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First published online July 20, 2007
Journal of Experimental Biology 210, 2691-2699 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.003715
Growth in the slow lane: protein metabolism in the Antarctic limpet Nacella concinna (Strebel 1908)
British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge, CB3 OET, UK
* Author for correspondence (e-mail: kppf{at}bas.ac.uk)
Accepted 26 April 2007
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Summary |
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1°C in N. concinna, the approximate summer water
temperature at the study site, and protein synthesis rates decreased above
this temperature. In the absence of adaptation, predicted increases in
Antarctic water temperatures would result in reduced, rather than increased,
rates of protein synthesis and, in turn, possibly growth.
Key words: polar, limpet, growth, protein synthesis
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Introduction |
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; Barnes, 1995;
Clarke et al., 2004;
Barnes et al., 2006;
Bowden et al., 2006), although
there are some reported exceptions (Dayton
et al., 1974; Dayton,
1989; Rauschert,
1991; Barnes,
1995). Previous studies have suggested that low annual growth
rates in Antarctic primary consumers are largely caused by highly seasonal
primary productivity, which results in very low growth rates for the majority
of the year (Clarke, 1985;
Clarke, 1988;
Clarke and Leakey, 1996;
Fraser et al., 2004), although
some studies do report strong temperature effects on growth
(Heilmayer et al., 2004) and
embryonic and larval development are markedly slowed due to temperature
constraints (Hoegh-Guldberg and Pearse,
1995; Peck et al.,
2006). Furthermore, during the austral summer, short-term growth
rates in some polar species may approach those seen in temperate species
(Nolan and Clarke, 1993;
Peck and Bullough, 1993).
Although reduced winter food availability is likely to be a major factor
constraining annual growth in Antarctic ectotherms, it is possible that
fundamental biochemical constraints may also limit growth at polar water
temperatures.
Soft tissue somatic growth in an organism is primarily the result of
protein growth, with the energetic cost of synthesising proteins dominating
the overall costs of growth (Fraser and
Rogers, 2007). The proportion of synthesised protein that is
retained as protein growth is termed the protein synthesis retention
efficiency (PSRE) (Houlihan et al.,
1995) and is an important determinate of both growth rate and
growth efficiency. PSRE can vary both within species, driven by factors such
as food consumption and age, and between species
(Houlihan et al., 1995;
Carter and Houlihan, 2001). To
date, no studies have examined protein synthesis and protein growth
simultaneously in any adult Antarctic species. Although whole animal protein
synthesis rates have been measured in several species (e.g.
Whiteley et al., 1996;
Marsh et al., 2001; Robertson
et al., 2001a; Robertson et al.,
2001b; Whiteley et al.,
2001; Fraser et al.,
2002a; Fraser et al.,
2004), it is currently unclear whether temperature influences PSRE
in polar ectotherms, and hence whether low growth rates in polar ectotherms
could be partially determined by a reduced PSRE.
Global seawater temperatures are increasing in many regions, with Antarctic
temperatures increasing at an above average rate, both in sub-surface water
masses and in particular along the West Antarctic peninsula
(Levitus et al., 2000;
Gille, 2002;
Meredith and King, 2005). In
temperate ectotherms, an increase in temperature typically results in an
increase in protein synthesis (Loughna and
Goldspink, 1985; McCarthy et
al., 1999). Current climate models predict a 2°C increase in
global seawater temperatures over the next century, albeit with large
confidence intervals, and sea temperatures in the Bellingshausen sea have
increased by 1°C in the last 50 years (Meridith and King, 2005).
However, we have little idea what effect this will have on protein synthesis
and, in turn, growth rates of Antarctic species. Previous studies have
suggested that many Antarctic invertebrates have an extremely limited ability
to acclimate to water temperatures even a few degrees above their normal
summer maxima (Peck, 2002;
Peck et al., 2004), although
some fish species have been acclimated to temperatures of 4°C and above
(Lowe and Davison, 2006).
The primary aim of this study was therefore to establish whether a
thermally induced reduction in PSRE could be contributing to reported low
annual growth rates in the Antarctic limpet Nacella concinna (Strebel
1908) (Clarke et al., 2004).
To provide an environmental context for this work, we also examined whether an
increase in seawater temperature could result in increased rates of protein
synthesis and hence growth in this species.
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Materials and methods |
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). Limpets were returned immediately to the laboratory and
maintained in flow-through aquaria with ambient seawater. For
temperature-controlled experiments, limpets were held in experimental aquaria
with the seawater temperature maintained using jacketed tanks and
thermocirculators (Grant Instruments, Cambridge, UK).
Seasonal protein turnover: experimental protocol
In December 1999 (the austral summer), 98 limpets were weighed (to
±1 mg), measured (to ±0.05 mm) using vernier callipers, and
individually numbered with enamel paint (Humbrol, Kingston upon Hull, UK).
Three days later the marked animals were returned to the field site from which
they were collected. During the short period that the animals were held in the
laboratory, they were maintained at similar water temperatures to those they
experienced in the sea (mean water temperature during growth period,
–0.47±0.12°C) and under a simulated natural photoperiod.
