Browsing by Subject "Dispersal"

In chimpanzees, most females disperse from the community in which they were born to reproduce in a new community, thereby eliminating the risk of inbreeding with close kin. However, across sites, some females breed in their natal community, raising questions about the flexibility of dispersal, the costs and benefits of different strategies and the mitigation of costs associated with dispersal and integration. In this dissertation I address these questions by combining long-term behavioral data and recent field observations on maturing and young adult females in Gombe National Park with an experimental manipulation of relationship formation in captive apes in the Congo.

To assess the risk of inbreeding for females who do and do not disperse, 129 chimpanzees were genotyped and relatedness between each dyad was calculated. Natal females were more closely related to adult community males than were immigrant females. By examining the parentage of 58 surviving offspring, I found that natal females were not more related to the sires of their offspring than were immigrant females, despite three instances of close inbreeding. The sires of all offspring were less related to the mothers than non-sires regardless of the mother’s residence status. These results suggest that chimpanzees are capable of detecting relatedness and that, even when remaining natal, females can largely avoid, though not eliminate, inbreeding.

Next, I examined whether dispersal was associated with energetic, social, physiological and/or reproductive costs by comparing immigrant (n=10) and natal (n=9) females of similar age using 2358 hours of observational data. Natal and immigrant females did not differ in any energetic metric. Immigrant females received aggression from resident females more frequently than natal females. Immigrants spent less time in social grooming and more time self-grooming than natal females. Immigrant females primarily associated with resident males, had more social partners and lacked close social allies. There was no difference in levels of fecal glucocorticoid metabolites in immigrant and natal females. Immigrant females gave birth 2.5 years later than natal females, though the survival of their first offspring did not differ. These results indicate that immigrant females in Gombe National Park do not face energetic deficits upon transfer, but they do enter a hostile social environment and have a delayed first birth.

Next, I examined whether chimpanzees use condition- and phenotype-dependent cues in making dispersal decisions. I examined the effect of social and environmental conditions present at the time females of known age matured (n=25) on the females’ dispersal decisions. Females were more likely to disperse if they had more male maternal relatives and thus, a high risk of inbreeding. Females with a high ranking mother and multiple maternal female kin tended to disperse less frequently, suggesting that a strong female kin network provides benefits to the maturing daughter. Females were also somewhat less likely to disperse when fewer unrelated males were present in the group. Habitat quality and intrasexual competition did not affect dispersal decisions. Using a larger sample of 62 females observed as adults in Gombe, I also detected an effect of phenotypic differences in personality on the female’s dispersal decisions; extraverted, agreeable and open females were less likely to disperse.

Natural observations show that apes use grooming and play as social currency, but no experimental manipulations have been carried out to measure the effects of these behaviors on relationship formation, an essential component of integration. Thirty chimpanzees and 25 bonobos were given a choice between an unfamiliar human who had recently groomed or played with them over one who did not. Both species showed a preference for the human that had interacted with them, though the effect was driven by males. These results support the idea that grooming and play act as social currency in great apes that can rapidly shape social relationships between unfamiliar individuals. Further investigation is needed to elucidate the use of social currency in female apes.

I conclude that dispersal in female chimpanzees is flexible and the balance of costs and benefits varies for each individual. Females likely take into account social cues present at maturity and their own phenotype in choosing a settlement path and are especially sensitive to the presence of maternal male kin. The primary cost associated with philopatry is inbreeding risk and the primary cost associated with dispersal is delay in the age at first birth, presumably resulting from intense social competition. Finally, apes may strategically make use of affiliative behavior in pursuing particular relationships, something that should be useful in the integration process.

The deleterious effects of inbreeding have been well-documented in both captive and wild populations. Mechanisms of inbreeding avoidance such as mate choice and sex-biased dispersal have also been documented across a variety of taxa. However, studies of inbreeding avoidance via mate choice are surprisingly scarce, and those that explicitly compare maternal and paternal kin are entirely absent in mammals. Here, we provide the first study to assess how behavioral inbreeding avoidance varies across kin classes in a population of wild baboons. We first examine the series of isolating barriers that prevent inbreeding, including death, dispersal, and mate choice, and we next use pedigree data to assess how behavioral inbreeding avoidance varies across kin classes. We found that while the demographic barriers of death and male-biased dispersal are extremely effective in limiting inbreeding in this population, we still found strong evidence for inbreeding avoidance via mate choice. In particular, while most kin classes exhibited inbreeding avoidance, maternal kin (mother-son pairs, maternal siblings) were more avoidant than paternal kin (father-daughter pairs, paternal siblings) despite having identical coefficients of relatedness. Finally, by taking advantage of a natural experiment in our study population, we also found that social groups with reduced sex-biased dispersal and reduced inbreeding avoidance via mate choice produced ten times as many inbred offspring.

