- University of Utah
Summary
In North American sunfishes (Lepomis: Centrarchidae) ♂♂ build nests and provide solitary parental care for the young. In this paper I provide for bluegill (L. macrochirus) a detailed account of ♂♂ which do not build nests, but steal fertilizations from the nests of other ♂♂. I begin by giving data on the behavior, morphology, and population demography of ♂♂. Next, through an analysis of individual male life‐histories, I show that cuckoldry and parenting are discrete alternative reproductive strategies. This is followed by a theoretical analysis and an empirical test of cuckoldry and parental care as evolutionarily stable strategies (a mixed ESS). Several predictions are made concerning how natural selection will influence the life‐history dynamics of these strategies. A general theory is then developed for sunfishes, and a first test made on the pumpkinseed (L. gibbosus). Finally, I note the parallels between male cuckoldry in sunfishes and precocial male life‐histories in salmon and cichlids.
Methodology
Lake Opinicon (Leeds County, Ontario, Canada) is a 900 ha mesotrophic lake typical of many in northeastern North America (Keast 1978). I have used this site for behavioral ecology studies of natural populations of bluegill, pumpkinseed, and other sunfishes from 1976 through 1979. A map locating my individual study areas and detailed physical descriptions of the habitats are given in Gross and Nowell (1980) and Gross and MacMillan (1981).
Bluegill colonies in Lake Opinicon contain 5 to 150 nests approximately rim to rim in water 0.4 to 1.4 m deep. Nests are shallow, bowl-shaped depressions constructed in the lake floor by ♂♂ using lateral sweeping movements with their caudal fins. ♂♂ smaller in size gather near the colonies. Gravid ♀♀, in schools, approach the colonies and enter the nests individually, releasing eggs with horizontal dipping motions. The small ♂♂ without nests intrude and release sperm. Members of a colony actively spawn for several hours before the ♀♀ leave for deeper water. The ♂♂ on nests fan and guard the eggs until hatching, and guard the larvae until they become free-swimming fry and leave the nest area. Parental care lasts approximately 7 days. The ♂♂ then return to deeper water and feed until the next spawning period. There are 4-5 breeding periods seasonally, separated by as many as 10 days.
The following data were collected: (1) behavioral and physical descriptions of ♂♂ at colonies; (2) the frequency of male intrusions into nests during colony spawning; (3) relative frequencies of intruder and parental ♂♂ in the population; and (4) male life-time reproductive histories.
Data on spawning behavior were recorded by observers standing on 3-m towers on the shoreline near nesting areas, or while using a mask and snorkel or SCUBA while kneeling and swimming near colonies. Some selective trapping was done within the colonies using hand nets. Neither sampling nor the presence of observers appeared to disrupt colony activity.
Unbaited funnel traps (0.5 m by 1.0 m) and seines (2 m by 50 m beach seines) were used to collect random samples of ♂♂ in the population at large. These ♂♂ were sampled throughout the peak breeding season of mid-June to mid-July, between breeding periods. Samples were collected at six widely spaced sites representative of the major habitats in Lake Opinicon: weedy, muddy, sandy, and gravel substrates (Harker 1976).