The use of microsatellite markers for species delimitation in Antarctic Usnea subgenus Neuropogon

Lichens are symbiotic associations consisting of a fungal (mycobiont) and one or more photosynthetic (photobionts) partners and are the dominant component, and most important primary producers, of Antarctic terrestrial ecosystems. The most common lichens in the maritime Antarctic are Usnea antarctica and U. aurantiacoatra, a so-called “species pair” in which U. antarctica shows asexual reproduction and propagation via soredia and U. aurantiacoatra forms ascospores in apothecia. Previous molecular analyses were not able to unambiguously distinguish the two morphotypes as species. Therefore, the goal of this study was to find out whether fast-evolving SSR (single sequence repeat) markers are able to separate morphotypes more clearly and help to clarify their taxonomy. We investigate 190 individuals from five mixed stands of both morphotypes collected in King George Island and Elephant Island (South Shetland Islands, Antarctica). Based on 23 microsatellite markers designed from sequenced genomes, discriminant analysis of principal components (DAPC), Bayesian clustering analysis, and coalescent-based estimation of gene flow show clear evidence for the existence of two different species distinguishable by reproductive mode. We did not detect any statistical association between genetic clusters and three previously reported chemical races of each species.

地衣是由真菌共生体（mycobiont）与一种或多种光合共生体（photobionts）组成的共生联合体，同时也是南极陆地生态系统的优势组分与最重要的初级生产者。南极海洋性区域最常见的地衣为南极松萝（Usnea antarctica）与橙黄松萝（U. aurantiacoatra），二者构成所谓的“物种对”：南极松萝通过粉芽进行无性繁殖与扩散，而橙黄松萝则在子囊盘（apothecia）中形成子囊孢子（ascospores）。过往的分子分析无法将这两种形态型作为物种进行明确区分。因此，本研究旨在探究快速进化的简单序列重复（single sequence repeat, SSR）标记能否更清晰地区分这两种形态型，并助力厘清二者的分类学地位。我们对采集自南极南设得兰群岛乔治王岛与象岛的5个混合样地中的190个个体进行了分析。基于从测序基因组中开发的23个微卫星标记，主成分判别分析（DAPC）、贝叶斯聚类分析以及基于溯祖理论的基因流估计结果均提供了明确证据，证明存在两种可通过繁殖模式区分的不同物种。本研究未检测到遗传簇与此前报道的每个物种的三种化学宗之间存在任何统计学关联。