DiDomenico Angela, Hedin Marshal
Department of Biology, 5500 Campanile Drive, San Diego State University, San Diego, CA 92182-4614, USA.
Zookeys. 2016 May 4(586):1-36. doi: 10.3897/zookeys.586.7832. eCollection 2016.
The western United States is home to numerous narrowly endemic harvestman taxa (Arachnida, Opiliones), including members of the genus Sitalcina Banks, 1911. Sitalcina is comprised of three species groups, including the monospecific Sitalcina californica and Sitalcina lobata groups, and the Sitalcina sura group with eight described species. All species in the Sitalcina sura group have very small geographic distributions, with group members distributed like disjunct "beads on a string" from Monterey south to southern California and southeast to the sky-island mountain ranges of southern Arizona. Here, molecular phylogenetic and species delimitation analyses were conducted for all described species in the Sitalcina sura group, plus several newly discovered populations. Species trees were reconstructed using multispecies coalescent methods implemented in *BEAST, and species delimitation was accomplished using Bayes Factor Delimitation (BFD). Based on quantitative species delimitation results supported by consideration of morphological characters, two new species (Sitalcina oasiensis sp. n., Sitalcina ubicki sp. n.) are described. We also provide a description of the previously unknown male of Sitalcina borregoensis Briggs, 1968. Molecular phylogenetic evidence strongly supports distinctive desert versus coastal clades, with desert canyon taxa from southern California more closely related to Arizona taxa than to geographically proximate California coastal taxa. We hypothesize that southern ancestry and plate tectonics have played a role in the diversification history of this animal lineage, similar to sclerophyllous plant taxa of the Madro-Tertiary Geoflora. Molecular clock analyses for the Sitalcina sura group are generally consistent with these hypotheses. We also propose that additional Sitalcina species await discovery in the desert canyons of southern California and northern Baja, and the mountains of northwestern mainland Mexico.
美国西部是众多狭域分布的长脚蛛类群（蛛形纲，盲蛛目）的家园，其中包括1911年命名的西塔尔辛纳属（Sitalcina Banks）的成员。西塔尔辛纳属由三个物种组组成，包括单物种的加利福尼亚西塔尔辛纳（Sitalcina californica）和洛巴塔西塔尔辛纳（Sitalcina lobata）组，以及包含八个已描述物种的苏拉西塔尔辛纳（Sitalcina sura）组。苏拉西塔尔辛纳组的所有物种地理分布都非常狭窄，该组成员分布呈间断的“串珠”状，从蒙特雷向南至南加利福尼亚，向东南至亚利桑那州南部的天空岛屿山脉。在此，我们对苏拉西塔尔辛纳组所有已描述物种以及几个新发现的种群进行了分子系统发育和物种界定分析。使用BEAST中实现的多物种溯祖方法重建物种树，并使用贝叶斯因子界定法（BFD）完成物种界定。基于形态特征考量支持的定量物种界定结果，描述了两个新物种（绿洲西塔尔辛纳（Sitalcina oasiensis sp. n.）、乌氏西塔尔辛纳（Sitalcina ubicki sp. n.））。我们还描述了1968年布里格斯（Briggs）命名的博雷戈西塔尔辛纳（Sitalcina borregoensis）此前未知的雄性个体。分子系统发育证据有力地支持了独特的沙漠与沿海分支，来自南加利福尼亚的沙漠峡谷类群与亚利桑那州类群的亲缘关系比与地理上相邻的加利福尼亚沿海类群更近。我们推测，南方起源和板块构造在这个动物谱系的多样化历史中发挥了作用，这与马德雷 - 第三纪植物区系的硬叶植物类群类似。苏拉西塔尔辛纳组的分子钟分析总体上与这些假设一致。我们还提出，在南加利福尼亚和北下加利福尼亚的沙漠峡谷以及墨西哥大陆西北部的山脉中，有待发现更多的西塔尔辛纳物种。
