Widespread intraspecific organismal stoichiometry among populations of the Trinidadian guppy

Abstract

Summary1. Ecological stoichiometry expresses ecological interactions as the balance between multiple elements. It relates the ecological function of organisms to their elemental composition, or their organismal stoichiometry. Organismal stoichiometry is thought to reflect elemental investments in life history and morphology acting in concert with variability in abiotic or environmental conditions, but the relative contribution of these factors to natural variability in organismal stoichiometry is poorly understood. 2. We assessed the relative contribution of stream identity, predation, body size and sex to the organismal stoichiometry of guppies (Poecilia reticulata) in six streams in Trinidad. In this system, guppy life-history phenotype evolves in response to predation. Guppies adapted to highpredation (HP) pressure grow faster, mature earlier, produce fewer and smaller offspring and eat a higher-quality diet than guppies adapted to low-predation (LP) pressure. This pattern of lifehistory evolution is repeated in many rivers encompassing a wide range of abiotic conditions. 3. Organismal stoichiometry of guppies was widely variable, spanning up to $70% of the range of variability reported across freshwater fish taxa. Streams from where guppies were sampled were the most important predictor of organismal stoichiometry. In many cases, guppy populations from sites within the same stream varied as much as from sites in different streams. 4. Surprisingly, predation regime was a minor predictor of % C, C : P and C : N in female guppies, despite its strong correlation with life-history phenotype and other organismal traits in this species. Body size and sex were not significant predictors of organismal stoichiometry. 5. Guppies from HP sites were more stoichiometrically balanced with their diets than guppies from LP sites. The latter appeared to be more vulnerable to phosphorus limitation than the former, suggesting that dietary specialization associated with guppy life-history phenotype may have stoichiometric consequences that can affect guppy physiology and nutrient recycling. 6. Our findings suggest that local environmental conditions are a stronger predictor of organismal stoichiometry than organismal traits. We recommend that future work should explicitly consider correlations between organismal traits and organismal stoichiometry in the context of environmental heterogeneity.

Ontogenetic differences in Atlantic salmon phosphorus concentration and its implications for cross ecosystem fluxes

“…We were surprised that river explained only a small portion of variation in salmon %P because spatial differences in %P have been found in other fishes (Boros et al 2012, El-Sabaawi et al 2012. El-Sabaawi and colleagues (2012) found that the presence of limestone in watersheds had a greater influence on %P of Trinidadian guppies than did genetic lineage because limestone deposits have direct effects on the amount of P cycling in aquatic ecosystems and thus a different biogeochemical setting for juvenile growth.…”

“…However, work on other fishes has documented significant intraspecific variation in %P arising from sex, ontogeny, size, physical habitat, feeding history, and geographic location (Hendrixson et al 2007, McIntyre and Flecker 2010, El-Sabaawi et al 2012. The magnitude of variation in %P within salmonid species in the wild is unknown.…”

“…We chose to evaluate P dynamics because this element exhibits the highest intraand interspecific variation in fishes (Sterner and George 2000, Vanni et al 2002, El-Sabaawi et al 2012 and is commonly considered to be the dominant limiting nutrient in freshwater ecosystems. First, we quantified whole body %P of three life stages of Atlantic salmon from three populations inhabiting rivers of insular Newfoundland, Canada, to assess whether ontogeny and population can explain intraspecific variation in wild Atlantic salmon %P.…”

Divergence across diet, time and populations rules out parallel evolution in the gut microbiomes of Trinidadian guppies

“…Both field surveys were conducted during the dry seasons in 2010 and 2011, respectively, and took place in mountain streams in the Northern Range of Trinidad, West Indies (Supplementary Table 1). The 2010 field survey was carried out to assess gut bacterial diversity across streams and guppy populations; from 20 April through 2 May 2010, 40 Trinidadian guppies were collected from previously categorized HP and LP habitats El-Sabaawi et al, 2012) that tend to differ in a number of ecosystem characteristics, including canopy coverage and primary productivity (Grether et al, 2001). …”

Phosphorus body content in an herbivorous fish in environments with different trophic state

“…This ability of a heterotrophic organism to maintain its body elemental composition relatively constant, despite varying diets, is defined as homeostasis (Sterner and Elser, 2002). However, some studies have pointed out that in animal species organismal stoichiom etry may not be as constant as previously thought, so that consumers may not be strictly homeostatic (Hendrixson et al, 2007;Boros et al, 2012Boros et al, , 2015El-Sabaawi et al, 2012a;El-Sabaawi et al, 2012b;Benstead et al, 2014).…”