Physiology & physiological ecology
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  Thermal stresses
  The topic of physiology & physiological ecology is divided into a section on thermal stresses considered here, and sections on pH & OCEAN ACIDIFICATION, CHEMORECEPTION, GAS EXCHANGE & METABOLISM, LOCOMOTION & TENACITY, DIEL SEASONAL & TIDAL RHYTHMS, and OSMOTIC REGULATION & SALINITY TOLERANCE presented elsewhere.
Research study 1

histogram showing temperature effect on survival of zoeal larvae of Dungeness crabs Cancer magisterA laboratory study at the Shannon Point Marine Center, Washington on the effects of temperature on survival and duration of zoeal larval stages of Dungeness crabs Cancer magister shows that overall best survival is at lower temperatures of 10-15oC.  As expected, stage duration varies inversely with temperature at all stages (data not shown).  As shown in the accompanying figure, the terminal 5th zoeal stage is the most sensitive to temperature stress.  Sulkin & McKeen 1989 Mar Biol 103: 31.

Research study 2

photograph of porcelain crabs Petrolisthes eriomerus and P. cinctipes courtesy Dave Zitten, Some 40-50 species of porcelain crabs Petrolisthes spp. inhabit rocky intertidal shores along the west coasts of both North and South America, including at least 5 from Alaska to southern California.  A comparison of physiological tolerance limits in relation to their vertical distributions in 20 of these species reveals that thermal limits of many of the high-intertidal species are near current habitat-temperature maxima.  This puts them at additional risk should climate change lead to significant environmental warming.  Stillman 2002 Integ Comp Biol 42: 790; for another brief review of thermal stresses and tolerances in porcelain crabs Petrolisthes see Stillman & Somero 2000 Physiol Biochem Zool 73: 200. Photograph courtesy Dave Zitten, University of British Columbia.



Two of the most common porcelain-crab species
on the west coast of North America. Other species
include cabrilloi, manimaculis, amd rathbunae.

Research study 3

What exactly is involved when a crab is thermally stressed?  We know that heat-shock proteins and ubiquitins are formed, but what about other cellular pathways that may be regulated in response to heat stress.  This question is addressed by researchers at San Francisco State University, California using a proteomics approach.  They first stress adult male porcelain crabs Petrolisthes cinctipes for 4h at temperatures ramped from 11-30oC, then dissect out and analyse hepatopancreases at 9 recovery times from 0.5-30h for levels of genes that are up- or down-regulated following the stress.  Results show, to quote the authors, that “genes upregulated following heat stress were invoved with protein folding, protein degradation, protein synthesis and gluconeogenesis”, suggesting an acceleration of protein turnover.  Down-regulated genes are ones involved with detoxification, oxygen transport, oxidative phosphorylation, and lipid metabolism, suggesting an avoidance of reactive oxygen species.  The proteomics approach used here, and transcriptomics methods employed in investigations on thermal and acidification stresses in other west-coast invertebrates, are becoming increasingly popular tools in west-coast climate-change studies.  Teranishi & Stillman 2007 Comp Biochem Physiol D 2: 53.

NOTE  heat-shock proteins are molecular “chaperones” that function to repair and otherwise tend to heat-damaged proteins.  Ubiquitins are a type of small-molecular-size regulatory protein found in all tissues that serve to monitor activity states in other cellular proteins.  Attachment of ubiquitins to a substrate protein may signal its degradation, relocation, or future activity level

NOTE   this large organ in crustaceans has multiple functions relating to energy metabolism, digestion and so on.  In many respects, it has the combined functions of liver, pancreas, and possibly spleen of vertebrates

Research study 4

map showing locations for collection of porcelain crabs Petrolisthes cintipesOther research on thermal stress in porcelain crabs Petrolisthes cinctipes at San Francisco State University, California monitors transcriptomic responses in cardiac tissue under heat and cold stresses similar to those encountered by crabs in their natural habitats.  Test crabs are maintained in coolers that either ramp temperatures up (from ambient to 31oC) or down (from ambient to 0oC) over a 4h period, or kept at steady ambient temperature.   Results show that genetic expression of beta tubulin and several other unknown genes is significantly higher in crabs acclimatised to the most thermally variable sites as compared with ones from less variable sites.  The study identifies several novel genes that seem especially sensitive to thermal acclimatisation in habitats with fluctuating temperatures.  It seems, in fact, that degree of temperature fluctuation in a certain habitat is actually more important in setting thermal performance than the mean seasonal habitat temperature.  Stillman & Tagmount 2009 Molec Ecol 18: 4206.

NOTE  identification of specific RNA molecules in response to external stimulus

NOTE  3 habitat areas are sampled, at Bamfield British Columbia, Cape Arago Oregon, and Montery California

Research study 5

map showing current 2011 west-coast distribtution of invasive green crabs Carcinus maenasThe successful invasion of green crabs Carcinus maenas into various areas of the world from Europe suggests a remarkable range in thermotolerance.  This is investigated by researchers from Portland State University, Oregon using crabs from the southern and northern parts1 of its west-coast distribution.  Summer seawater temperatures in the 2 areas differ by about 9oC and winter temperatures by about 5oC.  After acclimation2 for 6wk to either 6 or 23oC, the CA group has a significantly higher critical thermal maximum (CTmax) than the BC group.  The differences are only 0.7-3.0oC, but are strongly suggestive of the development of a physiological “race” within the overall invasive population.  This idea is supported, at least in part, by evidence of significant elevation in levels of heat-shock proten 70 (Hsp70) in the 6oC-acclimation CA group over the 6oC-acclimation BC group measured at the times of their deaths in the CTmax experiments (but there is no difference in the 23oC-acclimation groups).  Interestingly, the researchers also find morphological differences between the 2 groups, specifically, of carapace widths of the BC group being significantly greater than the CA group by about 5mm for both males and females (during late-summer samplings at both sites in 2008).  These findings, representing changes occurring in the founder population over a period of only 2 decades or so, prompt the authors to suggest that a northern cold-water phenotype may already have risen.  Kelley et al. 2011 J Exp Mar Biol Ecol 409: 70.

NOTE1  these are Stinson Beach, CA and Pipestem Inlet, BC.  Initial invasion of the species occurred near San Francisco, CA with later spread northwards into British Columbia.  For more information on green crabs on the west coast see LEARN ABOUT CRABS & RELATIVES: HABITAT & COMMUNITY ECOLOGY: COMPETITION: INTERSPECIFIC: INVASIVE GREEN CRABS

NOTE2  the low temperature of 6oC used represents winter seawater temperature at the BC site, while the high temperature of 23oC represents the summer temperature at the CA site

NOTE3  the upper critical thermal maximum (CTmax) is the temperature at which death occurs in individuals treated to temperature rises of 2oC every 30min starting from either 6 or 23oC
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