Abstract Detail

Systematics

Mastin, Jared [1], Bruederle, Leo [2].

Ecological niche modeling reveals divergence between tetraploid and hexaploid populations of Eutrema edwardsii R. Br. (Brassicaceae).

Ecological niche modeling of polyploid complexes has revealed variation for niche differentiation between ploidies or cytotypes. Within polyploid complexes, both niche expansion and niche contraction have been observed for higher ploidies resulting from whole genome duplication. Eutrema edwardsii (Brassicaceae) is a near circumpolar allopolyploid species that comprises tetraploid, hexaploid, and octaploid populations, which occupy arctic-alpine wetlands across much of the Northern Hemisphere. The evolution of E. edwardsii was largely influenced by Pleistocene glaciations during which harsh conditions and repeated fragmentation promoted hybridization and polyploidization in refugia where species persisted. Newly formed polyploids were presumably more fit in recently deglaciated areas, where the absence of intraspecific competition allowed new cytotypes to establish. Here we test the hypothesis that higher ploidy confers a broader niche that would allow polyploids to colonize habitats outside the niche of their progenitors. To test this, we employed ecological niche modeling to discover differentiation between tetraploid and hexaploids populations of E. edwardsii, specifically. Cytotype was determined by flow cytometry using leaf tissue that was harvested from herbarium accessions (COLO, ALA, CAN by comparing fluorescence with that of a known diploid and putative progenitor, Eutrema penlandii. The distribution of ploidies along with environmental data acquired from WORLDCLIM was used to model the niche for tetraploid and hexaploid cytotypes, specifically. A principle components analysis reduced the number of explanatory variables to those describing the majority of variation with the least amount of correlation among them. These variables were used for Maxent modeling in R to estimate the niche for each cytotype. Niche models reveal a wide range of lowland and coastal habitats for tetraploids, while hexaploids occupy a narrow range of alpine areas. This is supported by niche breadth, which was 0.551 and 0.182 for tetraploids and hexaploids, respectively. Niche overlap (D = 0.388) supports niche divergence between ploidies. Likewise, niche identity (I = 0.713) indicates that niches are distinct, such that randomization of presence points creates models with only 71.3% overlap with original models. The results of these analyses support the hypothesis of niche differentiation between tetraploid and hexaploid E. edwardsii. The hypothesis of niche expansion is rejected based on lower niche breadth for hexaploids; however, niche shift is evident from PCA analysis showing greater temperature seasonality, lower wind speed, and lower January precipitation for hexaploids. Our results suggest polyploidy in E. edwardsii facilitated the colonization of habitat outside the niche of their progenitors.

1 - Univeristy of Colorado Denver, Integrative Biology, Denver, CO, USA
2 - University Of Colorado Denver, CB171, P.O. 173364, DENVER, CO, 80217-3364, USA

Keywords:
Polyploidy
ecological niche modeling
cryptic species
flow cytometry
allopolyploid
Brassicaceae.

Presentation Type: Oral Paper
Session: 19, ASPT Cooley Awards
Location: Sundance 5/Omni Hotel
Date: Tuesday, June 27th, 2017
Time: 9:45 AM
Number: 19007
Abstract ID:188
Candidate for Awards:George R. Cooley Award