Physiological correlates of paternal care in male threespine stickleback

Abstract

In threespine stickleback, Gasterosteus aculeatus, paternal care of eggs requires nesting males to remain in their territories to defend their nests from intruding males or bands of marauding females, thus decreasing feeding opportunities, which presumably leads to reserve mobilisation. To evaluate whether physiological consequences of paternal care are apparent in stickleback nesting in their breeding grounds, we examined whether males which were tending eggs (paternal males) differed in their physiological capacities from males without eggs in their nests (bachelor males). As female choice of males and nest sites could influence which males obtain matings, we also examined whether externally visible indicators of male quality (ectoparasite infestation, coloration and skin carotenoid content) and nest site quality (algal cover) are related to the physiological attributes of the nesting males. We examined biochemical correlates of burst and endurance swimming, as well as energy reserves and tissue masses. The physiological attributes varied little between paternal and bachelor males, suggesting limited costs of parental care. However, the number of eggs in the nests was negatively correlated with the dry mass of the axial musculature, suggesting reserve mobilisation during parental care. The number of eggs was positively correlated with the activity of pyruvate kinase in the pectoral muscle. The nests of paternal males had greater algal cover than those of bachelor males. The percent algal cover of a nest was positively correlated with the nesting male’s skin carotenoid levels. In contrast, the males whose nests had greater algal cover had lower total and soluble protein levels in the axial muscle. The coloration of the males at the time of capture was positively correlated with the activity of creatine phosphokinase (CPK) in the pectoral and axial muscles, but did not reflect condition, ectoparasite infestation, tissue masses or water contents. Skin carotenoid levels were positively correlated with the activity of CPK and LDH in the pectoral muscle as well as with that of CPK in the axial muscle, without reflecting energy reserves. Of the tissue masses, only the wet and dry masses of the kidney were correlated (negatively) with carotenoid levels. Whereas the externally visible attributes upon which females could base mate choice showed little correlation with energetic reserves (glycogen levels, condition factor or tissue masses), coloration and carotenoid contents were positively correlated with the levels of several enzymes involved in anaerobic ATP production in skeletal muscle.