Testing the stages model in the adaptive radiation of cichlid fishes in East African Lake Tanganyika

Moritz Muschick 1 2 3 4 Patrik Nosil 1 2 4 Marius Roesti 2 3 4 Marie Theres Dittmann 0 2 4 6 Luke Harmon 2 4 5 Walter Salzburger 2 3 4 0 Institute of Agricultural Sciences, ETH Zurich , Zu rich 8092 , Switzerland 1 Department of Animal and Plant Sciences, University of Sheffield , Sheffield S10 2TN , UK 2 One contribution to a Special feature 'Evolution of specialization: insights from phylogenetic analysis' 3 Zoological Institute, University of Basel , Basel 4051 , Switzerland 4 Subject Areas: evolution 5 Department of Biological Sciences and Institute for Bioinformatics and Evolutionary Studies (IBEST), University of Idaho , Moscow, ID , USA 6 Clinic for Zoo Animals, Wildlife and Exotic Pets, Vetsuisse Faculty, University of Zurich , Zu rich 8057 , Switzerland Adaptive radiation (AR) is a key process in the origin of organismal diversity. However, the evolution of trait disparity in connection with ecological specialization is still poorly understood. Available models for vertebrate ARs predict that diversification occurs in the form of temporal stages driven by different selective forces. Here, we investigate the AR of cichlid fishes in East African Lake Tanganyika and use macroevolutionary model fitting to evaluate whether diversification happened in temporal stages. Six trait complexes, for which we also provide evidence of their adaptiveness, are analysed with comparative methods: body shape, pharyngeal jaw shape, gill raker traits, gut length, brain weight and body coloration. Overall, we do not find strong evidence for the 'stages model' of AR. However, our results suggest that trophic traits diversify earlier than traits implicated in macrohabitat adaptation and that sexual communication traits (i.e. coloration) diversify late in the radiation. 1. Introduction 2. Material and methods (a) Sampling We collected trait data for 51 LT cichlid species, which is approximately one-quarter of the endemic species of this lake. The dataset comprises 36 genera (of 53) and 10 of the 16 tribes [29] (see the electronic supplementary material) described for LT cichlids and is thus representative of the phylogenetic, morphological, ecological and behavioural diversity. In subsets of specimens (electronic supplementary material, table S1), we measured six trait complexes: body shape, the LPJ apparatus, the gill raker apparatus, brain weight, intestine tract length and colour. The data for body and LPJ shape, stable isotopes and phylogenetic relationships were taken from [21]. Measurements of gill raker traits, gut length, brain weight and scoring for coloration were newly generated for this study. (c) Trait data 3. Results d15N Lamprologini Tropheini Boulengerochromini Cyprichromini Perissodini Ectodini Benthochromini Cyphotilapiini Eretmodini Tylochromini body shape LPJ shape gut length brain weight 0.0286 0.0015 0.0027 0.0001 gut length brain weight Mantel statistic body shape LPJ shape gill raker 0.0044 0.0001 gill raker 0.0035 0.0002 0.1744 4. Discussion 5. Conclusion (...truncated)