Diapause termination of Rhagoletis cerasi pupae is regulated by local adaptation and phenotypic plasticity: escape in time through bet‐hedging strategies

Abstract

Persistence and thriving of univoltine, herbivore insect species of the temperate zone rely on obligate diapause response that ensures winter survival and synchronization with host phenology. We used a stenophagous fruit fly (Rhagoletis cerasi) with obligate pupae diapause to determine genetic and environmental effects on diapause intensity of geographically isolated populations with habitat heterogeneity. Pupae from two Greek and one German populations with various gene flow rates were exposed at five constant chilling temperatures (0-12°C) for different durations and then incubated at a high temperature until all adults have emerged. Pupae diapause intensity differs among Greek and German populations, suggesting an adaptive response to habitat heterogeneity (mostly differences in phenology patterns of local host cultivars). Moderately warm winter temperatures, such as 8°C, promote diapause termination in all three populations. Insufficient chilling (short duration or warmer temperatures) regulates the expression of prolonged dormancy. Interestingly, extended chilling (longer than required for terminating diapause) 'return' pupae to another (facultative) cycle of dormancy enabling adults to emerge during the next appropriate 'window of time'; a strategy first time reported for univoltine insects. Consequently, diapause duration of R. cerasi is determined both by i) the adaptive response to local climatic conditions (annual dormancy) and ii) the plastic responses to interannual climatic variability resulting in two types of long life cycles within populations, prolonged and facultative dormancy as response to insufficient chilling and extended exposure to chilling, respectively. Long life cycles are expressed as a part of dormancy bet-hedging strategies of R. cerasi populations.

Adaptive significance of the prolonged diapause in the western Mediterranean lycaenid butterfly Tomares ballus (Lepidoptera: Lycaenidae)

“…In the fruit fl y Rhagoletis cerasi (Diptera: Tephritidae), both insuffi cient and extended exposure to chilling promote prolonged and facultative dormancy, respectively (Moraiti et al, 2014). In our experiment however, these factors can be ruled out as determinants of the prolonged diapause recorded for more than half of the pupae.…”

“…In the case of T. ballus, the factors determining diapause termination remain un-known. Due to the high variability in diapause duration recorded among the pupae, despite being exposed to the same climatic conditions, temperature, photoperiod and/or humidity do not appear to be the cues triggering diapause termination, as reported for other species (Templado, 1981;Powell, 2001;Moraiti et al, 2014;Sakamoto et al, 2015).…”

“…In the fruit fl y R. cerasi diapause duration is determined by both adaptation to local climatic conditions and phenotypic plasticity in response to inter-annual climatic variability (Moraiti et al, 2014). In the case of T. ballus, the factors determining diapause termination remain un-known.…”

Improvement of Management of Rhagoletis Cerasi in Bosnia and Herzegovina Based on a Phenological Model

“…However, some differences were observed between temperature sums calculated from soil and air temperatures for 5% cumulative hatch and more so for duration of flight period. Different populations of R. cerasi pupae exposed to constant chilling temperatures in the range 0-12°C for different times overcome diapause in relation to adaptation of the local populations (Moraiti et al, 2014). Our study showed that 5°C and 7°C can be used as thermal thresholds for accumulation of degree days for the studied population, since no major differences were observed between the two thresholds.…”

Phenotypic plasticity in morphological features of Thelaxes suberi (Del Guercio, 1911) (Hemiptera: Aphidoidea) feed on Quercus (L.) species

“…Recent findings support the importance of DNA methylation in phenotypic plasticity in aphids. Moraiti et al 2014;Ogawa & Miura 2014;Mukherjee & Baudach 2016). There commonly are differences among genotypes within a species in their ability to phenotypically adjust to environmental changes, in other words there is often genetic variation for phenotypic plasticity (Görür et al , 2007.…”