PREIMPLANTATION PREGNANCY DISRUPTION IN FEMALE MEADOW VOLES MICROTUS-PENNSYLVANICUS (RODENTIA, MURIDAE) - MALE COMPETITION OR FEMALE MATE CHOICE

I investigated alternative hypotheses concerning the functions of pre- implantation male-induced pregnancy disruption in meadow voles. Disrup tions may be viewed as: 1. Postcopulatory male competition; 2. A mecha nism for postcopulatory mate choice by females;and 3. A means of benef itting females by terminating investment in litters that may be harmed by new males. Female voles were paired with a second male 3 d after m ating with their first mate. Behavioural interactions between the fema le and each male were compared for females that disrupted or retained the pregnancy sired by the first male. Whether they were the females' first or second mates, males siring litters showed similar high levels of approach and moderately high aggression, behaviour that differed f rom the females' other mates. Disrupted females huddled sooner with th eir second mates than females that retained their original pregnancies , and females tended to approach males that approached them. These res ults suggest that females influence whether a disruption occurs by the amount of contact they initiate with the second male, and thus pregna ncy disruption may facilitate postcopulatory mate choice by females. T his pre-implantation disruption did not enhance female reproductive su ccess: pup survival was the same whether or nor a disruption occurred, and males living with pups they had sired (after a disruption) spent as much time with them as males with unrelated pups (females did not d isrupt).