Data from: How to assess Drosophila heat tolerance: unifying static and dynamic tolerance assays to predict heat distribution limits

1. Thermal tolerance is a critical determinant of ectotherm distribution,
which is likely to be influenced by future climate change. To predict such
distributional changes, simple and comparable measures of heat tolerance
are needed and these measures should ideally correlate with the
characteristics of the species current thermal environments. 2. A recent
model (thermal tolerance landscapes – TTLs) uses the exponential relation
between temperature and knockdown time to describe the thermal tolerance
of ectotherms across time/temperature scales. Here we established TTLs for
11 Drosophila species representing different thermal ecotypes by measuring
knockdown time at 9-17 stressful temperatures (0.5°C intervals). These
temperatures caused knockdown times ranging from <10 minutes to
>12 hours and all species displayed the expected exponential
relation between temperature and knockdown time (average R2=0.98). 3.
Previous studies using TTLs have reported a trade-off between tolerance to
acute and chronic heat stress in ectotherms. The present study did not
find evidence to support this trade-off in drosophilids. Instead, we show
how this “trade-off” can arise as an analytical artefact caused by
insufficient data collection and excessive data extrapolation. 4. Dynamic
assays represent an alternative method to describe heat tolerance of
ectotherms, where animals are exposed to gradually increasing temperatures
until knockdown. The comparability of static and dynamic assays has
previously been questioned, but here we show that static and dynamic
assays give comparable information on heat tolerance. Using the constants
derived from static TTLs we mathematically model the expected dynamic
knockdown temperature and subsequently confirm this model by comparison to
empirically obtained knockdown temperatures from all 11 species. 5.
Characterisation of heat tolerance in laboratory settings is an important
tool in thermal biology, but more so if the measures correlate with the
environmental gradients that characterise the fundamental niche of the
species. Here we show that both static and dynamic assays were
characterised by strong correlations to precipitation of the driest month
and maximum temperature of the warmest month combined (R2=0.68-0.71). This
demonstrates that both assay types offer simple measures of heat tolerance
that are ecologically relevant for the tested drosophilids.