Energetic Dimensions of Brazilian Free-tailed Bats

Frio Cave, like several other Texas caves, is home to one of the largest concentrations of mammals on the planet, Brazilian Free-tailed Bats. The number of bats living in this colony is impossible to determine, although many people have tried—estimates range up to 12 million bats. Every evening, a river of bats flows out of the cave and spreads across the landscape in search of insect prey. For decades, scientists and tourists alike have wondered at the spectacle of the Brazilian Free-tailed Bat emergence from this cave. With thermal imaging cameras, previous researchers have estimated that 25,000–30,000 bats emerge every minute during the peak emergence period. With so many bats trying to fly out of the cave, some are forced to emerge while it is still daylight, and the emergence continues until well after dark. This same awe-inspiring scene repeats itself night after night throughout the entire summer and into the fall.

But things aren't exactly the same for that entire period. And that's what has drawn the interests of Dr. Caleb Phillips (NSRL Curator of Genetic Resources and Assistant Professor in Biological Sciences) and Dr. Liam McGuire (NSRL Research Associate and Assistant Professor in Biological Sciences). Drs. Phillips and McGuire are interested in the ecological drivers, mechanisms, and consequences of seasonal variation. How does variation in environmental factors affect genetic and physiological processes in wild animals? And how are genetic and physiological processes affected by changes within animals, such as reproductive status?

Together with a team of graduate students, these researchers are working with the bats at Frio Cave to develop an integrative understanding of how flexible animals can be. The bats at Frio Cave arrive in the spring, having migrated perhaps 500 miles from their winter roosts in Mexico. Over the ensuing months, females go through pregnancy, nurse their pup, and then prepare for the return fall migration. Pregnancy, lactation, and long-distance migration are all extremely energetically demanding. In contrast, males do not experience any reproductive energetic costs through the summer, but rather must cope only with environmental variation.

Dr. McGuire is a physiological ecologist, with a particular interest in phenotypic flexibility; that is, how traits and characteristics of animals change over time in response to varying conditions. Amie Sommers (MS student, TTU Biological Sciences) is studying changes in digestive (e.g., intestines, kidneys, liver) and exercise organs (e.g., flight muscle, heart, lungs) in the context of exercise and energetic tradeoffs. Elizabeth Rogers (MS student, TTU Biological Sciences) will take a biochemical approach to address similar questions, measuring aerobic capacity and lipid metabolism in muscle and liver samples. All of this research will benefit from the use of Dr. McGuire's Mobile Ecological Research Laboratory (MERL). MERL allows researchers to bring the lab out to the field, including a non-invasive body composition analyzer that provides measurements of fat and lean tissue mass.

Dr. Phillips is a mammalian functional genomicist and investigates how microbiomes, the symbiotic bacterial communities that live in and on hosts, interact and help support host physiological processes. In the context of the bats of Frio Cave, Dr. Phillips and Oscar Sandate (MS student, TTU Biological Sciences) are studying the host-microbiome relationship over the course of pregnancy and how these changes relate to energetic demands. They are characterizing this relationship by studying changes in dietary energy extraction efficiency, changes in intestinal histology, host immunological response, and changes in microbiome community structure and function.

The research questions pursued by the Phillips and McGuire laboratories are being developed in conjunction and are based on the same set of specimens, enabling the emergence of systems-level understandings about physiology, reproduction, and genomics. The support of the NSRL is an invaluable resource for managing field work of this scope, which involves the collection, liquid nitrogen-transfer, cataloguing, and curation of all samples and specimens. Equally important, this research is growing the already world-leading Genetic Resources Collection. Samples collected as part of this research will be available for later studies, decades into the future. With a ready supply of study animals, an on-site mobile laboratory, and the support of the NSRL, the team from Texas Tech is on the cutting edge of research and technology that will contribute many novel insights into our understanding of how organisms cope with change.