蛙科物种背侧褶组织形态特征

Morphology of Dorsolateral Fold in Ranids(Amphibia, Anura, Ranidae)

背侧褶是无尾两栖类的重要形态特征,但对于其组织结构和功能缺乏了解。本文运用组织学技术,H.E、AB-PAS和Masson三色三种染色方法对蛙科4属的代表物种滇蛙(Dianrana pleuraden)、阔褶蛙(Sylvirana latouchii)、仙琴蛙(Nidirana daunchina)、沼蛙(Boulengerana guentheri)背侧褶和背部皮肤的显微结构进行了系统的比较研究。结果发现:1)蛙科物种的皮肤腺体单元丰富多样,由黏液腺和颗粒腺组成。其黏液腺均为普通黏液腺,按照其分泌物及分泌细胞形态将黏液腺分为Ⅰ型黏液腺和Ⅱ型黏液腺。Ⅰ型黏液腺在沼蛙和仙琴蛙中缺失,Ⅱ型普遍分布。颗粒腺分Ⅰ型颗粒腺、Ⅱ型颗粒腺及特化颗粒腺,Ⅱ型颗粒腺仅见于仙琴蛙,特化颗粒腺仅见于阔褶蛙和沼蛙的背侧褶;2)滇蛙与仙琴蛙背侧褶基本结构与其背部常规皮肤一致,且两种皮肤结构组成也较为相似,在真皮层下都有一层较厚的脂肪层,滇蛙脂肪层厚度约为真皮层厚度的1.52倍,仙琴蛙脂肪层厚度约为真皮层的1.60倍;阔褶蛙与沼蛙背侧褶基本结构也与其常规皮肤一致,且背侧褶结构组成也较为相似,阔褶蛙及沼蛙真皮层内具有单层排列、集中分布的大型特化颗粒腺,其分泌物为两种颗粒物的混合物。3)蛙科中两种背侧褶结构类型代表了两个进化方向,其功能分别为能量储存和反捕,推测其与环境适应进化相关。

The dorsolateral fold is an important morphological structure of Anurans, but little is known about its histological structure and function. We studied the histology and histochemistry of the dorsolateral fold and dorsal skin by using Hematoxylin-Eosin, Alcian Blue-Periodic Acid Schiff and Masson staining methods in four Ranid species： Dianrana pleuraden, Sylvirana latouchii, Nidirana daunchina and Boulengerana guentheri. Our results found that： 1） The skin gland units of Ranidae consist of rich and diversified mucous and granular glands. There were two types of ordinary mucous glands（OMGs）, types OMGⅠand Ⅱ, and the former was absent in B. guentheri and N. daunchina（Fig. 1 b2, d2）. The granular glands were categorized into typeⅠ, type Ⅱ and specialized type, but type Ⅱ was only found in N. daunchina（Fig. 1 b3, Fig 2 b3）. Specialized granular glands were only found in the dorsolateral fold of S. latouchii and B. guentheri（Fig. 2 c3, d3）. 2） The dorsolateral fold consists of a fat layer which is similar between D. pleuraden and N. daunchina（Table 1, Fig. 2 a3, b3）. The dorsal skin of N. daunchina had a fat layer whereas this layer was absent in D. pleuraden. The fat layer was 1.52 times and 1.60 times thick as their dermis in D. pleuraden and N. daunchina, respectively. The dorsolateral fold contained a layer of clustered and enlarged specialized granular glands in the dermis which was similar in S. latouchii and B. guentheri（Table 1, Fig. 2 c3, d3）. Two types of granule secretions were found in the specialized granular gland（Fig. 2 d3）. 3） Their functions included energy storage and antipredation. We speculate that the structural and functional evolution of the dorsolateral fold is related to environmental adaptation. The evolution of two types of dorsolateral fold in ranid species may represent two evolutionary orientations.