Lynn B. Martin - US grants

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

Invasive species are a large and growing threat to ecosystem function, biodiversity and even human health. However, the traits that enable some species to expand their ranges and become pests remain understudied. The focus of the project is to ascertain how the world?s most common songbird, the house sparrow, has been able to colonize most of the planet. Native to Eurasia, this species now is found on all continents but Antarctica. Some invasions are still ongoing, such as the one in Kenya that began about 50 years ago. Introduced to the coastal city of Mombasa, the species is spreading westward towards Uganda predominantly into areas occupied by humans. It is hypothesized that this range expansion is being facilitated by adjustments in physiological traits, namely sacrifices of expensive immune defenses.

The emerging field of ecological immunology is revealing that contrary to intuition, animals do not always possess maximal levels of immune defense; in some contexts, such as during invasions, they appear to sacrifice particularly costly components to allocate resources to more immediately lucrative activities, such as reproduction. To test the hypothesis that invasions are fostered by sacrifices of immune defenses, comparative field and lab studies across Kenya will be conducted over several years. This interdisciplinary approach will involve modern technologies in a 'wild' setting, and will provide new insight into how to control animal invasions. The impacts of the work will be broad involving the joint efforts of American students and scientists, staff at the National Museum of Kenya, and native Kenyan schoolchildren and their teachers. In sum, the work will provide new information for an underexplored area of evolutionary biology, improve our ability to preempt invasions, and simultaneously reinforce scientific relationships in parts of the world where such networks are yet rare.

Non-native species cause major ecological and economic damage in their introduced range; it is important to identify predictors of invasiveness to prevent future invasions. This information might also prove to be important is assessing the vulnerability of native species to environmental change. One of the most recent introduction events, the house sparrow (Passer domesticus) to Kenya, is still expanding beyond the site of initial introduction. Kenyan house sparrows do not have high genetic diversity, however still exhibit extensive behavioral and physiological variation; interestingly, the observed variation is correlated with the estimated age of the population. House sparrows closest to the edge of the range are more exploratory and release more stress hormones (glucocorticoids) in response to stressors than those closer to the site of initial introduction. However, what these trait differences mean in terms of fitness along the range expansion is unknown; further, how these differences arise given the lack of genetic diversity is also unknown. The goal of the present research is to determine A) if increased exploration and stress hormones grant a fitness advantage at the range edge, but a disadvantage in more familiar habitats; and B) whether these differences arise due to differences in maternal care during offspring development. To test these questions, observation of natural parental care as well as manipulattion of a mother's ability to provision during the nestling period in nestbox colonies will be carried out in Kenya. The PI predicts that increased exploration and stress hormones increase fitness at the edge of a range, but decrease it at the site of introduction. Further, it is also expected that food supplementation will generate offspring most like those naturally occurring at the site of introduction and a reduction of provisioning will produce offspring similar to those at the range edge. The proposed study will strengthen international collaborations and provide research opportunities for underrepresented minority STEM undergraduates.

This project addresses two long-standing questions in biology, how genomes become phenomes and how organisms maintain stability through change, by investigating how body size affects immune defenses in terrestrial mammals. Although body mass is one of the strongest influences on many physiological traits, effects of body size are not known for immune systems. Through an unprecedented comparative approach, the research tests whether body size explains why some species are more susceptible to parasites and more likely to act as parasite reservoirs, whereas other species are resistant. Specifically, the research will provide new information on how functional forms of innate immunity relate to body size among >150 zoo-housed terrestrial mammal species spanning a broad range of sizes. Results will provide a framework for understanding of mammalian immune variation has the potential to enhance models of disease spread by providing predictions about the level of immune defense expected in species never before studied. The project fosters career development for two young investigators, a postdoctoral researcher, and 8-10 undergraduate research students. Participants will develop outreach activities for zoos and for biology classes at local middle and high schools, to enhance the educational effectiveness of zoo exhibits and lesson plans. These activities will demonstrate how comparative research is relevant to understanding human and animal health.

