Variation among individual butterflies along a generalist–specialist axis: no support for the ‘neural constraint’ hypothesis

Abstract

Abstract 1. Degree of host specialisation was a continuous variable in a population of Edith’s checkerspot butterfly (Euphydryas editha). A novel host, Collinsia torreyi, had been added to the diet in response to anthropogenic disturbance, and then abandoned prior to the current study. Butterflies either showed no preference or preferred their traditional host, Pedicularis semibarbata.2. Strength of preference for Pedicularis over Collinsia was measured in the field and used to estimate host specialisation of individual butterflies. Efficiency was estimated from the times taken by each insect to perform two tasks: (i) identification of a Pedicularis plant as a host, and (ii) successful initiation of oviposition after the decision to do so had been made.3. There was no clear trend for association between host specialisation and either measure of efficiency. Generalists were not slower than specialists at identifying Pedicularis as a host or at handling it after deciding to oviposit.4. Prior work indicated that generalists paid no detectable cost in terms of reduced discrimination among individuals of their preferred host species.5. In contrast to other species, generalist E. editha paid in neither time nor accuracy. Why then does the diet not expand? Behavioural adaptations to the traditional host caused maladaptations to the novel host and generated short‐term constraints to evolutionary expansion of diet breadth. To date, however, no long‐term constraints have been found in this system. In those traits investigated to date, increased adaptation to the novel host has not caused reduced adaptation to the traditional host.