Understanding Evolutionary History
Using DNA and other data, we reconstruct the history of life—defining species, testing how traits evolved, and exploring why some organisms are so diverse.
Pat Leonard/Cornell Lab
By examining "ancient DNA," or DNA from old specimens, we can ask fascinating questions about extinct species or populations. But working with ancient DNA is technically demanding because degradation sets in soon after an animal's death. The Fuller Evolutionary Biology Program includes a dedicated ancient-DNA lab that we use when working with old or degraded specimens. We have successfully retrieved and analyzed old genetic material ranging from bird museum skins collected in the 1800s, to 5,000-year-old plant material recovered from receding glaciers in the Andes. Ancient DNA techniques also enable us to study materials from places that are difficult to access, and to examine the genetics of extremely rare, protected, or extinct species.
How Many Genes Does It Take to Make a Good Evolutionary Tree?
Many questions remain about how best to uncover evolutionary relationships among species. This is partly because a phylogenetic tree resolved from a single gene sequence will differ somewhat from trees of other genes sampled from the same species. We are exploring this problem by analyzing many genes from small groups of birds such as North American chickadees. These studies help us better understand the relationships of these birds and how best to deploy our laboratory and analytical resources.
Starlings, Mockingbirds and Oxpeckers: Evolutionary History and Behavior
© Dustin Rubenstein
We recently generated detailed phylogenetic trees for nearly all species of starlings, mynas, oxpeckers, mockingbirds, and thrashers. These trees have revealed many otherwise hidden aspects of the evolutionary histories of these avian groups, and they are influencing how these groups are classified. In a broader sense, these trees have guided our exploration of the diverse behaviors of these birds. For example, we have shown that the social systems of starlings and the song complexities of the mockingbirds are both strongly influenced by the predictability of each species’ environment.
The Diversification of Catfish and Other Creatures
Catfish are among the most diverse groups of fishes, and they take many forms and habits. A DNA-based tree of catfishes, produced by our colleagues in the Cornell University Museum of Vertebrates and their many collaborators, has illuminated some deep relationships that analyses of specimens alone could only hint at. For example, the closest living relatives of an odd-looking catfish species that lives in a small area of southern Mexico turns out to be a family that is found exclusively in Africa. These studies further suggest that many early splits of lineages in catfish history date well back into the age of the dinosaurs.
The Diversification of Skinks
© Dan Rabosky
Skinks of the genus Ctenotus are the most diverse vertebrate radiation in Australia, although exactly how many species of them there are remains an open question. With our Australian collaborators, we are building a Ctenotus phylogeny to define species and learn how this impressive diversification came about. Why are there so many species of Ctenotus skinks? How can so many closely related species coexist in the same habitats? And What could have isolated these populations enough to allow such diversification, given Australia's lack of major geographic barriers such as mountains or bodies of water?
The Wood-Warbler Tree of Life
Our work on the evolutionary tree of the wood-warblers has yielded information on when and how this group of songbirds diversified. We have used this information to explore why some warbler species occur together in breeding communities, whereas others compete so strongly that they don't co-occur. We have shown that some wood-warbler lineages appeared rapidly early on in the group’s evolution, but diversification declined thereafter. This supports the idea that wood-warbler communities arose via “adaptive radiation” in which speciation slows as ecological niches fill. We have also taken an evolutionary approach to studying the life history, migration, and ecology of warbler species. We've found that warbler species living in taller trees or more open forest canopies tend to have higher frequency flight calls. View our Wood-Warbler Tree of Life for an introduction to our warbler work.
Diversification in Action
We use the new tools of genomics to explore the processes that have given rise to the earth’s biodiversity and that are still at work all around us.
Understanding the Origins of Biodiversity
We are exploring the process of speciation and how it is influenced by ecological factors and biological traits. Some species have patchy distributions, with areas of suitable habitat separated by uninhabitable areas. Are populations of these species more prone to diversify because of their physical isolation? Are sedentary populations more likely to diverge than those that are more mobile? When are differences in mating tactics and behaviors great enough to result in speciation? To investigate these questions, we gather information about the degree of genetic differentiation among populations, along with ecological and life-history data. Ongoing projects focus on the recent colonization of South America by breeding Barn Swallows, the effect of habitat on genetic divergence in cichlid fish and snails in Lake Tanganyika, Africa, and the influence of mate choice strategies on population differentiation in Australian fairywrens.
