Many studies assume that selection molds social traits and have investigated the manner in which this occurs, yet very few studies have measured the strength of selection on social traits in natural populations. In this paper, I report results of phenotypic selection analyses on two social traits – the size of social groups and the frequency of group foraging – in Phyllostomus hastatus, the greater spear-nosed bat. I found significant positive directional selection on individual group foraging frequency, but no directional selection on individuals in different-sized social groups. These results have implications for the structure of social groups, cooperative behavior among group mates, and maternal investment strategies. I argue that combining studies of natural selection on wild populations with experiments to identify the agents and mechanisms of selection can do much to increase our understanding of social evolution.

Selection on social traits in greater spear-nosed bats, Phyllostomus hastatus

We recorded acoustic signals during interactions between mother eastern red bats and their nursing young. Mothers and young produced tonal (structured change in frequency over time) frequency-modulated (FM) signals with varying harmonic components in situations ranging from reunion to just before nursing. Pups left by their mothers were usually silent, only occasionally producing tonal isolation calls. Adult females used FM signals in stressful situations, times when young usually produced clicks. Vibrational signals (‘hums’) composed of clicks (broadband, no structured change in frequency over time) characterized pup-pup and mother-pup interactions but pups also used other clicks that differed in frequency components from clicks comprising the hums. In stressful situations, adults produced FM signals, the pups, clicks. FM signals of pups decreased in frequencies with increasing age (size). Echolocation calls of adults and subadults hunting flying prey differed in frequency components. Differences in duration of echolocation calls coincided with setting (short calls in flight cages, open calls in the open). FM signals produced by pups searching for their mothers’ nipples showed little potential for individual signatures. Calls and calling behaviour of eastern red bats that are solitary and foliage-roosting, differed from those of more gregarious species roosting in more sheltered situations.

Vocalizations emitted during mother-young interactions by captive eastern red bats Lasiurus borealis (Chiroptera: Vespertilionidae)

Descripción de la dieta de un grupo de machos del murciélago Mormoops megalophylla en la cueva la Macaregua, Santander, Colombia

https://bioone.org/journals/Acta-Chiropterologica/volume-7/issue-2/1733-5329(2005)7[314:AOFBAI]2.0.CO;2/Acquisition-of-foraging-behavior-and-insect-preferences-by-naive-juvenile/10.3161/1733-5329(2005)7[314:AOFBAI]2.0.CO;2.pdf

Barbara Schmidt-French

Papers

Acquisition of foraging behavior and insect preferences by naive juvenile red bats (Lasiurus borealis)