Burlakova Lyubov E, Campbell David, Karatayev Alexander Y, Barclay Don
Great Lakes Center, Buffalo State College, 1300 Elmwood Ave, Buffalo, NY, 14222, USA.
Aquat Biosyst. 2012 Jun 25;8(1):12. doi: 10.1186/2046-9063-8-12.
Freshwater bivalves in the order Unionoida are considered to be one of the most endangered groups of animals in North America. In Texas, where over 60% of unionids are rare or very rare, 15 species have been recently added to the state's list of threatened species, and 11 are under consideration for federal listing. Due to insufficient survey efforts in the past decades, however, primary data on current distribution and habitat requirement for most of these rare species are lacking, thus challenging their protection and management. Taxonomic identification of endemic species based on shell morphology is challenging and complicates conservation efforts. In this paper we present historic and current distributional data for three rare Texas species, Fusconaia askewi, F. lananensis, and Pleurobema riddellii, collected during our 2003-2011 state-wide surveys and suggest appropriate conservation measures. In addition, we tested the genetic affinities of Fusconaia and similar species collected from eastern Texas and western Louisiana using cox1 and nad1 sequences.
We found that F. askewi still inhabits four river basins in eastern and northeastern Texas and can be locally abundant, while P. riddellii was found only in one river basin. Pleurobema riddellii was well-separated from F. askewi and grouped with the P. sintoxia clade. The sequences for F. lananensis were very similar to those for F. askewi, with a maximum difference of just over 1% for nad1 and only 0.7% for cox1, similar to the variation between F. askewi alleles. Except for one low difference (1.55%) with the partial cox1 sequence for F. burkei, all other Fusconaia populations, including those from the Calcasieu drainage, differed by over 2.3% for both genes.
Our study suggested that F. lananensis is not a valid species, and it is likely that only one Fusconaia species (F. askewi or its probable senior synonym F. chunii) is currently present in East Texas, thus simplifying conservation efforts. Distribution range of both these regional endemics (F. askewi and P. riddellii) has been reduced in the last 80 years.
北美地区，蚌目淡水双壳贝类被认为是最濒危的动物群体之一。在得克萨斯州，超过60%的蚌类物种稀有或极为稀有，近期有15个物种被列入该州濒危物种名单，另有11个物种正被考虑列入联邦濒危物种名单。然而，由于过去几十年调查力度不足，这些稀有物种中大多数的当前分布及栖息地需求的基础数据缺失，这给它们的保护和管理带来了挑战。基于贝壳形态对特有物种进行分类鉴定具有挑战性，也使保护工作变得复杂。本文展示了我们在2003 - 2011年全州调查期间收集的三种得克萨斯州稀有物种——阿斯克维珠蚌（Fusconaia askewi）、拉纳纳珠蚌（F. lananensis）和里氏侧扁蚌（Pleurobema riddellii）的历史和当前分布数据，并提出了适当的保护措施。此外，我们使用细胞色素氧化酶亚基I（cox1）和烟酰胺腺嘌呤二核苷酸脱氢酶亚基1（nad1）序列，测试了从得克萨斯州东部和路易斯安那州西部收集的珠蚌属物种及相似物种的遗传亲缘关系。
我们发现阿斯克维珠蚌仍栖息于得克萨斯州东部和东北部的四个流域，且在局部地区数量较多，而里氏侧扁蚌仅在一个流域被发现。里氏侧扁蚌与阿斯克维珠蚌明显分开，并与中华侧扁蚌分支聚在一起。拉纳纳珠蚌的序列与阿斯克维珠蚌的序列非常相似，nad1的最大差异略超过1%，cox1仅为0.7%，这与阿斯克维珠蚌等位基因之间的差异相似。除了与伯克氏珠蚌（F. burkei）的部分cox1序列有1.55%的低差异外，所有其他珠蚌属种群，包括来自卡尔卡苏河排水区的种群，这两个基因的差异均超过2.3%。
我们的研究表明拉纳纳珠蚌不是一个有效的物种，目前东得克萨斯州可能仅存在一种珠蚌属物种（阿斯克维珠蚌或其可能的先定同物异名春氏珠蚌F. chunii），从而简化了保护工作。在过去80年里，这两种地方特有物种（阿斯克维珠蚌和里氏侧扁蚌）的分布范围均已缩小。
