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Survey of the chytrid fungus Batrachochytrium dendrobatidis from montane and lowland frogs in eastern Nigeria


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The chytrid fungus Batrachochytrium dendrobatidis (Bd) that causes the amphibian disease chytridiomycosis might have originated in sub-Saharan Africa. Based on historical museum collections, it has been detected in frog specimens from Central Africa (Cameroon) as early as 1933. Yet, to date, there are few surveys of Bd for recently collected specimens from Central Africa. We present the results of a study undertaken to evaluate the presence and prevalence of Bd in eastern Nigeria at lowland and montane sites in Gashaka-Gumti National Park and in or near Ngel Nyaki Forest Reserve, respectively. Using quantitative real-time PCR, we detected three low-intensity cases of B. dendrobatiis infection each in a different genus of frog (Amietophrynus, Astylosternus, and Petropedetes), including in an undescribed species, at the lowland site in Gashaka-Gumti National Park. While it is promising that Bd was detected at only low intensities and at only one site, the extent to which Bd is distributed in this region of high amphibian diversity in Africa requires further evaluation.
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Many recent amphibian declines are associated
with the emergence of a pathogenic fungus,
Batrachochytrium dendrobatidis (Bd), that causes
the disease chytridiomycosis in amphibians (Berger
et al. 1998). This deadly disease has been linked to
the decline of over 200 amphibian species worldwide
(Skerratt et al. 2007), with the majority of these declines
observed in Australia and the New World (e.g., Fisher
et al. 2009). Recent studies have documented the
presence of Bd in a variety of genera in at least 13
countries in sub-Saharan Africa, mostly in southern and
eastern Africa (Blackburn et al. 2010). However, aside
from one possible Bd-caused decline in Tanzania (for
the toad Nectophrynoides asperginis: Weldon & du
Preez 2004; Channing et al. 2006), there have been no
reported declines in African amphibians associated with
Bd infection. Recent surveys of museum specimens
reveal that Bd has a long history of presence in sub-
Saharan Africa, beginning in at least the early 1930s
(Soto-Azat et al. 2010), bolstering previous suggestions
that this pathogen may be endemic to Africa (Weldon
et al. 2004). Weldon et al. (2004) further proposed that
the global trade of Xenopus laevis from South Africa
may have caused the spread of Bd from Africa to other
regions (Weldon et al. 2004).
The earliest potential record of Bd in Africa (1933)
derives from preserved museum specimens collected
in Cameroon (Soto-Azat et al. 2010), which hosts
one of Africa’s richest amphibian faunas. However,
there are few previously published surveys of Bd in
western and central Africa, including Cameroon and
neighboring Nigeria. Investigation of ve individuals
of Hoplobatrachus occipitalis collected in Nigeria
during 1971 did not detect Bd (Oullett et al. 2005).
Surveys in Okomu National Park in Nigeria between
2007 and 2008 found one individual of Chiromantis
rufescens with a conrmed Bd infection (Imasuen et
al. 2009). Bd has also been detected recently much
farther east in Central Africa (Greenbaum et al. 2008).
However, rather than view this record as suggestive of
Bd infection elsewhere in Central Africa, this record
of Bd from eastern Democratic Republic of Congo
might be best interpreted as indicative of the margins
of the Bd-positive region encompassing East African
countries such as Kenya (Kielgast et al. 2009), Tanzania
(Weldon and du Preez 2004; Channing et al. 2006), and
Uganda (Goldberg et al. 2007; Soto-Azat et al. 2010).
