A.C. Taylor

Diurnal and seasonal variation in physico-chemical conditions within intertidal rock pools

Abstract A study of the diurnal and seasonal variation in the physico-chemical conditions within intertidal rock pools on the West coast of Scotland was undertaken to provide data on the environmental conditions experienced by animals inhabiting these pools. The temperature, pH, partial pressure of oxygen ( P O 2 ) and salinity were measured every hour for 24 h and the total alkalinity, partial pressure of carbon dioxide ( P CO 2 ) and carbon dioxide content ( C CO 2 ) calculated. This sampling regime was carried out once a month for 12 months to determine the extent of seasonal variation in conditions within temperate pools. Large diurnal variations were recorded in nearly all the physico-chemical parameters measured. The greatest variation was recorded in the temperature and P O 2 of the water but significant changes in pH and P CO 2 were also recorded. Total alkalinity varied little during any 24 h period but carbonate alkalinity, which was always lower than total alkalinity, showed slightly greater variation. There was also considerable variation in the magnitude of these diurnal changes between pools at different heights on the shore. Diurnal variation in the physico-chemical conditions within the pools were observed throughout the year although the magnitude of these changes varied seasonally. Detailed studies on individual pools demonstrated that appreciable local variation existed in the physico-chemical conditions within each pool.

Proximate costs of fighting in male cichlid fish : the role of injuries and energy metabolism

While much is known about the functional significance of strategic decisions in animal fighting, relatively little is understood about the mechanisms that underlie the making of those decisions. In mechanistic terms, strategic decisions, such as either escalating a fight or giving up, are made in relation to the proximate costs that opponents inflict (or can potentially inflict) upon one another. These costs include physical injury and also the physiological consequences of engaging in an energetically demanding activity. We studied the role of injury and energy metabolism during fights between male cichlid fish, Tilapia zillii. In relation to injuries incurred during fights, scale loss differed depending on whether the winner was smaller or larger than its opponent; smaller winners inflicted significantly more damage on their opponents than they received, whereas this difference was not apparent in those fights won by the larger fish. In relation to energy metabolism, escalated fighting resulted in a significant depletion of total sugar reserves in the muscle and the liver. It appears that the muscle energy reserves are respired anaerobically, as was evident from the accumulation of lactate in the muscle. Losers had significantly higher levels of muscle lactate than winners. Together, the injury data and the metabolic data suggest that escalated fighting is costly for both winners and losers, but especially so for losers. These data are discussed in relation to models of animal decision making and we conclude that the difference between opponents in the proximate costs incurred during fighting is likely to underlie the making of decisions such as continuing, giving up or escalating the fight. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Weapon size versus body size as a predictor of winning in fights between shore crabs, Carcinus maenas (L.)

Relative body size (carapace width) and weapon size (chela length) were used as indicators of resource holding potential (RHP) in the agonistic behaviour of male shore crabs, Carcinus maenas (L.). Weapon size was found to be a more reliable predictor of the outcome of pairwise fights than body size. Crabs with longer chelae than their opponents were more likely to win fights than crabs with relatively larger bodies. Body size had less influence on the outcome of fights. Relative body and weapon size did not influence initiation of contests but did affect the likelihood of winning; however, this was significant only for weapon size. Winning crabs had heavier claws with greater surface area than losing crabs. There was no relationship between relative size and fight duration. The frequency of cheliped display increased with chela length and win- ners performed significantly more displays than losers.

Plasma Cortisol Concentrations Before and After Social Stress in Rainbow Trout and Brown Trout

Two related experiments examined the relationship between plasma cortisol concentrations and the development of social hierarchies in fish. In the first, rainbow trout, Oncorhynchus mykiss, and brown trout, Salmo trutta, were observed for dominance interactions when confined within single‐species pairs for 4, 48, or 168 h. Subordinate members of a pair exhibited significantly higher cortisol concentrations than dominant and single fish, but the pattern of cortisol elevation differed between the two species, being quicker to rise and increasing to a higher level in rainbow trout. Cortisol concentrations were correlated with behavioural measurements; the more subordinate the behaviour exhibited by a fish, the higher its cortisol concentration. Social stress was a chronic stressor, and no acclimation to social status occurred during the week. In the second experiment, measurements of plasma cortisol were made before pairing of rainbow trout and then after 48 h of confinement in pairs. Subordinate fish demonstrated significantly higher concentrations of plasma cortisol both before and after social stress. It therefore appears that in addition to cortisol being elevated during periods of social stress, an association may exist between initial cortisol levels and the likelihood of a fish becoming subordinate.

Does darkening signal submission in territorial contests between juvenile Atlantic salmon, Salmo salar ?

Communication by means of visual signals occurs during the competitive, aggressive and sexual interactions of many animals. Some animals such as fish are able to change their body coloration rapidly, and there is evidence that this is used as a means of signalling. However, the precise meaning of such signals is rarely understood. We examined whether (1) darkness in juvenile Atlantic salmon is associated with submission, and (2) changing to a darker colour could act as a signal to the opponent and hence induce a change in its behaviour. We found that both the sclera of the eye and the overall body coloration tended to darken in fish that were losing territorial encounters, while victors retained their original coloration. The darkening was rapid and usually occurred during a period of sustained attacks by the opponent; however, the aggression level decreased as soon as the losing fish had become darker. We suggest that the darkening of the losing fish was associated with submission and may result in a change in the behaviour of its opponent, so minimizing the potential risk of injury during unnecessarily prolonged fights. Copyright 1999 The Association for the Study of Animal Behaviour.

