Eric M. Patterson

Social networks reveal cultural behaviour in tool-using dolphins

Animal tool use is of inherent interest given its relationship to intelligence, innovation and cultural behaviour. Here we investigate whether Shark Bay bottlenose dolphins that use marine sponges as hunting tools (spongers) are culturally distinct from other dolphins in the population based on the criteria that sponging is both socially learned and distinguishes between groups. We use social network analysis to determine social preferences among 36 spongers and 69 non-spongers sampled over a 22-year period while controlling for location, sex and matrilineal relatedness. Homophily (the tendency to associate with similar others) based on tool-using status was evident in every analysis, although maternal kinship, sex and location also contributed to social preference. Female spongers were more cliquish and preferentially associated with other spongers over non-spongers. Like humans who preferentially associate with others who share their subculture, tool-using dolphins prefer others like themselves, strongly suggesting that sponge tool-use is a cultural behaviour.

Home range overlap, matrilineal and biparental kinship drive female associations in bottlenose dolphins

Few studies of kinship in mammalian societies have been able to consider the complex interactions between home range overlap, association patterns and kinship, which have created a critical gap in our understanding of social evolution. We investigated the association patterns of female bottlenose dolphins, Tursiops aduncus, in the eastern gulf of Shark Bay, Western Australia and found that they depended upon the complex interplay of at least three factors: home range overlap, matrilineal kinship and biparental kinship. While home range overlap was positively correlated with female association patterns, preferred associations were found between females showing as little as 27% home range overlap, and some pairs showed avoidance despite 100% home range overlap. Furthermore, on average, both casual and preferred associations took place between females that were more closely biparentally related than expected by chance and this pattern varied depending upon whether or not pairs of females shared the same matriline.

Tool use by aquatic animals

Tool-use research has focused primarily on land-based animals, with less consideration given to aquatic animals and the environmental challenges and conditions they face. Here, we review aquatic tool use and examine the contributing ecological, physiological, cognitive and social factors. Tool use among aquatic animals is rare but taxonomically diverse, occurring in fish, cephalopods, mammals, crabs, urchins and possibly gastropods. While additional research is required, the scarcity of tool use can likely be attributable to the characteristics of aquatic habitats, which are generally not conducive to tool use. Nonetheless, studying tool use by aquatic animals provides insights into the conditions that promote and inhibit tool-use behaviour across biomes. Like land-based tool users, aquatic animals tend to find tools on the substrate and use tools during foraging. However, unlike on land, tool users in water often use other animals (and their products) and water itself as a tool. Among sea otters and dolphins, the two aquatic tool users studied in greatest detail, some individuals specialize in tool use, which is vertically socially transmitted possibly because of their long dependency periods. In all, the contrasts between aquatic- and land-based tool users enlighten our understanding of the adaptive value of tool-use behaviour.

Thar She Blows! A Novel Method for DNA Collection from Cetacean Blow

Background Molecular tools are now widely used to address crucial management and conservation questions. To date, dart biopsying has been the most commonly used method for collecting genetic data from cetaceans; however, this method has some drawbacks. Dart biopsying is considered inappropriate for young animals and has recently come under scrutiny from ethical boards, conservationists, and the general public. Thus, identifying alternative genetic collection techniques for cetaceans remains a priority, especially for internationally protected species. Methodology/Principal Findings In this study, we investigated whether blow-sampling, which involves collecting exhalations from the blowholes of cetaceans, could be developed as a new less invasive method for DNA collection. Our current methodology was developed using six bottlenose dolphins, Tursiops truncatus, housed at the National Aquarium, Baltimore (USA), from which we were able to collect both blow and blood samples. For all six individuals, we found that their mitochondrial and microsatellite DNA profile taken from blow, matched their corresponding mitochondrial and microsatellite DNA profile collected from blood. This indicates that blow-sampling is a viable alternative method for DNA collection. Conclusion/Significance In this study, we show that blow-sampling provides a viable and less invasive method for collection of genetic data, even for small cetaceans. In contrast to dart biopsying, the advantage of this method is that it capitalizes on the natural breathing behaviour of dolphins and can be applied to even very young dolphins. Both biopsy and blow-sampling require close proximity of the boat, but blow-sampling can be achieved when dolphins voluntarily bow-ride and involves no harmful contact.

Becoming a High-Fidelity--"Super"--Imitator: What Are the Contributions of Social and Individual Learning?.

In contrast to other primates, human childrens imitation performance goes from low to high fidelity soon after infancy. Are such changes associated with the development of other forms of learning? We addressed this question by testing 215 children (26-59 months) on two social conditions (imitation, emulation) - involving a demonstration - and two asocial conditions (trial-and-error, recall) - involving individual learning - using two touchscreen tasks. The tasks required responding to either three different pictures in a specific picture order (Cognitive: Airplane→Ball→Cow) or three identical pictures in a specific spatial order (Motor-Spatial: Up→Down→Right). There were age-related improvements across all conditions and imitation, emulation and recall performance were significantly better than trial-and-error learning. Generalized linear models demonstrated that motor-spatial imitation fidelity was associated with age and motor-spatial emulation performance, but cognitive imitation fidelity was only associated with age. While this study provides evidence for multiple imitation mechanisms, the development of one of those mechanisms - motor-spatial imitation - may be bootstrapped by the development of another social learning skill - motor-spatial emulation. Together, these findings provide important clues about the development of imitation, which is arguably a distinctive feature of the human species.

