The physiology of climate change:
mechanisms establishing thermal optima and tolerance limits
Hopkins Marine Station, Stanford University, USA
Comparisons of congeneric species and
conspecific populations that encounter only slight differences in habitat
temperature are yielding insights into the mechanisms that establish thermal
optima and tolerance limits and that determine the relative sensitivities of
species to climate change. For several groups of congeneric intertidal and
subtidal crustaceans and molluscs, thermal limits of cardiac function, which
correlate strongly with whole-organism lethal temperature, exhibit adaptive
variation that correlates strongly with biogeography and vertical zonation.
Perhaps counter-intuitively, the most warm-adapted species face the most
serious challenges from global warming because their upper thermal limits of
heart function lie near current habitat temperature maxima, and acclimatory
capacity for increasing thermal tolerance is relatively small. Differences in
heat tolerance among latitudinally separated conspecific populations of
intertidal invertebrates reveal genetically based local adaptation and the
importance of the timing of the tidal cycle in establishing thermal stress.
Intertidal species found at mid-latitude Ôhot spotsÕ where midday low tides
occur in summer may be more warm-adapted than conspecifics found at lower
latitudes. Thermal optima for protein stability and function vary adaptively
among congeners and conspecifics. A single amino acid substitution is
sufficient to adaptively modify a protein, a finding with implications for
rates of adaptive evolutionary change. The increasing number of cases in which
closely related cryptic congeners and populations of a single species from
different latitudes manifest temperature-adaptive variation is providing new
insights into how climate change will affect coastal marine ecosystems.