Understanding the early evolutionary stages of a tandem drosophila melanogaster-specific gene family: A structural and functional population study

Bryan D. Clifton, Jamie Jimenez, Ashlyn Kimura, Zeinab Chahine, Pablo Librado, Alejandro Sanchez-Gracia, Mashya Abbassi, Francisco Carranza, Carolus Chan, Marcella Marchetti, Wanting Zhang, Mijuan Shi, Christine Vu, Shudan Yeh, Laura Fanti, Xiao Qin Xia, Julio Rozas, Jose M. Ranz

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Gene families underlie genetic innovation and phenotypic diversification. However, our understanding of the early genomic and functional evolution of tandemly arranged gene families remains incomplete as paralog sequence similarity hinders their accurate characterization. The Drosophila melanogaster-specific gene family Sdic is tandemly repeated and impacts sperm competition. We scrutinized Sdic in 20 geographically diverse populations using reference-quality genome assemblies, read-depth methodologies, and qPCR, finding that ∼90% of the individuals harbor 3-7 copies as well as evidence of population differentiation. In strains with reliable gene annotations, copy number variation (CNV) and differential transposable element insertions distinguish one structurally distinct version of the Sdic region per strain. All 31 annotated copies featured protein-coding potential and, based on the protein variant encoded, were categorized into 13 paratypes differing in their 30 ends, with 3-5 paratypes coexisting in any strain examined. Despite widespread gene conversion, the only copy present in all strains has functionally diverged at both coding and regulatory levels under positive selection. Contrary to artificial tandem duplications of the Sdic region that resulted in increasedmale expression, CNV in cosmopolitan strains did not correlate with expression levels, likely as a result of differential genome modifier composition. Duplicating the region did not enhance sperm competitiveness, suggesting a fitness cost at high expression levels or a plateau effect. Beyond facilitating a minimally optimal expression level, Sdic CNV acts as a catalyst of protein and regulatory diversity, showcasing a possible evolutionary path recently formed tandemmultigene families can follow toward long-term consolidation in eukaryotic genomes.

Original languageEnglish
Pages (from-to)2584-2600
Number of pages17
JournalMolecular Biology and Evolution
Issue number9
StatePublished - 1 Sep 2020


  • CNV
  • Complex genomic regions
  • Expression variation
  • Gene conversion
  • Sexual selection
  • Tandem multigene families


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