Additional information is sorely needed to determine
the prevalence and potential impact of Bd in central and
Herpetology Notes, volume 4: 083-086 (2011) (published online on 24 February 2011)
Survey of the chytrid fungus Batrachochytrium dendrobatidis from
montane and lowland frogs in eastern Nigeria
Natalie M. M. Reeder1,$, Tina L. Cheng1,$, Vance T. Vredenburg1, and David C. Blackburn2*
1 Department of Biology, San Francisco State University, San
Francisco, California, 94132, USA;
2 Division of Herpetology, Biodiversity Institute, University of
Kansas, Lawrence, Kansas 66045, USA;
* Corresponding author
$ These authors contributed equally
Abstract. The chytrid fungus Batrachochytrium dendrobatidis (Bd) that causes the amphibian disease chytridiomycosis might
have originated in sub-Saharan Africa. Based on historical museum collections, it has been detected in frog specimens from
Central Africa (Cameroon) as early as 1933. Yet, to date, there are few surveys of Bd for recently collected specimens from Central
Africa. We present the results of a study undertaken to evaluate the presence and prevalence of Bd in eastern Nigeria at lowland
and montane sites in Gashaka-Gumti National Park and in or near Ngel Nyaki Forest Reserve, respectively. Using quantitative
real-time PCR, we detected three low-intensity cases of B. dendrobatiis infection each in a different genus of frog (Amietophrynus,
Astylosternus, and Petropedetes), including in an undescribed species, at the lowland site in Gashaka-Gumti National Park. While
it is promising that Bd was detected at only low intensities and at only one site, the extent to which Bd is distributed in this region
of high amphibian diversity in Africa requires further evaluation.
Keywords. Amphibian declines, Africa, chytridiomycosis, Gashaka-Gumti National Park, Mambilla Plateau, Ngel Nyaki
Forest Reserve.
Natalie M. M. Reeder et al.
western Africa as well as to help resolve whether Bd
may have originated in Africa. We conducted a survey
of the distribution and prevalence of Bd in eastern
Nigeria at lowland and montane sites on or near the
Mambilla Plateau.
Materials and Methods
During the course of short opportunistic surveys in April 2009,
chytrid screening was carried out (by DCB) at lowland and mon-
tane sites near or on, respectively, the Mambilla Plateau (Fig. 1;
Table 1). The lowland eld site is based near the Kwano eld
camp of the Gashaka Primate Project within Gashaka-Gumti Na-
tional Park (Adamawa State). At this site, most frogs were coll-
ected in close proximity to a stream, including in the leaf litter, in
the water of the streams, on sandy banks, or on rock faces within
the stream. Frogs were collected from a handful of montane loca-
lities all near the eld station of the Nigerian Montane Forest Pro-
ject adjacent to the Ngel-Nyaki Forest Reserve near Yelwa village
(Taraba State). These montane sites included forested streams in
the forest reserve as well as tree-lined riparian corridors, grass-
land streams, eucalyptus plantations, and farms outside of the re-
serve. Nearly all frogs were collected active in the grass and leaf
litter, though some, especially male Leptopelis nordequatorialis,
were collected calling from trees at night. All specimens screened
for chytrid are deposited in the herpetology collections of the Mu-
seum of Comparative Zoology (Harvard University).
Infection status was determined through a standardized swabbing
protocol (Hyatt et al. 2007). Using a synthetic cotton swab, each
individual was swabbed with 30 strokes (ve times between the
toes on each hindfoot, ve times on each thigh, and ve times on
each side of the ventral abdomen). Swabs were extracted using a
PrepMan extraction and run in duplicate by quantitative real-time
PCR (qPCR) as described by Boyle et al. (2004) and Hyatt et al
(2007). Each plate contained negative controls. Standard samples
of known Bd quantity served as positive controls on each plate;
standards were obtained from the Australian Animal Health La-
boratory (courtesy of A. Hyatt). Samples were considered posi-
tive for Bd if qPCR revealed a measurable quantity (Genomic
Equivalent, GE > 0) of Bd in either of the two replicates during
the 40 cycle thresholds (CT) of the run. False positives were eli-
minated by ensuring that amplication curves followed standard
exponential growth patterns (Hyatt et al. 2007). Infection levels
on individual amphibians were quantied as zoospore equivalents
obtained by multiplying genomic equivalents by 80 to correct for
dilution during extraction and PCR.
