An analysis of the fitness of interspecific, intraspecific and nonhybrid Raphanus populations in Michigan
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Authors
Muir, Kathryn B.
Issue Date
2008
Type
Thesis
Language
en_US
Keywords
Alternative Title
Abstract
Speciation is a continuous process; yet the study of speciation can be
problematic as it generally occurs in evolutionary time. It is possible however, to
postulate when a group of organisms is in the process of speciation based on factors
such as partial reproductive barriers, gene flow, and hybridization. Hybridization can
be used as a tool for elucidating the genetic and evolutionary relationships between the
species and sub-species of a given genus. Within the genus Raphanus, hybridization
is known to occur both inter- and intraspecifically. Using a Michigan field study, we
have quantified the fitness of Raphanus hybrids made from crossing six parental
populations. We found that some interspecific hybrids had higher fitness than several
intraspecific hybrids, as well as several pure parental populations. Using previously
collected molecular data, we compared fitness levels found in this study to gene flow
between the parental populations of radish. Several of the most distantly related
radish populations formed hybrid offspring that were more fit than some of the pure
parental populations. This brings into question the existence of two distinct species
within the genus; perhaps R. sativus (cultivated radish) and R. raphanistrum (wild and
weedy radish) should actually be classified as the same species. In addition, molecular
data shows significantly more gene flow within weedy radish populations, probably
due to worldwide grain shipping, than between weedy radish and natural populations.
The high genetic differentiation between native populations suggests incipient
speciation. These data taken together indicate that perhaps R. raphanistrum is
currently undergoing speciation. This hypothesis is supported by data collected during
this field study.
Description
iv, 30 p.
Citation
Publisher
Kalamazoo College
License
U.S. copyright laws protect this material. Commercial use or distribution of this material is not permitted without prior written permission of the copyright holder.