After 64 days growing in the field, SCUBA divers collected as many of the
marked animals as possible and returned them to the laboratory, where they
were re-weighed and measured. A subset of 16 animals was selected to measure
protein synthesis and protein growth. These animals were maintained in the
aquarium overnight before protein synthesis was measured the next day (see
below), and were not fed, although they were observed grazing biofilms on the
sides of the tank.
In June 2000 (the austral winter), a second group of 67 unmarked limpets were collected from the same sampling site and returned to the laboratory. The limpets were weighed, measured and marked as described above before being returned to the collection site. After a 96-day field growth period, as many of the second group of marked limpets as possible were recovered, re-weighed and measured. A subset of 17 were selected to measure protein synthesis and protein growth (as above). The mean water temperature during the growth period was –1.62±0.16°C.
For both studies, further groups of approximately 100 animals were collected to allow the relationship between fresh mass (total mass less shell mass) and total body mass to be determined. The total protein content of these limpets was also measured (see below) to estimate the protein content of the marked animals at the start of the growth period.
Effect of temperature on protein synthesis: experimental protocol
In a separate study, freshly collected N. concinna were held in
aerated water (temperature –1.3°C to –1.5°C) under a
simulated natural photoperiod for 30 days prior to experimental work. The
majority of the water in each tank was exchanged every 48 h with clean water
of the same temperature. The animals were allowed to feed ad libitum
on biofilms on the sides of the tanks, but were not provided with additional
food sources. After the 30-day acclimatisation period, animals were
transferred to experimental aquaria that contained water at the same
temperature as the holding tanks. Experimental tank water temperatures were
adjusted to the required temperatures (–1.5, 1.0, 3.5 and 6.0°C) at
a rate of 0.5 K day–1. After reaching the experimental water
temperature, animals were allowed to acclimate for 30 days prior to the
measurement of protein synthesis. Husbandry conditions, excluding water
temperature, were as previously described. The day before protein synthesis
was measured a unique identifying number was glued to each animal's shell with
cyanacrolyte.
Measurement of protein synthesis
The flooding dose method has previously been validated for measurement of
whole animal protein synthesis in N. concinna, as described in detail
previously (Fraser et al.,
2002a). In summary, each limpet was weighed (to ±1 mg)
after surface drying with a tissue. The fresh mass was estimated from the
previously determined relationship between total and fresh mass, and this
value was used to calculate the required injection volume of radiolabelled
amino acid (Fraser et al.,
2002a). Each experimental animal was injected into the pedal sinus
with a solution containing [3H]-labelled and unlabelled
phenylalanine (Phe) (10 µl g–1 fresh mass of 135 mmol
l–1 L-[2,6-3H]Phe at 3.6 MBq
ml–1; Amersham, Little Chalfont, UK). After injection the
animals were placed in a beaker containing 4 l of aerated seawater at the same
water temperature at which the limpets were previously held. In each
temperature experiment a time course (1, 2 and 4 h) of intracellular free-pool
stability and protein-bound radiolabelling was determined, to validate the
flooding dose methodology.
Sample analysis
At the end of the experiment limpets were removed from the beaker, shucked,
and the fresh mass measured. The shucked body of the limpet was then
homogenised (X120 Status homogeniser, PolyScience, Niles, IL, USA) in a known
volume of ice-cold 0.2 mol l–1 perchloric acid (PCA) and the
homogenate stored at 4°C prior to analysis. Sample analysis was carried
out as described previously (Fraser et
al., 2002a). The data were corrected for 3H
scintillation counting efficiency, which was 32±0.5% (Hionic Fluor
scintillation fluid, LKB-Wallac Rack Beta scintillation counter). All
radioactivities were expressed as disintegrations per minute (d.p.m.) per nmol
Phe. Where free-pools were stable (all experiments with the exception of
summer protein turnover animals), whole animal fractional protein synthesis
rates were calculated using Eqn
1:
 | (1) |
;
Houlihan et al., 1995):
 | (2) |
The absolute rate of protein synthesis (As) was
calculated using the following equation:
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The whole animal RNA concentration was expressed as the RNA:protein ratio
(µg RNA mg–1 protein). The RNA activity,
kRNA (mg protein mg–1 RNA
day–1) was calculated using the following equation
(Preedy et al., 1988):
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;
Houlihan et al., 1994):
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w1 was calculated from the estimated initial protein
concentration and fresh mass, and w2 was directly
measured. Protein synthesis retention efficiencies (PSRE, %) were calculated
using the following equation, where ks and
kg are expressed as % day–1:
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Statistical analysis
All data are expressed as mean ± s.e.m. The stability of
intra-cellular free-pools was tested using ANOVA, and linear radiolabelling of
bound protein was tested using least-squares regression analysis. Comparison
of summer and winter physiological parameters was carried out using one- or
two-sample tests where appropriate. In the temperature and protein synthesis
experiments, comparisons between temperatures were carried out using ANOVA.
The threshold for statistical significance was set at P<0.05.
