A Review on Fish Sensory Systems and Amazon Water Types With Implications to Biodiversity

Elio de Almeida Borghezan,Tiago Henrique da Silva Pires,Shiro Kohshima,Jansen Zuanon,Takehide Ikeda

doi:10.3389/fevo.2020.589760

Abstract

The Amazon has the highest richness of freshwater organisms in the world, which has led to a multitude of hypotheses on the mechanisms that generated this biodiversity. However, most of these hypotheses focus on the spatial distance of populations, a framework that fails to provide an explicit mechanism of speciation. Ecological conditions in Amazon freshwaters can be strikingly distinct, as it has been recognized since Alfred Russel Wallace’s categorization into black, white, and blue (= clear) waters. Water types reflect differences in turbidity, dissolved organic matter, electrical conductivity, pH, amount of nutrients and lighting environment, characteristics that directly affect the sensory abilities of aquatic organisms. Since natural selection drives evolution of sensory systems to function optimally according to environmental conditions, the sensory systems of Amazon freshwater organisms are expected to vary according to their environment. When differences in sensory systems affect chances of interbreeding between populations, local adaptations may result in speciation. Here, we briefly present the limnologic characteristics of Amazonian water types and how they are expected to influence photo-, chemical-, mechano-, and electro-reception of aquatic organisms, focusing on fish. We put forward that the effect of different water types on the adaptation of sensory systems is an important mechanism that contributed to the evolution of fish diversity. We point toward underexplored research perspectives on how divergent selection may act on sensory systems and thus contribute to the origin and maintenance of the biodiversity of Amazon aquatic environments.

Highlights

Fish comprise the most diverse group of vertebrates, with nearly 35.635 extant species
Wallace (1853) highlighted the differences of Amazon fish composition varied according to a classification based on water color and suggested that those environmental differences could represent an important component of fish diversification
We acknowledge the importance of all of these aspects in driving adaptations of fish sensory systems; here we focus on how limnologic differences between Amazon water types may have resulted in local adaptation and contributed through divergent selection processes to Amazon fish diversity

Summary

INTRODUCTION

Fish comprise the most diverse group of vertebrates, with nearly 35.635 extant species (as listed in Catalog of Fishes in October 2020, Fricke et al, 2020). Black and clear waters are more transparent than white waters (Muntz, 1978), increasing the importance of vision and allowing the development of adaptions of the visual system in relation to other sensory modalities This is aligned with the aforementioned early observation of Roberts (1972), who proposed that most colorful Amazon fish species are found in black and clear water. Because sexually dichromatic species are dependent on visual communication during mating, studies focusing on the interplay of lighting environment and color peak sensitivity of fish populations exposed to different water types could contribute to our understanding of speciation via the sensory drive and sensory exploitation hypotheses (Endler, 1992; Boughman, 2002). The influence of different Amazon water types on the number, morphology and sensitivity of electroreceptors could result in reproductive barriers and ecological speciation

CONCLUSION

DATA AVAILABILITY STATEMENT