Mitotic Chromosomes of Sooglossidae (Amphibia: Anura)

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Abstract
Frogs of the family Sooglossidae have 2n = 26, 5 large and 8 small pairs of chromosomes, no heteromorphic pairs of chromosomes in either sex, and terminal chiasmata. Chromosome Nos. 1, 2, and 5 are metacentric in all three species, No. 4 is submetacentric in all three, and No. 3 is submetacentric in Nesomantis thomasseti and Sooglossus sechellensis and subtelocentric in Sooglossus gardineri. Nos. 6–9 are metacentric and Nos. 10–13 telocentric in N. thomasseti and S. sechellensis, whereas Nos. 6–8 are metacentric and Nos. 9–13 telocentric in S. gardineri. Chromosome No. 3 of N. thomasseti has a secondary constriction on the long arm; no other markers were observed. There are no microchromosomes nor supernumeraries. The sooglossid karyotype is unique among frogs in that it is the only 26 chromosome karyotype in which the 4 smallest (5 in Sooglossus gardineri) chromosomes have telocentric (t) centromeres. This fact lends support to the cohesiveness of the sooglossid unit. Karyotypically, sooglossids are most similar to the pelobatid-myobatrachid-leptodactyloid groups of frogs. This result does not support the contention of some authorities who would derive the Seychellean sooglossids from African ranoids.