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Flooding dose validation
In summer limpets, intracellular free-pool specific radioactivities
decreased linearly during the time course
(Fig. 1A: F=5.59,
P<0.05). Protein synthesis rates could therefore only be
calculated using protein synthesis Eqn
2. In winter limpets, intracellular free-pool specific
radioactivities did not significantly change during the time course
measurement (Fig. 1B:
P>0.05), and protein synthesis rates could be calculated with
Eqn 1. In both summer
(Fig. 1C) and winter
(Fig. 1D) limpets,
incorporation of radiolabelled Phe into proteins was both significant and
linear (all P<0.001), and the intercepts of the regression lines
were not significantly different from zero. To ensure that the flooding dose
injection had successfully flooded the animal's intracellular free-pools, the
post-injection increase in Phe was calculated. The pre-injection Phe
concentration of N. concinna was 0.34 nmol mg–1
fresh mass, the injection of radiolabelled and unlabelled Phe should therefore
theoretically raise the free-pool concentrations by 1.35 nmol
mg–1 fresh mass to a final concentration of 1.69 nmol
mg–1 fresh mass (Fraser
et al., 2002a). The mean Phe concentration after injection in both
protein turnover experiments was 1.71±0.08 nmol mg–1
fresh mass: Phe concentrations had increased to 101% of the theoretical
concentration, a 4.6-fold increase in tissue Phe levels, indicating that the
free-pools had flooded successfully.
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Seasonal protein turnover
The measured protein contents of the summer and winter limpets at the end
of the experimental periods were significantly different
(Table 1:
T=–3.37, d.f.=30, P<0.01). Summer fractional and
absolute protein growth rates were not significantly different to winter
values (Table 4:
P>0.05). Fractional protein synthesis rates in summer animals were
0.802% day–1 (error bars cannot be calculated due to the
calculation method, see Eqn 2)
and were significantly higher than winter protein synthesis rates of
0.55±0.06% day–1
(Table 4:
T=–4.07, d.f.=16, P<0.001). While absolute protein
synthesis rates and protein synthesis retention efficiencies were not
significantly different between seasons
(Table 4: P>0.05),
protein degradation, the difference between protein synthesis and protein
growth, was significantly (T=–2.78, d.f.=24,
P<0.01) higher in summer than winter.
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RNA:protein ratios were significantly (T=3.56, d.f.=21, P<0.01) lower in winter than summer, while kRNA was unchanged (Table 4: T=0.95, d.f.=22, P>0.05)
Effect of temperature on protein synthesis
Whole animal protein content was not affected by water temperature
(Table 2; ANOVA,
F=2.50, P=0.067). The mean limpet protein content for all
water temperatures was 11.86±0.21%. Temperature had a significant
effect on fractional protein synthesis rates
(Fig. 2A) and RNA activity
(Fig. 2D) with the rates at
1.0°C significantly higher than at the other experimental temperatures.
The absolute protein synthesis rate at 1°C was significantly higher than
at 6.0°C (Fig. 2B), while
the RNA:protein ratio was significantly different at all measurement
temperatures (Fig. 2C).
RNA:protein ratios initially decreased with increasing water temperature, but
after reaching a minimum value at 1.0°C, subsequently increased with
temperature.
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;
Houlihan et al., 1994;
Langar and Guillaume, 1994;
Meyer-Burgdorff and Rosenow,
1995; Sveier et al., 2000).
Flooding dose validation
As there were no seasonal differences in the length or tissue mass of
limpets in summer and winter, or between experimental groups held at different
temperatures (Tables 1,
2) data were not corrected for
mass prior to statistical comparisons. Stable (winter,
Fig. 1B; –1.5 to
6.0°C temperature range) or linearly decreasing (summer,
Fig. 1A) intracellular
free-pools, significant and linear incorporation of radiolabelled Phe into
protein in all experiments (Fig.
1C,D, Table 3), and
the increase in intra-cellular free-pool Phe concentrations after injection,
indicated that the criteria for the flooding dose technique
(Houlihan et al., 1995;
Fraser et al., 2002a;
Fraser et al., 2004;
Fraser and Rogers, 2007) had
been fully met.
Seasonal protein turnover
Seasonal variations in the protein synthesis rate of Nacella
concinna have previously been reported, with reduced rates in winter,
while faecal egestion rates in N. concinna were 11.9 and 7.35 mg dry
mass animal–1 day–1 in February and October,
respectively (Fraser et al.,
2002a; Fraser et al.,
2002b). Although faecal egestion rates are not a direct measure of
food consumption they do provide an indication that food consumption decreases
in winter. Protein synthesis rates in the current study were higher than those
previously reported (Fraser et al.,
2002a), probably as a result of inter-annual variability in food
availability and consumption. Food consumption is known to have a significant
effect on protein synthesis rates
(Houlihan et al., 1989;
Mente et al., 2001;
Fraser et al., 2002a;
Fraser et al., 2002b), and it
is well established that both benthic and pelagic primary productivity show
considerable inter-annual variability in the Antarctic
(Clarke, 1988;
Clarke et al., 1988;
Gilbert, 1991;
Fraser et al., 2004;
Grange et al., 2004). Whole
animal protein synthesis rates in N. concinna were very low in
comparison to rates reported for temperate and tropical ectotherms, and a
recent analysis (Fraser and Rogers,
2007) has suggested that protein synthesis rates decrease markedly
below 5°C (for reviews, see
Houlihan, 1991;
Houlihan et al., 1995;
Carter and Houlihan, 2001).
