Resource-allocation tradeoffs in caddisflies facing multiple stressors.

Francisco Correa‐Araneda,Alan Mosele Tonin,Roberto T Abdala‐Díaz,Luz Boyero,Ana Basaguren

doi:10.1002/ece3.3094

Abstract

The replacement of native forests by exotic tree monocultures, such as those of Eucalyptus, decreases the quality of leaf litter inputs to streams and often reduces riparian cover, which can elevate water temperature. The combined effects of these stressors on the survival and performance of detritivores may be important, as detritivore species loss leads to reduced litter breakdown, a key ecosystem process. Potential loss of cased caddisfly larvae is of particular concern because they are the predominant detritivores in many streams, they are sensitive to warming, and they expend energy on building and carrying their cases, which may be an added burden under times of stress. In a microcosm experiment, we tested whether (i) poor‐quality Eucalyptus globulus litter impaired case construction by larvae of Sericostoma pyrenaicum (due to preferential allocation of the scarcer available energy to larval fitness) compared to high‐quality Alnus glutinosa litter; (ii) whether this effect was enhanced by higher temperatures (15 vs. 10°C) resulting in faster metabolism and greater energy expenditure; but (iii) reduced in the presence of chemical cues from a predatory fish (due to greater investment in more protective cases). We found that Eucalyptus had lethal and sublethal effects on larval caddisflies, increasing mortality, reducing growth, and impairing case construction, compared to larvae fed Alnus. Temperature did not reinforce the effects of exotic litter on case construction, but predator chemical cues triggered the construction of more protective cases (i.e., longer and better cemented) despite the lower resource quality, providing evidence for environmentally mediated resource‐allocation tradeoffs.

Highlights

Many inland waters are subject to multiple anthropogenic stressors (Dudgeon, 2010), which negatively affect biodiversity and cause far-reaching impacts on ecosystems (Hooper et al, 2012; Vörösmarty et al, 2010)
Of particular concern are larvae of some insect groups such as caddisflies (Trichoptera), because (i) they generally are the dominant leaf-feeding detritivores in streams (Boyero et al, 2011a); (ii) they are sensitive to warming, being evolutionarily adapted to cool waters (Boyero et al, 2012); and (iii) their energetic requirements are high because they construct and carry a portable case, which offers protection from predators (Otto & Svenson, 1980) but involves substantial energy expenditure (Otto, 1974)
The experiment was undertaken in microcosms, which consisted of glass jars containing a mixture (50:50) of dechlorinated tap water and filtered (50 μm) stream water (350 ml), sand collected from the stream substrate and incinerated (600°C, 4 hr), and leaf litter (0.4 g ± 0.006 SD dry mass) of either Eucalyptus or Alnus that had been previously leached for 24 hr in separate jars

Summary

Introduction

Many inland waters are subject to multiple anthropogenic stressors (Dudgeon, 2010), which negatively affect biodiversity and cause far-reaching impacts on ecosystems (Hooper et al, 2012; Vörösmarty et al, 2010). Reduced litter quality and rising temperature are known to have synergistic effects on the performance of some organisms that are key processors of leaf litter in streams (i.e., leaf-feeding detritivores) (Correa-Araneda et al, 2015; Ferreira, GonçAlves, Godbold, & Canhoto, 2010). In these ecosystems, where food webs often are detritus-based (Wallace, Eggert, Meyer, & Webster, 1997), the impacts of environmental changes on the survival and performance of detritivores are very important because the loss of detritivore species directly impacts key ecosystem processes (Gessner et al, 2010). Of particular concern are larvae of some insect groups such as caddisflies (Trichoptera), because (i) they generally are the dominant leaf-feeding detritivores in streams (Boyero et al, 2011a); (ii) they are sensitive to warming, being evolutionarily adapted to cool waters (Boyero et al, 2012); and (iii) their energetic requirements are high because they construct and carry a portable case, which offers protection from predators (Otto & Svenson, 1980) but involves substantial energy expenditure (Otto, 1974)

Methods

Results

Conclusion