The morphological constraint hypothesis suggests that primates with less dexterity show more consistent motor planning because there is less flexibility to compensate for inefficient actions. Spiders monkeys offer a unique opportunity to test this hypothesis because they do not have a functional thumb. Colombian spider monkeys (Ateles fusciceps rufiventris, n = 8) housed at a wildlife park were tested on a standard motor planning task. A trial began when a dowel baited on one end was placed on an elevated apparatus and ended when a monkey grasped the dowel with the hands. Grip use was coded from video as radial (pronated overhand grip with the radius bone towards food) or non-radial. The percentage of radial grips was used in analyses for comparison to other platyrrhines. As a group, spider monkeys used a radial grip significantly more than chance (M ± SD=73.38% ± 18.91), indicating spider monkeys engage in second-order motor planning. Spider monkeys differed in radial grip use from captive cotton-top tamarins (Saguinus oedipus) but not captive (Sapajus spp) or wild capuchins (Sapajus libidinosus) tested on the elevated dowel task in prior work by other investigators. Together, these findings have mixed implications for the morphological constraint hypothesis that merit further study.
Laterality, the preference for using one side of the body over the other, has been observed in various animal species, including frogs and toads. While laterality has been studied widely during locomotion in anurans, its role during other behaviours, such as hunting-related toe-tapping (the quick up and down movement of the middle toe of the hind feet while foraging), remains largely unstudied. This study investigated the toe-tapping rate of the left and right toes (versus both toes simultaneously) in a captive colony of green-and-black poison dart frogs (Dendrobates auratus, Dendrobatidae). We assessed the time spent tapping with each toe (right, left, or both toes simultaneously) in response to prey-mimicking videos, based on behavioural observations of 25 individuals. Simultaneous toe-tapping was rare, and laterality tests showed that frogs had an overall preference to toe-tap with their right toes (i.e., most individuals are right-lateralised) when presented with visual artificial prey. Since anurans prefer to strike at their prey once it is apparent in their right visual field, predator-prey interaction on the predator’s right body side (i.e., with its right toe) might be beneficial for the predator, and a potential clue towards a better understanding of the function of hunting-related toe-tapping in frogs.
Yawning is a stereotyped behavioural pattern observed across vertebrates and is considered multifunctional, but how its function changed during major physiological transitions remains poorly understood. Lungfishes provide an ideal model to address this question because species vary in their relative reliance on branchial and pulmonary respiration. We investigated whether yawning occurs in one individual each of the branchial-dominant Australian lungfish and three pulmonary-dominant species (marbled, spotted, and West African lungfishes) and, when present, characterized yawning frequency, yawning investment (frequency × duration), and activity levels before and after yawning. Yawning was observed exclusively underwater in all species. The branchial-dominant Australian lungfish showed a significantly higher yawning frequency than the three individual pulmonary-dominant lungfishes (negative binomial model: p = 0.007), whereas yawning investment was broadly comparable among the four individuals. In the branchial-dominant Australian lungfish, activity levels significantly increased following yawning (Wilcoxon signed-rank test: p = 0.041), whereas no significant post-yawning increase was observed in the two pulmonary-dominant individuals. The magnitude of activity-level change associated with yawning differed significantly from that observed during control periods in the branchial-dominant Australian lungfish (Wilcoxon rank-sum test: p = 0.006), but not when the pulmonary-dominant individuals were pooled. These observations indicate that lungfish yawning occurs underwater regardless of respiratory mode and is associated with differences in yawning characteristics and post-yawning activity among the individuals. Although these findings cannot establish species-level differences, they suggest that yawning function may vary with respiratory mode and warrant further comparative study.
Acoustic monitoring has been touted as an automatable monitoring technique to study the presence, activity or acoustic communication of soil animals. Yet current acoustic approaches have been criticized for lacking understanding of what soil fauna behaviours they are detecting. We investigate whether specific insect behaviours could be identified with sound by recording Red Wood Ants (Formica rufa) behaviours (running, struggling, biting and stridulation-like behaviour) with a contact microphone. We label recordings by hand, then extract two types of acoustic features, spectral and cepstral features, and show that most of the selected ant behaviours could be separated from each other based on their acoustic profiles. Based on our results, we propose an analytical workflow including principal component analysis as well as random forest classification that generates correct behavioural classifications in 67–90% of the sound snippets. Key features to separate behaviours include cepstral skewness, duration of sound events and mean frequency of the generated sound. Even if we encountered background noise, our pipeline could select relevant features from audio files and train a machine learning classifier. Our study demonstrates that acoustic features can be used to inform about specific insect behaviours and thus broaden the application of passive acoustic monitoring to species that do not communicate acoustically.
