Meeting Abstract
Organisms respond to variation in energy availability and demand by altering behavior, physiology, and morphology; collectively, this is called phenotypic flexibility. We studied Brazilian free-tailed bats (Tadarida brasiliensis) to assess phenotypic flexibility driven by intrinsic and extrinsic factors. T. brasiliensis are small, volant endotherms that experience wide variation in energetic demand. Crucially, males and females experience reproductive energy demands at different times of the annual cycle. Pregnancy and lactation occur during the summer while males undergo spermatogenesis over winter. Thus females face both intrinsic (reproductive) and extrinsic (environmental) challenges in summer. Males cope with the same environmental variation as females, but experience little intrinsic variation in summer. We hypothesized the T. brasiliensis phenotype (lean and fat mass) would vary in response to energy demand. We predicted greater variance in females due to greater and more variable intrinsic energy demand during the summer active season. We used quantitative magnetic resonance to measure body composition (lean mass, fat mass, total body water) of adult T. brasiliensis during the summer active period. To provide context to changes in lean mass, we collected bats to measure organ sizes, considering organs associated with digestion and exercise. Female total lean mass increased through pregnancy, and again through lactation, while fat mass decreased through pregnancy and lactation. There was little variation in lean and fat mass of males over the summer. Organ size analysis is ongoing. Our results suggest that intrinsic factors have a greater effect than extrinsic factors on the T. brasiliensis phenotype during the summer season.
