Research

My research program aims to elucidate how biological diversity is generated and
maintained, with a special focus on understanding the evolution of premating
reproductive isolation. Despite decades of intense research, understanding how new
species arise remains a controversial and central issue in evolutionary biology. To
address this key topic, I use a diverse set of taxa and approaches, including molecular
phylogenetics, evolutionary genetics, microbiology, and behavioral and sensory ecology.
Below I highlight four projects that illustrate the questions and approaches tackled by my
lab group.

Sexual selection & speciation in bowerbirds. Changes in female mating preferences
and correspoding male display traits can cause reproductive isolation between
populations and thus cause speciation. We tested this possibility using the Vogelkop
bowerbird Amblyornis inornatus of New Guinea. Populations of this species vary in
display traits, with males of some populations building hut-like bowers decorated with
colorful flowers while males of other populations building spire bowers with drab
decorations. Our work suggests that females use aspects of the bower and decorations
in mate choice, suggesting that these divergent display traits can act as premating
reproductive barriers if divergent populations come into contact.

Island Speciation in Solomon Island Flycatchers. Because islands are
characterized by rich patterns of endemism and striking intraspecific variation, island
systems have featured prominently in our understanding of many evolutionary
processes. Populations of the Monarcha castaneiventris flycatcher have diverged in
song, plumage color, and extent of sexual dimorphism throughout the Solomon
Archipelago (below). Taking advantage of this classic system (Mayr 1942,
Systematics and the Origin of Species), we are attempting to understand the factors
that drive trait divergence and how this divergence, in turn, results in premating
reproductive isolation (i.e., biological species).

Found in the mountains of New Guinea, Vogelkop
bowerbirds Amblyornis inornatus show geographic
variation in bowers and decorations. Above is a bower
from the Arfak Mountains, where males build hut-like
bowers by weaving sticks around a sapling and use colorful
decorations. The pictured hut bower is over 5 feet wide and
4 feet tall. In contrast, males from the Fakfak Mountains
(right) build open, spire bowers that are decorated with
drab objects. The pictured spire bower is over 5 feet tall.
Amazingly, males from both populations weigh only 100 g.

The four color forms of the bearded manakin complex. From left to right: 1) the white-bearded
manakin has a white collar/beard and grey belly; 2) the white-collared manakin has a white
collar/beard and yellow belly; 3) the golden-collared manakin has a golden collar/beard and
green belly; 4) the orange-collared manakin has an orange collar/beard and olive belly. In
contrast, other morphological traits, such as size, show less variation. We have initiated a long-
term project in Latin America aimed at understanding why male coloration has dramatically
diverged across Manacus populations.

The four color forms of the chestnut-bellied flycatcher complex of the Solomon Islands. From left
to right: 1) the all-black M. c. ugiensis, 2) the nominate chestnut-bellied M. c. castaneiventris, 2)
the Bougainville M. c. erythrostictus, and 4) the white-capped M. c. richardsii subspecies.
These subspecies also vary in song structure, as well as extent of dichromatism between sexes.

Hybrid Zone Dynamics in Manakins. In addition to geographic variation among
islands, hybrid zones, which are regions where genetically distinct taxa meet and
produce hybrids, offer unique and excellent opportunities to understand speciation and
the evolutionary consequences of trait divergence. The white-collared (Manacus
candei) and golden-collared (M. vitellinus) manakins form a hybrid zone,
characterized by several concordant genetic and morphometric clines, centered in
Western Panama. The cline for plumage color, however, is displaced 50 km into the
white population, indicating that golden plumage is moving into the white population.
Our recent work suggests that the dynamics of this trait introgression is mediated by
positive frequency dependent sexual selection favoring golden males, and
geographically variable habitats favoring golden plumage at the hybrid zone and white
plumage at the allopatric white population.

The Evolution of Color Polymorphism in Fish. Intraspecific, genetic
polymorphism provides unique opportunities to understand the origin and maintenance
of trait diversity within populations. Poecilia parae, a close relative of the guppy
Poecilia reticulata, is unique in having five, sympatric male color forms: two forms that
have carotenoids coloration (red & yellow), one form that has structural coloration
(blue), one form with vertical stripes and an elaborate dorsal fin, and a final form that
lacks the elaborate traits and resembles young females (right). Using a combination of
field and lab experiments, our aim is to understand the persistence of this Y-linked
polymorphism.

Other projects in the lab. Other ongoing projects include: 1) the effects of urban
development on the operation of sexual selection in the common yellowthroat
Geothlypis trichas in New York, 2) niche partitioning in the arrowhead spider
Verrucosa arenata of Virginia, 3) phylogeography of the variable common paradise
kingfisher Tanysiptera galatea of New Guinea, and 4) phylogeography of the volcano
hummingbird Selasphorus flammula of Costa Rica. For additional details and
figures, follow the link to Project Descriptions below.

In my research program, we use various study systems and approaches to obtain
a more comprehensive understanding of the evolution of biological diversity. I plan to
continue with this integrative approach, and welcome students who are interested in
similar questions and approaches.