Results and Discussion
We tested 34 individuals from ve currently
recognized families and ten genera from the lowland
and montane sites (Table 1). The overall prevalence
of Bd for our survey was 8.8% (3/34), with 0% (0/18)
prevalence at the montane site, and 18.8% (3/16)
prevalence at the lowland site (Table 1). Positive
samples all produced low-level infections (less than
1 zoospore equivalents), and were detected in three
lowland species: Astylosternus sp., Amietophrynus sp.,
Petropedetes sp. nov. Specimens from these species
were all collected in or adjacent to a large stream
running past the Kwano eld camp within Gashaka
Gumti National Park.
Specimens of two of the species tested for Bd
comprise type specimens of species described only
recently (Artholeptis palava: Blackburn et al. 2010;
Phrynobatrachus danko: Blackburn 2010) Other
specimens represents an undescribed species of
Petropedetes (Blackburn unpublished data). Bd was not
detected in Artholeptis palava and Phrynobatrachus
Locality Coordinates Elevation Species (Family) No. Tested No. Positive
Kwano Camp,
Gashaka Gumti N.P.
07 19' 47.9'' N
011 35' 06.0'' E
~540 m Amietophrynus sp. (Bufonidae)
Astylosternus sp. (Arthroleptidae)
Cardioglossa leucomystax (Arthroleptidae)
Hylarana galamensis (Ranidae)
Hyperolius sp. (Hyperoliidae)
Petropedetes sp. nov. (Petropedetidae)
Phrynobatrachus cornutus (Ranidae)
Phrynobatrachus natalensis (Ranidae)
Ngel Nyaki F.R. 07 05' 53.3'' N
011 03' 19.6'' E
~1460 m Phrynobatrachus steindachneri (Ranidae) 2 0
Kurmi Danko F.R. 07 06' 54.6'' N
011 01' 35.8'' E
~1500 m Phrynobatrachus danko (Ranidae) 3 0
Ngel Nyaki F.R. 07 05' 10.0'' N
011 03' 59.9'' E
~1550 m Arthroleptis palava (Arthroleptidae)
Astylosternus sp. (Arthroleptidae)
Leptodactylodon cf. bicolor (Arthroleptidae)
Yelwa 07 05' 17.0'' N
011 04' 41.1'' E
~1550 m Amietophrynus cf. villiersi (Bufonidae)
Leptopelis nordequatorialis (Arthroleptidae)
Yelwa 07 05' 18.1'' N
011 05' 06.6'' E
~1580 m Arthroleptis palava (Arthroleptidae) 1 0
Riparian forest,
near Ngel Nyaki F.R.
07 05' 00.5'' N
011 03' 51.0'' E
~1630 m Leptopelis nordequatorialis (Arthroleptidae) 3 0
Table 1. Species screened for Bd in this study.
Survey of the chytrid fungus in eastern Nigeria 85
danko, both from montane sites, but was detected in one
specimen of the undescribed species of Petropedetes.
The data presented here expand our knowledge of
the geographic and taxonomic distribution of Bd in
Nigeria and Africa. Though Bd was present in three
frog specimens, we did not observe any sick or dying
frogs associated with Bd infection during our survey.
In addition, the animals that were positive have very
low zoospore equivalents or low infection intensities.
Previous eld studies showed that high infection
intensities lead to disease and eventually population
extinctions whereas frogs with low infection intensities
(at the levels we found in this study) show no signs of
disease and populations persist with Bd (Vredenburg et
al. 2010; Briggs et al. 2010). Our results showing low
levels of Bd infection intensities corresponds with the
observation that there are no reports of mortality events
associated with Bd infection anywhere in central or
western Africa. Unfortunately, it is impossible to know
the dynamics of this host-pathogen system in the areas
surveyed in this study because of the opportunistic
nature of the survey and the lack of previous Bd
surveys at these sites.
Further studies are needed to test the susceptibility or
resistance of Nigerian amphibians to Bd. At present,
it remains difcult to evaluate the potential threat that
Bd represents to these amphibian populations. Future
studies could also potentially benet from a better
understanding of the natural immune responses of
these species to Bd infection. In addition, the testing of
additional historical museum specimens from Nigeria
should be conducted to determine the prevalence of Bd
in Nigeria, at least over the past century. Finally, due
to our limited sample sizes and geographic sampling,
our understanding of the distribution and threat of Bd
in Nigeria remains incomplete. With our discovery of
several low-level Bd-positive individuals, we hope
that this will lead to more thorough, repeated, and
widespread surveys of Bd in Nigeria.
