Abstract
Mechanisms which prevent gene flow will maintain differentiation between species, and therefore contribute to biological diversity. We describe an experimental study of such mechanisms in a hybrid zone between the fire-bellied toad Bombina bombina and the yellow-bellied toad B. variegata . In this system, preference for different breeding habitats reduces the frequency of hybridization. A comparison of habitat ecology shows that the semi-permanent ponds in which B. bombina usually breeds have higher densities of aquatic predators than the temporary puddles typically used by B. variegata . We test for behavioural adaptations in tadpoles to these different levels of predation. B. bombina tadpoles are significantly less active than B. variegata , both before and after the introduction of a predator to an experimental arena; this reduces their vulnerability as many predators detect prey through movement. Behavioural differences translate into differential survival: B. variegata suffer higher predation rates in laboratory experiments with three main predator types ( Triturus sp., Dytiscus larvae, Aeshna nymphs). This differential adaptation to predation will help maintain preference for alternative breeding habitats, and thus serve as a mechanism maintaining the distinctions between the two species.
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More From: Proceedings of the Royal Society of London. Series B: Biological Sciences
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