Abstract Detail

Hybrids and Hybridization

Andreev, Victor [1], Fishbein, Mark [2].

Phenotypic characterization of the Asclepias syriaca-A. speciosa hybrid zone in the Great Plains of the United States.

Hybridization in the milkweed genus Asclepias (Apocynaceae) is not common, although there are over 20 cases of interspecific hybridization documented among the approximately 130 species in the Americas. The most promiscuous among these is common milkweed, Asclepias syriaca. It hybridizes with at least seven other species, including showy milkweed A. speciosa. The hybrid zone extends from Kansas to North Dakota and Minnesota, with A. syriaca distributed to the east and A. speciosa to the west. Despite the great geographic extent, the hybrid zone has not been well studied. These species are distinguished by differences in reproductive and vegetative morphology. Asclepias syriaca has inflorescences with many, relatively small flowers and ovate to narrowly oblong leaves, whereas A. speciosa has inflorescences with fewer, big flowers and broadly ovate leaves. In apparent hybrids these traits show intermediate morphology between the parental species. We present the results of a morphological study of the hybrids based on analysis of 9 vegetative and 6 floral traits measured on 193 specimens sampled during the 2018 field season and on herbarium specimens. Specimens for morphological analysis were pressed and dried using standard methods. Dried specimens were imaged with a digital camera on a copy stand and through an Olympus SZX-10 stereomicroscope and processed using ImageJ and CellSens. Differences among A. speciosa, A. syriaca, and hybrids were explored with principle component analysis tested with ANOVA, and geographic structure of morphological variation was assessed with Mantel tests. As expected, hybrids exhibit a spectrum of morphological traits intermediate between the parental species, which implies an introgressive nature of the ongoing hybridization between A. syriaca and A. speciosa. Most morphological traits are significantly different between hybrids and parental populations. Further, principal component analysis of vegetative traits revealed that most hybrids morphologically gravitate to A. speciosa. The hybrid zone occurs on a strong precipitation gradient that separates the parental species and a geographical cline in their morphology might be expected. However, the Mantel test showed no significant correlation between morphological and geographical distances in the parental species, thus the intermediate morphology of individuals where the parental ranges converge can be explained better by ongoing introgressive hybridization than the existence of clines. In the future, genetic analysis will be used to elucidate the genetic basis of this process.

1 - Oklahoma State University, 301 Physical Sciences, 301 Physical Sciences, Stillwater, OK, 74078, United States
2 - Oklahoma State University, Dept Of Plant Biology, Ecology & Evolution, 301 Physical Science, Stillwater, OK, 74078, United States

Keywords:
Asclepias
hybrid zone
Great Plains.

Presentation Type: Poster
Session: P, Hybrids and Hybridization Posters
Location: Arizona Ballroom/Starr Pass
Date: Monday, July 29th, 2019
Time: 5:30 PM This poster will be presented at 5:30 pm. The Poster Session runs from 5:30 pm to 7:00 pm. Posters with odd poster numbers are presented at 5:30 pm, and posters with even poster numbers are presented at 6:15 pm.
Number: PHH003
Abstract ID:933
Candidate for Awards:None