Journal Article

Complex cytogeographical patterns reveal a dynamic tetraploid–octoploid contact zone

Mariana Castro, Sílvia Castro, Albano Figueiredo, Brian Husband and João Loureiro

in AoB PLANTS

Volume 10, issue 2
Published online February 2018 | e-ISSN: 2041-2851 | DOI: https://dx.doi.org/10.1093/aobpla/ply012

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  • Ecology and Conservation
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Abstract

The distribution of cytotypes in mixed-ploidy species is crucial for evaluating ecological processes involved in the establishment and evolution of polyploid taxa. Here, we use flow cytometry and chromosome counts to explore cytotype diversity and distributions within a tetraploid–octoploid contact zone. We then use niche modelling and ploidy seed screening to assess the roles of niche differentiation among cytotypes and reproductive interactions, respectively, in promoting cytotype coexistence. Two cytotypes, tetraploids and octoploids, were dominant within the contact zone. They were most often distributed parapatrically or allopatrically, resulting in high geographic isolation. Still, 16.7 % of localities comprised two or more cytotypes, including the intermediate hexaploid cytotype. Tetraploids and octoploids had high environmental niche overlap and associated with similar climatic environments, suggesting they have similar ecological requirements. Given the geographical separation and habitat similarity among cytotypes, mixed-ploidy populations may be transitional and subject to the forces of minority cytotype exclusion which lead to pure-ploidy populations. However, seed ploidy analysis suggests that strong reproductive barriers may enforce assortative mating which favours stable cytotype coexistence. High cytogenetic diversity detected in the field suggests that unreduced gamete formation and hybridization events seem frequent in the studied polyploid complex and might be involved with the recurrent polyploid formation, governing, as well, the gene flow between cytogenetic entities.

Keywords: Contact zone; distribution patterns; Gladiolus communis; hexaploid; hybridization; niche modelling; niche overlapping; octoploid; tetraploid

Journal Article.  11505 words.  Illustrated.

Subjects: Ecology and Conservation ; Plant Evolution ; Plant Sciences and Forestry

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