Academic journal article The American Midland Naturalist

Endophyte-Infected and Uninfected Fescue Seeds Suppress White-Footed Mouse (Peromyscus Leucopus) Reproduction

Academic journal article The American Midland Naturalist

Endophyte-Infected and Uninfected Fescue Seeds Suppress White-Footed Mouse (Peromyscus Leucopus) Reproduction

Article excerpt

MICHAEL G. TANNENBAUM,1 SARA L. SEEMATTER AND DANA M. ZIMMERMAN Division of Science, Truman State University, Kirksville, Missouri 63501

ABSTRACT.-Growth, reproduction, circulation, and thermoregulation in domestic livestock and laboratory rodents are adversely affected by consumption of tissues derived from plants infected with endophytic fungi. Because little is known about the systemic effects of infected diets on wild rodent granivores, we conducted a series of laboratory experiments to assess the effects of consuming endophyte-infected (E+) and uninfected (E-) seeds of tall fescue (Festuca arundinacea) on reproduction in the white-footed mouse, Peromyscus leucopus. Groups of mice (paired and single-sex) were fed diets of either rodent chow, E+, or E- seeds; in several experiments, chow and seeds were ground and mixed in a 1:1 ratio. Eseeds alone suppressed reproductive output compared to chow-fed mice, but consumption of E+ seeds did not further reduce reproductive performance. Furthermore, paired testes mass was more strongly reduced by the presence of seeds in the diet than was the mass of the female reproductive tract, but reproductive tract mass in both sexes was not further diminished by endophyte consumption. These results suggest that males are more sensitive than females to the presence of seed in the diet, and that white-footed mice and related rodent granivores cannot rely upon a diet of grass seeds alone to support reproduction. Depending upon the time of year that such seeds are eaten, suppression of breeding may be advantageous to consumers.

INTRODUCTION

Because seeds may be seasonally abundant, calorically and/or nutritionally attractive (Kelrick and MacMahon, 1985; Crawley, 1992), easy to transport and cache (Smith and Reichmann, 1984) and relatively resistant to spoilage (Stiles, 1992), they form an important part of the diet of many small mammals. Moreover, seeds may exert an important influence on mammal population dynamics, as high mast years may be positively correlated with greater fecundity during subsequent springs (Gashwiler, 1979). Yet, except for desert dwellers, diets of small rodents are rarely composed solely of seeds because many seeds are deficient in minerals such as calcium and sodium, both of which appear to be required for successful reproduction (Batzli, 1986).

In addition to deficits in specific nutrients, many seeds also contain secondary compounds (Freeland, 1991) or other plant products such as the cinnamic acids (Leopold and Kriedemann, 1975; Berger et al., 1977) that are potentially harmful to invertebrate and vertebrate consumers. For example, tall fescue (Festuca arundinacea) and several other grasses may become infected with endophytic fungi, such as Acremonium coenophialum (Clay, 1990a). Infection frequencies are typically high in natural populations of grasses (Clay, 1993b), suggesting that endophytes increase the fitness of their host plants. Indeed, endophyte-infected tall fescue plants have higher survival rates in field studies and produce more biomass under controlled conditions than uninfected individuals (Clay, 1990b). Other effects of endophytic fungi on their host plants include faster developmental rates (Clay, 1987) and greater drought resistance (Arachevaleta et al., 1989). Fungal endophytes, which are passed from one grass generation to the next via seeds, produce an array of alkaloids that make plant tissues unpalatable to herbivores. Tissues from infected host plants, as well as alkaloids extracted from them, deter feeding by insects (Hardy et aL, 1986) and nematodes (Pedersen et al., 1988), and induce deleterious effects (including lower food intake, slower growth rates, and depressed reproductive performance) in livestock (Porter and Thompson, 1992), laboratory rodents (Varney et al., 1992; Godfrey et al., 1994) and the prairie vole, Microtus ochrogaster (Durham, 1996). Seeds of Acremonium-infected plants also deter seed predators such as birds (Madej and Clay, 1991; Conover and Messmer, 1996), resulting in a selective advantage over uninfected seeds, giving them a better chance of surviving until germination. …

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