Effects of the natural tidal cycle and artificial temperature cycling on Hsp levels in the tidepool sculpin Oligocottus maculosus

The rocky intertidal zone is characterized by a predictable cycle of environmental change cued by the ebb and flow of the tides. Tidepools are thus an excellent environment in which to determine whether predictability of environmental change can entrain an endogenous rhythmicity in heat shock protein (Hsp) levels. In this study, we monitored changes in Hsp mRNA and protein levels that occurred over the tidal cycle in tidepool sculpins and investigated whether there was an endogenous tidal rhythm in Hsp expression that persisted once the sculpins were transferred to a stable environment. Fluctuations in the tidepool environment increased hsc70, hsp70, and hsp90 mRNA levels, which translated into increased Hsc/Hsp70 and Hsp90 protein levels; however, this was not due to an endogenous tidal rhythm in Hsp levels because sculpins held under constant conditions did not show any rhythmicity in the expression of these genes. By exposing sculpins to an artificial temperature cycling regime that mimicked the temperature changes of a mid-intertidal pool, we were able to account for the direct role of temperature in regulating Hsp expression. However, there are additional extrinsic factors that likely integrate with temperature and result in differences between the hsp induction profiles that were observed in sculpins inhabiting their natural environment and those in cycling conditions in the laboratory.     

Prevalence and intensity of Pseudodelphis oligocotti n. gen., n. sp. (Dracunculoidea; Guyanemidae) in the tidepool sculpin, Oligocottus maculosus (Scorpaeniformes; Cottidae)

Pseudodelphis oligocotti n. gen., n. sp. (Dracunculoidea; Guyanemidae) is described from the tidepool sculpin, Oligocottus maculosus (Scorpaeniformes; Cottidae), from various localities in coastal British Columbia. The species is placed in Guyanemidae because of its reduced buccal capsule, divided esophagus, functional vulva, and single ovary. It is distinguished from Guyanema, the only other genus in the family, by the absence of caudal alae and the arrangement of caudal papillae in the male. Females of the new genus are distinguished from those of Guyanema by the presence of a blind uterine diverticulum, without associated oviduct and ovary, extending anteriorly from the junction of the posterior uterus and vagina, and a more posteriorly positioned vulva. Fish were sampled every 2 wk throughout 1988. Worms were overdispersed in the host population. Prevalence and mean intensity of infection were highest from February to March.     

Growth and reproduction of the tidepool sculpinOligocottus maculosus

Growth and reproduction of tidepool sculpins (Oligocottus maculosus) from three sites in Puget Sound, Washington State, USA were characterized. One site was a sandy, gently sloping beach, the second was an exposed rock headland with minimal algal cover, and the third was an exposed rock headland with numerous tidepools containing abundant algal cover. Length-weight relationships for sculpins did not differ significantly between sexes within sites. Population age structure, growth rate and recruitment varied among the three study sites using data pooled across both sexes. Young-of-the-year sculpins comprised 91% of the population at the exposed headland site with minimal algal cover but only 6% at the headland with abundant algal cover. Selective predation by great blue herons (Ardea herodias) upon tidepool sculpins larger than 45 mm total length assisted in the maintainance of these age structures. A maximum gonadosomatic index of 28.5 was calculated; this index correlated poorly with either age, length or somatic weight. Diameters of unshed ova from preserved tidepool sculpins sampled prior to spawning fell into three classes. Comparison of the mean egg size of each mode and the number of modes present in preserved sculpins with similar data from tidepool sculpins that spawned in the laboratory suggested that spawning occurred twice yearly from at least January through August.     