Acknowledgements. Field research in Nigeria was facilitated
through collaboration with Hazel Chapman (University of
Canterbury, New Zealand) and the Nigerian Montane Forest
Project as well as Volker Sommer (University College London,
United Kingdom) and the Gashaka Primate Project. The Vice
Chancelor of Gombe State University, A. Mahadi, facilitated
components of eld research. Funding for the eld component
of this research was provided by the Museum of Comparative
Zoology (Harvard University) to DCB, the lab work, conducted
at San Francisco State University, was funded by NSF grant EF-NSF grant EF-
0723563 as part of the joint NSF-NIH Ecology of Infectious
Disease program.
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Accepted by Zoltán T. Nagy
Natalie M. M. Reeder et al.
... In addition, we reviewed primary publication (Reeder et al., 2011) and unpublished report of fauna in GGNP for obtaining names of other existing herpetofauna of GGNP. However, we omitted records of individuals with uncertain taxonomic classifications from our checklist. ...
... With a total of 44 amphibian and reptile species, our study presents a more comprehensive inventory of herpetofauna of GGNP. Previous herpetological surveys of GGNP recorded anuran species of the genera Astylosternus, Leptodactylodon and Petropedetes (Reeder et al., 2011) and reptile species previously documented in GGNP such as Panaspis togoensis (Werner, 1902), Hemidactylus mabouia (Moreau de Jonnès, 1818), Varanus exanthematicus (Linnaeus, 1758), Naja nigricollis (Hallowell, 1857), Bitis arietans arietans (Merrem, 1820), Bitis gabonica rhinoceros [= B. rhinoceros] (Schlegel, 1855) and Causus maculatus (Hallowell, 1842). However, none of these species was recorded during our field study. ...
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... McLaughlin, personal Tomé and Bioko Island specimens (Supplemental Material S1). Despite this apparent widespread distribution, some surveys in Gabon, Cameroon, and eastern Nigeria (Cameroon Volcanic Line) have not detected Bd at several sites that range from lowland forests (Daversa et al. 2011;Gratwicke et al. 2011) to savannah-forest mosaics (Zimkus and Larson 2013) and montane forests (Doherty-Bone et al. 2008;Blackburn et al. 2010;Reeder et al. 2011;Baláž et al. 2012). Due to the opportunistic nature of these field surveys, most do not include sufficient sample sizes to conclude that negative results indicate low or zero pathogen prevalence at these sites. ...
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... By contrast, amphibians colonized the oceanic islands in the Gulf of Guinea via sweepstakes overseas dispersal (Bell et al., 2015;Measey et al., 2007), and thus, the islands host lower overall amphibian diversity: four frog and one caecilian species on São Tomé and three frog species on Príncipe, all of which are endemic (Bell, 2016;Jones, 1994;Uyeda, Drewes, & Zimkus, 2007). Recent surveys in Nigeria (Imasuen et al., 2011;Reeder, Cheng, Vredenburg, & Blackburn, 2011), Cameroon (Balaz, Kopecky, & Gvoždík, 2012;Doherty-Bone et al., 2013;Hirschfeld et al., 2016), Gabon (Bell, Gata Garcia, Stuart, & Zamudio, 2011;Jongsma et al., 2016), and São Tomé Island (Hydeman, Bell, Drewes, & Zamudio, 2013) report Bd across a range of host species, elevations, and habitats in these assemblages. Thus, Lower Guinean forests present a unique opportunity to characterize Bd prevalence among related amphibian assemblages that naturally differ in species richness. ...
