A long post-reproductive lifespan is a shared trait among genetically distinct killer whale populations

This is the final version. Available on open access from Wiley via the DOI in this recordData availability: Data to replicate the analyses are available from the online repository: https://doi.org/10.5061/dryad.6t1g1jwxx. Requests for access to raw data can be directed to the authors, the Center for Whale Research (www.whaleresearch.com) or Fisheries and Oceans Canada (www.dfo-mpo.gc.ca)The extended female post-reproductive lifespan found in humans and some toothed whales remains an evolutionary puzzle. Theory predicts demographic patterns resulting in increased female relatedness with age (kinship dynamics) can select for a prolonged post reproductive lifespan due to the combined costs of inter-generational reproductive conflict and benefits of late-life helping. Here we test this prediction using >40 years of longitudinal demographic data from the sympatric yet genetically distinct killer whale ecotypes: resident and Bigg’s killer whales. The female relatedness with age is predicted to increase in both ecotypes, but with a less steep increase in Bigg’s due to their different social structure. Here, we show that there is a significant post-reproductive lifespan in both ecotypes with >30% of adult female years being lived as post-reproductive, supporting the general prediction that an increase in local relatedness with age predisposes the evolution of a post reproductive lifespan. Differences in the magnitude of kinship dynamics however, did not influence the timing or duration of the post-reproductive lifespan with females in both ecotypes terminating reproduction before their mid-40s followed by an expected post reproductive period of ~20 years. Our results highlight the important role of kinship dynamics in the evolution of a long post-reproductive lifespan in long-lived mammals, while further implying that the timing of menopause may be a robust trait that is persistent despite substantial variation in demographic patterns among populations.Nuffield FoundationNatural Environment Research Council (NERC)Leverhulme TrustEarthwatch InstituteNOAA FisheriesFisheries and Oceans Canada Species At Risk Progra

Age and sex influence social interactions, but not associations, within a killer whale pod

This is the author accepted manuscript. The final version is available from the Royal Society via the DOI in this record.Data accessibility: The processed contact, surfacing, and association networks, measures of dyadic sampling effort, estimated maternal kinship, individual attributes, and functions to conduct GLMQAP and general double-semi-partialling are included in the “aninet” R package on GitHub (https://github.com/MNWeiss/aninet). The raw time-series of detections and interactions, and R code necessary to reproduce all analyses, are available in the online supplementary material.Social structure is a fundamental aspect of animal populations. In order to understand the function and evolution of animal societies, it is important to quantify how individual attributes, such as age and sex, shape social relationships. Detecting these influences in wild populations under natural conditions can be challenging, especially when social interactions are difficult to observe and broad-scale measures of association are used as a proxy. In this study, we use unoccupied aerial systems to observe association, synchronous surfacing, and physical contact within a pod of southern resident killer whales (Orcinus orca). We show that interactions do not occur randomly between associated individuals, and that interaction types are not interchangeable. While age and sex did not detectably influence association network structure, both interaction networks showed significant social homophily by age and sex, and centrality within the contact network was higher among females and young individuals. These results suggest killer whales exhibit interesting parallels in social bond formation and social life histories with primates and other terrestrial social mammals, and demonstrate how important patterns can be missed when using associations as a proxy for interactions in animal social network studies.Natural Environment Research Council (NERC)National Fish and Wildlife FoundationPaul G Allen Family FoundationUW Center for Conservation BiologyCenter for Whale Researc

Multi-site mark-racapture for cetaceans: population estimates with Bayesian model averaging

Mark-recapture techniques are widely used to estimate the size of wildlife populations. However, in cetacean photo-identification studies, it is often impractical to sample across the entire range of the population. Consequently, negatively biased population estimates can result when large portions of a population are unavailable for photographic capture. To overcome this problem, we propose that individuals be sampled from a number of discrete sites located throughout the population's range. The recapture of individuals between sites can then be presented in a simple contingency table, where the cells refer to discrete categories formed by combinations of the study sites. We present a Bayesian framework for fitting a suite of log-linear models to these data, with each model representing a different hypothesis about dependence between sites. Modeling dependence facilitates the analysis of opportunistic photo-identification data from study sites located due to convenience rather than by design. Because inference about population size is sensitive to model choice, we use Bayesian Markov chain Monte Carlo approaches to estimate posterior model probabilities, and base inference on a model-averaged estimate of population size. We demonstrate this method in the analysis of photographic mark-recapture data for bottlenose dolphins from three coastal sites around NE Scotland.</p

Costly lifetime maternal investment in killer whales

This is the author accepted manuscript.Data and code availability All data and code necessary to replicate analyses in this study have been deposited on Zenodo (DOI: 10.5281/zenodo.7457806).Parents often sacrifice their own future reproductive success to boost the survival of their offspring, a phenomenon referred to as parental investment. In several social mammals, mothers continue to improve the survival of their offspring well into adulthood, however whether this extended care comes at a reproductive costs to mothers, and therefore represents maternal investment, is not well understood. We tested whether lifetime maternal care is a form of parental investment in fish-eating “resident” killer whales. Adult killer whales, particularly males, are known to receive survival benefits from their mothers, however whether this comes at a cost to mothers’ reproductive success is not known. Using multiple decades of complete census data from the “southern resident” population, we found a strong negative correlation between females’ number of surviving weaned sons and their annual probability of producing a viable calf. This negative effect did not attenuate as sons grew older, and the cost of sons could not be explained by long-term costs of lactation or group composition effects, supporting the hypothesis that caring for adult sons is reproductively costly. This is the first direct evidence of lifetime maternal investment in an iteroparous animal, revealing a previously unknown life history strategy.Natural Environment Research Council (NERC)Leverhulme Trus