West Africa - A Safe Haven for Frogs? A Sub-Continental Assessment of the Chytrid Fungus (Batrachochytrium dendrobatidis)

Abstract

A putative driver of global amphibian decline is the panzootic chytrid fungus Batrachochytrium dendrobatidis (Bd). While Bd has been documented across continental Africa, its distribution in West Africa remains ambiguous. We tested 793 West African amphibians (one caecilian and 61 anuran species) for the presence of Bd. The samples originated from seven West African countries - Bénin, Burkina Faso, Côte d'Ivoire, Ghana, Guinea, Liberia, Sierra Leone - and were collected from a variety of habitats, ranging from lowland rainforests to montane forests, montane grasslands to humid and dry lowland savannahs. The species investigated comprised various life-history strategies, but we focused particularly on aquatic and riparian species. We used diagnostic PCR to screen 656 specimen swabs and histology to analyse 137 specimen toe tips. All samples tested negative for Bd, including a widespread habitat generalist Hoplobatrachus occipitalis which is intensively traded on the West African food market and thus could be a potential dispersal agent for Bd. Continental fine-grained (30 arc seconds) environmental niche models suggest that Bd should have a broad distribution across West Africa that includes most of the regions and habitats that we surveyed. The surprising apparent absence of Bd in West Africa indicates that the Dahomey Gap may have acted as a natural barrier. Herein we highlight the importance of this Bd-free region of the African continent - especially for the long-term conservation of several threatened species depending on fast flowing forest streams (Conraua alleni (“Vulnerable”) and Petropedetes natator (“Near Threatened”)) as well as the “Critically Endangered” viviparous toad endemic to the montane grasslands of Mount Nimba (Nimbaphrynoides occidentalis).

Overview of chytrid emergence and impacts on amphibians

“…Bd has been present in South Africa since at least 1938 and is commonly found in Ghana, Kenya, South Africa and Western Africa [62]. Bd is widespread in many of the highland regions [63], whereas tropical West African areas regions are reported to be clear of Bd [64]. Recent reports from Cameroon [65] found Bd present in several species, several of which had shown recent declines and they suggested Bd as a likely cause.…”

Spatial Assessment of Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis) in South Africa Confirms Endemic and Widespread Infection

“…Swab samples from threatened South African frog species (IUCN Red List categories: Vulnerable, Endangered and Critically Endangered) were collected at known historic sites known from the South African frog atlas [25] as well as from new sites where the target species occur, which were detected during the course of the field work between 2008 and 2012, primarily during the rainy months (August – March). Individuals of each species were detected via visual, acoustic or opportunistic searches and caught by hand or net.…”

“…Subsequent detection of Bd with no adverse effects in wild populations from central and east Africa support this hypothesis [19], [20], [21], [22], . However, failure to detect Bd in West Africa and Bd -related population declines in one species from East Africa [24], [25] challenge this hypothesis. Despite the long-term presence of Bd in South Africa little has been done by way of investigating the threat it may pose to indigenous species, in particular those that are Red Listed.…”

Prevalence and genetic diversity of Batrachochytrium dendrobatidis in Central African island and continental amphibian communities

“…Vast expanses of the African continent have yet to be surveyed for Bd ; however, the pathogen appears to have a widespread historical presence in Africa (Soto‐Azat, Clarke, Poynton, & Cunningham, ). With the exception of Upper Guinean rain forests, west of the Dahomey Gap in West Africa (Penner et al., ) and the Seychelles (Labisko et al., ), the contemporary distribution of Bd encompasses a range of environments and amphibian hosts across the African continent (Doherty‐Bone et al., ; Kielgast, Rödder, Veith, & Lötters, ; Olson et al., ). The Lower Guinean forests extend along western Central Africa and collectively host much of Africa's amphibian species richness and endemism (Jenkins, Pimm, & Joppa, ; Myers, Mittermeier, Mittermeier, da Fonseca, & Kent, ).…”