Genetics, Morphology, Advertisement Calls, and Historical Records Distinguish Six New Polyploid Species of African Clawed Frog (Xenopus, Pipidae) from West and Central Africa

Abstract

African clawed frogs, genus Xenopus, are extraordinary among vertebrates in the diversity of their polyploid species and the high number of independent polyploidization events that occurred during their diversification. Here we update current understanding of the evolutionary history of this group and describe six new species from west and central sub-Saharan Africa, including four tetraploids and two dodecaploids. We provide information on molecular variation, morphology, karyotypes, vocalizations, and estimated geographic ranges, which support the distinctiveness of these new species. We resurrect Xenopus calcaratus from synonymy of Xenopus tropicalis and refer populations from Bioko Island and coastal Cameroon (near Mt. Cameroon) to this species. To facilitate comparisons to the new species, we also provide comments on the type specimens, morphology, and distributions of X. epitropicalis, X. tropicalis, and X. fraseri. This includes significantly restricted application of the names X. fraseri and X. epitropicalis, the first of which we argue is known definitively only from type specimens and possibly one other specimen. Inferring the evolutionary histories of these new species allows refinement of species groups within Xenopus and leads to our recognition of two subgenera (Xenopus and Silurana) and three species groups within the subgenus Xenopus (amieti, laevis, and muelleri species groups).

<b><i>Silurana</i></b> Chromosomal Evolution: A New Piece to the Puzzle

“…This unusual pattern of locus localization on 2 different chromosomes (2, 9) and the findings that X. mellotropicalis is a relatively young species [Evans et al, 2015] with morphologically very similar chromosomes within the quartets [Knytl et al, 2017] can be associated with the idea of a still ongoing diploidization process [Tymowska, 1991].…”

“…The remaining species X. calcaratus , whose genome reorganization after/before tetraploidization is still unclear, has probably originated from the same allotetraploidization event [Evans et al, 2015].…”

Overland movement in African clawed frogs (Xenopus laevis): a systematic review

“…The results of this revision mean that what was previously known as X. l. laevis by a number of authors (e.g., Kobel, Loumont & Tinsley, 1996; Poynton, 1964) is now known as X. laevis with all other subspecies being recognised as full species, as well as some newly described species (e.g., Evans et al, 2015). The full range of X. laevis is now known to cover much of southern Africa: South Africa, Lesotho, Swaziland, Namibia, parts of Botswana, Zimbabwe, parts of Mozambique and extending north into Malawi.…”

Sequential Turnovers of Sex Chromosomes in African Clawed Frogs (Xenopus) Suggest Some Genomic Regions Are Good at Sex Determination

“…These two species are members of different subgenera that are distinguished from each other by the number of chromosomes ( x ) carried by the gametes of their respective diploid ancestors, i.e. , x = 10 for subgenus Silurana and x = 9 for subgenus Xenopus (Evans et al 2015). All extant species in subgenus Xenopus are polyploid, but with disomic chromosomal inheritance, and tetraploids in this subgenus have 4 x = 36 chromosomes.…”

“…Within subgenus Xenopus , species in a clade including X. borealis (Parker 1936), X. muelleri (Peters 1844), and X. fischbergi (Evans et al 2015) appear to lack DM-W (Bewick et al 2011), hinting at additional diversity of sex chromosomes in this group. The phylogenetic placement of this clade within Xenopus remains uncertain, making unclear the evolutionary histories of potentially diverse triggers for sex determination.…”