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Although naturally heterogeneous environments can lead to mosaic hybrid zones, human-induced habitat fragmentation can also lead to environmental heterogeneity and hybridization. Here we quantify phenotypic and molecular divergence across a reed frog mosaic hybrid zone on São Tomé Island as a first step towards understanding the consequences of hybridization across this heterogeneous landscape. The São Tomé giant reed frog (Hyperolius thomensis) is strongly tied to cool, wet, forest habitats whereas the distribution of Moller's reed frog (H. molleri) spans cool, wet, forests to warm, dry, disturbed habitats. Correspondingly, hybridization is concentrated in the more forested, cool, wet sites relative to non-forested, warmer, drier habitats. Four of six sites with hybrid frogs are artificial water bodies near the forest edge, indicating that both breeding habitat and broader scale environmental variation are probably important for understanding interspecific interactions and the extent of hybridization in this system. Phenotypic variation (body size and ventral coloration) largely tracks genetic and environmental variation across the hybrid zone with larger and more pigmented frogs occurring in forested, cool, wet habitats. Understanding whether human-induced changes in habitat break down reproductive barriers will be essential for conservation management of the less abundant, forest-associated H. thomensis in the face of rampant hybridization. [ABSTRACT FROM AUTHOR]

Differences in mating signals among incipient species are an important mechanism driving reproductive isolation and speciation. Here, we investigate male advertisement call divergence across a radiation of reed frogs from the Gulf of Guinea archipelago and the most closely related species on the African continent (Hyperolius olivaceus). The two species endemic to the island of São Tomé (Hyperolius molleri and Hyperolius thomensis) differ in body size, coloration and breeding ecology, yet they hybridize where their habitats overlap. A third species, Hyperolius drewesi, is sister to H. molleri and endemic to Príncipe Island. We found significant differences in average dominant frequency and average number of pulses per call among the four species. The strong relationship between body size and dominant frequency irrespective of geographical history, breeding habitat or acoustic environment suggests that differences in this component of the mating signal may be a by-product of adaptive changes in body size among the four species. Hybrid males are intermediate in size between H. molleri and H. thomensis and produce calls at intermediate dominant frequencies. Future efforts to characterize courtship behaviour and breeding habitat preference in allopatric and sympatric populations will provide additional insights as to the potential for reinforcement in this system. [ABSTRACT FROM AUTHOR]

I describe a new species of reed frog ( Hyperolius: Hyperoliidae) from the island of Príncipe in the Gulf of Guinea archipelago. The new species is within the Hyperolius cinnamomeoventris species complex, which includes four described species: H. cinnamomeoventris, H. veithi, H. molleri, and H. thomensis. The new species is sexually monochromatic (males and females have green dorsal coloration) and is thus distinguished from H. cinnamomeoventris, which is sexually dichromatic, and from H. veithi, in which both males and females are tan with yellow dorsolateral lines. The new species is smaller in size than H. thomensis, and differs in coloration from H. molleri and H. thomensis by lacking a black contour along the edges of the green/yellow band of coloration that extends down the dorsal side of the thigh, by lacking red/orange coloration on the dorsal and ventral sides of the thigh, and in the mitochondrial 16s and cytochrome-b genes. Furthermore, previous work indicates that the new species is distinct from H. molleri and H. thomensis in analyses of genome-wide single-nucleotide polymorphisms. This new species is the third endemic amphibian described from this small oceanic island. The type material for the closely related H. molleri and H. thomensis was destroyed or lost; therefore, I designate neotype material for these two species to enable the description of the new species. [ABSTRACT FROM AUTHOR]

Aim To infer the colonization history of reed frog species endemic to the oceanic islands of São Tomé and Príncipe, Hyperolius molleri and H. thomensis, we quantified phylogeographical structure in the closely related H. cinnamomeoventris species complex, which is broadly distributed across continental Central Africa. Location The Lower Guineo-Congolian Forest and the Gulf of Guinea islands of São Tomé and Príncipe, Central Africa. Methods We combined gene and species tree analyses to investigate diversity and divergence among H. cinnamomeoventris populations, to identify the most likely dispersal route to the islands, and to infer the order in which the islands were colonized. One of the endemics ( H. molleri) is distributed on both islands and we quantified genetic divergence between populations. Results We recovered three clades in H. cinnamomeoventris corresponding to West-Central, North/East-Central and South-Central Africa. The island endemics form a monophyletic group most closely related to the West-Central African H. cinnamomeoventris clade. Populations of H. molleri on São Tomé and Príncipe are reciprocally monophyletic at mitochondrial loci but nuclear gene trees do not support this divergence. Main conclusions Genetic structure in the H. cinnamomeoventris species complex coincides with biogeographical barriers identified in previous studies of Central African rain forest taxa. Individual gene tree and species tree analyses support a single dispersal event from the Ogooué or Congo river basins (West-Central Africa) to the island of São Tomé, with subsequent divergence within São Tomé and dispersal to Príncipe. [ABSTRACT FROM AUTHOR]