MALE FITNESS, BODY-SIZE AND TIMING OF REPRODUCTION IN SMALLMOUTH BASS, MICROPTERUS-DOLOMIEUI

We conducted a mark-recapture study and a survey of nesting male small mouth bass, Micropterus dolomieui, to determine the relationship betwe en age at first reproduction and fitness among males of several cohort s. Males that spawned at 3 yr of age obtained on average many more egg s than males that delayed reproduction, suggesting that age at reprodu ction is a conditional strategy. Body size appears to be the trait use d to determine the value of the life history decision; small age-3 mal es were more likely to delay reproduction than large males. The tactic adopted by males may also depend on events that occur well before the time of the life history decision, as males of a cohort that were lar ge at age 3 were also large at age 1. Furthermore, growth over that ti me period was depensatory. Thus, environmental influences during early ontogeny could potentially direct males into alternative life history pathways. Males that delayed reproduction ultimately reproduced at a larger body size than males that spawned at age 3. Due to size-depende nt reproduction within a spawning season, and indeterminate growth, ma les that delayed reproduction also reproduced relatively early within a spawning season. The progeny of males that spawn at age 3 should con sequently experience a relatively short period of growth prior to wint er; males that delay reproduction should produce progeny that are larg e at age 1, whereas the progeny of males that spawn at age 3 should be relatively small. These patterns suggest that the association between timing of reproduction and body size within a spawning season will pr oduce a negative paternal effect for age at reproduction such that the life history alternates in successive generations; males that spawn a t age 3 produce progeny that delay reproduction and vice versa. Enviro nmental changes at various stages of the life cycle could alter the pr oportion of males that adopt each tactic. Our findings suggest that de tails of early ontogeny and inheritance, in combination with estimates of fitness, may be necessary to understand the evolution of life hist ory pathways in some systems.