The tropical clawed frog, Xenopus tropicalis [Pipidae], is native to several countries of southwestern Africa including notably Cote d'Ivoire, Nigeria, Senegal, and Sierra Leone. Sometimes also called the Western clawed frog and previously Silurana tropicalis, X. tropicalis is fully aquatic like X. laevis and inhabits mostly rainforests in West Africa. It is a smaller species than X. laevis, with adult males measuring 3-4cm and females 4.5-5.5cm from snout to vent. Typical of Xenopus species, it has a flattened body with a mottled or blotchy dark gray, green and/or brown dorsal skin, with a pale or unpigmented belly. X. tropicalis is another Xenopus species widely used in biological and biomedical research. While there are fewer eggs per brood in X. tropicalis than in X. laevis, the former may be better suited for certain genetic studies due to its simpler, diploid genome. X. tropicalis was the first frog to have it's genome sequenced in 2010. The X. tropicalis genome, currently available in annotation v10.0 on Xenbase, has considerable sequence and gene order conservation with other tetrapod vertebrates including mammals, birds, reptiles and fish.

The African clawed frog, Xenopus laevis [Pipidae], is endemic to the African Rift Valley and southern Africa with introduced populations in Europe, Asia and North America. It is a large, fully aquatic species with a flattened appearance and pronounced sexual dimorphism; Males are generally smaller (4.5-10cm) than females (6-15cm). The forelimbs are held extended, while hindlimbs are large muscular with fully webbed toes. Both hands and feet have distinct black toe tips resembling claws. Adults have dorsal skin patterns of blotchy green, gray and brown with lighter colored bellies, while albino varieties are also common in captivity. It is the most widely used Xenopus species in biomedical research, with a long history of use in embryology, cell biology and developmental biology. The genome of X. laevis, sequenced in 2016, is allotetraploid due to a hybridization event that occurred 17–18 MYA between two extinct diploid ancestors. X. laevis thus carries 2 subgenomes, referred to as the ‘Long’ and ‘Short’ chromosomes. We assign a ‘.L’ or ‘.S’ suffix respectively to gene symbols to indicate to which ancestral genome they belong. It is estimated that X. tropicalis and X. laevis, diverged approximately 48 MYA. The X. laevis genome annotation v10.1 is available on Xenbase and other resources.

The Tibetan frog, Nanorana parkeri [Dicroglossidae], is endemic to the Tibetan Plateau and the Himalayan mountain regions in China, Nepal, India and Bhutan. It is commonly known as Parker’s slow frog, the mountain slow frog, the Himalaya frog, or the Xizang Plateau frog. Adults have olive green dorsal skin with brown or black stripes, including a characteristic pair of stripes from the snout to each side of the face. These frogs have adaptations to high elevations that include changes to the cardiovascular system and tolerance to UV radiation and hypoxia. They breed naturally in high altitude marshes and streams and can also be found in highland forests, grasslands and rivers.

The genome of N. parkeri was sequenced in 2015 and has current assembly v1.0 available on Xenbase via these links below:

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The Congo dwarf clawed frog, Hymenochirus boettgeri [Pipidae], is found in the Democratic Republic of Congo, the Central African Republic, Nigeria, Cameroon, Gabon, Equatorial Guinea. Previously known as Xenopus boettgeri, or otherwise commonly as the Zaire dwarf clawed frog or the dwarf African clawed frog, it is now considered the closest outgroup for the Xenopus genus. Smaller than other Xenopus frogs, they have long and thin legs, clawed hind feet, tapered heads and gray-brown dorsal skin with small dark spots. The natural habitat is slow moving or still waters in rainforest lowlands, although it is a common species in the aquarium trade worldwide. The genome of H. boettgeri was sequenced in 2021 and the current assembly v1.0 is available on Xenbase via these links below:

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The Mexican axolotl, Ambystoma mexicanum [Ambystomatidae], is endemic to only two lakes, Lake Xochimilco and Lake Chalco, near Mexico City, Mexico. It is a large species of neotenic salamander reaching lengths of 30cm with short limbs and protruding gills. The axolotl’s skin is dark in the wild however an albino variety is commonly bred in captivity for the aquarium trade. Prominently known for its neoteny, it remains in its larval body form into adulthood, however it can metamorphose into the Mexican salamander in conditions of environmental desiccation. The axolotl is an emerging model organism notably for the study of tissue regeneration and repair, neurulation, genomics, eye and heart development and other topics.

Sequenced in 2021, the axolotl genome assembly v6.0 is available on Xenbase via these links below:

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The American bullfrog, Rana (Lithobates) catesbeianus [Ranidae], is native to Canada, Mexico and the United States, however is invasive to several countries in Europe, Asia and South America. Previously known as Rana catesbeiana, it was reassigned to the genus Lithobates in 2006 and has since been argued that Lithobates may best be considered a subgenus of the genus Rana. It is also known by its homotypic synonym as Aquarana catesbeiana.

These are the largest frogs in North America, with the larger females growing up to 180mm in length from snout to vent. Males have large, defining tympanums wider in diameter than the eyes. Adults have green dorsal skin with a dark, netlike pattern on top, however skin colour varies by region. They live and breed in vegetation-covered shallow waters of lakes and marshes. Bullfrogs are territorial of breeding sites and prey on any animal smaller than themselves including other amphibians, insects, fish, mice and crayfish. They are an important source of food consumption and are used for pest control in certain regions. The genome of L. catesbeianus was sequenced in 2017 with the v2.1 assembly currently available on Xenbase via these links below:

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