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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 north‐eastern 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.

West Africa is a region characterised by high species diversity and endemism, making it an ideal region to study the evolution of genetic and phenotypic differentiation. Species in this region ofte...

Forty-nine years after the last description of a slippery frog, we describe a seventh species of the genus Conraua. The new Conraua is endemic to the Atewa Range Forest Reserve, central Ghana, and is described based on genetic, bioacoustics, and morphological evidence. Recent molecular phylogenetic and species delimitation analyses support this population as distinct from nominotypical C. derooi in eastern Ghana and adjacent Togo. The new species is sister to C. derooi, from which it differs ~4% in the DNA sequence for mitochondrial ribosomal 16S. Genetic divergences in 16S to other species of Conraua range from 4–12%. The new species is distinguished morphologically from its congeners, including C. derooi, by the combination of the following characters: medium body size, robust limbs, lateral dermal fringing along edges of fingers, cream ventral color with brown mottling, the presence of a lateral line system, indistinct tympanum, the presence of inner, outer, and middle palmar tubercles, and two subarticular tubercles on fingers III and IV. We compare the advertisement calls of the new species with the calls from C. derooi and find that they differ by duration, frequency modulation, and dominant frequency. We discuss two potential drivers of speciation between C. derooi and the new species, including river barriers and fragmentation of previously more widespread forests in West Africa. Finally, we highlight the importance of the Atewa Range Forest Reserve as a critical conservation area within the Upper Guinean biodiversity hotspot.

In many species, sexual differentiation is a vital prelude to reproduction, and disruption of this process can have severe fitness effects, including sterility. It is thus interesting that genetic systems governing sexual differentiation vary among—and even within—species. To understand these systems more, we investigated a rare example of a frog with three sex chromosomes: the Western clawed frog, Xenopus tropicalis. We demonstrate that natural populations from the western and eastern edges of Ghana have a young Y chromosome, and that a male-determining factor on this Y chromosome is in a very similar genomic location as a previously known female-determining factor on the W chromosome. Nucleotide polymorphism of expressed transcripts suggests genetic degeneration on the W chromosome, emergence of a new Y chromosome from an ancestral Z chromosome, and natural co-mingling of the W, Z, and Y chromosomes in the same population. Compared to the rest of the genome, a small sex-associated portion of the sex chromosomes has a 50-fold enrichment of transcripts with male-biased expression during early gonadal differentiation. Additionally, X. tropicalis has sex-differences in the rates and genomic locations of recombination events during gametogenesis that are similar to at least two other Xenopus species, which suggests that sex differences in recombination are genus-wide. These findings are consistent with theoretical expectations associated with recombination suppression on sex chromosomes, demonstrate that several characteristics of old and established sex chromosomes (e.g., nucleotide divergence, sex biased expression) can arise well before sex chromosomes become cytogenetically distinguished, and show how these characteristics can have lingering consequences that are carried forward through sex chromosome turnovers., Author summary Sex chromosomes often come in pairs (e.g., an X and a Y, or a Z and a W) and variation among species evidences widespread rapid evolutionary changes of sex chromosomes. To understand why, we examined a rare example of a frog (Xenopus tropicalis) with three sex chromosomes. We discovered a small sex-linked sliver of the genome that has a high proportion of genes with higher expression in males than females during gonadal differentiation. Molecular variation in expressed transcripts from this genomic region suggests that this pattern stems from decreased or lost expression of alleles on the W chromosome combined with a recent origin of the Y chromosome from an ancestral Z chromosome. These findings are consistent with theoretical expectations associated with reduced genetic recombination, and demonstrate that features of ancestral chromosomes have persistent genomic effects that bleed through sex chromosome transitions.

Comparative phylogeographic studies often support shared divergence times for co-distributed species with similar life histories and habitat specializations. During the late Holocene, West Africa experienced aridification and the turnover of rain forest habitats into savannas. These fragmented rain forests harbor impressive numbers of endemic and threatened species. In this setting, populations of co-distributed rain forest species are expected to have diverged simultaneously, whereas divergence events for species adapted to savanna and forest-edge habitats should be absent or idiosyncratic. We conducted a Bayesian analysis of shared evolutionary events to test models of population divergence for 20 species of anurans (frogs) and squamates (lizards and snakes) that are distributed across the Dahomey Gap, a climate change-induced savanna barrier responsible for fragmenting previously contiguous rain forests of Ghana into two regions: the Togo-Volta Hills and the Southwestern Forests. A model of asynchronous diversification is supported for anurans and squamates, suggesting that drivers of diversification are not specifically related to ecological and life history associations with habitat types. Instead, the wide variability of genetic divergence histories exhibited by these species suggests that biodiversity in this region has been shaped by diversification events that extend beyond the Holocene. Comparisons of the genealogical divergence index, a measure of the genetic divergence between populations due to the combined effects of genetic isolation and gene flow, illustrate that these populations represent a broad sampling of the speciation continuum.