This project investigates whether and how body mass is related to the architecture of antimicrobial immune defenses in terrestrial mammals, an unstudied aspect of size-scaling. Host size likely affects i) the chance of exposure to infectious organisms, ii) the ability of immune defenses to keep pace with pathogen replication, iii) the ability of host surveillance mechanisms to detect threats in a comparatively large risk space. The project will determine how functional forms of innate immunity relate to body size among >150 zoo-housed species of terrestrial mammals spanning 7 orders of magnitude in body mass. In addition, protein expression for innate immune defenses as a function of body mass among 10 primate species spanning 5 orders of magnitude in size will be quantified. Using zoo-housed animals, which experience similar developmental histories in common environments, minimizes effects of confounding variables inherent to the study of wild individuals. Measuring functional antimicrobial responses is preferable to less direct assays of host defense. The transcriptomic methods will show which innate immune genes, gene networks, and/or gene modules are most sensitive to body mass. This project addresses two Grand Challenges in Organismal Biology, and has the potential to transform how scientists think about host-parasite interactions. The transcriptomic data generated will contribute to other systems biology pursuits, including understanding how size may constrain the evolution of regulatory processes in vertebrate animals. The participants, including 8-10 undergraduates, will develop interpretive displays and exhibits for zoos, and lesson plans for middle- and high-school biology classes to engage and educate students and the public and to demonstrate the relevance of comparative research.

Understanding the factors that reduce infections in animals is an essential step towards reducing human disease risk because an estimated 60% of pathogens that infect humans can also infect animals (including the virus that causes COVID-19). However, it is difficult to predict infectious disease risk in animal populations because it is not understood how changes in the quality of an animal’s environment (e.g., temperature, abundance of food) may change disease rates. This project will investigate how variation in habitat quality affects the ecological dynamics of Lyme disease, the most common vector-borne disease in the US, affecting the health and well-being of over 300,000 people annually. Through a collaboration with the National Ecological Observatory Network, the research team will measure the effects of habitat quality on the behavioral and immune system traits of mice at 8 sites across the northeastern U.S. and develop statistical models to link these animal data to Lyme disease risk. This project will benefit society by improving our ability to identify the times and places where risk of Lyme disease exposure can be minimized, directly benefitting hundreds of thousands of people each year. Through outreach, the project will educate the public about the factors that affect infectious disease and provide significant opportunities for training of high-school students, undergraduates, graduate students, and postdocs underrepresented in STEM fields.

Many behavioral and immune system traits are sensitive to the environment. But the extent to which this variation drives infectious disease risk in nature remains obscure. For example, although it is known that particular rodent species are critical hosts of B. burgdorferi, the causative agent of Lyme disease, it is unknown how the environment affects traits that influence disease risk. This research project will leverage the continental scale of the National Ecological Observatory Network (NEON) to quantify behavioral and immunological traits of two keystone rodent hosts for B. burgdorferi, a pathogen that affects over 300,000 people in the U.S. each year. This project tests the hypothesis that variation in the environment couples and decouples individual host traits, altering the abundance of competent hosts and driving the emergence of disease hot and cold spots. This project will quantify B. burgdorferi competence in two rodent species across 8 NEON sites over 3 years, and use statistical modeling to link individual variation in infection susceptibility to variation in the abiotic and biotic environment and hence variation in Lyme disease risk. The utility of this approach will be evaluated by using these models to forecast disease prevalence as a function of current climatic and habitat conditions at additional NEON sites in future years. Ultimately, the project will identify how organism-environment interactions drive the susceptibility of individual hosts to infection, and will also identify the level(s) of biological organization (e.g., individuals, populations, species) at which small changes have large consequences for increased disease risk.

This award was co-funded by the Symbiosis, Infection and Immunity Program in the Division of Integrative Organismal Systems and the Macrosystems Biology and NEON Enabled Science Program in the Division of Environmental Biology.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.