Cross-tolerance in the tidepool sculpin: the role of heat shock proteins

Cross-tolerance, or the ability of one stressor to transiently increase tolerance to a second heterologous stressor, is thought to involve the induction of heat shock proteins (Hsp). We thus investigated the boundaries of cross-tolerance in tidepool sculpins (Oligocottus maculosus) and their relationship to Hsp70 levels. Survival of sculpins exposed to severe osmotic (90 ppt, 2 h) and hypoxic (0.33 mg O(2)/L, 2 h) stressors increased from 68% to 96%, and from 47% to 76%, respectively, following a +12 degrees C heat shock. The magnitude of this heat shock was critical for protection. A +10 degrees C heat shock did not confer cross-tolerance, while a +15 degrees C heat shock was deleterious. Sculpins required between 8 and 48 h of recovery following the +12 degrees C heat shock to develop cross-tolerance. There was no association between Hsp70 levels before the onset of the secondary stressor and cross-tolerance. However, branchial Hsp70 levels following osmotic shock were highly correlated with the time frame of cross-tolerance. Thus, Hsp70 induction by the priming stressor may be less important than the ability of the cell to mount an Hsp response to subsequent stressors. The time frame of cross-tolerance is similar to the interval between low tides, suggesting the possible relevance of this response in nature.     

The Response of the Tidepool Sculpin,Oligocottus maculosus,to Chemical Stimuli from Injured Conspecifics,Alarm Signalling in the Cottidae (Pisces)

The tidepool sculpin, Oligocottus maculosus, a small, cottiid fish of the Pacific coast of North America, shows reduced movement, less feeding activity, a greater tendency to attach itself to the substrate, and a shift from exposed areas to shelters and crevices when presented with water that has contained injured conspecifics. This alarm reaction does not occur in response to water that has contained uninjured, but disturbed, O. maculosus, or injured guppies, Poecilia reticulata, O. maculosus are not toxic or distasteful to piscine predators. They do possess large, epidermal sacciform cells that may contain the active chemical(s) released by injured individuals. This is the first report of chemical alarm signalling in Cottidae.     

The 70-kDa heat shock protein response in two intertidal sculpins,Oligocottus maculosus and O. snyderi: relationship of hsp70 and thermal tolerance

The role that hsp70 plays in influencing thermal tolerance of a whole animal is not clearly understood. We explored this question by examining liver hsp70 response in the tidepool sculpin (Oligocottus maculosus) and fluffy sculpin (O. snyderi), which have distinct distribution patterns in the intertidal zone. The tidepool sculpin is in upper and lower tidepools, while the fluffy sculpin is exclusively in lower tidepools during a low tide. We conducted experiments in order to investigate: (1) habitat water temperatures; (2) upper thermal tolerance limits; (3) the cellular hsp70 response to changes in water temperature in nature; (4) induction temperatures for hepatic hsp70 and hsp70 mRNA; and (5) effects of long-term heat stress on liver hsp70 levels, in these sculpins. Accordingly, we found: (1) the tidepool sculpin was exposed to a wider temperature range in nature; (2) the tidepool sculpin had higher lethal and induction temperatures for hsp70; (3) the liver hsp70 level of the tidepool sculpin was less sensitive to changes in water temperatures; and (4) the tidepool sculpin had higher constitutive hsp70 levels in nature, compared with the fluffy sculpin. From these results, we proposed that the less thermally sensitive tidepool sculpin may enhance its thermal tolerance by having a large pool of cellular hsp70, thus allowing it to inhabit the upper intertidal zone with relatively large and unpredictable fluctuations in environmental variables.     

The Influence of Substrate Color on the Alarm Response of Tidepool Sculpins (Oligocottus maculosus; Pisces,Cottidae)

For animals that use crypsis to avoid predators, immobility reduces the risk of detection. The magnitude of this immobility benefit depends upon the probability that a predator is present, since a predator must be present for crypsis to be valuable. Thus, cryptic animals typically reduce their movement rates upon detection of a nearby predator or signs of its activity. Such a response occurs in tidepool sculpins (Oligocottus maculosus) when presented with water-borne compounds released from the skin of injured conspecifics (Hugie et al. 1991). The benefit of immobility should also depend upon the animal's background, or substrate, since animals on a matching substrate achieve a higher level of crypticity than those on a nonmatching substrate, and have more to gain by remaining still. Therefore, we predicted that the response of tidepool sculpins to conspecific skin extract would involve a greater reduction in movement rates for fish on sand (matching) than for those on white (nonmatching) substrate. The results of a laboratory experiment supported this prediction, with fish on sand showing a large decrease in movement rates in response to skin extract, while the movement rates of those on white substrate remained unchanged.     

