Linking reproduction, locomotion, and habitat use in the Trinidadian guppy (Poecilia reticulata).

Pregnancy inhibits locomotion, increases predation risk and may translate into reduced survival. The extent to which animals modify behavior in the wild to compensate for the locomotor costs of pregnancy remains poorly understood. We have investigated how reproductive allocation (RA-the proportion of body mass devoted to reproduction) affects locomotor performance and habitat use in Trinidadian guppy (Poecilia reticulata) populations from low- and high-predation regimes. During steady swimming, females with high RA had increased tail beat amplitudes, indicating increased swimming costs. Females with high RA also exhibited slower escape velocities, which may result in an increased risk of predation. In low-predation localities, females with high RA used habitats with a lower water velocity, suggesting that females may be modifying behavior to offset the locomotor costs of pregnancy. Habitat use in high-predation localities was severely restricted to areas without predators, which had a relatively slower water velocity with little or no variation in current. These results provide a link between the performance-related costs of reproduction and behavior in a natural setting and show that animals may compensate for reproductive traits that constrain locomotor performance by modifying habitat use.