Department of Biology, Keio University, Yokohama, Japan.
Urban Entomology Laboratory, Vector Control Research Unit, School of Biological Sciences, Universiti Sains Malaysia, Penang, Malaysia.
J Evol Biol. 2019 Aug;32(8):844-855. doi: 10.1111/jeb.13486. Epub 2019 May 27.
The evolution of laterality, that is the biased use of laterally paired, morphologically symmetrical organs, has attracted the interest of researchers from a variety of disciplines. It is, however, difficult to quantify the fitness benefits of laterality because many organs, such as human hands, possess multimodal functions. Males of the earwig Labidura riparia (Insecta: Dermaptera: Labiduridae) have morphologically similar laterally paired penises, only one of which is used for inseminating the female during a single copulation bout, and thus provide a rare opportunity to address how selection pressure may shape the evolution of population-level laterality. Our population studies revealed that in 10 populations, located at 2.23-43.3° north, the right penis is predominantly used for copulating (88.6%). A damaged penis was found in 23% of rare left-handers, suggesting that the left penis can function as a spare when the right one is damaged. By pairing L. riparia females with surgically manipulated males, we found that males forced to use the right penis outperformed left-handed males in copulation (the probability of establishing genital coupling during the 1-hr observation period: odds ratio [OR] of 3.50) and insemination (probability of transferring a detectable amount of sperm: OR of 2.94). This right-handed advantage may be due to the coiled morphology of the sperm storage organ with a right-facing opening. Thus, female genital morphology may play a significant role in the evolution of handedness and may have acted as a driving force to reduce penis number in related taxa.
侧行性（即偏向使用形态对称的侧向配对器官）的进化引起了来自多个学科的研究人员的兴趣。然而，由于许多器官（如人手）具有多种模态功能，因此很难量化侧行性的适应度益处。直翅目螽斯科的耳夹子蜚蠊（Labidura riparia）雄性具有形态相似的侧向配对阴茎，在单次交配中，只有一个阴茎用于使雌性受精，因此为解决选择压力如何塑造群体水平侧行性的进化提供了难得的机会。我们的种群研究表明，在位于北纬 2.23-43.3°的 10 个种群中，右侧阴茎主要用于交配（88.6%）。在罕见的左撇子中发现了 23%的受损阴茎，这表明当右侧阴茎受损时，左侧阴茎可以作为备用。通过将螽斯科雌性与经过手术处理的雄性配对，我们发现，被迫使用右侧阴茎的雄性在交配（在 1 小时观察期内建立生殖器连接的概率：3.50 的优势比[OR]）和授精（转移可检测量精子的概率：2.94 的 OR）方面优于左撇子雄性。这种右手优势可能归因于精子储存器官的卷曲形态，其开口朝向右侧。因此，雌性生殖器形态可能在偏手性的进化中发挥重要作用，并可能成为减少相关类群阴茎数量的驱动力。
