Only 10 vaquita porpoises survive, but species may not be doomed,
scientists say
If they can escape death in poachers' nets, the endangered marine mammal
is well poised to rebound despite inbreeding

Date:
May 5, 2022
Source:
University of California - Los Angeles
Summary:
The world's smallest marine mammal -- the critically endangered
vaquita porpoise, which lives only in Mexico's Sea of Cortez --
is believed to have only 10 living members, if that, of the
species. The vaquita is widely thought to be on the verge of
extinction, but a new scientific analysis by a team of biologists
concludes the species remains relatively healthy and can survive --
if the illegal use of 'gillnet' fishing ceases promptly.



FULL STORY ==========================================================================
The vaquita porpoise, the world's smallest marine mammal, is on the
brink of extinction, with 10 or fewer still living in Mexico's Gulf
of California, their sole habitat. But a genetic analysis by a team of
UCLA biologists and colleagues has found that the critically endangered
species remains relatively healthy and can potentially survive -- if
illegal "gillnet" fishing ceases promptly.


========================================================================== "Interestingly, we found the vaquita is not doomed by genetic factors,
like harmful mutations, that tend to affect many other species whose
gene pool has diminished to a similar point," said Christopher Kyriazis,
a UCLA doctoral student in ecology and evolutionary biology and a co-lead author of the research. "Outlawed fishing remains their biggest threat."
The small porpoises, which range from 4 to 5 feet in length, often become entangled and die in the large mesh gillnets used by poachers hunting
the totoaba, an endangered fish highly valued in some countries for
its perceived medicinal properties. While Mexico has outlawed totoaba
fishing and made the use of these nets in the vaquitas' habitat illegal,
many say the bans are not always enforced.

The researchers analyzed the genomes of 20 vaquitas that lived between
1985 and 2017 and conducted computational simulations to predict the
species' extinction risk over the next 50 years. They concluded that
if gillnet fishing ends immediately, the vaquita has a very high chance
of recovery, even with inbreeding. If, however, the practice continues,
even moderately, the prospects of recovery are less optimistic.

The research is published May 6 in the journal Science.

"Relative to other species, the vaquita has a higher chance of
rebounding from an extreme population crash without suffering severe
genetic consequences from inbreeding," said co-lead author Jacqueline
Robinson, a postdoctoral scholar at UC San Francisco who earned her
doctorate in biology at UCLA. "Genetic diversity in vaquitas is not so
low that it constitutes a threat to their health and persistence. It
simply reflects their natural rarity." Genetic diversity is a measure
of the differences that exist across the genome among individuals in
a population. Large populations tend to have many differences, while
naturally smaller or decimated ones have fewer, resulting in individuals
that are more genetically similar. That similarity can often result in
a greater incidence of harmful mutations that endanger the population
since individuals are more likely to inherit the same muted gene from
both parents, said senior author Kirk Lohmueller, UCLA associate professor
of ecology and evolutionary biology and of human genetics.



==========================================================================
"A prevailing view in conservation biology and population genetics is that small populations can accumulate deleterious mutations," Lohmueller said.

"However, our finding that the vaquita likely has fewer strongly
deleterious mutations hiding in the population means that they are
better poised to survive future inbreeding, which bodes well for their
overall recovery." So what protects the vaquitas from the genetic perils
of inbreeding? Much of it has to do with the fact that they have always
been a small population in a very small habitat in the northern tip of
the gulf, the researchers said. While their historic numbers are unknown,
the first comprehensive survey in 1997 counted roughly 570 porpoises --
a number that has declined steadily over the last 25 years but which
was not large to begin with.

"They're essentially the marine equivalent of an island species," said Robinson, who noted that the species has survived for tens of thousands of years with low genetic diversity. "The vaquitas' naturally low abundance
has allowed them to gradually purge highly deleterious recessive gene
variants that might negatively affect their health under inbreeding."
In fact, Robinson said, of the 12 marine mammal species -- including
vaquitas - - the researchers genetically analyzed, vaquitas had the
lowest number of potentially harmful mutations.

While the interplay among small population size, inbreeding and harmful
genetic variations is complex, the approach used by the team in this
study can help shed light on these dynamics.



========================================================================== "With genomic datasets, we now have the ability to address this
complexity," Robinson said. "Species can vary in their levels of harmful genetic variation, and they will not all be affected exactly the same way
by reduced population size or inbreeding. There are now many examples
of species recovering from extreme declines." "We hope our analysis
is useful not only in demonstrating the potential for the vaquita to
recover," Kyriazis said, "but also in highlighting a novel genomics-
based simulation approach for endangered species." Encouragingly,
the surviving vaquitas in the northern Gulf of California are actively reproducing and appear healthy. But poachers' gillnets continue to pose
an existential threat to the species, and unless further measures are
taken to protect the porpoises, there is a distinct possibility they may
go extinct. The loss would be a great tragedy, said the study's senior
author, UCLA's Robert Wayne.

"The vaquita is symbolic of the unique diversity found in the Gulf
of California, which was described by John Steinbeck in his wonderful
1951 book 'The Log From the Sea of Cortez,'" said Wayne, a distinguished professor of ecology and evolutionary biology and a Howard Hughes Medical institute professor. "It represents a unique evolutionary lineage -- there
is no similar species anywhere in the world -- and its loss would rob the ecosystem of an important predator adapted to this unique ecosystem."
Funding sources for the research included the National Institutes of
Health, the National Oceanic and Atmospheric Administration (NOAA)
and the Mexican National Council for Science and Technology.

Co-authors included Phillip Morin of the NOAA's Southwest Fisheries
Science Center; vaquita researchers Barbara Taylor of the NOAA and
Lorenzo Rojas- Bracho; Sergio Nigenda Morales of the Advanced Genomics
Unit in Irapuato, Guanajuato, part of Mexico's National Laboratory of
Genomics for Biodiversity; and Annabel Beichman of the University of Washington. Morales and Beichman earned their doctorates at UCLA studying
under Wayne and Lohmueller.


========================================================================== Story Source: Materials provided by
University_of_California_-_Los_Angeles. Original written by Stuart
Wolpert. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jacqueline A. Robinson, Christopher C. Kyriazis, Sergio F. Nigenda-
Morales, Annabel C. Beichman, Lorenzo Rojas-Bracho, Kelly
M. Robertson, Michael C. Fontaine, Robert K. Wayne, Kirk
E. Lohmueller, Barbara L.

Taylor, Phillip A. Morin. The critically endangered vaquita is not
doomed to extinction by inbreeding depression. Science, 2022; 376
(6593): 635 DOI: 10.1126/science.abm1742 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/05/220505143218.htm

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