Abstract
Science has shown that the introgression or hybridization of modern humans (Homo sapiens) with Neanderthals up to 40,000 YBP may have led to the swarm of modern humans on earth. However, there is little doubt that modern trade and transportation in support of the humans has continued to introduce additional species, genotypes, and hybrids to every country on the globe. We assessed the utility of species distributions modeling of genotypes to assess the risk of current and future invaders. We evaluated 93 locations of the genus Tamarix for which genetic data were available. Maxent models of habitat suitability showed that the hybrid, T. ramosissima x T. chinensis, was slightly greater than the parent taxa (AUCs > 0.83). General linear models of Africanized honey bees, a hybrid cross of Tanzanian Apis mellifera scutellata and a variety of European honey bee including A. m. ligustica, showed that the Africanized bees (AUC = 0.81) may be displacing European honey bees (AUC > 0.76) over large areas of the southwestern U.S. More important, Maxent modeling of sub-populations (A1 and A26 mitotypes based on mDNA) could be accurately modeled (AUC > 0.9), and they responded differently to environmental drivers. This suggests that rapid evolutionary change may be underway in the Africanized bees, allowing the bees to spread into new areas and extending their total range. Protecting native species and ecosystems may benefit from risk maps of harmful invasive species, hybrids, and genotypes.
Highlights
By way of definition, the human species may be an instructive example of a hybrid swarm: the interbreeding of Homo sapiens and Neanderthal (Homo neanderthalensis) and other archaic human forms may have led to gains in disease immunity and cold-hardiness that helped modern humans spread to all corners of the globe [1]
We focus on two areas of study receiving limited attention including: (1) the direct invasion of hybrid species, such as tamarisk and Africanized honey bees, a genetic mixing of African and European honey bees; and (2) the potential for newly establishing alien species to hybridize with native or earlier-arriving alien species resulting in a hybrid swarm
The species are distinct in their home lands: T. ramosissima is widely distributed across temperate Asia, while T. chinensis is restricted to China, Korea, and Japan [25]
Summary
The human species may be an instructive example of a hybrid swarm: the interbreeding (or introgression) of Homo sapiens and Neanderthal (Homo neanderthalensis) and other archaic human forms may have led to gains in disease immunity and cold-hardiness that helped modern humans spread to all corners of the globe [1]. In terms of species distribution modeling [4, 5], it seems reasonable to assume that the inclusion of Neanderthal genes for cold-hardiness or disease resistance may have helped expand the “potentially suitable habitat” for modern humans. The increasing mobility of modern humans greatly diminished the former geographic isolation of other species. Many harmful, invasive plants, animals, and diseases are being spread across the globe with alarming consequences [8]. We focus on two areas of study receiving limited attention including: (1) the direct invasion of hybrid species, such as tamarisk (saltcedar; Tamarix) and Africanized honey bees, a genetic mixing of African and European honey bees; and (2) the potential for newly establishing alien species to hybridize with native or earlier-arriving alien species resulting in a hybrid swarm (i.e., a rapidly spreading hybrid taxon)
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