MARINE ECOLOGY PROGRESS SERIES Vol. 156: 151-156, 1997 Published September 25 Mar Ecol Prog Ser I Metabolism and habitat competition in the polychaete Nereis virens Helene Lemieuxl, Pierre U. Blierl**,France ~ufresne',Gaston ~esrosiers~ 'Departement de Biologic, 'Departement d'oceanographie, Universite du Quebec a Rimouski. 300 allee des Ursulines, Rimouski, Quebec, Canada G5L 3A1 ABSTRACT: The relationship between lnetabolism and performance during habitat competition in the polychaete Nereis vire~s(Sars) was determined. Twenty palred habitat competition experiments were inltlated between Individuals of similar body mass. The outcome of the competition and the time spent competing for the burrow were noted for each encounter. Protein and lipld contents as well as enzyme activlty (cytochrome C oxidase, lactate dehydrogenase, and pyruvate kinase) were compared between wlnners and losers. There were no significant differences between winners and losers for all para- meters. Thc,re was, however, a significant relationship between fight duratlon and enzyme activity for winners. Individuals that won a fight rapidly had more cytochrome C oxidase actlvlty than individuals who fought longer to gain access to the burrow. We conclude that metabolic capacltles are not corre- lated with the outcome of habitat competition but that aerobic capacity 1s an Important predictor of fight duration. KEY WORDS: Polychaete . Metabolism . Habitat competition . Cytochrome C oxidase . Lactate dehydrogenase . Pyruvate kinase INTRODUCTION parameters have been burst speed, maximal exertion, and endurance (reviewed by Bennett 1991). While One major focus of physiological ecology is to exam- minor differences in speed or exertion may mean suc- ine the adaptive value of physiological performance. cess or failure in predator-prey interactions, these In order to evolve by natural selection, physiological differences in physiological activities remain only in- traits must be variable, heritable, and directly associ- directly correlated with fitness. ated with fitness. Significant individual variation in In this study we examine the relationship between physiological performance has been reported for many metabolic capacities and territorial defense in the poly- physiological traits including oxygen consumption, chaete Nereis vjrens (Sars). This worm is a common enzymatic activities, and locomotor capacities (Pough species of the estuary and the Gulf of St. Lawrence, 1989). In addition, several types of physiological per- Canada (Desrosiers & Brethes 1984, Desrosiers et al. formance (speed, defensive behaviors, growth rates, 1984). Immature individuals of N. virens occur at high thermoregulation) show some degree of heritability densities in the upper intertidal zone (Miron & (Bennett 1987). Energetic metabolism is tightly corre- Desrosiers 1990, Desrosiers et al. 1994). These individ- lated to activity capacity in animals (Holloszy & Coyle uals migrate downshore in the fall of their third year 1984, Guderley & Blier 1988) and could be a functional (Caron et al. 1993, Desrosiers et al. 1994) and compete link between the genotype and physiological per- for burrows with mature individuals already estab- formance. Very few studies have examined whether lished. Encounters between immature and mature variation in physiological traits is directly correlated individuals are highly aggressive and often terminated with fitness. The most commonly studied physiological by the expulsion of the intruder (Miron et al. 1992a). Thus Nereis populations may be regulated by com- 'Addressee for correspondence. petition for habitat. Territorial behavior in N. virens E-mail: [email protected] has been shown to be a predator refuge function and 0 Inter-Research 1997 Resale of full article not permitted 152 Mar Ecol Prog Ser directly related to fitness (Miron 1991).Maximal meta- penetration as the prospecting behavior of this species bolic capacity may be a determinant of success in com- is inhibited by light (Miron 1991). The worms were peting for hdbitats and thereby affect fitness. introduced in a container connected to the burrow but This study compares the metabolic profiles of indi- exposed to light to further force the settlement into the viduals after confrontation for the occupation of a bur- burrow. row in order to determine if these are correlated with Prior to confrontations each worm was individually the outcome of competition. The 3 enzymes used as acclimated in an artificial burrow for 24 h. The experi- metabolic markers were cytochrome C oxidase (CCO), ment was initiated by placing 2 worms of similar mass pyruvate kinase (PK), and lactate dehydrogenase head to head at each extremity of a new unoccupied (LDH). CC0 was chosen as a marker of aerobic metab- burrow. As after every confrontation only 1 individual olism since a previous study on pelagic worms has gained access and occupation of the burrow, this one shown that oxygen