A comprehensive, accurate, and revisable alpha taxonomy is crucial for biodiversity studies, but is challenging when data from reference specimens are difficult to collect or observe. However, recent technological advances can overcome some of these challenges. To illustrate this, we used modern approaches to tackle a centuries-old taxonomic enigma presented by Fraser's Clawed Frog, Xenopus fraseri, including whether X. fraseri is different from other species, and if so, where it is situated geographically and phylogenetically. To facilitate these inferences, we used high-resolution techniques to examine morphological variation, and we generated and analyzed complete mitochondrial genome sequences from all Xenopus species, including >150-year-old type specimens. Our results demonstrate that X. fraseri is indeed distinct from other species, firmly place this species within a phylogenetic context, and identify its minimal geographic distribution in northern Ghana and northern Cameroon. These data also permit novel phylogenetic resolution into this intensively studied and biomedically important group. Xenopus fraseri was formerly thought to be a rainforest endemic placed alongside species in the amieti species group; in fact this species occurs in arid habitat on the borderlands of the Sahel, and is the smallest member of the muelleri species group. This study illustrates that the taxonomic enigma of Fraser's frog was a combined consequence of sparse collection records, interspecies conservation and intraspecific polymorphism in external anatomy, and type specimens with unusual morphology.

The savannah and tropical forest biomes of Africa have a long history of expansion and contraction, and the recent and rapid spread of dry savannah habitats has influenced the spatial and temporal diversification of vertebrate taxa across this region. We used a combination of species tree and phylogeographic methods to describe the spatio-temporal changes through time and across space (= species diffusion) in a clade of seven West African lizard species in the Agama agama species group. A Bayesian species tree diffusion approach was used to compare the relative rates at which species ranges changed across the landscape. We found that some species have high diffusion rates characterized by significant movement in their range location and minor changes to their overall range size, whereas other species show little movement in their range centre with an exponential increase in range size. This discrepancy between the rates that range locations shift versus change in their relative area could be linked to pop...

Theory predicts that sexually dimorphic traits under strong sexual selection, particularly those involved with intersexual signaling, can accelerate speciation and produce bursts of diversification. Sexual dichromatism (sexual dimorphism in color) is widely used as a proxy for sexual selection and is associated with rapid diversification in several animal groups, yet studies using phylogenetic comparative methods to explicitly test for an association between sexual dichromatism and diversification have produced conflicting results. Sexual dichromatism is rare in frogs, but it is both striking and prevalent in African reed frogs, a major component of the diverse frog radiation termed Afrobatrachia. In contrast to most other vertebrates, reed frogs display female-biased dichromatism in which females undergo color transformation, often resulting in more ornate coloration in females than in males. We produce a robust phylogeny of Afrobatrachia to investigate the evolutionary origins of sexual dichromatism in this radiation and examine whether the presence of dichromatism is associated with increased rates of net diversification. We find that sexual dichromatism evolved once within hyperoliids and was followed by numerous independent reversals to monochromatism. We detect significant diversification rate heterogeneity in Afrobatrachia and find that sexually dichromatic lineages have double the average net diversification rate of monochromatic lineages. By conducting trait simulations on our empirical phylogeny, we demonstrate that our inference of trait-dependent diversification is robust. Although sexual dichromatism in hyperoliid frogs is linked to their rapid diversification and supports macroevolutionary predictions of speciation by sexual selection, the function of dichromatism in reed frogs remains unclear. We propose that reed frogs are a compelling system for studying the roles of natural and sexual selection on the evolution of sexual dichromatism across micro- and macroevolutionary timescales.

