New evidence for distinctiveness of the island-endemic Príncipe giant tree frog (Arthroleptidae: Leptopelis palmatus)

Abstract

The Príncipe giant tree frog Leptopelis palmatus is endemic to the small oceanic island of Príncipe in the Gulf of Guinea. For several decades, this charismatic but poorly known species was confused with another large tree frog species from continental Africa, L. rufus. Phylogenetic relationships within the African genus Leptopelis are poorly understood and consequently the evolutionary history of L. palmatus and its affinity to L. rufus remain unclear. In this study, we combined mitochondrial DNA (mtDNA), morphological, and acoustic data for L. palmatus and L. rufus to assess different axes of divergence between the species. Our mtDNA gene tree for the genus Leptopelis indicated that L. palmatus is not closely related to L. rufus or other large species of Leptopelis. Additionally, we found low mtDNA diversity in L. palmatus across its range on Príncipe. We found significant morphological differences between females of L. rufus and L. palmatus, but not between males. We characterised the advertisement call of L. palmatus for the first time, which is markedly distinct from L. rufus. Finally, we summarised our observations of L. palmatus habitats and additional notes on phenotypic variation and behaviour. Our study reinforces the distinctiveness of L. palmatus and provides information important for the conservation of this endangered species. A rã gigante de Príncipe, Leptopelis palmatus, é endêmica da pequena ilha oceânica de Príncipe no Golfo da Guiné. Por várias décadas, esta espécie carismática mas pouco conhecida foi confundida com outra espécie grande de rã da África continental, L. rufus. As relações filogenéticas dentro do gênero africano Leptopelis são mal compreendidas e, conseqüentemente, a história evolutiva de L. palmatus e sua afinidade com L. rufus permanecem obscuras. Neste estudo, combinamos dados de DNA mitocondrial (mtDNA), morfológicos e acústicos de L. palmatus e L. rufus para avaliar diferentes eixos de divergência entre as espécies. Nossa árvore de genes de mtDNA para o gênero Leptopelis indicou que L. palmatus não está proximamente relacionada a L. rufus ou outras espécies grandes de Leptopelis, e encontramos baixa diversidade de mtDNA em L. palmatus em toda a sua distribuição em Príncipe. Encontramos diferenças morfológicas significativas entre as fêmeas de L. rufus e L. palmatus, mas não entre os machos. Caracterizamos o canto reprodutor de L. palmatus pela primeira vez, que é marcadamente distinto do de L. rufus. Finalmente, resumimos nossas observações dos habitats de L. palmatus e notas adicionais sobre variação fenotípica e comportamento. Nosso estudo fornece informações importantes para a conservação dessa espécie ameaçada de extinção

The Amphibians of the Gulf of Guinea Oceanic Islands

“…Previous studies have hypothesized that L. palmatus is closely related to a group of large-bodied species in West and Central Africa (L. macrotis, L. millsoni, and L. rufus) based on a combination of mtDNA and morphological data (Idris 2004). A more recent mtDNA phylogeny with expanded taxonomic sampling does not support this relationship (Jaynes et al 2021), and a more robust phylogenetic inference is sorely needed. The distribution of L. palmatus ranges from sea level to over 600 m elevation on Príncipe, primarily in forested habitats (Loumont 1992;Drewes and Stoelting 2004).…”

“…By contrast, large females have been encountered on or near the ground both in the evening and during the day (Drewes and Stoelting 2004; RCB and LAS pers obs). Although males lack vocal sacs (Drewes and Stoelting 2004), they produce advertisement calls at breeding sites (characterized in Jaynes et al 2021). Both male and female dorsal coloration is variable, ranging from dark green/black with or without small white spots to bright green and even bright yellow (Manaças 1958;Loumont 1992;Drewes and Stoelting 2004;Jaynes et al 2021).…”

“…Although males lack vocal sacs (Drewes and Stoelting 2004), they produce advertisement calls at breeding sites (characterized in Jaynes et al 2021). Both male and female dorsal coloration is variable, ranging from dark green/black with or without small white spots to bright green and even bright yellow (Manaças 1958;Loumont 1992;Drewes and Stoelting 2004;Jaynes et al 2021). It does not appear that this variation is sexually dimorphic or related to ontogeny, as has been described in many species of the African genus Hyperolius (Schiøtz 1967;Portik et al 2019).…”

Giant Tree Frog diversification in West and Central Africa: Isolation by physical barriers, climate, and reproductive traits

“…These species occur both in allopatry and in broad parapatry, and collectively their distributions span all major physical barriers and ecological gradients across West and Central Africa including the land-bridge island Bioko and the 'climatic hinge', a north-to-south seasonal inversion at 0-3ºN along the southern border of Cameroon (Hardy et al, 2013; Figure 1). Despite this vast distribution and the recognition of multiple distinct lineages (Jaynes et al, 2021;Portik et al, 2019), the species are remarkably challenging to identify based on morphology alone, which resulted in taxonomic confusion for over a century (Ahl, 1929(Ahl, , 1931Noble, 1924;Perret, 1973;Schiøtz, 1967). As a legacy of this confusion, the extent to which L. rufus and L. millsoni occur in true sympatry (i.e.…”

“…millsoni ; [Boulenger, 1895], L . rufus ; Reichenow, 1874) Africa (Figure 1; Jaynes et al, 2021). All three species are arboreal and amongst the largest in the genus, with females reaching up to 87 mm snout–vent length (Channing & Rödel, 2019; Schiøtz, 1999).…”