A recent re-evaluation of morphological and advertisement call variation in the large species of frogs of the Leptodactylus pentadactylus cluster discovered more examples of sibling species as defined by Ernst Mayr in his influential book Animal Species and Evolution. All previously documented instances of sibling species in frogs demonstrated advertisement call differentiation consistent with the calls serving as pre-mating isolating mechanisms. However, we find one instance of two species with nondistinguishable adult morphologies as well as nondistinguishable advertisement calls. Presumably, the new instances of sibling species reflect retention of ancestral adult morphologies and advertisement calls. Larval and habitat differentiation appear to be important factors in the speciation processes in this group of frogs.

Ernst Mayr defined sibling species as, ''morphologically similar or identical natural populations that are reproductively isolated," in his influential book Animal Species and Evolution (Mayr, 1963: 34). He considered the phenomenon to be important to understanding the complexity and scope of speciation processes in animals.

Mayr's concept of sibling species has been documented in the frog genus Leptodactylus (Barrio, 1973; Heyer et al., 1996). In these examples, reproductive isolation among sibling species was documented through analysis of advertisement calls. That is, advertisement calls are very different from each other among species whose adults are morphologically identical. Females use the calls to distinguish and select males of their own species to mate with in any mixed chorus where sibling species co-occur.

In the process of re-evaluating variation in the Leptodactylus pentadactylus species cluster, we discovered instances of sibling species that do not demonstrate reproductive isolation on the basis of advertisement calls. Herein we summarize the nature of the differentiation involved and discuss the evolutionary implications of our findings.

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Copyright © 2005 SEH. This proceeding first appeared in Herpetologia Petropolitana: Proceedings of the 12th Ordinary General Meeting of the Societas Europaea Herpetologica, 12-16 August 2003, Saint-Petersburg, Russia, 35-39.

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