Subterranean Fishes of the World

3201

2013

AIM 2013

A scientific paradigm is a framework containing all of the commonly accepted views about a subject. As new knowledge is acquired, paradigms shift. In many cases, these shifts tend to follow pendulum swings. For example, depending on if the analysis was on their morphology, mitochondrial DNA or genomes, perception of Neanderthal man has swung between them being of the same species as humans, to different species, and back to the same species multiple times. A similar pendulum swing can be seen regarding single or multiple origin models for Astyanax cavefish. A plethora of bibliography has accumulated term such as phylogenetically old/new populations, lineages A/B, phylogenetically old/new clusters, and old/new epigean stocks, with individual cave fish populations having been assigned contradictorily to one or the other. Much of the confusion has developed from failing to incorporate data obtained by previous authors, the reliance of single gene phylogenies, or conversely, on averaging phylogenetic data when gene flow is a confounding factor. Geology and an understanding of erosional processes are also underused. Within the single/multiple paradigms, a mistaken assumption is that the Astyanax populations that we currently see in caves are the result of original colonization events of those particular caves, without taking in consideration that those particular caves may be of more recent geological age than the cavefish themselves. It will be reviewed how the Sierra de El Abra has been “emerging” as limestone is exposed by erosion, following the progressive lowering of the base level to the current elevation of the present coastal plain. Throughout this process, the rivers Tampaon and Boquillas, which currently limit the southern and northern portions of the Sierra de El Abra, had vastly different courses over the Sierra de Guatemala and the Sierra de El Abra. It will be highlighted that, at the time of cave colonization by Astyanax, few of the caves we currently see with populations of fish had yet formed. The cave systems have varied greatly and under this scenario, a karstic and therefore biologic differentiation between the Sierra de El Abra and the Sierra de Guatemala may be of recent origin. When data from mitochondrial DNA guided the Neanderthal/Homo and the Guatemala/El Abra single or multiple origin paradigms, the accepted view was for separate entities. With the advent of genome analyses, will the pendulum swing back to a single unit?

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