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Review Article

Myrmecophily in beetles (Coleoptera): evolutionary patterns and biological mechanisms

Parker, J.

Abstract: Socially parasitic myrmecophily has evolved numerous times in arthropods, but myrmecophilous lineages are non-randomly distributed across phylogeny. Evolution of this way of life is heavily biased towards the Coleoptera, within this order towards rove beetles (Staphylinidae), and within rove beetles to two subfamilies. Here, I provide an overview of the diversity of myrmecophilous beetles and discuss advances in comprehending their biology, systematics, and evolution. I address possible factors underlying the skewed phylogenetic distribution of myrmecophily across the Coleoptera. Accounting for this trend requires knowledge of ancestral ecologies and phenotypic attributes in clades where taxa are predisposed to undergo the evolutionary transition from free-living to myrmecophilous. Clades that are primitively predatory, small in body size, and possess defensive strategies, either physical or chemical, that permit some degree of protection from policing worker ants, appear to be preadapted to evolve myrmecophily repeatedly. I propose that the mode of colony exploitation employed during the initial phase of evolution, combined with the potential evolvability of the body plan, has important consequences for subsequent evolutionary steps: These parameters influence if and how different taxa undergo specialisation to colony life and the mechanisms the most advanced myrmecophiles employ to achieve social integration. Myrmecophily is a paradigm of intricate symbiosis, which in certain clades of beetles evolves recurrently from an ancestral preadaptive ground state and follows a relatively predictable phenotypic trajectory. These clades are potentially powerful systems to explore the evolution and mechanistic bases of symbiotic relationships in animals.