Data from: Size-assortative choice and mate availability influences hybridization between red wolves (Canis rufus) and coyotes (Canis latrans)

Anthropogenic hybridization of historically isolated taxa has become a primary conservation challenge for many imperiled species. Indeed, hybridization between red wolves (Canis rufus) and coyotes (Canis latrans) poses a significant challenge to red wolf recovery. We considered 7 hypotheses to assess factors influencing hybridization between red wolves and coyotes via pair-bonding between the two species. Because long-term monogamy and defense of all-purpose territories are core characteristics of both species, mate choice has long-term consequences. Therefore, red wolves may choose similar-sized mates to acquire partners that behave similarly to themselves in use of space and diet. We observed multiple factors influencing breeding pair formation by red wolves and found that most wolves paired with similar-sized conspecifics and wolves that formed congeneric pairs with non-wolves (coyotes and hybrids) were mostly female wolves, the smaller of the two sexes. Additionally, we observed that lower red wolf abundance relative to non-wolves and the absence of helpers increased the probability that wolves consorted with non-wolves. However, successful pairings between red wolves and non-wolves was associated with wolves that maintained small home ranges. Behaviors associated with territoriality are energetically demanding and behaviors (e.g., aggressive interactions, foraging, and space use) involved in maintaining territories are influenced by body size. Consequently, we propose the hypothesis that size disparities between consorting red wolves and coyotes influence positive assortative mating and may represent a reproductive barrier between the 2 species. We offer that it may be possible to maintain wild populations of red wolves in the presence of coyotes if management strategies increase red wolf abundance on the landscape by mitigating key threats, such as human-caused mortality and hybridization with coyotes. Increasing red wolf abundance would likely restore selection pressures that increase mean body and home-range sizes of red wolves and decrease hybridization rates via reduced occurrence of congeneric pairs.

人为活动引发的历史隔离类群间杂交，已成为诸多濒危物种面临的核心保护挑战。其中，红狼（Canis rufus）与郊狼（Canis latrans）之间的杂交，对红狼的种群恢复构成了严峻考验。本研究基于7项假说，评估了通过两个物种种间配偶结合影响红狼与郊狼杂交的各类因素。由于长期单配制与全域领地防御是两个物种的核心特征，配偶选择会产生长期的演化后果。因此，红狼可能会选择体型相近的配偶，以获得在空间利用与食性上与自身行为模式相似的伴侣。我们观测到多个影响红狼繁殖配对形成的因素：绝大多数红狼会选择体型相近的同种个体作为配偶；而与非狼类群（郊狼与杂交个体）形成同属配对的个体，大多为两个性别中体型更小的雌性红狼。此外，研究发现红狼种群丰度相对低于非狼类群，以及抚育帮手的缺失，会提升红狼与非狼类群结伴配对的概率。但红狼与非狼类群的成功配对，则与维持较小家域的个体相关。领地防御相关行为的能量消耗极高，而维持领地所需的行为（如攻击性互动、觅食与空间利用）均受体型大小的影响。据此，我们提出假说：结伴配对的红狼与郊狼之间的体型差异，会影响正向选型交配（positive assortative mating），并可能成为两个物种种间的生殖隔离屏障。我们认为，若通过缓解人为致死、与郊狼杂交等核心威胁因子的管理策略，提升景观尺度下红狼的种群丰度，那么在郊狼共存的环境中仍可维持红狼的野生种群。提升红狼种群丰度，或可恢复选择压力，进而提高红狼的平均体型与家域面积，并通过减少同属跨物种配对的发生概率，降低杂交发生率。