Multiple Transitions between Y Chromosome and Autosome in Tago's Brown Frog Species Complex

Area of Science:

• Evolutionary Biology
• Genetics
• Herpetology

Background:

• Sex chromosome turnover, the transition between sex chromosomes and autosomes, is a poorly understood evolutionary process in vertebrates.
• While documented in cold-blooded vertebrates, the specific causes and genetic mechanisms remain elusive.

Purpose of the Study:

• To investigate sex chromosome turnover in the Japanese Tago's brown frog complex (Rana tagoi and Rana sakuraii).
• To explore the evolutionary causes and genetic mechanisms underlying these transitions, particularly in relation to hybridization.

Main Methods:

• Chromosome banding and molecular analyses, including sex-linked and autosomal single nucleotide polymorphisms (SNPs), were employed.
• Geographic populations from northern to southern Japan were analyzed, with a focus on specific populations of R. tagoi.

Main Results:

• Three distinct sex chromosomes (chromosomes 3, 7, and 13) were identified across the studied frog species.
• Repeated transitions between the Y chromosome (chromosome 7) and autosomes were observed, driven by inter- or intraspecific hybridization and subsequent chromosome introgression.

Conclusions:

• Dynamic sex chromosome turnovers, involving transitions between Y chromosomes and autosomes, were identified in Japanese brown frogs.
• These findings suggest that hybridization plays a crucial role in driving sex chromosome turnover and may be linked to speciation in anurans.