G’day Marmamers,

We are most pleased to bring to your attention two papers on dolphin social complexity in the forthcoming issue of Current Biology, both stemming from our long-term research programme in Shark Bay, Western Australia (www.sharkbaydolphins.org).

In the first paper, led by University of Bristol MSc graduate Emma Chereskin, we show that vocal exchanges can function as a replacement of physical bonding in dolphin alliances. This is the first evidence for Robin Dunbar’s social bonding hypothesis and, interestingly, comes from outside of the primate lineage.

Paper 1: Chereskin E, Connor RC, Friedman WR, Jensen FH, Allen SJ, Sørensen PM, Krützen M, King SL (2022). Allied male dolphins use vocal exchanges to ‘bond-at-a-distance’. Current Biology https://doi.org/10.1016/j.cub.2022.02.019

Summary: Vocal interactions are intrinsic features of social groups and can play a pivotal role in social bonding. Dunbar’s social bonding hypothesis posits that vocal exchanges evolved to “groom at a distance” when social groups became too large or complex for individuals to devote time to physical bonding activities. Tests of this hypothesis in non-human primates, however, suggest that vocal exchanges occur between more strongly bonded individuals that engage in higher grooming rates and thus do not provide evidence for replacement of physical bonding. Here, we combine data on social bond strength, whistle exchange frequency, and affiliative contact behavior rates to test this hypothesis in wild male Indo-Pacific bottlenose dolphins, who form multi-level alliances that cooperate over access to females. We show that, although whistle exchanges are more likely to occur within the core alliance, they occur more frequently between those males that share weaker social bonds, i.e., between core allies that spend less time together, while the opposite occurs for affiliative physical contact behavior. This suggests that vocal exchanges function as a low-cost mechanism for male dolphins that spend less time in close proximity and engage in fewer affiliative contact behaviors to reinforce and maintain their valuable alliance relationships. Our findings provide new evidence outside of the primate lineage that vocal exchanges serve a bonding function and reveal that, as the social bonding hypothesis originally suggested, vocal exchanges can function as a replacement of physical bonding activities for individuals to maintain their important social relationships.

In the second paper, led by University of Zürich PhD graduate Livia Gerber, we show that ‘popular’ allied male dolphins (those that are well-integrated and have homogenous social bonds with their allies) enjoy higher reproductive success.

Paper 2: Gerber L, Connor RC, Allen SJ, Horlacher K, King SL, Sherwin WB, Willems E, Wittwer S, Krützen M (2022). Social integration influences fitness in allied male dolphins. Current Biology. https://doi.org/10.1016/j.cub.2022.03.027

Summary: Understanding determinants of differential reproductive success is at the core of evolutionary biology because of its connection to fitness. Early work has linked variation in reproductive success to differences in age, rank, or size, as well as habitat characteristics. More recently, studies in group-living taxa have revealed that social relationships also have measurable effects on fitness. The influence of social bonds on fitness is particularly interesting in males who compete over reproductive opportunities. In Shark Bay, Western Australia, groups of 4-14 unrelated male bottlenose dolphins cooperate in second-order alliances to compete with rival alliances over access to females. Nested within second-order alliances, pairs or trios of males, which can vary in composition, form first-order alliances to herd estrus females. Using 30 years of behavioral data, we examined how individual social factors, such as first-order alliance stability, social connectivity, and variation in social bond strength within second-order alliances, affect male fitness. Analyzing the reproductive careers of 85 males belonging to 10 second-order alliances, we found that the number of paternities a male achieved was positively correlated with his cumulative social bond strength but negatively correlated with his variation in bond strength. Thus, well-integrated males with more homogeneous social bonds to second-order allies obtained most paternities. Our findings provide novel insights into the fitness benefits of polyadic cooperation among unrelated males and highlight the adaptive value of social bonds in this context.

If you’d like a PDF or have any queries, please don’t hesitate to reach out to the primary authors (emma.chereskin@bristol.ac.uk and livia.gerber@uzh.ch).

All the best,

Simon

~~~~~~~~~~~~~

Dr Simon J Allen

Senior Lecturer

School of Biological Sciences

University of Bristol

Mob: +44 (0) 77047 53101 [UK] / +61 (0) 416 083 653 [AU]

Email: Simon.Allen@bristol.ac.uk / Simon.Allen@uwa.edu.au

Web: http://www.sharkbaydolphins.org

Twitter: @SimonJAllen1

Recent papers: Estimating sustainable limits to human-caused wildlife mortality https://conbio.onlinelibrary.wiley.com/doi/abs/10.1111/cobi.13897

Cooperation-based concept formation in bottlenose dolphins https://www.nature.com/articles/s41467-021-22668-1

Non-vertical transmission of a dolphin foraging innovation https://www.cell.com/current-biology/fulltext/S0960-9822(20)30756-9

Declines in dolphin survival and reproduction following a heatwave https://www.cell.com/action/showPdf?pii=S0960-9822%2819%2930217-9

“Believe me, my young friend, there is nothing–absolutely nothing–half so much worth doing as simply messing about in boats.” (Kenneth Grahame)

“I must say here, in passing, that those captains who have scientists… aboard their ships, must take with them a good supply of patience. I admit that although I have no lack of it, the scientists have frequently driven me to the end of my tether...” (Nicolas Baudin)