consumption rates are correlated was classified as the winner and the one that was with mitochondrial markers (Thuesen & Childress rejected outside was classified as the loser. The dura- 1993). PK is a regulatory enzyme of glycolysis and its tion before settlement in the burrow was recorded for activity is correlated with the intensity of glucose or each confrontation. After confrontation, worms were glycogen catabolism that can be supported by a tissue frozen and kept at -80°C for a maximum of 2 mo. or an orga.nism.As the glucose or glycogen metabolism Enzymatic assays. Whole animals were homoge- usually provides a greater yield of ATP per unit time nized In 4 volumes of ice cold imidazole-HC1 buffer than lipid metabolism, we postulated that the energy (100 mM, pH 7.4) using three 10 S bursts with a Tekmar demand generated by bursts of activity during con- homogenizer. Enzyme activities were measured at frontations would be supported primarily by glycolysis. 25°C using a Perkin Elmer UV-Visible spectrophoto- The pyruvate produced by glycolysis can be trans- meter (lambda 11 ). All assays were run in duplicate formed to lactate by lactate dehydrogenase (anaerobic and specific activities were expressed as pm01 min-l glycolysis) or it can be fully oxidized in the mitochon- mg-' protein. Condition for enzyme assays were as fol- dria. Anaerobic glycolysis is usually the metabolic lows: pathway that is mobilized when a high level of energy (1)Cytochrome C oxidase (CCO):100 mM potassium production is required for a short burst of activity (for a phosphate and 0.05 mM cytochrome C; pH 7.4. complete survey of animal exercise biochemistry, see Cytochrome C was reduced by the addition of dithion- Newsholme & Leech 1983, Hochachka & Somero ite and the solution was bubbled with air to eliminate 1984). As LDH is the only strictly anaerobic enzyme of the excess reducing agent (Hodges & Leonard 1974). glycolysis, its activity combined with PK is a good Reactions were run against a control consisting of marker of the anaerobic capacity of an organism. As 50 mM cytochrome C oxidized with the addition of fights require short and powerful peaks of activity potassium ferncyanide (0.03%). Activity was mea- which may be modulated by energetic metabolism, we sured by following the oxidation of cytochrome C at predicted that winners would have higher metabolic 550 nm. capacity (as expressed by enzyme activities) than (2)Lactate dehydrogenase (LDH):100 mM imidazole- losers. HCI, 0.16 mM NADH and 6.0 mM pyruvate; pH 7.4. (3) Pyruvate kinase (PK): 100 mM imidazole-HC1, 10 mM MgC12, 50 mM KC1,5 mM ADP, 0.2 mM NADH, MATERIALS AND METHODS LDH in excess and 5.0 mM phosphoenolpyruvate; pH 7.4.~ctibities of LDH and PK were measured following Competition experiments. Nereis virens were col- the oxidation of NADH at 340 nm. lected from homogeneous sandy sediments in the Vv'e used millimolar extinction coefficients of 29.5 for intertidal flat of 1'Anse a l'ongnal, 25 km from reduced cytochrome C and 6.22 for NADH. Rimouski, Quebec, Canada. They were maintained in Protein and lipid analyses. Total protein and lipid the laboratory at 10°C and 20 ppm salinity in sandy contents were determined using the Bradford (1976) sediments for a minimum of 5 d. No supplementary and Frings et al. (1972) methods respectively. food was provided prior to the experiments. The exper- Statistical analyses. SYSTAT software was used for imental set-up consisted of a U-shaped plastic burrow all statistical analyses. Student's paired t-tests were (6 mm diameter and 15 cm depth) placed into a 15 cm used to compare average mass, protein content, lipid plastic container with foam and seawater. The foamy content, and enzyme activities between overall win- sediment was used to prevent worms from digging ners and losers. We also compared physiological para- other burrows and hence forced the establishment of a meters among winners of encounters that lasted from: single worm in the plastic burrow. The plastic con- (1) 0 to 1 min, (2) 1 to 2 min, and (3) 2 rnin and more. tainer was covered wlth dark plastic to prevent light Kruskal-Wallis tests were used for these analyses since Lemleux et a1 Metabolism and habitat competition in Nereis virens 153 Table 1. Nereis virens. Comparisons of dliferent physiolog~calparameters for overall winners and losers. CCO: cytochrolne C oxi- dase; LDH lactate dehydl-ogenase; PK. pyruvate kinase p-values from a palred Student's t-test Body mass Protein content Lipid content CC0 activity LDH activity PK activ~ty (9) (mg g-'1 (mgi g-'1 (U g ' proteln) (U g.' protein) (U g-l protein) W~nners(n = 20) 13k09 364k 100 10.8 5.1 51 + 23 750 + 300 1180 + 460 Losers (n = 20) 1.3k 10 387k 101 12.3 + 5.8 58 + 34 800 + 340 1220 + 430 p=10 p = 0 386 p = 0 224 p = 0.258 p = 0.585 p = 0.720 some categories included a small number of individu- p = 0.949; PK: p = 0.905),and inore than 2 min (CCO: als and normality assumptions were violated.