Gender and Timing during Ontogeny Matter: Effects of a Temporary High Temperature on Survival, Body Size and Colouration in Harmonia axyridis

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.

Impact of hot events at different developmental stages of a moth: the closer to adult stage, the less reproductive output

“…In addition to reproduction, morphological traits were impacted more by heat stress closer to adult stage than at earlier stages. In the Coleoptera species, Harmonia axyridis, adult body size and coloration were affected by heat stress at the 4 th -instar larval or pupal stages but not at early development stages42. Moreover, in the butterfly, Bicyclus anynana , wing pattern was sensitive only to late larval stage temperatures43.…”

Heat resistance throughout ontogeny: body size constrains thermal tolerance

“…Our data clearly indicate that eggs and hatchlings are very sensitive to heat while others such as pupae are less susceptible. Some other studies also showed variation in heat resistance throughout ontogeny, indicating large differences with respect to the most heat‐tolerant developmental stage ranging from early via intermediate up to late ones (Krebs & Loeschcke, ; Abdelghany et al ., ; Amarasekare & Sifuentes, ; Knapp & Nedvěd, ).…”

Stage-specific heat effects: timing and duration of heat waves alter demographic rates of a global insect pest

“…These hypotheses have been supported in laboratory experiments. For example, exposing early life-stages of P. xylostella (Xing et al 2014;Zhang et al 2015), eggs of Manduca sexta and Wyeomyia smithii (Zani et al 2005) and early instar nymphs/larvae of Metopolophium dirhodum (Ma et al 2004b) and Harmonia axyridis (Knapp and Nedvěd 2013) to acute [i.e. high amplitude but short duration (few hours)] heat stress did not affect female fecundity or adult phenotype.…”