Phenotypic trait variation in the North American Tragopogon allopolyploid complex

Premise: Recently formed allopolyploids Tragopogon mirus and T. miscellus and their diploid parental species, T. dubius, T. porrifolius, and T. pratensis, offer a rare opportunity to study the earliest stages of allopolyploidy. The allopolyploid species have also been resynthesized, allowing comparisons between the youngest possible allopolyploid lineages and their natural, established counterparts. For the first time, we compared phenotypic traits on a large scale in Tragopogon diploids, natural allopolyploids, and three generations of synthetic allopolyploids.

Methods: Our large common-garden experiment measured traits in growth, development, physiology, and reproductive fitness. We analyzed trait differences between allopolyploids and their parental species, and between synthetic and natural allopolyploids.

Results: As in many polyploids, the allopolyploid species had some larger physical traits and a higher capacity for photosynthesis than diploid species. Reproductive fitness traits were variable and inconsistent. Allopolyploids had intermediate phenotypes compared to their diploid parents in several traits, but patterns of variation often varied between allopolyploid complexes. Resynthesized and natural allopolyploid lines generally showed minor to nonexistent trait differences.

Conclusions: In Tragopogon, allopolyploidy results in some typical phenotypic changes, including gigas effects and increased photosynthetic capacity. Being polyploid did not produce a significant reproductive advantage. Comparisons between natural and synthetic T. mirus and T. miscellus are consistent with very limited, idiosyncratic phenotypic evolution following allopolyploidization.