Wildfire and time since fire effects on length and asymmetry of Cicada orni (Cicadidae) nymphs

Abstract

The Mediterranean Basin has a long history of wildfires, thus many species have

coevolved with these disturbances. However, recent shifts in the fire regime could

threaten the resilience of Mediterranean ecosystems. Cicadas spend their entire nymph

stage belowground, feeding on xylem fluids from roots, emerging only to molt one last

time and become adults. This unique life cycle makes them important contributors to

ecosystem functioning both below and above ground, but it could also make them

vulnerable to root degradation due to fire disturbances. The aim of this study is to

investigate whether wildfires can be detrimental to the development of cicada nymphs

using body, wing, and foreleg length, as well as wing and foreleg asymmetry as

indicators of growth. We also analyzed how these traits vary across time since fire.

The research was conducted by photographing the final instar exuviae (i.e., the sheds

from the last molt that preserve nymph morphology) and measuring the length of body

structures using ImageJ software. A sample of 456 exuviae of Cicada orni males was

selected from burned and unburned sites at 5 different study areas in Spain and for 1, 2,

3, 6, and 11-12 years since fire. We analyzed the data using ANOVA, GLM, GLMM, and

Kruskal-Wallis tests.

We expected body, wing, and foreleg lengths to be shorter in burned sites, while

asymmetry would be lower in unburned sites. Moreover, we hypothesized that there

would be changes throughout the years since fire. Our results show a significantly longer

body, wing and foreleg length in unburned sites. However, only body length exhibited a

consistent post-fire temporal trend, increasing in the third year after the disturbance.

These parameters were also significantly influenced by the study area. The wing

asymmetry index was not significantly different between treatments and over time since

fire, whereas the foreleg asymmetry index showed a higher asymmetry in unburned sites

possibly due to an unknown stressor.

Our results suggest that cicada size is negatively affected by wildfires, probably caused

by nutritional constraints. Further research is needed to better understand the potential

correlation with time since fire and the effects on asymmetry

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