Abstract
Hybridization events are frequently demonstrated in natural butterfly populations. One interesting butterfly complex species is the Enantia jethys complex that has been studied for over a century; many debates exist regarding the species composition of this complex. Currently, three species that live sympatrically in the Gulf slope of Mexico (Enantia jethys, E. mazai, and E. albania) are recognized in this complex (based on morphological and molecular studies). Where these species live in sympatry, some cases of interspecific mating have been observed, suggesting hybridization events. Considering this, we employed a multilocus approach (analyses of mitochondrial and nuclear sequences: COI, RpS5, and Wg; and nuclear dominant markers: inter-simple sequence repeat (ISSRs) to study hybridization in sympatric populations from Veracruz, Mexico. Genetic diversity parameters were determined for all molecular markers, and species identification was assessed by different methods such as analyses of molecular variance (AMOVA), clustering, principal coordinate analysis (PCoA), gene flow, and PhiPT parameters. ISSR molecular markers were used for a more profound study of hybridization process. Although species of the Enantia jethys complex have a low dispersal capacity, we observed high genetic diversity, probably reflecting a high density of individuals locally. ISSR markers provided evidence of a contemporary hybridization process, detecting a high number of hybrids (from 17% to 53%) with significant differences in genetic diversity. Furthermore, a directional pattern of hybridization was observed from E. albania to other species. Phylogenetic study through DNA sequencing confirmed the existence of three clades corresponding to the three species previously recognized by morphological and molecular studies. This study underlines the importance of assessing hybridization in evolutionary studies, by tracing the lineage separation process that leads to the origin of new species. Our research demonstrates that hybridization processes have a high occurrence in natural populations.
Highlights
At the beginning of 20th century, hybrid specimens were considered rare in nature and a phenomenon with little evolutionary importance [1]
They suggested that hybridism was reinforced by the action of a bacterial symbiont male-killer, Spiroplasma, which forced females in female-biased populations to mate with heterotypic males
Haplotype networks (S1 Fig) of c oxidase subunit I (COI) and ribosomal protein subunit 5 (RpS5) showed a clear separation among the three morphospecies, whereas for the wingless gene (Wg) haplotype network, E. jethys and E. mazai share its haplotypes
Summary
At the beginning of 20th century, hybrid specimens were considered rare in nature and a phenomenon with little evolutionary importance [1]. Lushai and colleagues [6,7] revealed the existence of a hybrid zone between the tropical Danaus chrysippus (L.) subspecies They suggested that hybridism was reinforced by the action of a bacterial symbiont male-killer, Spiroplasma, which forced females in female-biased populations to mate with heterotypic males. Other studies have demonstrated hybridization and introgression events among Neotropical Heliconius species using mitochondrial and nuclear sequences [9], DNA sequences and amplified fragment length polymorphism (AFLP) [10], and genome-wide genotypic and DNA sequences [11], among others. A new view of hybridization has emerged and is currently regarded as forces that oppose diversification and species stability, but to have the potential to increase biodiversity [12,13]
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