Study finds little genetic basis for some sea stars staying healthy amid deadly wasting syndrome

Date:
February 1, 2022
Source:
Oregon State University
Summary:
Healthy-looking ochre sea stars have minimal genetic difference
from those displaying symptoms of sea star wasting syndrome,
say researchers who examined whether genetic variation was the
reason some animals went unaffected during an epidemic of the
deadly disease.



FULL STORY ========================================================================== Healthy-looking ochre sea stars have minimal genetic difference from
those displaying symptoms of sea star wasting syndrome, say Oregon
State University researchers who examined whether genetic variation
was the reason some animals went unaffected during an epidemic of the
deadly disease.


========================================================================== Without genes promoting resistance to wasting syndrome, the iconic
Pacific Ocean sea star's ability to persist through future outbreaks is
in greater doubt, the scientists say.

Findings were published in Molecular Ecology.

Also called the purple ochre and known scientifically as Pisaster
ochraceus, the ochre sea star saw its populations hit hard for three
years starting in 2013 by a wasting syndrome epidemic that scientists
believe to be the largest marine wildlife disease event in history.

Wasting syndrome affected populations of 20 species of sea stars ranging
from Baja California to the Gulf of Alaska, including P. ochraceus,
considered a keystone species -- one on which other species in an
ecosystem lean heavily.

The ochre sea star was pummeled over a large portion of its range. Along
the Oregon coast, for example, the researchers note that populations
underwent declines ranging from 50% to 94%.

The interplay between climate change and disease is threatening wildlife species as never before, said Oregon State's Andrea Burton, particularly
when the result is rapid and extreme drops in population.



==========================================================================
"A changing climate is causing the ocean to warm and those rising
sea water temperatures are putting more and more stress on marine
ecosystems," said Burton, who led the genetic variation study. "As a
result of that stress, marine diseases have become more prevalent over
the last few decades. Disease outbreaks cause changes in ecosystems'
community structure and the age distribution within species. A lot
of marine taxa have suffered severe declines in population because
of outbreaks." Burton, a doctoral candidate in integrative biology,
and OSU collaborators Sarah Gravem and Felipe Barreto examined a total
of 200 individual purple ochre to look for genetic variation between
healthy specimens and sick ones. The sea stars were collected from six
sites on the central Oregon coast in 2016, when apparently normal sea
stars and wasting sea stars were both common at each site.

"Our reasoning was that a sick sea star and healthy sea star nearby were
likely exposed to similar conditions, so maybe the ones that looked
healthy had some type of genetic predisposition toward resistance or
tolerance to sea star wasting syndrome," Burton said. "It was a unique
chance to compare apparently normal and wasting individuals from the
same time and place during the sea star wasting syndrome epidemic."
The scientists took note of observable disease symptoms based on
a six-level ranking protocol, ranging upward from twisting arms to
deflation, lesions, missing arms, loss of grip on rocks and finally disintegration or "melting." Only animals with none of those symptoms
were considered healthy.

"Through a number of genomic techniques, we found that genomic
differentiation between normal-looking and wasting sea stars was very
low," Burton said. "With little genetic variation to propel adaptation,
we definitely have even more concerns regarding how this species of
sea star will fare in future outbreaks." But while a genetic basis for
wasting syndrome resilience is probably weak, researchers did identify
a list of genomic regions with some association with disease resistance,
she said. Those parts of P. ochraceus DNA may have small but cumulative
effects in determining how a sea star does in the face of wasting syndrome
and thus should be studied further, Burton added.

"Assessing the potential for natural population resilience is a huge piece
of predicting the long-term prospects for affected species and all of the species and communities they influence," she said. "Some marine species
are suitable for selective breeding but many others are not, so examining genomic variation in natural populations can help answer the question
of whether a species has the genetic makeup to withstand diseases on its
own." Oregon State University financially supported this research with
startup funds to Barreto, an associate professor of integrative biology,
and the National Science Foundation also provided funding. Gravem, the
other scientist involved with the study, is a research associate at OSU.

========================================================================== Story Source: Materials provided by Oregon_State_University. Original
written by Steve Lundeberg. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Andrea R. Burton, Sarah A. Gravem, Felipe S. Barreto. Little
evidence for
genetic variation associated with susceptibility to sea star wasting
syndrome in the keystone species Pisaster ochraceus. Molecular
Ecology, 2021; 31 (1): 197 DOI: 10.1111/mec.16212 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220201115141.htm

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