Zulekha Karachiwalla, Tagide deCarvalho, Mercedes Burns
Department of Biological Sciences, University of Maryland, Baltimore County, Baltimore MD.
Keith R. Porter Imaging Facility, University of Maryland, Baltimore County, Baltimore MD.
Integr Comp Biol. 2020 Aug 17;63(1):188-97. doi: 10.1093/icb/icaa120.
Most arachnid fertilization occurs internally, allowing for a variety of post-copulatory mechanisms to take place. Females are expected to exert some level of control over sperm fate when 1) the point of gametic fusion is particularly distant from the point of oogenesis, 2) the time of syngamy is significantly later than the time of mating, 3) sperm are non-motile, and/or 4) the morphology of females allows for selective containment of sperm. Many of these conditions are met in Opiliones (a.k.a. "harvesters," "harvestmen," or "daddy-longlegs"), where we have evidence of sexual antagonism, multiple mating, and delayed oviposition for a number of species. We used confocal laser scanning microscopy to capture and analyze images of harvester spermathecae, structures within the genitalia of female arthropods that store and maintain sperm after copulation. Spermathecal morphology may have critical function in controlling seminal movement. We anticipated that species with previously identified traits associated with sexual antagonism would also have thicker and/or relatively more complex spermathecae. We examined spermathecal morphology in thirteen species of Leiobunum and one species of Hadrobunus, which were collected from North America and Japan. Our results show that eight species had structures consisting of a single chamber with no or partial invagination, and the remainder had multiple cuticular invaginations producing 2-3 lumina within the spermathecae. Using phylogenetic multivariate comparative methods, we estimated a trend towards cross-correlation between conflict and spermathecal traits. Some, but not all, of the species with thicker, more complex spermathecae had morphological traits associated with sexual conflict (larger body size, thicker genital muscle). In conclusion, we discuss methods to elucidate spermathecal mechanism and sperm precedence in these species. Confocal microscopy allowed us to visualize internal structures difficult to interpret with two-dimensional brightfield microscopy, a technique that could be applied to the characterization of internal reproductive structures in other arthropods.
大多数蛛形纲动物的受精过程在体内进行，这使得多种交配后机制得以发生。当出现以下情况时，预计雌性会对精子的命运施加一定程度的控制：1）配子融合点与卵子发生点相距甚远；2）受精时间明显晚于交配时间；3）精子无运动能力；和/或4）雌性的形态结构允许对精子进行选择性容纳。在盲蛛目（又称“收割者”“长脚蛛”或“ daddy-longlegs”）中，许多这些条件都得到了满足，我们有证据表明该目中的一些物种存在性对抗、多次交配和产卵延迟的现象。我们使用共聚焦激光扫描显微镜来捕捉和分析收割者受精囊的图像，受精囊是雌性节肢动物生殖器内用于储存和维持交配后精子的结构。受精囊的形态可能在控制精液移动方面具有关键作用。我们预计，具有先前确定的与性对抗相关特征的物种，其受精囊也会更厚和/或相对更复杂。我们研究了从北美和日本采集的13种平腹蛛属和1种粗腹蛛属物种的受精囊形态。我们的结果表明，8个物种的受精囊结构由单个腔室组成，没有或部分内陷，其余物种的受精囊有多个表皮内陷，在受精囊内产生2至3个腔室。使用系统发育多元比较方法，我们估计了冲突与受精囊特征之间存在交叉相关的趋势。一些受精囊更厚、更复杂的物种具有与性冲突相关的形态特征（体型更大、生殖肌肉更厚），但并非全部如此。总之，我们讨论了阐明这些物种受精囊机制和精子优先顺序的方法。共聚焦显微镜使我们能够可视化难以用二维明场显微镜解释的内部结构，该技术可应用于其他节肢动物内部生殖结构的表征。
