The underestimated role of temperature–oxygen relationship in large‐scale studies on size‐to‐temperature response

Abstract

The observation that ectotherm size decreases with increasing temperature (temperature‐size rule; TSR) has been widely supported. This phenomenon intrigues researchers because neither its adaptive role nor the conditions under which it is realized are well defined. In light of recent theoretical and empirical studies, oxygen availability is an important candidate for understanding the adaptive role behind TSR. However, this hypothesis is still undervalued in TSR studies at the geographical level. We reanalyzed previously published data about the TSR pattern in diatoms sampled from Icelandic geothermal streams, which concluded that diatoms were an exception to the TSR. Our goal was to incorporate oxygen as a factor in the analysis and to examine whether this approach would change the results. Specifically, we expected that the strength of size response to cold temperatures would be different than the strength of response to hot temperatures, where the oxygen limitation is strongest. By conducting a regression analysis for size response at the community level, we found that diatoms from cold, well‐oxygenated streams showed no size‐to‐temperature response, those from intermediate temperature and oxygen conditions showed reverse TSR, and diatoms from warm, poorly oxygenated streams showed significant TSR. We also distinguished the roles of oxygen and nutrition in TSR. Oxygen is a driving factor, while nutrition is an important factor that should be controlled for. Our results show that if the geographical or global patterns of TSR are to be understood, oxygen should be included in the studies. This argument is important especially for predicting the size response of ectotherms facing climate warming.

Body size variability across habitats in theBrachionus plicatiliscryptic species complex

“…Therefore, in our study system, salinity (indirectly) and pH (directly) affected the response 366 of size to temperature, causing the absence of the expected decrease with increasing temperature. 367 Intriguingly, under such conditions, the rotifer species exhibited smaller sizes at lower oxygen 368 levels, as predicted by the theory, confirming the crucial role of the oxygen concentration in 369 driving body size patterns (Walczyńska & Sobczyk, 2017). The only exception to the "when 370 there is less oxygen, grow smaller" rule was observed for the smallest species, B. rotundiformis.…”

“…The lack of a relationship between temperature and oxygen seems to be sufficient to 292 explain the lack of an influence of temperature or oxygen on rotifer body size that was found 293 when individuals of the different species were merged. The importance of the link between 294 temperature and the oxygen concentration in modulating species size was previously shown for 295 Icelandic diatoms (Walczyńska & Sobczyk, 2017). Sur.…”

The temperature‐size rule in Daphnia magna across different genetic lines and ontogenetic stages: Multiple patterns and mechanisms

“…In support of a role of oxygen in setting body size limits, we previously showed that the TSR in a freshwater isopod crustacean was manifested most strongly under hypoxic conditions, whereas hyperoxia could reverse the TSR (Hoefnagel & Verberk, ). Recent studies have also highlighted the potential role of oxygen in setting body size limits (DeLong et al., ; van Rijn, Buba, DeLong, Kiflawi, & Belmaker, ; Walczyńska & Sobczyk, ) shifting the focus toward explanations for a TSR to asymptotic size. von Bertalanffy's model provides an explanation for smaller asymptotic size in warmer environments, but does not make explicit predictions about the effect of temperature on size at maturity.…”

Bioassessment of Mandakini River with the help of aquatic macroinvertebrates in the vicinity of Kedarnath Wildlife Sanctuary

“…The reason for such fluctuation is that during summers (pre-monsoon), the river velocity, temperature, rainfall, and anthropogenic activities are higher as compared to post-monsoon. High temperature is inversely proportional to the dissolved oxygen (Connolly et al 2004;Buckup et al 2007;Walczyńska and Sobczyk 2017), which might results in a decrease in the diversity of macroinvertebrates in that region. The results correlate with the studies wherein the anthropogenic and other environmental factors are responsible for the statistically significant difference in macroinvertebrates assemblage seasonally (Kang and King 2013;Sartori et al 2014;Goswami and Singh 2017;Roy and Homechaudhuri 2017;Verdura et al 2019;Xue et al 2019).…”