Abstract
The worldwide increase of hybridization in different groups is thought to have become more important with the loss of isolating barriers and the introduction of invasive species. This phenomenon could result in the extinction of endemic species. This study aims at investigating the hybridization dynamics between the endemic and threatened Lesser Antillean iguana (Iguana delicatissima) and the invasive common green iguana (Iguana iguana) in the Lesser Antilles, as well as assessing the impact of interspecific hybridization on the decline of I. delicatissima. 59 I. delicatissima (5 localities), 47 I. iguana (12 localities) and 27 hybrids (5 localities), who were all identified based on morphological characters, have been genotyped at 15 microsatellites markers. We also sequenced hybrids using ND4 mitochondrial loci to further investigate mitochondrial introgression. The genetic clustering of species and hybrid genetic assignment were performed using a comparative approach, through the implementation of a Discriminant Analysis of Principal Component (DAPC) based on statistics, as well as genetic clustering approaches based on the genetic models of several populations (Structure, NewHybrids and HIest), in order to get full characterization of hybridization patterns and introgression dynamics across the islands. The iguanas identified as hybrids in the wild, thanks to morphological analysis, were all genetically F1, F2, or backcrosses. A high proportion of individuals were also the result of a longer-term admixture. The absence of reproductive barriers between species leads to hybridization when species are in contact. Yet morphological and behavioral differences between species could explain why males I. iguana may dominate I. delicatissima, thus resulting in short-term species displacement and extinction by hybridization and recurrent introgression from I. iguana toward I. delicatissima. As a consequence, I. delicatissima gets eliminated through introgression, as observed in recent population history over several islands. These results have profound implications for species management of the endangered I. delicatissima and practical conservation recommendations are being discussed in the light of these findings.
Highlights
Hybridization between two closely related species is a natural phenomenon observed in around 10% of animals and 25% of plant species [1]
The genetic clustering of species and hybrid genetic assignment were performed using a comparative approach, through the implementation of a Discriminant Analysis of Principal Component (DAPC) based on statistics, as well as genetic clustering approaches based on the genetic models of several populations (Structure, NewHybrids and HIest), in order to get full characterization of hybridization patterns and introgression dynamics across the islands
With the loss of isolating barriers, due to anthropogenic factors and the introduction of invasive species, hybridization has become a threat to biodiversity, as endangered species could be lost in the case of intensive hybridization with congeners from exotic species [4]
Summary
Hybridization between two closely related species is a natural phenomenon observed in around 10% of animals and 25% of plant species [1]. Hybridization brings novelty in a gene pool, increasing fitness in new environments, and even speciation [2]. It requires gene flow and can occur when species are found in sympatry and when reproductive isolation is incomplete [3]. Numerous examples [5] of the harmful effects of hybridization in plant and animal taxa have been known to yield to extinction, with or without introgression. Several cases of hybridizations have been reported within and between different genera in iguanas [6, 7]. Gutsche & Köhler [8, 9] demonstrated that Ctenosaura similis, a coastal species, hybridizes with the insular C. bakeri and poses serious conservation issues for this latter
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