N.M. Whiteley

Protein synthesis and specific dynamic action in crustaceans: effects of temperature

Temperature influences the specific dynamic action (SDA), or rise in oxygen uptake rate after feeding, in eurythermal and stenothermal crustaceans by changing the timing and the magnitude of the response. Intra-specific studies on the eurythermal crab, Carcinus maenas, show that a reduction in acclimation temperature is associated with a decrease in SDA magnitude, resulting from an increase in SDA duration but a decrease in peak factorial scope (the factorial rise in peak SDA over prefeeding values). Inter-specific feeding studies on stenothermal polar isopods revealed marked differences in SDA response between the Antarctic species, Glyptonotus antarcticus and the Arctic species, Saduria entomon. Compared to S. entomon held at 4 and 13 degrees C, the SDA response in G. antarcticus held at 1 degrees C was characterised by a lower absolute oxygen uptake rate at peak SDA and an extended SDA duration. At peak SDA, whole animal rates of protein synthesis increased in proportion to the postprandial increase in oxygen uptake rate in the Antarctic and the Arctic species. Rates of oxygen uptake plotted against whole animal rates of protein synthesis gave similar relationships in both isopod species, indicating similar costs of protein synthesis after a meal, despite their differences in SDA response and thermal habitat.

Probing marine Gammarus (Amphipoda) taxonomy with DNA barcodes

Abstract The genus Gammarus (Amphipoda) is one of the most speciose genera of Crustacea, yet much uncertainty remains concerning taxonomy and systematic relationships, particularly for brackish and marine forms. We used DNA barcode sequences from the mitochondrial cytochrome c oxidase I (COI) gene to probe the taxonomy of prominent members of marine and brackish water Gammarus of the North Atlantic, Baltic, Mediterranean and Black Seas. We investigated 16 putative Gammarus spp. at an average number of 9 specimens per species. This constitutes the most taxonomically and geographically comprehensive molecular study of marine Gammarus to date. Average between‐species sequence divergence (26.8%) was much higher than intraspecific distances (0.8%), enabling clear molecular species identification and highlighting several possible misidentifications from previously published studies. Specimens of Gammarus aequicauda and G. insensibilis from the Black Sea were at least 14% distant from their putative conspecifics elsewhere. Placing these findings in a geographic context provides strong indication of cryptic speciation. Further, we detected phylogeographic splits in G. oceanicus and G. duebeni. Our analyses also suggest phylogenetic positioning of G. marinus with members of the genus Echinogammarus, thus confirming its classification as Echinogammarus marinus. We have demonstrated that comprehensive analyses of taxonomically complex groups using DNA barcodes can result in a diversity of complementary data on taxonomy, phylogeography and phylogenetics. The combination of these results, with further morphological and ecological data, will enable significant progress in our understanding of this ecologically important group of crustaceans.

Ionoregulatory Changes in the Gill Epithelia of Coho Salmon during Seawater Acclimation

Short‐term exposure of coho salmon smolts (Oncorhynchus kisutch) to a gradual increase in salinity over 2 d (0‰–32‰) resulted in a decrease in proton pump abundance, detected as changes in immunoreactivity with a polyclonal antibody against subunit A of bovine brain vacuolar H+‐ATPase. N‐ethylmaleimide (NEM)–sensitive H+‐ATPase activities in gill homogenates remained unchanged over 8 d to coincide with a 3.5‐fold increase in Na+/K+‐ATPase activities. A transient increase in plasma [Na+] and [Cl−] levels over the 8‐d period was preceded by a 10‐fold increase in plasma cortisol levels, which peaked after 12 h. Long‐term (1 mo) acclimation to seawater resulted in the loss of apical immunoreactivity for vH+‐ATPase and band 3–like anion exchanger in the mitochondria‐rich cells identified by high levels of Na+/K+‐ATPase immunoreactivity. The polyclonal antibody Ab597 recognized a Na+/H+ exchanger (NHE‐2)–like protein in what appears to be an accessory cell (AC) type. Populations of these ACs were found associated with Na+/K+‐ATPase rich chloride cells in both freshwater‐ and seawater‐acclimated animals.

