Biotic interactions govern genetic adaptation to toxicants

Jeremias Martin Becker,Matthias Liess

doi:10.1098/rspb.2015.0071

Abstract

The genetic recovery of resistant populations released from pesticide exposure is accelerated by the presence of environmental stressors. By contrast, the relevance of environmental stressors for the spread of resistance during pesticide exposure has not been studied. Moreover, the consequences of interactions between different stressors have not been considered. Here we show that stress through intraspecific competition accelerates microevolution, because it enhances fitness differences between adapted and non-adapted individuals. By contrast, stress through interspecific competition or predation reduces intraspecific competition and thereby delays microevolution. This was demonstrated in mosquito populations (Culex quinquefasciatus) that were exposed to the pesticide chlorpyrifos. Non-selective predation through harvesting and interspecific competition with Daphnia magna delayed the selection for individuals carrying the ace-1R resistance allele. Under non-toxic conditions, susceptible individuals without ace-1R prevailed. Likewise, predation delayed the reverse adaptation of the populations to a non-toxic environment, while the effect of interspecific competition was not significant. Applying a simulation model, we further identified how microevolution is generally determined by the type and degree of competition and predation. We infer that interactions with other species—especially strong in ecosystems with high biodiversity—can delay the development of pesticide resistance.

Highlights

Genetic adaptation to anthropogenic toxicants has become increasingly important to the survival of populations because of environmental pollution
To ascertain the mechanisms that probably explain these results, we developed a simulation model based on the combined equations for predation and interspecific competition from Lotka–Volterra
We observed that non-selective predation and interspecific competition slowed microevolution within a population, delaying both the genetic adaptation to a pesticide and the genetic recovery after pesticide exposure

Summary

Introduction

Genetic adaptation to anthropogenic toxicants has become increasingly important to the survival of populations because of environmental pollution. The ace-1R allele, which has evolved in several mosquito species, is characterized by a point mutation that leads to a modified acetylcholinesterase (AChE), which provides high resistance against organophosphorus and carbamate insecticides [8]. Individuals carrying such a resistance allele typically display reduced fitness under non-toxic conditions, manifested, for example, in lower survival and delayed development [9,10]. This phenomenon facilitates the genetic recovery of a largely resistant population back to one dominated by susceptible individuals when toxicants are not present [11]

Methods

Findings

Discussion

Conclusion