The role of epigenetics, transposable elements, and genome size variation in speciation

Abstract: Species formation occurs when lineages diverge and incompatibilities between their genomes lead to reproductive isolation. Such incompatibilities can involve genomic content (including protein coding and regulatory sequences, as well as repetitive DNA) or overall genome architecture (including karyotype, epigenetic marks, genome size). To date, most theoretical and empirical research focused on the genetics of speciation has examined the protein-coding portion of the genome. I am interested in testing hypothesis about the potential role of transposable elements, cytosine methylation, and genome size variation in establishing isolating barriers. Salamanders provide a good system in which to test these hypotheses because they 1) have very large genomes with large numbers of transposable elements, 2) methylation levels are higher in amphibians than in most other animals, and 3) significant intra-specific genome size variation exists. The salamander Ensatina eschscholtzii is an ideal system in which to investigate speciation. E. eschscholtzii is comprised of seven subspecies distributed in a ring around the Central Valley of California and is a classic example of a ring species. Although adjacent subspecies are generally connected by some gene flow, their levels of genetic differentiation are comparable to closely related species, and the two southernmost subspecies show nearly complete reproductive isolation where they reconnect at the base of the Central Valley. Thus E. eschscholtzii provides a perfect system in which to study whether differences in genome size, transposable elements, and methylation can produce genomic incompatibilities and establish reproductive isolation.

Experimental evolution and behavioral plasticity in the Trinidadian guppy

Abstract: The question of ‘nature versus nurture’ remains a fundamental problem in evolutionary ecology, though we now address the degree to which each is important. Despite much research on this topic, the role of environmentally induced plasticity in evolutionary processes remains unclear and controversial, specifically the role of behavioral plasticity, when behavior varies depending on the environment. Plasticity is thought to play an important role in the initial establishment and subsequent adaptation of a population by allowing it to persist long enough to evolve new traits. I will take advantage of a recent introduction of Trinidadian guppies to a new environment and investigate behavioral plasticity during early adaptation in order to shed light on this fundamental question. The Trinidadian guppy, Poecilia reticulata, is a small freshwater fish that varies in color, morphology, life history, and behavior based on the presence or absence of predators. Although guppies have been shown to adapt to new environments, this will be the first time that behavioral changes will be monitored over a fine time scale and attributed to plastic versus genetic change.

Density dependence in two seasons: demographic effects of competition and climate

Abstract: Density dependence is central to our understanding of population dynamics. Theory predicts that populations must be regulated by density-dependent mechanisms during at least some time periods or life stages, but detecting and measuring the strength of density dependence is notoriously difficult. For example, population density is likely to interact with ecological conditions such as food availability to affect demographic rates, and these interactions may mask the signal of density dependence. Relatively simple ecological communities, such as those on islands, provide an opportunity to disentangle the effects of density dependence from demographic variation due to fluctuating ecological conditions. Here, we analyze the fecundity and apparent survival of Orange-crowned Warblers (Oreothlypis celata) breeding on Catalina Island, California to test for evidence of density dependence. We found that within the island’s mediterranean climate, rainfall was the primary driver of food abundance, and was positively correlated with fecundity. After accounting for variation in rainfall, fecundity showed a strong pattern of negative density dependence. In addition, apparent survival was negatively correlated with population density on the wintering grounds, providing a rare example of potential regulatory mechanisms acting in multiple seasons of a migratory bird.

Investigating the mating system and primary sex ratio in the Island Scrub-Jay: Implications
for conservation

Abstract: The study of reproductive behavior can provide information about the maintenance of both processes and patterns of genetic diversity, a central
theme in conservation biology. The maintenance of genetic diversity is an important conservation goal because it allows populations to adapt to future environmental conditions as well as to avoid the detrimental effects of genetic drift and inbreeding. Genetic diversity in wild populations is best maintained by preserving large populations. However, even a large population can lose genetic variation over time, depending on factors that influence its effective population size. Mating systems and primary sex ratio biases are two reproductive characteristics that have the potential to influence effective population sizes. This study will investigate the rate and origin of extra pair paternity, as well as testing for the presence of a primary sex ratio bias in a species of conservation concern, the Island Scrub-Jay, Aphelocoma insularis. All data will be shared with managers who are creating a management plan for the species and conducting a population viability analysis.

