Maunder, K. G. | bioRxiv Science

bioRxiv2026

Selection shapes the evolution of genome size in a globally invasive plant

O_LIBiological invasions provide powerful natural experiments for understanding how genome architecture responds to novel climatic environments. Transposable elements (TEs) can rapidly restructure genomes, yet their role in adaptive genome size evolution during invasion remains poorly understood. C_LIO_LIHere, we examined genome size and TE abundance in 439 individuals of globally invasive common ragweed (Ambrosia artemisiifolia L.) across native (North American) and invasive (European, Australian) ranges. By integrating whole-genome resequencing, flow cytometry, and trait versus genetic differentiation comparison (QST-FST), we tested whether genome size evolution is shaped by selection, climate, and life-history traits. C_LIO_LIGenome size was significantly larger in Australian genotypes, driven by increased TE and rRNA (ribosomal RNA) abundance. Crucially, trait versus genetic differentiation comparison provided evidence of divergent selection on genome size in North American and European populations, but not in Australia. Genome size was correlated with mean annual temperature (MAT) across all ranges, linking genomic traits to environmental variables. C_LIO_LIGenome size evolution during invasion can be rapid, adaptive, and range-specific, with TE-driven genome expansion emerging as a potential genomic response to the demographic and environmental pressures accompanying colonization of novel environments. C_LI

evolutionary biology↗

bioRxiv2025

Random and non-random variation in flower color along an urban-rural gradient in the introduced mustard Hesperis matronalis

PremiseUrbanization can alter the interplay of stochastic genetic drift and natural selection but these effects will depend on the biology and history of a species. To explore the influences of drift and selection we investigated patterns of flower color variation among populations of the introduced ornamental mustard, Hesperis matronalis, along an urban-rural gradient in eastern Ontario Canada. MethodsWe surveyed 136 naturalized stands of H. matronalis over three generations, and for each stand estimated the diversity of the three color morphs (white, pink, purple), the number of reproductive plants, and the degree of urbanization based on night sky brightness. Key ResultsFlower color morph diversity increased with both stand size and urbanization which is consistent with effects of genetic drift during colonization combined with multiple introductions of this horticultural plant in urban areas. However, the frequency and fixation of the purple morph systematically increased towards the rural end of the gradient. Although lifetime seed production did not vary among morphs, pre-dispersal seed predation by a recently adventive weevil was higher in the purple morph, particularly in rural areas. Estimated seed production in the absence of predation suggests a previous fitness advantage for the purple and pink morphs in rural areas and for the white morph in urban areas. ConclusionsRandom variation in flower color diversity may be influenced by stochastic processes and colonization history, while systematic variation in color morph frequencies may reflect past fitness differences among morphs that have been recently erased by seed predation.

evolutionary biology↗