Understanding the Maintenance of Biodiversity
In addition to investigating the origins of diversity, we explore how closely related species maintain their uniqueness. When two species interbreed, they may produce offspring that look, sound, and act intermediate between the parent species. So why, despite this occasional hybridization, do most species remain distinct? We are investigating the genetic reasons for this in pairs of species that often hybridize, such as Baltimore and Bullock’s orioles, and Indigo and Lazuli buntings.
We use genetic information to decipher animals’ family relationships and test hypotheses about behavior and social organization. We are especially interested in the evolution of the diversity of mating systems.
More than 90 percent of all bird species behave as if they are monogamous, but genetic work reveals that, in most species, chicks in the same nest can have different fathers. This "extra-pair paternity" varies substantially among species, populations, and years. Our research examines the costs, benefits, and likelihood that individuals will engage in extra-pair copulations. We test hypotheses that birds choose mates because of “good genes” that confer higher survivorship on offspring, increase their fitness, or are dissimilar to avoid inbreeding and produce high genetic variability. These are some of the species we have studied:
Banded Wren (Thryothorus pleurostictus)—Costa Rica
This species inhabits the tropical dry deciduous forest of the Pacific slope of Central America. Males sing 20 to 25 different song types and engage in intense vocal exchanges with rivals. We examine whether males with larger repertoires are more likely to sire extra-pair offspring, and whether males with smaller repertoires are more likely to be cuckolded. We developed and used a combination of single nucleotide polymorphisms and microsatellites to examine extra-pair paternity in this species with unusually low genetic diversity.
House Wren (Troglodytes aedon)—New York and Argentina
We are examining whether extra-pair paternity rates in the northern and southern subspecies of House Wren are higher when breeding is synchronized. In the northern subspecies, we are determining whether eggs fertilized by extra-pair mates are more likely to be laid earlier in the clutch. We are also investigating whether hatching order may explain survivorship and reproduction differences between nestlings sired by the social father and those sired by extra-pair males, using comparisons of nestling growth rates. We are also assessing how a male’s singing ability relates to his reproductive success, using paternity data to better understand mate choice.
Black-throated Blue Warbler(Dendroica caerulescens)—New Hampshire
Climate change is predicted to increase environmental variation. In species that engage in extra-pair copulations, adverse weather could cause males to spend less time and effort looking for mates, and reduce the incidence of extra-pair paternity. But the effects of weather on reproductive behavior remain poorly understood. We are examining the influence of weather on rates of extra-pair paternity in Black-throated Blue Warblers along an elevational gradient with a range of climatic conditions.
Western Bluebird (Sialia mexicana)—California
We are analyzing more than 20 years of data from a Western Bluebird population to discover the costs and benefits of extra-pair mating from the perspective not just of females, but of their extra-pair and social mates as well. We are investigating how nongenetic factors affect offspring survival and reproduction as a way to distinguish who benefits from multiple matings. We are also examining lifetime survival and reproductive success of offspring, a crucial comparison that will help us find out whether within-pair young are genetically superior to extra-pair young, and whether the tendency to mate outside the pair is inherited.
Many social insects have a “haplodiploid” genetic system in which workers are females and are more closely related to their sisters than to their offspring. However, in colonies with multiple queens or sires the situation is more complex. We examine relatedness of workers in one such system, as a way of understanding how inclusive fitness and ecological factors contributed to the evolution of sociality in insects.
Acacia Ant (Crematogaster mimosae)—Kenya
We developed microsatellite DNA markers to study an ant species that lives in colonies with multiple queens. Our new methods allowed us to assess the parentage of female workers when neither parent was known. The work suggests that offspring from multiple queens may give an acacia ant colony a competitive advantage against foreign, neighboring colonies.
