SYMBIVORE · Losing genes but gaining symbionts: Why beetles outsource key metabolic traits

Herbivorous beetles represent one of the most successful animal radiations. The cooption of microbial enzymes is cited as a key innovation that endowed beetles with the catalytic tools to breach the plant cell wall and facilitated the evolution of remarkably diverse herbivorous habits. Beetles incorporated microbial plant cell wall-degrading enzymes either through horizontal gene transfer or symbiosis. This binary distribution is most evident in leaf beetles (Coleoptera: Chrysomelidae), where the loss of horizontally acquired pectinases coincided with the evolution of functionally convergent digestive symbioses. Prior efforts either examined the role of horizontal gene transfer or symbiosis in shaping the phenotypic complexity of herbivorous beetles. But a comprehensive approach reconciling both fields is lacking. SYMBIVORE aims to fill this gap by defining the metabolic requirements and determining the physiological and ecological conditions favoring symbiosis as an alternative strategy for beetles to deconstruct pectin. The proposed research is integrative and extends beyond the state-of-the-art by examining the adaptive importance of symbiosis relative to horizontal gene transfer across multiple scales of biological organization. From the molecular and genetic mechanisms underlying symbiont acquisition, to the biochemical, physiological, and ecological consequences of outsourcing a key metabolic trait. Through comparative genomics, transcriptomics, structural biochemistry, bioassays, and nutritional geometry, SYMBIVORE will address the hypothesis that symbiosis upgraded the digestive physiology in a subset of beetle clades, thereby relaxing selection for these insects to endogenously maintain essential genes. SYMBIVORE capitalizes on the functional overlap conferred by symbiosis and horizontal gene transfer to define how these processes differentially shape the adaptive potential of beetles, Earth’s most speciose animal order.