Department of Physiology and Neurobiology, University of Connecticut, 75 N. Eagleville Road, Unit 3156, Storrs, CT, 06269, USA.
J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2019 Feb;205(1):151-161. doi: 10.1007/s00359-018-01312-2. Epub 2019 Jan 16.
Fireflies (Coleoptera: Lampyridae) have distinct visual systems at different stages of development. Larvae have stemmata and adults have compound eyes. Adults use compound eyes to mediate photic communication during courtship. Larvae do not manifest this behavior, yet they are bioluminescent. We investigated the structure of stemmata in Photuris firefly larvae to identify anatomical substrates (i.e., rhabdomeres) conferring visual function. Stemmata were located bilaterally on the antero-lateral surfaces of the head. Beneath the ~ 130 µm diameter lens, we identified a pigmented eye-cup. At its widest point, the eye-cup was ~ 150 µm in diameter. The optic nerve exited the eye-cup opposite the lens. Two distinct regions, asymmetric in size and devoid of pigmentation, were characterized in stemmata cross-sections. We refer to these regions as lobes. Each lobe contained a rhabdom of a radial network of rhabdomeres. Pairs of rhabdomeres formed interdigitating microvilli contributed from neighboring photoreceptor cell bodies. The optic nerve contained 88 axons separable into two populations based on size. The number of axons in the optic nerve together with distinct rhabdoms suggests these structures were formed from 'fusion stemmata.' This structural specialization provides an anatomical substrate for future studies of visually mediated behaviors in Photuris larvae.
萤火虫（鞘翅目：萤科）在不同的发育阶段具有独特的视觉系统。幼虫有小眼，成虫有复眼。成虫利用复眼在求偶期间进行光通讯。幼虫没有表现出这种行为，但它们会发光。我们研究了 Photuris 萤火虫幼虫的小眼结构，以确定赋予视觉功能的解剖基质（即小眼杆）。小眼位于头部前侧表面的两侧。在直径约 130 µm 的透镜下方，我们识别出一个色素眼杯。眼杯最宽处直径约 150 µm。视神经从与透镜相对的眼杯处离开。小眼横截面中存在两个大小不对称且没有色素沉着的明显区域。我们将这些区域称为叶。每个叶包含一个由小眼杆的辐射状网络组成的小眼杆。来自相邻光感受器细胞体的对生的微绒毛形成了成对的小眼杆。视神经包含 88 根可根据大小分为两类的轴突。视神经中的轴突数量和独特的小眼杆表明这些结构是由“融合小眼”形成的。这种结构特化提供了 Photuris 幼虫中视觉介导行为的未来研究的解剖学基础。
