The reproductive success of male dolphins isn’t determined by strength or age, but by their social bonds with other males, according to a new study. Scientists have found that the more integrated male dolphins are within their social network, the more offspring they produce.
But how do they stay so popular? These dolphins maintain key relationships within their large social groups by whistling, according to another study. The vocal exchanges function as a replacement for physical bonding and are much less time demanding, allowing allied male dolphins to ‘bond-at-a-distance’.
Both studies, published in Current Biology, studied Indo-Pacific bottlenose dolphins (Tursiops adunctus) in Shark Bay, Western Australia.
Popular male dolphins produce more offspring
Male dolphins in Shark Bay live in complex social groups, where they form long-lasting bonds to cooperate with other males. Within large, stable alliances they form smaller, less stable groups of two to three to mate with females.
In most species stronger or more experienced males were more likely to sire offspring. The international team of researchers were interested in discovering if dolphins’ complex reproductive social life affected their reproductive success.
They analysed 30 years of behavioural data from 85 male dolphins and used genetic data to analyse the paternity for more than 400 dolphins, finding that the well-integrated “popular” males with strong bonds to multiple group members produced the most offspring.
Their standing within the smaller groups of two to three, as well as their age difference in relation to other members of the alliance, had no impact.
“Well-integrated males might be in a better position to harness the benefits of cooperation and access crucial resources such as food or mates,” explains first author Dr Livia Gerber, former PhD student at the University of Zurich, Switzerland, and current postdoctoral researcher at the University of New South Wales in Australia.
“They may also be more resilient to partner loss compared to those with few, but closer, partners.”
But how do they maintain these social bonds within their alliances, especially in such large groups?
Male dolphins whistle to maintain social relationships
“Many animals, including humans, use tactile contact – touch – to strengthen and reaffirm important relationships,” explains lead author Emma Chereskin, from the University of Bristol’s School of Biological Sciences, UK. “But as the number of close social relationships increases, so too do the demands on the time and space available for relationship maintenance through physical contact.
“Male bottlenose dolphins form strategic, multi-level alliances, and we wanted to know how they maintained multiple alliance relationships in large groups.”
Scientists analysed nine years of acoustic and behavioural data, gathered by following groups of affiliated males.
The research team was able identify the different ways that these males bonded with each other. While physical contact – such as gentle petting – to connect with strongly bonded allies was already documented, they found that the dolphins also maintain weaker, but still vital, social relationships by whistling.
“We found that within the core dolphin alliances, strongly bonded allies engaged in more affiliative contact behaviour, such as petting and rubbing, while weakly bonded allies engaged in more whistle exchanges,” says senior author Dr Stephanie King from the University of Bristol.
“This illustrates that these weaker, but still key, social relationships can be maintained with vocal exchanges.”