Abstract Detail

Species delimitation in polyploid complexes

Ramsey, Justin [1], Ramsey, Tara [2].

Prezygotic reproductive barriers in the Achillea millefolium aggregate (Asteraceae): effects of polyploidization on phenology, water relations, and fitness in contrasting environments.

Polyploidy – whole genome duplication – is regarded as a major speciation mechanism based on its frequent incidence in plants and well-known effects on postzygotic reproductive barriers (hybrid inviability and sterility).  Circumstantial evidence suggests a role of polyploidy in ecological adaptation and evolution of prezygotic barriers, such as habitat isolation and phenological isolation.  Diploids and polyploids often have distinct geographic and environmental distributions, for example, and polyploidization alters anatomical and growth features in a manner likely to affect survival in different environments.  It is difficult to quantify impacts of ploidy per se on ecological speciation, however, because traits underlying prezygotic barriers evolve rapidly by conventional processes of selection.  Here we report on long-term experiments conducted with neopolyploids (first-generation mutants) and wild polyploids of the Achillea millefolium aggregate.  North American Achillea (A. borealis) is an autopolyploid complex of tetraploid and hexaploid cytotypes and ~10 taxonomic varieties; widespread across the U.S.A and Canada, A. borealis is closely-related to A. asiatica and arrived in North America during the Pleistocene.  Our studies of neopolyploids focus on California's North Coast, where morphologically similar tetraploids (var. litoralis) and hexaploids (var. arenicola) occur.  In this region, late-flowering tetraploids reside in mesic coastal prairies and early-flowering hexaploids are found in xeric dunes.  While growing in proximity, the two cytotypes rarely cohabitate in populations.  Transplant experiments suggest intrinsic differences in cytotype fitness between grassland vs. dunes, with drought stress being a major factor affecting survivorship in sandy habitats occupied by hexaploids.  To test effects of ploidy on phenological and habitat isolation, we screened neohexaploids among progeny of tetraploid plants; these first-generation hexaploids have the genetic background of var. litoralis and ploidy of var. arenicola.  Transplant experiments in a mesic grassland reveal that neohexaploids have larger stems and increased leaf biomass compared to tetraploids, but reproduce earlier and produce fewer flower heads.  Experiments in xeric dunes indicate increased survivorship and growth of neohexaploids, which in turn were outperformed by wild hexaploids.  In greenhouse experiments, we find substantial size and architectural differences between neohexaploids and tetraploids, and anatomical features shared between neohexaploids and wild hexaploids.  However, water relations (transpiration rates, times-to-wilt) differ fundamentally between neohexaploids and wild hexaploids.  These findings point to strong, ecologically-mediated prezygotic barriers between cytotypes that may in part reflect phenotypic consequences of polyploidization.  Neohexaploids do not recapitulate drought tolerance adaptations that seem critical for winter-wet, summer-dry habitats occupied by A. borealis hexaploids (vars. arenicola, californica).

1 - Black Hills State University, School Of Natural Sciences, 1200 University Street, Unit 9095, Spearfish, SD, 57799, United States
2 - Black Hills State University, School Of Natural Sciences, 1200 University Street, Unit 9095, Spearfish, SD, 57799, USA


Presentation Type: Colloquium Presentations
Number: 0001
Abstract ID:634
Candidate for Awards:None

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