Differential patterns of hybridization and introgression between the swallowtailsPapilio machaonandP. hospitonfrom Sardinia and Corsica islands (Lepidoptera, Papilionidae)

Abstract

Proportions of hybridization and introgression between the swallowtails Papilio hospiton, endemic to Sardinia and Corsica, and the holarctic Papilio machaon, were characterized using nine fully diagnostic and two differentiated allozyme loci and a mitochondrial DNA marker. Very low frequencies of F1 hybrids were detected in both Sardinia (0-4%, average 1.4%) and Corsica (0-3%, average 0.5%), as well as of first generation backcrosses (B1). No F2 were observed, in agreement with the hybrid breakdown detected in laboratory crosses. In spite of this minimal current gene exchange, specimens carrying introgressed alleles were found in high proportions in P. machaon but in lower proportions in P. hospiton. Introgression apparently occurred through past hybridization and repeated backcrossing, as evidenced by hybrid index scores and Bayesian assignment tests. Levels of introgression were low (0-1%) at two sex-linked loci and mitochondrial DNA, limited (0.4-2%) at three autosomal loci coding for dimeric enzymes, and high (up to 43%) at four autosomal loci coding for monomeric enzymes. Accordingly, selective filters are acting against foreign alleles, with differential effectiveness depending on the loci involved. The low levels of introgression at sex-linked loci and mitochondrial DNA are in agreement with Haldane's rule and suggest that introgression in P. machaon proceeds mainly through males, owing to a lower fitness of hybrid females. Papilio machaon populations showed higher levels of introgression in Sardinia than in Corsica. The role of reinforcement in the present reproductive isolation between P. machaon and P. hospiton is examined, as well as the evolutionary effects of introgressive hybridization between the two species.

Haldane's rule in the 21st century

“…Studies include work on taxa with male heterogamety, where maternally inherited loci are seen to introgress further than autosomal and paternally inherited loci (for example, in the Mus musculus-M. domesticus hybrid zone, mitochondrial DNA introgresses to a greater degree than autosomal loci (Raufaste et al, 2005)), as well as taxa with female heterogamety (where biparentally inherited loci are seen to introgress deeper than maternally inherited ones; Jiggins et al, 1997;Helbig et al, 2001;Cianchi et al, 2003;Kronforst et al, 2006). As a particularly comprehensive example, Carling and Brumfield (2008) studied cline width in a (female-heterogametic) avian hybrid zone and found that Z-linked and mitochondrial genes introgressed less deeply than autosomal markers, which is consistent with HR.…”

Dos and Don’ts for butterflies of the Habitats Directive of the European Union

“…(Aubert et al 1997;Aubert et al 1996;Cianchi et al 2003;Manil and Diringer 2003) Papilio alexanor esper, 1800 E: Southern Swallowtail F: l'Alexanor…”

The influence of hybridization on colony structure in the ant species Temnothorax nylanderi and T. crassispinus

“…Hybrids frequently have lower fitness than the parental species, and hybrid zones, where two closely related, parapatric species meet, are stabilized by hybrid inferiority or breakdown (e.g., Barbash et al, 2000;Cianchi et al, 2003). However, research during the last decade has shown that gene introgression may increase the genetic diversity of the hybrid relative to its parental species and can lead to hybrid vigor (Grant andGrant, 1994, Wang et al, 1997).…”