Male alliance behaviour and mating access varies with habitat in a dolphin social network

Abstract

Within-species variation in social structure has attracted interest recently because of the potential to explore phenotypic plasticity and, specifically, how demographic and ecological variation influence social structure. Populations of bottlenose dolphins (Tursiops spp.) vary in male alliance formation, from no alliances to simple pairs to, in Shark Bay, Western Australia, the most complex nested alliances known outside of humans. Examination of ecological contributions to this variation is complicated by differences among populations in other potentially explanatory traits, such as phylogenetic distance, as well as female reproductive schedules, sexual size dimorphism, and body size. Here, we report our discovery of systematic spatial variation in alliance structure, seasonal movements and access to mates within a single continuous social network in the Shark Bay population. Participation in male trios (versus pairs), the sizes of seasonal range shifts and consortship rates all decrease from north to south along the 50 km length of the study area. The southern habitat, characterised by shallow banks and channels, may be marginal relative to the open northern habitat. The discovery of variation in alliance behaviour along a spatial axis within a single population is unprecedented and demonstrates that alliance complexity has an ecological component.

Multi-modal sexual displays in Australian humpback dolphins

“…populations 13 – 15 . One such population, Indo-Pacific bottlenose dolphins ( T. aduncus ) in Shark Bay, Western Australia, exhibits the most complex alliance structure known outside of humans, in which ‘alliances of alliances’ within an open fission-fusion network may remain stable over decades 16 – 18 .…”

Season-specific carryover of early life associations in a monogamous bird species

“…Social relationships in males often take the form of coalitions or alliances (Connor et al, 2017;Gilby et al, 2013;Schulke et al, 2010), benefiting individuals by providing cooperation partners in agonistic interactions with conspecifics. But reduced aggression, for instance, via dear-enemy effects (Temeles, 1994), can likewise be an important benefit of maintaining long-term social relationships, especially in territorial animals (Chuang et al, 2017;Jaeger, 1981;Siracusa et al, 2019).…”

“…In a monogamous prey species such as barnacle geese, in which the male spends much of its time during the breeding season on vigilance at the expense of foraging (Forslund, 1993), such benefits can be especially substantial. The expected benefits of maintaining long-term social relationships vary with ecological and social conditions (Connor et al, 2017;Kappeler et al, 2013;Maher & Burger, 2011), and studying the social structure of both sexes in taxa with distinct space use (e.g., natal philopatry), life history (e.g., long life-span), social organization (e.g., fission-fusion), and mating system (e.g., monogamy) characteristics, offers us greater insight into the drivers and constraints of maintaining long-term stable associations in animal societies.…”

Season-specific carry-over of early-life associations in a monogamous bird species

“…Social bonds in males often take the form of coalitions or alliances (Schulke, Bhagavatula, Vigilant & Ostner 2010; Gilby et al . 2013; Connor et al . 2017), benefiting individuals by providing cooperation partners in agonistic interactions with conspecifics.…”

“…Lastly, familiarity-based associations have been linked to faster predator-evasion responses and increased foraging success (Griffiths, Brockmark, Höjesjö & Johnsson 2004; Carter, Macdonald, Thomson & Goldizen 2009). The expected benefits of maintaining long-term social bonds vary with ecological and social conditions (Maher & Burger 2011; Kappeler, Barrett, Blumstein & Clutton-Brock 2013; Connor et al . 2017), and studying the social structure of both sexes in taxa with distinct space use (e.g., natal philopatry), life history (e.g., long life-span), social organization (e.g., fission-fusion), and mating system (e.g., monogamy) characteristics, offers us greater insight into the drivers and constraints of maintaining long-term stable bonds in animal societies.…”