Hybrid dysfunction in fire-bellied toads (Bombina) Journal Article

Author(s): Kruuk, Loeske E; Gilchrist, Jason S; Barton, Nicholas H
Article Title: Hybrid dysfunction in fire-bellied toads (Bombina)
Abstract: Reproductive isolation between two taxa may be due to endogenous selection, which is generated by incompatibilities between the respective genomes, to exogenous selection, which is generated by differential adaptations to alternative environments, or to both. The continuing debate over the relative importance of either mode of selection has highlighted the need for unambiguous data on the fitness of hybrid genotypes. The hybrid zone between the fire-bellied toad (Bombina bombina) and the yellow-bellied toad (B. variegata) in central Europe involves adaptation to different environments, but evidence of hybrid dysfunction is equivocal. In this study, we followed the development under laboratory conditions of naturally laid eggs collected from a transect across the Bombina hybrid zone in Croatia. Fitness was significantly reduced in hybrid populations: Egg batches from the center of the hybrid zone showed significantly higher embryonic and larval mortality and higher frequencies of morphological abnormalities relative to either parental type. Overall mortality from day of egg collection to three weeks after hatching reached 20% in central hybrid populations, compared to 2% in pure populations. There was no significant difference in fitness between two parental types. Within hybrid populations, there was considerable variation in fitness, with some genotypes showing no evidence of reduced viability. We discuss the implications of these findings for our understanding of barriers to gene flow between species.
Keywords: Hybrid zone; Speciation; Natural selection; Reproductive isolation
Journal Title: Evolution; International Journal of Organic Evolution
Volume: 53
Issue 5
ISSN: 0014-3820
Publisher: Wiley-Blackwell  
Date Published: 1999-10-01
Start Page: 1611
End Page: 1616
DOI: 10.2307/2640907
Open access: no