Selective browsing by abundant, generalist herbivores on preferred species could allow less-preferred invasive species to flourish. We tested such an effect by examining rates at which white-tailed deer (Odocoileus virginianus Zimmermann) consume Amur honeysuckle [Lonicera maackii (Rupr.) Herder], an invasive shrub, relative to native woody species across eight forested sites in southwestern Ohio. We tested three hypotheses: (1) deer prefer to browse on L. maackii versus other woody plants; (2) L. maackii is not a preferred source of browse, but is consumed where preferred foods are scarce; and (3) L. maackii provides an important food resource for deer in early spring when other foods are scarce. We used counts of browsed and unbrowsed twigs of each species to calculate, for each site, both the proportion of each species’ twigs browsed and the degree to which deer selectively favor each species (“electivity”) during early to mid-growing season. Across the eight sites, electivity of L. maackii correlated with the proportion of its twigs browsed, and both measures were negatively associated with the density of L. maackii twigs. Lonicera maackii electivity was negative at most sites, indicating it is generally not preferred, undermining hypothesis 1. The hypothesis that deer consume L. maackii when more-preferred foods are depleted was not supported, as there was no negative relationship between L. maackii browse and the density of twigs of more-preferred species. We found a negative relationship between the proportion of L. maackii twigs browsed and the density of L. maackii among sites, which supports the third hypothesis. This finding, combined with seasonal patterns of deer browse on L. maackii, indicates that this invasive shrub is an important source of browse for deer during early spring, regardless of its abundance.

Parasites in the genus Onchocerca infect humans, ruminants, camels, horses, suids, and canids, with effects ranging from relatively benign to debilitating. In North America, Onchocerca cervipedis is the sole species known to infect cervids, while at least 5 Onchocerca species infect Eurasian cervids. In this study, we report the discovery of a cervid-parasitizing Onchocerca only distantly related to O. cervipedis. To reconstruct the phylogenetic history of the genus Onchocerca, we used newly acquired DNA sequence from O. cervipedis (from moose in Northwest Territories, Canada) and from the newly discovered species (from white-tailed deer in upstate New York), as well as previously published sequences. Ancestral host reconstructions suggest that host switches have been common throughout the evolutionary history of Onchocerca, and that bovid- and cervid-parasitizing species have been particularly important sources of descendant species. North America cervids might therefore serve as a source for Onchocerca invasions into new hosts. Given the high density of deer populations, the potential for zoonotic infections may also exist. Our discovery of a new Onchocerca species with relatively limited sampling suggests that the diversity of Onchocerca associated with cervids in North America may be greater than previously thought, and surveys utilizing molecules and morphology are necessary.