The Identification of the Sex Chromosome and Karyotype of Four Toad Species (Genus Bufo) in Thailand by T-lymphocyte Cell Culture

Abstract

Summary Our knowledge is the first report on karyotypic study of four toad species (genus Bufo) in Thailand namely; large-eared toad (Bufo macrotis Boulenger 1887), Indochinese dwarf toad (Bufo parvus Boulenger 1887), common Indian toad (Bufo melanostictus Schneider 1799) and river giant toad (Bufo asper Gravenhorst 1829). Blood samples were taken from 5 males and 5 females of each four toad species. After the standard whole blood T-lymphocyte culture in the presence of colchicine, the metaphase spreads were performed on microscopic slides and air-dried. Conventional staining, G-banding and C-banding techniques were applied to stain the chromosomes. The results indicated 2nϭ22 and fundamental number (NF) 44 in both male and female of four toad species. The autosomes of B. macrotis and B. melanostictus is being as 18 metacentric and 4 submetacentric chromosomes while B. parvus and B. asper is as 16 metacentric and 6 submetacentric chromosomes. Gbanding technique showed a B. melanostictus's constriction on short arm of Y chromosome (the largest chromosome) but did not show on X chromosome. C-banding technique demonstrated a dark band constriction on Y chromosome of B. melanostictus, the representative of constitutive heterochromatin. However, there is no dark band constriction on X chromosome. So, we conclude that the sex determination of B. melanostictus is XY system. Although we do not treat B. macrotis, B. parvus and B. asper with G-banding and C-banding technique, we also predict that those three species have the same sex determination as B. melanostictus. We extremely appreciate to public our present research, the first cytogenetic study of B. macrotis and B. asper.

Hybridization and introgression between toads with different sex chromosome systems

“…2011), Strauchbufo (Deng and Shang 1984), and Duttaphrynus (Siripyasing et al. 2008) are male‐heterogametic. Female heterogamety is probably the ancestral state in Bufo , since ZW chromosomes were also characterized in B. gargarizans (Wen et al.…”

A cryptic heterogametic transition revealed by sex‐linked DNA markers in Palearctic green toads

“…They found wide concordance with expectations from female heterogamety, but also noticed several exceptions, raising questions on the consistency of a ZW/ZZ system in the entire genus. Suggestions for an XX/XY system have similarly been made for a few Eurasian Bufo species, based on patterns of replication asynchrony ( Bufo raddei ; Chongxin & Kegang, 1984) or C‐ and G banding ( Bufo melanostictus ; Siripiyasing et al. , 2008).…”

Cytogenetic Study of Three Microhylid Species (Anura, Microhylidae) from Thailand

“…Cytological evidence that was supportive of male heterogamety (XX/XY sex chromosome) has been published by Iturra and Veloso (1981) and Schmid 1981), as well as Eupsophus insularis (Cuevas and Formas 1996), R. tagoi and R. sakuraii from Tokyo (Ryuzaki et al 1999). Additionally, the XX/XY sex chromosome system was found in the genus Bufo (Siripiyasing et al 2008) and also in rice frogs, Fejervarya limnocharis (Patawang et al 2014). The existence of the highly differentiated XX/XY sex chromosome has been reported in Gastrotheca riobambae by Schmid et al (1983), in G. ovifera and G. walkeri by Schmid et al (1988), in G. pseustes by Schmid et al (1990), and in Eleutherodactylus maussi by Schmid et al (1992).…”