Zooplankton response to shading effects of free-floating plants in shallow warm temperate lakes: a field mesocosm experiment

Dense mats of free floating plants (FFP) often produce severe underwater light attenuation and strong oxygen depletion in the water column. In this study, we experimentally assessed the zooplankton response to artificial shading using field mesocosms. During 30 days, we simulated three different light scenarios by mimicking the persistence, absence, and fluctuation of FFP typically encountered in vegetated shallow subtropical lakes. We used dark meshes to simulate the abiotic effects engineered by FFP. Both in the permanently covered and fluctuating situations, anoxia impaired zooplankton development. Anoxia constituted a major driving force in shaping the zooplankton response, whereas the feeding resource availability (phytoplankton) seemed to play a minor role; no top down effect on phytoplankton occurred in anoxic situations. In the fluctuating cover regime (periodic darkness and anoxia), the temporal variation of nanophytoplankton was not affected by zooplankton; once again oxygen availability seemed the main force shaping the zooplankton dynamics. Either periodical or permanent shading, associated to anoxic conditions, impaired the success of small herbivores. Large herbivores and microphytoplankton were negatively affected only under persistent shade and anoxia. In contrast, when neither light nor oxygen limitation occurred, such as in the scenario without shading, top-down control occurred. This study highlights the importance that the oxygen dynamics driven by the presence of FFP exert on the structure and dynamics of zooplankton assemblages and on the top down cascading effects on phytoplankton in warm temperate or subtropical shallow lakes.     

Photosynthetic traits in C3 and C4 grassland species in mesocosm and field environments

The North American tallgrass prairie is composed of a diverse mix of C₃ and C₄ plant species that are subject to multiple resource limitations. C₄ grasses dominate this ecosystem, purportedly due to greater photosynthetic capacity and resource-use efficiency associated with C₄ photosynthesis. We tested the hypothesis that intrinsic physiological differences between C₃ and C₄ species are consistent with C₄ grass dominance by comparing leaf gas exchange and chlorophyll fluorescence variables for seven C₄ and C₃ herbaceous species (legumes and non-legumes) in two different settings: experimental mesocosms and natural grassland sites. In the mesocosms, C₄ grasses had higher photosynthetic rates, water potentials and water-use efficiency than the C₃ species. These differences were absent in the field, where photosynthetic rates declined similarly among non-leguminous species. Thus, intrinsic photosynthetic advantages for C₄ species measured in resource-rich mesocosms could not explain the dominance of C₄ species in the field. Instead, C₄ dominance in this ecosystem may depend more on the ability of the grasses to grow rapidly when resources are plentiful and to tolerate multiple limitations when resources are scarce.     

Beta-hydroxybutyrate and response to hypoxia in the ground squirrel, Spermophilus tridecimlineatus

1. Previous studies have suggested that elevated ketone levels are associated with increased survival time in rodents exposed to hypoxia. In this study the association between whole blood BHB (beta-hydroxybutyrate) and hypoxic survival time was investigated in hibernating and non-hibernating ground squirrels and in rats. 2. Non-hibernating ground squirrels and rats were exposed to hypoxia (4.5% O2). One hundred per cent of ground squirrels survived 1 hr of hypoxia vs 20% of rats. 3. Ketone levels were significantly higher in ground squirrels than rats during hypoxia, and rats surviving the longest had the highest ketone levels. 4. When hibernation was induced in ground squirrels there was a significant increase in beta-hydroxy-butyrate from 0.45 to 1.6 mM (P = 0.0005). 5. Ground squirrel heart mitochondrial respiratory control ratios and ATP synthesis rates indicated no preferential ketone utilization which might suggest a possible extramitochondrial role of BHB during hypoxia. 6. We conclude that elevated blood BHB levels are associated with increased hypoxic survival and they may have evolved in response to life-threatening hypoxia as experienced during hibernation.     

