The recurrent colonization of freshwater habitats and subsequent loss of diadromy is a major ecological transition that has been reported in many ancestrally diadromous fishes. Such residency is often accompanied by a loss of tolerance to seawater. The amphidromous Galaxias maculatus has repeatedly colonized freshwater streams with evidence that freshwater‐resident populations exhibit stark differences in their tolerance to hi...

Movement is a fundamental aspect of fish ecology, and it therefore represents an important trait to monitor for the management and conservation of fish populations. This is especially true for small benthic fish, as they often inhabit part of the catchment where their movement may be restricted by alterations to river connectivity due to human activity. Still, the movement of these small benthic fish remains poorly understood,...

Diadromy is known for having major effects on the distribution and richness of aquatic species, and so does its loss. The loss of diadromy has led to the diversification of many species, yet research focusing on understanding its molecular basis and consequences are limited. This is particularly true for amphidromous species despite being the most abundant group of diadromous species. Galaxias maculatus , an amphidromous speci...

Rivers and lake systems in the southern cone of South America have been widely influenced by historical glaciations, carrying important implications for the evolution of aquatic organisms, including prompting transitions between marine and freshwater habitats and by triggering hybridization among incipient species via waterway connectivity and stream capture events. Silverside fishes ( Odontesthes ) in the region comprise a ra...

Understanding the evolutionary mechanisms that affect the genetic divergence between diadromous and resident populations across heterogeneous environments is a challenging task. While diadromy may promote gene flow leading to a lack of genetic differentiation among populations, resident populations tend to be affected by local adaptation and/or plasticity. Studies on these effects on genomic divergence in nonmodel amphidromous...

It is well documented that hydropower plants can affect the dynamics of fish populations through landscape alterations and the creation of new barriers. Less emphasis has been placed on the examination of the genetic consequences for fish populations of the construction of dams. The relatively few studies that focus on genetics often do not consider colonization history and even fewer tend to use this information for conservat...

The construction of fishways for upstream and downstream connectivity is the preferred mitigation measure for hydropower dams and other riverine barriers. Yet empirical evidence for effective design criteria for many species is missing. We therefore assembled a group of international fishway designers and combined their knowledge with available empirical data using a formal expert elicitation protocol and Bayesian networks. Th...

Interpreting the genetic structure of a metapopulation as the outcome of gene flow over a variety of timescales is essential for the proper understanding of how changes in landscape affect biological connectivity. Here we contrast historical and contemporary connectivity in two metapopulations of the freshwater fish Galaxias platei in northern and southernmost Patagonia where paleolakes existed during the Holocene and Pleistoc...

Southern South America provides a set of unusual geographic features that make it particularly interesting for studying phylogeography. The Andes Mountains run along a north‐to‐south axis and act as a barrier to gene flow for much of the biota of this region, with southern portions experiencing extensive historical glaciation. Geological data reveal a series of drainage reversals, shifting from Pacific Ocean outlets to Atlanti...

Patagonia is one of the few areas in the Southern Hemisphere to have been directly influenced by Quaternary glaciers. In this study, we evaluate the influence that Quaternary glacial ice had on the genetic diversity of two congeneric fish species, the diadromous Galaxias maculatus and the nondiadromous Galaxias platei , using multilocus estimates of effective population size through time. Mid‐Quaternary glaciations had far‐rea...