Abstract Detail

Hybrids and Hybridization

Andreev, Victor [1], Puzey, Joshua [2], Davies, Lizzy [2], Olson-Manning, Carrie [3], Kreutzmann, Sydney [3], Fishbein, Mark [1].

Morphological and genetic analyses provide novel evidence for introgressive hybridization between two milkweed species.

Understanding patterns of variation in closely related species is essential for studying their evolution. One system that can help us better understand the evolution of plant species in prairie ecosystems includes two milkweeds, Asclepias speciosa and A. syriaca. The ranges of these species overlap on the Great Plains, and many individuals of intermediate morphology can be found in this area. Several researchers proposed hybridization as an explanation for the observed pattern of morphological variation. However, presence of a range of morphological intermediates does not necessarily imply hybridization. Alternative explanations would include preservation of ancestral polymorphism or the action of selective pressure imposed by environmental clines. Since the species meet on a strong precipitation gradient, a longitudinal cline in their morphology would not be surprising.Our goals were to characterize putative hybrids and validate the hybrid origin of intermediates using morphological and genetic approaches. We analyzed a range-wide sample of about 600 individuals obtained from herbarium and field-collected samples. Our morphological analyses were based on measurements of 15 floral and vegetative traits, and genetic analyses were based on 7480 genome-wide SNPs.The analyses revealed that there is no evidence of continuous morphological variation between A. speciosa and A. syriaca that is correlated with geographic distance. These species can be reliably distinguished on morphological and genetic levels, and putative hybrids are morphologically and genetically intermediate between them.Even though the parental species represent two distinct genetic pools, there is evidence of interspecific gene flow in sympatric populations of A. speciosa and A. syriaca. Individuals in the zone of sympatry demonstrate various degrees of admixture, and the pattern of shared genetic variation corresponds to that of advanced generation hybridization. Thus, we conclude that the individuals of intermediate morphology are indeed hybrids, since their existence cannot be explained by environmental clines or preservation of ancestral polymorphism.This research helps us to understand the spatial distribution of morphological and genetic variation in plant species on the Great Plains and the processes that shape this variation.

1 - Oklahoma State University, Dept Of Plant Biology, Ecology & Evolution, 301 Physical Science, Stillwater, OK, 74078, United States
2 - College Of William And Mary, Biology Dept., 540 Landrum Dr., Williamsburg, VA, 23185, United States
3 - Augustana University, Biology Dept., 2001 S. Summit Ave., Sioux Falls, SD, 57197, United States

gene flow.

Presentation Type: Oral Paper
Number: HH1003
Abstract ID:941
Candidate for Awards:Margaret Menzel Award

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