Bayesian inference of evolutionary history from chloroplast microsatellites in the cosmopolitan weed Capsella bursa‐pastoris (Brassicaceae)

Abstract

Besides showing an extraordinary degree of phenotypic variability, Capsella bursa-pastoris (Brassicaceae) is also one of the world's most common plant species and a serious weed in many countries. We have employed a coalescent-based Bayesian analysis of chloroplast microsatellite data to infer demographic and evolutionary parameters of this species. Two different demographic models applied to data from seven chloroplast microsatellite loci among 59 accessions show that the effective population size of C. bursa-pastoris is very small indicating a rapid expansion of the species, a result that is in accordance with fossil and historical data. Against this background, analysis of flowering time variation among accessions suggests that ecotypic differentiation in flowering time has occurred recently in the species' history. Finally, our results also indicate that mononucleotide repeat loci in the chloroplast genome can deteriorate in relatively short periods of evolutionary time.

Splicing Variation at a FLOWERING LOCUS C Homeolog Is Associated With Flowering Time Variation in the Tetraploid Capsella bursa-pastoris

“…In agreement with studies of variation at chloroplast microsatellites (Ceplitis et al 2005) and nuclear genes (Slotte et al 2008), we find overall low levels of nucleotide diversity in C. bursa-pastoris. Reduced diversity levels are expected in a polyploid if the origin of the species was recent and constituted a severe bottleneck.…”

“…The flowering time of all accessions from western Eurasia was determined previously (Ceplitis et al 2005). Briefly, seeds were germinated in petri dishes and seedlings were transferred to individual pots and grown in the greenhouse in fully randomized blocks with a 16-hr photoperiod.…”

“…bursa-pastoris is a predominantly selfing, disomic tetraploid with a nearly worldwide distribution. Although it has low levels of variation at cpDNA and nuclear genes (Ceplitis et al 2005;Slotte et al 2008), it is very variable for many morphological and life-history traits, including flowering time (Hurka and Neuffer 1997). Flowering is induced by long days, and natural accessions differ in their requirement of vernalization (a prolonged cold treatment) for flowering (Slotte et al 2007).…”

Two haplotypes of Capsella bursa-pastoris (Brassicaceae) in Continental Chile support multiple introduction

“…On the one hand, it could be argued that one of them (haplotype B) arose in Chile by mutation from the other previously introduced (probably the haplotype A). We believe that this is improbable because it has been stated that the evolutionary rate (μ) for these markers is too low, because it varies between 2.5×10 -5 and 2.9×10 -4 mutations per locus per generation (Cregan & Quigley 1997, Provan et al 1999, 2001, Ceplitis et al 2005. This would imply, assuming a single mutation event, an introduction time for C. bursa-pastoris longer than 500 years, which is clearly an erroneous estimate.…”

“…Samples of C. bursa-pastoris were submitted to analyses of three microsatellite loci (cpSSR), amplified from cpDNA. These markers correspond to the ATCP46615, ATCP66701 and ATCP31017 loci, documented by Ceplitis et al 2005 (Table II). GENOME EXTRACTION AND MARKER AMPLIFICATION A total extraction of genomic DNA was carried out using CTAB extraction buffer procedure described by Doyle & Doyle (1990) and modified by Allen et al (2006).…”