Coprophagy in detritivores: methodological design for feeding studies in terrestrial isopods (Crustacea, Isopoda, Oniscidea)

ABSTRACT Isopods consume feces in laboratory conditions. We investigated the effects of coprophagy on food consumption and assimilation and on isopod biomass to determine the best methodological design for feeding performance experiments. We used three species of isopods representing different eco-morphological groups and two leaves with different nitrogen content. We tested three treatments: (1) free access to feces; (2) periodic removal of feces and (3) net acting as a barrier to the feces. We did not find significant difference in any isopod or leaf species for consumption rate. Assimilation efficiency did not differ significantly for any isopod or leaf either. Only growth rate was significantly different, but only for the species Atlantoscia floridana (Van Name, 1940) with the leaf Machaerium stipitatum, and it may be due to the short duration of experiments and the isopods’ susceptibility to environmental changes. Thus, we recommend the treatment access to study consumption and growth rates since it does not require any special material or extra time. If the focus is assimilation efficiency, we suggest the treatment removal because it provides more accurate values. Furthermore, more fragile species such as A. floridana require larger sample number and/or longer experiment duration for more reliable data analyses.摘要 等足类动物（Isopods）在实验室条件下存在食粪行为。本研究旨在明确取食性能实验的最优方法学设计，探究了食粪行为对等足类动物取食、同化作用及生物量的影响。实验选用隶属于不同生态形态类群的3种等足类动物以及2种氮含量存在差异的植物叶片作为材料，设置3组处理：（1）可自由接触粪便；（2）定期清除粪便；（3）以网具作为粪便阻隔屏障。结果显示，无论针对何种等足类动物或植物叶片，其取食速率均未出现显著组间差异；各类群的同化效率亦无显著组间差异。仅生长速率存在显著差异，且该差异仅见于佛罗里达等足虫（Atlantoscia floridana (Van Name, 1940)）取食Machaerium stipitatum叶片的实验组，该结果或与实验周期较短以及等足类动物对环境变化的敏感性有关。据此，若研究目标为取食速率与生长速率，推荐采用自由接触粪便的处理方案，因其无需特殊实验材料或额外耗时；若聚焦于同化效率测定，则建议选用定期清除粪便的处理组，该方案可获得更为精准的数值。此外，诸如佛罗里达等足虫这类脆弱物种，需增大样本量和/或延长实验周期，以获取更可靠的数据分析结果。