Abstract
BackgroundNutrients such as protein may be actively sought by foraging animals. Many predators exhibit foraging plasticity, but how their foraging strategies are affected when faced with nutrient deprivation is largely unknown. In spiders, the assimilation of protein into silk may be in conflict with somatic processes so we predicted web building to be affected under protein depletion.Methodology/Principal FindingsTo assess the influence of protein intake on foraging plasticity we fed the orb-web spiders Argiope aemula and Cyclosa mulmeinensis high, low or no protein solutions over 10 days and allowed them to build webs. We compared post-feeding web architectural components and major ampullate (MA) silk amino acid compositions. We found that the number of radii in webs increased in both species when fed high protein solutions. Mesh size increased in A. aemula when fed a high protein solution. MA silk proline and alanine compositions varied in each species with contrasting variations in alanine between the two species. Glycine compositions only varied in C. mulmeinensis silk. No spiders significantly lost or gained mass on any feeding treatment, so they did not sacrifice somatic maintenance for amino acid investment in silk.Conclusions/SignificanceOur results show that the amount of protein taken in significantly affects the foraging decisions of trap-building predators, such as orb web spiders. Nevertheless, the subtle differences found between species in the association between protein intake, the amino acids invested in silk and web architectural plasticity show that the influence of protein deprivation on specific foraging strategies differs among different spiders.
Highlights
Foraging models predict that animals should maximize their energetic gain from the environment while minimizing energetic output [1]
While trap plasticity has been well studied in spiders in relation to variations in prey type and quantity [11,13,14,15,16], how nutrient deprivation influences foraging plasticity in trap building predators is not well understood because it is difficult to decouple the influence of nutrients from the multitude of other prey attributes, e.g. size, sensory modalities, that may act as cues to induce plasticity [11,12]
In Cyclosa mulmeinensis webs, the number of radii differed between treatments, with spiders fed the high protein (HP) treatment having significantly more radii than both the low protein (LP) and no protein (NP) treatments (Table 1; Tukey’s HSD; P,0.05; Fig. 1E)
Summary
Foraging models predict that animals should maximize their energetic gain from the environment while minimizing energetic output [1]. While trap plasticity has been well studied in spiders in relation to variations in prey type and quantity [11,13,14,15,16], how nutrient deprivation influences foraging plasticity in trap building predators is not well understood because it is difficult to decouple the influence of nutrients from the multitude of other prey attributes, e.g. size, sensory modalities, that may act as cues to induce plasticity [11,12] Nutrients such as protein may be actively sought by foraging animals. The assimilation of protein into silk may be in conflict with somatic processes so we predicted web building to be affected under protein depletion
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