Effects of Fertility Control on Behavior and Disease Transmission in Brushtail Possums

Abstract

Abstract: Fertility control is currently under development for the control of brushtail possums (Trichosurus vulpecula), one of New Zealand's most serious vertebrate pests. Despite intensive research into various methods for achieving infertility, including immunocon‐traception and disrupting endocrine control of reproduction, researchers know little about the potential effects of these methods on the behavior of wild possums. We assessed the effects of surgically imposed sterility, either to block fertilization (tubal ligation) or to disrupt endocrine control of fertility (gonadectomy), by using radiotelemetry on the movement patterns and site fidelity of wild brushtail possums. In addition, we assessed the effect of gonadectomy on the transmission rate of a commonly occurring, directly transmitted pathogen in possums, Leptospira interrogans serovar balcanica (hereafter L. balcanica), to determine the effect of any behavioral changes on possum contact rates. Both tubal ligation and gonadectomy of females did not appear to have any appreciable effect on behavior, with sterilized females having space‐use patterns and fidelity to seasonal breeding ranges similar to those of fertile females. However, gonadectomy of male possums resulted in a significant reduction of 42% and 47% in the 95% and 70% isopleth seasonal breeding ranges, respectively. Furthermore, the transmission rate of L. balcanica in gonadectomized male and female possums was reduced by 88% and 63%, respectively, compared with that in fertile male and female possums. Overall, these results suggest that fertility control, either by blocking fertilization (e.g., immunocontraception) or by disrupting endocrine control of reproduction (e.g., gonadotropin‐releasing hormone vaccines), is unlikely to have an impact on social organization and behavior of brushtail possums in ways that may compromise the efficacy of fertility control for reducing population density. However, the reduction in the transmission rate of L. balcanica indicates that fertility control that interferes with endocrine control of reproduction is likely to reduce the contact rate between possums. This could have implications for the control of other wildlife diseases requiring direct contact for transmission.