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The fungal pathogen Batrachochytrium dendrobatidis (Bd) infects hundreds of amphibian species and is implicated in global amphibian declines. Bd is comprised of several lineages that differ in pathogenicity, thus, identifying which Bd strains are present in a given amphibian community is essential for understanding host–pathogen dynamics. The presence of Bd has been confirmed in Central Africa, yet vast expanses of this region have not yet been surveyed for Bd prevalence, and the genetic diversity of Bd is largely unknown in this part of the world. Using retrospective surveys of museum specimens and contemporary field surveys, we estimated the prevalence of Bd in Central African island and continental amphibian assemblages, and genotyped strains of Bd present in each community. Our sampling of museum specimens included just a few individuals collected in the Gulf of Guinea archipelago prior to 1998, yet one of these individuals was Bd-positive indicating that the pathogen has been on Bioko Island since 1966. We detected Bd across all subsequent sample years in our study and found modest support for a relationship between host life history and Bd prevalence, a positive relationship between prevalence and host community species richness, and no significant relationship between elevation and prevalence. The Global Panzootic Lineage (BdGPL) was present in all the island and continental amphibian communities we surveyed. Our results are consistent with a long-term and widespread distribution of Bd in amphibian communities of Gabon and the Gulf of Guinea archipelago.
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Introduction: Emerging infectious diseases are increasingly recognized as a global threat to wildlife. Pandemics in amphibians, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), have resulted in biodiversity loss at a global scale. Genomic data suggest a complex evolutionary history of Bd lineages that vary in pathogenicity. Africa harbors a significant proportion of global amphibian biodiversity, and multiple Bd lineages are known to occur there; yet, despite the decline of many host species, there are currently no described Bd-epizootics. Here, we describe the historical and recent biogeographical spread of Bd and assess its risk to amphibians across the continent of Africa. Methods: We provide a 165-year view of host-pathogen interactions by (i) employing a Bd assay to test 4,623 specimens (collected 1908-2013); (ii) compiling 12,297 published Bd records (collected 1852-2017); (iii) comparing the frequency of Bd-infected amphibians through time by both country and region; (iv) genotyping Bd lineages; (v) histologically identifying evidence of chytridiomycosis, and (vi) using a habitat suitability model to assess future Bd risk. Results: We found a pattern of Bd emergence beginning largely at the turn of the century. From 1852–1999, we found low Bd prevalence (3.2% overall) and limited geographic spread, but after 2000 we documented a sharp increase in prevalence (18.7% overall), wider geographic spread, and multiple Bd lineages that may be responsible for emergence in different regions. We found that Bd risk to amphibians was highest in much of eastern, central, and western Africa. Discussion: Our study documents a largely overlooked yet significant increase in a fungal pathogen that could pose a threat to amphibians across an entire continent. We emphasize the need to bridge historical and contemporary datasets to better describe and predict host-pathogen dynamics over larger temporal scales.
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Despite increasing interest in determining the population-level effects of emerging infectious diseases on wildlife, estimating effects of disease on survival rates remains difficult. Even for a well-studied disease such as amphibian chytridiomycosis (caused by the fungus Batrachochytrium dendrobatidis [Bd]), there are few estimates of how survival of wild hosts is affected. We applied hierarchical models to long-term capture-mark-recapture data (mean = 10.6 yrs, range = 6–15 yrs) from >5500 uniquely-marked individuals to estimate the effect of Bd on apparent survival of four threatened or endangered ranid frog species (Rana draytonii, R. muscosa, R. pretiosa, R. sierrae) at 14 study sites in California and Oregon (USA) and one bufonid toad (Anaxyrus boreas) at two study sites in Wyoming and Montana. Our models indicated that the presence of Bd on an individual reduced apparent survival of ranid frogs by ~6–15% depending on species and sex. The estimated difference between toads with and without Bd was 19% for the Montana population and 55% for the Wyoming population; however, the 95% Credible Interval of these estimates included zero. These results provide evidence for negative effects of Bd on survival in wild populations even in the absence of obvious die-offs. Determining what factors influence the magnitude of the effects of Bd on wildlife populations is an important next step toward identifying management actions. These estimates of Bd effects are important for understanding the extent and severity of disease, whether disease effects have changed over time, and for informing management actions.
