Abstract Detail

Molecular Ecology and Evolution

Sutherland, Brittany [1], Galloway, Laura [1].

Patterns of reproductive isolation are not consistent across cytotypes within a polyploid complex.

Whole genome duplication is widely considered an important mechanism of plant speciation due to induction of strong, rapid reproductive isolation. Although interploid reproductive isolation is well-studied in diploid-tetraploid systems, less is known about reproductive isolation among higher-order polyploids. The Campanula rotundifolia polyploid complex consists of diploid, tetraploid, and hexaploid cytotypes, and natural mixed-ploidy populations have been found. In previous greenhouse experiments, we observed that offspring from 4X-6X crosses had much higher germination and higher overall fitness than those from 2X-4X crosses. To determine if observed differences in reproductive isolation were also present in natural populations, we used two approaches: mixed-ploidy open-pollinated arrays, and surveys of naturally-occurring mixed-ploidy populations. To assess interploid reproductive barriers, we used arrays that varied by cytotype distribution (2X-4X or 4X-6X) and frequency. Within each array, cytotypes could be minorities (25% or 8%) or majorities (75% or 92%). F1 offspring were scored for intermediate cytotypes (triploid and pentaploid). In 2X-4X arrays, triploids were rare; only six were observed from over 700 offspring, all from 4X plants in very low frequency (8%). By contrast, pentaploid offspring were common in 4X-6X arrays. Pentaploids comprised 30-50% of all offspring from 4X plants, and 40-75% of all offspring from 6X plants. Pentaploid incidence varied inversely with maternal cytotype frequency, suggesting that mating probability plays a more important role than selection against interploid mating.Next, we inferred presence of interploid mating in natural mixed-ploidy populations. Using leaf tissue from four populations—two 2X-4X and two 4X-6X—for flow cytometry, we found no triploids in 2X-4X populations, but 20-24% pentaploids in 4X-6X populations. Furthermore, 17-20% of each 4X-6X population scored as aneuploids, suggesting backcrossing between 5X and 6X individuals. In total, our results suggest that interploid reproductive capacity in diploid-tetraploid systems differs markedly from polyploid-only systems. Because interploid mating allows continued gene flow among ploidy levels, divergence among polyploids may be slower than between polyploids and diploids. Ongoing gene flow in polyploid complexes could be a factor in the lower than expected diversification rates found in polyploid lineages.

1 - University Of Virginia, P.O. Box 400328, CHARLOTTESVILLE, VA, 22904-4328, USA

Keywords:
polyploidy
reproductive isolation
polyploid diversification
Campanulaceae
polyploid complex.

Presentation Type: Oral Paper
Session: 44, Molecular Ecology and Evolution II
Location: 102/Savannah International Trade and Convention Center
Date: Wednesday, August 3rd, 2016
Time: 2:15 PM
Number: 44004
Abstract ID:715
Candidate for Awards:Margaret Menzel Award