Biology subjects

C S, D.

Publications and source records attributed to C S, D..

2 recordsLinked to original sources

bioRxiv2025

Reinforcement of speciation by behavioural and reproductive barriers in the Drosophila bipectinata species complex

Speciation mainly depends on different mechanisms involved in reproductive isolation; Understanding such barriers that consistently develop to avoid the fitness cost through reinforcement until the speciation continuum completes helps clarify the role of pre-mating and post-mating isolating mechanisms. The Drosophila bipectinata species complex, comprising four closely related taxa, provides a natural system for studying the interplay of behavioural, sensory, and genetic mechanisms underlying reproductive isolation. In this study, a comprehensive characterization was undertaken on twelve different types of sterile F1 hybrid males among the crosses between four species of Drosophila bipectinata species complex which are experiencing reproductive isolation. Comparing the mating latency and copulation duration among the pure species and hybrids, showed a significant increase in the mating latency of hybrids but the duration of copulation among certain hybrids of Drosophila bipectinata, Drosophila parabipectinata and Drosophila malerkotliana showed no significant reduction in the copulation time and emphasized the strong influence of X chromosome inheritance of hybrid genome. Experimental ablation of antennae demonstrated that male olfactory input is indispensable for heterospecific mating success, consistent with the role of pheromone detection in conspecific recognition, while tarsi ablation revealed striking sex-specific asymmetry: male tarsi removal increased heterospecific success, whereas female tarsi removal abolished mating entirely, highlighting the role of gustatory receptors in female mate choice. Testis dissections further confirmed that post-meiotic defects in hybrids, including failure of spermatid elongation and individualization, these findings demonstrates that reproductive isolation in the D. bipectinata species complex arises from the collective action of multiple barriers, prezygotic isolation mediated by pheromonal and gustatory divergence, and postzygotic sterility driven by spermatogenic failure. Our study underscores how behavioural and physiological divergence interact to reinforce reproductive barriers, providing a comprehensive framework for understanding speciation in Drosophila.

genetics↗

bioRxiv2025

Cis-regulatory divergence and misexpression of spermatogenesis genes underlie hybrid male sterility in the Drosophila bipectinata species complex

Hybrid male sterility (HMS) is one of the most common and earliest forms of postzygotic reproductive isolation in Drosophila, often arising from defects in spermatogenesis linked to regulatory divergence of rapidly evolving male-biased genes. The Drosophila bipectinata species complex (D. bipectinata, D. malerkotliana, D. parabipectinata, and D. pseudoananassae) provides a valuable system to study the speciation paradigm, since, all the twelve F hybrid males are sterile, the precise stage of spermatogenic failure differs among crosses. Here, we integrate cytological, transcriptional, and regulatory sequence analyses to examine the basis of sterility in this sub-complex. Cytological assays revealed that hybrid testes exhibit developmental arrest at different spermatogenesis stages, covering from reduced primary spermatocytes to absence of individualized sperm. Quantitative RT-PCR of seven spermatogenesis genes--aly, bam, sa, dj, topi, can, and Mst98Ca--showed significant downregulation among hybrid males relative to parental species, linking transcriptional misregulation with observed phenotypic defects in spermatogenesis. To test whether regulatory divergence underlies this misexpression, we analyzed [~]1-2 kb promoter regions of five genes (aly, bam, sa, dj, and topi). Motif scans using FIMO identified several lineage-specific turnover of transcription factor binding sites, also PWM-delta analysis revealed substantial interspecific differences in predicted binding strength for many key testis transcription factors. These results demonstrate that HMS in the D. bipectinata complex is consistently associated with spermatogenic arrest and misregulation of genes essential for germline proliferation, meiotic progression, and spermiogenesis. The concordance between expression changes and promoter divergence supports a role for cis-regulatory evolution in hybrid dysfunction, while also leaving open the contribution of trans-acting factors. This study situates the D. bipectinata complex within the broader framework of Drosophila hybrid sterility, extending and highlighting the evolutionary sensitivity of spermatogenesis and regulatory divergence in speciation.

evolutionary biology↗