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M.S. Clark et al.
provide a natural laboratory with species living in clearly defined tidal zones with
different stresses and organism thermal limits (Roberts et al. 1997, Tomanek and
Somero 2000, Tomanek 2002, Halpin et al. 2002, Tomanek 2005). As stated previously, this work has largely concentrated on monitoring the production of heat shock
genes/proteins, particularly the inducible form of HSP70 as these are regulated, not
only by temperature but are also generalised stress proteins.
The general findings of this body of research indicates that a species ability
to colonise the inter-tidal zone is at least partly dictated by its thermal tolerance.
Although a certain amount of temperature acclimation can occur, the most exposed
animals (i.e. those furthest up the shoreline) actually have a relatively lower capacity to further adjust their heat shock response than those closer to the inter-tidal
region and therefore are the most vulnerable to climate change. This initially appears
counter-intuitive, as these are the animals which inhabit the harshest environment
and so might be expected to be the most robust in the face of change. This is almost
certainly due to cellular energy budgets and protein production, so the requirement
for increased HSP production on the high shoreline has to be traded off against
other cellular processes. For example reciprocal transplant experiments in inter-tidal
mussels resulted in those higher up the shoreline growing more slowly (Hofmann
2005).
Relatively local scale experiments are also mirrored on the larger scale (reviewed
in Hofmann 2005), where HSP production is correlated with biogeography. Efforts
have concentrated on studying species along latitudinal gradients (Halpin et al.
2002, Osovitz and Hofmann 2005) and species at their edge ranges (Hofmann 2005).
This work has recently been expanded using microarray profiling. A 2,496 feature cDNA array was produced for the inter tidal mussel Mytilus californianus and
probed with RNA from four different populations across a 17º latitudinal gradient
along the west coast of North America (Place et al. 2008). Analysis concentrated
on genes associated with environmental stress (protein folding, protein degradation
and apoptosis) and several showed particularly high levels of expression including the heat shock cognate HSC71, the beta subunit of the proteasome, elf2-α,
a stress regulated translation initiation factor and an integral membrane protein
involved in the stress response in yeast. These genes potentially provide biomarkers of stress for future work in this organism. Overall, the four location-specific
gene expression profiles revealed the complexity of local habitat environment overriding latitude. The expression of the majority of the genes varied significantly as
a function of the collection site and provided support for the original hypothesis
that the physical response of M. californianus to emersion and abiotic factors is
population-specific.
In such work involving sampling over latitudinal gradients or global regions, it
is important to work either on the same species or closely related congeners, so that
the adaptive effects of genetic variation can be clearly demonstrated as being independent of phylogeny. With more genome data becoming available from non-model
species, this work is now rapidly progressing from the analysis of single genes to
thousands with the use of gene chips. Thus producing a more holistic genome level
analysis of the trade-offs involved in habitat selection.
M.S. Clark et al.
provide a natural laboratory with species living in clearly defined tidal zones with
different stresses and organism thermal limits (Roberts et al. 1997, Tomanek and
Somero 2000, Tomanek 2002, Halpin et al. 2002, Tomanek 2005). As stated previously, this work has largely concentrated on monitoring the production of heat shock
genes/proteins, particularly the inducible form of HSP70 as these are regulated, not
only by temperature but are also generalised stress proteins.
The general findings of this body of research indicates that a species ability
to colonise the inter-tidal zone is at least partly dictated by its thermal tolerance.
Although a certain amount of temperature acclimation can occur, the most exposed
animals (i.e. those furthest up the shoreline) actually have a relatively lower capacity to further adjust their heat shock response than those closer to the inter-tidal
region and therefore are the most vulnerable to climate change. This initially appears
counter-intuitive, as these are the animals which inhabit the harshest environment
and so might be expected to be the most robust in the face of change. This is almost
certainly due to cellular energy budgets and protein production, so the requirement
for increased HSP production on the high shoreline has to be traded off against
other cellular processes. For example reciprocal transplant experiments in inter-tidal
mussels resulted in those higher up the shoreline growing more slowly (Hofmann
2005).
Relatively local scale experiments are also mirrored on the larger scale (reviewed
in Hofmann 2005), where HSP production is correlated with biogeography. Efforts
have concentrated on studying species along latitudinal gradients (Halpin et al.
2002, Osovitz and Hofmann 2005) and species at their edge ranges (Hofmann 2005).
This work has recently been expanded using microarray profiling. A 2,496 feature cDNA array was produced for the inter tidal mussel Mytilus californianus and
probed with RNA from four different populations across a 17º latitudinal gradient
along the west coast of North America (Place et al. 2008). Analysis concentrated
on genes associated with environmental stress (protein folding, protein degradation
and apoptosis) and several showed particularly high levels of expression including the heat shock cognate HSC71, the beta subunit of the proteasome, elf2-α,
a stress regulated translation initiation factor and an integral membrane protein
involved in the stress response in yeast. These genes potentially provide biomarkers of stress for future work in this organism. Overall, the four location-specific
gene expression profiles revealed the complexity of local habitat environment overriding latitude. The expression of the majority of the genes varied significantly as
a function of the collection site and provided support for the original hypothesis
that the physical response of M. californianus to emersion and abiotic factors is
population-specific.
In such work involving sampling over latitudinal gradients or global regions, it
is important to work either on the same species or closely related congeners, so that
the adaptive effects of genetic variation can be clearly demonstrated as being independent of phylogeny. With more genome data becoming available from non-model
species, this work is now rapidly progressing from the analysis of single genes to
thousands with the use of gene chips. Thus producing a more holistic genome level
analysis of the trade-offs involved in habitat selection.