Partitioning of respiratory energy and environmental tolerance in the copepods Calanipeda aquaedulcis and Arctodiaptomus salinus

Summary Reduced metabolic rates of groundwater taxa, compared to those of surface water species, have long been inferred to be an adaptive trait where there is a low and discontinuous food supply and unpredictable shifts between hypoxic and normoxic conditions. However, there have been neither measurements of the respiratory rate of groundwater copepods nor a comparison of rates between closely related groundwater and surface water species. We measured the metabolic rates of two species of Cyclopoida: Cyclopidae, the stygobiotic (hypogean) copepod Diacyclops belgicus and the epigean Eucyclops serrulatus, which co‐occur in the same alluvial aquifer. We expected the metabolic rate of the hypogean to be lower than that of the epigean species, irrespective of the ontogenetic stage, which would be consistent with the hypothesis that there is a generally lower metabolic rate in groundwater species. The metabolic rate of D. belgicus was significantly lower than that of the epigean E. serrulatus irrespective of the ontogenetic stage. We found an allometric relationship between oxygen consumption and body mass for E. serrulatus, an isometric one for D. belgicus juveniles and a rate of oxygen consumption that apparently does not change systematically with body mass for D. belgicus adults. The low metabolic rate of D. belgicus may be advantageous in oligotrophic groundwater habitats, where large fluctuations in oxygen availability occur. However, these physiological adaptations can put hypogean species at risk of replacement by more metabolically active epigean taxa, whenever the availability of organic matter increases, as happens with organic pollution. Moreover, the low metabolic rate of the hypogean species may entail an inability to cope with toxicants, rendering them more sensitive to pollutants. A higher metabolic rate in juvenile D. belgicus compared to that of adults allows copepodids to mature quickly when food is briefly abundant.

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“…We calculated the dry mass of each individual (DM ind ) in the pool according to Svetlichny et al . () measured as:

{DM}_{normalind} = CF {normalL}_{normalind} * {normalW}_{ind}^{2}

, where CF is stage‐ and species‐specific condition factor calculated as

CF = {DM}_{normalp} / {normalL}_{normalm} * {normalW}_{m}^{2}

, where DM p is the dry mass of a pool, and L m and W m are the mean values of pool‐specific size metrics.…”

Section: Methodsmentioning

confidence: 99%

Metabolic rates of a hypogean and an epigean species of copepod in an alluvial aquifer

et al. 2014

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“…S1B) and reported contributions of foraging costs to total consumers’ energy budgets range from negligible to >40% (Svetlichny et al. ). Contrasting results may partly be explained by changes in the relative importance of foraging costs with food quantity (Fig.…”

Section: Model Constructionmentioning

confidence: 99%

Food quantity–quality interactions and their impact on consumer behavior and trophic transfer

Burian

Nielsen

Winder

2019

Ecological Monographs

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Food quantity–quality interactions determine growth rates and reproductive success of consumers and thereby regulate community dynamics and food web structure. Predator–prey models that shape our conceptual understanding of foraging ecology typically rely on the parametrization of fixed consumer responses to either food quantity or food quality. In nature, however, consumers optimize their fitness by responding simultaneously to changes in food quantity and quality. Therefore, we assessed consumer responses to changing food environments using a new fitness optimization model that accounted for food quality–quantity interactions to better capture the regulatory flexibility of consumers. Our simulations demonstrated that the impact of food quality on important consumer traits can be altered or even reversed by changes in food quality. Low food quality, for example, affected feeding rates negatively at low food concentrations but triggered surplus feeding at high food concentrations. The scope of surplus feeding was thereby mainly dependent on dynamics of nutrient digestion and in contrast to previous assumptions, energy costs of feeding played a minor role. Further, the regulation of digestive enzyme production, a crucial factor determining assimilation efficiencies, was strongly dependent on whether nonessential or essential nutrients were limiting growth. Consequently, not only the degree but also the type of nutrient limitation mediated the impact of the food environment on consumers’ fitness. At the community level, food quality was key in shaping predator–prey biomass ratios. High food qualities resulted in top‐heavy systems with larger consumer than prey biomass. Decreases of prey digestibility or the availability of essential nutrients, however, triggered a switch from inverted to classical pyramid shapes of bi‐trophic systems. The impact of food quantity on trophic transfer and emerging structural ecosystem properties thus critically hinges on behavioral and physiological responses of consumers. The inclusion of the regulatory flexibility of consumers is therefore an essential next step to improve predator–prey models and our conceptual understanding of trophic interactions.

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“…This suggests different physiological responses to the dual stressors of temperature and oxygen between the sexes, potentially in response to different energetic demands between males and females or reproduction behaviors (Burrows & Tarling 2004, Kessler 2004. Specifically, oxygen demand and respiration rate have been shown to increase for reproductively active female copepods (Svetlichny et al 2012, Castellani & Altunbas 2014, which may require females to reside in shallower and more oxygenated water. In addition, the behavior which drives them to reside in surface waters where they release their eggs at night (White & Roman 1992) would serve to maximize the probability that they hatch before reaching hypoxic bottom waters.…”

Section: Discussionmentioning

confidence: 99%

Synergistic effects of seasonal deoxygenation and temperature truncate copepod vertical migration and distribution

Pierson¹,

Slater²,

Elliott³

et al. 2017

Mar. Ecol. Prog. Ser.

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The vertical distribution of copepods in coastal and estuarine systems is altered by the concentration of dissolved oxygen in the water column. We studied the combined effects of temperature and dissolved oxygen on vertical distribution and migration behavior of the copepod Acartia tonsa in the Chesapeake Bay throughout the period of seasonal deoxygenation in 2010 and 2011. Vertically stratified net tows and hydrographic casts were conducted at 2 stations over diel cycles in spring, summer, and autumn. The partial pressure of dissolved oxygen (pO 2 ) was used as a metric for the condition of copepod habitat during each cruise instead of oxygen concentration, because partial pressure incorporates the temperature dependence of dissolved oxygen solubility, making it a more useful indication of available oxygen supply than concentration. Habitat conditions were described as having pO 2 above limiting conditions, below the maximum respiratory demand but above potentially lethal conditions, or below the minimum basal respiratory demand. In general, adult males were found deeper in the water than females in most oxygen conditions. Regression tree analysis supported these findings and showed that pO 2 was a key predictor of the fraction of copepodites, adult females, and adult males above the pycnocline, and for copepodites and adult females below the pycnocline. Temperature was a strong predictor of the fraction of adult males below the pycnocline, with a smaller fraction found there at higher temperatures. These findings suggest sex-specific responses to deoxygenation, potentially as a result of different oxygen demands or behavior.

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Partitioning of respiratory energy and environmental tolerance in the copepods Calanipeda aquaedulcis and Arctodiaptomus salinus

Cited by 31 publications

References 54 publications

Metabolic rates of a hypogean and an epigean species of copepod in an alluvial aquifer

Metabolic rates of a hypogean and an epigean species of copepod in an alluvial aquifer

Food quantity–quality interactions and their impact on consumer behavior and trophic transfer

Synergistic effects of seasonal deoxygenation and temperature truncate copepod vertical migration and distribution

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