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Exploring reversibility and contrasting patterns in temperature-size relationships across spatial and temporal scales using subfossil chironomids

Belle, Simon1; Matera, Tymoteusz2; Liiv, Merlin3; Stivrins, Normunds4; Poska, Anneli3; Heinsalu, Atko3; McKie, Brendan1

Published Jul 01, 2025 on Dryad. https://doi.org/10.5061/dryad.2280gb64w

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Jul 01, 2025 version files 11.29 KB

Abstract

The extent to which different magnitudes and directions of temperature fluctuations explain long-term trends in aquatic invertebrate body size in nature is largely unknown. Using elevation gradients and paleolimnological reconstructions, we tested the hypotheses that variations in subfossil chironomid (non-biting midges) head capsules (HC) will covary with temperature changes, with opposite morphometric changes occurring during warming and cooling phases, and that body size variation can be modified by other environmental conditions unassociated with temperature variations. Results indicated that the effects of increasing temperatures on chironomid HC size were reversed when temperatures decreased, with both warming and cooling producing similar effect sizes, corresponding to a change in HC length of ~3% per 1°C. Additionally, our results showed that other environmental drivers can mask temperature effects on chironomid HC sizes. Specifically, we found that bottom water oxygen concentration was negatively associated with HC lengths of Chironomus anthracinus-type. We hypothesize that this pattern is driven by prolonged larval development in oxygen-depleted lakes and/or changes in basal food sources used by chironomid larvae, ultimately affecting their final body size. To gain a better understanding of aquatic insect size variation over long timescales, it is essential to uncover the underlying mechanisms that control their body size, as these factors may either enhance or compound the temperature-size relationship.