Ignacio T. Moore - US grants

One of the main goals in environmental endocrinology during the last two decades has been to understand the interactions between aggression and sex steroids within males, as modeled by the Challenge Hypothesis. This hypothesis proposes that male-male territorial aggression results in an increase in testosterone levels, which then feeds back to support the aggressive behavior. However, less attention has been focused on the role of sex steroids in male-female social interactions. One area where sex steroids could have a profound effect on male-female interactions is in fine-tuning the timing of breeding within socially monogamous pairs. In tropical birds, breeding seasons are generally long and there is significant variation within the population as to when breeding occurs. This presents an ideal opportunity to elucidate the importance of male-female interactions in the timing of breeding. Previous findings in tropical male rufous-collared sparrows, Zonotrichia capensis, have suggested that male-male interactions do not affect testosterone levels, implying that testosterone is not functioning within the Challenge Hypothesis model. In addition, preliminary data indicate that within monogamous pairs, gonadal state is similar, and independent of the rest of the population. This presents the possibility that male-female interactions may be more important than male-male interactions in determining gonadal activity and testosterone levels. The proposed research will investigate the role of hormonally mediated social cues between males and females in timing of breeding. The following specific questions will be addressed: 1) Within monogamous pairs, is there a correlation between male and female gonadal stage and plasma sex steroid levels? 2) Are hormonally mediated social cues used to fine tune and coordinate reproductive timing within breeding pairs? The results of these studies will clarify the differences documented between high latitude and tropical birds in terms of hormone-behavior interactions. This is important as two-thirds of the world's vertebrates are tropical and thus the typical high-latitude mechanistic relationships may not be adequate to describe them.

CAREER: Mechanisms of Seasonal Reproduction in the Tropics
Ignacio T. Moore
Virginia Tech


A crucial challenge that animals face is timing reproduction to maximize offspring survival. Most of our understanding of how animals time reproduction comes from studies of mid- to high latitude species. For these animals, changes in day length are the primary cue they use to predict seasons and thus time seasonal processes. However, the majority of animals inhabit tropical latitudes where seasonal changes in day length are minimal. Yet many tropical species still breed seasonally and it appears that many rely on more localized cues to time reproduction. This can lead to wide disparity in reproductive timing between populations in close proximity. Previous studies have described populations of rufous-collared sparrows (Zonotrichia capensis) near the equator in Ecuador, that are separated by only 25km, yet breed at very different times of years. Interestingly, these populations have also diverged genetically. This system, where day length does not change seasonally, provides an ideal opportunity to further investigate mechanisms of seasonal reproduction. The proposed studies will investigate seasonal reproduction in terms of environmental and social cues, endogenous rhythms, breeding synchrony, population genetic differentiation, and nutrition. There are two primary components of the education portion of this project. For the first part, Ecuadorian locals and students will be incorporated into the research program, primarily as research assistants in the field. For the second part, a foreign studies class will be initiated at Virginia Tech to expose students to the culture and nature of Ecuador. Through this program, twelve students per year will travel for a month to Ecuador, interact with locals at four field sites and experience one of the most bio-diverse places on earth. Some of these students may also stay in Ecuador and work on the research project. This award is co-funded by the NSF's Office of International Science and Engineering.

Despite intense public and media attention given to steroid use by humans to enhance athletic performance, surprisingly little is known about how hormones regulate whole-animal performance traits, such as running, biting, and swimming ability. There is clear evidence that such traits are important to individual survival and reproduction, but there is a lack of a general understanding of how selection on performance, and indirectly it's underlying physiology (including hormones), affects the phenotype via the wide-ranging effects of hormones. One key aspect of the symposium at the 2009 Society for Integrative and Comparative Biology (SICB) meeting in Boston, MA will be to highlight the diverse ways in which hormones may affect various performance traits across a range of animal species. This symposium will encourage a synthetic approach by bringing together, for the first time, an international group of researchers working on hormones and performance in both vertebrates and invertebrates. These researchers span a wide range of career stages and geographic locations that do not normally have the opportunity to interact directly. Nearly one-half of the symposium presenters are from outside the USA, and several of the participants do not regularly attend SICB meetings. One benefit of this symposium is that it will provide an excellent opportunity for students and junior researchers to exchange ideas with more established investigators. This will be accomplished through direct interaction during the symposium, planned social events involving symposium participants and students, and a complementary contributed paper session. Participation by historically underrepresented groups, with nearly one-third of participants being women or minorities, is also being accomplished. Publication of the symposium's proceedings in SICB's journal, Integrative and Comparative Biology, will ensure that the intellectual products of the symposium are broadly disseminated.