Absolute protein synthesis rates did not vary seasonally
(Table 4), and hence similar
amounts of energy were allocated to synthesising protein in both summer and
winter, presuming the thermodynamic cost of synthesising a unit of protein did
not alter. Neither the PSRE nor kg differed significantly
between summer and winter, but the calculated PSRE values were very low in
comparison to previously reported values, suggesting that only a small
proportion of the proteins synthesised were retained as protein growth.
Previously reported PSRE values in a wide selection of non-Antarctic
ectotherms ranged between 25 and 95%, with a mean value of 52%, and in
most cases PSREs were considerably higher than the values of 16 and 21%
reported in this study (Houlihan et al.,
1995). The low protein synthesis rates reported here for N.
concinna, coupled with the reduced PSRE, will result in both a low growth
efficiency and a low overall growth rate.
Our observation of a very low PSRE in polar organisms poses the obvious
question as to whether there is a general relationship between PSRE and body
temperature, or whether Nacella concinna is simply an unusual
organism. To examine whether ambient temperature has a general effect on PSRE,
we compiled the available PSRE data from the literature. As both protein
synthesis and protein growth scale with body mass, both variables were
standardised to a body mass of 64.0 g (the mean value of all organisms in the
compiled data set). The scaling coefficients used were calculated from the
fitted relationship between fresh mass M and protein synthesis
(lnks=1.869–0.2506xlnM,
r2=41.4%, P<0.01), and between fresh mass and
protein growth (lnkg=0.8389–0.1912xlnM,
r2=21.2%, P<0.05). Data were only utilised from
studies in which the animals had been fed daily and not maintained under
husbandry conditions likely to affect protein metabolism, such as exposure to
pollution or temperatures outside of their normal thermal envelope. The data
set is dominated by fish species with only two molluscs and a single
crustacean species, and the analysis thus needs to be interpreted with
caution, as the data set available is not phylogenetically diverse. However,
there was a significant relationship between PSRE and temperature
(Fig. 3). Animals living at
polar temperatures (<0°C) retain as growth only about 30% of the
protein they synthesise, whereas a typical tropical organism would retain
about 70%, a difference of 2.3x. This finding has important
implications, as it suggests that in ectotherms living at low temperatures,
growth is far less efficient than at warmer temperatures, presumably as a
result of fundamental biochemical constraints associated with the synthesis of
proteins. This result is in contrast to earlier data reported
(Heilmayer et al., 2004),
which suggests that scallop growth efficiencies decrease with increasing
temperature. Why a higher proportion of body proteins are degraded at low
temperatures is currently unclear, although there is growing evidence of
increased levels of cold-induced protein denaturation at polar water
temperatures (Buckley et al.,
2004; Place et al.,
2004; Hofmann et al.,
2005; Place and Hofmann,
2005).
|
;
Place et al., 2004;
Hofmann et al., 2005;
Place and Hofmann, 2005). In
the wolfish, Anarhichas lupus, acclimatised to water temperatures
ranging between 5 and 14°C, the relationship between PSRE and temperature
was quadratic, with lower PSRE at temperatures near both the lower and upper
extremes of its thermal range (McCarthy et
al., 1999). It would therefore appear, that in A. lupus,
protein degradation rates are either elevated at low temperatures or decrease
at a slower rate than ks. Further studies are required to
obtain a better understanding of the effects of temperature on protein
degradation. What is currently clear, however, is that the generally accepted
view that Antarctic ectotherms grow slowly simply because of a highly seasonal
food supply, is far from the complete story. In fact in the current study,
protein growth rates, kg, were not significantly different
in summer or winter in spite of a previously reported tenfold difference in
seasonal faecal egestion rates, a proxy measure of food consumption in this
species (Fraser et al.,
2002b). It therefore appears that temperature effects on
fundamental biochemical factors may also limit the capacity of cold-water
marine organisms to grow quickly and efficiently. It should be noted that
other authors have suggested that growth efficiencies in scallops are elevated
at low temperatures, and that stenothermal ectotherms maximise growth ability
by minimising their standard metabolic rates, thereby maximising the energy
available for growth (Heilmayer et al.,
2004; Pörtner et al.,
2005). However, protein growth efficiency, a major determinate of
overall animal growth, appears to be lower, not higher, in Antarctic limpets.
The reason for these conflicting results remains to be resolved.
The single data point (13) in Fig.
3 that does not appear to fit well within the data set is for the
sole crustacean species available, Homarus gammarus
(Mente et al., 2001). Growth
in arthropods is achieved by periodic moulting and loss of the old
exoskeleton; in turn this will result in the loss of some protein, thereby
resulting in a reduction in the PSRE
(O'Brien et al., 1991). Direct
comparison of PSREs between arthropods and other animals is therefore
problematic.
The RNA:protein ratios and kRNA values measured in
summer and winter animals in this study fall within the range of those
previously reported in N. concinna
(Fraser et al., 2002a).
