Genomic evidence for gene flow between monarchs with divergent migratory
phenotypes and flight performance
- Venkat Talla,
- Amanda Pierce,
- Kandis Adams,
- Tom de Man,
- Sumitha Nallu,
- Francis Villablanca,
- Marcus Kronforst,
- Jacobus de Roode
Abstract
Monarch butterflies are known for their spectacular annual migration in
eastern North America, with millions of monarchs flying up to 4,500
kilometers to overwintering sites in central Mexico. Monarchs also live
west of the Rocky Mountains, where they travel shorter distances to
overwinter along the Pacific Coast. It is often assumed that eastern and
western monarchs form distinct evolutionary units, but genomic studies
to support this notion are lacking. We used a tethered flight mill to
show that migratory eastern monarchs have greater flight performance
than western monarchs, consistent with their greater migratory
distances. However, analyzing more than 20 million SNPs in 43 monarch
genomes, we found no evidence for genomic differentiation between
eastern and western monarchs. Genomic analysis also showed identical and
low levels of genetic diversity, and demographic analyses indicated
similar effective population sizes and ongoing gene flow between eastern
and western monarchs. Gene expression analysis of a subset of candidate
genes during active flight revealed differential gene expression related
to non-muscular motor activity. Our results demonstrate that eastern and
western monarchs maintain migratory differences despite ongoing gene
flow, and suggest that migratory differences between eastern and western
monarchs are not driven by select major-effects alleles. Instead,
variation in migratory distance and destination may be driven by
environmentally induced differential gene expression, or by many alleles
of small effect.20 Mar 2020Submitted to Molecular Ecology 23 Apr 2020Reviewer(s) Assigned
05 Jun 2020Review(s) Completed, Editorial Evaluation Pending
05 Jun 2020Editorial Decision: Accept