Why do species exist where they do? Understanding the forces and processes that shape species’ ranges—and that affect their dispersal and range expansion—have long fascinated biologists. In this work, I focus on understanding diversity and dispersal in Cheilanthes ferns. I first describe a species new to science, Cheilanthes ecuadorensis, from among the understudied South American members of this genus. I then turn to studying the widely distributed, asexual, Australasian species C. distans. Careful review of samples from this species allowed me to find sexual specimens previously unknown to science that exist in a narrow range, as well as to catalogue extensive spore diversity that has gone unrecorded. I find strong evidence for trade-offs related to spore size, with larger spores having higher germination while smaller spores have greater dispersal. Excitingly, I find that spores previously catalogued as abortive are in fact viable, and contribute to the spore size diversity I observe. I then place these findings into phylogenetic context by building a phylogeny for all Australasian Cheilanthes, and use it to explore the relationships of sexual and asexual lineages, of different ploidy levels, and of geographic distributions. These analyses reveal that most dispersal in C. distans occurs over shorter rather than longer distances, in contrast to previous hypotheses posited by fern biologists. I observe that lineages are not limited to particular geographic regions, as well finding that dispersal is asymmetrical and seems to be tracking trade winds. For all my work I rely heavily on herbarium specimens and use them to catalogue morphological variation as well as to obtain DNA sequences that are used for phylogenetic analysis. I implement a variety of statistical and systematic analyses to explore correlations between spore size, reproductive mode, ploidy, germination, and dispersal. While this work expands our knowledge of fern diversity and biogeography, much still remains to be understood, including cataloguing possible novel species, understanding the biology behind spore size determination, and exploring the role of niche in the dispersal and range expansion of C. distans.

This dissertation is an investigation of the systematics, phylogeography, and ecology of a globally distributed fungal family, the Elaphomycetaceae. In Chapter 1, we assess the literature on fungal phylogeography, reviewing large-scale phylogenetics studies and performing a meta-data analysis of fungal population genetics. In particular, we examined the possible effects of asexuality, trophic niche, dispersal method, and ocean barriers on population structure. In Chapter 2, we examine the systematics and phylogeography of the Elaphomycetaceae, a family consisting of the truffle genus Elaphomyces and the stalked genus Pseudotulostoma, hypothesizing that the mammal-dispersed truffle would show evidence of dispersal limitation. Using DNA sequence data, we determined that Pseudotulostoma is derived from a lineage of Elaphomyces, indicating that Elaphomyces as currently defined is paraphyletic. The distribution of each subgenus of Elaphomyces is nearly global; representative species have been found on every continent save Africa and Antarctica. This biogeographic pattern does not follow the pattern expected by a scenario of continental vicariance. Dating analysis in BEAST confirmed that broadly distributed clades are, in most cases, too young for this pattern to be explained by continental vicariance, indicating that occasional long-distance dispersal has been a significant component in the biogeographic history of the Elaphomycetaceae. This finding contradicts our initial hypothesis that the mammal-dispersed truffles would be dispersal- limited. In Chapter 3, we investigate the role of Elaphomyces as a host for the fungal parasite Elaphocordyceps, a parasite derived from insect pathogens that attacks both insect larvae and Elaphomyces, its only fungal host. We examined the biogeography of Elaphocordyceps isolated from Elaphomyces specimens in order to test whether it, like its host, showed recent connections between the Southern and Northern Hemispheres. We also evaluated the pathogenicity of infection as determined by a visual rubric for the truffle gleba, the phylogenetic distribution of Elaphocordyceps species on its host, testing for seasonal, climate, and host-parasite effects. In Chapter 4, based on the phylogeographic pattern seen in Elaphomyces that resembles that of some air-dispersed fungi, we used theoretical and experimental methods to test whether Elaphomyces could be dispersed by air. We tested the capacity for air dispersal with an experimental test of passive air dispersal on the powdery spores of Elaphomyces morettii and found that these large spores could disperse over a short distance (10 m) in comparable numbers with the spores of the giant puffball Calvatia cyathiformis, which is known to be air-dispersed. The major findings of this thesis are that 1) fungi in general show high dispersal ability, but that trophic niche and dispersal mode may affect population structure, 2) that Pseudotulostoma, a stalked genus, is derived from the truffle Elaphomyces, 3) that the Elaphomycetaceae have experienced frequent long-distance dispersal despite 4) that the fitness of Elaphomyces as indicated by glebal development varies with host-parasite interactions based on species identity, but not with climate or season, and that 5) Elaphomyces spores, should they be released into the air, can remain in the air long enough to be dispersed long distances by the wind. The overall conclusion of this thesis is that, while Elaphomyces is clearly reliant on animal vectors for excavation and dispersal, its past history of long-distance dispersal and current spore trajectories indicate it can be passively air-dispersed as well.

