Ewa Krzyszczyk

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.

A framework for the identification of long-term social avoidance in longitudinal datasets

Animal sociality is of significant interest to evolutionary and behavioural ecologists, with efforts focused on the patterns, causes and fitness outcomes of social preference. However, individual social patterns are the consequence of both attraction to (preference for) and avoidance of conspecifics. Despite this, social avoidance has received far less attention than social preference. Here, we detail the necessary steps to generate a spatially explicit, iterative null model which can be used to identify non-random social avoidance in longitudinal studies of social animals. We specifically identify and detail parameters which will influence the validity of the model. To test the usability of this model, we applied it to two longitudinal studies of social animals (Eastern water dragons (Intellegama lesueurii) and bottlenose dolphins (Tursiops aduncus)) to identify the presence of social avoidances. Using this model allowed us to identify the presence of social avoidances in both species. We hope that the framework presented here inspires interest in addressing this critical gap in our understanding of animal sociality, in turn allowing for a more holistic understanding of social interactions, relationships and structure.

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.

Sexual segregation in Indo-Pacific bottlenose dolphins is driven by female avoidance of males

In many species, males and females segregate from each other because they allocate time differently, forage on different foods, or tolerate predators differently. In Indo-Pacific bottlenose dolphins, male aggression can deter mixed-sex groups. When males and females encounter each other, males often join females while females often leave males. Females likely evade males to avoid aggression.

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.

Senescence impacts reproduction and maternal investment in bottlenose dolphins

Reproductive senescence is evident across many mammalian species. An emerging perspective considers components of reproductive senescence as evolutionarily distinct phenomena: fertility senescence and maternal-effect senescence. While fertility senescence is regarded as the ageing of reproductive physiology, maternal-effect senescence pertains to the declining capacity to provision and rear surviving offspring due to age. Both contribute to reproductive failure in utero making it difficult to differentiate between the two prenatally in the wild. We investigated both components in a long-lived mammal with prolonged maternal care through three parameters: calf survival, interbirth interval (IBI) and lactation period. We provide clear evidence for reproductive senescence in a wild population of bottlenose dolphins (Tursiops aduncus) using 34+ years of longitudinal data on 229 adult females and 562 calves. Calf survival decreased with maternal age, and calves with older mothers had lower survival than predicted by birth order, suggesting maternal-effect senescence. Both lactation period and IBIs increased with maternal age, and IBIs increased regardless of calf mortality, indicating interactions between fertility and maternal-effect senescence. Of calves that survived to weaning, last-born calves weaned later than earlier-born calves, evidence of terminal investment, a mitigating strategy given reduced reproductive value caused by either components of reproductive senescence.