In the heat of the moment: including realistic thermal fluctuations
results in dramatically altered key population parameters’
Abstract
1. Temperature is commonly acknowledged as one of the primary forces
driving ectotherm vector populations, most notably by influencing
metabolic rates and survival. Although numerous experiments have shown
this for a wide variety of organisms, the vast majority has been
conducted at constant temperatures and changes therein, while
temperature is far from constant in nature, and includes seasonal and
diurnal cycles. As fluctuating temperatures have been described to
affect metabolic processes at (sub)cellular level, this calls for
studies evaluating the relative importance of temperature fluctuations
and the changes therein. 2. To gain insight in the effects of
temperature fluctuations on ectotherm development, survival, and
sex-ratio, we developed an inexpensive, easily reproducible, and
open-source, Arduino-based temperature control system, which emulates
natural sinusoidal fluctuations around the average temperature. We used
this novel setup to compare the effects of constant (mean) temperatures,
most commonly used in experiments, block schemes and natural sinusoidal
fluctuations as well as an extreme variant with twice its amplitude
using the cosmopolitan mosquito species Culex pipiens s.l. as a study
organism. 3. Our system accurately replicated the preprogrammed
temperature treatments under outdoor conditions, even more accurately
than traditional methods. While no effects were detected on survival and
sex-ratio within the ranges of variation evaluated, development was sped
up considerably by including temperature fluctuations, especially during
pupation, where development under constant temperatures took almost a
week (30%) longer than under natural fluctuations. Doubling the
amplitude further decreased development time by 1.5 days. 4. These
results highlight the importance of including (natural) oscillations in
experiments on ectotherm organisms – both aquatic and terrestrial –
that use temperature as a variable. Ultimately, these results have major
repercussions for downstream effects at larger scales that may be
studied with applications such as ecological niche models, disease risk
models and assessing ecosystem services that rely on ectotherm
organisms.