Hybridization between <i>Calopteryx splendens</i> and <i>C. haemorrhoidalis</i> confirmed by morphological and genetic analyses

<div><p>Hybridization between <i>Calopteryx haemorrhoidalis</i> and any of its congeners has not been reported until now. We observed spontaneous matings between male <i>C. splendens</i> and female <i>C. haemorrhoidalis</i> at a locality in Central Italy, together with some putative hybrid individuals that had a mixed phenotype. Here, we report the morphological and molecular characterization of five suspected hybrids collected from this population during 2001 (<i>n</i>=1), 2012 (<i>n</i>=2) and 2013 (<i>n</i>=2). A discriminant analysis based on 13 morphological variables correctly separated both parental species (with 100% assignation success) and classified the hybrid from 2001 as <i>splendens</i> phenotype and those from 2012 and 2013 as <i>haemorrhoidalis</i>. Genotype data (microsatellite loci) was used to confirm the hybrid origin of these specimens, although there were differences between the individual from 2001 and those from 2012 and 2013; the 2001 individual had alleles that were present in both parent species, suggesting it is an F1 hybrid, but the individuals collected in 2012 and 2013 had private alleles at eight (out of 12) loci and only a small portion of the genome in common with <i>C. splendens</i>, which suggests that introgression is occurring in this population. Similarities in mitochondrial DNA sequences indicate that the 2001 hybrid and the 2012–2013 hybrids have <i>splendens</i> and <i>haemorrhoidalis</i> maternal origins respectively, which, in contrast with behavioural observations, indicates that interspecific matings in both directions are possible. This is the first demonstration that <i>C. haemorrhoidalis</i> can hybridize with other congeners to produce viable offspring.</p></div>