Variation in thermal tolerance of the giant kelp's gametophytes: suitability of habitat, population quality or local adaptation?
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2022Metadata
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Becheler, Ronan
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Variation in thermal tolerance of the giant kelp's gametophytes: suitability of habitat, population quality or local adaptation?
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Abstract
The giant kelp Macrocystis pyrifera is a cosmopolitan species of cold-temperate coasts. Its
South-American distribution ranges from Peru to Cape Horn and Argentina, encompassing
a considerable temperature gradient, from 3 to 20°C. Temperature is known to strongly
affect survival, growth and reproduction of many kelp species, and ongoing global
warming is already eroding their range distribution. Their response to thermal variability
was shown to vary among genetically differentiated regions and populations, suggesting
a possible adaptive divergence in thermal tolerance traits. This study aimed at testing
the existence of local adaptation in the giant kelp, in regions separated by up to 4000km
and strong thermal divergence. Two complementary experiments mimicked reciprocal
transplants through a common garden approach, each habitat being represented by a
given temperature corresponding to the regional average of the sampled populations.
Several proxies of fitness were measured in the haploid stage of the kelp, and sympatric
versus allopatric conditions (i.e. individuals at the temperature of their region of origin versus
in a different temperature and versus individuals from other regions in that temperature)
were compared. Additionally, a heat wave at 24°C was applied to measure the tolerance
limits of these gametophytes. A significant interaction between experimental temperature
and region of origin revealed that temperature tolerance varied among regions. However,
depending on the fitness parameter measured, high latitude populations from the sub-
Antarctic region were not always less heat resilient than populations from the warmer region
of Peru. Even at 24°C, a temperature that is exceptionally reached in the southernmost
part of the kelp’s natural habitat, all the gametophytes survived, although with strong
differences in other traits among regions and populations within regions. This large range
of temperature tolerance supports the idea of kelp gametophytes being a resistant stage.
Finally, local adaptation sensu stricto was not detected. Fertility was more influenced by
the geographic origin than by temperature, with possible effects of marginal conditions at the extremes of the distribution range. The latter results also suggest that stochastic
dynamics such as genetic drift restricts adaptive processes in some populations of
M. pyrifera.
Patrocinador
ANID/CONICYT
Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT)
CONICYT FONDECYT 1160930
3170597
FB-0001
CeBiB
ANID MIllenium Science Initiative Program NCN2021_033
CNRS International Research Network: Diversity and Biotechnology of Marine Algae
IDEALG project ANR-10-BTBR-04
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Frontiers in Marine Science July 2022 Volume 9 Article 802535
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