Appetite regulating genes may contribute to herbivory versus carnivory trophic divergence in haplochromine cichlids

Abstract

Feeding is a complex behaviour comprised of satiety control, foraging, ingestion and subsequent digestion. Cichlids from the East African Great Lakes are renowned for their diverse trophic specializations, largely predicated on highly variable jaw morphologies. Thus, most research has focused on dissecting the genetic, morphological and regulatory basis of jaw and teeth development in these species. Here for the first time we explore another aspect of feeding, the regulation of appetite related genes that are expressed in the brain and control satiety in cichlid fishes. Using qPCR analysis, we first validate stably expressed reference genes in the brain of six haplochromine cichlid species at the end of larval development prior to foraging. We next evaluate the expression of 16 appetite related genes in herbivorous and carnivorous species from the parallel radiations of Lake Tanganyika, Malawi and Victoria. Interestingly, we find increased expression of two appetite-regulating genes (anorexigenic genes), cart and npy2r, in the brain of carnivorous species in all the three lakes. This supports the notion that appetite gene regulation might play a part in determining trophic niche specialization in divergent cichlid species, already prior to exposure to different diets. Our study contributes to the limited body of knowledge on the neurological circuitry that controls feeding transitions and adaptations in cichlids and other teleosts.

Conserved Molecular Players Involved in Human Nose Morphogenesis Underlie Evolution of the Exaggerated Snout Phenotype in Cichlids

“…Validation of DE genes from RNA-seq was accomplished via real-time quantitative polymerase chain reaction (qPCR), normalized to stably expressed reference genes ( Kubista et al 2006 ). In our previous studies of East African cichlids, we found that validation of reference gene(s) is an essential step as genes only selected from literature are not necessarily the best choice and can vary a lot between different species and tissue types ( Ahi, Singh, et al 2019 ; Ahi, Richter, et al 2019 ; Pashay Ahi and Sefc 2018 ; Ahi et al 2020a , 2020b ). We chose six candidate reference genes with a small log 2 fold change and the lowest coefficient of variation (CV) throughout all the samples ( supplementary table S4, Supplementary Material online).…”

Expression variations in ectodysplasin-A gene (eda) may contribute to morphological divergence of scales in haplochromine cichlids

“…We selected eight candidate reference genes which have been frequently used in different studies of Haplochromine cichlids and have shown high expression levels in various connective tissues including skeletal tissues [10,[30][31][32][33][34][35]. Furthermore, we chose 16 target candidate genes, which are implicated in scale development and morphogenesis (Table 1).…”

“…To quantify the expression levels of the selected target genes, the validation of stable reference gene(s) with least variation in expression across the anterior and posterior scales of different species is a necessary step [51]. The eight candidates were selected from frequently used reference genes in studies of different tissues in East African cichlids [10,[30][31][32][33][34][35]. The candidate reference genes showed variable expression levels in the scales, and from highest to lowest expressed were respectively; actb1, hsp90a, rps11, rps18, hprt1,gapdh, elf1a and tbp.…”

Appetite regulating genes in zebrafish gut; a gene expression study

“…Validation of stably expressed gene(s) in every specific experimental conditions (so-called reference genes) is an essential step, in order to calculate the relative gene expression levels of target genes [97][98][99]. In this study, we assessed the expression levels of 8 candidate reference genes in the gut of lepr mutant and wild-type zebrafish, under different feeding conditions.…”