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Effect of temperature on protein synthesis
Previous studies have demonstrated the inability of Antarctic organisms to
tolerate water temperatures even a few degrees above their normal summer
maxima (Peck, 2002;
Peck and Conway, 2000), with
many species, including Nacella concinna, starting to lose some
critical functions at water temperatures only slightly in excess of 0°C
(Peck et al., 2004). The data
presented in Fig. 2 suggest
that the thermal optimum for ks and As
in N. concinna is around 1°C. Interestingly, although RNA:protein
ratios initially decrease as water temperatures increase, as has been reported
in many other studies, at water temperatures above 1°C, RNA:protein ratios
start to increase again (Foster et al.,
1992; Mathers et al.,
1993; McCarthy and Houlihan,
1996; McCarthy et al.,
1999; Fraser et al.,
2002a). Conversely kRNA increases with water
temperature, reaching a maximum value at 1°C before then decreasing. In
previous studies kRNA was found typically to increase with
temperature, while RNA:protein ratios decrease
(McCarthy and Houlihan, 1996;
McCarthy et al., 1999;
Fraser et al., 2002a). It has
been suggested that the typically observed linear increases in RNA:protein
ratios with temperature occur to offset a thermally induced linear reduction
in kRNA (Fraser et
al., 2002a), although it has been reported that in the Antarctic
eelpout Pachycara brachycephalum and the Antarctic scallop
Adamussium colbecki, low temperature compensation of protein
synthesis is achieved primarily by cold-adaptation of the protein synthesis
machinery rather than an increase in RNA concentration
(Storch et al., 2003;
Storch et al., 2005).
Why kRNA decreases at water temperatures above 1°C
is not clear. It is possible that evolutionary modifications have occurred to
RNA in N. concinna to compensate protein synthesis rates at low water
temperatures, with the trade-off for these modifications being a loss of
function at even slightly elevated temperatures. Even though RNA:protein
ratios increase at temperatures above 1°C, protein synthesis rates still
decrease. Mean summer water temperatures, at the depths from which the limpets
were sampled for this study, currently reach 1–2°C at Rothera
Research station, around the optimum protein synthesis temperature for N.
concinna measured in this study
(Fraser et al., 2004).
Therefore any future increase in seawater temperatures, even if only in the
order of a few degrees, is at least in the short-term, likely to decrease,
rather than increase summer protein synthesis rates. Extrapolating these data
to absolute protein growth rates is complicated by our lack of knowledge of
the effect of temperature on protein degradation rates in N.
concinna. However, it is worth noting that the protein synthesis rates
measured at –1.5 and 1.0°C in the temperature study are almost
identical to those measured in the seasonal protein turnover study in winter
and summer, respectively. In that study, although protein synthesis rates
varied with season, protein growth rates did not, due to an increase in summer
protein degradation rates. It is therefore not currently possible to speculate
whether the measured decrease in protein synthesis rates at water temperatures
above 1°C, will actually result in a decrease in protein growth and
therefore overall growth rates. What is clear, however, is that protein and
RNA metabolism in N. concinna are extremely sensitive to even small
alterations in water temperature, with deleterious effects at water
temperatures even a few degrees above the current summer maxima.
Conclusions
We have found that the PSRE in the polar limpet N. concinna is
greatly reduced in comparison to temperate and tropical species. We have also
for the first time demonstrated a significant relationship between PSRE and
temperature, suggesting temperature has a fundamental influence on the
efficiency of protein metabolism and thereby ectotherm growth. It therefore
seems likely that although seasonal variability in food consumption
undoubtedly reduces annual growth rates in Antarctic ectotherms, maximum
growth rates (typically in summer) are also constrained by inefficient protein
metabolism. Over the range of temperatures examined it would appear that
maximal protein synthesis rates in N. concinna occur at around
1°C, with rates decreasing at higher temperatures. This suggests, in turn,
that any increase in water temperature along the Antarctic Peninsula, driven
by the current regional warming (Clarke et
al., 2007), is likely to result in reduced protein synthesis rates
in N. concinna, which could result in reduced growth.
List of abbreviations
|
Acknowledgments |
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References |
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TOPSummaryIntroductionMaterials and methodsResultsDiscussionReferences |
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Barnes, D. K. A. (1995). Seasonal and annual growth in erect species of Antarctic bryozoans. J. Exp. Mar. Biol. Ecol. 188,181 -198.[CrossRef]
Barnes, D. K. A., Webb, K. and Linse, K. (2006). Slow growth of Antarctic bryozoans increases over 20 years and is anomalously high in 2003. Mar. Ecol. Prog. Ser. 314,187 -195.
Bowden, D. A., Clarke, A., Peck, L. S. and Barnes, D. K. A. (2006). Antarctic sessile marine benthos: colonisation and growth on artificial substrata over three years. Mar. Ecol. Prog. Ser. 316,1 -16.
Brown, K. M., Fraser, K. P. P., Barnes, D. K. A. and Peck, L. S. (2004). Links between community structure of an Antarctic shallow-water community and ice-scour frequency. Oecologia 141,121 -129.[Medline]
Buckley, B. A., Place, S. P. and Hofmann, G. E.
(2004). Regulation of heat shock genes in isolated hepatocytes
from an Antarctic fish, Trematomus bernacchii. J. Exp.
Biol. 207,3649
-3656.
Carter, C. G. and Houlihan, D. F. (2001). Protein Synthesis. In Fish Physiology: Nitrogen Excretion. Vol. 20 (ed. P. A. Wright and P. M. Andersen), pp. 31-75. London: Academic Press.[CrossRef]
Carter, C. G., Houlihan, D. F., Buchanan, B. and Mitchell, A. I. (1993a). Protein-nitrogen flux and protein growth efficiency of individual Atlantic salmon (Salmo salar L.). Fish Physiol. Biochem. 12,305 -315.[CrossRef]
Carter, C. G., Houlihan, D. F., Brechin, J. and McCarthy, I. D. (1993b). The relationships between protein intake and protein accretion, synthesis, and retention efficiency for individual grass carp, Ctenopharyngodon idella (Valenciennes). Can. J. Zool. 71,392 -400.
