Dolphin social intelligence: complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals

Abstract

Bottlenose dolphins in Shark Bay, Australia, live in a large, unbounded society with a fission-fusion grouping pattern. Potential cognitive demands include the need to develop social strategies involving the recognition of a large number of individuals and their relationships with others. Patterns of alliance affiliation among males may be more complex than are currently known for any non-human, with individuals participating in 2-3 levels of shifting alliances. Males mediate alliance relationships with gentle contact behaviours such as petting, but synchrony also plays an important role in affiliative interactions. In general, selection for social intelligence in the context of shifting alliances will depend on the extent to which there are strategic options and risk. Extreme brain size evolution may have occurred more than once in the toothed whales, reaching peaks in the dolphin family and the sperm whale. All three 'peaks' of large brain size evolution in mammals (odontocetes, humans and elephants) shared a common selective environment: extreme mutual dependence based on external threats from predators or conspecific groups. In this context, social competition, and consequently selection for greater cognitive abilities and large brain size, was intense.

Increased juvenile predation is not associated with evolved differences in adult brain size in Trinidadian killifish (Rivulus hartii)

“…Research has shown that ecological variables, such as social environment (Connor, 2007; Kotrschal, Rogell, Maklakov, & Kolm, 2012a; Shultz & Dunbar, 2006b), diet (Allen & Kay, 2012; Shultz & Dunbar, 2006a), habitat (Crispo & Chapman, 2010; Gonda et al., 2009b; Kotrschal, Sundstrom, Brelin, Devlin, & Kolm, 2012b), and predators (Gonda et al., 2009a,b, 2011; Walsh et al., 2016), play an important role in brain size plasticity and brain size evolution (see also Gonda, Herczeg, & Merila, 2013). These latter studies exploring the connection between predators and selection on brain size have largely compared populations where adults are susceptible to predators (Gonda et al., 2009a,b, 2011; Walsh et al., 2016).…”

Triadic awareness predicts partner choice in male–infant–male interactions in Barbary macaques

“…The capacity to recognize who outranks whom, who is closely bonded with whom, who is likely to support whom or intervene against whom, and to adjust one's behaviour accordingly has been documented in apes (e.g. Tomasello and Call 1997;De Waal 2007), Old World (Cheney et al 1986;Cheney and Seyfarth 1999), New World monkeys (Perry et al 2004; but see also Ferreira et al 2006), other mammals (Engh et al 2005;Connor 2007;Johnson 2010) and in birds (Peake et al 2002;Seed et al 2007). …”

Cognitive adaptations of social bonding in birds

“…We now know that these biological preconditions are not exclusive to primates and have been demonstrated in many social mammals, such as elephants (McComb 2001), hyenas (Holekamp et al 2007) and cetaceans (Connor 2007). What about birds?…”

“…Although there appears to be a clear relationship between social group size and brain (i.e. neocortex) size within primates (Dunbar 1992), carnivores, insectivores (Dunbar & Bever 1998), bats (Barton & Dunbar 1997) and cetaceans (Marino 2002;Connor 2007), no such relationship exists within another mammalian order, ungulates (Shultz & Dunbar 2006). Although the brain size analyses presented later in the paper were performed at the class rather than family level, it should be kept in mind that such analyses have yet to be performed in mammals.…”

“…However, from its inception, the SIH was discussed primarily with respect to the evolution of primate intelligence, and not other animals. It rapidly became clear that other social animals, such as dolphins, hyenas and elephants, also demonstrated many of the biological, ecological and behavioural preconditions for intelligence; sophisticated cognitive skills in the lab and field; and many of the complex social skills found in monkeys and apes (McComb 2001;de Waal & Tyack 2003;Connor 2007;Holekamp et al 2007).…”