Lisette M.C. Leliveld

Acoustic correlates of individuality in the vocal repertoire of a nocturnal primate (Microcebus murinus)

In mammals individual distinctiveness in vocalizations provides the basis for individual recognition and thus plays an important role in social behavior. In this study, first evidence is provided for a nocturnal primate that variation in individual distinctiveness across the vocal repertoire is to some extent determined by the context and the acoustic structure of the call types. Individual distinctiveness was investigated across call types in the gray mouse lemur, a nocturnal primate, living in a dispersed multi-male multi-female social system. To explore to what degree context and acoustic structure predict variations in individual distinctiveness, four major call types were examined (grunts, tsaks, short whistles, and trills). Call types differed in context and acoustic structure and were recorded under controlled experimental conditions. A discriminant function analysis revealed that all call types are individually distinct, but not to the same degree. The findings suggest that variations in individual distinctiveness can to some extent be explained by the context and the acoustic structure of the call types.

Does body posture influence hand preference in an ancestral primate model

BackgroundThe origin of human handedness and its evolution in primates is presently under debate. Current hypotheses suggest that body posture (postural origin hypothesis and bipedalism hypothesis) have an important impact on the evolution of handedness in primates. To gain insight into the origin of manual lateralization in primates, we studied gray mouse lemurs, suggested to represent the most ancestral primate condition. First, we investigated hand preference in a simple food grasping task to explore the importance of hand usage in a natural foraging situation. Second, we explored the influence of body posture by applying a forced food grasping task with varying postural demands (sit, biped, cling, triped).ResultsThe tested mouse lemur population did not prefer to use their hands alone to grasp for food items. Instead, they preferred to pick them up using a mouth-hand combination or the mouth alone. If mouth usage was inhibited, they showed an individual but no population level handedness for all four postural forced food grasping tasks. Additionally, we found no influence of body posture on hand preference in gray mouse lemurs.ConclusionOur results do not support the current theories of primate handedness. Rather, they propose that ecological adaptation indicated by postural habit and body size of a given species has an important impact on hand preference in primates. Our findings suggest that small-bodied, quadrupedal primates, adapted to the fine branch niche of dense forests, prefer mouth retrieval of food and are less manually lateralized than large-bodied species which consume food in a more upright, and less stable body posture.

Manual lateralization in early primates: A comparison of two mouse lemur species

In humans, 90% of the population is right handed. Although population hand preference has been found in some primate species, the evolution of manual lateralization in primates is not yet clear. To gain insight into manual lateralization of ancestral primates, we studied hand usage in unspecialized quadrupedal, nocturnal lemurs, using a large sample size. We compared two closely related mouse lemur species to explore the variation of hand preference within the same genus. We tested 44 gray mouse lemurs and 19 Goodmans mouse lemurs in a forced food grasping task. The tests were videotaped. Measures of hand preference (i.e. the hand that is spontaneously chosen for a specific task) and successful hand usage (i.e. the hand that is successful in completing a specific task) were taken to explore manual lateralization. Both species showed manual lateralization at an individual, but not at a population level. Goodmans mouse lemurs showed stronger individual hand preferences than gray mouse lemurs. This suggests that strength in hand preference is variable within the same genus. No sex and age effects were found. The hand preference of offspring was negatively correlated to that of their mothers, but not correlated to that of their fathers. Thus, no clear genetic effect can be derived from these results. In the Goodmans mouse lemurs, hand preference increased with increasing task experience. However, successful hand usage was not affected by task experience, suggesting that successful hand usage is a more stable measurement for manual lateralization than hand preference.

