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<p>Whereas phenotypic plasticity via body size variation is widely recognized as a common response to warming, other drivers and mechanisms influencing body size in aquatic invertebrates remain incompletely understood. Here, we used laboratory experiments on <i>Chironomus riparius</i> to disentangle the effects of temperature (20, 22, and 24&#xa0;°C), food quality (eight food sources varying in quality), and intraspecific competition (high and low larval densities) on head capsule (HC) size across different larval instars. We found that both larval density and temperature influenced larval development time, with faster development observed at higher temperatures and lower densities. However, the expected temperature–size relationship (i.e., smaller HC at higher temperatures) was evident only under high-larval density conditions characterized by intense intraspecific competition for space and resources. These findings suggest that variation in development time alone does not fully explain the temperature–size relationship, and that density-dependent processes may also play an important role. In addition, variation in food source composition produced greater differences in chironomid HC size than the 4&#xa0;°C temperature increase applied in our experiment, underscoring the importance of resource quality as a driver of HC size variability. We also found a strong positive correlation between HC length in third- and fourth-instar larvae, suggesting that third-instar HC measurements provide a reliable proxy for final HC size and that the effects of food quality and temperature are already apparent at earlier developmental stages. Overall, our findings suggest that widely reported large-scale shifts in aquatic invertebrate body size cannot be fully explained by temperature alone.</p>

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Unravelling the influence of food quality, larval density, and temperature in shaping chironomid head capsule size in rearing experiments: ecological implications and future research needs

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月3日

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  • Jeanne Salenbier,
  • Peshmi Pabodha Balasooriya Vee Baddage,
  • Tymoteusz Matera,
  • Simon Belle

摘要

Whereas phenotypic plasticity via body size variation is widely recognized as a common response to warming, other drivers and mechanisms influencing body size in aquatic invertebrates remain incompletely understood. Here, we used laboratory experiments on Chironomus riparius to disentangle the effects of temperature (20, 22, and 24 °C), food quality (eight food sources varying in quality), and intraspecific competition (high and low larval densities) on head capsule (HC) size across different larval instars. We found that both larval density and temperature influenced larval development time, with faster development observed at higher temperatures and lower densities. However, the expected temperature–size relationship (i.e., smaller HC at higher temperatures) was evident only under high-larval density conditions characterized by intense intraspecific competition for space and resources. These findings suggest that variation in development time alone does not fully explain the temperature–size relationship, and that density-dependent processes may also play an important role. In addition, variation in food source composition produced greater differences in chironomid HC size than the 4 °C temperature increase applied in our experiment, underscoring the importance of resource quality as a driver of HC size variability. We also found a strong positive correlation between HC length in third- and fourth-instar larvae, suggesting that third-instar HC measurements provide a reliable proxy for final HC size and that the effects of food quality and temperature are already apparent at earlier developmental stages. Overall, our findings suggest that widely reported large-scale shifts in aquatic invertebrate body size cannot be fully explained by temperature alone.