We describe a new species of Phrynobatrachus from swamp forests in the southern border region of Ivory Coast and Ghana. The new species differs from all other known West African Phrynobatrachus by the combination of adult snout-vent-length being between 20 and 30 mm; absence of a spiny tubercle on the eyelid; presence of a dark face mask; a black throat in adult males; narrow and partly indistinct scapular ridges or comma shaped warts; distinct spinulae on males’ throats and dorsal surfaces; pronounced pedal webbing; round finger- and toe tips, not enlarged to discs; a white belly with small blackish spots in both sexes; more than one wide dark cross bar on hind legs; and rosé to reddish colour on ventral parts of hind legs in both sexes. It is further defined by its genetic and acoustic characters. It is morphologically and genetically most similar to P. liberiensis and P. intermedius.

We describe a new species of Phrynobatrachus from the eastern part of the Upper Guinea forest region, Ghana, West Africa. Morphologically, the new species can be distinguished from all of its congeners by the combination of a slender body, short and pointed snout, a relatively warty dorsum, a black-spotted throat in both sexes, a gular flap in males, a dark spotted chest, a white-greyish venter with occasional blackish spots, rudimentary pedal webbing, none to slightly dilated finger tips and strongly delated toe tips, presence of both inner and outer metatarsal tubercles and absence of a dark face mask, eyelid tubercles and longer dorsal ridges. We collected mitochondrial DNA (mtDNA) sequence data from the 16S rRNA gene to measure the genetic diversity of the new species, and to estimate phylogenetic relationships. The new species is a distinct and monophyletic evolutionary lineage most closely related to Phrynobatrachus gutturosus, P. fraterculus and P. maculiventris. The discovery of this new species highlights that the biodiversity of West African forests is still incompletely known and that the few remaining forests need urgent protection.

Because tropical forests face serious threats and are usually situated in developing countries, cheap and easy Rapid Biodiversity Assessment (RBA) seems an ideal strategy for documenting changes in habitat quality and setting conservation priorities. Fruit-feeding butterflies are often used as focal taxa to document biodiversity trends in tropical forests. However, the choice of inappropriate sampling strategies may nullify its value. More extensive data sets that sample multiple months and seasons and incorporate the vertical dimension are needed as a baseline for designing reliable sampling regimes. Therefore, we performed a butterfly trapping study in Ghana, using both understorey and canopy traps, and sampling seven periods covering dry and wet seasons. Both individual numbers and species richness were on average three to four times higher in the understorey than in the canopy traps with strikingly different species composition (only 11% overlap in species). The number of species and individual abundance recorded in a month varied extensively. This study underlined the importance of taking into account temporal variation and vertical stratification when designing RBAs of fruit-feeding butterflies in West African forests. We recommend the use of both understorey and canopy traps and inclusion of both ‘wet’ and ‘dry’ seasons into RBA sampling regimes. Resume Comme les forets tropicales font face a des menaces graves et qu'elles sont en general situees dans des pays en developpement, une evaluation rapide de la biodiversite (RBA) semble une strategie ideale pour documenter les changements de qualite de l'habitat et etablir des priorites de conservation. On se sert souvent des papillons frugivores comme taxons focaux pour documenter les tendances de la biodiversite dans des forets tropicales. Cependant, le choix de strategies d’echantillonnage inappropriees risque d'annuler leur valeur. Il faut des ensembles de donnees plus complets, qui echantillonnent sur des mois et des saisons et qui integrent une dimension verticale pour etablir la base de reference permettant de concevoir des regimes d’echantillonnage fiables. C'est pourquoi nous avons fait une etude de piegeage des papillons au Ghana, en utilisant des pieges en sous-bois et dans la canopee, et en couvrant sept periodes comptant des saisons seches et des saisons des pluies. Aussi bien les chiffres individuels que la richesse en especes etaient en moyenne 3 a 4 fois superieurs dans les pieges places en sous-bois que dans la canopee, avec une composition des especes remarquablement differente (seulement 11% de recouvrement des especes). Le nombre d'especes et l'abondance individuelle enregistres en un mois variaient enormement. Cette etude souligne qu'il est important de prendre en compte la variation temporelle et la stratification verticale lorsque l'on prepare une RBA de papillons frugivores dans des forets d'Afrique de l'Ouest. Nous recommandons l'emploi de pieges en sous-bois et dans la canopee et l'inclusion de saisons « seches » et « humides » dans les regimes d’echantillonnages d'une RBA.