Epidermal capillariasis in South African clawed frogs (Xenopus laevis)

Significant morbidity and mortality of South African clawed frogs, Xenopus laevis, can be caused by parasitism of the epidermis by a capillarid nematode. These worms produce an erosive dermatitis that is complicated by infection with gram-negative microorganisms. The nematode apparently has a direct life cycle that can be completed within the epidermis of the frog. These characteristics are suggested by the lack of an intermediate host and failure to detect visceral migration. Another unique feature of the parasite was the presence of larvated eggs, in utero. Some have named the parasite Capillaria xenopodis, whereas others called it Pseudocapillaroides xenopi to distinguish it form the typical members of the genus Capillaria.     

Disease attributed to Mycobacterium chelonae in South African clawed frogs (Xenopus laevis)

The fast-growing nontuberculous mycobacterial species Mycobacterium chelonae was isolated from six captive South African clawed frogs (Xenopus laevis) with chronic weight loss and nonhealing ulcerative skin lesions. Three of the M. chelonae isolates were evaluated to confirm the species identification using polymerase chain reaction restriction analysis. Disease associated with M. chelonae is reported mainly in people and in fish. To our knowledge, this is the first report of disease associated with M. chelonae in a colony of captive Xenopus sp.     

Testis-derived microRNA profiles of African clawed frogs (Xenopus) and their sterile hybrids

Gene regulation was long predicted to play a vital role in speciation and species divergence. Only recently with the advent of new technologies, however, has it been possible to address the question of the relative contributions of different mechanisms of gene expression to the evolution of phenotypic diversity. Here we broaden the question and ask whether microRNAs, a large class of small regulatory RNAs, play a role in reproductive isolation between species by contributing to hybrid male sterility. MicroRNAs from the testes of clawed frogs (Xenopus) were extracted and the expression profiles of sterile hybrids were compared with males of a parental species. Hybrid testes were largely microRNA-depleted relative to those of nonhybrids, and this pattern was validated with quantitative RT-PCR. A number of candidate differential microRNAs from this study have previously been described as testis-specific in the mouse, suggesting that microRNA structural conservation may be associated with functional retention.     

Clinical diagnosis and treatment of epidermal chytridiomycosis in African clawed frogs (Xenopus tropicalis)

An investigation was conducted to determine the cause of morbidity and mortality in a collection of 55 adult male Xenopus (Silurana) tropicalis at the University of California, Berkeley. More than 80% of affected frogs died during the epizootic. All frogs were anorectic and lethargic, had dark pigmentation and excess skin sloughing, and lacked a slime layer. Histologic examination revealed severe hyperplastic and spongiotic dermatitis associated with colonization of the stratum corneum by large numbers of zoosporangia diagnostic of Batrachochytrium dendrobatidis. Treatment with a commercial formalin/malachite green solution at a dilution of 0.007 ml/L of tank water for 24 h, repeated every other day for four treatments, eliminated the organism and was curative. These findings are indicative of epidermal chytridiomycosis as a primary cause of death in this collection of X. tropicalis.     

Characterization of a Mycobacterium ulcerans-like infection in a colony of African tropical clawed frogs (Xenopus tropicalis)

A nontuberculous Mycobacterium ulcerans-like organism was identified as the causative agent of an epizootic of mycobacteriosis in a colony of African tropical clawed frogs, Xenopus (Silurana) tropicalis, at the University of California, Berkeley. Diverse clinical signs of disease were observed, including lethargy, excess buoyancy, coelomic effusion, cutaneous ulcers, and granulomas. Visceral granulomas, ulcerative and granulomatous dermatitis, coelomitis, and septicemia were common findings at necropsy. Identification of M. ulcerans-like organisms was based on molecular and phenotypical characteristics. The findings of this investigation indicate that this M. ulcerans-like organism is a primary cause of morbidity and mortality in aquatic anurans and should be considered in the differential diagnosis of coelomic effusion in amphibians. Furthermore, if this Mycobacterium species ultimately is identified as M. ulcerans, X. tropicalis should be considered a potential source of this important public health pathogen.     