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Emerging infectious diseases may be contributing to the global decline of amphibian populations. In particular, chytridiomycosis, a cutaneous fungal infection of amphibians caused by the chytrid Batrachochytrium dendrobatidis, gained attention in the 1990s as an apparently new pathogen. This fungus has been implicated as the causative agent of widespread mortalities among wild amphibians in geographically disparate parts of the world. To investigate the global distribution, historical occurrence, and infectiousness of this pathogen, we examined 3371 postmetamorphic and adult amphibians collected between 1895 and 2001 from 25 countries for the presence of chytrid fungi in the epidermis. Cutaneous chytrid infection was diagnosed in 383 of 2931 (13.1%) specimens of 12 common amphibian species from five Canadian provinces and seven American states, including 30 of 69 locations examined in the St. Lawrence River Valley of Québec. Chytrids were observed in 7.0% (46/655) of the adults collected in the 1960s, the earliest cases being two green frogs ( Rana clamitans) collected in 1961 from Saint-Pierre-de-Wakefield, Québec. In recent studies, morbidity and mortality attributable to chytridiomycosis were not observed in infected amphibians from Québec despite a 17.8% (302/1698) prevalence of chytrid infection during the period 1990–2001. The prevalence of infection during this latter period was not statistically different when compared with the period 1960–1969. Epidermal chytrid infections were not observed in 440 amphibians examined from 23 other countries. In light of the fact that infection by B. dendrobatidis is widely distributed and apparently enzootic in seemingly healthy amphibians from eastern North America, lethal outbreaks of chytridiomycosis among amphibian populations appear to have complex causes and may be the result of underlying predisposing factors.
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A new species of squeaker frog (genus Arthroleptis) is described from the northern mountains of the Cameroon Volcanic Line, a species-rich region within the West African biodiversity hotspot. This new species is associated with human-altered landscapes, including farms and grasslands, and is known from the highland areas near Bamenda, including Mt. Oku, Cameroon, as well as the Obudu and Mambilla Plateaus of eastern Nigeria. The known distribution suggests that it may eventually also be found throughout the Acha-Tugi Ridge that traverses the Cameroon-Nigeria border. More than 40 years ago, a specimen from one of these populations was recognized as probably representing a new species, but no further work was published on this material. We posit that the taxonomy of this new species has proven problematic because of morphological similarity to Arthroleptis poecilonotus . Although in some ways resembling A. poecilonotus, a molecular phylogeny based on mitochondrial gene sequence data demonstrates that the new species is not closely related to A. poecilonotus and, instead, forms a clade with A. krokosua, A. perreti, and A. variabilis. The new species is diagnosable by the combination of medium-small body size (24-29 mm snout-vent length in adult females), the color patterns of the venter and head, and a relatively stout hindlimb with a prominent inner metatarsal tubercle. The description of this new species further highlights these mountains as an important region of endemism within the Cameroon Volcanic Line.
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A new species of puddle frog (Phrynobatrachus) is described from the Kurmin Danko Forest Reserve on the western edge of the Mambilla Plateau in eastern Nigeria. The new species is distinguished from both geographically proximate and closely related Phrynobatrachus species by the combination of its body size (larger than the closely related P. chukuchuku, P. manengoubensis, and P. werneri), degree of development of male traits, and a unique ventral colour pattern in males. Molecular phylogenetic analysis reveals that this new species is closely related to P. werneri and P. manengoubensis, which, together with several other species, form a clade restricted to the mountains of the Cameroon Volcanic Line. This new Phrynobatrachus is the first known amphibian species hypothesized to be endemic to the Mambilla Plateau of eastern Nigeria.
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Epidermal changes caused by a chytridiomycete fungus (Chytridiomycota; Chytridiales) were found in sick and dead adult anurans collected from montane rain forests in Queensland (Australia) and Panama during mass mortality events associated with significant population declines. We also have found this new disease associated with morbidity and mortality in wild and captive anurans from additional locations in Australia and Central America. This is the first report of parasitism of a vertebrate by a member of the phylum Chytridiomycota. Experimental data support the conclusion that cutaneous chytridiomycosis is a fatal disease of anurans, and we hypothesize that it is the proximate cause of these recent amphibian declines.
