Cooperation and conflict in conspecific brood parasitism : an alternative reproductive tactic

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Title: Cooperation and conflict in conspecific brood parasitism : an alternative reproductive tactic
Author: Jaatinen, Kim
Contributor: University of Helsinki, Faculty of Biosciences, Department of Biological and Environmental Sciences
Thesis level: Doctoral dissertation (article-based)
Abstract: Interactions among individuals give rise to both cooperation and conflict. Individuals will behave selfishly or altruistically depending on which gives the higher payoff. The reproductive strategies of many animals are flexible and several alternative tactics may be present from which the most suitable one is applied. Generally, alternative reproductive tactics may be defined as a response to competition from individuals of the same sex. These alternative reproductive tactics are means by which individuals may fine-tune their fitness to the reigning circumstances and which are shaped by the environment individuals are occupying as well as by the behaviour of other individuals sharing the environment. By employing such alternative ways of achieving reproductive output, individuals may alleviate competition from others. Conspecific brood parasitism (CBP) is an alternative reproductive strategy found in several egg laying animal groups, and it is especially common among waterfowl. Within this alternative reproductive strategy, four reproductive options can be identified. These four options represent a continuum from low reproductive effort coupled with low fitness returns, to high reproductive effort and consequently high benefits. It may not be evident how individuals should allocate reproductive effort between eggs laid in their own nest vs. in nests of others, however. Limited fecundity will constrain the number of eggs donated by a parasite, but also the tendency for hosts to accept parasitic eggs may affect the allocation decision. Furthermore, kinship, individual quality and the costs of breeding may play a role in complicating the allocation decision. In this thesis, I view the seemingly paradoxical effects of kinship on conflict resolution in the context of alternative reproductive tactics, examining the resulting features of cooperation and conflict. Conspecific brood parasitism sets the stage for investigating these questions. By using both empirical and theoretical approaches, I examine the nature of CBP in a brood parasitic duck, the Barrow's goldeneye (Bucephala islandica). The theoretical chapter of this thesis gives rise to four main conclusions. Firstly, variation in individual quality plays a central role in shaping breeding strategies. Secondly, kinship plays a central role in the evolution of CBP. Thirdly, egg recognition ability may affect the prevalence of parasitism. If egg recognition is perfect, higher relatedness between host and parasite facilitates CBP. Finally, I show that the relative costs of egg laying and post-laying care play a so far underestimated role in determining the prevalence of parasitism. The costs of breeding may outweigh possible inclusive fitness benefits accrued from receiving eggs from relatives. Several of the patterns brought out by the theoretical work are then confirmed empirically in the following chapters. Findings include confirmation of the central role of relatedness in determining the extent of parasitism as well as inducing a counterintuitive host clutch reduction. Furthermore, I demonstrate a cost of CBP inflicted on hosts, as well as results suggesting that host age reflects individual quality, affecting the ability to overcome costs inflicted by CBP. In summary, I demonstrate both theoretically and empirically the presence of cooperation and conflict in the interactions between conspecific parasites and their hosts. The field of CBP research has traditionally been divided, but the first steps have now been taken toward the acceptance of the opposite side of the divide. Especially the theoretical findings of chapter 1 offer the possibility to view seemingly contrasting results of various studies within the same framework, and may direct future research toward more general features underlying differences in the patterns of CBP between populations or species.Knipor kan få mer avkomma genom att lägga ägg i andra knipors bon. Mottagaren måste dock ta hand om en större kull ungar, vilket är krävande. Därför kallas fenomenet kullparasitism. Denna avhandling studerar effekterna av kullparasitism på värdhonors häckningsframgång samt konflikt- och samarbetssituationer relaterade till kullparasitism. Denna studie följde islandsknipor i Västra Kanadas ödemarker under fyra häckningssäsonger. Vart annat bo innehöll parasitägg. Även om kullparasitism är vanligt hos knipor och andra andfåglar är detta en mycket hög grad av parasitism. Kullparasitism innebär kostnader för värdar och de överger sina bon om för många parasit ägg läggs i deras kullar. Knipor tycks dock tolerera sina parasiterande släktingar och sköter deras ungar tills de är flygfärdiga. Parasiterna tycks veta var deras släktingar häckar. Ju närmare släkt parasiten är med dess värd desto fler ägg lade parasiten. Även avståndet mellan parasitens eget bo och värdboet hade en effekt på antalet ägg som lades. Värdbon nära parasitens bo fick mer parasitägg än mer avlägsna bon. Som följd av parasitism lade värdhonor färre ägg i sina bon, som om de gav rum för släktingars parasitägg. Kullparasitism studerades även med hjälp av en matematisk modell för att klargöra när parasitism är skadligt och när det kan vara fördelaktigt. Resultaten visade att kullparasitism parasit kan leda till ömsesidiga fördelar om värd och parasit är besläktade. Detta beror på att den som hjälper sin släkting att föröka sig får själv fördelar. Det lönar sig för värdar att förkasta parasitägg om parasiten inte är en släkting. Resultaten av denna forskning visar att kullparasitism mellan individer av samma art är en konflikt som kan lösas genom släktskap. Då värd och parasit är släktingar kunde kullparasitism vara samarbete.
URI: URN:ISBN:978-952-10-5467-9
Date: 2009-05-08
Subject: evoluutiobiologia
Rights: This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.

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