Evolution of the closely related, sex-related genes DM-W and DMRT1 in African clawed frogs (Xenopus)

DM-W is a dominant, female-specific, regulator of sex determination in the African clawed frog Xenopus laevis. This gene is derived from partial duplication of DMRT1, a male-related autosomal gene. We set out to better understand sex determination in Xenopus by studying this pair of genes. We found that DM-W evolved in Xenopus after divergence from the sister genus Silurana but before divergence of X. laevis and X. clivii, and that DM-W arose from partial duplication of DMRT1β, which is one of the two DMRT1 paralogs in the tetraploid ancestor of Xenopus. Using the rate ratio of nonsynonymous to synonymous substitutions per site and multilocus polymorphism data, we show that DM-W evolved non-neutrally. By cloning paralogs and using a pyrosequencing assay, we also demonstrate that DMRT1 underwent phylogenetically biased pseudogenization after polyploidization, and that expression of this gene is regulated by mechanisms that vary through development. One explanation for these observations is that the expression domain of DMRT1β was marginalized, which would explain why this paralog is dispensable in Xenopus polyploids and why DM-W has a narrow expression domain. These findings illustrate how evolution of the genetic control of stable phenotypes is facilitated by redundancy, degeneration, and compartmentalized regulation.     

The benthic and weed-bed faunas of Lake Awasa (Rift Valley,Ethiopia)

The community structures of the benthic and weed-bed faunas of Lake Awasa, Ethiopia Rift Valley, are described and related to the various types of substratum present. L. Awasa is non-saline (conductivity 860 µS cm^-1), and lies in a shallow basin with maximum depths of 21–22 m. It supports an important commercial fishery mainly based on the tilapia Oreochromis niloticus.The large weed beds of the lake extend out to the 4 m. isobath in most places; they consist mainly of the grass Paspalidium geminatum. Below the 6–8 m isobaths the bottom is covered with a deep layer of flocculant mud, with organic matter constituting about one third of the dry weight. No benthic animals are able to colonize this mud. In shallower regions the bottom consists of hard sand covered with a thin layer of organic detritus, except for a narrow region around the 6 m isobath where the sand is covered with a layer of ostracod shells up to 25 cm deep. All this firmer bottom is colonized by a benthic community consisting mainly of cyclopoids, ostracods, Limnodrilus and chironomids; there are no prosobranch or bivalve molluscs. The weed-bed community consists mainly of Cladocera, ostracods, Ephemeroptera, Heteroptera, chironomids and pulmonate molluscs. These communities are compared with those of other Afro-tropical lakes, and are shown to have much in common with that of Lake Chad (Dejoux, 1983), specially the chironomids (Dejoux, 1976) but L. Awasa has fewer species, the most noticeable absentees being the decapod Crustacea.     

Peptidomic analysis of skin secretions provides insight into the taxonomic status of the African clawed frogs Xenopus victorianus and Xenopus laevis sudanensis (Pipidae)

Peptidomic analysis was used to compare the distribution of host-defense peptides in norepinephrine-stimulated skin secretions from Xenopus victorianus Ahl, 1924 (also described as the subspecies X. laevis victorianus) and Xenopus laevis sudanensis Perret, 1966 with the previously determined distributions in Xenopus laevis (Daudin, 1802) and Xenopus petersii Bocage, 1895. Peptides belonging to the magainin, peptide glycine-leucine-amide (PGLa), and caerulein precursor fragment (CPF) families were purified by reversed-phase HPLC and characterized by electrospray mass spectrometry. Magainin-P2, PGLa-P1, CPF-P1, CPF-P2, and CPF-P3 previously isolated from X. petersii and structurally different from orthologous peptides from X. laevis, were identified in X. victorianus and X. laevis sudanensis skin secretions whereas the corresponding X. laevis peptides were absent. Magainin-1, identical in X. petersii and X. laevis, was also identified in the secretions. Xenopsin-precursor fragment (XPF) peptides, absent from X. petersii but present in X. laevis skin secretions, were not identified in the X. victorianus and X. laevis sudanensis secretions. The data indicate that X. victorianus and X. laevis sudanensis are more closely related to X. petersii than to X. laevis and support separate species status. The study illustrates the value of analysis of host-defense peptides in the evaluation of taxonomic and phylogenetic relationships between closely related frog species.     

