title for learn-about section on whelks & relatives in A SNAIL'S ODYSSEY
  Physiological ecology
 

photograph showing all 5 west-coast whelks Nucella spp.

The accompanying photographs may be helpful in the Research Studies to follow. Note, however, that all species are highly variable in shape and colour, and a single image can only act as a general reference. Photographs of the 4 northern species courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC, and photograp of N. emarginata courtesy Joseph Dougherty, California CALPHOTOS.

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  Heat-shock proteins
  Topics in this section on physiological ecology include heat-shock proteins, considered here, and TRAIL-FOLLOWING, GAS EXCHANGE, and TEMPERATURE EFFECTS considered in other sections.
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Research study 1
 

graph showing body temperatures through the day in whelks Nucella ostrina at sites in Oregon with wave-exposure or wave-protectedgraph showing rates of food consumption in whelks Nucella ostrina at wave-exposed and wave-protected sites in OregonStudies on whelks Nucella ostrina in Oregon show that individuals living in wave-exposed habitats1 eat more, have higher rates of oxygen consumption, and are generally more physiologically “robust” than individuals living in wave-protected habitats.  Although body temperatures are generally lower in the wave-exposed population (see graph upper Left), rates of food2 consumption (see histogram upper Right) and oxygen uptake (see histogram lower Left) are somewhat more elevated as compared with those in the wave-protected population.

histogram comparing rates of oxygen consumption in whelks Nucella ostrina in wave-exposed and wave-protected areas of Strawberry Hill, Oregonhistogram comparing levels of heat-shock proteins in whelks Nucella ostrina in wave-exposed and wave-protected areas of Strawberry Hill, OregonLevels of heat-shock proteins3 are significantly elevated in whelks in wave-protected areas as compared with ones in wave-exposed areas, presumably owing to stress of elevated temperatures during the hot summer months. Allocation of energy for synthesis of these repair proteins will draw energy away from growth and reproductive processes.  Rather than stress being greater for the whelks in areas with greater wave exposure, then, it seems actually to be less, with overall fitness being correspondingly greater.  Dahlhoff et al. 2001 Ecology 82: 2816.

NOTE1 2 sites are included in the study, Strawberry Hill and Boiler Bay, but only the first is featured here

NOTE2  data are obtained from caged whelks caged with access to mussels Mytilus trossulus as food for 2wk

NOTE3  levels of Hsp70 are measured in samples of foot tissues in snails translocated to wave-exposed and wave-sheltered areas from an area of intermediate wave exposure.  Heat-shock proteins are molecular chaperones, produced as part of the heat-shock response, which assist in the refolding of stress-denatured proteins in the cell.  More information on heat-shock proteins in west-coast invertebrates can be found in the ODYSSEY at: LEARN ABOUT MUSSELS: LIFE IN THE INTERTIDAL ZONE: HEAT-SHOCK PROTEINS; LEARN ABOUT ABALONES & RELATIVES: PHYSIOLOGICAL ECOLOGY: HEAT-SHOCK PROTEINS, and LEARN ABOUT LIMPETS & RELATIVES: HABITATS & ECOLOGY: LIFE IN THE INTERTIDAL ZONE: TEMPERATURE STRESS

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Research study 2
 

map showing west-coast distribution of whelks Nucella canaliculata histograms showing comparative abundances of whelks Nucella canaliculata at different sites throughout its west-coast rangeAnother interesting and testable idea relating to heat-shock proteins is that individuals in the centre of distribution of a species are predicted to be less stressed physiologically than ones at the fringes.  Range boundaries occur where the severity of environmental conditions exceed a species' physiological tolerances.  This is tested with whelks Nucella canaliculata collected at range-centre sites in Oregon and range-edge sites in southern California (see map) and compared for amounts of Hsp70 present in their foot muscles. 

histograms comparing levels of heat-shock proteins Hsp70 in whelks Nucella canaliculata in different parts of their distributionResults show, as the researchers predict, that N. canaliculata is less abundant (by a factor of 35; see histogram upper Right) and more stressed (see histogram lower Right) at its southern range edge in California than at its range centre in Oregon. Causes of elevated Hsp levels could involve temperature, salinity, desiccation, anoxia, UV, and trace metals, acting singly or multiplly, and oftentimes synergistically. The fact that Hsps are additive means that a spot analysis using chromatography can provide a measure of total stress ‘load’ on an organism.  The authors posit that range-edge abundances of a species will decrease as global temperatures increase.  If so, these could act as indicators of a sort of global climate change. The study is interesting and provocative, but one wonders what results would have been obtained had the whelks been tested at the other, northern, range end. Sorte & Hofmann 2004 Mar Ecol Progr Ser 274: 263.

NOTE  2 sites are sampled at each location: in Oregon at Strawberry Hill and Fogarty Creek; in California at Piedras Balancas and Soberanes Point

NOTE  abundances at the 4 sites are estimated by timed counts, ranging from 2-6 “person-minutes” at the range-centre sites to 118-138 “person-minutes” at the range-edge sites, replicated 3 times

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Research study 3
 

map showing distributions of 5 west-coast whelk species NucellaFive species of Nucella inhabit west-coast shorelines. Three species N. lamellosa, N. canaliculata, and N. ostrina coexist from southern Alaska to mid-California.  The other 2 species N. lima and N. emarginata live in Alaska and southern California/Baja California, respectively.  Two of the species, N. lamellosa and N. canaliculata, live lower on the shore, while the other 3 species live higher on the shore.  Questions addressed in the study are 1) do the species differ in thermal tolerances, 2) if so, do the differences correlate with latitudinal and/or intertidal-height differences in habitats occupied, and 3) are heat-shock protein levels correlated with thermal tolerances? 
histogram showing levels of heat-shock proteins in 5 species of west-coast whelks Nucella
Thermal tolerances are tested by first acclimating1 snails to 10oC seawater over periods up to 7wk, then subjecting them to a slow rise in temperature to 32oC over 100min, then keeping them at 32oC for 20min, and then monitoring2 their recovery.  Results show that tolerances are significantly greater for species such as N. emarginata and N. ostrinathat live higher intertidally than for species such as N. canaliculata and N. lamellosa that live lower intertidally or a species such as N. lima that lives mainly in Alaska (see histogram upper Right).  

histogram showing temperature tolerances of 5 species of west-coast whelks NucellaLevels of total heat-shock protein (Hsp703 ) show some correlation with thermal tolerance, with lower levels being found in N. emarginata, a southern species more accustomed to higher environmental temperatures, than in the other species.  The results show the same magnitude of differences in thermal tolerance between species inhabiting different tidal heights as between those occurring at different latitudes.  Sorte & Hofmann 2005 Mar Biol 146: 985.

NOTE1 3 acclimation periods are used (0.7, 3, and 7wk) but, as differences between them are small and inconsistent, only the 7wk data are presented here

NOTE2 the "thermotolerance index" shown on the graph (upper Right) is based on the following "recovery scores": 0=dead, 1=moribund, 2=signs of life, and 3=completely recovered. The different letters over the coloured bars in the graph indicate significant differences between the means

NOTE3 values for both total and inducible Hsp70 are given in the paper but, as the authors note that the former is a better predictor of thermotolerance than the latter, only data for
total Hsp70 are given here

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