Fission and fusion of Darwin's finches populations

Abstract

This study addresses the causes and evolutionary consequences of introgressive hybridization in the sympatric species of Darwin's ground finches (Geospiza) on the small island of Daphne Major in the Galápagos archipelago. Hybridization occurs rarely (less than 2% of breeding pairs) but persistently across years, usually as a result of imprinting on the song of another species. Hybrids survive well under some ecological conditions, but not others. Hybrids mate according to song type. The resulting introgression increases phenotypic and genetic variation in the backcrossed populations. Effects of introgression on beak shape are determined by the underlying developmental genetic pathways. Introgressive hybridization has been widespread throughout the archipelago in the recent past, and may have been a persistent feature throughout the early history of the radiation, episodically affecting both the speed and direction of evolution. We discuss how fission through selection and fusion through introgression in contemporary Darwin's finch populations may be a reflection of processes occurring in other young radiations. We propose that introgression has the largest effect on the evolution of interbreeding species after they have diverged in morphology, but before the point is reached when genetic incompatibilities incur a severe fitness cost.

Natural hybridization generates mammalian lineage with species characteristics

“…A critical observation is that bats of the genus Artibeus are one of the youngest and most specious lineages of the family Phyllostomidae (46,47). Thus, the patterns of differential rates of reproductive isolation described herein are comparable to empirical studies of young radiations that have identified similar evolutionary patterns regarding the presence/absence of pre-and postmating isolating mechanisms and introgressive hybridization (48)(49)(50).…”

Transitions between phases of genomic differentiation during stick-insect speciation

“…Evidence for divergent selection promoting this process (rather 13 than genome-wide drift) is bolstered if: (1) gene flow is still appreciable, (2) genome-wide 14 differentiation is correlated with environmental differences or traits under divergent selection 15 (i.e., genome-wide 'isolation-by-adaptation', IBA) 11,12 , and (3) genome-wide responses to 16 selection are confirmed with experiments [13][14][15] . Genome-wide differences have been 17 documented in herring 16 , mosquitoes 17 , and apple-maggot flies 10,14 , and genome-wide IBA has 18 been reported in many organisms 11,12 . Notably, theory predicts genomic differentiation can be 19 promoted by polygenic adaptation 3 , epistasis 18 , the coupling of differentiation across loci (as in 20 hybrid zone theory) 19 , and mate choice 20,21 .…”

Two new endemic species of Chrysopodes (Neosuarius) (Neuroptera, Chrysopidae) from the Galapagos Islands

“…However, in one case, e.g., a male specimen in the series of C. (N.) nigripilosus from Pinta has particularly weakly pigmented wings and genitalia that resemble those of C. (N.) nigripilosus. As in some species of Darwin's fi nches on the Galápagos (Grant and Grant 2008), there may be a low incidence of hybridization between the Chrysopodes species.…”