The importance of phenotypic plasticity and local adaptation in driving intraspecific variability in thermal niches of marine macrophytes

Climate change is driving the redistribution of species at a global scale and
documenting and predicting species’ responses to warming is a principal
focus of contemporary ecology. When interpreting and predicting their
responses to warming, species are generally treated as single homogenous
physiological units. However, local adaptation and phenotypic plasticity can
result in intraspecific differences in thermal niche. Therefore, population
loss may also not only occur from trailing edges. In species with low
dispersal capacity this will have profound impacts for the species as a
whole, as local population loss will not be offset by immigration of warm
tolerant individuals. Recent evidence from terrestrial forests has shown
that incorporation of intraspecific variation in thermal niche is vital to
accurately predicting species responses to warming. However, marine
macrophytes (i.e. seagrasses and seaweeds) that form some of the world’s
most productive and diverse ecosystems have not been examined in the
same context. We conducted a literature review to determine how common
intraspecific variation in thermal physiology is in marine macrophytes. We
find that 90% of studies identified (n = 42) found clear differences in
thermal niche between geographically separated populations. Therefore,
non-trailing edge populations may also be vulnerable to future warming
trends and given their limited dispersal capacity, such population loss will
not be offset by immigration. We also explore how Next Generation
Sequencing (NGS) is allowing unprecedented mechanistic insight into
plasticity and adaptation. We conclude that in the ‘genomic era’ it may be
possible to link understanding of plasticity and adaptation at the genetic
level through to changes in populations providing novel insights on the
redistribution of populations under future climate change.