Stoichiometric implications of a biphasic life cycle

Abstract

Animals mediate flows of elements and energy in ecosystems through processes such as nutrient sequestration in body tissues, and mineralization through excretion. For taxa with biphasic life cycles, the dramatic shifts in anatomy and physiology that occur during ontogeny are expected to be accompanied by changes in body and excreta stoichiometry, but remain little-explored, especially in vertebrates. Here we tested stoichiometric hypotheses related to the bodies and excreta of the wood frog (Lithobates sylvaticus) across life stages and during larval development. Per-capita rates of nitrogen (N) and phosphorus (P) excretion varied widely during larval ontogeny, followed unimodal patterns, and peaked midway through development (Taylor-Kollros stages XV and XII, respectively). Larval mass did not increase steadily during development but peaked at stage XVII and declined until the termination of the experiment at stage XXII. Mass-specific N and P excretion rates of the larvae decreased exponentially during development. When coupled with population-biomass estimates, population-level excretion rates were greatest at stages VIII-X. Percent carbon (C), N, and C:N of body tissue showed weak trends across major life stages; body P and C:P, however, increased sixfold during development from egg to adult. Our results demonstrate that intraspecific ontogenic changes in nutrient contents of excretion and body tissues can be significant, and that N and P are not always excreted proportionally throughout life cycles. These results highlight the dynamic roles that species play in ecosystems, and how the morphological and physiological changes that accompany ontogeny can influence ecosystem-level processes.

Does the Growth Rate Hypothesis Apply across Temperatures? Variation in the Growth Rate and Body Phosphorus of Neotropical Benthic Grazers

“…Variation in %P among populations of Rhinella and Thraulodes can lead to variation in P export to the surrounding terrestrial ecosystem. However, the biphasic life cycles of these organisms could lead to dramatic changes in the %P of adults (Tiegs et al, 2016), which we did not consider in this study. Rhinella metamorphs in particular may exhibit strong differences in %P from preossification tadpoles if bone density is unrelated to tadpole growth rates.…”

“…A further difference is that tadpoles at the lowland Frijolito site developed more rapidly and reached later stages by the end of our study (Table 2; Figure 6); thus, ontogenetic variation could explain variation in %P (Main et al, 1997;Pilati and Vanni, 2007). This is particularly true of developing Anurans, which exhibit extreme ontogenetic changes in %P as bone ossification begins at later Gosner stages (Tiegs et al, 2016). In the related European toad (Bufo bufo), tadpole bones begin ossification at Gosner stage 38 (Dunlap and Sanchiz, 1996).…”

“…Further, the storage of P by consumers can represent a substantial P sink in aquatic ecosystems, particularly when those consumers have biphasic life cycles and migrate to terrestrial ecosystems as adults (Vanni et al, 2013;Tiegs et al, 2016); thus, this finding has implications for ecosystem-scale fluxes of P in these streams. However, growth rate and %P of these grazers did vary among streams both in field collections and in our experiment; thus, it is important to discuss what may have driven this variation.…”

Understanding variation in salamander ionomes: A nutrient balance approach

“…This abstraction is useful because information on the elemental content of a species enables the application of mass-balance principles to make predictions about sequestration and excretion of elements, both of which have strong impacts on ecological dynamics (Reiners, 1986). Capps, Berven, & Tiegs, 2015;Tiegs, Berven, Carmack, & Capps, 2016;Villar-Argaiz, Medina-Sánchez, & Carrillo, 2002). In addition to species-level differences, it is apparent that there is considerable intraspecific variation in organismal elemental composition (Jeyasingh et al, 2014;Prater, Wagner, & Frost, 2017).…”

“…C, Ca, N, P and S;Capps et al, 2015;Tiegs et al, 2016;Luhring et al, 2017). Based on stoichiometric theory, we hypothesised that the ionomes of each species should vary due to differences in life-history and ontogeny, and we sought to identify linkages among elements, including those already known to vary significantly (i.e.…”