A comparison of laboratory and field studies of cold response

The recent application of physiological techniques to anthropological studies of cold stress in different human groups has produced evidence of considerable variation in response to cold. The usual anthropological procedure has been to compare the adult males of two different ethnic groups under standardized laboratory conditions, and then to generalize the conclusions in an evolutionary or ecological context. Several assumptions behind this procedure are examined. Four studies of response to cold in the same Quechua Indian group of Southern Peru are discussed. Two of the studies deal with variation in response to cold in a standardized laboratory situation. The other two describe responses as detected under actual cold conditions experienced by the subjects as they go about their daily routines. The results of the laboratory and field studies are compared. It is suggested that adult males studied in the laboratory may represent only a minor part of the variation which exists in the group and that their responses may not be indicative of those of the entire population. It is also proposed that the validity of laboratory studies for an evolutionary interpretation may be limited by the laboratory approximation of the actual cold stress experienced by the group.     

Predator biomass determines the magnitude of non-consumptive effects (NCEs) in both laboratory and field environments

Predator body size often indicates predation risk, but its significance in non-consumptive effects (NCEs) and predator risk assessment has been largely understudied. Although studies often recognize that predator body size can cause differing cascading effects, few directly examine prey foraging behavior in response to individual predator sizes or investigate how predator size is discerned. These mechanisms are important since perception of the risk imposed by predators dictates behavioral responses to predators and subsequent NCEs. Here, we evaluate the role of predator body size and biomass on risk assessment and the magnitude of NCEs by investigating mud crab foraging behavior and oyster survival in response to differing biomasses of blue crab predators using both laboratory and field methods. Cues from high predator biomass treatments including large blue crab predators and multiple small blue crab predators decreased mud crab foraging and increased oyster survival, whereas mud crab foraging in response to a single small blue crab did not differ from controls. Mud crabs also increased refuge use in the presence of large and multiple small, but not single small, blue crab predators. Thus, both predator biomass and aggregation patterns may affect the expression of NCEs. Understanding the impact of predator biomass may therefore be necessary to successfully predict the role of NCEs in shaping community dynamics. Further, the results of our laboratory experiments were consistent with observed NCEs in the field, suggesting that data from mesocosm environments can provide insight into field situations where flow and turbulence levels are moderate.     

The role of ATM and ATR in the cellular response to hypoxia and re-oxygenation

ATM and ATR are stress-response kinases which respond to a variety of insults including ionizing radiation, replication arrest, ultraviolet radiation and hypoxia/re-oxygenation. Hypoxia occupies a unique niche in the study of both ATR- and ATM-mediated checkpoint pathways. Hypoxia is a physiologically significant stress that occurs in virtually all solid tumors and differs from most other stresses in that it does not induce DNA damage. Previous studies have indicated that hypoxia provides a unique way to induce ATR in response to inhibition of DNA replication. During tumor expansion hypoxia is inevitably followed by periods of re-oxygenation which in vitro has been shown to induce significant levels of DNA damage and an ATM response. Therefore both ATR and ATM have a role to play in hypoxia/re-oxygenation.     

Siah proteins, HIF prolyl hydroxylases, and the physiological response to hypoxia

New evidence suggests that at least two members of the family of hypoxia-inducible factor (HIF) prolyl hydroxylases that regulate HIF stability in response to oxygen (O2) availability are also targeted for proteosome-dependent degradation by the E3 ubiquitin ligases Siah1a and Siah2. This preview examines cellular responses to O2 deprivation (hypoxia) and the complexity of the regulation of the HIF O2 sensing pathway in mammals.