks to university students, mainly at the University of Córdoba in Spain.
The fellowship did not only benefit the researcher individually, but also reinforced the contribution of Mediterranean biology into ERA and the collaboration between women (the fellow and the supervisor in Spain and Portugal, respectively) heading research lines in Europe.
The dissemination of the results has been done by two main kinds of actions. On one hand, directed to the scientific community through presentations at international conferences and publications in peer-reviewed scientific journals and book chapters. On the other hand, we intended to reach the audiences beyond the specialized scientific community, by participating in the European Researcher's Night (Marie Sklodowska-Curie actions) and giving open seminars at the CIBIO institute in Portugal and talks to university students, mainly at the University of Córdoba in Spain.
The fellowship did not only benefit the researcher individually, but also reinforced the contribution of Mediterranean biology into ERA and the collaboration between women (the fellow and the supervisor in Spain and Portugal, respectively) heading research lines in Europe.