Dimorphism, Polyploidy, and Genetic Diversity in the Australian Endemic Lycium australe (Solanaceae)

Abstract

Premise of research. Whole-genome duplication is often associated with the evolution of dimorphic sexual systems; however, the association is not universal, and the evolutionary pathway(s) underlying the association remain unresolved. The genus Lycium has been demonstrated as a useful system for investigating ploidy and sexual system variation. Here, we describe ploidy and floral variation in L. australe and document genetic diversity and dimorphism across its range. Methodology. Sexual system and size dimorphism were assessed using morphological measurements of 486 flowers. Flow cytometry was used to determine DNA content and ploidy level for 167 plants from across the species range. Using the plastid region trnH-psbA and restriction site-associated DNA sequencing (RADseq), we explored the genetic structure of the species, including an examination of associations of ploidy and sexual system with genetic structure. Pivotal results. We find correlated variation in ploidy level, sexual system, and genetic structure in L. australe. Both gynodioecy and dioecy are documented and are associated with diploidy and polyploidy, respectively. Floral size dimorphism is also found among morphs in both sexual systems. We find significant genetic structure associated with ploidy level and geography based on genome-wide single-nucleotide polymorphisms and plastid haplotypes. Conclusions. We show that L. australe has associated polymorphism in sexual system and ploidy, but the association is an exception to the pattern in the genus. Genetic and ploidy variation in the species suggests potential reproductive barriers and ecological differentiation between cytotypes of differing ploidies. The widespread parapatric distributions of diploid and polyploid L. australe make it an ideal system for studying questions related to reproductive compatibility, ecological differentiation, and polyploid speciation.