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.     

Artificial fertilization of gametes from the South African clawed frog,Xenopus laevis

A reproducible and effective method for fertilization eggs of Xenopus laevis was developed based of systematic manipulation of environmental factors. The effects of varying concentrations of individual components of a fertilization medium were tested by measuring jelly swelling, sperm motility, and sperm longevity. Results were used to develop an improved medium for fertilization, consisting of 41.25 mM NaCl, 1.25 mM KCl, 0.25 mM CaCl₂, 0.0625 mM MgCl₂, 0.5 mM Na₂HPO₄, 2.5 mM HEPES, 1.9 mM NaOH, final pH(2°) 7.8.     

Factors affecting oogenesis in the South African clawed frog (Xenopus laevis)

Xenopus laevis, commonly known as the South African Clawed frog, is a hardy adaptable species that is relatively easy to maintain as a laboratory animal. Gametogenesis in wild Xenopus laevis is continuous and under ideal conditions, reproduction can occur year round. This unique aspect of amphibian reproduction offers an advantage over mammalian model systems: the eggs and oocytes collected from laboratory maintained Xenopus laevis provide an abundant and readily obtainable supply of material for cellular and biological research. However, many investigators report that laboratory Xenopus laevis go through periods of unexplained inefficient or complete failure of oocyte production or the production of poor quality oocytes. This results in experimental delays, inability to reproduce data, and ultimately the use of more animals. There is a lack of evidenced based information regarding the housing conditions that are necessary to optimize the health and fecundity of this species in captivity, but studies of wild Xenopus laevis have shown that temperature, age of the female, and nutrition are of key importance. The objective of this report is to review oogenesis with a special emphasis on these factors as they pertain to laboratory Xenopus laevis maintained for the purpose of providing a steady supply of eggs and oocytes. Harvesting methods and other experimental techniques that affect the quality of eggs and oocytes are also discussed.     

Immunologic reactivity to TNP-Ficoll during development and ageing in Xenopus laevis, the South African clawed toad

The immunological response of Xenopus laevis to haptenated Ficoll was examined throughout development. The capacity to respond to TNP-Ficoll originated with the first appearance (at stage 48, 8 days post-fertilisation) of mature thymic lymphocytes, and preceded the ability to respond to heterologous erythrocytes. During premetamorphosis the response increased, while during prometamorphosis , particularly at stages 57-58, there was a marked reduction. The response recovered during the metamorphic climax and immature adult stages, increasing further at the onset of sexual maturity. The reduced response during prometamorphosis parallels the reported reduction in other thymus-dependent responses.     

Cutaneous acariasis in the African clawed frog (Xenopus laevis)

Increased mortality was observed in a single colony of 50 Xenopus laevis. The frogs were used as oocyte donors in developmental biology studies. Necropsy findings included dermal erythema and petechiation consistent with red leg syndrome; dermal ulcerations and white, filamentous growths on the skin were consistent with Saprolegnia sp. Microscopic evaluation of the skin and fungus revealed an astigmatid mite similar to those of the genus Rhizoglyphus. The mite was also found in the water and the biological filter of the tanks housing the frogs. This mite is considered not to be a parasite of X. laevis; instead, it feeds off moss, fungi, and detritus. Subsequent evaluation of the sphagnum moss used for shipping the frogs from the supplier revealed the same mite in the moss. Our hypothesis is that the mite was introduced into the tank with the shipment of new frogs in sphagnum moss. The mites lived within the biological filter, and were only found after the growth of Saprolegnia sp. attracted the mites to the frogs. Laboratory animal care and veterinary personnel should consider non-pathogenic species of mites in the differential diagnosis of acariasis in Xenopus frogs.     

