Home range overlap, matrilineal and biparental kinship drive female associations in bottlenose dolphins

Abstract

Few studies of kinship in mammalian societies have been able to consider the complex interactions between home range overlap, association patterns and kinship, which have created a critical gap in our understanding of social evolution. We investigated the association patterns of female bottlenose dolphins, Tursiops aduncus, in the eastern gulf of Shark Bay, Western Australia and found that they depended upon the complex interplay of at least three factors: home range overlap, matrilineal kinship and biparental kinship. While home range overlap was positively correlated with female association patterns, preferred associations were found between females showing as little as 27% home range overlap, and some pairs showed avoidance despite 100% home range overlap. Furthermore, on average, both casual and preferred associations took place between females that were more closely biparentally related than expected by chance and this pattern varied depending upon whether or not pairs of females shared the same matriline.

Social networks reveal cultural behaviour in tool-using dolphins

“…We documented matrilineal relatedness for 28 of 36 spongers (known mother and/or offspring, including some offspring that did not adopt sponging) and for 98 of non-spongers; genetic relatedness was known for only 14 of these spongers 13,15 . As we have documented matrilineal relationships for 27 years, these data represent kinship that dolphins themselves would recognize through association with the mother, although additional kin recognition mechanisms are possible 30 . Centroid distances (km) between each dyad were calculated as a measure of geographic proximity.…”

“…We do not argue that foraging type is the primary determinant of association. Dolphin association is likely to be driven by multiple factors, including a suite of contexts such as behavioural state 42 , foraging type, the history of interactions, reproductive state, and enduring traits such as sex 25,26,31 , kinship 30,43 , age 44 and geography 30 . Homophily on a variety of traits has a critical role in human (sub)cultures 22 and this may be true for dolphin society as well.…”

“…Males cannot afford to compromise their fitness by specializing in foraging tactics that would restrict their ability to form and maintain alliances, or range widely to find females. To date, at least three attributes, matrilineal kinship, sex and geographic proximity, influence dolphin association 25,26,30,31 , but affiliation based on foraging type has never been tested.…”

Kinship and sociability in eastern grey kangaroos

“…Examples involving weak female associations are found in greater horseshoe bats (Rhinolophus ferrumequinum) (Rossiter et al 2002), chimpanzees (Pan troglodytes), spider monkeys (Ateles geoffroyi) (Symington 1990), giraffes (Giraffa camelopardalis) (Carter et al 2013), Grevy's zebra (Equus grevyi), onagers (Equus hemionus khur) (Sundaresan et al 2007) and bottlenose dolphins (Tursiops aduncus) (Frère et al 2010b). Kinship appears to play an important role in those female relationships in greater horseshoe bats and bottlenose dolphins.…”

Personalities, social patterns, and reproductive success in female eastern grey kangaroos (Macropus giganteus)

“…Such associations have been reported in some bat species Kerth et al 2011), Grevy's zebra (Equus grevyi) ), chimpanzees (Langergraber et al 2009), bottlenose dolphins (Tursiops spp.) (Frère et al 2010b), eastern grey kangaroos (Macropus giganteus) ), and giraffe (Giraffa camelopalardis) (Bercovitch and Berry 2013;). The strongest associations within a higher fission-fusion social context often occur between relatives, especially among females where female-biased philopatry occurs.…”