Rozanski Sarah R, May Emily M, El-Sabaawi Rana W
Department of Biology University of Victoria Victoria British Columbia Canada.
Ecol Evol. 2025 Sep 16;15(9):e71920. doi: 10.1002/ece3.71920. eCollection 2025 Sep.
In freshwater ecosystems, fish play a critical role in regulating the standing stock and turnover rates of biologically important elements such as nitrogen (N) and phosphorus (P). They do so by assimilating dietary nutrients, storing them, and recycling a subset as liquid (excreta) or solid (egesta) waste. The elemental composition of fish diets, bodies and waste varies considerably both within and between species. However, the mechanistic link between intraspecific variation in particular traits, such as bone investment, and variation in waste elemental composition and release rates remains poorly understood. Using the framework of Ecological Stoichiometry, we investigate how phenotypic traits impact nutrient storage and recycling. The threespine stickleback serves as an ideal model because it has undergone significant phenotypic diversification following its relatively recent colonisation of freshwater environments. Specifically, we examine variation in P-rich bony armour along a river continuum, where estuarine sticklebacks are typically heavily armoured (fully plated), and freshwater sticklebacks have less armour (low plated). We collected sticklebacks from five sites along the Sooke River, ranging from the estuary to the upper reaches, and measured their excretion rates in the field. We quantified the P content of their bodies, diet, egesta and excreted wastes, and the N:P of their bodies and excreta. Our results revealed substantial variation in body P content (2.2%-5.9%), with fully plated fish exhibiting higher body %P and lower body N:P. Dietary P was highly variable, with fully plated fish showing marginally higher dietary %P. Notably, P excretion rates were positively correlated with body %P but not diet %P, suggesting that contrary to predictions, bone content may decrease P demand. This study demonstrates that differences in stickleback bone investment have led to meaningful differences in nutrient storage and recycling.
在淡水生态系统中，鱼类在调节氮（N）和磷（P）等生物重要元素的存量和周转率方面发挥着关键作用。它们通过吸收膳食营养、储存营养，并将一部分营养以液体（排泄物）或固体（粪便）废物的形式循环利用来实现这一点。鱼类的饮食、身体和废物的元素组成在物种内部和物种之间都有很大差异。然而，特定性状（如骨投入）的种内变异与废物元素组成和释放率变异之间的机制联系仍知之甚少。利用生态化学计量学框架，我们研究了表型性状如何影响营养储存和循环利用。三刺鱼是一个理想的模型，因为自从它相对较新地定殖于淡水环境后，经历了显著的表型多样化。具体而言，我们沿着河流连续体研究了富含磷的骨甲的变异，河口三刺鱼通常骨甲厚重（全板），而淡水三刺鱼的骨甲较少（低板）。我们从索科河沿岸的五个地点收集了三刺鱼，范围从河口到上游，并在野外测量了它们的排泄率。我们量化了它们身体、饮食、粪便和排泄废物中的磷含量，以及它们身体和排泄物的氮磷比。我们的结果显示身体磷含量有很大差异（2.2% - 5.9%），全板鱼的身体磷百分比更高，身体氮磷比更低。饮食中的磷变化很大，全板鱼的饮食磷百分比略高。值得注意的是，磷排泄率与身体磷百分比呈正相关，但与饮食磷百分比无关，这表明与预测相反，骨含量可能会降低磷需求。这项研究表明，三刺鱼骨投入的差异导致了营养储存和循环利用方面有意义的差异。
