Galloway, Laura , Kubow, Karen , Dai , Can Ashley , Barringer, Brian .
Range-wide pattern of reproductive isolation between populations of an autotetraploid herb.
With limited gene exchange, populations of a species become differentiated due to a combination of natural selection and genetic drift. The accumulation of genetic differences may lead to speciation; however in plants, post-zygotic reproductive isolation, commonly equated with speciation, is often not complete. Incomplete reproductive isolation is often expressed as poor hybrid performance, termed outbreeding depression. Intraspecific reproductive isolation therefore provides a glimpse into the earliest stages of speciation. We estimated outbreeding depression in a range-wide sample of populations of Campanulastrum americanum, an autotetraploid herb. Crosses were conducted between populations separated by a range of geographic distances, some of which likely shared post-glaciation migration routes while others were across biogeographic barriers. Parental populations and intraspecific F1 hybrids were grown for crosses between 28 pairs of populations. In contrast to expectations, there was no overall evidence for outbreeding depression associated with isolation by distance. Hybrid fitness was similar to the average of the parental populations regardless of the geographic distance between the populations. Crosses that included populations from the Appalachian Mountains were an exception to this pattern. These populations showed isolation by distance expressed as reduced germination and survival of hybrids relative to their parents. For example, hybrid germination and juvenile survival of one cross was less than 20% that of their parents. In addition, performance of the reciprocal hybrids differed for crosses with an Appalachian parent, suggesting differentiation in nuclear and cytoplasmic genes between these populations. Results suggest that populations from the Appalachian region are highly genetically differentiated from the rest of the species, potentially indicating incipient speciation. Ongoing work will evaluate whether patterns of population genetic differentiation support these results.
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1 - University of Virginia, Department of Biology, Charlottesville, VA, 22904-4328, USA
2 - Franklin and Marshall College , Department of Biology , Lancaster, PA, 17604, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 555A/Convention Center
Date: Monday, August 2nd, 2010
Time: 2:15 PM