Populations genetically rifting within a complex geological system: The case of strong structure and low genetic diversity in the migratory freshwater catfish,Bagrus docmak,in East Africa

Abstract

The complex geological history of East Africa has been a driving factor in the rapid evolution of teleost biodiversity. While there is some understanding of how macroevolutionary drivers have shaped teleost speciation in East Africa, there is a paucity of research into how the same biogeographical factors have affected microevolutionary processes within lakes and rivers. To address this deficiency, population genetic diversity, demography, and structure were investigated in a widely distributed and migratory (potamodromous) African teleost species, Ssemutundu (Bagrus docmak). Samples were acquired from five geographical locations in East Africa within two major drainage basins; the Albertine Rift and Lake Victoria Basin. Individuals (N = 175) were genotyped at 12 microsatellite loci and 93 individuals sequenced at the mitochondrial DNA control region. Results suggested populations from Lakes Edward and Victoria had undergone a severe historic bottleneck resulting in very low nucleotide diversity (π = 0.004 and 0.006, respectively) and negatively significant Fu values (−3.769 and −5.049; p < .05). Heterozygosity deficiencies and restricted effective population size (N eLD) suggested contemporary exposure of these populations to stress, consistent with reports of the species decline in the East African Region. High genetic structuring between drainages was detected at both historical (ɸST = 0.62 for mtDNA; p < .001) and contemporary (microsatellite F ST = 0.460; p < .001) levels. Patterns of low genetic diversity and strong population structure revealed are consistent with speciation patterns that have been linked to the complex biogeography of East Africa, suggesting that these biogeographical features have operated as both macro‐ and micro‐evolutionary forces in the formation of the East African teleost fauna.

DNA Barcoding Silver Butter Catfish (Schilbe intermedius) Reveals Patterns of Mitochondrial Genetic Diversity Across African River Systems

“…However, results obtained showed that populations from East (matrilines C and D) and West (matriline E) Africa had low haplotype diversity. This finding is similar to a previous study that also reported low genetic diversity in an East African catfish, Bagrus docmak 18 . Other studies have associated low genetic diversity in fishes with founder events and population bottlenecks that occurred due to the recent introduction of species into the environment [20][21][22] .…”

“…Understanding biogeography using molecular data is important for the interpretation of the distribution patterns of geographically distant populations. High haplotype diversity coupled with low nucleotide diversity as was observed in S. intermedius populations, is a pattern consistent with other catfish species such as Chinese Leiocassis longirostris 24 and East African B. docmak 18 . Our study, therefore, provides evidence that historical biogeographic factors and contemporary environmental variations across sub-Saharan Africa accounted for the population divergence and geographic structuring within S. intermedius.…”

“…In concordance with previous studies 11,17 , this could indicate genetic adaptation of these populations in response to local selective challenges and environmental pressures. Although the paucity of genetic studies on African freshwater fishes hindered comparison, we note that previous studies 18,19 have exemplified the roles of local adaptation to environmental changes on the population genetic structure of African fauna. Further studies are therefore needed to investigate the evolutionary mechanisms or processes governing the diversification of S. intermedius in these regions, as well as to estimate the divergence events that could have accounted for the prolonged period of isolation of the matrilines.…”

Where ichthyofaunal provinces meet: the fish fauna of the Lake Edward system, East Africa

“…However, as these species also occur natively in Lake Victoria, except for O. niloticus , which has been introduced there, the most plausible hypothesis would be that these species entered Lake Edward from the east. Yet, this scenario was contradicted by a population‐genetic study on B. docmak , which revealed a larger similarity between populations from the Lake Edward system with those of Lake Albert, than with those of Lake Victoria (Basiita et al ., ). Similar population‐genetic studies could also provide more information on the origin of the other species from the Lake Edward system.…”

Genetic variation of endangered Jankowski’s Bunting (Emberiza jankowskii): High connectivity and a moderate history of demographic decline

“…Furthermore, the isolation effect between habitat patches often blocks gene flow between populations, ultimately resulting in genetic isolation and accelerated extinction (Nei, 1973). Numerous empirical studies have shown that low genetic diversity and gene flow between populations appear to have become the "tags" of endangered species (Wang et al, 2015;Hague and Routman, 2016;Basiita et al, 2017). However, several recent studies in birds, amphibians, and mammals have shown that large historical effective population size (N e ) and long generation time can act as buffers against the loss of genetic variation, leading to an observed high genetic diversity in threatened populations (Brekke et al, 2011;Torres-Florez et al, 2014;Zhang et al, 2015).…”