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My research can be divided into three broad areas of
investigation: 1) studies of mating system and sexual selection, 2) phylogenetic
systematics of populations or species of reptiles and amphibians, and
3) application of my basic research to conservation. The conceptual thread
that ties these together is my interest in disentangling the relative
roles of organismal attributes and microevolution in shaping phylogenetic
relationships among populations or species. Thus, in my studies of mating
systems and sexual selection, I have focused on characterizing the determinants
of reproductive success, with the goal of understanding the evolutionary
consequences of large disparities in fitness within breeding groups. For
instance, high variance in reproductive success among individuals and
fluctuations in population size over time are two factors that can greatly
influence the genetic effective population size and hence genetic drift.
Population parameters such as these can be tied closely to organismal
traits, so ecology, behavior, and demography at the individual level can
have important effects on overall patterns of population structure at
larger spatial scales. I relate my findings in the study of mating systems
to patterns of population differentiation at multiple geographic scales
ranging from local genetic variation among populations, to rangewide genetic
variation and phylogenetic relationships among groups of species. Finally,
I take every opportunity to apply my findings to the conservation genetics
and management of amphibians and reptiles.
Genetic characterization of mating systems and
sexual selection
The diverse array of mating systems exhibited by reptiles and amphibians
presents an ideal opportunity to examine the selective costs and benefits
of mating strategies and choices. Despite the diversity of mating systems
and the behavioral intricacies of ectotherm reproductive behavior, sexual
selection in ecothermic lineages has not received the same degree of attention
as in endotherms. Certain life history traits such as large clutch sizes,
inaccessibility of nests or breeding groups, and primarily nocturnal behaviors
have historically limited studies of mating systems and sexual selection
in many ectothermic lineages. This “clade bias” is changing
rapidly. Over the last decade we have seen an increased emphasis on the
study of behavior, reproductive success, and kinship in all animal lineages.
The absence of extended parental care in most ectotherms makes it easier
to estimate the cost-benefit ratio of mate choice. Likewise, it is now
feasible to establish reproductive success (via paternity typing) of large
numbers of offspring, allowing us to accurately quantify the outcome of
male-male competition and female choice (intra- and inter-sexual selection).
My research has focused particularly on the following questions, with
the overall goal of understanding the diversity and evolution of mating
systems in these lineages:
- What are the ecological and evolutionary contexts
for the evolution of alternative mating strategies?
- What are the determinants of reproductive fitness,
especially in systems with high variance in reproductive success?
- What are the population-level consequences (genetic)
of high variance in reproductive success?
My goal is to design experiments in the lab and in the
field to test hypotheses about mate choice, reproductive success, and
fitness. I use field experiments and behavioral observations coupled with
laboratory studies for molecular assessment of paternity and maternity
rates in natural populations. As is often the case in science, I have
been surprised by my results on a number of occasions, underscoring the
importance of exploring a variety of mating systems before drawing general
conclusions about their evolution.
Phylogenetic systematics: population differentiation, phylogeography,
and species relationships
I extend my studies of kinship, relatedness and family genealogies with
phylogenetic studies of diversification among populations, lineages, and
species. I focus on microevolutionary processes that contribute to differentiation
among populations, with particular attention on how species-specific traits
(such as demography, dispersal capacity, reproductive skew) influence
the rate or direction of differentiation. In systematic studies at larger
geographic scales I focus on the patterns and inferred processes of historical
diversification among populations and species.
- How do limits to dispersal and changes in habitat availability
(due to past climatic changes) interact to determine the pattern of
evolutionary diversification of population lineages?
- Do co-occuring species exhibit similar patterns of
population-level diversification (i.e. similar phylogeographic patterns)?
- How do species- specific characteristics (such as life-history,
behavior, mating system) influence phylogeographic patterns.
As lineages diversify, what mechanisms play a role in reproductive isolation
and eventually speciation?
- Once speciation has occurred, resulting in reciprocally
monophyletic lineages, can we reconstruct from phylogenies the modes
and patterns of differentiation by examination of neontological data?
Conservation genetics of reptiles and amphibians
It is probably impossible for an organismal biologist to conduct research
without consideration of the threats to habitats and the flora and fauna
that occupy them. I have found myself repeatedly intrigued by the implications
of my research for the management of endangered or threatened species.
Thus far, I have focused primarily on conservation genetics of individual
threatened taxa and on how science is used in policies and recovery actions
for these taxa. In the near future I hope to extend my use of population
genetic methods to inform management and conservation decisions.
In my conservation efforts I focus on the following questions:
- How is genetic variability partitioned among populations
of endangered or threatened species that inhabit patchy or fragmented
landscapes?
- Does fragmentation impede historical levels of population
connectivity through limits on gene flow, and if so, at what scale?
- Do mating systems (especially those resulting in high
variance in reproductive success) exacerbate problems associated with
inbreeding and reduced genetic variability in small isolated populations
of threatened taxa?
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