The secrets of dolphins DNA

Unravelling the secrets of dolphin DNA

DNA inherited along maternal lineages holds the secret to the relationship between New Zealand’s bottlenose dolphin populations and could help conservation efforts, according to researchers at The University of Auckland.

Gabriela de Tezanos Pinto, a PhD student based at the Faculty of Science’s School of Biological Sciences, is studying the population structure and relationship between New Zealand bottlenose dolphins.

In the third year of her research, Gabriela is analysing the DNA dolphins inherit from their mothers (mitochondrial DNA) to see if there are connections between different populations in New Zealand and around the Pacific Ocean.

“I’ve found that we have three small and isolated populations in the coastal waters of New Zealand which includes Northland, Marlborough Sound and Fiordland.”

Bottlenose dolphins are highly mobile and some individuals are capable of long-range dispersal for over a thousand kilometres. But long-range movement doesn’t seem to be the common rule for New Zealand coastal bottlenose dolphins.

“For example, the Doubtful Sound population was thought to be completely isolated with no apparent movement of individuals but genetic evidence indicates some interchange with oceanic (those that live in the open sea) populations,” Gabriela says.

Gabriela says the conservation value of her work is the highlight.

“Compared with other dolphin populations in New Zealand, such as the dusky and Hector’s dolphins, bottlenoses are less abundant, are more isolated and have lower rates of reproduction.”
This is of concern, she says, because the ability of a population to adapt and evolve to environmental changes is determined by genetic variation, and the more variability in a gene pool the easier it is to adapt, evolve and survive.

“Before my research, we didn’t know whether bottlenose dolphins represented one single robust population with individuals moving form one place to the other or whether they were three isolated and vulnerable populations. This is an important question for the long-term management of the species in New Zealand.

“The number of dolphins that are actively reproducing in Doubtful Sound is expected to be only about 20, less than the number of reproducing kakapos. This is a concern for the future of this population.”

Gabriela says the kapako and Hector’s dolphin have received a lot of attention and funding for conservation efforts as they are New Zealand native species, whereas bottlenose dolphins can be found elsewhere in the world.

However, she says what is being overlooked is that New Zealand’s bottlenose dolphins have certain special characteristics which make them different from other populations in the world, and they need to be protected.

“The three populations in New Zealand are ecologically different from each other, and how the dolphins have adapted to such different conditions is intriguing. For example, the Doubtful Sound dolphins live in a complex and unique environment composed of at least three metres of fresh water on top of the salt water. That is unusual for dolphins as they are used to saltwater environments and this adaptation to a semi-freshwater environment is especial.”

Originally from Argentina, Gabriela now lives in Auckland and spends time collecting samples in the Bay of Islands and Hauraki Gulf and analysing them at the University’s Molecular Ecology Laboratory.

She has found that the Northland dolphins have the highest genetic variability in New Zealand, and also when compared with other coastal bottlenose dolphin populations around the world.

The preliminary analysis of genetic data in New Zealand shows that movements of individuals among populations is very low, perhaps less than one female per generation. So, if the variability of the Northland population is not a result of movements of individuals from other populations, you have to wonder where it comes from,” says Gabriela.

To answer this question, she requested scientists from around the world for samples of bottlenose dolphins and also reconstructed mitochondrial DNA sequences from published surveys.

Her findings so far suggest that there may be oceanic populations of bottlenose dolphins that occasionally interbred with the coastal ones, mixing their gene pool and representing a source of genetic variation; also reflecting the long-term contact between the New Zealand bottlenose dolphins and other populations throughout the Pacific Ocean.