Variations in larval instar number are common among arthropods.Here, we assess the implications of temperaturemediated variations in larval instar number for larval development time, larval growth rates, and juvenile dry weight within the palaemonid shrimp, Palaemonetes varians.In contrast with previous literature, which focuses on terrestrial arthropods, particularly model and pest species often of laboratory lines, we use wild shrimp, which differ in their life history from previous models.Newly-hatched P. varians larvae were first reared at 5, 10, 17, 25, and 30uC to assess their thermal scope for development.Larvae developed at 17, 25, and 30uC.At higher temperatures, larvae developed through fewer larval instars.Two dominant developmental pathways were observed; a short pathway of four instars and a long pathway of five instars.Longer developmental pathways of six to seven instars were rarely observed (mostly at lower temperatures) and consisted of additional instars as 'repeat' instars; i.e. little developmental advance over the preceding instar.To assess the implications of temperature-mediated variation in larval instar number, newly-hatched larvae were then reared at 15, 20, and 25uC.Again, the proportion of larvae developing through four instars increased with temperature.At all temperatures, larval development time and juvenile dry weight were greater for larvae developing through five instars.Importantly, because of the increasing proportion of larvae developing through four instars with increasing temperature, larval traits associated with this pathway (reduced development time and juvenile dry weight) became more dominant.As a consequence of increasing growth rate with temperature, and the shift in the proportion of larvae developing through four instars, juvenile dry weight was greatest at intermediate temperatures (20uC).We conclude that at settlement P. varians juveniles do not follow the temperature-size rule; this is of importance for life-history ecology in response to environmental change, as well as for aquaculture applications.
Abstract Global average temperatures and seawater pCO 2 have rapidly increased due to the oceanic uptake of atmospheric carbon dioxide producing severe consequences for a broad range of species. The impacts on marine ectotherms have been largely reported at short-term scales (i.e. from days to weeks); however, the prolonged effects on long-term processes such as reproduction have received little attention. The gastropod Ocenebra erinaceus is a key predator structuring communities on rocky shores of the French and UK coasts. Even though rocky shore species are regarded as being very tolerant to changes in temperature and pH, many of them are living near their upper tolerance limits, making them susceptible to rapid environmental changes. Here, we report that future mean seawater conditions (RCP8.5, + 3 °C and ~ 900 μatm CO 2 ) do not significantly affect the physiology and molecular response of O. erinaceus adults after 132 days. During the first 50 days, there was a slight impact on oxygen consumption rates and body weight; however, after 95 days of exposure, gastropods fully acclimated to the experimental condition. Despite this, reproduction in females exposed to these future seawater conditions ceased after long-term exposure (~ 10 months). Therefore, in the short-term, O. erinaceus appear to be capable of full compensation; however, in the long-term, they fail to invest in reproduction. We conclude studies should be based on combined results from both short- and long-term effects, to present realistic projections of the ecological consequences of climate warming.
Mineral prospecting in the deep sea is increasing, promoting concern regarding potential ecotoxicological impacts on deep-sea fauna. Technological difficulties in assessing toxicity in deep-sea species has promoted interest in developing shallow-water ecotoxicological proxy species. However, it is unclear how the low temperature and high hydrostatic pressure prevalent in the deep sea affect toxicity, and whether adaptation to deep-sea environmental conditions moderates any effects of these factors. To address these uncertainties we assessed the effects of temperature and hydrostatic pressure on lethal and sublethal (respiration rate, antioxidant enzyme activity) toxicity in acute (96 h) copper and cadmium exposures, using the shallow-water ecophysiological model organism Palaemon varians. Low temperature reduced toxicity in both metals, but reduced cadmium toxicity significantly more. In contrast, elevated hydrostatic pressure increased copper toxicity, but did not affect cadmium toxicity. The synergistic interaction between copper and cadmium was not affected by low temperature, but high hydrostatic pressure significantly enhanced the synergism. Differential environmental effects on toxicity suggest different mechanisms of action for copper and cadmium, and highlight that mechanistic understanding of toxicity is fundamental to predicting environmental effects on toxicity. Although results infer that sensitivity to toxicants differs across biogeographic ranges, shallow-water species may be suitable ecotoxicological proxies for deep-sea species, dependent on adaptation to habitats with similar environmental variability.
There are few factors more important to the mechanisms of evolution than stress. The stress response has formed as a result of natural selection, improving the capacity of organisms to withstand situations that require action. The ubiquity of the cellular stress response suggests that effective mechanisms to counteract stress emerged early in the history of life, and their commonality proves how vital such mechanisms are to operative evolution. The cellular stress response ( CSR ) has been identified as a characteristic of cells in all three domains of life and consists of a core 44 proteins that are structurally highly conserved and that have been termed the ‘minimal stress proteome’ ( MSP ). Within the MSP , the most intensely researched proteins are a family of heat‐shock proteins known as HSP 70. Superficially, correlations between the induction of stress and HSP 70 differential expression support the use of HSP 70 expression as a nonspecific biomarker of stress. However, we argue that too often authors have failed to question exactly what HSP 70 differential expression signifies. Herein, we argue that HSP 70 up‐regulation in response to stressors has been shown to be far more complex than the commonly accepted quasi‐linear relationship. In addition, in many instances, the uncertain identity and function of heat‐shock proteins and heat‐shock cognates has led to difficulties in interpretation of reports of inducible heat‐shock proteins and constitutive heat‐shock cognates. We caution against the broad application of HSP 70 as a biomarker of stress in isolation and conclude that the application of HSP 70 as a meaningful index of stress requires a higher degree of validation than the majority of research currently undertakes.
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