Gender and timing during ontogeny matter: effects of a temporary high temperature on survival, body size and colouration in Harmonia axyridis.

Michal Knapp,Oldřich Nedvěd

doi:10.1371/journal.pone.0074984

Abstract

The ambient temperature experienced during development is a crucial factor affecting survival and adult phenotype in ectotherms. Moreover, the exact response of individuals to different temperature regimes is frequently sex-specific. This sex-specific response can result in varying levels of sexual dimorphism according to the experienced conditions. The majority of studies have investigated the effects of temperature on individuals reared under a constant temperature regime throughout their whole preimaginal development, whereas information on stage-dependent variation in temperature effects is scarce. Here we investigate how the stage at which elevated temperature is experienced influences survival, adult body size and colouration in the harlequin ladybird Harmonia axyridis form succinea. The effects of timing of exposure to elevated temperature on the adult phenotype are assessed separately for males and females. Control individuals were reared at a constant temperature of 20°C. Beetles in other treatments were additionally exposed to 33°C for 48 hours during the following developmental stages: egg, 1st to 2nd larval instar, 3rd larval instar, 4th larval instar and pupa. Exposure to an elevated temperature during the early developmental stages resulted in lower survival, but the adult phenotype of survivors was almost unaffected. Exposure to an elevated temperature during the later developmental stages (4th larval instar or pupa) resulted in the decreased melanisation of elytra, decreased structural body size and increased dry mass. Furthermore, the timing of high temperature exposure affected the degree of sexual dimorphism in elytral melanisation and dry mass. We demonstrate that the effects of elevated temperature can vary according to the developmental stage at exposure. Detailed information on how ambient temperature affects the developmental biology of ectotherms is crucial for modeling population growth and predicting the spread of invasive species such as Harmonia axyridis.

Highlights

Environmental conditions play a crucial role in the development of individual organisms because many crucial life-history traits demonstrate a considerable degree of phenotypic plasticity [1,2]
Particular treatments employed were: ‘‘C’’ beetles reared at constant temperature (20uC); beetles reared at constant temperature (20uC) with the exception of period with elevated temperature (48 hours at 33uC) during egg stage (‘‘E’’), 1st and partially 2nd larval instar (‘‘L1’’), 3rd larval instar (‘‘L3’’), 4th larval instar (‘‘L4’’) or pupal stage (‘‘P’’)
The influence of ambient temperature experienced during juvenile development on adult phenotype is well documented for ectotherms (e.g., [8,9,51,52,53])

Summary

Introduction

Environmental conditions play a crucial role in the development of individual organisms because many crucial life-history traits demonstrate a considerable degree of phenotypic plasticity [1,2]. Adult body size is usually negatively related to developmental temperature in ectotherms This relationship, often referred to as the temperature-size rule, has received broad attention in the last few decades [4,5,6]. Growth rate (increase in mass per day) and developmental rate (progress in development – i.e. reciprocal of development duration in days) differ in their response to temperature. This decoupling of temperature dependence in growth rate and development rate has been identified as probable mechanism responsible for the change in body size with temperature. There is only limited knowledge of how the decoupling of these rates progresses throughout ontogeny and which life stages are most sensitive to temperature changes with respect to adult body size [6]

Methods

Results

Conclusion