Pelvic Bones in Whales Are an Example of Structures
Both whales and dolphins accept pelvic (hip) bones, evolutionary remnants from when their ancestors walked on land more than forty meg years ago. Common wisdom has long held that those basic are simply vestigial, slowly withering away like tailbones on humans.
New research from USC and the Natural History Museum of Los Angeles County (NHM) flies straight in the face of that assumption, finding that not only do those pelvic basic serve a purpose, only their size and peradventure shape are influenced by the forces of sexual selection.
“Everyone’s always assumed that if you gave whales and dolphins a few more than million years of evolution, the pelvic bones would disappear. Just information technology appears that’s not the example,” said Matthew Dean, assistant professor at the USC Dornsife Higher of Messages, Arts and Sciences, and co-corresponding author of a paper on the research that was published online past
on Sept. 3.
Dean collaborated with fellow co-corresponding author Jim Dines, collections manager of mammalogy at NHM and a old graduate student in Dean’south lab, on a painstaking iv-year project to analyze cetacean (whale and dolphin) pelvic basic.
The muscles that control a cetacean’s penis — which has a high degree of mobility — attach direct to its pelvic bones. As such, it made sense to Dean and Dines that the pelvic bones could affect the level of control over the penis that an private cetacean has, perhaps offering an evolutionary advantage.
To examination this hypothesis, the researchers examined hundreds of pelvic bones — first at the NHM, which has the second-largest collection of marine mammal specimens in N America then at the Smithsonian Institution, which has the largest.
“Cetacean skeletons are stored every bit boxes of bones on warehouse shelves, with each box containing an individual specimen. You have to comb through each box looking for the specific bone you need. The pelvic bones are insufficiently minor and aren’t e’er collected with the residuum of the skeleton, but subsequently the beginning couple hundred boxes, nosotros got very expert at finding them when they were present,” said Dines, who graduated from USC Dornsife’s Integrative and Evolutionary Biology programme while maintaining his part at NHM.
Using a 3-D laser scanner, Dean and Dines created digital models of the curved basic, offering an unprecedented level of detail virtually their shape and size, besides every bit giving them the option to computationally dispense them — say, to compare ii different bones.
Next, they gathered reams of information going as far back as the days of whalers about testis size relative to trunk mass in whales. Throughout nature, more than “promiscuous” creature species — that is, those with females who mate with several males, creating a more competitive mating environment — develop larger testes relative to their torso mass equally a style of outperforming the competition.
Finally, they compared the size of the pelvic bones (relative to torso size) to the size of the animate being’s testis (again, relative to body size). The results were articulate: The bigger the relative testis, the bigger the relative pelvic bone — meaning that more competitive mating environments seem to drive the evolution of larger pelvic basic. Males from more promiscuous species also evolve larger penises, so larger pelvic basic announced necessary to attach larger muscles for penis control.
As a negative control, Dean and Dines too compared testis size to the size of one of the animate being’s ribs. If pelvic bone size were simply a reflection of overall skeletal size, there should be a corresponding correlation in the ribs — merely there was not, strengthening the interpretation that whale pelvic bones are specifically targeted by selection related to mating system.
“Our inquiry really changes the way we recall almost the evolution of whale pelvic bones in particular, but more generally most structures nosotros call ‘vestigial.’ Equally a parallel, we are now learning that our appendix is actually quite important in several immune processes, non a functionally useless structure,” Dean said.
Over the form of their four-year project, the team created a new way of measuring and quantifying the complicated iii-D structures of bones, using laser scanners to generate 3-D images of the bones and developing novel computational methods to analyze bones that lack obvious landmarks.
The process has pregnant potential for the recording and study of basic past museums, Dines said.
Revolutionary engineering science
When doing their information drove, the team had to asking loans from the Smithsonian and several other museums, which would ship out the basic themselves for study. However, if all specimens were recorded using Dean and Dines’ arrangement, digital copies could exist sent anywhere in the earth for free — without risking the loss or harm of the original specimen. The data that Dean and Dines collected are detailed plenty to generate 3-D printed versions of the bones, if desired.
“Cutting-border imaging technologies similar 3-D laser scanning are revolutionizing how museum collections are used. Not only do they give us a new way of analyzing bones and other specimens, they as well permit us to make precise replicas of those specimens. The replicas tin can then, for example, be sent to colleagues abroad or placed on exhibit while the original specimen stays in the museum researcher’s lab for further report,” Dines said.
Their collaborators included Peter Ralph and Andrew Smith of USC Dornsife; Due east. Otarola-Castillo of Harvard University and Iowa Land University; and Jesse Alas of West Adams Preparatory Loftier School.
High school students are rarely listed as co-authors on peer-reviewed scientific periodical articles, but Alas more than earned his place on the list, Dean said.
Currently a educatee at the University of California, Irvine, Alas crossed Dean’southward path by chance when, on a bout of USC with other local loftier schoolers, he spotted a fleck of Python programming language that Dean had written on a white lath for his undergraduate students. Dean said, “when I asked where he learned it, information technology turned out he was self-taught.”
Dean hired Alas to navigate much of the complicated computation that encoded 3-D data of the pelvic os structure.
The research was funded by USC startup funds, the National Institutes of Health (grant number 1R01GM098536) and the William Cheney Jr. Memorial Fund for Mammalogy.
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Pelvic Bones in Whales Are an Example of Structures