Reproductive Ecology of the Island Scrub-Jay

Abstract: The Island Scrub-Jay (Aphelocoma insularis) is currently found solely on Santa Cruz Island, California, giving it the most restricted range of any North American bird species. Despite emerging conservation concerns, little is known about this species’ demography or the factors that limit its annual fecundity. In 2008 and 2009, we followed nearly 50 pairs over two breeding seasons, documented all nesting attempts, quantified nest success, parental feeding rates, and nest attendance during incubation. Daily nest survival probability (± SE) was 0.963 ± 0.003 (n=145 nests). Nest depredation was the principal cause of nest failure, accounting for 79% of failed attempts. Mean annual fecundity (± SE) was 1.16 ± 0.10 fledglings per pair (n=95), with 36% of pairs fledging young. Our data suggest that this population, given estimated adult survival, has sufficiently high annual fecundity to sustain a stable population size.

“Energetic stress as a potential cause of risky foraging in honeybees infected with Nosema ceranae“

Abstract: Despite disease being ubiquitous selective pressure, it is rarely considered in optimality models of animal decision making processes. I am investigating how diseases can change the predictions of behavioral ecology theory.  More specifically, using the honeybee as a model organism, I would like discover the applicability of the risk-sensitivity theory to social organisms.  If the predictions hold true for honeybees then how does an infection change predictions of the risk-sensitivity theory? Providing answers to these questions may elucidate the scope of the risk-sensitivity theory and a general mechanism to explain the recent disappearance of honeybees from hives – termed Colony Collapse Disorder (CCD).

Mechanisms of local adaptation in Trinidadian guppies (Poecilia reticulata)

Abstract: Natural selection is one of several key mechanisms driving the diversification of organisms. However, despite laboratory experiments frequently demonstrating the potential for traits to undergo selection, detecting selection in the wild is far less frequent. The failure to detect selection in the wild is likely due to the various limitations associated with obtaining quantitative data on performance traits for natural populations over time. Previous work with Trinidadian guppies from high and low predation populations has shown that evolution can proceed far faster than previously thought and, for life history traits, occurs on ecological time scales. Although these evolutionary patterns are repeatable in guppy populations throughout Trinidad, the underlying mechanism of local adaptation remains elusive. Taking advantage of recent introduction experiments we are beginning to unravel the roles of phenotypic plasticity and directional selection in local adaptation. Through a combination of laboratory experiments and field observations, heritabilities and plasticity in morphology, performance and life history traits are being measured and used to make predictions on how populations respond during the early stages of evolutionary divergence.

Does size matter? Fitness, larval size, and strange behavior related to the Acanthocephalan parasite Leptorhynchoides thecatus

Abstract: Modification of host behavior by parasites has been documented in a large variety of parasite systems. To understand how these phenomena evolve and operate, scientists have developed models and theoretical frameworks. Much of this literature explicitly assumes that there is a cost to a parasite when it actively changes host behavior, despite the fact that no study has demonstrated such a cost. The parasite Leptorhynchoides thecatus (Acanthocephala) presents an opportunity to investigate such a cost. Smaller larval cystacanths are less likely to survive transmission to the final host and establish as adults. Because transmission and establishment success are essential components of fitness, parasite larval size provides an important potential link to a fitness cost if behavioral modification is related to larval size. In this study, behavioral changes were demonstrated in a series of three behavioral tests on the crustacean intermediate host, Hyalella azteca (Amphipoda). Behavioral scores compared between infected and uninfected hosts show significant differences in behavior between groups. When infected amphipod behavior was considered in relation to parasite volume, none of the behaviors showed a strong influence of larval size. These results may be explained by a number of factors, which will be highlighted for future directions for this research.

Fine scale habitat partitioning between sympatric sister species Mimulus guttatus and M. laciniatus: effects on competition and reproductive isolation