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<p>The size structure of the cladoceran <i>Bosmina</i> spp. (Crustacea: Cladocera: Bosminidae) is commonly used to reconstruct predation dynamics in sediment cores through temporal variation in mucro (tail spine) length. Longer mucros act as a defense mechanism against invertebrate predators, while shorter mucros may indicate that invertebrate predators are suppressed by planktivorous fish. However, paleolimnological interpretations are limited by variability in measured mucro lengths which arises as sedimentary <i>Bosmina</i> spp. remains represent different growth stages that often show differing predation responses. We present a simple statistical approach to improve the use of measurements from sedimentary <i>Bosmina</i> spp. remains by adjusting for the confounding influence of carapace length (as a proxy for body size). We use 5891 measured individuals from eight sediment cores representing five freshwater systems from across Canada to characterize the allometry (scaling relationship between morphological variables) for <i>Bosmina</i> spp. subfossil remains. Overall <i>Bosmina</i> spp. mucro length was positively related to carapace length (standardized major axis regression r<sup>2</sup> = 0.25, <i>p</i> &lt; 0.001). However, the direction of this relationship differed significantly between lakes (<i>p</i> &lt; 0.001), with two lakes showing a negative allometric relationship (mucro length decreasing with size). This may reflect differing predation regimes, as the lakes with negative allometric relationships currently support piscivorous fisheries. For each sediment core, modelling mucro length as a function of carapace length and sample interval explained significantly more variation than modelling either of the predictors individually. To improve visualization of temporal trends, we modelled mucro lengths and 95% confidence intervals for each sediment-core interval while holding carapace length constant. In the three sediment cores selected to demonstrate this method, average error was reduced by 39.5, 72.5, and 76.4% respectively, and temporal change in modelled mucro lengths corresponded with known historic impacts (e.g., eutrophication, invasive species, aerial insecticide application). Overall, this approach clarifies temporal trends in mucro length to assist paleolimnological reconstructions and allows a better understanding of the long-term consequences of environmental stressors on predation dynamics.</p>

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Allometry improves water flea (Crustacea: Cladocera) size-structure interpretations in lake sediments

  • 期刊论文

  • 发表日期：

    2025年6月10日

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  • Isaac Armstrong,
  • Abbie Jones,
  • Jamie A. Would,
  • Emma L. Graves,
  • Annie J. Dysart,
  • Joshua Kurek,
  • Brian F. Cumming

摘要

The size structure of the cladoceran Bosmina spp. (Crustacea: Cladocera: Bosminidae) is commonly used to reconstruct predation dynamics in sediment cores through temporal variation in mucro (tail spine) length. Longer mucros act as a defense mechanism against invertebrate predators, while shorter mucros may indicate that invertebrate predators are suppressed by planktivorous fish. However, paleolimnological interpretations are limited by variability in measured mucro lengths which arises as sedimentary Bosmina spp. remains represent different growth stages that often show differing predation responses. We present a simple statistical approach to improve the use of measurements from sedimentary Bosmina spp. remains by adjusting for the confounding influence of carapace length (as a proxy for body size). We use 5891 measured individuals from eight sediment cores representing five freshwater systems from across Canada to characterize the allometry (scaling relationship between morphological variables) for Bosmina spp. subfossil remains. Overall Bosmina spp. mucro length was positively related to carapace length (standardized major axis regression r2 = 0.25, p < 0.001). However, the direction of this relationship differed significantly between lakes (p < 0.001), with two lakes showing a negative allometric relationship (mucro length decreasing with size). This may reflect differing predation regimes, as the lakes with negative allometric relationships currently support piscivorous fisheries. For each sediment core, modelling mucro length as a function of carapace length and sample interval explained significantly more variation than modelling either of the predictors individually. To improve visualization of temporal trends, we modelled mucro lengths and 95% confidence intervals for each sediment-core interval while holding carapace length constant. In the three sediment cores selected to demonstrate this method, average error was reduced by 39.5, 72.5, and 76.4% respectively, and temporal change in modelled mucro lengths corresponded with known historic impacts (e.g., eutrophication, invasive species, aerial insecticide application). Overall, this approach clarifies temporal trends in mucro length to assist paleolimnological reconstructions and allows a better understanding of the long-term consequences of environmental stressors on predation dynamics.