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Contemporary global declines and mortality events in amphibian populations have been often attributed to infectious disease and climate change, separately and in combination. We report on an enigmatic mortality event in the only known population of the Critically Endangered frog species Xenopus longipes. This aquatic and biologically distinctive species is restricted to Lake Oku, a high-elevation crater lake on Mt. Oku in Cameroon. Neither a quantitative PCR-based screen nor histopathological analysis revealed the presence of the chytrid fungus Batrachochytrium dendrobatidis, which is believed to be responsible for many declines and mortality events in amphibian populations around the world. Histopathology revealed widespread epidermal hyperplasia and multifocal saprolegniasis suggesting that the animals have been exposed to a source of skin irritation. These sources might include acidified surface waters, perhaps derived from inorganic fertilisers or other human-related pollutants, or to local geological processes distinctive of the Cameroonian Volcanic Line. Currently, the causes underlying this mortality event remain obscure.
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Aim Amphibian chytridiomycosis, an emerging infectious disease caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), is associated with global amphibian population declines and species extinctions. Current evidence indicates that the pathogen has recently spread globally from an enzootic focus, with Xenopus spp. (family Pipidae) in South Africa having been identified as a likely source. The aim of this study was to investigate further the likelihood of African Xenopus spp. as the original source of Bd.
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The global emergence and spread of the pathogenic, virulent, and highly transmissible fungus Batrachochytrium dendrobatidis, resulting in the disease chytridiomycosis, has caused the decline or extinction of up to about 200 species of frogs. Key postulates for this theory have been completely or partially fulfilled. In the absence of supportive evidence for alternative theories despite decades of research, it is important for the scientific community and conservation agencies to recognize and manage the threat of chytridiomycosis to remaining species of frogs, especially those that are naive to the pathogen. The impact of chytridiomycosis on frogs is the most spectacular loss of vertebrate biodiversity due to disease in recorded history.
The ovoviviparous Kihansi spray toad Nectophrynoides asperginis is known from only one locality in the Udzungwa Mountains, Tanzania. At the time of discovery in 1996 the species occurred in a spray wetland habitat of about 4 ha maintained by spray from falls on the Kihansi River. River flow was diverted for hydropower production in late 1999, causing the habitat to desiccate, threatening the toad population and other plants and animals dependent on the spray wetland habitat. We conducted field studies from January 2001 to November 2002 in 12 visits, with additional counts through to June 2003. Here we report on the changes in population numbers in the light of the mitigation measures introduced from 2001 in an attempt to maintain a habitat suitable for the Kihansi spray toad. Some data on life history are presented. This small toad is now restricted to an area of less than 2 ha. Due to a reported population crash in late 2003, variously attributed to pesticide use upstream, chytrid fungus, or safari ants (Dorylus sp.), the Kihansi spray toad may be effectively extinct in the wild. The actual cause of the population crash is not known.
Amphibians at the global scale are dramatically declining and the pathogenic fungus Batrachochytrium dendrobatidis (Bd) has been suggested to be an important driver in this biodiversity crisis. Increasing evidence points towards the global emergence of Bd being a panzootic caused by pathogen pollution. Africa has been suggested to be the origin of the pathogen but remains one of the least-studied areas. We have conducted the most comprehensive survey on the continent to date focusing on Kenya for investigating taxonomic and environmental components in the distribution of Bd in tropical Africa. Eleven sites along a 770 km transect from the coast up to the border of Uganda were surveyed. Using quantitative PCR, we screened 861 samples from 23 different species in nine genera. The pathogen was confirmed at all studied sites, with an overall prevalence of 31.5%. No dead or symptomatic specimens were found and no declines have been reported in the region so far. Both prevalence and parasite load ranged from the detection limit to some of the highest ever reported. The parasite load showed a significant taxonomic bias and a strong inverse correlation with temperature. Our findings suggest that Bd may be enzootic in the region. We recommend that further research should focus on comparative experimental studies of susceptibility to Bd in African species. Moreover, we stress the need for improved knowledge on the conservation status of the tropical African amphibian fauna to confirm the enzootic nature of widespread Bd infections.