Hybridization between the African clawed frogs Xenopus laevis and Xenopus muelleri (Pipidae) increases the multiplicity of antimicrobial peptides in skin secretions of female offspring

Peptidomic analysis was used to compare the distribution of host-defense peptides in norepinephrine-stimulated skin secretions from laboratory-generated female F1 hybrids of the common clawed frog Xenopus laevis (Daudin, 1802) and Mueller's clawed frog Xenopus muelleri (Peters, 1844) with the corresponding distribution in skin secretions from the parent species. A total of 18 peptides were identified in secretions from the hybrid frogs. Eleven peptides (magainin-1, magainin-2, CPF-1, CPF-3, CPF-4, CPF-5, CPF-6, CPF-7, XPF-1, XPF-2, and PGLa) were identified in secretions of both the hybrids and X. laevis. Four peptides (magainin-M1, XPF-M1, CPF-M1, and tigerinin-M1) were previously found in skin secretions of X. muelleri but magainin-M2 and CPF-M2 from X. muelleri were not detected. Three previously undescribed peptides (magainin-LM1, PGLa-LM1, and CPF-LM1) were purified from the secretions of the hybrid frogs that were not detected in secretions from either X. laevis or X. muelleri. Magainin-LM1 differs from magainin-2 from X. laevis by a single amino acid substitution (Gly¹³ → Ala) but PGLa-LM1 and CPF-LM1 differ appreciably in structure from orthologs in the parent species. CPF-LM1 shows potent, broad-spectrum antimicrobial activity and is hemolytic. The data indicate that hybridization increases the multiplicity of skin host-defense peptides in skin secretions. As the female F1 hybrids are fertile, hybridization may represent an adaptive strategy among Xenopus species to increase protection against pathogenic microorganisms in the environment.     

Diversification of African tree frogs (genus Leptopelis) in the highlands of Ethiopia

The frog genus Leptopelis is composed of ~50 species that occur across sub‐Saharan Africa. The majority of these frogs are typically arboreal; however, a few species have evolved a fossorial lifestyle. Most species inhabit lowland forests, but a few species have adapted to high elevations. Five species of Leptopelis occupy the Ethiopian highlands and provide a good opportunity to study the evolutionary transition from an arboreal to a fossorial lifestyle, as well as the diversification in this biodiversity hot spot. We sequenced 14 nuclear and three mitochondrial genes, and generated thousands of SNPs from ddRAD sequencing to study the evolutionary relationships of Ethiopian Leptopelis. The five species of highland Leptopelis form a monophyletic group, which diversified during the late Miocene and Pliocene. We found strong population structure in the fossorial species L. gramineus, with levels of genetic differentiation between populations similar to those found between arboreal species. This could indicate that L. gramineus is a complex of cryptic species. We propose that after the original colonization of the Ethiopian highlands by the ancestor of the L. gramineus group, episodes of vicariance fragmented the ancestral populations of this group. We also report the re‐evolution of arboreality in L. susanae, which evolved from a fossorial ancestor, a rare ecological switch in frogs that had previously been reported only once.     

The Rift Valley complex as a barrier to gene flow for Anopheles gambiae in Kenya

Recent studies of Anopheles gambiae, the principal mosquito vector of malaria in Africa, suggested that the eastern Rift Valley and its surrounding areas act as a barrier to gene flow. To quantify the unique effect of these areas on gene flow, we measured genetic variation within and between populations from each side of the Rift. Low differentiation was measured between populations on each side of the Rift (mean FST < 0.008, mean RST < 0.002). However, high differentiation was measured across the Rift (mean FST = 0.104; mean RST = 0.032). Genetic diversity within populations was lower in eastern populations, suggesting that the effective population sizes (Ne) of these populations were lower than those of western populations. We partitioned the overall differentiation across the Rift into three factors: variation in Ne between populations contributed 7-20%; distance contributed 10-30%, and the remainder, corresponding to the unique effect of the Rift was 50-80%. The Rift's effect was highly significant based on FST. The greater sensitivity of FST in measuring differentiation indicated that drift and not mutation generated the differences between populations. Restricted gene exchange across several hundred kilometers on the face of intense human transportation implies that active mosquito dispersal is the major form of migration, and that migration is a multistep process, where step length is relatively short.     

