Low genetic variation and morphological uniformity throughout the Congolian forest zone do not support the validity of Cryptothylax minutus Laurent, 1976 (Anura: Hyperoliidae), rendering the genus Cryptothylax monotypic

Abstract

Central Africa is characterized by exceptionally high amphibian diversity, including members of the family Hyperoliidae, a group restricted to sub-Saharan Africa, Madagascar, and the Seychelles. The genus Cryptothylax is easily recognized from other hyperoliids by its brownish-orange (males) to orange-red (females) colouration and the typical large gular gland covering the entire throat of males. The genus presently contains two recognized species, the large-bodied and widespread C. greshoffii and the small-bodied C. minutus, a supposed endemic of the Lake Tumba region in the western Democratic Republic of the Congo. Cryptothylax greshoffii is a common inhabitant of open sites in the Congolian forest zone, typically riverbanks, while C. minutus has not been recorded since 1955, when its type series was collected from open habitats at two sites near Mabali, eastern Lake Tumba area. The latter taxon was described by its collector after >20 years (1976), but since the description its species status has been disputed as the only ‘clear’ diagnostic feature is its smaller size. During a recent field survey at the type locality, a series of small-bodied adult Cryptothylax individuals corresponding to C. minutus was collected. Here, we present molecular and morphological investigations of the newly collected material in comparison with C. greshoffii from across its range and morphological comparisons with the holotype of C. minutus. Molecular analyses uncovered low genetic variation across the genus’ range, including shared alleles in both mitochondrial and nuclear markers between the small and large Cryptothylax, confirming their conspecificity. Morphometric analyses also found no significant differences except for the body size. Therefore, we place C. minutus in the synonymy of C. greshoffii, making the genus Cryptothylax monotypic. We also document small adult individuals of C. greshoffii from other distant areas in the Congo Basin. Whether the small body size represents a young age cohort or an ecological morphotype remains a subject for further research.