Apple drops were removed from a portion of an apple orchard in September and apples left available in the remainder of the orchard. Presence of apples had little effect on the immature:adult ratio or on body weight. However, adult males and juveniles of both sexes had higher values for reproductive characteristics in November and December in the area with apples available. In a laboratory experiment adult voles fed a rabbit chow diet supplemented with apple consumed less digestible energy but had higher body weights and more body fat, and males had heavier testes than those fed only chow. Adults on a 14L:10D photoperiod had higher values for reproductive characteristics than those on a declining photoperiod. In a third experiment juveniles fed a horse chow diet supplemented with apples had higher body weights and more body fat, initiated and completed molt to adult pelage at higher body weights and had heavier reproductive organs than those given only chow. In these experiments voles with access to apples dia not consume more digestible energy but they grew faster, were in better condition and were more likely to produce offspring. The consumption of apples possibly stimulated the hypothalamus anu;or pituitary gland, increasing synthesis or release of gonadotropins. Adult pine voles on a declining or short photoperiod may be inhibited reproductively because of antigonadotropic substances produced by the pineal gland. Consuming apples could affect the degree of inhibition. It was hypothesized pine voles use both photoperiod and nutrition as cues fox reproduction. / Master of Science

I examined parental behaviour of three vole species, the brandt{\crq}s vole (Microtus brandti), the common vole (M. arvalis) and the levant vole (M. guentheri) in laboratory conditions. Monogamous and highly social Brandt{\crq}s voles displayed high levels of parental and paternal care. However, mostly promiscuous and solitary common voles also exhibited an intensive parental care. In contrast, polygynous and social levant voles displayed very low levels of parental care. Males of both latter species engaged in parental activities but spent less time in contact with pups then females. These findings suggest that intensive parental care may be connected rather with the high growth rate a slower postnatal development of the species than with social or reproductive system.