Cryptosporidiosis associated with emaciation and proliferative gastritis in a laboratory-reared South African clawed frog (Xenopus laevis)

A 2-year-old emaciated female South African clawed frog (Xenopus laevis) was euthanized because of chronic weight loss. At necropsy, there was no evidence of bacterial, fungal or viral disease; however, the histopathologic findings indicated a proliferative gastritis and the presence of numerous cryptosporidial stages throughout the intestinal tract. Crytosporidial oocysts were present in the water taken from the aquarium housing the infected frog and were likely shed by the sick frog; however, the exact source of the oocysts could not be identified. Water samples from other frog aquaria in the facility did not contain cryptosporidial oocysts. Some Cryptosporidium species are important zoonotic pathogens and, to our knowledge, this is the first report of disease associated with Cryptosporidium infection in a laboratory Xenopus laevis.     

Biomass and production of the major dominant crustacean zooplankton in a tropical Rift Valley lake, Awasa, Ethiopia

Seasonal variation of the biomass (B), production (P) and P/Bratio of the numerically dominant crustaceans in Lake Awasa(Mesocydops aequatonalis stmilts, Thermocyclops consunilis andDiaphanosoma exisum) were studied during 1986 and 1987. Quantitativenet samples (64 (xm mesh) were taken at three stations on 10day intervals throughout 1986, and the dry weights and developmenttimes for each life stage were obtained from laboratory measurementsand cultures Total biomass of most of the dominant crustaceans,determined from 390 samples during 1986, was 44.85 mg m^–3(dry weight, DW) with adult females of Mesocyclops making >43.5%.Alona diaphana, another common crustacean, is dealt with ina separate paper, as are the Rotifera. Production of the dominantcrustaceans during 1986 was estimated by the growth incrementsummation (Winberg) and instantaneous growth (Ricker) methodsThe annual integrated production of the two dominant cyclopoidsis 535.2 mg (DW) m^–3 (Winberg) while annual crustaceanproduction totals 2.5 g (DW) m^–3 (Ricker) The mean annualP/B ratio for individual species and stages varied from 221.0for Diaphanosoma, to 121.7-143.0 for nauplii and 9.8–187 for copepodites of the cyclopoids It was 55 8 for the dominantzooplankton species Low or high zooplankton production and biomassturnover rates (P/B) cannot be used to characterize all tropicallakes consistently However, production per unit biomass is likelyto be higher in tropical lakes.     

The ongoing invasion of African clawed frogs (<Emphasis Type="Italic">Xenopus laevis</Emphasis>) in Chile: causes of concern

We review the existing data on the African clawed frog in Chile (Xenopus laevis, Pipidae) and report new and alarming information on its distribution, provide physical data on water courses and bodies that hold populations of this frog, report observations on its diet, on mass migration overland, and on predation by native birds. Our findings reveal that: (a) the spread of the invasion is currently covering 4 of the 13 regions of Chile; (b) clawed frogs are found at higher densities in artificial water bodies (ponds and dams and irrigation canals) rather than in natural lagoons or streams or rivers; (c) there is no evidence of predation on native anurans, but rather on their own larvae; (d) they face predation from native birds. Causes of concern include (a) that African clawed frogs in Chile reach both lower and higher altitudes than formerly estimated, and (b) that they are able to migrate overland to colonize other water bodies. They are spreading at a rate of 3.1–3.9?km/year in an optimistic scenario, and at a rate of 4.4–5.4?km/year in a pessimistic one. The most troubling aspects of the African clawed frog invasion in Chile involve: (a) their unaided spread through central Chilean agricultural areas, using irrigation canals and overland migration; and (b) the type of interactions that they may be establishing with native anurans (are they competitors, predators, habitat modifiers, disease vectors, or all things together?). As a precautionary action, we propose that the pet trade of African clawed frogs in Chile should be banned.     

