A history of the biogeography of Amazonian fishes

ABSTRACT The history of knowledge about Amazonian biogeography is as rich as its fish community, and a fascinating theme of study in itself. Several current paradigms and controversies about Amazonian fish biogeography are rooted in principles dating from the second half of the 18th to the first half of the 19th centuries. The present work establishes a relationship between current biogeographical ideas and their old predecessors, on the basis of a chronologically-oriented historical continuity analysis. The advent of evolutionary theory has not contributed significantly to a transformation of the knowledge on the biogeography of Amazonian fishes. On the other hand, the two main schools of biogeographical thought (dispersalist and vicariant) had major implications on how Amazonian fish distribution is interpreted. The process was gradual and many hypotheses have combined elements from each of the two schools. Chronologically, practically the entire tradition of Amazonian biogeography takes place within the evolutionary paradigm, although its founder Louis Agassiz was himself an anti-evolutionist. The birth of Amazonian biogeography is Agassiz´s travel in Amazon. That document makes it clear that the author did not consider dispersal as a valid explanation for the biogeographical patterns he found. Later, Carl Eigenmann helps to spread the dispersalist tradition as a model for biogeographical explanations in fish distributions, a phase which lasted until the late 20th century. A major shift occurs with the contributions of Marylin Weitzman, Stanley Weitzman and Richard Vari, who associated the temporal framework of phylogenetic hypotheses with distribution patterns, underscoring the predictive power of vicariant biogeography. The present-day paradigm begins with the work of John Lundberg and attempts to incorporate geomorphological and phylogenetic information into integrative biogeographical hypotheses. Some emblematic problems have delayed proposition of general hypotheses on the phylogenetic biogeography of South American fishes, such as the poor state of knowledge of their species-level systematics; an incomplete distributional record for most species and sparse or non-existent data on the phylogenetic history of most supraspecific taxa. Such drawbacks are now being corrected at a fast pace. Recent advances on geographical distribution and an increasing number of phylogenetic hypotheses will allow unprecedented large-scale biogeographic analyses, including those based on event models and Bayesian inference. Thus, the biogeography of South American fishes, especially Amazonian ones, should soon experiment a new age of progress. The success of that new phase will depend on its ability to recognize and segregate multiple overlapping temporal layers of hydrological changes, and to develop analytical tools that can deal with temporal mixing.

摘要
亚马孙生物地理学（Amazonian biogeography）的知识发展历程与其鱼类区系（fish community）一样丰富多彩，本身亦是极具吸引力的研究主题。当前诸多关于亚马孙鱼类生物地理学的研究范式（paradigms）与学术争议，其理论根源可追溯至18世纪下半叶至19世纪上半叶。本研究基于以时间序列为导向的历史连续性分析，梳理了当代生物地理学思想与其早期雏形之间的传承关系。进化论（evolutionary theory）的诞生并未对亚马孙鱼类生物地理学的认知变革产生显著推动作用。另一方面，生物地理学思想的两大主流学派——扩散论学派（dispersalist）与替代分化论学派（vicariant）——对亚马孙鱼类分布格局的解读方向产生了深远影响。这一认知演进过程循序渐进，诸多假说均融合了两大学派的核心观点。从时间脉络来看，亚马孙生物地理学的整个研究传统几乎都处于进化论范式之下，尽管其创立者路易斯·阿加西斯（Louis Agassiz）本人是反进化论者。亚马孙生物地理学的肇始源于阿加西斯的亚马孙考察之旅。该文献明确表明，阿加西斯并不认为扩散可以合理解释其所观测到的生物地理学格局。此后，卡尔·艾根曼（Carl Eigenmann）推动扩散论学派成为鱼类分布生物地理学解释的主流范式，这一阶段一直持续至20世纪末期。玛丽琳·韦茨曼（Marylin Weitzman）、斯坦利·韦茨曼（Stanley Weitzman）与理查德·瓦里（Richard Vari）的研究成果带来了重大范式转变：他们将系统发育假说（phylogenetic hypotheses）的时间框架与分布格局相结合，凸显了替代分化生物地理学（vicariant biogeography）的预测能力。当代的研究范式始于约翰·伦德伯格（John Lundberg）的研究工作，其核心目标是将地貌学（geomorphological）与系统发育学（phylogenetic）信息整合至统一的生物地理学假说中。若干标志性难题延缓了南美鱼类系统发育生物地理学通用假说的提出：例如，物种级分类学（species-level systematics）研究认知匮乏、多数物种的分布记录不完整，以及大多数超种阶元类群（supraspecific taxa）的系统发育历史数据稀缺甚至缺失。如今，这些缺陷正以较快的速度得到修正。近期在地理分布研究领域取得的进展，以及日益增多的系统发育假说，将为前所未有的大规模生物地理学分析提供支撑，其中包括基于事件模型（event models）与贝叶斯推断（Bayesian inference）的分析方法。因此，南美鱼类生物地理学，尤其是亚马孙鱼类类群，即将迎来全新的发展纪元。这一新阶段的成功与否，取决于研究者能否识别并区分水文变化的多重重叠时间层，以及能否开发出可处理时间混合问题的分析工具。