The role of phenotypic plasticity in rapid adaptation

Plasticity is defined as an organism's ability to alter phenotype expression in response to environmental change [1]. Plastic changes can result both from abiotic and social conditions, altering structure, physiology, metabolism and behaviour (e.g.[2] [3] [4] [5]). Previous research has highlighted the role of plasticity in rapid adaptation, suggesting it may be the key to understanding how organisms cope with the challenge of a rapidly changing world (e.g. global warming, deforestation, pollution)(e.g. [6][7]). Furthermore, the strength of plastic responses themselves have been shown to evolve and diversify [8]. These findings have sparked interest for an updated modern synthesis of evolution, accounting for developmental plasticity (e.g. [9] [10] [11]). However, it has also been suggested that plasticity may shield populations from selection, slowing down adaptation (e.g. [12]). Furthermore, when plasticity to the social environment is present, complexity increases, and it is still unclear how this form of plasticity affects evolutionary trajectories. In order to update evolutionary models and predict how organisms cope with rapid environmental change, it is imperative to define the underlying genetic and environmental factors which promote rapid phenotypic change; determine how social and abiotic plasticity interact to shape evolutionary outcomes; and definitively settle the debate over whether or not phenotypic plasticity is an evolved adaptation. Combining field and laboratory studies, and using robust experimental designs, this project aims to use the rapidly evolving Hawaiian cricket to achieve these tasks, definitively determining the role of plasticity in rapid adaptation.
In Hawaiian cricket populations (Teleogryllus oceanicus) a percentage of males have lost ability to sing due to mutations which erase sound producing structures on the forewings [13]. This alteration is beneficial for survival as it protects individuals from predation from an acoustically-oriented parasitoid fly (Ormia ochracea). In contrast, the mutation removes the male's main strategy for attracting females, singing. Despite this, since first appearing in the island of Kauai in 2003, the silent morph has spread rapidly across Hawaiian Islands [13]. The reproductive success of silent morphs is indicative that their proliferation is enabled by plasticity to the social environment: males alter sexual signalling strategies and females adjust the criteria to determine male quality. In fact, previous research has found that plasticity to the social environment is significantly higher in "silent" populations than in normal-wing populations [6], and it has been hypothesised that plasticity to the social environment may be co-evolving with the "silent" mutation [6]. Hawaiian cricket populations then present an optimal opportunity to study the role of plasticity in rapid adaptation. This project will be comprised of three main stages: 1) conduct field studies to survey abiotic and social conditions, determine how they covary in nature and test what factors promote or hinder the invasion success of silent morphs; 2) experimentally test how plasticity to the abiotic and social environments interact to shape adaptation by exploring how different levels of nutritional availability affect plastic responses to the social environment; and 3) test the role of plasticity to the social environment as an evolved adaptation by manipulating social environments to either match or mismatch previous social experience, subsequently measuring fitness.