Abstract
Life histories of species may be shaped by nutritional limitations posed on populations. Yet, populations contain individuals that differ according to sex and life stage, each of which having different nutritional demands and experiencing specific limitations. We studied patterns of resource assimilation, allocation and excretion during the growth of the solitary bee Osmia bicornis (two sexes) under natural conditions. Adopting an ecological perspective, we assert that organisms ingest mutable organic molecules that are transformed during physiological processes and that the immutable atoms of the chemical elements composing these molecules may be allocated to specific functions, thereby influencing organismal fitness and life history. Therefore, using the framework of ecological stoichiometry, we investigated the multielemental (C, N, S, P, K, Na, Ca, Mg, Fe, Zn, Mn, Cu) compositions of six components of the bee elemental budget: food (pollen), eggs, pupae, adults, cocoons and excreta. The sexes differed fundamentally in the assimilation and allocation of acquired atoms, elemental phenotypes, and stoichiometric niches for all six components. Phosphorus, which supports larval growth, was allocated mainly (55–75%) to the cocoon after larval development was complete. Additionally, the majority (60–99%) of the Mn, Ca, Mg and Zn acquired during larval development was allocated to the cocoon, probably influencing bee fitness by conferring protection. We conclude that for holometabolous insects, considering only the chemical composition of the adult body within the context of nutritional ecology does not provide a complete picture. Low ratios of C to other nutrients, low N:P and high Na concentrations in excreta and cocoons may be important for local-scale nutrient cycling. Limited access to specific nutritional elements may hinder bee development in a sex-dependent manner, and N and P limitations, commonly considered elsewhere, may not play important roles in O. bicornis. Sexual dimorphism in nutritional limitations due to nutrient scarcity during the larval stage may influence bee population function and should be considered in bee conservation efforts.
Highlights
Life histories of species may be shaped by nutritional limitations posed on populations
The challenges appear even more complex if we consider that the relative importance of each type of supply can shift throughout life; e.g., compared to energetically limited adults, growing juveniles can experience severe limitations imposed by limited access to body-building m atter[6,7]
We obtained the overall picture of the elemental budget by analyzing all the data together with a PERMANOVA followed by a principal component analysis (PCA)
Summary
Life histories of species may be shaped by nutritional limitations posed on populations. We assert that organisms ingest mutable organic molecules that are transformed during physiological processes and that the immutable atoms of the chemical elements composing these molecules may be allocated to specific functions, thereby influencing organismal fitness and life history. We can predict that a match between the elemental ratios of an organism’s body and its food has a fundamental impact on fitness-related organismal functions[15,16,17] This match could have especially pronounced fitness consequences if the nutritional quality of resources obtained by an organism at the juvenile stage strongly determines its future life history characteristics during the adult s tage[6,7]. Processes involved in life-history evolution and population dynamics may be sex-specific, leading to different nutritional limitations for each s ex[17,22]
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