Carter, C. G., Houlihan, D. F. and Owen, S. F. (1998). Protein synthesis, nitrogen excretion and long-term growth of juvenile Pleuronectes flesus. J. Fish Biol. 53,272 -284.
Clarke, A. (1985). The physiological ecology of polar marine ectotherms: energy budget, resource allocation and low temperature. Oceanis 11,11 -26.[Medline]
Clarke, A. (1988). Seasonality in the Antarctic marine environment. Comp. Biochem. Physiol. 90B,461 -473.[CrossRef]
Clarke, A. and Leakey, R. J. G. (1996). The seasonal cycle of phytoplankton, macronutrients, and the microbial community in a nearshore Antarctic marine ecosystem. Limnol. Oceanogr. 41,1281 -1294.
Clarke, A. and North, A. W. (1991). Is the growth of polar fish limited by temperature? In Biology of Antarctic Fish (ed. G. de Prisco, B. Maresca and B. Tota), pp.54 -69. Berlin: Springer-Verlag.
Clarke, A., Holmes, L. J. and White, M. G. (1988). The annual cycle of temperature, chlorophyll and major nutrients at Signy Island, South Orkney Islands, 1969-82. Br. Antarct. Surv. Bull. 80,65 -86.
Clarke, A., Prothero-Thomas, E., Beaumont, J. C., Chapman, A. L. and Brey, T. (2004). Growth in the limpet Nacella concinna from contrasting sites in Antarctica. Polar Biol. 28,62 -71.
Clarke, A., Murphy, E. J., Meredith, M. P., King, J. C., Peck, L. S., Barnes, D. K. A. and Smith, R. C. (2007). Climate change and the marine ecosystem of the western Antarctic peninsula. Philos. Trans. R. Soc. Lond. B Biol. Sci. 362,149 -166.[CrossRef][Medline]
Dayton, P. K. (1989). Interdecadal variation in
an Antarctic sponge and it's predators from oceanographic climate shifts.
Science 245,1484
-1486.
Dayton, P. K., Robilliard, J. S., Paine, R. T. and Dayton, L. B. (1974). Biological accommodation in the benthic community at McMurdo Sound, Antarctica. Ecol. Monogr. 44,105 -128.[CrossRef]
Foster, A. R., Houlihan, D. F., Hall, S. J. and Burren, L. J. (1992). The effects of temperature acclimation on protein synthesis rates and nucleic acid content of juvenile cod (Gadus morhua L.). Can. J. Zool. 70,2095 -2102.
Fraser, K. P. P. and Rogers, A. D. (2007). Protein metabolism in marine animals: the underlying mechanism of growth. Adv. Mar. Biol. 52,267 -362.[CrossRef][Medline]
Fraser, K. P. P., Lyndon, A. R. and Houlihan, D. F. (1998). Protein synthesis and growth in juvenile Atlantic halibut, Hippoglossus hippoglossus (L.): application of 15N stable isotope tracer. Aquac. Res. 29,289 -298.[CrossRef]
Fraser, K. P. P., Clarke, A. and Peck, L. S.
(2002a). Low-temperature protein metabolism: seasonal changes in
protein synthesis and RNA dynamics in the Antarctic limpet Nacella
concinna Strebel 1908. J. Exp. Biol.
205,3077
-3086.
Fraser, K. P. P., Peck, L. S. and Clarke, A. (2002b). Feast and famine in Antarctica: seasonal physiology in the limpet Nacella concinna. Mar. Ecol. Prog. Ser. 242,169 -177.
Fraser, K. P. P., Peck, L. S. and Clarke, A. (2004). Protein synthesis, RNA concentrations, nitrogen excretion, and metabolism vary seasonally in the Antarctic holothurian Heterocucumis steineni (Ludwig 1898). Physiol. Biochem. Zool. 77,556 -569.[CrossRef][Medline]
Garlick, P. J., Fern, M. and Preedy, V. R. (1983). The effect of insulin infusion and food intake on muscle protein synthesis in postabsorptive rats. Biochem. J. 210,669 -676.[Medline]
Gilbert, N. S. (1991). Primary production by benthic microalgae in nearshore marine sediments of Signy Island, Antarctica. Polar Biol. 11,339 -346.
Gille, S. T. (2002). Warming of the Southern Ocean since the 1950s. Science 295,1275 -1277.[CrossRef][Medline]
Grange, L. J., Tyler, P. A., Peck, L. S. and Cornelius, N. (2004). Long-term interannual cycles of the gametogenic ecology of the Antarctic brittle star Ophionotus victoriae. Mar. Ecol. Prog. Ser. 278,141 -155.
Heba, H. A. A. (1992). Protein turnover in temperate and tropical fish. PhD thesis, University of Aberdeen, UK.
