Alternative mating tactics in the gobiid fish, Eviota prasina

Diversity of alternative reproductive phenotypes within sexes has recently been reported in various animals. Gross (1996) reviewed empirical and theoretical studies, and classified three kinds of strategy in the context of game theory: alternative, mixed and conditional strategies. Although little is known of alternative and mixed strategies, empirical evidence for conditional strategies has been accumulating. In most cases, larger males aggressively defend mating territories, while smaller males act as sneakers or satellites. Mating success of larger males is much greater than that of the smaller ones. Fishes provide many examples of conditional strategies. In this paper, we report two different tactics of male mating behavior in the goby Eviota prasina; viz. nest holder (NH), waiting for females to visit the nest, and trapper (TR), trapping wandering females. Body sizes, home ranges and female preference for each tactic are compared. The present study was conducted at Hanaze Beach, Kaimon Town, Kagoshima Prefecture, Japan. The shore comprises of volcanic rocks, with well-developed, variously-sized tide pools. Eviota prasina was abundant in the study area (2 m x 10 m) in one of the larger pools. Snorkeling observations were made daily from 06:00-14:00 from 25 June to 22 August 1986. The location of each fish was recorded 1-6 times each day, in order to establish the home range. Behavioral interactions among individuals were also noted, in addition to the time, location and code numbers of participants during observations of courtship and spawning behaviour.