Conserved switch genes that arose via whole-genome duplication regulate a cannibalistic nematode morph

Abstract

Developmental plasticity facilitates morphological and behavioral novelty. Nematodes have emerged as a powerful model to study developmental plasticity and its evolution. Here, we show that the predatory nematode Allodiplogaster sudhausi evolved an additional third mouth morph, concomitant with whole-genome duplication (WGD) and a strong increase in body size. The three mouth morphs are induced by different diets: bacteria, fungi, and nematodes. CRISPR experiments indicate that regulation of the third morph involves co-option of a conserved developmental switch gene, which, through WGD, resulted in two mouth-form regulators. Gene dosage studies revealed a diverged role of these developmental switches, with functional redundancy and quantitative effects in the two mouth-form decisions, respectively. The third morph is cannibalistic and kills isogenic kin, whereas the other two morphs do not. Thus, a recently evolved new morph relies on preexisting regulatory mechanisms and adds behavioral and social complexity.