Damming shapes genetic patterns and may affect the persistence of freshwater fish populations

Abstract

River damming threatens freshwater biodiversity worldwide by isolating populations, reducing both gene flow and genetic variation, and affecting the ability of a given population to adapt to environmental changes. Herein, we employed a microsatellite DNA marker panel and a multitemporal approach to assess the effects of damming on the genetic diversity of a long‐lived species from both contemporary and historical perspectives. To accomplish this, we used the migratory catfish Pseudoplatystoma corruscans as a model and sampled it in two South American basins. We tested whether: (1) populations from dammed and undammed environments would display different levels of genetic diversity; (2) ecosystem size would influence the level of genetic diversity; and (3) projected whether fish populations would maintain their current genetic diversity in the long term. Our findings reveal that P. corruscans populations from dammed landscapes with smaller ecosystems showed smaller estimated effective population size, lower genetic diversity, and higher relatedness coefficient than in intermediate ecosystem size in both dammed and undammed environments. We also noticed changes in estimated gene flow and effective population size from both contemporary and historical perspectives, probably because of dams. Predictive genetic diversity analysis revealed a critical scenario for the long‐term persistence of P. corruscans in dammed environments with smaller ecosystem sizes. Our study suggests that anthropogenic barriers have substantially impacted genetic diversity and genetic structuring of the migratory fish P. corruscans. Thus, the formation of conservation policies is urgently needed to avoid local extinctions of this species in fragmented riverscapes. We highlighted the effectiveness of large ecosystems and connectivity between populations in conserving genetic diversity of migratory fishes.

Past and Present Environmental Factors Differentially Influence Genetic and Morphological Traits of Italian Barbels (Pisces: Cyprinidae)

“…Within each species, we found populations with relative higher haplotype and nucleotide diversity, and populations with intermediate to low levels of one or both genetic diversity indices, independently from the latitudinal positioning of the inhabited river. The RDA analysis revealed some weak correlations between both nucleotide and haplotype diversity indices and some environmental characteristics, some of which are consistent with previous studies, which found correlations between genetic diversity and ecosystem size (i.e., river length in the RDA analysis [32]), habitat features (i.e., refuges and geology in this study [28]), and hydrological regime (represented in this study by the Q/A [92]). Although these results may suggest an influence of local environmental conditions on genetic variability, the RDA scores of both the genetic indices were too low to support a strong relationship between genetic variability and the environmental parameters.…”

“…In contrast, genetic diversity, particularly in neutral (i.e., not under selection) DNA regions, such as those commonly used for population genetic studies, typically reflect historical demographic evolution due to past climatic and geological changes e.g., [28]. Nevertheless, both genetic and phenotypic variabilities can also be altered by recent anthropogenic activities such as the introduction of exotic species (e.g., following hybridization [29]) and river damming [30][31][32]. Thus, separating genetic and phenotypic variations induced by local adaptation developed during historical evolution from the variations deriving by relatively recent events, provides valuable insights for both eco-evolutionary processes and for a conservation perspective [33].…”

Genetic population structure of Pseudoplatystoma corruscans (Siluriformes: Pimelodidae) and evidence of temporal variation in structure

“…These results are consistent with previous population genetic studies of Pseudoplatystoma . Similar levels of genetic diversity in P. corruscans samples obtained from Paraguay, Paraná and São Francisco basins have been reported before (Carvalho et al ., 2012; Dantas et al ., 2013; do Prado et al ., 2018; Machado et al ., 2022; Pereira et al ., 2009; Vaini et al ., 2016). Some of these studies reported population structure in the Upper Parana basin, consistent with the weak signal obtained in this study's results (F ST = 0.02 between samples from the Upper Paraná and Grande River sites).…”

“…Because of the construction of the dam, the formerly separated populations have been able to hybridize, a likely explanation for the admixture of genetic clusters observed at sites 2‐RI and 3‐CAM, both upstream of the Itaipú reservoir. Other studies also reported that dam construction and alteration of the ecosystem results in changes in population effective sizes and genetic diversity in P. corruscans (Machado et al ., 2022). Given that P. corruscans undertakes long‐distance migrations during its life cycle, gene flow among formerly isolated populations is naturally expected when former geographic barriers are no longer present.…”

Effectiveness of the Natura 2000 network for freshwater fish conservation in a Mediterranean region

“…Several studies documented the effects of dams along the river which can cause alteration of flow condition and the creation of lentic waters above the dam, and also obstruct the movement of fish along the river and alter the taxonomical diversity and the genetic patterns and the functional diversity of fish community (Oliveira et al, 2018;Machado et al, 2022). Unfortunately, in our study, long range migratory fish species, such as the Adriatic sturgeon (Acipenser naccarii), were not sampled in a sufficient number of sites to investigate fragmentation effects on these species and at widest scale.…”