Within-generation variation of critical thermal limits in adult Mediterranean and Natal fruit flies Ceratitis capitata and Ceratitis rosa: thermal history affects short-term responses to temperature

Abstract

Insect thermal tolerance shows a range of responses to thermal history depending on the duration and severity of exposure. However, few studies have investigated these effects under relatively modest temperature variation or the interactions between short-and longer-term exposures. In the present study, using a full-factorial design, 1 week-long acclimation responses of critical thermal minimum (CT min ) and critical thermal maximum (CT max ) to temperatures of 20, 25 and 30 • C are investigated, as well as their interactions with short-term (2 h) sub-lethal temperature exposures to these same conditions (20, 25 and 30 • C), in two fruit fly species Ceratitis capitata (Wiedemann) and Ceratitis rosa Karsch from South Africa. Flies generally improve heat tolerance with high temperature acclimation and resist low temperatures better after acclimation to cooler conditions. However, in several cases, significant interaction effects are evident for CT max and CT min between short-and long-term temperature treatments. Furthermore, to better comprehend the flies' responses to natural microclimate conditions, the effects of variation in heating and cooling rates on CT max and CT min are explored. Slower heating rates result in higher CT max , whereas slower cooling rates elicit lower CT min , although more variation is detected in CT min than in CT max (approximately 1.2 versus 0.5 • C). Critical thermal limits estimated under conditions that most closely approximate natural diurnal temperature fluctuations (rate: 0.06 • C min −1 ) indicate a CT max of approximately 42 • C and a CT min of approximately 6 • C for these species in the wild, although some variation between these species has been found previously in CT max . In conclusion, the results suggest critical thermal limits of adult fruit flies are moderated by temperature variation at both short and long time scales and may comprise both reversible and irreversible components.

Climate warming may increase aphids’ dropping probabilities in response to high temperatures

“…These results are in line with other studies which show that acclimation has limited effect on insects' upper thermal tolerances (Chown, 2001;Chown et al, 2002;Hazell et al, 2010;Hoffmann et al, in press). Nevertheless, high-temperature acclimation increases estimates of upper thermal tolerances in insects (Allen et al, 2012;Hazell et al, 2010;Jumbam et al, 2008;Nyamukondiwa and Terblanche, 2010) whereas it decreases the behavioral thresholds (preferred temperature, HET and DOT in present study) in response to heat stress (Forsman et al, 2002;Krstevska and Hoffmann, 1994;Ma and Ma, 2012), implying opposing responses to temperature acclimation between physiological tolerance and behavioral thermoregulation.…”

Effects of acclimation on the thermal tolerance of the brown planthopper Nilaparvata lugens (Stål)

“…Thermal acclimation (in the laboratory) or acclimatization (in nature where many environmental factors change) forms part of the range of insect responses to their environment known as phenotypic plasticity, which can occur only within limits imposed by the genotype (Gibbs et al, 1998). lethality) depends on the temperature and the duration of exposure; for example, Culex pipiens pipiens (Buffington, 1969), Periplaneta americana (Piccione & Baust, 1977), Sitophilus granaries L. and Oryzaephilus surinamensis L. (Mignon et al, 1996), Sitobion avenae (Powell & Bale, 2005), Locusta migratoria L. (Wang et al, 2006), Drosophila melanogaster (Frazier et al, 2008;Overgaard et al, 2008), Acheta domesticus L. (Lachenicht et al, 2010), Ceratitis capitata and Ceratitis rosa (Nyamukondiwa & Terblanche, 2010), Cydia pomonella (Chidawanyika & Terblanche, 2011) and Myzus persicae (Alford et al, 2011). Behaviourally-based changes represent a more flexible response to environmental variation than physiological processes because animals can respond actively to sensory information to avoid or mitigate lethal conditions (Schowalter, 2006); this is particularly true for highly mobile insects, although limited mobility is not necessarily detrimental in environments with gradients.…”

Evolutionary capacity of upper thermal limits: beyond single trait assessments

“…The temperature was increased gradually by 0.06°C min −1 , which is representative of maximal rates of temperature increase in southeastern Australia (van Heerwaarden et al, 2012) and other parts of the world (Nyamukondiwa and Terblanche, 2010;Terblanche et al, 2011). A data logger (Maxim Integrated i-button DS1923) was submerged into the heated water bath (along with the flies) to record the temperature of the heated water bath throughout the experiment.…”