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 ( M b ) 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 measured BMR , absolute thermal conductance ( C ’), lower and upper critical temperatures ( T LC and T UC ), and the breadth of the thermoneutral zone ( TNZ b ) of 15 bat species varying in M b from ∼ 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 between M b and thermal traits, and 2) mapped the thermal energetic values along the phylogeny to explore how they may have evolved. We found a positive relationship between M b and BMR and absolute C’ , and a negative relationship between M b and T LC and T UC . However, we did not find a relationship between M b and TNZ b in bats. The phylogenetic approach suggested that over the evolutionary history of bats, BMR and C ’ have decreased while T LC and T UC have increased. Our results suggest that adaptive changes in M b and 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.