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Recurrent camouflaged invasions and dispersal of an Asian freshwater gastropod in tropical Africa.

Van Bocxlaer B, Clewing C, Mongindo Etimosundja JP, Kankonda A, Wembo Ndeo O, Albrecht C - BMC Evol. Biol. (2015)

Bottom Line: Assessing ecological and evolutionary consequences of invasions simultaneously may therefore be the most effective approach to study taxa with complex invasion histories.Finally, the results of geographic modeling indicate that cryptic M. tuberculata invasions occurred primarily in densely populated areas.We draw suggestions for more effective conservation strategies from our integrated approach.

View Article: PubMed Central - PubMed

Affiliation: Department of Animal Ecology and Systematics, Justus Liebig University Giessen, Heinrich-Buff-Ring 26-32 (IFZ), D-35392, Giessen, Germany. bert.vanbocxlaer@ugent.be.

ABSTRACT

Background: Non-indigenous taxa currently represent a large fraction of the species and biomass of freshwater ecosystems. The accumulation of invasive taxa in combination with other stressors in these ecosystems may alter the habitats to which native taxa are adapted, which could elicit evolutionary changes in native populations and their ecological interactions. Assessing ecological and evolutionary consequences of invasions simultaneously may therefore be the most effective approach to study taxa with complex invasion histories. Here we apply such an integrated approach to the cerithioid gastropod Melanoides tuberculata, a model system in invasion biology.

Results: Molecular phylogenetics and ancestral range reconstructions allowed us to identify several independent Asian invasions in Lakes Malawi and Tanganyika, the Congo River, Nigeria and Cameroon. Some invasive M. tuberculata populations display much variation in shell morphology, and overlap in morphospace with M. tuberculata populations native to Africa. Experiments confirmed great ecophenotyic plasticity in some invasive populations, which, in combination with the overlap in disparity with native populations, masks invaders and their dispersal through Africa. Finally, the results of geographic modeling indicate that cryptic M. tuberculata invasions occurred primarily in densely populated areas.

Conclusions: We reveal the continental nature of invasions of Asian M. tuberculata to Africa. Several of the affected ecosystems have high endemicity in Cerithioidea: Lake Tanganyika has an unparalleled diversity in freshwater cerithioids (>10 endemic genera) and the Congo Basin and Lake Malawi are home to the two largest endemic species clusters of Melanoides in Africa (~12 and ~8 species, respectively). Cerithioids perform ecologically important functions in the benthic ecosystems of African freshwaters, but invaders and ecosystem change pose risks to their native diversity. We draw suggestions for more effective conservation strategies from our integrated approach.

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Frequency distribution of summed human population counts in 6 randomly selected grid cells in sub-Saharan Africa. The distribution was constructed from 10,000 sampling runs and compared to the observed summed human population counts in the 6 grid cells where invasions were observed (red line). Grey zone indicates the 95% samples with lowest human population counts. Only 2 of the 10,000 random sampling runs resulted in sums higher than the observed value, suggesting that invasions were non-random with respect to human population (as a proxy for anthropogenically-induced stress).
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Fig6: Frequency distribution of summed human population counts in 6 randomly selected grid cells in sub-Saharan Africa. The distribution was constructed from 10,000 sampling runs and compared to the observed summed human population counts in the 6 grid cells where invasions were observed (red line). Grey zone indicates the 95% samples with lowest human population counts. Only 2 of the 10,000 random sampling runs resulted in sums higher than the observed value, suggesting that invasions were non-random with respect to human population (as a proxy for anthropogenically-induced stress).

Mentions: Invasive lineages of Melanoides tuberculata were documented from 6 major localities in 5 countries (Ede, Nigeria; Eseka, Cameroon; Kinshasa, Kisangani, DR Congo; Bujumbura, Burundi; Monkey Bay/Cape Maclear, Malawi). At >500 people/km2, all these localities are densely populated. To be conservative, we divided grid cells into a group with more, and one with less than 100 people/km2. Adjusted to the spatial scale of the NASA human population grid this resulted in 76,391 and 911,833 cells in the first and second groups, respectively. The probability that the 6 localities with invasions represent a random sample with respect to human population density is very small (p = 2.13e-07). Comparing the sum of human population counts from the grid cells where invasions were observed (~257,000 people) to the frequency distribution of summed human population counts from randomly selected grid cells in sub-Saharan Africa resulted in 2 out of 10,000 simulations having counts higher than observed (Figure 6). Modeling results indicate that colonization was non-random and mainly in highly populated, and hence anthropogenically disturbed areas.Figure 6


Recurrent camouflaged invasions and dispersal of an Asian freshwater gastropod in tropical Africa.

