Influence of Photoperiod and Nutrition on Pine Vole Reproduction

Abstract

Two experiments were conducted to determine the relative influence of photoperiod and nutrition on reproduction and related characteristics of pine voles (Microtus pinetorum). In a laboratory experiment, adult voles fed a rabbit chow diet supplemented with fresh apples had more body fat and males had heavier testes than those fed only rabbit chow. Voles of both sexes on a 14L:I OD photoperiod had heavier reproductive organs than those on a naturally declining photoperiod. In a field study, the presence of apples as a food source during the autumn had little effect on vole body fat content. However, more females were pregnant and males had heavier testes and seminal vesicles and higher spermatoza counts in areas with apples. We conclude that both photoperiod and nutrition influence the extent of late autumn and winter breeding of pine voles and that their effects are additive. INTRODUCTION The pine vole, a pest that causes economic losses in apple orchards along the eastern seaboard (Byers et al., 1976), has a longer breeding season and higher reproductive rates in maintained orchards than in abandoned orhards (Noffsinger, 1976; Cengel et al., 1978). Cengel et al. (1978) hypothesized these differences arose from the higher nutritional quality of forage and greater availability of fallen apples in maintained orchards. Lochmiller (1980) demonstrated that forage biomass was higher in maintained orchards, and differences in habitat or supplemental feeding have been shown to cause higher rates of reproduction and growth in other microtine rodents (Krebs and DeLong, 1965; Andrzejewski, 1975; Cole and Batzli, 1978, 1979). There are few studies of the influence of photoperiod on reproduction in pine voles. Geyer and Rogers (1979) reported that exposure to low light intensity reduced the number of litters and number of young per litter in pine voles. However, Lepri and Noden (1984) reported that reproductive function was independent of photoperiod in adult male pine voles in North Carolina. Short photoperiod has been shown to reduce litter size, number of litters or reproductive organ weights in Microtus agrestis (Baker and Ransom, 1932a,b), M. pennsylvanicus (Imel and Amann, 1979) and M. californicus (Nelson et al., 1983). The additive effects of photoperiod and nutrition have been demonstrated in M. montanus (Pinter and Negus, 1965) and M. californicus (Nelson et al., 1983). In the present study, two experiments were conducted to determine the relative influence of nutrition and photoperiod on reproduction in pine voles. MATERIALS AND METHODS Laboratory experiment. -The objective of this experiment was to test the influence of nutrition and photoperiod on reproductive activity in adult pine voles under controlled conditions. The experiment was conducted in an unheated, metal frame building with translucent skylight panels. Three to 5 cm of soil were placed in the bottom of four concrete troughs (originally constructed as fish raceways) inside the building. Troughs were divided into 12 sections of 2.2 by 1.1 m each. Adult pine voles were trapped from an orchard near Roanoke, Virginia, in late July and immediately placed in the troughs. On 15 September, groups of two male and five female voles were formed at random and placed in each of the 12 sections. Half of these groups was fed ground Purina Rabbit Chow (C) ad lib. The other half was fed ad lib amounts of both sliced apple and ground rabbit chow (A). The six groups on each diet