The effect of social stress on the Standard Metabolic Rate (SMR) of brown trout, Salmo trutta

The effect of social stress, induced by confinement in pairs, on the SMR of the brown trout, Salmo trutta (L.), was investigated. Fish were confined in pairs under laboratory conditions and allowed to establish social hierarchies, with one fish becoming dominant and the other subordinate. The change in SMR of the subordinate fish was significantly greater than that of their respective dominant. Also, the more aggressive the dominant behaved towards the subordinate with which it was paired, the greater the increase in the SMR of the subordinate fish appeared to be. It is concluded that social stress causes an increase in SMR in subordinate fish and therefore imposes a metabolic disadvantage.

Competitive asymmetries in territorial juvenile Atlantic salmon, Salmo salar

Many animals may face briet periods of extreme intraspecific competition for resources, an example being when populations of territorial species first migrate into a habitat. The factors that determine an individuals success in obtaining a territory will then depend on its relative competitive ability, which in turn is influenced by many potential asymmetries between contestants. Here we compare the relative importance to competing Atlantic salmon fry of several such asymmetries (size, prior residence and relative Standard Metabolie Rate (rSMR)) that have previously been suggested to be important when examined in isolation. Concurring with earlier studies. SMR was higher in the carliest fry from a nest to begin feeding and was a better predictor of dominance than body size in pairwise contests for territories. However, prior residence (where one fish was resident on a territory for 48 h before the arrival of the other) was found to be the best predictor of dominance, masking any effect of relative SMR. Moreover, body size also played a role in encounters territory holder if it was larger. The outcome of competition for territories among dispersing salmon fry is therefore likely to be a complex interaction between these asymmetrics.

Physiological and metabolic responses of the shore crab Carcinus maenas (L.) during environmental anoxia and subsequent recovery

The degree of hypoxia experienced by Carcinus maenas (L.) in littoral rock pools varies throughout the year. In summer, conditions may become extremely hypoxic or even anoxic at night. Crabs which remain in the pools utilize anaerobic metabolism for energy production as indicated by an increase in tissue lactate. In the laboratory, l-lactate was found to be the major end-product of anaerobic metabolism for although fumarate and alanine accumulated during anoxia, the amounts accumulated indicate that alternative metabolic pathways are of only very limited importance in C. maenas. Survival for long periods under anoxic conditions necessitates a considerable reduction in metabolic rate. Calorimetric measurements indicated that, during anoxia, the metabolic rate of C. maenas is reduced to <20% of the normoxic rate. Exposure to anoxia resulted in significant acid-base disturbances. Although a marked metabolic acidosis developed, there was no indication that exoskeletal carbonates were important in buffering these changes. Recovery from anoxia resulted in a pronounced increase in the rates of O2 consumption and heart rate. A transient but significant increase in tissue lactate concentration was observed during the initial stages of recovery suggesting that anaerobic glycolysis may also be important in meeting the high energy demands of the crabs at this time.

Physiological effects of dominance hierarchies within groups of brown trout, Salmo trutta, held under simulated natural conditions

While the existence of dominance hierarchies within natural populations of salmonids is well known, little is known about the physiological consequences of these social interactions. To investigate such physiological effects, replicate groups of four brown trout (Salmo trutta) were held under simulated natural conditions in an artificial stream tank. Behavioural observations allowed the fish to be ranked for dominance. After two weeks, physiological status was assessed through measurements of specific growth rate, condition factor, plasma cortisol and ion concentrations, haematocrit, leucocrit, hepatosomatic index, hepatic glycogen concentration, interrenal cell nuclear area and gill epithelium chloride cell density. Weight gain in the first-ranking (dominant) fish was significantly higher than in the second-ranking fish. In addition, the condition factor of the second-ranking fish decreased over the experimental period while those of the first- and third- ranking fish increased, resulting in significant differences among the three groups. The only other physiological parameter which varied significantly among the ranked fish was chloride cell density, which was significantly higher in the second-ranking fish than in the dominant fish. Cortisol concentrations were low in all fish and did not vary significantly with dominance status. Overall, the least beneficial position, in physiological terms, appears to be the second rank in the dominance hierarchy.

Metabolic responses of the prawns Palaemon elegans and P. serratus (Crustacea: Decapoda) to acute hypoxia and anoxia

Using prawns, Palaemon elegans (Rathke) from intertidal pools on the Isle of Cumbrae, Scotland, and P. serratus (Pennant) from the subtidal at Plymouth, England, some metabolic responses to hypoxia and anoxia have been studied. P. elegans was found to have a greater tolerance of severe hypoxia than P. serratus. Tolerance of totally anoxic conditions, however, was limited to only 4 h in P. elegans and to approximately 1 h in P. serratus. exposure to moderate hypoxia (30 torr) resulted in little change in the concentration of L-lactate in the blood or in the tissues of either P. elegans or P. serratus. When exposed to extreme hypoxia (10 or 5 torr for P. elegans), however, there was a progressive increase in the concentration of L-lactate in the blood and in the tissues of both species. After normoxic conditions had been restored, the concentration of L-lactate in the blood and in the tissues returned to normal resting levels more rapidly in P. elegans than in P. serratus. Under hypoxic conditions, both P. elegans and P. serratus showed an increase in the concentration of blood glucose and a slight reduction in the glycogen content of the tissues. The concentrations of blood glucose and of tissue glycogen returned to normal levels within 6 h of the prawns being returned to normoxic conditions. The results of an in situ study in April and August 1986 to examine the metabolic responses of P. elegans to the hypoxic conditions normally experienced in high-shore rock pools are also presented. The ecological significance of the differing abilities of these species to survive hypoxic exposure is discussed.