Heilmayer, O., Brey, T. and Pörtner, H. O. (2004). Growth efficiency and temperature in scallops: a comparative analysis of species adapted to different temperatures. Funct. Ecol. 18,641 -647.[CrossRef]
Hoegh-Guldberg, O. and Pearse, J. S. (1995). Temperature, food availability, and the development of marine larvae. Am. Zool. 35,415 -425.
Hofmann, G. E., Lund, S. G., Place, S. P. and Whitmer, A. C. (2005). Some like it hot, some like it cold: the heat shock response is found in New Zealand but not Antarctic notothenioid fishes. J. Exp. Mar. Biol. Ecol. 316, 79-89.[CrossRef]
Houlihan, D. F. (1991). Protein turnover in ectotherms and its relationships to energetics. Adv. Comp. Environ. Physiol. 7,1 -43.
Houlihan, D. F., Hall, S. J., Gray, C. and Noble, B. S. (1988). Growth rates and protein turnover in Atlantic cod, Gadus morhua. Can. J. Fish. Aquatic Sci. 45,951 -964.
Houlihan, D. F., Hall, S. J. and Gray, C. (1989). Effects of ration on protein turnover in cod. Aquaculture 79,103 -110.[CrossRef]
Houlihan, D. F., McMillan, D. N., Agnisola, C., Genoino, I. T. and Foti, L. (1990). Protein synthesis and growth in Octopus vulgaris. Mar. Biol. 106,251 -259.[CrossRef]
Houlihan, D. F., Wieser, W., Foster, A. R. and Brechin, J. (1992). In vivo protein synthesis rates in larval nase (Chondrostoma nasus L.) Can. J. Zool. 70,2436 -2440.
Houlihan, D. F., Pannevis, M. C. and Heba, H. (1993). Protein synthesis in juvenile tilapia, Oreochromis mossambicus. J. World Aquat. Soc. 24,145 -151.[CrossRef]
Houlihan, D. F., Costello, M. J., Secombes, C. J., Stagg, R. and Brechin, J. (1994). Effects of sewage exposure on growth, feeding and protein synthesis of dab, Limanda limanda. Mar. Environ. Res. 37,331 -353.[CrossRef]
Houlihan, D. F., Carter, C. G. and McCarthy, I. D. (1995). Protein turnover in animals. In Nitrogen Metabolism and Excretion (ed. P. J. Walsh and P. Wright), pp.1 -32. Boca Raton: CRC Press.
Langar, H. and Guillaume, J. (1994). Effect of feeding pattern and dietary protein source on protein synthesis in European sea bass. Comp. Biochem. Physiol. 108A,461 -466.
Langar, H., Guillaume, J., Metailler, R. and Fauconneau, B.
(1993). Augumentation of protein synthesis and degradation by
poor amino acid balance in European sea bass (Dicentrarchus labrax).
J. Nutr. 123,1754
-1761.
Levitus, S., Antonov, J. I., Boyer, T. P. and Stephens, C.
(2000). Warming of the world ocean.
Science 287,2225
-2229.
Loughna, P. T. and Goldspink, G. (1985). Muscle
protein synthesis rates during temperature acclimation in a eurythermal
(Cyprinus carpio) and a stenothermal (Salmo gairdneri)
species of teleost. J. Exp. Biol.
118,267
-276.
Lowe, C. J. and Davison, W. (2006). Thermal sensitivity of scope for activity in Pagothenia borchgrevinki, a cryopelagic Antarctic nototheniid fish. Polar Biol. 29,971 -977.[CrossRef]
Marsh, A. G., Maxson, R. E. and Manahan, D. T.
(2001). High macromolecular synthesis with low metabolic cost in
Antarctic sea urchin embryos. Science
291,1950
-1952.
Mathers, E. M., Houlihan, D. F., McCarthy, I. D. and Burren, L. J. (1993). Rates of growth and protein synthesis correlated with nucleic acid content in fry of rainbow trout, Oncorhynchus mykiss: effects of age and temperature. J. Fish Biol. 43,245 -263.[CrossRef]
McCarthy, I. D. and Houlihan, D. F. (1996). The effect of temperature on protein metabolism in fish: the possible consequences for wild Atlantic salmon (Salmo salar L.) stocks in Europe as a result of global warming. In Global Warming: Implications for Freshwater and Marine Fish (Society for Experimental Biology Seminar Series 61) (ed. C. M. Wood and D. G. McDonald), pp.51 -77. Cambridge: Cambridge University Press.
McCarthy, I. D., Houlihan, D. F. and Carter, C. G. (1994). Individual variation in protein turnover and growth efficiency in rainbow trout, Oncorhynchus mykiss (Walbaum). Proc. R. Soc. Lond. B Biol. Sci. 257,141 -147.
McCarthy, I. D., Moksness, E., Pavlov, D. A. and Houlihan, D. F. (1999). Effects of water temperature on protein synthesis and protein growth in juvenile Atlantic wolfish (Anarhichas lupus). Can. J. Fish. Aquat. Sci. 56,231 -241.[CrossRef]
Mente, E., Houlihan, D. F. and Smith, K. (2001). Growth, feeding frequency, protein turnover, and amino acid metabolism in European lobster Homarus gammarus L. J. Exp. Zool. 289,419 -432.[CrossRef][Medline]
Meredith, M. P. and King, J. C. (2005). Rapid climate change in the ocean west of the Antarctic Peninsula during the second half of the 20th century. Geophys. Res. Lett. 32, L19604.[CrossRef]
Meyer-Burgdorff, K.-H. and Rosenow, H. (1995). Protein turnover and energy metabolism in growing carp. 3. Energy cost of protein deposition. J. Anim. Physiol. Anim. Nutr. 73,134 -139.
