Sneakers, Satellites, and Helpers: Parasitic and Cooperative Behavior in Fish Reproduction

Michael Taborsky    Konrad Lorenz-Institut für Vergleichende, Verhaltensforschung, A-II60 Vienna, Austria

I INTRODUCTION

Organisms compete for various resources in the course of sexual reproduction. First, there is intrasexual competition for obtaining mates. Then, there is the need to exclude reproductive competitors who might displace or affect the individual’s own gametes (e.g., sperm competition, egg dumping). There is competition for sites that are used to raise progeny and/or that will optimally support them, and it may be highly advantageous to monopolize the resources that are essential for offspring survival and development.

In this chapter I review our current knowledge of the ways in which fish compete at these different levels. I further describe how competition for resources may lead to cooperative behavior, even between the competitors themselves. Finally, I draw attention to the model character of fish social systems and suggest crucial directions for future research.

II REPRODUCTIVE COMPETITION

I begin with a description of different levels of reproductive competition among males. Group spawning appears to be a mating pattern with little competition between males, but this impression may result from our ignorance of the subtleties involved in this mating pattern and in its reproductive consequences. The competitive character of male behavior that serves the purpose of gaining access to females is much more obvious when it is coupled with some sort of resource or mate monopolization. The attempt to monopolize resources or females to obtain fertilizations (i.e., the “bourgeois” tactic) may not always be the best choice for a male. He may be better off choosing alternative tactics when he is not in the position to compete successfully, for example, because of a weak resource holding potential (sensu Parker, 1974), or when there are “cheaper” ways to obtain fertilizations, that is, when the cost/benefit ratio of the alternative tactic will fall below that of the bourgeois tactic (see Rubenstein. 1980; Dunbar, 1982; Arak, 1984; Magurran, 1986; for general discussions).

Basically, the monopolization of mates may be overcome in two alternative ways. Males may either obtain partners from others who have already invested in their acquisition, or they may directly try to obtain parasitic fertilizations, that is, release sperm when a female spawns with another male. The first route is chosen by males taking over a nest, mating site, or breeding hole from its owner who already invested in behaviors like nest building, preparation of a spawning surface, site advertisement, or defense (nest takeover). A specific version of this tactic is to take charge of the nest for only a limited spawning period and then leave the broodcare to the previous nest owner (piracy). Males may also try to steal females within other males’ territories or intercept females who are on their way to a spawning site that is monopolized by another male (female theft and interception).

The second alternative route to obtain fertilizations differs from the first one in that parasitic males do not attempt to get exclusive access to a female, that is, monopolize her for some period of time, but rather shed sperm while a bourgeois competitor spawns (sperm competition). This “simultaneous parasitic fertilization” tactic is very widespread in fish and I will give an overview of its taxonomic distribution (see Table I). I summarize the information on the different types of males participating in kleptogamic fertilizations, from bourgeois territory neighbors to males behaviorally and morphologically specialized for this type of mating (e.g., female mimics). In live-bearers, fertilization stealing often involves coercive copulations that may also be at the expense of males investing in courtship to attract females.