Rebecca L Young , Chelsea Weitekamp, Zegni Triki , Yiheng Su, Redouan Bshary, Hans Hofmann

Despite the remarkable diversity of life forms on earth, evolutionary biologists have discovered numerous instances where even distantly related species share astonishing similarities in how they behave, look, and function. Given the importance of happenstance in evolution (e.g., random mutations, genetic drift, environmental stochasticity), it is often assumed that the mechanisms underlying such convergent phenotypes are distinct. Nevertheless, recent discoveries that the same pathways can underlie convergently evolved phenotypes have reinvigorated questions about the predictability of evolution and whether broadly conserved genomic mechanisms facilitate phenotypic convergence. Here, we generated transcriptomes of the putative teleost homologs of the mammalian hippocampus and basolateral amygdala, broadly associated with spatial and social cognition, in six sympatric species of Labridae wrasses that vary in mutualistic cleaning behavior (including three non-cleaning, two facultative cleaning, and one obligate cleaning species) and combined differential gene expression, gene co-expression, and phylogenetic comparative analyses to test two hypotheses about convergent evolution and specialization of mutualistic cleaning behavior. We first identify genes and gene modules exhibiting parallel neurotranscriptomic patterns in the repeated evolution of facultative cleaning. We then examined whether expression and co-expression patterns associated with facultative cleaning are also shared in the obligate cleaner species in our dataset and found evidence for transcriptomic concordance, though no evidence for additional specialization. Taken together, our results provide insights into the convergent evolution and the neuromolecular basis of cooperative behavior and, more generally, illustrate the potential of phylogenetic comparative transcriptomics to unravel the mechanistic underpinnings of the repeated evolution of complex organismal phenotypes.