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Data from: Developmental timing of extreme temperature events (heat waves) disrupts host-parasitoid interactions

Citation

Moore, M. Elizabeth; Kingsolver, Joel; Hill, Christina (2023), Data from: Developmental timing of extreme temperature events (heat waves) disrupts host-parasitoid interactions, Dryad, Dataset, https://doi.org/10.5061/dryad.8kprr4xn4

Abstract

1. When thermal tolerances differ between interacting species, extreme temperature events (heat waves) will alter the ecological outcomes. The parasitoid wasp Cotesia congregata suffers high mortality when reared throughout development at temperatures that are non-stressful for its host, Manduca sexta. However, the effects of short-term heat stress during parasitoid development are unknown in this host-parasitoid system.

2. Here, we investigate how duration of exposure, daily maximum temperature, and the developmental timing of heat waves impact the performance of C. congregata and its host¸ M. sexta. We find that the developmental timing of short-term heat waves strongly determines parasitoid and host outcomes.

3. Heat waves during parasitoid embryonic development resulted in complete wasp mortality and the production of giant, long-lived hosts. Heat waves during the 1st-instar had little effect on wasp success, whereas heat waves during the parasitoid’s nutritionally and hormonally critical 2nd instar greatly reduced wasp emergence and eclosion. The temperature and duration of heatwaves experienced early in development determined what proportion of hosts had complete parasitoid mortality and abnormal phenotypes.

4. Our results suggest that the timing of extreme temperature events will be crucial to determining the ecological impacts on this host-parasitoid system. Discrepancies in thermal tolerance between interacting species and across development will have important ramifications on ecosystem responses to climate change.

Methods

The current study consisted of two experiments: one determining how parasitoid sensitivity to heat shock varies across ontogeny (developmental timing experiment), and the other investigating the effects of heat shock temperature and number of heat shock exposures on C. congregata survival and development early in parasitization (temperature/duration experiment). The rearing treatment was the same for both experiments (25°C±10°C), and has been determined to be non-stressful for both parasitoid and host (Moore et al., 2021). The temperature/duration experiment was conducted in January—April, 2018, and the developmental timing experiment took place in October—December, 2018. Organisms were housed in climate control chambers (Percival Scientific 36VL) under 14L/10D hour light cycle. An open container of water was placed in each chamber to prevent desiccation of organisms or artificial diet (Moore et al., 2020). Newly hatched caterpillars were reared on an artificial diet in communal petri dishes until the molt to the 3rd instar. On the day of the molt to 3rd instar (day 0), caterpillars were assigned a unique ID, allocated to a heat shock treatment, weighed, parasitized, and housed individually in small petri dishes. Caterpillars were parasitized by exposing individual caterpillars to a colony of adult wasps, and observing until an oviposition event of  >2-3 seconds occurred. 

 

The development timing experiment consisted of three heat shock treatments and one control. The heat shock regime was the same for all treatments: three days at 31°C±11°C (daily maximum of 42°C). Recent work has shown that a single exposure to this heat wave regime does not reduce survival, development time or pupal mass of unparasitized M. sexta regardless of developmental stage (Kingsolver et al., 2021). The treatments differed in the developmental stage of the parasitoid larvae at which they experienced the heat shock temperatures (recall that caterpillars in all treatments were parasitized). Early Heat Shock started on day 0 of the 3rd instar, the same day as oviposition; the Middle Heat Shock treatment started 5 days after oviposition (when the majority of C. congregata eggs have hatched); the Late Heat Shock started on day 1 of the host 5th instar (when the majority of C. congregata larvae have molted to the 2nd instar), which ranged from 8-12 days after oviposition. Sample sizes for each treatment ranged from 30-60 parasitized M. sexta caterpillars (see SOM). Individuals in heat shock treatments were transferred to the heat shock chamber at least 2 hours before the DMT, and were removed at 4-5pm on the last day of the heat shock treatment. Parasitized hosts in the control treatment remained in the rearing temperature throughout development.

The temperature/duration experiment consisted of a 2x4 factorial design plus one control treatment for a total of 9 treatment combinations. All M. sexta caterpillars were parasitized for this experiment. Parasitized M. sexta were exposed to one of two fluctuating heat shock temperatures, one with a daily maximum temperature of 40°C (30°C±10°C) and the other with a DMT of 42°C (31°C±11°C). Both temperature treatments ramped continuously between 2-hour periods at the high and low temperatures in a 24-hour cycle. Parasitized M. sexta were placed in a heat shock treatment on the same day as oviposition, at least 2 hours before the daily maximum temperature. Experimental insects remained in the heat shock treatments for 1, 2, 3, or 4 days (i.e. they experienced the DMT 1-4 times). Caterpillars were removed from the heat shock treatment at 4 pm – 5pm on the day of their last heat shock, and then returned to the 25°C±10°C rearing treatment. Parasitized hosts in the control treatment remained in the rearing temperature throughout development.  

The data has been cleaned to remove most erroneous values, though some data cleaning is also required in the R scripts provided. Dates have been converted to Julian day, and life history metrics have been calculated.

Funding

National Science Foundation, Award: IOS 155559