Estimating the energetic cost of fighting in shore crabs by noninvasive monitoring of heartbeat rate

After establishing shore crabs, Carcinus maenas, individually in separate aquaria, we used a noninvasive infrared phototransducer to monitor their heartbeat rate continously before, during and after fights with intruder crabs. We confirmed that heartbeat rate is a reliable indicator of oxygen consumption and then used it to estimate indirectly the energetic cost of fights differing in duration and intensity, and its dependence on prior residence and relative size of opponent. Prior residence in aquaria significantly increased the probability that crabs would initiate fights against intruders. The majority of fights were resolved by aggressive contacts, display being used extensively only against smaller intruders. Fights between evenly sized opponents and between residents and larger intruders involved almost continuous aggression, whereas fights with smaller intruders involved several shorter bouts of aggression. Fight duration was weakly correlated with the relative size of opponents. Heartbeat rate, measured only in residents, was elevated above resting levels throughout fights, hence energy expenditure during fighting increased linearly with fight duration. Contrary to expectation, heartbeat rate was not significantly influenced by relative size of the opponent or by the intensity of aggression. After fighting, heartbeat rate usually returned to resting levels within 30-60 min, recovery taking longer in fights against larger intruders, when the fight was always lost. We propose that prolonged elevation of heartbeat rate in residents that had lost to larger intruders represented a state of alertness, adaptive against impending risks of resource loss or injury. Copyright 2000 The Association for the Study of Animal Behaviour.

Phylogeography and environmental diversification of a highly adaptable marine amphipod, Gammarus duebeni.

Genetic diversity and phylogeographic population structure in the gammarid amphipod, Gammarus duebeni, were investigated across its broad latitudinal distribution in the NE and NW Atlantic by analysis of mitochondrial DNA sequence. Gammarus duebeni has exceptional tolerance of salinity change and inhabits environments ranging from marine to freshwater. The longstanding debate on whether there are distinct marine and freshwater subspecies was assessed by sampling populations from sites characterized by different salinities. Our sequence data demonstrates that there are two major lineages, with little internal geographic structuring. Evidence is provided to suggest a pre-glacial divergence of these two clades, involving segregation between a region historically associated with the freshwater form and the majority of the marine localities on both sides of the Atlantic. A modern contact zone between the marine and freshwater forms is proposed in western Britain.

Ocean warming, more than acidification, reduces shell strength in a commercial shellfish species during food limitation.

Ocean surface pH levels are predicted to fall by 0.3–0.4 pH units by the end of the century and are likely to coincide with an increase in sea surface temperature of 2–4°C. The combined effect of ocean acidification and warming on the functional properties of bivalve shells is largely unknown and of growing concern as the shell provides protection from mechanical and environmental challenges. We examined the effects of near-future pH (ambient pH –0.4 pH units) and warming (ambient temperature +4°C) on the shells of the commercially important bivalve, Mytilus edulis when fed for a limited period (4–6 h day−1). After six months exposure, warming, but not acidification, significantly reduced shell strength determined as reductions in the maximum load endured by the shells. However, acidification resulted in a reduction in shell flex before failure. Reductions in shell strength with warming could not be explained by alterations in morphology, or shell composition but were accompanied by reductions in shell surface area, and by a fall in whole-body condition index. It appears that warming has an indirect effect on shell strength by re-allocating energy from shell formation to support temperature-related increases in maintenance costs, especially as food supply was limited and the mussels were probably relying on internal energy reserves. The maintenance of shell strength despite seawater acidification suggests that biomineralisation processes are unaffected by the associated changes in CaCO3 saturation levels. We conclude that under near-future climate change conditions, ocean warming will pose a greater risk to shell integrity in M. edulis than ocean acidification when food availability is limited.

Congeneric amphipods show differing abilities to maintain metabolic rates with latitude.

Metabolic variability across latitudinal populations of gammarid amphipods was examined in the summer by determining whole-animal rates of oxygen uptake () in four species with overlapping distribution patterns in the northeast Atlantic and Arctic oceans. Comparisons were made between an arctic/boreal species, Gammarus setosus, a subarctic/boreal species, Gammarus oceanicus, a boreal/temperate species, Gammarus duebeni duebeni, and a temperate species, Gammarus locusta. Measurements included acclimatized in all four species and after acclimation to 10°C in two populations of G. oceanicus and G. locusta. In G. oceanicus, acclimatized declined with latitude (13° to 5°C) so that metabolic rates were lower in subarctic (79°N) relative to temperate (58°N) populations and similar to the values in G. setosus at 79°N. Consequently, there was no evidence for metabolic rate compensation in the colder-water, high-latitude populations in the summer. Further examination of the specific effects of temperature revealed similarities in between populations of G. oceanicus acclimated at 10°C and similarities in thermal sensitivity (Q10) and activation energies (Ea) on exposure to acute temperature change. In sharp contrast, there was no variation in summer acclimatized with latitude in either G. d. duebeni between 48° and 70°N or G. locusta between 38° and 53°N. Instead, the two species maintained relatively high metabolic rates across latitudes, which were associated in G. locusta with differences in and with Q10 and Ea values in amphipods acclimated at 10°C. The ability to compensate metabolic rate with latitude in the summer suggests greater metabolic flexibility, which predicts a greater capacity for survival during climate change of the temperate/boreal over the subarctic and arctic gammarid species.

