[Coral-List] Two new papers on coral thermal adaptation

[Daniel Barshis]

Hi All,
     My research group just had a couple of complimentary coral thermal
adaptation papers (one tropical and one temperate) come out recently that
might be of interest to listers. Abstracts below and feel free to email me
for a pdf if you are interested and don't have access to current JEB
articles.
Best regards,
dan

*Adaptive signatures in thermal performance of the temperate coral
Astrangia poculata (Ellis & Solander, 1786)*
Hannah E. Aichelman, Richard C. Zimmerman, Daniel J. Barshis
Journal of Experimental Biology 2019 : jeb.189225 doi: 10.1242/jeb.189225
Published 4 February 2019
Abstract
Variation in environmental characteristics and divergent selection
pressures can drive adaptive differentiation across a species’ range.
Astrangia poculata is a temperate scleractinian coral that provides unique
opportunities to understand the roles of phenotypic plasticity and
evolutionary adaptation in coral physiological tolerance limits. A.
poculata inhabits hard bottom ecosystems from the northwestern Atlantic to
the Gulf of Mexico and withstands an annual temperature range up to 20°C.
Additionally, A. poculata is facultatively symbiotic and co-occurs in both
symbiotic (“brown”) and aposymbiotic (“white”) states. Here, brown and
white A. poculata were collected from Virginia (VA) and Rhode Island (RI),
USA and exposed to heat (18-32°C) and cold (18-6°C) temperatures during
which respiration (R) of the coral host along with photosynthesis (P) and
photochemical efficiency (Fv/Fm) of Breviolum psygmophilum photosymbionts
were measured. Thermal performance curves (TPCs) of respiration revealed a
pattern of countergradient variation with RI corals exhibiting higher
respiration rates overall, and specifically at 6, 15, 18, 22, and 26°C.
Additionally, thermal optimum (Topt) analyses show a 3.8°C (brown) and
6.9°C (white) higher Topt in the VA population, corresponding to the warmer
in situ thermal environment in VA. In contrast to respiration, no origin
effect was detected in photosynthesis rates or Fv/Fm, suggesting a possible
host-only signature of adaptation. This study is the first to consider A.
poculata’s response to both heat and cold stress across symbiotic states
and geography and provides insight into the potential evolutionary
mechanisms behind the success of this species along the East Coast of the
US.

*High-frequency temperature variability mirrors fixed differences in
thermal limits of the massive coral Porites lobata*
Daniel J. Barshis, Charles Birkeland, Robert J. Toonen, Ruth D. Gates,
Jonathon H. Stillman
Journal of Experimental Biology 2018 221: jeb188581 doi: 10.1242/jeb.188581
Published 10 December 2018
ABSTRACT
Spatial heterogeneity in environmental characteristics can drive adaptive
differentiation when contrasting environments exert divergent selection
pressures. This environmental and genetic heterogeneity can substantially
influence population and community resilience to disturbance events. Here,
we investigated corals from the highly variable back-reef habitats of Ofu
Island in American Samoa that thrive in thermal conditions known to elicit
widespread bleaching and mortality elsewhere. To investigate the relative
importance of acclimation versus site of origin in shaping previously
observed differences in coral tolerance limits at Ofu Island, specimens of
the common Indo-Pacific coral Porites lobata from locations with differing
levels of thermal variability were acclimated to low and high thermal
variation in controlled common garden aquaria. Overall, there were minimal
effects of the acclimation exposure. Corals native to the site with the
highest level of daily variability grew fastest, regardless of acclimation
treatment. When exposed to lethal thermal stress, corals native to both
variable sites contained elevated levels of heat shock proteins and
maintained photosynthetic performance for 1–2 days longer than corals from
the stable environment. Despite being separated by <5 km, there was
significant genetic differentiation among coral colonies (FST=0.206,
P<0.0001; nuclear ribosomal DNA), whereas Symbiodiniaceae were all
Cladocopium sp. (ITS type C15). Our study demonstrates consistent
signatures of adaptation in growth and stress resistance in corals from
naturally thermally variable habitats, suggesting that differences in the
amount of thermal variability may be an important contributor to adaptive
differentiation in reef-building corals.

-- 

  Daniel Barshis, Ph.D.
  Assistant Professor
  Department of Biological Sciences
  Old Dominion University
  Mills Godwin Building 302J
  Norfolk, VA 23529
  Office: 757-683-3614
  Lab: 757-683-5755
  Web: www.odu.edu/~dbarshis