Postzygotic isolation varies by ploidy level within a polyploid complex

Whole genome duplication is considered to be a significant contributor to angiosperm speciation due to accumulation of rapid, strong interploid reproductive isolation. However, recent work suggests that interploid reproductive isolation may not be complete, especially among higher order cytotypes. T...

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Bibliographic Details
Published in:	The New phytologist 2017-01, Vol.213 (1), p.404-412
Main Authors:	Sutherland, Brittany L., Galloway, Laura F.
Format:	Article
Language:	eng
Subjects:	Analysis of Variance Campanula rotundifolia Crosses, Genetic cytotype Genetic Fitness hexaploid Magnoliopsida - genetics Magnoliopsida - physiology Pollen - physiology polyploid complex Polyploidy postzygotic Reproductive Isolation tetraploid Zygote - physiology
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Summary:	Whole genome duplication is considered to be a significant contributor to angiosperm speciation due to accumulation of rapid, strong interploid reproductive isolation. However, recent work suggests that interploid reproductive isolation may not be complete, especially among higher order cytotypes. This study evaluates postzygotic reproductive isolation among three cytotypes within a polyploid complex. We conducted reciprocal crosses using two diploid and two hexaploid populations each crossed to tetraploid populations spanning the geographic and phylogenetic range of the Campanula rotundifolia polyploid complex. Interploid and intrapopulation crosses were scored for fruit set, seed number, germination proportion and pollen viability. Postzygotic isolation was calculated for each cross as the product of these fitness components. A subset of offspring was cytotyped via flow cytometry. Postzygotic isolation was significantly lower in tetraploid–hexaploid crosses than diploid–tetraploid crosses, mostly due to substantially higher germination among tetraploid–hexaploid crosses. Tetraploid–hexaploid crosses produced pentaploids exclusively, whereas diploid–tetraploid crosses produced both triploids and tetraploids in high frequencies. Postzygotic isolation was weaker among higher order polyploids than between diploids and tetraploids, and unreduced gametes may facilitate diploid–tetraploid reproduction. This incomplete postzygotic isolation could allow ongoing interploid gene flow, especially among higher order polyploids, which may slow divergence and speciation in polyploid complexes.
ISSN:	0028-646X 1469-8137