Genetic diversity of the feminising microsporidian parasite Dictyocoela: New insights into host-specificity, sex and phylogeography

Microsporidia of the genus Dictyocoela are parasites of gammarid amphipod Crustacea. They typically exhibit low virulence and efficient vertical transmission and at least some strains are capable of feminising their hosts. Sequencing of a region of the 16S rDNA of Dictyocoela spp. from various gammarid host species and localities in Europe and northern Asia indicates that Dictyocoela is genetically diverse and that different strains predominate in different host species. However, the presence of intermediate sequences casts doubt upon previous attempts to describe Dictyocoela spp. on the basis of rDNA divergence alone. Phylogenetic analysis provides little support for coevolution between gammarids and Dictyocoela. Furthermore, observations of heavily infected individuals, together with genetic evidence of recombination, suggest that some strains of Dictyocoela may be horizontally transmitted and are sexually reproducing. These findings suggest that Dictyocoela may be phenotypically, as well as genotypically, diverse, with the potential to exhibit a range of different interactions with its host populations.

Effects of salinity on rates of protein synthesis and oxygen uptake in the post-larvae and juveniles of the tropical prawn Macrobrachium rosenbergii (de Man).

Protein synthesis is a major determinant of growth and yet little is known about the environmental factors that influence protein synthesis rates in farmed freshwater prawns. To this end, post-larvae and juveniles of Macrobrachium rosenbergii were exposed to various salinities (0, 14, 30 per thousand) to determine whole-animal rates of fractional protein synthesis (k(s)) and oxygen uptake. In the post-larvae that migrate upstream from brackish to freshwater areas, whole-animal k(s) was unaffected by salinity, but rates of oxygen uptake were significantly lower at 14 per thousand. In the freshwater juveniles, a different response was observed, as mean k(s) was significantly higher at 14 per thousand compared with 0 per thousand, but rates of oxygen uptake remained unchanged. Such differences are thought to be related to the energetic costs of osmoregulation and to the ability to maintain osmotic gradients in freshwater. In an additional experiment, acclimation temperature (20, 26, 30 degrees C) had a direct effect on k(s) in juveniles held at 0 per thousand. In all cases, changes in k(s) resulted from alterations in RNA activity at constant RNA capacity. In juveniles at least, whole-animal rates of protein synthesis were highest at 14 per thousand and 30 degrees C which corresponds to the optimal salinity and temperature recommended for the growth and culture of M. rosenbergii.

Temperature Influences Whole-Animal Rates of Metabolism but Not Protein Synthesis in a Temperate Intertidal Isopod

The effects of temperature on two important biological rate processes, whole‐body rates of oxygen uptake (Ṁo2) and protein synthesis (ks), were investigated in the temperate intertidal isopod Ligia oceanica at two different times of the year. Animals were collected in January (winter) and June (summer) and either subjected to an acute temperature change after 24 h (acclimatized) or acclimated to various temperatures for 4 wk. In both cases, Ṁo2 increased with temperature, with a Q10 of 2.2 between 5° and 20°C, but increased in thermal sensitivity at 25°C. Winter isopods were characterized by significantly higher Ṁo2 levels, greater thermal sensitivities, and lower thermal tolerances than summer animals. Seasonal differences in Ṁo2 persisted after acclimation, indicating that temperature alone was not responsible for the changes. In sharp contrast, whole‐body ks showed no variation with temperature, although overall rates decreased upon acclimation. In acclimatized animals, ks was higher in the summer than in the winter. After acclimation, a compensatory increase in RNA capacity in winter animals reversed this situation. The temperature independence of whole‐body ks in L. oceanica could ensure survival in a highly liable thermal environment, as thermal tolerances of intertidal invertebrates are thought to be more closely related to protein than to energy metabolism.