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Variable genomic patterns of hybridization in an expanding hybrid zone of damselflies
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  • Rosa Ana Sánchez-Guillén,
  • Luis Rodrigo Arce-Valdés,
  • Janne Swaegers,
  • Pallavi Chauhan,
  • Jesús R Chávez-Rios,
  • Anais Rivas-Torres,
  • Maren Wellenreuther,
  • Bengt Hansson
Rosa Ana Sánchez-Guillén
Instituto de Ecología A. C., Xalapa 91070, Veracruz

Corresponding Author:[email protected]

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Luis Rodrigo Arce-Valdés
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Janne Swaegers
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Pallavi Chauhan
Lund University
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Jesús R Chávez-Rios
Instituto de Investigaciones Biomédicas, Unidad Foránea Tlaxcala. UNAM
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Anais Rivas-Torres
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Maren Wellenreuther
The University of Auckland
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Bengt Hansson
Lund University
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The outcome of hybridization is of major interest in evolutionary and conservation biology. Here, we investigate (i) the genomic signal of the hybridization dynamics, (ii) the strength of reproductive barriers preventing copulation in heterospecific and hybrid crosses, and (iii) the population dynamics (stability of species proportions) of the two damselfly species Ischnura elegans and I. graellsii in two differently aged Spanish hybrid regions. RAD sequencing in these hybrid regions and in allopatric populations was used to generate 5,702 SNPs to quantify population diversity and population differentiation, and a subset of 381 species-specific SNPs to analyze individual ancestry and the proportion of individuals in different hybrid classes. Our individual ancestry results showed the presence of F1 and F2 hybrids, in line with on-going hybridization and bidirectional backcrossing in both hybrid regions, with almost complete absence of genetically pure I. elegans and I. graellsii. Different admixture-class distributions were in part explained by 1) different mean strength of reproductive barriers in the hybrid regions, with stronger barrier in the older hybrid region, 2) local dynamics (continuous recolonization events), 3) proximity to introduction site, and 4) time elapsed since colonization. Consistent with theoretical expectations, introgression maintained (in the younger hybrid region) or increased genetic diversity (in the older hybrid region), and reduced genetic differentiation between local populations in both hybrid regions. Whether this will facilitate the ongoing range expansion of I. elegans in Spain is an interesting avenue for future research.