Basal cold but not heat tolerance constrains plasticity among Drosophila species (Diptera: Drosophilidae)

Abstract

Thermal tolerance and its plasticity are important for understanding ectotherm responses to climate change. However, it is unclear whether plasticity is traded‐off at the expense of basal thermal tolerance and whether plasticity is subject to phylogenetic constraints. Here, we investigated associations between basal thermal tolerance and acute plasticity thereof in laboratory‐reared adult males of eighteen Drosophila species at low and high temperatures. We determined the high and low temperatures where 90% of flies are killed (ULT90 and LLT90, respectively) and also the magnitude of plasticity of acute thermal pretreatments (i.e. rapid cold‐ and heat‐hardening) using a standardized, species‐specific approach for the induction of hardening responses. Regression analyses of survival variation were conducted in ordinary and phylogenetically informed approaches. Low‐temperature pretreatments significantly improved LLT90 in all species tested except for D. pseudoobscura, D. mojavensis and D. borealis. High‐temperature pretreatment only significantly increased ULT90 in D. melanogaster, D. simulans, D. pseudoobscura and D. persimilis. LLT90 was negatively correlated with low‐temperature plasticity even after phylogeny was accounted for. No correlations were found between ULT90 and LLT90 or between ULT90 and rapid heat‐hardening (RHH) in ordinary regression approaches. However, after phylogenetic adjustment, there was a positive correlation between ULT90 and RHH. These results suggest a trade‐off between basal low‐temperature tolerance and acute low‐temperature plasticity, but at high temperatures, increased basal tolerance was accompanied by increased plasticity. Furthermore, high‐ and low‐temperature tolerances and their plasticity are clearly decoupled. These results are of broad significance to understanding how organisms respond to changes in habitat temperature and the degree to which they can adjust thermal sensitivity.

Ontogenetic variation in cold tolerance plasticity in Drosophila: is the Bogert effect bogus?

“…A similar method was used for LLT 90 in adults (Nyamukondiwa et al 2011), 85 except that survival was estimated following acute transfer to the test temperatures 86 rather than the temperature ramp. Hardening was induced by exposing groups of 4-6 87 day old flies to a temperature 10°C above the estimated LLT 90 for 2 h before exposure 88 to the LLT 90 , resulting in a unique combination of temperatures for each species.…”

“…(Statistica, StatSoft Inc. 2011). Significant RCH responses were determined based on statistical tests in the original papers (Nyamukondiwa et al 2011;Strachan et al 2011)." The phylogenetic tree was constructed using branch lengths estimated from genetic sequence data.…”

“…Response: We apologise for the confusion and have now clarified these statements. We have replaced the word "constraint" with "signal" in the sentence "Both of the studies from which we extracted data found significant phylogenetic signal in the plasticity of cold tolerance as well as a negative correlation between RCH and basal resistance (Nyamukondiwa et al 2011;Strachan et al 2011 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 …”

“…We 171 suggest that thermal plasticity be explored across other arthropod groups and 172 additional life stages and the broad range of thermal tolerance traits that can be 173 measured in insects (Terblanche et al 2011) to better understand the nature and limits 174 of the Bogert effect in ectotherms. 175 …”

Plasticity in thermal tolerance has limited potential to buffer ectotherms from global warming

“…Comprehensive tests of the latitudinal and trade-off hypotheses are currently lacking for thermal tolerance plasticity, with tests coming from a few phylogenetically restricted analyses (i.e. within single genera) that have yielded mixed results [16,[20][21][22][23][24][25][26][27]. For example, multiple studies have assessed geographical patterns of thermal tolerance plasticity in Drosophila, but have produced little evidence that high-latitude species have greater plasticity [16,25,26].…”