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Sunday, October 17, 2021

Study shows link between whale size and diet

The immense variation in cetacean size has arisen as a popular question among scientists in recent years, only to be answered by a group of researchers from the UC system.

Samantha Price, a postdoctoral researcher in the department of evolution and ecology at UC Davis, along with co-author Graham Slater, evolutionary biologist at UCLA, led a group of researchers in studying why whales, dolphins and porpoises are all different sizes, though part of the same family.

Price’s interest in this subject started while in graduate school, she said.

“I have been working on cetacean macroevolution since I was a graduate student at the University of Virginia between 2001 and 2005,” Price said in an e-mail interview. “What really interests me is the contrast between the aquatic and terrestrial biomes and the evolutionary history of the cetaceans and their closest relatives the artiodactyls (even-toed hoofed mammals – cows, sheep, deer, pigs, giraffes etc.), which are land-based.”

Price said how these animals evolved from the same family with a variety of different sizes is interesting, considering their aquatic based environment.

“The evolution of size is particularly interesting within the aquatic environment as the buoyancy of the aquatic environment and the reduced gravitational constraints allow for larger sizes, hence the blue whale which is one of the largest vertebrates (living or extinct),” Price said.

The team took data from previous field studies to generate a list of almost all 84 living species’ body length in the cetacean family.

They then grouped the cetaceans according to their dietary inclination: filter feeders that gulp down large quantities of krill, cephalopod specialists that dive great depths to feed on squid and fish eaters.

“We used the family tree, which we built from DNA sequences and body size measurements,” Slater said. “We found that the tree told us that whales evolved gradually but body size differences indicated early, fast evolution that slowed through time.”

Further results indicated the link between size and food type.

First, filter-feeding mysticetes, such as the blue whale, became extremely large because copious amounts of krill exist and are easily caught. Cetaceans that eat fish, like dolphins, decreased in body size over time for reasons that have yet to be determined.

Daniel Rabosky, an evolutionary biologist at UC Berkeley, said that this study is very important to evolutionists and ecologists.

“It is the most comprehensive look at patterns of species diversification and morphological and ecological trait evolution in whales and reaches some conclusions that are important for understanding what triggered the diversification of modern whales,” he said. “There is a lot of interest in understanding why whales appear to have undergone such exceptional evolutionary diversification – they are charismatic, diverse, and are ecologically quite unlike any other group of mammals.”

DINA MORCOS can be reached at features@theaggie.org.

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