RUI: A Mosaic Model of Host-Microbe Thermal Relationships

Ectothermic vertebrate animals, such as fish, amphibians, and reptiles, show both adaptation to temperature in their environments and the ability to acclimate to changes in those thermal conditions. Similarly, their pathogens and parasites are also adapted, and have the ability to acclimate to changing environmental temperatures. Reptiles are the ectothermic animals most closely related to birds and mammals, but exactly how their immune systems react across widely varying body temperatures is not precisely known and has impacts for conservation as well as a general understanding of physiological reactions to infection, such as fevers and hypothermia.

This project will quantify how temperature effects one of the most basic functions of the immune system, phagocytosis, or the engulfment of harmful agents and pathogens by white blood cells. The desert tortoise will be used as a study organism, because prior research showed that phagocytosis by a wide variety of white blood cells - including lymphocytes - is important in limiting respiratory pathogens.

Therefore, the influence of a wide range of temperatures on white blood cell activity, bacterial growth, and their interactions will be quantified. Phagocytic lymphocytes exist across all classes of ectothermic vertebrates, but their role in limiting disease has not been quantified across varying body temperatures - despite the likely importance to conservation, medicine, and food production.

This project engages a large number of undergraduate and Masters students at a Hispanic-Serving Institute which supports a student body that is traditionally under-represented in STEM fields and experiences financial hardship.

This project focuses on quantifying seasonal thermal performance curves of phagocytic cells (heterophils, monocytes/macrophages, B1 lymphocytes) in tortoises, microbes (total and the tortoise-specific bacteria Pasteurella testudinis), and their interaction (bacteria-killing activity). These assays will be quantified in vitro, and we will also compare them to in vivo responses, which further can be influenced by physiological changes in the organism, such as stress responses.

Because phagocytosis by B1 lymphocytes is a process that is not well understood in ectothermic vertebrates, mechanisms (engulfment, acidification, bacteria-killing) across sub-populations of phagocytic leukocytes will be quantified. The prediction is that tortoises are in fact a “mosaic” of leukocytes, with different thermal performance abilities, to protect the animals across a wide range of body temperatures.

Viewing ectothermic animals as not just warm or cold-adapted, but composed of cells with different thermal preferences, represents a paradigm shift in ecological immunology and will help form a greater understanding of animals’ responses to changing environmental conditions. This research has wide-ranging impacts on topics as broad as the conservation of biodiversity, management of changing host-pathogen systems, and therapies to maintain health in animal populations.

The paid opportunities offered to both Masters and undergraduate students will increase representation of minorities in STEM and will strengthen our departments’ goal to increase experiential learning in our curriculum. Collaboration with the local Nature and Discovery Center will allow research students to act as role models and mentors to more than 1,500 grade school students enrolled in public schools in Pueblo, Colorado.

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.