Ventilatory behaviors of the toad Bufo marinus revealed by coherence analysis

Posture as a Non-Invasive Indicator of Arousal in American Toads (Anaxyrus americanus)

Animal welfare has become a priority for modern zoos and aquariums. However, amphibians have not yet been the focus of much welfare research, perhaps in part because they do not tend to display many quantifiable active behaviors. This study focused on nine zoo-housed American toads (Anaxyrus americanus), a species that displays long periods of sedentary behavior, to explore whether more subtle cues could serve as welfare indicators. A novel American toad posture index was developed that characterized toad posture based on the angle of their forelimbs, visibility of ventral regions, and body weight distribution. As an indicator of arousal, approximate breathing rates were assessed based on the rate of expansion of the toads’ throats. Subsequent analyses revealed that lower body postures were associated with slower rates of throat expansion and raised postures with faster rates of throat expansion, suggesting that posture may be a promising way to quickly and non-invasively assess toad arousal. This work lays important groundwork for assessing welfare of an understudied species, and we are optimistic that, with additional validation, these approaches can be applied in future amphibian welfare research.

Why do models of insect respiratory patterns fail?

Insects exchange respiratory gases using an astonishing diversity of patterns. Of these, discontinuous gas exchange cycles (DGCs) have received the most study, but there are many other patterns exhibited intraspecifically and interspecifically. Moreover, some individual insects transition between patterns based on poorly understood combinations of internal and external factors. Why have biologists failed, so far, to develop a framework capable of explaining this diversity? Here, we propose two answers. The first is that the framework will have to be simultaneously general and highly detailed. It should describe, in a universal way, the physical and chemical processes that any insect uses to exchange gases through the respiratory system (i.e. tracheal tubes and spiracles) while simultaneously containing enough morphological, physiological and neural detail that it captures the specifics of patterns exhibited by any species or individual. The second difficulty is that the framework will have to provide ultimate, evolutionary explanations for why patterns vary within and among insects as well as proximate physiological explanations for how different parts of the respiratory system are modified to produce that diversity. Although biologists have made significant progress on all of these problems individually, there has been little integration among approaches. We propose that renewed efforts be undertaken to integrate across levels and approaches with the goal of developing a new class of general, flexible models capable of explaining a greater fraction of the observed diversity of respiratory patterns.