A new subspecies of dolphin is evolving in the Pacific Ocean : ScienceAlert
The common bottlenose dolphin is one of the best studied marine mammals in the world. However, in recent decades, genetic research has revealed that scientists are not looking at a single species after all, but several lineages that are still in the process of evolving.
Researchers at the University of Miami have divided what was historically thought to be a species of dolphin (truncated tursiops) in the Pacific Ocean in a few different subtypes.
In the high seas waters of the Eastern Tropical Pacific (ETP), between Baja California and the Galapagos, bottlenose dolphins show clearly smaller skulls and bodies than those off the coast of southern California or Japan.
The scientists argue that these findings are strong enough evidence that ETP dolphins should be considered a separate subspecies.
“Different environmental conditions in the ETP may be driving the evolutionary differentiation of these bottlenose dolphins,” the authors say. to write.
“Given these results, we here recommend recognition of ETP offshore bottlenose dolphins as a distinct subspecies, Tursiops truncatum nuuanu.“
Bottlenose dolphins are found in ocean waters all over the world, and yet the way these mammals have adapted to certain coastal habitats has resulted in an incredible number of physiological Y genetic diversity overtime.
The lineage of the common bottlenose dolphins that live further offshore, for example, seems to have evolved later than their relatives closer to the coast.
Although scientists suspect that there are many subspecies that are overlooked, Very few have been identified to date.
In fact, the Black Sea bottlenose dolphin (T. pontic) and Lahille’s bottlenose dolphin (T. gephyreus), found off the coast of Brazil, are the only two that have been officially separated.
In the eastern Pacific, bottlenose dolphins occupy a particularly varied aquatic landscape, and these different habitats may have led dolphin populations to evolve in separate directions, branching off each other physically and genetically.
a 2020 to study on the genetics of bottlenose dolphins in the estuaries of Ecuador, for example, strongly suggests that there are other neglected dolphin lineages that should be classified separately.
When researchers at the University of Miami analyzed 135 bottlenose dolphin skulls, collected from across the Pacific, they also noticed a branch in the dolphin family tree near Ecuador. But this one was further from the coast.
Today, it is generally accepted that bottlenose dolphins in the northern temperate Pacific and bottlenose dolphins off the southern California coast each represent a unique ecotype, which is a distinct grouping formed by their local ecosystem. However, claims that these changes represent distinct subspecies remain controversial.
Dolphins swimming further south, on the ETP, have been comparatively overlooked. Because this population frequents deeper waters, further off the coast of South America, they have not been studied as much and their degree of differentiation is largely unknown.
Based on the current analysis of the skull, the researchers argue that ETP dolphins are, in fact, unique.
They are some of the smallest bottlenose dolphins ever identified, along with another possible species called the Tamanend bottlenose dolphin (T.erebennus), found in the western North Atlantic.
The small size of the skull and body was probably due to what mammals prefer to eat and how warm their habitat is.
ETP bottlenose dolphins, for example, feed primarily on squid and small fish, and although they live offshore and hunt in deeper water, the ocean in which they swim is still warmer than along the coast of California, where the cold currents flow.
A small body size suits this environment very well, as it allows heat to be given off more efficiently.
Interestingly, the researchers in Miami also noted some subtle morphological differences in the bottlenose dolphins that live off the California coast. Those who swam closer to shore in the Gulf of California had a slightly different appearance than those who lived farther from shore.
The contrast was not as stark as that of the ETP dolphins, but the authors say these two populations in California may be in the early stages of separating.
More genetic studies are needed to confirm these results, but in all likelihood, common bottlenose dolphins have less in common than scientists once thought.
“Bottlenose dolphin sightings also continue south of the ETP, into the eastern South Pacific (ESP), where more coastal and offshore ecotypes have been recognized,” the authors said. to write.
Perhaps we will find more subspecies further south.
The study was published in the Mammalian Evolution Magazine.