Look, no hands!

Contrary to Vaesens argument that humans are unique with respect to nine cognitive capacities essential for tool use, we suggest that although such cognitive processes contribute to variation in tool use, it does not follow that these capacities are necessary for tool use, nor that tool use shaped cognition per se, given the available data in cognitive neuroscience and behavioral biology.

The role of weighted and topological network information to understand animal social networks: a null model approach

Network null models are important to drawing conclusions about individual- and population-(or graph) level metrics. While the null models of binary networks are well studied, recent literature on weighted networks suggests that: (1) many so-called ‘weighted metrics’ do not actually depend on weights, and (2) many metrics that supposedly measure higher-order social structure actually are highly correlated with individual-level attributes. This is important for behavioural ecology studies where weighted network analyses predominate, but there is no consensus on how null models should be specified. Using real social networks, we developed three null models that address two technical challenges in the networks of social animals: (1) how to specify null models that are suitable for ‘proportion-weighted networks’ based on indices such as the half-weight index; and (2) how to condition on the degree- and strength-sequence and both. We compared 11 metrics with each other and against null-model expectations for 10 social networks of bottlenose dolphin, Tursiops aduncus, from Shark Bay, Australia. Observed metric values were similar to null-model expectations for some weighted metrics, such as centrality measures, disparity and connectivity, whereas other metrics such as affinity and clustering were informative about dolphin social structure. Because weighted metrics can differ in their sensitivity to the degree-sequence or strength-sequence, conditioning on both is a more reliable and conservative null model than the more common strength-preserving null-model for weighted networks. Other social structure analyses, such as community partitioning by weighted Modularity optimization, were much less sensitive to the underlying null-model. Lastly, in contrast to results in other scientific disciplines, we found that many weighted metrics do not depend trivially on topology; rather, the weight distribution contains important information about dolphin social structure.

Chapter 4 – Cetacean Innovation

In this chapter, we explore examples of novel, unusual, and atypical behavior by both wild and captive whales and dolphins in an effort to inform our understanding of cetacean innovative and creative abilities. While innovative and perhaps creative behavior occurs in a variety of contexts for both suborders, far more examples have been observed in odontocetes than mysticetes, which may be due to differences in ecology, morphology, life history, and/or cognitive ability, or simply reflect biases in the available data. In comparison to other taxa, data from cetacean research is less complete, but does provide important comparative insights into who innovates and why.

The transition to independence: sex differences in social and behavioural development of wild bottlenose dolphins

Sex differences in adult behaviour are well documented, but less is known about the ontogeny of these differences. In mammals, the transition to independence, from infancy to the juvenile period, is when these sex differences are likely to become prominent. Here, we examined sex differences in behavioural development among calf and juvenile bottlenose dolphins, Tursiops aduncus, from 2 years preweaning to 2 years postweaning and whether these differences were consistent, or not, with three nonmutually exclusive hypotheses regarding the function of the juvenile period: the social skills, protection/safety and energy allocation hypothesis. All hypotheses received some support, but strikingly so for females. First, sex differences in the nature and quality of juvenile social bonds appear to foreshadow adult association patterns. Juveniles had a greater proportion of same-sex associates than calves. Second, although neither sex increased their number of associates from infancy to juvenility, a pattern that might mitigate predation risk, avoidance between juveniles and adult males suggests that both sexes reduce the likelihood of conspecific aggression. This pattern was more marked for juvenile females. Third, females, but not males, increased foraging rates from late infancy to the early juvenile period, even surpassing typical adult female foraging rates. This is likely related to the future energetic demands of maternal investment and skill development required for specialized foraging tactics, which are female biased in this population. This study provides a first step towards understanding the transition into independence for cetaceans, insight into how sex differences develop and a glimpse into the function of the juvenile period.

Eastern water dragons use alternative social tactics at different local densities

Animals’ affiliative behaviour is, in many species, driven by population density. Although the causes of such an effect are probably varied, affiliative social behaviour can sometimes be used to minimise conflict and competition when conspecific density is high. However, individuals might instead use multiple different social tactics (e.g. social avoidance or social preference) in order to optimally minimise competition and social conflict at different local densities. Here, we investigated whether eastern water dragons (Intellegama lesueurii) use alternative social tactics at different local densities. Interestingly, we found that whilst the number of casual associations per individual increased linearly with density, as predicted by our null expectation, the relationship with density differed between social avoidance and social preference. In particular, individuals had more preferential associations at intermediate density but more avoidances at high density. This suggests that both male and female dragons use alternative social tactics according to the density of their social environment, possibly to optimally reduce social conflict.Significance statementThis study investigated the relationship between local density and social tactics (e.g. social preference and social avoidance) in eastern water dragons. We demonstrate that dragons use different social tactics according to local density. We therefore present evidence that dragons may use alternative social tactics to optimally reduce competition and conflict in their local environment.