In some birds, helpers assist breeding pairs in raising offspring. Helpers are typically male and either do not breed at all or sire some of the young. We use molecular markers to determine how adults and young are related at these complicated nests. We study how cooperative breeding evolved by examining the benefits of cooperation and the costs of delaying reproduction in helpers. Further, we investigate how environmental constraints have promoted this unique mating system. Some of the species we have studied include:
Florida Scrub-Jay (Aphelocoma coerulescens)—Florida
When molecular tools first showed that most birds mate with others besides their social mate, it came as a great surprise. Twenty years later, the discovery of a truly monogamous species is the surprise that begs explanation. The Florida Scrub-Jay is one such rare example. We are exploring whether this species deviates from monogamy in some parts of its range, which might help us to understand why genetic monogamy occurs in the first place.
Superb Starling (Lamprotornis superbus)—Kenya
© Dustin Rubenstein
Superb Starlings live in cooperative family groups of as many as 30 individuals; their social structure is one of the most complicated in the avian world. They are “plural cooperative breeders,” meaning that several breeding pairs share a large pool of helpers. Some individuals form mating pairs for as long as five years and are strictly monogamous, but promiscuity can be high within family groups. We are investigating what drives some individuals to cheat and others to stay faithful, and what environmental factors influence whether an individual chooses to breed or to help raise another's offspring.
Red-backed Fairywren (Malurus melanocephalus)—Queensland, Australia
Male Red-backed Fairywrens have fascinating breeding strategies: Some males breed in bright plumage, whereas others breed in dull, female-like plumage. We are studying the function of elaborate sexual signals and the hormonal mechanisms that underlie them. In particular, we are exploring the extent to which genetic and environmental factors influence whether a male is showy or dull, and the cascading effects of breeding strategy on survival and reproduction. This work will lead to a better understanding of how organisms use social and environmental cues as their behavior develops.
American Crow (Corvus brachyrhynchos)—New York
Parentage analysis of the socially monogamous American Crow have revealed that some offspring are sired incestuously, usually by the adult “helper” sons of breeding females. These incestuous matings are costly: genetically derived inbreeding coefficients suggest that disease probability is higher, and survival probability lower, for the most inbred birds in this population.
We use molecular tools to measure gene flow, genetic diversity, and other factors relevant to the conservation of threatened species.
Habitat Fragmentation and the Florida Scrub-Jay
The Florida Scrub-Jay (Aphelocoma coerulescens) is a federally threatened species restricted to remnant patches of oak scrub in Florida. Habitat fragmentation, development, and fire suppression have contributed to steep population declines of this species. We have used genetic techniques to learn about movement patterns, both past and present, between habitat patches across the scrub-jay's entire range. These analyses help wildlife managers preserve what remains of the genetic variation in this dwindling species, by translocating birds and preserving and restoring their habitat. We are also using genetic techniques to study why these jays are susceptible to periodic epidemics of viral disease.
Hybridization as a Conservation Threat
The Golden-winged Warbler (Vermivora chrysoptera) is declining precipitously, due in part to the expansion of the closely related Blue-winged Warbler (V. pinus) into its range. The incursion of blue-wings has led to widespread interbreeding between the two species, followed by the rapid disappearance of golden-wings. We are using genetic approaches to map the pattern of hybridization throughout the past and present range of Golden-winged Warblers. One objective of this survey is to identify the most genetically “pure” remaining golden-wing populations, which have special priority for conservation.
Tracking Vulture Declines
© Yula Kapetanakos
The catastrophic crash of White-rumped, Slender-billed, Long-billed, and Red-headed vultures in South Asia represents a particularly tragic case of wildlife being unintentionally harmed by human activity. In the past 20 years vulture populations in South Asia have fallen by more than 95 percent—likely the steepest population decline of any raptor group in modern history. It's largely due to an unexpected side-effect of an anti-inflammatory administered to cattle. We are striving to develop an understanding of population demographics (population size, rates of births/deaths, etc.) for several of these species in other parts of their Asian range as a crucial piece of information in saving them. To do this we are using noninvasive genetic mark-recapture techniques to obtain critical data on the biology and demographics of these birds that are otherwise very difficult to track and study in the wild.
