Scientists have long known that when it comes to reproductive success, age, rank, strength and size matter in the animal kingdom. But a team of scientists has just released two new studies that show male friends are pretty important too and it’s easier than you’d think for dolphins to maintain these relationships.
The researchers, including FIU biologist Richard Connor, studied dolphin relationships in Shark Bay, Australia, where males form long-term, multi-level alliances of unrelated males that can last for decades. They form second-order alliances of 4-14 males, who cooperate in pairs (sometimes trios) with each other to consort females. These alliances help males sire more offspring throughout their lives, according to the research.
Connor, who has researched dolphins in Shark Bay for 40 years, is part of the Shark Bay Dolphin Research Project along with Michael Krützen from the University of Zurich, Simon Allen from the University of Bristol and the University of Zurich and Stephanie King from the University of Bristol in the United Kingdom. This team led the two studies which were published this week in Current Biology.
While the promise of more paternities sounds great, maintaining multiple levels of relationships in a dolphin community can be a time and energy-consuming activity, especially when animals traditionally bond by contact. Unlike most other animals, however, the researchers say dolphins have opened lines of communication and engage in vocal exchanges to maintain relationships with those they share weaker bonds. Essentially, they whistle to each other in exchanges that function like greetings.
“It’s the males with weaker bonds that are doing most of the talking,” Connor said. “Dolphins maintain really complex little societies, and we’re seeing that these vocalizations are an important part of that.”
The international research team recorded vocalizations of the Shark Bay dolphins, an effort led by King and her Ph.D. student, Emma Chereskin. The team combined the vocalization data with data on social bond strength and affiliative contact in the group, finding that males with weaker social bonds are actually talking to each other more frequently. This suggests that vocal exchanges function as a convenient way for male dolphins to maintain valuable alliances without the constant need for physical grooming.
This observed behavior in Shark Bay’s dolphins, where communication is used to maintain relationships from a distance, is unique outside of humans. Connor says it likely has to do with dolphin intelligence. After humans, dolphins have the largest brains in proportion to their overall size. He says this could help explain why dolphins are such good communicators.
For the second study, led by University of Zurich Ph.D. student Livia Gerber, the research team analyzed the reproductive careers of 85 dolphins belonging to 10 second-order alliances in Shark Bay, looking at their relationships in both first-order and second-order alliances. They examined social connectivity and social bond strength. What they found was dolphins with stronger bonds in second-order alliances had greater success at fathering more dolphins.
“There’s a lot of variation in how often males consort females. Males that consort females more have strong homogenous bonds, and that means you’re popular — the cool kids,” Connor said.
Essentially, their reproductive fitness is a direct result of the dolphins working together to keep females within a group and warding off attacks by competing alliances, further stressing the importance of those open lines of communication.
In addition to the lead principal investigators from the Shark Bay this research, they were joined by researchers from the University of Massachusetts Dartmouth, University of California (UC) San Diego, UC Santa Barbara, Syracuse University, Woods Hole Oceanographic Institution, University of Western Australia, and University of New South Wales also contributed to these studies.