1. Understanding speciation in the face of gene flow in the Kolombangara Zosterops White-eyes
The Evolution publication resulting from this study can be found here:
https://academic.oup.com/evolut/article-abstract/73/8/1647/6882039
Rapidly speciating lineages play an important role in generating biodiversity. But many of these lineages are confined to small geographic areas (e.g. Darwin's finches in the Galapagos or cichlids in the African Rift lakes). However, some lineages, coined "Great Speciators," are able to produce high numbers of species while spreading over a wide geographic area. The ability to do both seems to be counterintuitive, as high dispersal ability should result in constant gene flow among populations, which hinders local adaptation, the evolution of reproductive isolation, and the ability to form new species. This is known as the "paradox of the great speciators."
I am studying this paradox with the Zosterops genus of birds, known as "White-eyes." This group is one of the most rapidly speciating yet widespread vertebrate lineages.
In my Ph.D. dissertation, I am focusing on two species of White-eyes that have naturally established secondary contact on the small island of Kolombangara located in the New Georgia Province of the Solomon Islands. The endemic Kolombangara White-eye (Z. murphyi) is found at higher altitudes, whereas the Solomons White-eye (Z. kulambangrae) is found at lower altitudes. These two species have a 400m contact zone around the island.
https://academic.oup.com/evolut/article-abstract/73/8/1647/6882039
Rapidly speciating lineages play an important role in generating biodiversity. But many of these lineages are confined to small geographic areas (e.g. Darwin's finches in the Galapagos or cichlids in the African Rift lakes). However, some lineages, coined "Great Speciators," are able to produce high numbers of species while spreading over a wide geographic area. The ability to do both seems to be counterintuitive, as high dispersal ability should result in constant gene flow among populations, which hinders local adaptation, the evolution of reproductive isolation, and the ability to form new species. This is known as the "paradox of the great speciators."
I am studying this paradox with the Zosterops genus of birds, known as "White-eyes." This group is one of the most rapidly speciating yet widespread vertebrate lineages.
In my Ph.D. dissertation, I am focusing on two species of White-eyes that have naturally established secondary contact on the small island of Kolombangara located in the New Georgia Province of the Solomon Islands. The endemic Kolombangara White-eye (Z. murphyi) is found at higher altitudes, whereas the Solomons White-eye (Z. kulambangrae) is found at lower altitudes. These two species have a 400m contact zone around the island.
I am using a combination of genomic techniques and field experiments to determine:
1) if allopatric (non-overlapping) and sympatric (overlapping) populations differ in the extent of song and plumage divergence, 2) if song and plumage differences mediate species recognition within the contact zone, and 3) the levels of historical and current hybridization. Together, these objectives will provide insight into how two closely-related species are able to remain intact when coming into secondary contact and will help to resolve the paradox of the great speciator. |
2. The evolutionary history of the six subspecies of the hummingbird Amazilia amazilia
The Ecology and Evolution publication resulting from this study can be found here: https://onlinelibrary.wiley.com/doi/abs/10.1002/ece3.8895
Species (according to the biological definition) are groups of actually or potentially interbreeding individuals that are reproductively isolated from other such groups. Examining intraspecific (i.e. within-species) variation, evolutionary relationships, and the level of gene flow across differentiated populations of the same species may lend insight into the initial stages of the speciation process. I am focusing specifically on the Amazilia Hummingbird (Amazilia amazilia). There are a total of 6 subspecies found throughout Ecuador and Peru that vary in size and plumage--particularly in gorget color, the presence/absence of a white throat patch, the amount of red on the belly, and the amount of red on the tail. I traveled to beautiful Ecuador for 11 weeks. My field assistants and I were able to catch the 3 subspecies of Amazilia Hummingbirds (see left) that are found in the South Coast and Southern Highlands regions of Ecuador. |
From each bird, we took phenotypic measurements and a few drops of blood for DNA extraction before giving the bird some sugar water and letting it fly away. For the other 3 Peruvian subspecies, we are obtaining museum samples from the University of New Mexico for DNA extraction.
