Newly found evidence shows that the rise of the exotic Nile perch in Lake Victoria had long-lasting impacts on the genetic diversity of several local cichlid species, Tokyo Tech scientists report. Through large-scale comparative genomic analyses, the researchers found concrete evidence in the collective genomes of multiple species that these artificially introduced bass were decimating many local fish populations, causing a ‘bottleneck effect’.
The careless introduction of exotic species into ecosystems by humans can lead to truly catastrophic consequences, as has been proven time and time again. A tragic example is the introduction of the Nile Perch, a large freshwater fish found in water bodies in Africa, into Africa’s largest lake: Lake Victoria.
The Nile perch, brought to Lake Victoria in the 1950s to meet commercial demand for its meat, devastated native fish populations known as haplochromine cichlids. By the 1990s, experts estimated that more than 200 species of endemic cichlids had been driven to extinction by this ferocious predator. Interestingly, the remaining species may also have been deeply affected by the severe population losses caused by the Nile perch, as such events often reduce the genetic diversity of surviving groups. However, how much the genetic structure of cichlids was affected by the introduction of the Nile perch remains unclear.
Against this backdrop, a research team from the Tokyo Institute of Technology (Tokyo Tech), the Graduate University for Advanced Studies, SOKENDAI in Japan and the Tanzania Fisheries Research Institute in Tanzania decided to shed some light on the issue. In their latest research, published in Molecular biology and evolution, the researchers conducted large-scale comparative genomics analyzes on multiple cichlid species endemic to Lake Victoria, providing detailed insights into the impacts of the invasive Nile Perch since its introduction to this environment. The team included Associate Professor Masato Nikaido and PhD student Minami Imamoto from Tokyo Tech.
Through a genomic analysis involving 137 haplochromine species, the researchers found that four species from the Gulf of Mwanza (located in the southern part of the lake) experienced a so-called ‘bottleneck event’. Simply put, the population of these species had been reduced so much that the genetic diversity within the population had significantly decreased.
Further investigation by the researchers identified the Nile perch as the culprit for the observed changes in the genetic structure of these four species. “The timing of the bottleneck, which started in the 1970s and 1980s and ended in the 1990s and 2000s, was consistent with the historical record of the disappearance and subsequent resurgence of these endemic haplochromines,” Nikaido explains. “This is probably related to the introduction of Nile perch due to commercial demand in Lake Victoria in the 1950s,” he further adds.
Of the four species, the researchers noted that they were egg-eating cichlids Haplochromis sp. ‘matumbi hunter’ and Haplochromis microdon had encountered particularly serious bottlenecks. For matumbi hunters, this effect was so pronounced that the genomes had diverged significantly, even from those of closely related species. “Our findings support the previously existing hypothesis that carnivorous fish, including egg eaters, should have experienced a stronger bottleneck,” Nikaido notes. “This study presents for the first time the impact of the Nile Perch emergence on the genetic structure of Lake Victoria haplochromines,” he further added.
It is worth noting that the loss of genetic diversity due to short-term bottleneck effects can seriously hinder a species’ long-term fitness and adaptability. Taken together, these new insights tell a cautionary tale about how bad the introduction of exotic species can be, even for species that survive extinction.
Researchers identified species that have suffered serious damage due to the introduction of Nile perch, providing new insights into conservation biology. Genetic assessments can provide practical solutions for protecting local wildlife, such as identifying species in urgent need of protection and establishing no-fishing zones. It is striking that some cichlid species, once thought extinct, are gradually being rediscovered. Furthermore, developing conservation strategies based on comparative genomics can facilitate ecosystem revival.
