Behavior and Ecology of Some North American Cyprinid Fishes

Abstract

Form of the nest, nest-building and reproductive be- havior, and social interactions are described in five species of cyprinids associated with Notropis cornutus, N. rubellus, and hybrid N. cornutus X N. rubellus during the breeding season. Environmental and social factors which maintain species isolation are discussed. Reproductive and social behavior of the three shiners is described and compared. The parent species differ in ten behavioral characteris- tics. In six characters the hybrid resembles N. cornutus and in three it resembles N. rubellus. The hybrid and N. cornutus often feed on the bottom and occur in backwaters. They usually form large, multispecies aggregates while N. rubellus often are in separate schools. Spawning temperature is 70 F or higher for N. rubellus and 60 F or more for the other two forms. Nest digging and defense of a definite bottom territory is present only in N. cornutus. A tilt display by the male preceding spawnings and a spawning clasp are present in N. cornutus, rare in the hybrid, and absent in N. rubellus. The number of head butts during a parallel-swimming behavior is low in N. cornutus, high in N. rubellus, and intermediate in the hybrid. Over-all aggression is higher in N. cornutus than in either N. rubellus or the hybrid. In the spring of 1959, 1960, and 1961 I studied the reproductive behavior and ecology of the cyprinid fishes Notropis cornutus (Mitchill), Notropis rubellus (Agassiz), and the hybrid between them. Much of the basic reproductive behavior of these forms was described by Raney (1940a; 1940b) and Pfeiffer (1955). The present study concerns the behavior of the three forms in a single population known consistently to contain many hybrids, attempts to determine how be- havioral characteristics of the parent species are represented in the hybrid, and considers the factors maintaining the high incidence of hybrids. I found that these fishes carry out most territorial and repro- ductive activities over the pebble nests of other cyprinids such as Hybopsis micropogon (Cope), Semotilus corporalis (Mitchill), Semo- tilus atromaculatus (Mitchill), and Exoglossum maxillingua (Le Sueur), a situation previously described by Hankinson (1932), Raney (1940a), and others. I also found that most shiners spawn over the nests during their construction or shortly after their completion and only rarely after the nests were deserted by the resident species. This circumstance facilitated observations on the nest-building, territorial, and reproductive behaviors of several species and on various kinds of interspecific encounters. This report presents additional information on the behavior of several cyprinids, with emphasis on nest-building, reproduction, and cohabitation of nest sites. This information may shed some light on the complex factors controlling interspecific encounters and their signi- ficance in species isolation and hybridization. 313