Van Bocxlaer B, Clewing C, Mongindo Etimosundja JP, Kankonda A, Wembo Ndeo O, Albrecht C - BMC Evol. Biol. (2015)

Frequency distribution of summed human population counts in 6 randomly selected grid cells in sub-Saharan Africa. The distribution was constructed from 10,000 sampling runs and compared to the observed summed human population counts in the 6 grid cells where invasions were observed (red line). Grey zone indicates the 95% samples with lowest human population counts. Only 2 of the 10,000 random sampling runs resulted in sums higher than the observed value, suggesting that invasions were non-random with respect to human population (as a proxy for anthropogenically-induced stress).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4373078&req=5

Fig6: Frequency distribution of summed human population counts in 6 randomly selected grid cells in sub-Saharan Africa. The distribution was constructed from 10,000 sampling runs and compared to the observed summed human population counts in the 6 grid cells where invasions were observed (red line). Grey zone indicates the 95% samples with lowest human population counts. Only 2 of the 10,000 random sampling runs resulted in sums higher than the observed value, suggesting that invasions were non-random with respect to human population (as a proxy for anthropogenically-induced stress).
Mentions: Invasive lineages of Melanoides tuberculata were documented from 6 major localities in 5 countries (Ede, Nigeria; Eseka, Cameroon; Kinshasa, Kisangani, DR Congo; Bujumbura, Burundi; Monkey Bay/Cape Maclear, Malawi). At >500 people/km2, all these localities are densely populated. To be conservative, we divided grid cells into a group with more, and one with less than 100 people/km2. Adjusted to the spatial scale of the NASA human population grid this resulted in 76,391 and 911,833 cells in the first and second groups, respectively. The probability that the 6 localities with invasions represent a random sample with respect to human population density is very small (p = 2.13e-07). Comparing the sum of human population counts from the grid cells where invasions were observed (~257,000 people) to the frequency distribution of summed human population counts from randomly selected grid cells in sub-Saharan Africa resulted in 2 out of 10,000 simulations having counts higher than observed (Figure 6). Modeling results indicate that colonization was non-random and mainly in highly populated, and hence anthropogenically disturbed areas.Figure 6

Bottom Line: Assessing ecological and evolutionary consequences of invasions simultaneously may therefore be the most effective approach to study taxa with complex invasion histories.Finally, the results of geographic modeling indicate that cryptic M. tuberculata invasions occurred primarily in densely populated areas.We draw suggestions for more effective conservation strategies from our integrated approach.

View Article: PubMed Central - PubMed

Affiliation: Department of Animal Ecology and Systematics, Justus Liebig University Giessen, Heinrich-Buff-Ring 26-32 (IFZ), D-35392, Giessen, Germany. bert.vanbocxlaer@ugent.be.

ABSTRACT

Background: Non-indigenous taxa currently represent a large fraction of the species and biomass of freshwater ecosystems. The accumulation of invasive taxa in combination with other stressors in these ecosystems may alter the habitats to which native taxa are adapted, which could elicit evolutionary changes in native populations and their ecological interactions. Assessing ecological and evolutionary consequences of invasions simultaneously may therefore be the most effective approach to study taxa with complex invasion histories. Here we apply such an integrated approach to the cerithioid gastropod Melanoides tuberculata, a model system in invasion biology.

Results: Molecular phylogenetics and ancestral range reconstructions allowed us to identify several independent Asian invasions in Lakes Malawi and Tanganyika, the Congo River, Nigeria and Cameroon. Some invasive M. tuberculata populations display much variation in shell morphology, and overlap in morphospace with M. tuberculata populations native to Africa. Experiments confirmed great ecophenotyic plasticity in some invasive populations, which, in combination with the overlap in disparity with native populations, masks invaders and their dispersal through Africa. Finally, the results of geographic modeling indicate that cryptic M. tuberculata invasions occurred primarily in densely populated areas.

Conclusions: We reveal the continental nature of invasions of Asian M. tuberculata to Africa. Several of the affected ecosystems have high endemicity in Cerithioidea: Lake Tanganyika has an unparalleled diversity in freshwater cerithioids (>10 endemic genera) and the Congo Basin and Lake Malawi are home to the two largest endemic species clusters of Melanoides in Africa (~12 and ~8 species, respectively). Cerithioids perform ecologically important functions in the benthic ecosystems of African freshwaters, but invaders and ecosystem change pose risks to their native diversity. We draw suggestions for more effective conservation strategies from our integrated approach.

Show MeSH