The Unique Birds of Hispaniola
The Caribbean island of Hispaniola (encompassing the Dominican Republic and Haiti) supports an unusually high number of endemic birds, including Broad- and Narrow-billed todies (Todus subulatus and T. angustirostris), Black-crowned and Gray-crowned palm-tanagers (Phaenicophilus palmarum and P. poliocephalus), Green-tailed Ground-Tanager (Microligea palustris), and Hispaniola Highland-Tanager (Xenoligia montana). Some populations of these species are critically endangered, particularly those in the poorly preserved forests remaining in Haiti. We study the genetic variation among these populations in order to identify those that are highly evolutionarily distinct. By prioritizing the preservation of these unique populations, we have a greater chance of preserving the adaptive diversity of these species and ensuring their long-term persistence.
We explore the interplay among birds, their diseases or parasites, and the vector species that connect them.
Genetics and House Finch Eye Disease
In the winter of 1994, people around Washington, D.C., began noticing House Finches with severe eye lesions caused by a bacterium called Mycoplasma gallisepticum. Within three years, this infection spread throughout House Finch populations east of the Rocky Mountains and killed many of them. We contribute to long-term studies of this epidemic by performing DNA-based diagnostics on samples taken from wild birds, and by studying the genetic diversity of House Finches in relation to their susceptibility to this disease. Among our findings is the discovery that the introduced population of House Finches in eastern North America is substantially less genetically diverse than the native population in western North America. We are also deciphering the evolutionary relationships between numerous strains of Mycoplasma, helping us learn where this infectious strain may have come from when it jumped into the House Finch population.
Evan Barbour/Cornell Lab
Past students working in the Fuller Evolutionary Biology Lab have investigated the ecology of avian malaria. These studies have surveyed the host distributions of particular avian malaria species and tested the ability of particular mosquito species to transmit avian malaria among hosts.
Mosquito Feeding Ecology
Many diseases and parasites are transmitted (or vectored) by insects and other arthropods, creating a complex transmission cycle involving the pathogens, the vector species, and the host species. To better understand this cycle we study the feeding patterns of one of the most notorious of all insect vectors, the mosquito. Using wild mosquitoes captured locally in Sapsucker Woods at the Cornell Lab of Ornithology, we use DNA bar-coding to analyze mosquito blood meals. After identifying each mosquito to species, we extract the blood meal from its abdomen to identify the species of bird or mammal the mosquito fed from.
Inbreeding and Disease in Crows
American Crows in Ithaca, New York, suffer from a suite of infectious diseases, including West Nile virus, avian pox, and numerous other bacterial, fungal, and viral infections. We have found evidence that there is a genetic basis for infection risk: Inbred crows have a higher probability of dying with disease symptoms than crows with unrelated parents. Inbreeding is rare and disadvantageous in nearly all animals, so it's a mystery why inbreeding is commonplace in these crows. We are now exploring the potential benefits of breeding with kin that might balance some of these disease costs.
Scientific Training and Collaboration
We collaborate widely and offer extensive training and research support to postdoctoral, graduate, and undergraduate scholars.
The Research Group at the Fuller Evolutionary Biology Program
The Fuller Evolutionary Biology Program includes a core group of permanent research staff and a much larger group of undergraduate, graduate student, postdoctoral, and visiting researchers. The program is overseen by Dr. Irby Lovette, who is also an associate professor in Cornell’s Department of Ecology and Evolutionary Biology. Members of our lab group come and go on cycles dictated by fieldwork schedules and graduations, but at any given time about two dozen people are typically at work here.
Our program is the primary institutional and intellectual home for about half of our lab group members. The others come to us from elsewhere at Cornell, and beyond, to gain help with the molecular-genetic aspects of their research. Many of our lab group members arrive with little or no previous molecular biology experience. We take pride in helping them become accomplished at both benchwork and the statistical techniques of genetic analysis. All of us enjoy the rich and ever-changing diversity of organisms, projects, and perspectives that characterizes our research group.