Global realized niche divergence in the African clawed frog Xenopus laevis

Although of crucial importance for invasion biology and impact assessments of climate change, it remains widely unknown how species cope with and adapt to environmental conditions beyond their currently realized climatic niches (i.e., those climatic conditions existing populations are exposed to). The African clawed frog Xenopus laevis, native to southern Africa, has established numerous invasive populations on multiple continents making it a pertinent model organism to study environmental niche dynamics. In this study, we assess whether the realized niches of the invasive populations in Europe, South, and North America represent subsets of the species’ realized niche in its native distributional range or if niche shifts are traceable. If shifts are traceable, we ask whether the realized niches of invasive populations still contain signatures of the niche of source populations what could indicate local adaptations. Univariate comparisons among bioclimatic conditions at native and invaded ranges revealed the invasive populations to be nested within the variable range of the native population. However, at the same time, invasive populations are well differentiated in multidimensional niche space as quantified via n‐dimensional hypervolumes. The most deviant invasive population are those from Europe. Our results suggest varying degrees of realized niche shifts, which are mainly driven by temperature related variables. The crosswise projection of the hypervolumes that were trained in invaded ranges revealed the south‐western Cape region as likely area of origin for all invasive populations, which is largely congruent with DNA sequence data and suggests a gradual exploration of novel climate space in invasive populations.     

Female sex behaviors in the South African clawed frog, Xenopus laevis: gonadotropin-releasing, gonadotropic, and steroid hormones

The goals of this study were to characterize sex behaviors of female South African clawed frogs, Xenopus laevis, and to explore the behavioral effects of endocrine manipulation. The responses of females to clasp assaults by sexually active males were observed. Two patterns of female responses predominated. In one, females exhibited extreme leg extension and ticking vocalizations when clasped (unreceptive behaviors). In the other, females responded to being clasped by adduction of the thighs and increased flexion at the knee; ticking vocalizations were absent (receptive behaviors). When the female was unreceptive, clasps by males generally lasted less than 1 min. With a receptive female, on the other hand, amplexus could last up to 2 days. In intact females, injection of human chorionic gonadotropin (HCG) or of luteinizing hormone-releasing hormone (LHRH) into the dorsal lymph sac results in significant increases in receptivity. These hormones do not promote receptivity in ovariectomized females. Neither estradiol (E) nor progesterone (P) when administered alone was effective in restoring receptivity to ovariectomized females. In combination, E + P increased sexual receptivity. The releasing hormone, LHRH, when given to ovariectomized, E + P-treated females, further increased receptivity and led to the prolonged amplexus otherwise observed with an HCG-injected intact female. The behavioral effects of LHRH may be independent of action on the pituitary since they are not mimicked by gonadotropin.     

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.     

Outgrowth dependency of forelimb regeneration on nerves in adult African clawed frog,Xenopus laevis

Summary The relationship between the size and shape of regenerative outgrowth and the quantity of innervation was studied in adult Xenopus laevis. The forelimbs, of which the nerve supply was artificially altered, were amputated midway through the stylopodium and were kept for 1 year. The regenerative outgrowths that formed in normal limbs with an intact nerve supply were mainly spike-shaped and occasionally rod-shaped. However, when the nerve supply to the distal part of the forelimb was augmented by surgically diverting ipsilateral sciatic nerve bundles, the quantity of innervation was increased to about two and a half times that of the normal limb. These hyperinnervated outgrowths were somewhat larger than those of the normally innervated outgrowths and the majority of them were oar-shaped, a type hardly ever encountered in normal regeneration. In contrast, when partial denervation was performed concomitantly with limb amputation, by ablation of the N. radialis at the shoulder joint, the quantity of innervation decreased to about one half that of the normal limb. The outgrowths obtained were spike-shaped in all cases, with their size being about half that of the normally innervated outgrowths. Furthermore, when both the N. radialis and N. ulnaris were ablated in the same way, the amputated limbs were mostly non-regenerative, but some of them regenerated small conical outgrowths. Based on these results, a discussion is presented concerning the relationship between a regenerative outgrowth and the innervation of the forelimb in Xenopus.     

Splenic white pulp as a thymus-independent area in the African clawed toad,Xenopus laevis

Summary An indirect immunofluorescence study of the frozen sections of the spleen of an anuran amphibian, Xenopus laevis, showed that lymphocytes bearing a small amount of immunoglobulin (Ig) were localized mostly in the white pulp of non-immunized toads. There were fewer fluorescent cells in the red pulp. In the toads hyperimmunized with human gamma globulin (HGG), cells with strong cytoplasmic fluorescence increased significantly in the outer part of the white pulp. Electron microscopy of spleens from these toads showed that plasma cells at different stages of maturation were abundant in the white pulp, whereas in the red pulp, a smaller number of maturer plasma cells were observed. These results indicate that, in contrast with its mammalian counterpart, the splenic white pulp of this anuran is the site where thymusin-dependent lymphocytes commence blast formation and transformation into plasma cells.     

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.