A genome size and phylogenetic survey of Mediterranean Tripleurospermum and Matricaria (Anthemideae, Asteraceae)

Abstract

The study of genome size variation can contribute valuable information on species relationships as well as correlate to several morphological or ecological features, among others. Here we provide an extensive report on genome sizes on genus Tripleurospermum and its closely related genus Matricaria, which are two typically Mediterranean genera particularly widespread and diverse in Turkey, the origin of most of the populations here studied. We analyse and discuss genome size variation in the first relatively complete molecular phylogenetic framework of Tripleurospermum (based on ITS and ETS ribosomal DNA-rDNA-regions). We find cases of intraspecific genome size variation, which could be taxonomically significant. Genome downsizing is also detected as the typical response to polyploidisation in Tripleurospermum taxa, being most conspicuous at the tetraploid level. Several positive correlations with genome size, including those with pollen and stomatal size or cypsela length, among others, are also found. Remarkably, taxa presenting rhizomes tend to present higher genome sizes, confirming a trend to accumulate nuclear DNA in such species, which could be explained by the nutrient reserves availability in their storage organs, allowing genome expansion, or by the lower rates of sexual reproduction in rhizomatous taxa.

Fig 1. Map of Turkey with the grid system classifying the different districts as it appears in the Flora of Turkey [25].

Districts colored in violet and pink correspond to those were populations of Tripleurospermum and Matricaria were collected, respectively (both for genome size assessments and molecular phylogeny). Mixed violet and pink indicates that both Tripleurospermum and Matricaria populations were found in those districts. Codes: * Anthemis Δ Matricaria ○ Tripleurospermum belong to those populations used for phylogenetic reconstruction only (the corresponding number is indicated in Table 1). Map created with mapchart.net.

Fig 2. Molecular phylogenetic reconstruction obtained through combined analysis of ITS and 3’ETS sequence data for 45 taxa.

The majority rule consensus tree (50%), based on Bayesian MCMC inference and with Bayesian clade-credibility values (posterior probability > 0.5) above branches, is displayed. A representation of genome sizes in bars (2C and 1Cx, in darker colours) is displayed in the right part of the image. Note, average higher genome sizes of species from clade A (purple) as compared to species from clade B (blue) in Tripleurospermum.