In collaboration with Dr. Chris Witt from the University of New Mexico and Dr. Elisa Bonaccorso from the Universidad San Francisco de Quito in Ecuador, we conducted a next-generation sequence analysis to build a phylogeny of the 6 subspecies of A. amazilia to examine the levels of interbreeding and introgression (i.e. gene flow) between the subspecies, as well as determined the evolutionary history and phylogeography of A. amazilia.
In collaboration with Dr. Chris Witt from the University of New Mexico and Dr. Elisa Bonaccorso from the Universidad San Francisco de Quito in Ecuador, we conducted a next-generation sequence analysis to build a phylogeny of the 6 subspecies of A. amazilia to examine the levels of interbreeding and introgression (i.e. gene flow) between the subspecies, as well as determined the evolutionary history and phylogeography of A. amazilia.
3. Trade-offs in behavior faced by males in lek mating systems (M.S. Research Project)
The Auk: Ornithological Advances publication resulting from this study can be found here: https://academic.oup.com/auk/article/132/1/82/5149135
I did my M.S. project in Dr. Robert Gibson's lab in the School of Biological Sciences at the University of Nebraska-Lincoln.
In lek mating systems, males aggregate together and perform courtship displays to visiting females. But increased display is energetically expensive and reduces time available for other important activities (such as foraging). I examined these trade-offs in behavior using two methods:
A) Empirical Field Study
We conducted an empirical study of how Sharp-tailed Grouse (Tympanuchus phasianellus) males allocate time between courtship display (“dancing”), agonism, foraging, and inactivity in relation to female numbers both within and across days on the lek during the breeding season. We also measured head turning rates during these same behaviors as a proxy measure for visual attentiveness to the surroundings.
We found that the proportion of males engaged in display increased significantly with female numbers whereas foraging decreased significantly with female numbers both within and across days. This indicates that males may increase display at the expense of reduced foraging time at periods of high female attendance. In addition, during display, males turned their head only half as frequently as during other activities, which suggests reduced visual attentiveness during display and the potential for increased predation risk.
Read more about the study here.
B) Stochastic-Dynamic Programming Model
We created a stochastic-dynamic programming (SDP) model and forward simulation (both coded in R) to investigate how the trade-off between reproductive success and survival (mediated by body condition) affects male reproductive strategies in lekking systems. We found initial body condition largely determines the optimal seasonal breeding strategy. Males with initially lower body condition are predicted to forage off the lek early in the season, maintain lower body condition throughout the season, and delay the onset of maximum display effort compared to males with initially higher body condition.
The Auk: Ornithological Advances publication resulting from this study can be found here: https://academic.oup.com/auk/article/132/1/82/5149135
I did my M.S. project in Dr. Robert Gibson's lab in the School of Biological Sciences at the University of Nebraska-Lincoln.
In lek mating systems, males aggregate together and perform courtship displays to visiting females. But increased display is energetically expensive and reduces time available for other important activities (such as foraging). I examined these trade-offs in behavior using two methods:
A) Empirical Field Study
We conducted an empirical study of how Sharp-tailed Grouse (Tympanuchus phasianellus) males allocate time between courtship display (“dancing”), agonism, foraging, and inactivity in relation to female numbers both within and across days on the lek during the breeding season. We also measured head turning rates during these same behaviors as a proxy measure for visual attentiveness to the surroundings.
We found that the proportion of males engaged in display increased significantly with female numbers whereas foraging decreased significantly with female numbers both within and across days. This indicates that males may increase display at the expense of reduced foraging time at periods of high female attendance. In addition, during display, males turned their head only half as frequently as during other activities, which suggests reduced visual attentiveness during display and the potential for increased predation risk.
Read more about the study here.
B) Stochastic-Dynamic Programming Model
We created a stochastic-dynamic programming (SDP) model and forward simulation (both coded in R) to investigate how the trade-off between reproductive success and survival (mediated by body condition) affects male reproductive strategies in lekking systems. We found initial body condition largely determines the optimal seasonal breeding strategy. Males with initially lower body condition are predicted to forage off the lek early in the season, maintain lower body condition throughout the season, and delay the onset of maximum display effort compared to males with initially higher body condition.