Spontaneous hybrids between native and exotic Rubus in the Western United
States produce offspring both by apomixis and by sexual recombination |
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Authors: | L V Clark M Jasieniuk |
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Institution: | 1.1.Department of Plant Sciences,
University of California, Davis, CA, USA |
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Abstract: | Facultative asexual reproduction is a trait commonly found in invasive species. With a
combination of sexual and asexual reproductive modes, such species may adapt to new
environments via sexual recombination during range expansion, while at the same time
having the benefits of asexuality such as the maintenance of fitness effects that depend
upon heterozygosity. In the Western United States, native species of Rubus
(Rosaceae) reproduce sexually whereas exotic naturalized Rubus species reproduce
by pseudogamous apomixis. We hypothesized that new asexual lineages of Rubus
could arise from hybridization in this range. To detect hybridization between native and
exotic Rubus, we genotyped 579 individuals collected across California, Oregon
and Washington with eight nuclear microsatellites and two chloroplast markers. Principal
Coordinate Analysis and Bayesian clustering revealed a limited amount of hybridization of
the native R. ursinus with the exotic R. armeniacus and R.
pensilvanicus, as well as cultivated varieties. Genetic distances between these
hybrids and their offspring indicated that both R. ursinus × R.
armeniacus and R. ursinus × R. pensilvanicus produced a mix
of apomictic and sexual seeds, with sexual seeds being more viable. Although neither of
these hybrid types is currently considered invasive, they model the early stages of
evolution of new invasive lineages, given the potential for fixed heterosis and the
generation of novel genotypes. The hybrids also retain the ability to increase their
fitness via sexual recombination and natural selection. Mixed reproductive systems such as
those described here may be an important step in the evolution of asexual invasive
species. |
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Keywords: | asexual reproduction hybridization invasive species polyploidy Rubus SSR |
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