Jeanette A. Thomas

Parental care and mating system of the prairie vole, Microtus ochrogaster

Summary1.The mating system of prairie voles (Microtus ochrogaster) was investigated by experimentally manipulating the sexual composition of vole societies, thereby providing each vole with a variety of mating choices.2.In male-female pairs, both parents appeared to contribute equally to the care of young, with the exception of lactation. Paternal activities included nest and runway construction, food caching, and grooming, retrieving, and brooding the young.3.Voles in 26 of 27 societies mated monogamously; those in the other group mated polygynously.4.Nonreproductive voles in the experimental societies generally lived in communal groups. Communal groups are known to occur in field populations of prairie voles, but it is not known if they exist during periods of reproductive activity.5.We address the questions of the adaptive significance of voles living communally and we consider the relationship between communal voles and dispersing voles in nature. The results of this study were interpreted relative to four mating systems that may be associated with paternal care in mammals. We conclude that M. ochrogaster is basically monogamous; a verbal model is presented for the evolution of monogamy in this species.

Relationships between underwater vocalizations and mating systems in phocid seals

In this paper, we considered the number and diversity of underwater vocalizations given by aquaticbreeding phocids, and two species that copulate both in the water and on ice, in relation to what is known or hypothesized about their mating systems. Underwater recordings made throughout the year by both bearded ( Erignathus barbatus ) and Weddell (Leptonychotes weddellii ) seals indicated that most of the vocalizations could be attributed to males and were given almost exclusively during the breeding season. Less extensive studies of other species indicated the same pattern. Thus, for this study, we considered only underwater vocalizations known, or suspected, to be given by adult males during intra-specie c agonistic behaviour, defence of territories or access to females, or attraction of females. A one-way ANOVA and linear regression indicated a signie cant relationship between the numbers of underwater vocalizations given by individual species and their mating systems. A Pearson’ s correlation analysis discerned the following: the mating system and the number of vocalizations were positively correlated; female gregariousness was positively correlated with the number of underwater vocalizations and geographic variation in vocalizations, but there was no correlation with the duration of lactation. The degree of predation was negatively correlated with the number of vocalizations, geographic variation in vocalizations, and the number of days of lactation. A principal component analysis showed that 66.1% of the variation in this data set was explained by Factor 1, a suite of variables that included mating system, number of underwater vocalizations, intensity of predation, female gregariousness, and geographic variation in vocalizations. The number of days of lactation explained an additional 19.5% of the variability. These results suggest that additional selection pressures, more specie c to the ecological circumstances of individual species, also ine uence the size of the underwater repertoire. The development of a diverse underwater repertoire with geographic variations was consistently associated with the development of population genetic structure and geographic e delity. Within each category of social system, the species with the greatest number of underwater vocalizations consistently occurred at higher densities during the breeding season than did the species with the lowest vocal diversity. The role of predators on the evolution of social systems is not well known, but could be signie cant for some species. Characteristics of the underwater vocalizations of walruses during the breeding season were found to share similar characteristics to phocids occurring at similar densities in similar habitats, suggesting that the most important selection factors ine uenced both phocids and odobenids similarly. On the basis of the available information from better-studied species, some testable hypotheses are proposed for further investigations of spotted ( Phoca largha ), Ross (Ommatophoca rossii ), Hawaiian monk (Monachus schauinslandi), and ribbon ( Phoca fasciata) seals.

Effects of boat activity on the behavior of bottlenose dolphins (Tursiops truncatus) in waters surrounding Hilton Head Island, South Carolina

During the summer of 1998, the effects of boat activity on the behavior of bottlenose dolphins (Tursiops truncatus) were investigated using 52 shore-based surveys along Hilton Head Island, South Carolina. Temporal autocorrelation indicated data collected on most variables should be analyzed in 6-min intervals. Responses to boats were categorized as “no response,” “behavioral response,” “change in direction of movement,” or “change in both behavior and direction.” Multiple boats had a greater influence on dolphin behavior and movement than the presence of a single boat. Dolphin-watching boats, motorboats, shrimp boats, and jet skis affected the group size and behavior of dolphin groups. Dolphin groups responded to dolphin-watching boats during 20% of observations, mainly with a change in both behavior and direction of movement. Motorboats caused a response in dolphins during 55% of observations, with a change in behavior or both behavior and direction. Jet skis had a more dramatic effect on dolphin groups, with 56% of groups changing their behavior and 11% changing both their behavior and direction. Shrimp boats always elicited a response. Dolphin groups changed both their behavior, and direction of movement to follow and feed behind these boats. In contrast, ships rarely caused a response, with groups changing their behavior but not their direction in 11% of observations. As the number of boats in the Hilton Head area increased, dolphin groups heightened responses—that is, changed both behavior and direction of movement. These boat-related effects on bottlenose dolphin behavior are considered “harassment” under the U.S. Marine Mammal Protection Act (1972) and should be scrutinized by agencies responsible for public education and enforcement of protective legislation.