Dietary Differentiation Between Sympatric Ecotypes of Astatotilapia calliptera From Lake Masoko (Kisiba), Tanzania Revealed by Metabarcoding

Sympatric speciation is defined as the formation of new species in the absence of geographic barriers, but the genomic and life history strategy mechanisms underpinning sympatric speciation are still far from clear. It has recently been discovered that the cichlid fish Astatotilapia calliptera from crater Lake Masoko in Tanzania have diverged sympatrically into littoral (shallow water) and benthic (deep water) ecotypes, which differ in head and pharyngeal jaw morphology. Carbon stable isotope analysis has also broadly indicated trophic differentiation between ecotypes. Here, we explore trophic niche divergence on a finer scale, using metabarcoding of stomach contents. A combination of the mitochondrial COI region and 18S V4 region from the eukaryotic nuclear small subunit ribosomal DNA was used to target macroinvertebrate and broader eukaryotic taxonomic diversity, respectively, revealing dietary divergence between the ecotypes. Large proportions of Arthropoda (dipterans and copepod) were found in both ecotypes, indicating some food sources common to both microhabitats. However, gut contents of benthic A. calliptera individuals were characterized by an abundance of annelids and diatoms, while Lepidoptera, mayflies, fungi, freshwater mussels, and bivalves were common in littoral ecotypes. The variation observed in the dietary contents of the ecotypes indicates the presence of resource partitioning, facilitating adaptation to unique feeding strategies.