Quantifying physiological and behavioral differences in caddisfly larvae

Abstract

The Mexican Cut Nature Preserve supports diverse populations of caddisflies (Limnephilus externus), whose larvae construct protective cases from environmental debris. Case morphology varies with ecological pressures, but gaps remain in understanding how intra- and interspecific interactions influence case size across larval development. This study quantified case size differences between permanent (high salamander density, HSD) and semi-permanent (low salamander density, LSD) ponds and assessed behavioral adaptations under controlled densities. Field surveys measured case sizes across larval instars via standardized net sweeps and photographic analysis. A semi-experimental design reared larvae from HSD and LSD sites at low (3 larvae/tank) and high (15 larvae/tank) densities to evaluate case construction and behavior. Contrary to predictions, larvae from LSD ponds constructed significantly larger cases across all instars (third: LSD 0.68±0.02 cm² vs HSD 0.52±0.03 cm², p<0.001; fifth: LSD 1.45±0.08 cm² vs HSD 1.82±0.07 cm², p<0.001). Experimentally, high density universally reduced case size (32% reduction, p=0.001), though LSD larvae maintained larger minimal cases. Behaviorally, HSD larvae showed threefold higher case-grazing probability (OR=2.85, p=0.003) and greater density- dependent increases in case-related behaviors. These results demonstrate that case size reflects integrated responses to predator identity (e.g., Dytiscus beetles in LSD ponds), intraspecific competition, and source-population adaptations, with behavioral plasticity compensating for structural defenses in HSD environments. Romo-Ornelas |2

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References (10)

1 in Knowledge Hub, 9 external