All organisms must allocate limited resources towards competing functions. These functions can be grouped into two broad categories: reproduction and self-maintenance. Reproduction can increase fitness through production of offspring, whereas self-maintenance can increase fitness by improving survival to a time in the future when the individual can reproduce. One central factor influencing strategies of investment in reproduction or self-maintenance is "reproductive value", or the relative fitness benefit of current versus future reproduction. We currently do not understand the mechanisms allowing animals to adaptively allocate resources to reproduction and self-maintenance in the face of changing environmental conditions, resource availability, and reproductive value. Glucocorticoids, or stress hormones, are crucial for maintaining energetic balance, and might play an important role in mediating allocation to reproduction and self-maintenance. This project will test three hypotheses about the role of glucocorticoids in mediating resource allocation through experimental manipulations of glucocorticoids, reproductive effort, and blood parasites in free-ranging Tree Swallows. Results of this work will improve our understanding of the mechanisms underlying variation in reproduction and survival and the evolution of strategies of resource allocation. This information is valuable because it will improve our understanding of evolution and physiology, and will also have implications for management of species of conservation concern. Glucocorticoid levels increase in response to habitat disturbance, and so, an understanding of how these hormones affect reproduction and survival can inform our understanding of dynamics of populations in disturbed habitat. Finally, because glucocorticoids are found in all vertebrates, including humans, the findings from this study might have important implications for human health.

Urban areas are rapidly expanding and present both opportunities and challenges for wild animals. While some species do poorly in urban areas, others do well. Previous research has documented many differences between urban and rural individuals of the same species, but little is known about how these differences are created and maintained. One possible mechanism is DNA methylation, a process that affects gene expression without changing the underlying genetic code. Patterns of DNA methylation can be inherited, but may also change within an individual's lifetime in response to environmental stimuli. Because DNA methylation enables rapid yet stable and heritable changes of an organism's outward characteristics, it is a prime candidate for explaining how species adapt to novel habitats and situations, including urbanization. This study will compare DNA methylation patterns of urban and rural songbirds and relate these patterns to previously observed differences, specifically aggressive behavior and stress hormone levels, between these same groups. Differences between urban and rural birds in DNA methylation levels and locations are predicted, as is a relationship between methylation patterns and observed differences in behavior and physiology. The results of this research will be broadly applicable, as DNA methylation is a process found in taxa ranging from fungi to plants to animals, including humans. This study will increase understanding of how urban habitats can affect current and future generations of organisms living in them, knowledge that is especially important as urban areas continue to grow. Finally, two undergraduate students will participate in this study, giving them valuable research experience that will advance them towards a career in science. In addition, activities exploring the impacts of urbanization on animals and humans will be created for the local nature center giving the broader public an awareness of why this research is important.

Social networks are a common characteristic of most animal societies. While we know that individual differences in behaviors such as cooperation or aggression influence the role that individuals play within their social network, we know little about the physiological mechanisms underlying those differences. Wire-tailed manakins provide a model system to study the links between hormones, behavior and social networking because males form cooperative partnerships that are the foundation of complex social networks. Using this model system this research will integrate evolutionary, behavioral, endocrine and neurogenetic approaches to understand the physiological and evolutionary basis of individual variation in cooperation and how those individual-level processes scale up to influence an individual's role and position within their social network in a dynamic fashion. Because endocrine function is similar across a wide variety of animals, the outcomes of this work will be broadly applicable. The project will train at least 16 undergraduate students and 1 graduate student in integrative research in the US and at the field site in Ecuador. This research will also be featured in a planned exhibit which will describe the hormonal basis of social behavior and highlight the similarities between human and animal social networks at the National Zoological Park's Amazonia Science Gallery. Research products will be integrated in to tropical ecology courses at the Tipunti Biodiversity Station which hosts the work in Ecuador. This project is jointly supported by the Animal Behavior Program and International Science and Engineering.


This project will link hormone-regulatory networks and social networks to transform our understanding of how the endocrine system regulates behavior and influences social dynamics at the individual and population levels. The project will test two alternative hypotheses for how selection has shaped the evolution of hormone-mediated social behaviors involving testosterone: the phenotypic integration hypothesis and the phenotypic independence hypothesis in wire-tailed manakins where males cooperate to perform mating displays on a lek. This highly integrative project will quantify male behaviors in nature (dominance, cooperation, display rate), use nanotags and proximity data loggers to capture all the social interactions and map the social network, measure circulating hormone levels across the year, describe the maximum capacity for testosterone production in males of different status using GnRH challenges, measure the effect of social intrusion on hormone titers, block or increase hormone titers to manipulate phenotype, and measure expression levels of candidate genes for steroidogenic enzymes, steroid receptors and steroid influenced peptide signaling systems in the brains of these males using RT-qPCR. These data from individual birds will then be combined to examine network structures using binary and weighted models and to examine the influence of hormones on network structure and dynamics. All data from the study will be archived at the Smithsonian Migratory Bird Center web site (http://www.si.edu/smbc). The brain transcriptome assembly for the wire-tailed manakin will be posted on NCBI GenBank.