Do mutualistic associations have broader host ranges than neutral or antagonistic associations? A test using myrmecophiles as model organisms

Abstract

Symbiotic associations are found across all kingdoms of life and are integral to ecosystem structure and function. Central to understanding the ecology and evolution of symbiotic relationships is an understanding of what influences host range; the number of host species that a symbiont can utilize. Despite the importance of host breadth among symbionts, relatively little is known about how the relationship that a symbiont has with its host influences its host range. Additionally, contrasts among interaction types often involve diverse groups of unrelated host species. To test how host range varied with interaction type, we used a global synthesis of over 1600 species of myrmecophiles, those organisms that have symbiotic associations with ants. We used an indexed literature search to collate known myrmecophile species and their hosts, and to determine how two degrees of dependence (facultative, obligate) and four types of relationships (mutualism, commensalism, kleptoparasitism, and parasitism) among myrmecophiles and their hosts influence host range. Our synthesis showed that, overall, myrmecophiles exhibited a high degree of host specialization, and facultatively dependent myrmecophiles had broader host ranges than those with obligate interactions. Myrmecophiles with mutualistic relationships had broader host ranges than neutral or antagonistic relationships. Additionally, lepidopteran myrmecophiles exhibited broader host range patterns than other taxa. Our results have important implications for how symbiotic associations are understood, with positive relationships (mutualisms) associated with broader host range, and antagonistic relationships (parasitism) associated with narrow host range.