Nolan, C. P. and Clarke, A. (1993). Growth in the bivalve Yoldia eightsi at Signy island, Antarctica, determined from internal shell increments and Calcium-45 incorporation. Mar. Biol. 117,243 -250.[CrossRef]
O'Brien, J. J., Kumari, S. S. and Skinner, D. M. (1991). Proteins of crustacean exoskeletons: 1. Similarities and differences among proteins of the four exoskeletal layers of four Brachyurans. Biol. Bull. 181,427 -441.[Abstract]
Peck, L. S. (2002). Ecophysiology of Antarctic marine ectotherms: limits to life. Polar Biol. 25, 31-40.[CrossRef]
Peck, L. S. and Bullough, L. (1993). Growth and population structure in the infaunal bivalve Yoldia eightsi in relation to iceberg activity at Signy Island, Antarctica. Mar. Biol. 117,235 -241.[CrossRef]
Peck, L. S. and Conway, L. Z. (2000). The myth of metabolic cold adaptation: oxygen consumption in stenothermal Antarctic bivalves. In The Evolutionary Biology of the Bivalvia (Special Publications 177) (ed. E. M. Harper, J. D. Taylor and J. A. Crame), pp. 441-450. London: Geological Society London.
Peck, L. S., Webb, K. E. and Bailey, D. M. (2004). Extreme sensitivity of biological function to temperature in Antarctic marine species. Funct. Ecol. 18,625 -630.[CrossRef]
Peck, L. S., Clarke, A. and Chapman, A. L. (2006). Metabolism and development of pelagic larvae of Antarctic gastropods with mixed reproductive strategies. Mar. Ecol. Prog. Ser. 318,213 -220.
Place, S. P. and Hofmann, G. E. (2005). Constitutive expression of a stress-inducible heat shock protein gene, hsp70, in phylogenetically distant Antarctic fish. Polar Biol. 28,261 -267.[CrossRef]
Place, S. P., Zippay, M. L. and Hofmann, G. E. (2004). Constitutive roles for inducible genes: evidence for the alteration in expression of the inducible hsp70 gene in Antarctic nototheioid fishes. Am. J. Physiol. 287,R429 -R436.
Pörtner, H. O., Storch, D. and Heilmayer, O. (2005). Constraints and trade-offs in climate-dependent adaptation: energy budgets and growth in a latitudinal cline. Sci. Mar. 69,271 -285.
Preedy, V. R., Paska, L., Sugden, P. H., Scofield, P. S. and Sugden, M. C. (1988). The effects of surgical stress and short-term fasting on protein synthesis in vivo in diverse tissues of the mature rat. Biochem. J. 250,179 -188.[Medline]
Rauschert, M. (1991). Ergebnisse der faunistischen arbeiten im benthal von King George Island (Südshetlandinseln, Antarctis). Ber. Polarforsch. 76, 1-75.
Ricker, W. E. (1979). Growth rates and models. In Fish Physiology. Vol. 8 (ed. W. S. Hoar, D. J. Randall and J. R. Brett), pp.677 -741. New York: Academic Press.
Roberston, R. F., El-Haj, A. J., Clarke, A. and Taylor, E. W. (2001a). Effects of temperature on specific dynamic action and protein synthesis rates in the Baltic isopod crustacean, Saduria entomon. J. Exp. Mar. Biol. Ecol. 262,113 -129.[CrossRef]
Robertson, R. F., El-Haj, A. J., Clarke, A., Peck, L. S. and Taylor, E. W. (2001b). The effects of temperature on metabolic rate and protein synthesis following a meal in the isopod Glyptonotus antarcticus Eights (1852). Polar Biol. 24,677 -686.[CrossRef]
Storch, D., Heilmayer, O., Hardewig, I. and Pörtner, H. O. (2003). In vitro protein synthesis capacities in a cold stenothermal and a temperate eurythermal pectinid. J. Comp. Physiol. B 173,611 -620.[CrossRef][Medline]
Storch, D., Lannig, G. and Pörtner, H. O.
(2005). Temperature-dependent protein synthesis capacities in
Antarctic and temperate (North Sea) fish (Zoarcidae). J. Exp.
Biol. 208,2409
-2420.
Sveier, H., Raae, A. J. and Lied, E. (2001). Growth and protein turnover in Atlantic salmon (Salmo salar L.); the effect of dietary protein level and particle size. Aquaculture 185,101 -120.[CrossRef]
Whiteley, N. M., Taylor, E. W. and El Haj, A. J. (1996). A comparison of the metabolic cost of protein synthesis in stenothermal and eurythermal isopod crustaceans. Am. J. Physiol. 271,R1295 -R1303.[Medline]
Whiteley, N. M., Robertson, R. F., Meagor, J., El Haj, A. J. and Taylor, E. W. (2001). Protein synthesis and specific dynamic action in crustaceans: effects of temperature. Comp. Biochem. Physiol. 128A,595 -606.
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