Reproductive Behavior of Smallmouth Bass


Life History Studies

Members of our laboratory are involved in a collaborative project with Jeffrey R. Baylis (University of Wisconsin-Madison), Lisa M. Angeloni (Colorado State University) and Steven P. Newman (Wisconsin Department of Natural Resources) on the reproductive behavior of smallmouth bass (Micropterus dolomieu).  The project also involves dedicated undergraduate volunteers.

Click on the image (left) to link to L. M. Angeloni.

Daniel D. Wiegmann

Department of Biological Sciences
J. P. Scott Center for Neuroscience, Mind and Behavior
Bowling Green State University
Bowling Green, OH 43403

Phone 419.372.2691
FAX 419.372.2024

The population we study is located in the Northern Highland State Forest in northern Wisconsin.  M. dolomieu in this region spawn in late spring and males build and defend nests until eggs hatch and progeny disperse, a developmental period that may last several weeks.

We locate and monitor nests throughout the spawning season and we capture parental males.  Individuals are marked, which allows us to monitor their reproductive behavior each season.

We estimate the lifetime fitness of males, which allows us to determine how life history decisions, such as age at first reproduction, influence fitness.  The fitness of males can be measured from estimates of the (right) number of eggs in nests, or from an estimate of the (below) number of progeny that disperse from a nest.

The results of our studies suggest that males who spawn early in life produce many more progeny than males that delay reproduction, largely due to annual mortality.  This observation implies that age at first reproduction is a conditional strategy and comparisons of the growth of males that initiate reproduction at different ages supports this conclusion.

Theoretical Developments

In an evolutionary game the behavioral strategy that returns the highest fitness wins.  Thus, the observation that fitness is unequal amongst males who initiate reproduction at different ages implies that age at first reproduction is a conditional strategy.   Joe Repka and Mart R. Gross developed a conditional strategy model that shows how two alternative tactics can be in a stable equilibrium, even if tactics are inherited and yield unequal fitness. 

Their model did not apply directly to our study, as our results suggest that age at first reproduction has a special form of inheritance.  In our system male progeny regularly express the behavioral tactic opposite to the tactic expressed by their father; that is, fathers who spawn at a young age tend to produce sons who delay reproduction, while fathers who delay reproduction produce sons who are young when they initiate reproduction.

The life history tactic alternates across generations (left) because male condition influences when he spawns within a season and the age at which he initiates reproduction.  Large males spawn early within a season and, as a consequence, produce progeny who attain a large size at the end of their first year of life.  These individuals remain larger than other members of their cohort and they tend to be young when they initiate reproduction.  But at the time they initiate reproduction they are small in absolute body size and, hence, they typically spawn late within a season.  This implies that they in turn produce progeny who are small at the end of their first year of life and who tend to delay reproduction, grow and spawn at a large size.

We modified the model developed by Repka and Gross to accommodate the pattern of tactic inheritance in our system and we showed that, even under this form of inheritance, the tactics of a conditional strategy can be in a stable equilibrium.  The prevalence of tactic alternation in natural populations is difficult to measure, but it clearly occurs in many animals.  The model is constructed of a limited number of parameters and some of these parameters can be measured relatively easily.  Information on these parameters allows us to estimate other parameters, like tactic inheritance, that are difficult to measure in natural populations.  We used this practical aspect of the model to estimate tactic alternation in our study population.  In our study system more than ninety percent of the progeny of males who spawn at a young age adopt the alternative tactic and delay reproduction.

Click on the image (left) to return to the home page.  (Photograph courtesy of J. R. Baylis.)

(Photograph of eggs and researcher tracing egg mass above and of the parental male at top courtesy of J. R. Baylis.)