Year: 2008
Type: dissertation
Abstract: Given its importance for understanding the evolution of our own species, describing the processes that shape the wide array of animal social systems has long fascinated many researchers and the study of social behaviour is constantly being pushed in new directions.One such direction has been to add genetic approaches to answer questions on the evolution of social behavior.The recent methodological advances in molecular methods have allowed application of genetic methods to a number of natural populations of different animal species.Detailed studies based on DNA analyses now exist for a wide variety of species, and have provided insights into patterns of paternity, relatedness and dispersal, as well as to clarify how selection has shaped individual strategies.In this thesis I used published data in comparative analyses, to see whether aspects of the social structure of animals are linked to the amount and distribution of genetic variation.This can provide a better understanding of the patterns of genetic variation within natural populations and allow inference of aspects of social structure.It also allows inferences about the selective factors that potentially have shaped the specific social structure of a species.In the first study I analyzed patterns of average relatedness within and among social groups of wild chimpanzees.In chimpanzees males are philopatric; that is, they remain in the groups they have been born.It has therefore been speculated that the high levels of cooperation observed among chimpanzees males can be explained by kin selection.I showed that average relatedness among chimpanzee males within groups only rarely exceeds that of the females in the group, and is also similar to the relatedness of males across groups.To explain this pattern, I derived an analytical model to predict relatedness levels based on group size, reproductive skew and which sex disperses.This produced results consistent with the empirical chimpanzee data, in that the model predicts high levels of relatedness only within very small groups with high reproductive skew, and that in general relatedness among male philopatric species should be lower than among female philopatric species.This pattern was confirmed more generally with a dataset of several bird and mammalian species, clearly showing the effect of group size. Summary viIn the second study I took a closer look at the factor of variance in lifetime reproductive success (vLRS).Individuals in natural populations differ in the number of surviving offspring they produce.Since this is the basis of evolutionary change, behavioural ecologists have been trying to measure this directly, and population geneticists seek to detect resulting unusual patterns in the genome.I derived analytical approaches to derive the vLRS from the pattern of variation found at sex-specific genetic markers on a local scale.The basic premise is that if individuals differ in their reproductive success, matri-and patrilines should also differ in their sizes.Six approaches were assessed for their accuracy to detect vLRS from genetic data and robustness to potentially confounding factors by indvidual-based computer simulations.Two which proved to be suitable were applied to published data on variation at mitochondrial and Y-chromosomal genes from several populations.The results indicate that there are detectable differences between populations in the degree of vLRS, as well as between the sexes in the same population.This highlights that the social system of a species can have a large influence on the genetic diversity detected within a sample, which potentially can confound population genetic analyses.In the last part, the two approaches were applied to published mitochondrial DNA to infer vLRS for females of several mammalian species.While many studies have looked at reproductive skew among males and its causes and consequences, differences among females and potential competition among them is less well understood.I performed comparative analyses to infer whether high or low vLRS among females are correlated with ecological, social or morphological characteristics which previously have been linked with competition among females.If resources critical for reproduction are limited so that only some females gain access, higher vLRS is expected.In fact, species in which females have a dominance hierarchy, species in which females can potentially produce a large number of offspring and species in which allonursing occurs all show higher levels of vLRS within groups as inferred from mtDNA variation.Furthermore, species in which individuals show territorial behaviour have higher levels of vLRS between social groups.This shows that in species where females show higher levels of competition there are also larger differences among them in the number of offspring they produce.While I did not detect correlation with crude measures of potential underlying ecological or social factors in this dataset, these new approaches would allow for testing of mechanisms as more detailed data becomes available.Summary v i i In general, the results of this study show a clear link between the social structure animals live in and the distribution of genetic variation they carry.They highlight the usefulness of adding genetic methods to studies of social behaviour, since analyzing DNA of animals allows inference of the dispersal and breeding strategies of these individuals.In addition though, they also allow for insights into the ultimate mechanisms of these behaviours.Determining genetic relatedness is for instance essential to understand the influence of kin selection or how inbreeding avoidance shapes patterns of dispersal.While detailed studies of populations are the most direct test of selection, investigating distributions of interspecies differences in traits is a useful tool to understand the function and adaptation of these traits.The general framework of comparative studies of patterns of genetic variation developed here should prove fruitful since my results indicate that it can add to our understanding about the evolution of the amazing diversity of animal social systems.
Source: MPG.PuRe (Max Planck Society)
Author: Dieter Lukas
Language: English
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2969422756