My field-based research program focuses on an integrative understanding of how the environment shapes the evolution of complex social behavior, especially reproductive strategies. I am particularly interested in the role of social behavior in population and evolutionary dynamics involving sexual selection, population differentiation, and adaptation to environmental change. My research is integrative, linking insights about the ecological and phylogenetic context of social behavior with the underlying neuroendocrine and molecular mechanisms. I combine hormone assays and genomic approaches with experimental manipulations and demographic field studies. I also draw on comparative and evolutionary approaches to explore the phylogenetic basis of social behaviors.
My research has focused on behavioral and demographic studies of warbler, sparrow, and thrush populations across North America and comparisons between temperate, New World, and Old World tropical birds. Current funding is for work at the Hubbard Brook Experimental Forest in New Hampshire and in the Caribbean Islands.
Conservation Genomics of Island Populations in the Caribbean
The geographic isolation of island populations can promote divergence by limiting the exchange of genetic and cultural information, such as learned vocalizations in songbirds. The behavioral mechanisms that lead to divergence and maintain barriers to gene flow is of particular importance in terrestrial species that have evolved migratory populations that come into contact with sedentary populations during their breeding cycle. The grasshopper sparrow (Ammodramus savannarum) populations in the Caribbean Islands provide an excellent system for studying the role of learned song as a behavioral barrier to gene flow between migratory and sedentary populations. Four sedentary populations of grasshopper sparrow are found on different islands of the Caribbean and one endangered population exists in central Florida. The migratory subspecies that breeds throughout eastern North America spends the non-breeding season in the southern U.S. states and parts of the Caribbean. I am testing the hypothesis that sedentary populations will be both genetically and vocally more divergent on islands that do not come into contact with the migratory populations than on islands where gene flow between sedentary and migratory populations is possible. I was awarded a competitive Smithsonian Grant to determine the genetic distinctiveness of the endangered Florida subspecies from the Caribbean and migratory subspecies to resolve their conservation status. This work will launch additional studies examining differences in the prevalence of social behaviors in Caribbean and temperate populations and the genetic basis of migratory behavior.
Evolution of Complex Social Systems in Songbirds of the Old World Tropics
Robert Fleischer, Smithsonian Center for Conservation Genomics
Thomas Martin, University of Montana
Juan Oteyza, University of Montana
Julie Danner, Smithsonian Center for Conservation Genomics
Laura Bergner, Smithsonian Center for Conservation Genomics
Madhvi Venkatramen, Smithsonian Center for Conservation Genomics
Ellen Martinsen, Smithsonian Center for Conservation Genomics
Andy Boyce, University of Montana
Connor Armstad, University of Montana
Robert Moyle, Kansas Biodiversity Institute & Natural History Museum
Frederick Sheldon, Louisiana State University
Cooperation between non-relatives is a long-standing puzzle in behavioral ecology. Most cooperative groups form when offspring delay dispersal and remain on their natal territory, resulting in groups composed of a breeding pair and non-breeding relatives that assist their parents in raising siblings. Recent work has revealed that social groups containing non-relatives are surprisingly common, but only a tiny fraction of group-living species has been studied. I explore how low genetic relatedness in social groups may select for different benefits of cooperation than in kin groups.
My research at the Smithsonian Center for Conservation Genomics explores the diversity of cooperative social systems in group-living birds in the tropical montane forests of Malaysian Borneo – a region where few social systems have been characterized. I discovered striking variation in the social behavior and genetic relatedness of social groups among five babbler species with different distributions along Mount Kinabalu. My ongoing work in this system uses genomic methods (targeted sequence capture) to identify dispersal patterns and to examine the ecological factors generating the composition and relatedness of groups. I published the development of novel molecular markers using pyroseq and RAD-seq (BMC Research Notes 2016) and on the unusual social structure of the grey-throated babbler (Stachyris nigriceps) (Behavioral Ecology 2018). Three articles on the social and genetic mating systems of babblers and offspring sex ratio bias in the Old World tropics are forthcoming.
Mechanisms of Adaptive Responses to Environmental Change
An emerging question in behavioral ecology is whether and how behavioral plasticity will enable organisms to adjust to rapid environmental change. Behavioral plasticity is one potential mechanism that can buffer individuals within a population against environmental change and facilitate adaptive evolution. Such plasticity depends on both the sensitivity to environmental stimuli and the physiological mechanisms that animals use to regulate seasonal reproduction. A strong candidate proximate mechanism underlying adaptive behavioral plasticity is the neuroendocrine system. A critical gap in our knowledge, however, is how environmental stimuli are perceived and then translated by the neuroendocrine system to mediate the phenotypically plastic expression of reproductive behaviors. Understanding these links is especially timely given that rapid environmental change has exposed animals to modifications in habitat quality and environmental stimuli such as food availability. These changes in breeding condition can influence mating decisions and reproductive success. Sensitivity of the neuroendocrine system to environmental stimuli, as well as plasticity and constraints in the signaling mechanism, will determine the extent to which animals will be able to respond. I explore the mechanisms underlying adaptive behavioral responses to determine the potential evolutionary constraints on these responses and whether adaptive plasticity in behavior is sufficient to compensate for rapid environmental change.
My research at Cornell University examined mechanistic links between environmental stimuli (food), hormone responses, plasticity in reproductive behaviors, and fitness consequences in a migratory songbird, the black-throated blue warbler, Setophaga caerulescens, at the HBEF. I integrated large-scale field experiments along an elevation gradient, novel SNP markers using RNA-seq (Molecular Ecology Resources 2016), hormone assays, population demographics, and population modeling. Collectively, this work demonstrated that plasticity in hormones and reproductive strategies enabled rapid responses to changes in resource conditions on their breeding grounds (Editor’s Choice in Animal Behaviour 2014), influenced individual fitness via extra-pair mating (Proceedings of the Royal Society London B 2015) and population dynamics (PLoS ONE 2013), and might have currently overlooked, evolutionary consequences (American Naturalist 2017). This work highlights the capacity of birds to respond to rapid environmental change via behavioral mechanisms.
Click each project to learn more about my previous scientific contributions.
©S.A. Kaiser 2012