Sweet tetra-trophic interactions: multiple evolutions of nectar secretion, a defensive extended phenotype in cynipid gallwasps

Graham Stone, James Nicholls, George Melika

Research output: Contribution to journalArticlepeer-review

Abstract

Many herbivores employ reward-based mutualisms with ants to gain protection from natural enemies. We examine the evolutionary dynamics of a tetra-trophic interaction in which gallwasp herbivores induce their host oaks to produce nectar-secreting galls, which attract ants that provide protection from parasitoids. We show that, consistent with other gall defensive traits, nectar secretion has evolved repeatedly across the oak gallwasp tribe and also within a single genus (Disholcaspis) that includes many nectar-inducing species. Once evolved, nectar secretion is never lost in Disholcaspis, consistent with high defensive value of this trait. We also show that evolution of nectar secretion is correlated with a transition from solitary to aggregated oviposition, resulting in clustered nectar-secreting galls, which produce a resource that ants can more easily monopolize. Such clustering is commonly seen in ant guard mutualisms. We suggest that correlated evolution between maternal oviposition and larval nectar-induction traits has enhanced the effectiveness of this gall defense strategy.
Original languageEnglish
JournalThe American Naturalist
Early online date2 Nov 2016
DOIs
Publication statusE-pub ahead of print - 2 Nov 2016

Keywords

  • trophic interactions
  • nectar secretion
  • Cynipini
  • Disholcaspis
  • co-evolution
  • defensive trait

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