Chromosome complements of the genus Xenopus

Two new polyploid Xenopus species from western Uganda

2 new species of the anuran genus Xenopus have been found in western Uganda: X. ruwenzoriensis sp.n. with the hexaploid chromosome number of 108 in the Semliki Valley, west of the Ruwenzori, and X. species nova with the tetraploid chromosome number of 72 in and near lake Bunyoni.

Albumin phylogeny for clawed frogs (Xenopus)

Comparisons of albumin indicate that the frogs commonly used by North American molecular and developmental biologists under the name of Xenopus muelleri belong to another species, X. borealis. Phylogenetic analysis of the albumin data reveals two major groups of Xenopus species, one containing only X. tropicalis and the other, called the X. laevis grou, containing the remaining species of the genus. The phylogenetic tree, in conjunction with evidence from chromosomes and DNA content, leads to the hypothesis that total genome duplication occurred in the common ancestor of the X. laevis group.

Diplotene chromosomes of Xenopus hybrid oocytes

Observation on meiotic diplotene chromosomes from oocytes of Xenopus species and subspecies hybrids are reported. Species interrelationships are established on the basis of the number of bivalent in the respective hybrids. Polyploid oocytes were found and their origin by supplementary endoreduplication placed at the differentiation stage of gametogenesis when oogonia become oocytes. The significance of polyploid oocytes for speciation is discussed.

DNA content in the genus Xenopus

Nuclear DNA amounts were determined by cytofluorometry for twelve species and subspecies of the genus Xenopus. Absolute values, in pg per nucleus, were obtained by direct comparison with human lymphocyte nuclei. The lowest DNA amount (3.55 pg) was found in X. tropicalis, which possess only 20 chromosomes, and the highest (16.25 pg), in the hexaploid X. ruwenzoriensis, with 108 chromosomes. The two recently discovered tetraploid species, X. sp.n. and X. vestitus have, respectively 12,57 and 12.83 pg of DNA. Among the species and subspecies with 36 chromosomes, the DNA content ranges from 6.35 to 8.45 pg.

Polyploid amphibians: three more diploid-tetraploid cryptic species of frogs

The nominal African species Pyxicephalus delalandii and Dicroglossus occipitalis have diploid and tetraploid populations. There are also cryptic tetraploid and diploid species similar to Bufo kerinyagae. These represent the first bisexual polyploid "species" so far encountered in the major frog families Ranidae and Bufonidae. The contention that polyploidy is a widespread and important evolutionary phenomenon in anuran amphibians is supported.

Studies on immunoglobulins of Xenopus borealis, Xenopus clivii and Xenopus muelleri

Following immunization with human IgG three species of anuran amphibians, Xenopus borealis, Xenopus clivii and Xenopus muelleri, were found to synthesize two molecular populations of antibodies associated with 19S and 7S fractions of the sera. These antibodies, designated high (HMW) and low (LMW) molecular weight immunoglobulins, were isolated and their constituent heavy (H) and light (L) polypeptide chains separated following extensive reduction and alkylation in a relative yield of about 70% and 30% respectively. The molecular weights of H and L chains of the three species were determined by SDS-acrylamide gel electrophoresis. The L chains from both molecules in the three species had a molecular weight of about 26,000. The H chains of the HMW and LMW immunoglobulins had a molecular weight of about 73,000 and 63,000 respectively. The two populations of immunoglobulins were analysed in immunodiffusion plates using rabbit antisera to LMW immunoglobulins. The HMW immunoglobulins were found to be antigenically deficient with respect to LMW immunoglobulins. From these results it was judged that the two populations in each species belonged to distinct classes. The antigenicities of the LMW and HMW immunoglobulins of different species within the genus Xenopus were compared.