Adaptations To The Deep Sea
To begin Dr. Somero's talk you can click here or read this brief overview, below, that provides links to the best places in the talk for specific topics.
The physical and chemical characteristics of the deep-sea environment
present daunting challenges to organisms and require a wide range of adaptations.
These adaptations are of two fundamental sorts, those that effect tolerance of the environment and others that
establish rates of metabolic function appropriate to the deep sea.
The high pressures of the deep sea (pressure rises by 1 atmosphere for
each 10 meters increase in depth) are perturbing to physiological and biochemical
processes. Selection has favored the evolution of pressure-resistant
proteins which are able to sustain their native structures and activities
under conditions that would seriously perturb proteins from shallow-living
species. Some proteins of deep-sea fishes have unusually rigid structures.
Deducing the molecular basis of this structural stability might benefit
biotechnologists anxious to create proteins with higher resistance to denaturation.
Although most of the deep sea is very cold, hydrothermal
vent regions present organisms with high and variable temperatures.
Proteins from hydrothermal vent animals resemble those from cold-living
deep-sea animals in their resistance to pressure, but unlike the latter
species' proteins, they are also able to function over wide ranges of temperatures.
Proteins of ultrathermophilic microbes (Archaea)
in the hottest vent waters have unusually high thermal stabilities, consistent
with the microbes' abilities to tolerate temperatures up to ~110 C, the
highest temperatures at which life is known to occur.
Rates of life also reflect adaptation to deep-sea conditions, but these
adaptations in metabolic capacity appear unrelated to the effects of high
pressure and, to a large extent, to life at low temperature. For many pelagic
organisms, notably fishes and crustaceans, rates
of metabolic activity decrease dramatically with depth between the surface
and approximately 800-1000 m. The ultimate causes of these depth-related
changes in metabolic rate include the effects of near-complete darkness.
For fishes and invertebrates that rely on vision in predator-prey interactions,
life-in-the-dark appears to allow a large reduction in locomotory activity
and, thereby, large decreases in metabolic rate. The swimming musculature
of deep-sea fishes contains greatly reduced levels of enzymatic activity
for generation of ATP, the cell's energy currency, consistent with reduced
locomotory capacity. Invertebrates such as gelatinous species that are not
visual predators do not exhibit depth-related decreases in metabolism or
in enzymatic activity.
The strong correlation between enzymatic activity and rate of metabolism
permits development of biochemical indices
of physiological state. Thus, the quantity of enzymatic activity present
in a biopsy sample of muscle tissue can serve as a proxy for the rate of
oxygen consumption by the whole organism. Through measuring enzymatic activities
in this way, it is possible to gauge the physiological condition of natural
populations, such as deep-sea fishes that have become of major commercial
importance. Analysis of deep-living rockfish suggests that some populations
may live under food-limiting conditions.
Low concentrations of oxygen also present challenges to some deep-living
animals. Fishes found in the oxygen minimum zone
(OMZ) have elevated capacities for extracting oxygen from seawater and exhibit
different patterns of gene expression for enzymes of aerobic and anaerobic
metabolism than related species from high-oxygen habitats.
In summary, studies of deep-sea animals are providing new insights into
issues ranging from mechanisms of evolutionary adaptation to the environment
to practical concerns about gauging the status of fisheries and designing
novel molecules through biotechnology.