Low genetic diversity of the successful invasive African clawed frog Xenopus laevis (Pipidae) in Chile

In Africa, the genus Xenopus presents cryptic species and diverse hybrids between species. It has been assumed that the invasive populations of this genus correspond to X. laevis and that they are derived from the subspecies that inhabits the Mediterranean Cape region of South Africa. In part, this is supported by the successful establishment of this species in several Mediterranean regions of the world. In Mediterranean Chile, Xenopus has invaded an area of about 21,000 km², with scarce attention to genetic aspects underlying its invasion. Using mitochondrial DNA sequences we determined that Xenopus laevis laevis from the Cape region of South Africa is the subspecies that invaded Chile. The analysis indicated that the invaders have low genetic diversity (only two haplotypes, compared to 10 in two localities of their native range), and that probably the invasion in Chile occurred only once. Landscape genetics revealed that factors such as aridity and elevation have determined the spread of the species, both from the ecological and genetic points of view. Our results show that the invasion of the African clawed frog in Chile has been successful for at least 30 years, in spite of low genetic variability, few events of introduction, low propagule pressure, and bottlenecks in the founding population.     

Prey-capture in the African clawed toad (Xenopus laevis): comparison of turning to visual and lateral line stimuli

Separately delivered visual and lateral line stimuli elicit similar but not identical orientation and approach by intact, sighted Xenopus. Response frequencies for visual stimuli declined sharply for distant or caudal stimuli while those for lateral line stimuli changed little. Turn angles correlated highly with stimulus angles but were smaller on average, so regression slopes were less than one. Regression slopes were smaller for visual than for lateral line stimuli, but this apparent difference was due to different distributions of stimulus distance interacting with the toad’s rotation center. Errors in final headings, most often under-rotations, did not differ by modality. Frequencies of lunges and arm capture movements were higher for visual stimuli both overall and especially for rostral proximal stimuli. The results demonstrate accurate orientation by sighted Xenopus to visual and lateral line stimuli; they are consistent with expectations based on in-register tectal maps. Orientation to lateral line stimuli is similar to previous results with blinded animals, revealing no heightened acuity in the latter. Modality differences indicate that the lateral line system is better for omnidirectional orientation and approach to distant stimuli whereas the visual system is more attuned to nearby rostral stimuli and more apt to mediate strikes.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Species composition,distribution and seasonal dynamics of Rotifera in a Rift Valley lake in Ethiopia (Lake Awasa)

The species composition of rotifers in Lake Awasa was studied and 40 species recorded. Seven species appeared in large numbers in the plankton seasonally. Brachionus and Keratella species made up more than 50% of the rotifer community by numbers during the observation period (1983–1987). The standing stock numbers of rotifer species are low with a maximum of 50 individuals L^–1, and some possible reasons for this observation are discussed. Most rotifer species are distributed randomly in the lake and show 3-fold fluctuations between consecutive days.The seasonal dynamics of most rotifer species are correlated with mixing periods in the lake, and the amplitude of seasonal fluctuation may be as high as 50-fold. Clear-cut seasonal succession of rotifer species was observed during the study period, but no consistent seasonal pattern for individual species was obvious. Also, observations indicate that rotifer biomass is partly sustained by availability of carbon through the bacterial pathway and that competitive exclusion for food by nauplii and ciliates probably keeps rotifer abundance low.     

Postoperative analgesics in South African Clawed frogs (Xenopus laevis) after surgical harvest of oocytes

Heightened awareness for the welfare of earlier-evolved laboratory species has prompted increasing inquiries by institutional animal care committees, investigators, and laboratory animal veterinarians regarding the need for post-surgical analgesics in laboratory Xenopus. Basic research into the mechanisms and regulation of pain in Rana pipiens has demonstrated the clinical potential of opioid, alpha2-adrenergic, and non-opioid analgesic agents in amphibians. However, clinical studies using objectively established indices of amphibian pain, or pharmacological studies in either Rana pipiens or laboratory Xenopus have not been conducted. As discussed above, comparison of limited lethality data suggests that the safety index for these agents is quite narrow in Rana pipiens. Analgesic use in laboratory Xenopus has the added risk of drowning due to over sedation. Drug doses extrapolated from such studies and intended to provide pain relief in Xenopus should therefore be considered very carefully. An additional concern for laboratory Xenopus is that the effects of these agents on amphibian oogenesis, oocyte quality, and embryogenesis are unknown. As the numbers of laboratory Xenopus used in basic and biomedical research continues to increase, clinical studies that address all of these issues cannot come too soon.