The Role of Dislodgement in the Territorial Ecology of the Owl Limpet, \u3cem\u3eLottia gigantea\u3c/em\u3e

Ascertaining the risks and benefits of different behaviors is a central goal of research on territoriality. Although most territorial behavior is ritualized, with concomitant reduced risks for both residents and intruders, this ritualization is generally found to be underpinned by rare, highly consequential, interactions. The agonistic behavior of the intertidal owl limpet, Lottia gigantea, involves defense of a feeding territory, and includes a relatively explosive thrusting response by territory holders against intruding conspecifics. We here ask whether this thrusting behavior is capable of entirely dislodging intruders from their rocky wave-swept substratum, thereby ridding the resident of future challenges by that intruder. Our field measurements of the strength of territorial thrusts, as well as thrust resistance, indicate that territorial limpets are strong enough to overcome the resistance of small to medium sized (\u3c40 mm) conspecifics encountered on their territories. Interestingly, at least 44% of the limpets dislodged from the rock substratum during a retreat or territorial response survived in a new location. Growth of these survivors was at least as rapid as that of undisturbed limpets in the old location. We conclude that shell thrusting during the territorial response of Lottia gigantea can reduce the cost of territorial defense by dislodging smaller conspecifics, thereby eliminating them from all future interactions. Conversely, the risk incurred by these smaller conspecifics while intruding onto territories of larger individuals is likely mitigated by the surprisingly high survival rate, and subsequent normal growth, of dislodged limpets

How demographic history shapes genetic architecture and influences fertility and immunity phenotypes in Southern African populations

Survival and reproduction—two traits that are crucial to the process of evolution. Those who survive have the opportunity to reproduce, and those who reproduce more contribute a greater amount of genetic material to the next generation. Thus, fertility and immunity phenotypes are especially strong selective pressures in shaping the course of human evolution. However, these traits that we observe today did not arise in a vacuum. They are the result of generations of demographic history—mutations, bottlenecks, founder events, cultural practices, migration, and selection—all acting simultaneously to shape the genetic architecture of immunity, fertility, and other complex phenotypes. The following chapters seek to elucidate the effects of demographic history on genetic architecture and its influence on various phenotypes. The first three chapters of this dissertation explore the demographic history and cultural practices of the Himba in northern Namibia and their effects on the complex phenotypes of height and fertility. Chapter 1 provides an important foundation for chapters 2 and 3 by investigating the rate of extrapair paternity (EPP) through the practice of concurrency and assessing paternity confidence. In Chapter 2, I explore the demographic history of the Himba using various population genetics methods and demonstrate how population bottleneck and endogamy, rather than consanguinity, have contributed to increased homozygosity and recessive mutation load. Additionally, I show that this increase in homozygosity is associated with reduced fertility in women. Chapter 3 investigates whether this increase in homozygosity is associated with reduced height in the Himba, a relationship that has previously been reported in European populations. In Chapter 4, I switch directions and focus on disease- and immunity-related genes in the ≠Khomani San population. I investigate, through complex simulations and the use of genetic data from the HLA region of the genome, how the demographic history and introduction of novel disease pressures to this South African population effects signatures of recent selection in immune-related genes

Examination of runs of homozygosity in relation to height in an endogamous Namibian population

ObjectivesHeight is a complex, highly heritable polygenic trait subject to both genetic composition and environmental influences. Recent studies suggest that a large proportion of height heritability is determined by the cumulative effect of many low allele frequency variants across the genome. Previous research has also identified an inverse relationship between height and runs of homozygosity (ROH); however, this has yet to be examined within African populations. We aim to identify this association within the Himba, an endogamous Namibian population who are recently bottlenecked, resulting in elevated haplotype sharing and increased homozygosity.Materials and methodsHere, we calculate the fraction of the genome composed of long runs of homozygosity (FROH) in a sample of 245 adults and use mixed effects models to assess its effect on height.ResultsWe find that Himba adults exhibit increased homozygosity. However, in contrast to previous studies in other populations, we do not find a significant effect of FROH on height within the Himba. We further estimated heritability of height, noting both an enrichment of distant relatives and greater developmental homogeneity across households; we find that h g 2 = 0.59 (SE ± 0.146), comparable to estimates reported in Europeans.DiscussionOur results may be due to other environmental variables we were not able to include, measurement error, or low statistical power, but may also imply that phenotypic expression resulting from increased homozygosity may vary from population to population