THE EFFECTS OF KINSHIP ON GROWTH AND DEVELOPMENT IN TADPOLES OF RANA CASCADAE.

Abstract

Tadpoles of the frog, Rana cascadae can discriminate between kin and nonkin (kin recognition) and preferentially associate with kin in laboratory and field experiments (e.g., O'Hara and Blaustein 1981, 1985; Blaustein and O'Hara 1982, 1987). Such association, combined with rapid metamorphosis from small, ephemeral breeding sites and the tendency to form aggregations in nature may lead to intense intraspecific competition among R. cascadae tadpoles (O'Hara 1981; Blaustein 1988). Kin recognition may allow tadpoles to direct competitive interactions away from kin, perhaps by altering behavioral interference or by selectively releasing chemical growth inhibitors (Waldman 1986, 1991; Blaustein 1988; Blaustein and Waldman 1992). In tadpoles, the effects of kin association on growth and development remain controversial (Shvarts and Pyastolova 1970; Travis 1980; Waldman 1986, 1991; Jasienski 1988; Smith 1990; reviewed by Blaustein and Waldman 1992). In particular, the direction of the kinship effect (i.e., whether individuals in kin groups grow faster/larger or slower/smaller than those in mixed groups) appears to depend upon the species examined and the experimental conditions. For example, kinship effects vary for American toads (Bufo americanus). Some family groups show increased larval growth rate when reared with siblings, whereas the growth rate in other families is slower when reared with sibling competitors (Waldman 1986). Individual growth rate is greater in sibling groups of the chorus frog (Pseudacris triseriata) than in mixed groups but only at high density (Smith 1990). However, with the exception of B. americanus (Waldman 1986, 1991), none of the species previously examined for kinship effects on growth and development are known to discriminate kin from nonkin. Using R. cascadae, we examined whether individuals within groups of full-sibling tadpoles and groups of tadpoles of mixed relatedness differ in several key components of reproductive success including the lengths of the larval period, proportions of metamorphs produced, and body lengths and masses at metamorphosis. These traits correlate with fitness in some amphibians (e.g., Berven and Gill 1983; Smith 1987; Semlitsch et al. 1988).