Abstract
Historical events, such as changes in sea level during the Pleistocene glacial cycles, had a strong impact on coastal habitats, limiting connectivity and promoting the genetic divergence of various species. In this study, we evaluated the influence of climate oscillations and the possibility of estuary function as a barrier to gene flow among populations of the four-eyed fish, Anableps anableps. This species is fully estuarine-resident, has internal fertilization, is viviparous and does not migrate across long distances. These features make the four-eyed fish an excellent model for the study of evolutionary processes related to genetic differentiation of species and populations in estuaries. The evolutionary history of A. anableps was inferred from phylogeographic and population analyses using sequences of the mitochondrial DNA Control Region of 13 populations distributed in the Amazon and Northeast Coast of Brazil from Calcoene (Amapa) to Parnaiba (Piaui). The 83 retrieved haplotypes show a pattern of four distinct mitochondrial lineages, with up to 3.4% nucleotide divergence among them. The evolutionary reconstruction suggests that these lineages diverged recently in the late Pleistocene/early Holocene after the Atlantic Ocean reaching current levels. Analysis of variability, neutrality and the genetic expansion pattern revealed that the lineages have distinct characteristics, which were shaped by the different geomorphological features of coastal regions combined with sea level oscillations over a very long period of time. Only few neighboring populations show a discreet gene flow. This study may also be helpful for designing new experiments to better understand the geomorphological evolutionary history of the estuaries of the Amazon and the Northeast Coast of Brazil using estuarine-resident species as a model.
Highlights
Organisms that inhabit coastal waters such as estuaries or lagoons may show more genetic differentiation than strictly marine species due to the discontinuity of these natural ecosystems and the relative isolation of the great ocean currents [1]
The present study revealed high genetic divergence among populations of Anableps and uncovered four distinct mitochondrial lineages for A. anableps on the North and Northeast Amazon coast of Brazil
The study suggested that the genetic structuring of these populations is correlated to events of the Holocene (11,700 to present)
Summary
Organisms that inhabit coastal waters such as estuaries or lagoons may show more genetic differentiation than strictly marine species due to the discontinuity of these natural ecosystems and the relative isolation of the great ocean currents [1]. Estuaries represent an environment of high productivity and are considered natural nurseries for many marine and estuarine species [4,5]. Historical events, such as changes in the sea level during the Pleistocene glacial cycles, may have exerted a strong impact on coastal habitats by limiting connectivity and promoting genetic divergence between species [6,7,8,9]. In the Holocene, the current interglacial period that began approximately 10,000 years ago, the sea level began to rise, creating the current estuaries approximately 5100 years ago [3]
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