Ecologists have long sought to uncover the mechanisms behind large-scale, macroecological patterns in the distribution and abundance of species. Macroecological patterns are often attributed to the dynamics of dispersal (e.g. dispersal limitation or widespread dispersal). However, few studies actually measure dispersal to determine if dispersal rates are commensurate with the observed macroecological patterns. In this dissertation, I use population genetic analyses across many species to obtain community-level estimates of dispersal rates for two different ecological systems: birds on islands and trees in tropical rainforests. These independent estimates of dispersal then allow me to determine if macroecological patterns in these two systems can be attributed to dispersal dynamics.

In chapter two, I explore the contrasting macroecological patterns of two groups of Lesser Antillean birds. The groups' differing macroecological patterns could be due to differences in dispersal, but other authors have advocated different mechanisms. Population genetic analyses show that the two groups do differ significantly in rates of inter-island dispersal, indicating that dispersal dynamics can explain their contrasting macroecological patterns. In chapter three, I turn my attention to tropical tree communities. In contrast to studies of birds on islands, studies of trees in tropical rainforests may suffer from misidentification of individuals in the field. Using a phylogenetic approach, I determine errors rates in identification, and then assess the effect of these errors on macroecological patterns and other ecological analyses of tropical tree communities. I find that error rates are substantial, but that they have little effect on macroecological patterns. In contrast, species-level ecological analyses can be dramatically affected by these errors.

In chapter four, I return to the influence of dispersal on macroecological patterns, this time in tropical tree communities. One notable macroecological pattern in Amazonian tree communities is a high correlation in the relative abundances of species shared across communities, which could indicate high rates of dispersal between communities. However, population genetic analyses show that dispersal is severely limited between communities. Thus, some factor besides dispersal, such as differences in competitive ability or susceptibility to disease, must be driving species to achieve similar relative abundances in geographically separated communities. In contrast, I show that dispersal limitation is the likely cause of another macroecological pattern frequently observed in tropical tree communities: the decline in the compositional similarity of communities with distance. However, this is not steady-state dispersal limitation in an equilibrium framework as is conventionally thought. Instead, the dispersal limitation appears to be historical in nature, which implies a heretofore unnoticed role for historical contingency in the assembly of Amazonian tree communities.

Adaptation is central to our understanding of the origin of biological diversity. Yet whether adaptive divergence promotes the formation of new lineages remains poorly understood. My dissertation addresses the role of adaptive divergence in diversification and speciation. I also investigate an alternative mechanism: dispersal, which can promote diversification and speciation through its effects on gene flow and allopatry. To address the role of divergent adaptation and dispersal in the process of diversification, I take an integrated approach, combining both comparative methods with quantitative genetics to characterize patterns of diversification and speciation in the tribe Brassiceae and genus Cakile. I start with a comparative study of the role of dispersal and adaptation in diversification, and then focus on the role of climatic and latitudinal divergence in the processes of adaptive divergence and speciation. In general, I find limited evidence for the role of divergent adaptation in the evolution of intrinsic reproductive isolation. Diversification in the tribe Brassiceae appears to be mediated by dispersal ability, while in the genus Cakile, the evolution of intrinsic reproductive isolation is largely independent of ecological divergence. Thus, while divergent adaptation to novel habitats and climate are likely occurring in Brassiceae, mediated in part by the evolution of long-distance dispersal, the evolution of intrinsic genic reproductive barriers appears to not be influenced by adaptation.