Relaxed selection for tick-defense grooming in Père David’s deer?

Abstract

Relaxed selection following extirpation of predators or as a consequence of captive breeding may result in the loss of adaptive antipredator behavior. We propose that it is equally possible for relaxed selection to result in the loss or reduced effectiveness of parasite-defense behaviors such as grooming. In both cases, the reintroduction of captive-bred animals into a predator- or parasite-rich area could have disastrous consequences for the survival of the population. Tick infestation is a powerful force for the evolution of adaptive tick-defense grooming behavior in the wild. The regulation of anti-tick grooming has been well-studied in ungulates and consists of endogenous and exogenous mechanisms, corresponding to the programmed and stimulus-driven grooming models. These models predict that (1) smaller animals will groom more frequently than larger ones, (2) breeding males will groom less than females, (3) animals will groom more during the high-tick season, and (4) animals will groom more in tick-rich vs. tick-sparse habitat. We studied the grooming behavior of Père David’s deer (Elaphurus davidianus), which has experienced genetic bottlenecks and possible relaxed selection as a result of hundreds of years in captivity and was recently reintroduced into the wild in China. Our results indicate that most but not all patterns of adaptive anti-tick grooming behavior have been retained, indicating that some aspects of parasite defense have not undergone relaxed selection even after many years of captivity. Nonetheless, we propose that plans to reintroduce captive-bred animals should take into consideration the historical tick exposure and present grooming behavior of the species in selecting suitable habitat for reintroduction.