Research Themes
MAJOR RESEARCH THEMES
Ecology and evolution of avian social and genetic mating system
What drives inter- and intra-specific variation in the social and genetic mating patterns of organisms? This question has motivated behavioral ecology for some time, but molecular advances have revolutionized the way we tackle it. In particular, next-generation genomics methods have allowed researchers to interrogate genetic parentage of species, especially free-living ones, for which genetic markers were previously unavailable. I employ such techniques to tackle hypotheses regarding social and mating systems in hitherto poorly known Neotropical bird species.
Causes and consequences of sociality, especially group-living
Animal life exhibits a kaleidoscopic diversity in social systems. For some species, a solitary existence predominates, with social interactions restricted to brief moments of parental care or mating. In contrast, life in a group is the only option to ensure survival and successful reproduction for other species. The diversity of social environments results in different adaptive landscapes for each species, yielding a spectrum of phenotyopic consequences corresponding to different social pressures. My approach to studying social diversity is to investigate the ecological and evolutionary causes and consequences in, primarily, poorly known Neotropical birds. Some of my current efforts in this area include studying alarm-calling behavior in Greater Anis and describing the genetic structure of Palmchat colonies. I am also finishing up some work on understanding colony size variation in the Hispaniolan Woodpecker and whether it is influenced by spatiotemporal distribution of resources and rainfall.
Below, I elaborate on some of the other research projects I've undertaken.
Ecology and evolution of colonial breeding in the Hispaniolan Woodpecker (Melanerpes striatus)
Understanding intra- and inter-specific variation in sociality remains an important focus of behavioral ecology. The Hispaniolan Woodpecker is potentially a valuable model system for answering questions about variation within species due to its evolutionary history and its relatively unique facultatively colonial nesting behavior. The vast majority of the more than 250 woodpecker species are either known or thought to nest solitarily, with nesting pairs using one cavity. And a nontrivial percentage of woodpecker species exhibit cooperative breeding, with some species like the Acorn Woodpecker exhibiting fairly complex social organization. Yet these species mostly defend exclusive territories so nests are spread out across the habitat. In contrast, both solitary and colonially nesting pairs of the Hispaniolan Woodpecker occur in the same population. Colonial nesting in this species takes the form of two or more pairs concurrently nesting in the same tree or, more rarely, two adjacent (~1 m apart) trees. This variation begs an explanation: what proximate and ultimate factors can explain this variation in social behavior?
In my Ph.D., I tackled this problem by asking whether reproductive success differed between solitary and colonially nesting pairs, whether reproductive success was correlated with colony size, and whether colony size correlated with any relevant ecological factors. I also used a next-generation sequencing approach (ddRAD-seq: double-digestion restriction site associated DNA sequencing) to investigate whether the high levels of breeding density associated with colonial nesting impacted Hispaniolan Woodpecker reproductive strategies (e.g., do colonial nests exhibit higher rates of extra-pair paternity and conspecific brood parasitism than solitary nests?).
After six field seasons of climbing trees, banding birds, and collecting blood and data, I uncovered some intriguing aspects of the Hispaniolan Woodpecker's natural history. Unfortunately for you, you'll have to wait until my manuscripts make it through peer review and get published to know more! You could also just e-mail if you're eager to learn about this fascinating and under-appreciated bird.
Factors affecting Philornis parasitism
Ornithologists are increasingly appreciating the importance of parasitism by Philornis botfly larvae for new world bird species. In particular, the invasive Philornis downsi has wreaked havoc on the avifauna of the Galápagos. On the island Hispaniola, many native and endemic birds are affected by what is thought to be a native Philornis. The Hispaniolan Woodpecker is no exception, exhibiting wide inter- and intra-annual variation in levels of parasitism, but in spite of these flies, the woodpecker population I study seems to be fine. However, other species on the island, including endemics and some of conservation concern, are not so fortunate. I am currently analyzing data to address questions about the ecological factors that affect Philornis infestation in my population in order to contribute to our understanding of this very important parasite. Thus far, one paper is in review, and I hope to have another submitted sometime soon.
Evolution of sexual size dimorphism
Sexual dimorphism is widespread across animal taxa, but the degree and direction of the dimorphism (i.e., which sex is larger) vary extensively. Sexual size dimorphism, especially male-biased size dimorphism, is often attributed to sexual selection, involving intrasexual competition and to a lesser degree intersexual selection, or mate choice. Under these scenarios, larger individuals have increased mating access to members of the opposite sex, typically via defending groups of mates or by being chosen for mating. An alternative driver of sexual dimorphism evolution is non-sexual social competition over resources for reproduction. This competition is “non-sexual” because it influences variance in reproductive success through direct competition over resources for reproduction but not mating or fertilization opportunities. For example, larger size can increase an individual’s ability to defend a high quality foraging area against others of the same sex, increasing the quantity or quality of food available to the individual. Lastly, non-sexual natural selection (i.e., ecological causes) can also play an important, often overlooked, role in the evolution of sexual dimorphism. In environments that favor reduced ecological resource competition between the sexes, for example, males and females might diverge to exploit different resource niches. Few studies have clearly identified examples of ecologically-driven sexual size dimorphism, and even fewer have tested alternative adaptive hypotheses concerning sexual size dimorphism in the same system.
The Hispaniolan Woodpecker has been invoked as a classic example of sexual size dimorphism via non-sexual natural selection based on observations that the sexes forage differently, especially during the non-breeding season. But the previous studies documenting these differences relied entirely on observations of unmarked individuals, and the authors never tested alternative hypotheses. Through extensive observations of color-banded birds and relevant components of fitness (i.e., survival and genetic parentage), I am testing the various predictions corresponding to all four alternative adaptive hypotheses.