Effects of Caller Characteristics on Auditory Laterality in an Early Primate (Microcebus murinus)

Background Auditory laterality is suggested to be characterized by a left hemisphere dominance for the processing of conspecific communication. Nevertheless, there are indications that auditory laterality can also be affected by communicative significance, emotional valence and social recognition. Methodology/Principal Findings In order to gain insight into the effects of caller characteristics on auditory laterality in the early primate brain, 17 gray mouse lemurs were tested in a head turn paradigm. The head turn paradigm was established to examine potential functional hemispheric asymmetries on the behavioral level. Subjects were presented with playbacks of two conspecific call types (tsak calls and trill calls) from senders differing in familiarity (unfamiliar vs. familiar) and sex (same sex vs. other sex). Based on the head turn direction towards these calls, evidence was found for a right ear/left hemisphere dominance for the processing of calls of the other sex (Binomial test: p = 0.021, N = 10). Familiarity had no effect on the orientation biases. Conclusions/Significance The findings in this study support the growing consensus that auditory laterality is not only determined by the acoustic processing of conspecific communication, but also by other factors like the sex of the sender.

Modeling the origins of mammalian sociality: moderate evidence for matrilineal signatures in mouse lemur vocalizations

IntroductionMaternal kin selection is a driving force in the evolution of mammalian social complexity and it requires that kin are distinctive from nonkin. The transition from the ancestral state of asociality to the derived state of complex social groups is thought to have occurred via solitary foraging, in which individuals forage alone, but, unlike the asocial ancestors, maintain dispersed social networks via scent-marks and vocalizations. We hypothesize that matrilineal signatures in vocalizations were an important part of these networks. We used the solitary foraging gray mouse lemur (Microcebus murinus) as a model for ancestral solitary foragers and tested for matrilineal signatures in their calls, thus investigating whether such signatures are already present in solitary foragers and could have facilitated the kin selection thought to have driven the evolution of increased social complexity in mammals. Because agonism can be very costly, selection for matrilineal signatures in agonistic calls should help reduce agonism between unfamiliar matrilineal kin. We conducted this study on a well-studied population of wild mouse lemurs at Ankarafantsika National Park, Madagascar. We determined pairwise relatedness using seven microsatellite loci, matrilineal relatedness by sequencing the mitrochondrial D-loop, and sleeping group associations using radio-telemetry. We recorded agonistic calls during controlled social encounters and conducted a multi-parametric acoustic analysis to determine the spectral and temporal structure of the agonistic calls. We measured 10 calls for each of 16 females from six different matrilineal kin groups.ResultsCalls were assigned to their matriline at a rate significantly higher than chance (pDFA: correct = 47.1%, chance = 26.7%, p = 0.03). There was a statistical trend for a negative correlation between acoustic distance and relatedness (Mantel Test: g = -1.61, Z = 4.61, r = -0.13, p = 0.058).ConclusionsMouse lemur agonistic calls are moderately distinctive by matriline. Because sleeping groups consisted of close maternal kin, both genetics and social learning may have generated these acoustic signatures. As mouse lemurs are models for solitary foragers, we recommend further studies testing whether the lemurs use these calls to recognize kin. This would enable further modeling of how kin recognition in ancestral species could have shaped the evolution of complex sociality.

Behavioural lateralization in domestic pigs (Sus scrofa)—variations between motor functions and individuals

ABSTRACT Motor lateralization is hypothesized to depend on the complexity of the motor function, but it might at the same time reflect hemispheric dominance within an individual across motor functions. We investigated possible motor lateralization patterns in four motor functions of different complexity (snout use in a manipulative task, foot use in two-stepping tasks and tail curling) in the domestic pig, a tetrapod species relevant as farm animal but also as a model in human neuroscience. A significant majority of our sample showed individual biases for manipulation with their snout and for curling their tail. Interestingly, the tail curling was lateralized towards the right at the population level and showed stronger lateralization patterns than the snout. Using a cluster analysis with combined tail and snout laterality, we identified groups of individuals with different lateralization patterns across motor functions that potentially reflect the individuals’ hemispheric dominance. To conclude, our results suggest that pigs show lateralization patterns that depend on the motor function and on the individual. Such individual lateralization patterns might have broader implications for animal personality and welfare. Our study lays the methodological groundwork for future research on laterality in pigs.