Dynamic meiotic behavior and evolutionary insights of supernumerary B chromosomes in the hangingfly Bittacus cirratus (Mecoptera, Bittacidae)

作者：Le-Le He, Ying Miao, He-Hong Wang, Jie Zhang, Bao‐Zhen Hua · 发表于：Comparative Cytogenetics · 年份：2025 · DOI：10.3897/compcytogen.19.153340 · 被引用次数：3 · 研究领域：Chromosomal and Genetic Variations、Insect Resistance and Genetics、Plant Virus Research Studies

Supernumerary B chromosomes are significant dispensable genetic elements that follow their own species-specific evolutionary pathways. Despite their widespread occurrence, comprehensive analyses of their meiotic behavior remain limited. In this study, we present the first systematic investigation of B chromosome morphology and meiotic behavior in the hangingfly Bittacus cirratus Tjeder, 1956 using cytogenetic approaches. The male basal chromosome numbers of B. cirratus is 2n = 30 + XO, with 0–5 polymorphic B chromosomes. Intraspecific B chromosome polymorphism manifests as various distinct morphotypes ranging from punctiform, bicentric, and ring-shaped to larger coiled forms, indicating that the B chromosomes may undergo rapid structural changes. During meiosis, B chromosomes display transmission drive through asymmetric segregation, preferentially accumulating in one daughter cell. Most B chromosomes formed univalents, with few forming bivalents or trivalents at meiosis I. Three unconventional retention mechanisms were identified in univalent B chromosomes: (1) associating with a nonhomologous chromosome, (2) accumulating near spindle poles, and (3) contributing to unequal spindle formation. Based on the abundant chromosomal changes of A chromosomes and stable XX/XO sex determination, we infer that the B chromosomes likely originated from multiple A chromosomes in B. cirratus . The roles of B chromosomes in the cell cycle and individual fitness are briefly discussed, and the...