Natural selection drives leaf divergence in experimental populations ofSenecio lautusunder natural conditions

Abstract

Leaf morphology is highly variable both within and between plant species. This study employs a combination of common garden and reciprocal transplant experiments to determine whether differences in leaf shape between Senecio lautus ecotypes has evolved as an adaptive response to divergent ecological conditions. We created a synthetic population of hybrid genotypes to segregate morphological variation between three ecotypes and performed reciprocal transplants where this hybrid population was transplanted into the three adjacent native environments. We measured nine leaf morphology traits across the experimental and natural populations at these sites. We found significant divergence in multivariate leaf morphology toward the native character in each environment, suggesting environmental conditions at each site exert selective pressure that results in a phenotypic shift toward the local phenotype of the wild populations. These associations suggest that differences in leaf morphology between S. lautus ecotypes have arisen as a result of divergent selection on leaf shape or associated traits that confer an adaptive advantage in each environment, which has led to the formation of morphologically distinct ecotypes.

Why More Leaflets? The Role of Natural Selection in Shaping the Spatial Pattern of Leaf-Shape Variation in Oxytropis diversifolia (Fabaceae) and Two Close Relatives

“…Our results are consistent with two previous studies using reciprocal transplant experiments at a reduced geographical scale to test for the adaptive feature of leaf shape ( Ferris and Willis, 2018 ; Richards et al, 2019 ), both of which found dissected leaves performed better in dry environments. However, unlike the consistent adaptation to drought, previous studies found that lobed/dissected leaves are likely adaptive in either particularly hot or cold habitats.…”

“…However, leaf-shape variation between or within natural populations or closely related species can be controlled by genetic loci ( Kidner and Umbreen, 2010 ) and thus may also be influenced by neutral processes, such as genetic drift and restricted gene flow. Yet few studies have detected genetic signatures of natural selection on leaf shape and related variation to putative adaptive function ( Ferris, 2019 ; but see Bright and Rausher, 2008 ; Campitelli and Stinchcombe, 2013 ; Ferris and Willis, 2018 ; Richards et al, 2019 ), the adaptive feature of leaf shape still needs to be further elucidated.…”

“…This approach, typically performed by reciprocally transplanting individuals that are the product of controlled crosses into divergent natural field sites, can be very powerful ( Rausher and Delph, 2015 ; Ferris, 2019 ). A few studies have detected natural selection on leaf shape with this approach, including I. hederacea ( Bright and Rausher, 2008 ), the Mimulus guttatus species complex ( Ferris and Willis, 2018 ), and the Senecio lautus species complex ( Richards et al, 2019 ). However, this approach can have limitations.…”

Senecio as a model system for integrating studies of genotype, phenotype and fitness

“…The benefit of using Senecio as a model system to overcome such difficulties is two‐fold. First, many Senecio species show evidence of recent rapid adaptive radiation, providing the opportunity to characterize the strength and direction of selection during the early stages of adaptive diversification using transplant experiments (Walter et al , ; Richards et al , ). Second, Senecio species often display high levels of intraspecific variation, often with a well‐defined structure among populations (i.e.…”

“…In many cases, species also produce viable hybrids (unlike highly divergent taxa), allowing their use in multigeneration artificial hybridization experiments (e.g. Richards et al , ; Walter et al , ; Wilkinson et al , ). These crosses can be used to recreate genetic and phenotypic variation that is currently absent in natural populations and may reflect earlier stages of divergence among sister species.…”