Comparative energetics and physiology of parental care in smallmouth bass Micropterus dolomieu across a latitudinal gradient.

The energetic and physiological status of parental smallmouth bass Micropterus dolomieu was investigated across the majority of their latitudinal range at the onset and near the end of care. Variables such as tissue lipid stores, plasma indicators of nutritional status and chronic stress and white muscle were used to define energetic and physiological status. Results showed that northern males (48 degrees N) were larger and heavier than mid-northern (44 degrees N) and southern (36 degrees N) latitude males. For a given body size, northern males had greater whole-body lipid across the parental care period and tended to feed more (based on gut contents) than mid-northern and southern latitude conspecifics. Indicators of nutritional status were also highest in northern males. Conversely, the southern males exhibited the greatest capacity for biosynthesis across the entire parental care period as indicated by the highest level of nucleoside diphosphate kinase activities. Collectively, these finding suggest that the energetic costs and physiological consequences of care vary across latitudes, providing some of the first mechanistic evidence of how environmental conditions can influence both the ecological and physiological costs of reproduction for wild animals during parental care. The data also suggest that lake-specific processes that can vary independently of latitude may be important, necessitating additional research on fish reproductive physiology across landscapes.