Sawada Yuna, Sato Nozomu, Osawa Takeshi, Matsumoto Kazuma, Chiu Ming-Chung, Okada Ryuichi, Sakura Midori, Sato Takuya
Department of Zoology, Division of Biological Sciences, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8224, Japan.
Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, Minami-Osawa 1-1, Hachiouji, Tokyo 192-0397, Japan.
PNAS Nexus. 2024 Oct 15;3(10):pgae464. doi: 10.1093/pnasnexus/pgae464. eCollection 2024 Oct.
Human activities introduce new environmental cues to wild organisms, leading to maladaptive behavioral and life history decisions known as the "evolutionary trap." This trap is thought to be a major conservation concern for free-living organisms. However, it has never been studied in endosymbionts, one of the most successful and diverse life forms on Earth. Here, we examine this trap in the extended phenotype of a parasite that exploits the visual system of hosts to alter host behavior for its benefit. Arboreal mantids infected by nematomorph parasites are drawn to horizontally polarized light, thereby inducing them to enter the water. In this study, we found that the degree of linear polarization (DOP) of reflected light served as a reliable environmental cue for identifying perennial waters, where nematomorphs can survive in their aquatic life stage without drying out. Infected mantids exhibit attraction to horizontally polarized light with higher DOP in behavioral assays and jumped into pools reflecting light with higher DOP in field experiments. The asphalt road reflected horizontally polarized light closely resembling the polarization levels observed in perennial waters, likely leading to a higher prevalence of mantids on asphalt roads compared with those found in natural arboreal habitats. In a field experiment, we observed infected mantids walking on asphalt roads more often than on cement roads. These findings imply that evolutionary traps can endanger endosymbionts beyond their hosts that directly perceive environmental cues.
人类活动给野生生物带来了新的环境线索，导致被称为“进化陷阱”的适应不良的行为和生活史决策。这种陷阱被认为是自由生活生物面临的一个主要保护问题。然而，它从未在地球上最成功、最多样化的生命形式之一——内共生体中得到研究。在这里，我们在一种寄生虫的扩展表型中研究了这种陷阱，这种寄生虫利用宿主的视觉系统来改变宿主行为以使其受益。被线形动物寄生虫感染的树栖螳螂会被水平偏振光吸引，从而诱使它们进入水中。在这项研究中，我们发现反射光的线性偏振度（DOP）作为一种可靠的环境线索，用于识别常年水域，线形动物可以在那里的水生阶段生存而不会干涸。在行为试验中，被感染的螳螂对DOP较高的水平偏振光表现出吸引力，并且在野外实验中会跳入反射DOP较高的光的水池中。柏油路反射的水平偏振光与常年水域中观察到的偏振水平非常相似，这可能导致柏油路上的螳螂数量比自然树栖栖息地中的螳螂数量更多。在一项野外实验中，我们观察到被感染的螳螂在柏油路上行走的频率比在水泥路上更高。这些发现意味着进化陷阱可能会危及内共生体，而不仅仅是直接感知环境线索的宿主。
