Harmonizing hybridization dissonance in conservation

Abstract

A dramatic increase in the hybridization between historically allopatric species has been induced by human activities. However, the notion of hybridization seems to lack consistency in two respects. On the one hand, it is inconsistent with the biological species concept, which does not allow for interbreeding between species, and on the other hand, it is considered either as an evolutionary process leading to the emergence of new biodiversity or as a cause of biodiversity loss, with conservation implications. In the first case, we argue that conservation biology should avoid the discussion around the species concept and delimit priorities of conservation units based on the impact on biodiversity if taxa are lost. In the second case, we show that this is not a paradox but an intrinsic property of hybridization, which should be considered in conservation programmes. We propose a novel view of conservation guidelines, in which human-induced hybridization may also be a tool to enhance the likelihood of adaptation to changing environmental conditions or to increase the genetic diversity of taxa affected by inbreeding depression. The conservation guidelines presented here represent a guide for the development of programmes aimed at protecting biodiversity as a dynamic evolutionary system. B iodiversity is in crisis and the main reasons are human activities inducing habitat modifications and the introduction of invasive species 1. In addition, global climate change will probably alter habitat characteristics, migration patterns, reproduction time, and place of various species 2. Such human disturbances may produce new breeding overlaps, breaking the independent evolution of organisms and leading to hybridization (see Glossary, Table 1) 3. The role of hybridization in the evolution of several plant and animal taxa has been recognized in the light of newly developed molecular tools 4. This has also alerted biologists about the threat this phenomenon may represent to biodiversity when enhanced by anthropogenic factors 5. We identified three types of hybridization regarding the reproductive properties of first-generation

Consequences of Hybridization in Mammals: A Systematic Review

“…Depending on species and environmental conditions, hybridization may have either negative or positive impacts, and sometimes there may be very limited consequences. In some cases, hybridization can drive species toward extinction, while in others it provides an opportunity to create new species [ 124 ]. Genetic swamping, outbreeding depression, introgression of variants originating from domesticated lineages, and morphological anomalies are typically associated with negative consequences, such as loss of adaptive variation [ 26 , 125 , 126 , 127 , 128 , 129 , 130 ], high mortality rates [ 131 ], and even extinction [ 30 ].…”

“…This could include cases where hybridization was rare or did not occur, as well as cases where limitations in sampling and the use of low number of genetic makers could result in poor detection of hybridization [ 216 , 217 , 218 , 219 , 220 , 221 , 222 , 223 , 224 , 225 ]. The number of genetic markers is important to detect signatures of hybridization, especially if cross-breeding and/or back-crossing events are rare [ 56 , 124 ]. Moreover, small data sets may show only a preliminary assessment of hybridization [ 226 ], and comprehensive sampling is necessary to obtain reliable results.…”

Extensive genome introgression between domestic ferret and European polecat during population recovery in Great Britain.

“…Hybridisation and introgression may increase the adaptive potential of species by the fixation of beneficial alleles or removal of detrimental alleles and can be used as a tool for species recovery (Chan, Hoffmann, & van Oppen, 2019;Quilodran, Montoya-Burgos, & Currat, 2020). Whole genome sequencing has allowed quantitative assessment of introgression in British polecats.…”

Demystifying Negative Connotations of Hybridization for Less Biased Conservation Policies

“…Yet, what would then happen with the Florida panther that has been bred intentionally with an introduced species for genetic rescue? This poses a dilemma especially considering that hybridization resulted in increased population levels, colonization of new areas and improvement of its demographical trend (Pimm et al, 2006).…”