Evolution of the African slippery frogs (Anura: Conraua), including the world’s largest living frog

Abstract

Although Conraua goliath is well known as the largest living frog species, the diversity and evolution of the genus Conraua across sub-Saharan Africa remain poorly understood. We present multilocus phylogenetic analyses of the six currently recognized species that provide insights into divergence times, biogeography, body size evolution and undescribed species. An analysis of divergence times demonstrates that crown-group Conraua arose some time during the latest Oligocene to mid-Miocene followed by divergence into major lineages in the mid-Miocene that may reflect the fragmentation of widespread tropical forests in Africa that began at this time. We find three pairs of sister species, C. crassipes + C. beccarii, C. alleni + C. derooi and C. goliath + C. robusta, each of which diverged during the Miocene. These relationships reject phylogenetic hypotheses based solely on biogeography as the geographically peripheral C. beccarii from northeastern Africa is nested within western African species and the Central African species do not form a clade. Our species delimitation analyses provide support for undescribed species in C. alleni, C. beccarii and C. derooi, and possibly C. crassipes, suggesting that the current taxonomy substantially underestimates species diversity. There is no clear directional trend of either increasing or decreasing body size in Conraua and the three largest species do not form a clade. With a robust phylogenetic hypothesis in hand, further field-based studies are needed to understand the evolution of morphology and life history in this charismatic African anuran clade.

Phylogeny of African Long-Fingered Frogs (Arthroleptidae: Cardioglossa) Reveals Recent Allopatric Divergences in Coloration

“…The deep divergence between C. occidentalis and C. leucomystax, which for many years were treated as a single species (Blackburn et al, 2008), likely reflects the fragmentation of equatorial forests associated with the expansion of open woodlands and savannas during the Miocene (Jacobs et al, 2010). Similar spatiotemporal patterns of divergence have been found in other African anurans, including torrent frogs (Petropedetes and Arthroleptides; Barej et al, 2014), toads (Nimbaphrynoides and Didynamipus;Liedtke et al, 2016), and slippery frogs (Conraua; Blackburn et al, 2020).…”

A new slippery frog (Amphibia, Conrauidae, Conraua Nieden, 1908) from the Fouta Djallon Highlands, west-central Guinea

“…We examined four Conraua specimens from Konkouré Fetto, five specimens from Hörè Binti and five specimens from Chute de Ditinn, all of which are from the Fouta Djallon Region in Guinea and all are deposited in the collection of the Museum für Naturkunde Berlin, Germany (ZMB). The holotype and two paratypes of the new species were included in the study by Blackburn et al (2020). All individuals were preserved in 75% ethanol.…”

“…For statistical comparisons of morphological characters with the new taxa, we focused on populations of the C. alleni complex that were included in the recent phylogeny of the genus (see Blackburn et al 2020). Our analyses included thirteen individuals of C. alleni sensu lato (Table 4, Appendix 2), three individuals from Soyah, Fouta Djallon (Appendix 2) and 10 from Konkouré Fetto, Hörè Binti and Chute de Ditinn, Fouta Djallon.…”

“…They are distributed in East (C. beccarii), Central (C. goliath, C. crassipes, C. robusta) and West Africa (C. alleni, C. derooi, C. sagyimase). A recent phylogenetic analysis of the genus Conraua indicated that the frogs, known as C. alleni, actually comprise a species complex, including lineages from the Fouta Djallon (Blackburn et al 2020). Here, we take a step forward in disentangling the taxonomy of this species complex.…”

“…Here, we take a step forward in disentangling the taxonomy of this species complex. Through a combination of comparative morphology and the recent molecular phylogenetic analyses of Blackburn et al (2020), we describe a new species of Conraua that is known from Konkouré Fetto, Hörè Binti and Chute de Ditinn in the Fouta Djallon Highlands, central Guinea.…”