Using the “placeholder” concept to reduce genetic introgression of an endangered carnivore

Abstract

One of the most endangered species is the red wolf, Canis rufus. Reintroduction of the red wolf began in 1987, but in 1993 hybridization between coyotes (Canis latrans) and wolves was documented. To reduce genetic introgression, coyotes and coyote-wolf hybrids were captured, sterilized, and released as "placeholders". Placeholders held territories until either displaced or killed by a wolf, or management personnel removed them before releasing a wolf. We evaluated the placeholder concept by examining the number of animals sterilized and released, likelihood of displacement by a wolf, factors influencing displacements, territory fidelity of placeholders, and survival rates and causes of mortality of placeholders and wolves. Of the 182 placeholders, 125 were coyotes and 57 were hybrids. From 1999 to 2013, 51 placeholders were displaced or killed by wolves, and 16 were removed by management personnel. Thus, 37% of the placeholders were displaced leading to occupancy by a wolf. Most displacements occurred in winter (43%) and were always by the same sex. Males were more likely to be displaced than females. Home range characteristics influencing the probability of displacement included home-range size (i.e., more placeholders displaced from larger home ranges) and road density (i.e., more placeholders displaced from home ranges with lower road density). Annual survival of placeholders was higher than wolves in 12 of 14 years, with cause-specific mortality similar among wolves and placeholders. Placeholders provided territories for wolves to colonize, yet reduced the production of hybrid litters, thereby limiting genetic introgression to b4% coyote ancestry in the wolf population.Published by Elsevier Ltd.

Survival and population size estimates of the red wolf

“…Consequently, when no red wolf mates were available, surviving resident wolves paired with coyotes creating congeneric breeding pairs responsible for hybridization. Indeed, hybridization was considered a primary threat to the persistence of the wild population and, in response, the RWAMP was developed and implemented to prevent coyote introgression via sterilization of coyotes paired with red wolves (Stoskopf et al , Hinton et al , Gese and Terletzky , Gese et al ). Regardless of whether coyote mates are fertile or sterile, congeneric pairings with coyotes represents lost reproductive effort by the red wolf population (Brzeski et al , Hinton et al ).…”

“…Anthropogenic mortality and hybridization were identified as the 2 primary threats to red wolves (Kelly et al , USFWS , Rabon and Bartel 2013). Despite measures taken to address hybridization via the RWAMP (Stoskopf et al , Gese and Terletzky , Gese et al ), the USFWS has not addressed threats of anthropogenic mortality for red wolves. Ultimately, understanding how causes of red wolf mortalities change over time will allow the USFWS to respond with effective management to reduce excessive mortality and achieve population sizes essential to recovery.…”

Space Use and Habitat Selection by Resident and Transient Red Wolves (Canis rufus)

“…Hinton [69–70] suggested as red wolves and coyotes approached each other in body size, similar use of prey and space may reduce behavioral incompatibilities between consorting individuals and permit the successful formation of congeneric pairs responsible for creating red wolf/coyote hybrids. Because hybridization is a primary threat to the conservation and persistence of eastern wolves [14,18,71–72] and red wolves [3,16,38,21–22,73], we suggest further studies are needed to better understand behaviors and conditions that allow individuals of Canis populations to successfully form congeneric breeding pairs responsible for hybridization.…”

“…Because red wolf and coyote packs maintain exclusive territories, resident red wolves are capable of excluding coyotes from areas they occupy [21]. Indeed, Gese and Terletzky [21] reported that all displacement of canids was unidirectional with larger red wolves displacing smaller coyotes and hybrids and not vice versa. The goal of recovery efforts was to ensure that all Canis breeding pairs within the Recovery Area were red wolves [22].…”

Describing a developing hybrid zone between red wolves and coyotes in eastern North Carolina, USA

“…; Stoskopf et al. ), yet this study and additional evidence suggest this is incorrect (Bohling and Waits ; Gese and Terletzky ; Gese et al. ; Hinton et al.…”