Thermal energetics of bats of the family Vespertilionidae: an evolutionary approach

Abstract

Thermal energetics define the way animals spend energy for thermoregulation. In this regard, numerous studies have determined that body mass (Mb) is the most influential morphological trait affecting the thermal traits in different species of birds and mammals. However, most of the studies have been focused on the basal metabolic rate (BMR), while other thermal traits have been less studied.We addressed this gap by examining thermal variables on bats of the family Vespertilionidae. Using open-flow respirometry, we measuredBMR, absolute thermal conductance (C’), lower and upper critical temperatures (TLCandTUC), and the breadth of the thermoneutral zone (TNZb) of 15 bat species varying inMbfrom ∼ 4.0 to 21.0 g from central Mexico. We: 1) combined our empirical data with information gathered from the bibliography and conducted phylogenetic analyses to investigate the relationship betweenMband thermal traits, and 2) mapped the thermal energetic values along the phylogeny to explore how they may have evolved.We found a positive relationship betweenMbandBMRand absoluteC’, and a negative relationship betweenMbandTLCandTUC. However, we did not find a relationship betweenMbandTNZbin bats. The phylogenetic approach suggested that over the evolutionary history of bats,BMRandC’ have decreased whileTLCandTUChave increased.Our results suggest that adaptive changes inMband thermal traits may have influenced the geographical distribution and the use of energy-saving strategies of the different species of bats of the family Vespertilionidae.