Geographic distribution and climatic niche comparison between diploid and polyploid cytotypes of a South American genus Lessingianthus H.Rob. (Vernonieae, Asteraceae)

Abstract

The distribution of ploidy levels and their ecological associations were studied using the genus Lessingianthus (Vernonieae, Asteraceae) as a model system. This genus is very complex from a cytogenetic point of view, with high cytotype diversity at the interspecific and intraspecific levels and with a continuous distribution throughout South America. So far, no previous studies have summarized chromosome count data for Lessingianthus or addressed the cytogeography of the genus. In this study, the ploidy levels of Lessingianthus species were determined by chromosome counts during mitosis and ecological niche modelling (ENM) was used to compare the environmental associations of the diploid and polyploid cytotypes. In total, 28 chromosome counts and six ploidy levels (2x, 4x, 6x, 8x, 10x, and 11x) were recorded. Among these counts, the chromosome numbers for three hexaploids with 2 n = 96 (L. parvifolius, L. vepretorum and L. “bolivianensis” sp. ined.) and one decaploid taxon with 2 n = 160 (L. roseus) were reported for the first time. In addition, a new cytotype for L. laniferus (2 n = 6x = 96) was also reported. The cytogeographic analysis resulted in detecting two geographic zones with high diversity of cytotypes and species. The ENMs showed that the areas of climatic suitability of diploids and polyploids are similar in extent, as well as the climatic requirements, showing high values of niche overlap within the environmental space. Our findings suggested that polyploidization in Lessingianthus has not caused expansion to novel environmental conditions and phylogenetic niche conservatism (PNC) may explain the lack of niche differentiation between diploids and polyploids.