Lima Sergio Q, Costa Carinne M, Amemiya Chris T, Schneider Igor
Instituto de Ciências Biológicas, Universidade Federal do Para, Belem, Brazil.
Benaroya Research Institute at Virginia Mason, Seattle, Washington.
J Exp Zool B Mol Dev Evol. 2017 Jan;328(1-2):97-105. doi: 10.1002/jez.b.22711. Epub 2016 Nov 9.
The pelvic fins of male South American lungfish, Lepidosiren paradoxa, are adorned with a distinctive array of filaments, which grow and become highly vascularized during the breeding season. The resemblance between these pelvic fin filaments (PFFs) and external gills of other vertebrates suggested that this gill-like structure was used for physiological gas exchange. It has been proposed that the unique pelvic fin of male L. paradoxa is used for release of oxygen from its blood into the environment in order to aerate its nesting brood, or, conversely, as an auxiliary respiratory organ by absorbing oxygen from the environment into its bloodstream. Here, we employed histology, scanning electron microscopy (SEM) and quantitative PCR (qPCR) to assess whether the morphology and molecular profile of PFFs are compatible with a role in gas exchange. First, we closely examined its external morphology and showed that PFFs develop from short papillae during the rainy season, but remain covered by a thick nonvascularized epithelium. Histological examination confirmed that capillaries within the filaments are separated from the exterior by a basement membrane and a stratified epithelium composed of four to five cell layers. In addition, SEM analysis revealed significant differences between the fin filament epithelium and typical gill epithelium. Finally, our qPCR results showed that five genes commonly expressed in gills were downregulated in PFFs relative to their expression in regular pectoral fin epidermis. Collectively, our results do not directly support a role for PFFs, commonly referred to as "limb gills", in oxygen release or uptake.
雄性南美肺鱼（Lepidosiren paradoxa）的腹鳍上装饰着一系列独特的细丝，这些细丝在繁殖季节生长并高度血管化。这些腹鳍细丝（PFFs）与其他脊椎动物的外鳃之间的相似性表明，这种鳃状结构用于生理气体交换。有人提出，雄性南美肺鱼独特的腹鳍用于将血液中的氧气释放到环境中，以便为其巢穴中的幼鱼充气，或者相反，作为辅助呼吸器官，通过从环境中吸收氧气进入其血液。在这里，我们采用组织学、扫描电子显微镜（SEM）和定量PCR（qPCR）来评估PFFs的形态和分子特征是否与气体交换功能相匹配。首先，我们仔细检查了其外部形态，发现PFFs在雨季从短乳头发育而来，但仍被一层厚厚的无血管上皮覆盖。组织学检查证实，细丝内的毛细血管与外部被基底膜和由四到五层细胞组成的复层上皮隔开。此外，SEM分析揭示了鳍丝上皮与典型鳃上皮之间的显著差异。最后，我们的qPCR结果表明，相对于它们在正常胸鳍表皮中的表达，鳃中通常表达的五个基因在PFFs中下调。总的来说，我们的结果并不直接支持通常被称为“附肢鳃”的PFFs在氧气释放或摄取中的作用。
