Almeida Susana C, Neiva João, Sousa Filipe, Martins Neusa, Cox Cymon J, Melo-Ferreira José, Guiry Michael D, Serrão Ester A, Pearson Gareth A
Centre of Marine Sciences, Universidade do Algarve, Faro, Portugal.
cE3c - Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal.
Mol Ecol. 2022 Sep;31(18):4797-4817. doi: 10.1111/mec.16623. Epub 2022 Aug 8.
Geologically recent radiations can shed light on speciation processes, but incomplete lineage sorting and introgressive gene flow render accurate evolutionary reconstruction and interpretation challenging. Independently evolving metapopulations of low dispersal taxa may provide an additional level of phylogeographic information, given sufficiently broad sampling and genome-wide sequencing. Evolution in the marine brown algal genus Fucus in the south-eastern North Atlantic was shaped by Quaternary climate-driven range shifts. Over this timescale, divergence and speciation occurred against a background of expansion-contraction cycles from multiple refugia, together with mating-system shifts from outcrossing (dioecy) to selfing hermaphroditism. We tested the hypothesis that peripheral isolation of range edge (dioecious) F. vesiculosus led to parapatric speciation and radiation of hermaphrodite lineages. Species tree methods using 876 single-copy nuclear genes and extensive geographic coverage produced conflicting topologies with respect to geographic clades of F. vesiculosus. All methods, however, revealed a new and early diverging hermaphrodite species, Fucus macroguiryi sp. nov. Both the multispecies coalescent and polymorphism-aware models (in contrast to concatenation) support sequential paraphyly in F. vesiculosus resulting from distinct evolutionary processes. Our results support (1) peripheral isolation of the southern F. vesiculosus clade prior to parapatric speciation and radiation of hermaphrodite lineages-a "low-latitude species pump". (2) Directional introgressive gene flow into F. vesiculosus around the present-day secondary contact zone (sympatric-allopatric boundary) between dioecious/hermaphrodite lineages as hermaphrodites expanded northwards, supported by concordance analysis and statistical tests of introgression. (3) Species boundaries in the extensive sympatric range are probably maintained by reproductive system (selfing in hermaphrodites) and reinforcement.
近期的地质辐射能够为物种形成过程提供线索，但不完全的谱系分选和渐渗基因流使得准确的进化重建和解释颇具挑战性。对于低扩散类群独立演化的集合种群而言，若有足够广泛的采样和全基因组测序，可能会提供额外层面的系统地理学信息。北大西洋东南部的海洋褐藻墨角藻属的演化受到第四纪气候驱动的范围变化的影响。在这个时间尺度上，分歧和物种形成发生在来自多个避难所的扩张-收缩循环背景下，同时交配系统从异交（雌雄异株）转变为自交雌雄同体。我们检验了这样一个假设，即边缘（雌雄异株）的泡叶墨角藻的边缘隔离导致了雌雄同体谱系的邻域物种形成和辐射。使用876个单拷贝核基因和广泛地理覆盖范围的物种树方法，针对泡叶墨角藻的地理分支产生了相互冲突的拓扑结构。然而，所有方法都揭示了一个新的且早期分化的雌雄同体物种，即大圭里墨角藻（Fucus macroguiryi sp. nov.）。多物种溯祖模型和多态性感知模型（与串联法相反）均支持泡叶墨角藻中由于不同进化过程导致的序列并系。我们的结果支持：（1）在雌雄同体谱系的邻域物种形成和辐射之前，泡叶墨角藻南部类群的边缘隔离——一种“低纬度物种泵”。（2）随着雌雄同体向北扩张，在现今雌雄异株/雌雄同体谱系之间的二次接触带（同域-异域边界）周围，有方向性的渐渗基因流入泡叶墨角藻，这得到了渐渗的一致性分析和统计检验的支持。（3）广泛同域分布范围内的物种边界可能由生殖系统（雌雄同体中的自交）和强化作用维持。
