Depth segregation and diet disparity revealed by stable isotope analyses in sympatric herbivorous cichlids in Lake Tanganyika.

Hiroki Hata,Masanori Kohda,Koji Omori,Jyunya Shibata,Michio Hori

doi:10.1186/s40851-015-0016-1

Hiroki Hata, Masanori Kohda + Show 3 more

Open Access

https://doi.org/10.1186/s40851-015-0016-1

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Abstract

BackgroundLake Tanganyika in the African Great Rift Valley is known as a site of adaptive radiation in cichlid fishes. Diverse herbivorous fishes coexist on a rocky littoral of the lake. Herbivorous cichlids have acquired multiple feeding ecomorphs, including grazer, browser, scraper, and scooper, and are segregated by dietary niche. Within each ecomorph, however, multiple species apparently coexist sympatrically on a rocky slope. Previous observations of their behavior show that these cichlid species inhabit discrete depths separated by only a few meters. In this paper, using carbon (C) and nitrogen (N) stable isotope ratios as markers, we followed the nutritional uptake of cichlid fishes from periphyton in their feeding territories at various depths.Resultsδ15N of fish muscles varied among cichlid ecomorphs; this was significantly lower in grazers than in browsers and scoopers, although δ15N levels in periphyton within territories did not differ among territorial species. This suggests that grazers depend more directly on primary production of periphyton, while others ingest animal matter from higher trophic levels. With respect to δ13C, only plankton eaters exhibited lower values, suggesting that these fishes depend on production of phytoplankton, while the others depend on production of periphyton. Irrespective of cichlid ecomorph, δ13C of periphyton correlated significantly with habitat depth, and decreased as habitat depth became deeper. δ13C in territorial fish muscles was significantly related to that of periphyton within their territories, regardless of cichlid ecomorph, which suggests that these herbivorous cichlids depend on primary production of periphyton within their territories.ConclusionsCarbon and nitrogen stable isotope ratios varied among ecomorphs and among cichlid species in the same ecomorphs sympatrically inhabiting a littoral area of Lake Tanganyika, suggesting that these cichlids are segregated by nutrient source due to varying dependency on periphyton in different ecomorphs (especially between grazers and browsers), and due to segregation of species of the same ecomorph by feeding depth, grazers and browsers in particular.Electronic supplementary materialThe online version of this article (doi:10.1186/s40851-015-0016-1) contains supplementary material, which is available to authorized users.

Highlights

Lake Tanganyika in the African Great Rift Valley is known as a site of adaptive radiation in cichlid fishes
As a result of generalized linear mixed model (GLMM), both δ13C and δ15N values of cichlid muscles were significantly different among feeding ecomorphs (Table 2)
Carbon and nitrogen stable isotope ratios revealed the material flows from primary producers to herbivorous cichlids that inhabit various depths on a rocky littoral area of Lake Tanganyika

Summary

Introduction

Lake Tanganyika in the African Great Rift Valley is known as a site of adaptive radiation in cichlid fishes. Results: δ15N of fish muscles varied among cichlid ecomorphs; this was significantly lower in grazers than in browsers and scoopers, δ15N levels in periphyton within territories did not differ among territorial species. This suggests that grazers depend more directly on primary production of periphyton, while others ingest animal matter from higher trophic levels. In a rocky littoral of Lake Tanganyika, 17 species of herbivorous cichlids coexist [5,6] These include 11 Tropheini, three Lamprologini, one Ectodini, one Eretmodini, and one Tilapini species (Table 1). Five tribes of the family have acquired multiple herbivorous feeding ecomorphs; grazer, browser, scooper, and scraper [7,8,9,10]

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