Auditory opportunity and visual constraint enabled the evolution of echolocation in bats

Substantial evidence now supports the hypothesis that the common ancestor of bats was nocturnal and capable of both powered flight and laryngeal echolocation. This scenario entails a parallel sensory and biomechanical transition from a nonvolant, vision-reliant mammal to one capable of sonar and flight. Here we consider anatomical constraints and opportunities that led to a sonar rather than vision-based solution. We show that bats' common ancestor had eyes too small to allow for successful aerial hawking of flying insects at night, but an auditory brain design sufficient to afford echolocation. Further, we find that among extant predatory bats (all of which use laryngeal echolocation), those with putatively less sophisticated biosonar have relatively larger eyes than do more sophisticated echolocators. We contend that signs of ancient trade-offs between vision and echolocation persist today, and that non-echolocating, phytophagous pteropodid bats may retain some of the necessary foundations for biosonar

Sensory and Cognitive Constraints and Opportunities in Bats

Here I report on three comparative studies and one review chapter addressing the relationships between sensory reliance, neuroanatomy, skull morphology and body size, as they relate to diet and foraging in bats. In chapter two, I use morphological and echolocation data to test whether (i) mass-signal frequency allometry or (ii) emitter-limited (maximum gape) signal directionality better explain the negative relationship between size and peak frequency in bats. The results suggest that body mass and forearm length were important predictors of open space echolocation call peak frequency in ways that (i) reflect species-specific size differences, and (ii) suggest the influence of preferred foraging habitat. In chapter three, I test the predictions that the ancestral bat had (i) an auditory brain design capable of supporting early laryngeal echolocation, but (ii) eyes of insufficient absolute size to allow insect tracking at night. The results suggest that bats’ common ancestor had eyes too small to allow for successful aerial hawking of flying insects at night, but an auditory brain design sufficient to afford echolocation. Further, we find that those with less sophisticated biosonar have relatively larger eyes than do sophisticated echolocators. In chapter four, I continue to explore apparent trade-offs between echolocation call design and vision in predatory bats. I also explored the effects of foraging strategy, roost preference, and migration on the brains and eyes of predatory bats. I found that external roosters had large relative eyes, as did those with conserved calls which also had larger visual regions than those with more derived calls. The results also suggest that gleaners and sedentary bats have larger brains than aerial hawking and migrating bats, respectively. In chapter five, I provide an overview of sensory and cognitive ecology as they relate to foraging ecology and diet in the Phyllostomidae. These bats have a wide spectrum of feeding ecologies and sensory system specializations. Here, I use the Phyllostomidae to illustrate the influences that foraging ecology and diet selection have on the evolution of sensory systems and relative brain and brain region volumes.Ph.D

RCode for Analyses_R2

Condensed version of R code used to implement analyses outlined in the main text

Data from: Phylogeny matters: revisiting ‘a comparison of bats and rodents as reservoirs of zoonotic viruses’

Diseases emerging from wildlife have been the source of many major human outbreaks. Predicting key sources of these outbreaks requires an understanding of the factors that explain pathogen diversity in reservoir species. Comparative methods are powerful tools for understanding variation in pathogen diversity and rely on correcting for phylogenetic relatedness among reservoir species. We reanalyzed a previously published dataset, examining the relative effects of species’ traits on patterns of viral diversity in bats and rodents. We expanded on prior work by using more highly resolved phylogenies for bats and rodents and incorporating a phylogenetically controlled principal components analysis. For rodents, sympatry and torpor use were important predictors of viral richness and, as previously reported, phylogeny had minimal impact in models. For bats, in contrast to prior work, we find that phylogeny does have an effect in models. Patterns of viral diversity in bats were related to geographic distribution (i.e., latitude and range size) and life history (i.e., lifespan, body size, and birthing frequency). However, the effects of these predictors were marginal relative to citation count, emphasizing that the ability to accurately assess reservoir status largely depends on sampling effort and highlighting the need for additional data in future comparative studies

Auditory opportunity and visual constraint enabled the evolution of echolocation in bats

Substantial evidence now supports the hypothesis that the common ancestor of bats was nocturnal and capable of both powered flight and laryngeal echolocation. This scenario entails a parallel sensory and biomechanical transition from a nonvolant, vision-reliant mammal to one capable of sonar and flight. Here we consider anatomical constraints and opportunities that led to a sonar rather than vision-based solution. We show that bats’ common ancestor had eyes too small to allow for successful aerial hawking of flying insects at night, but an auditory brain design sufficient to afford echolocation. Further, we find that among extant predatory bats (all of which use laryngeal echolocation), those with putatively less sophisticated biosonar have relatively larger eyes than do more sophisticated echolocators. We contend that signs of ancient trade-offs between vision and echolocation persist today, and that non-echolocating, phytophagous pteropodid bats may retain some of the necessary foundations for biosonar

Auditory opportunity and visual constraint enabled the evolution of echolocation in bats

Substantial evidence now supports the hypothesis that the common ancestor of bats was nocturnal and capable of both powered flight and laryngeal echolocation. This scenario entails a parallel sensory and biomechanical transition from a nonvolant, vision-reliant mammal to one capable of sonar and flight. Here we consider anatomical constraints and opportunities that led to a sonar rather than vision-based solution. We show that bats’ common ancestor had eyes too small to allow for successful aerial hawking of flying insects at night, but an auditory brain design sufficient to afford echolocation. Further, we find that among extant predatory bats (all of which use laryngeal echolocation), those with putatively less sophis- ticated biosonar have relatively larger eyes than do more sophisticated echolocators. We contend that signs of ancient trade-offs between vision and echolocation persist today, and that non-echolocating, phytophagous pteropodid bats may retain some of the necessary foundations for biosonar