Abstract
For insects, choosing a favorable oviposition site is a type of parental care, as far as it increases the fitness of its offspring. Niche theory predicts that crickets should show a bell-shaped oviposition response to substrate moisture. However, lab experiments with mole crickets showed a linear oviposition response to substrate moisture. Studies with the house cricket Acheta domesticus also showed a linear juvenile body growth response to water availability, thus adult ovipositing females should respond positively to substrate moisture. We used a field experiment to evaluate the relationship between oviposition preference and substrate moisture in forest litter-dwelling cricket species. We also evaluated oviposition responses to substrate moisture level in Ubiquepuella telytokous, the most abundant litter cricket species in our study area, using a laboratory study. We offered cotton substrate for oviposition which varied in substrate moisture level from zero (i.e., dry) to maximum water absorption capacity. We used two complementary metrics to evaluate oviposition preference: (i) presence or absence of eggs in each sampling unit as binary response variable, and (ii) number of eggs oviposited per sampling unit as count response variable. To test for non-linear responses, we adjusted generalized additive models (GAMM) with mixed effects. We found that both cricket oviposition probability and effort (i.e., number of eggs laid) increased linearly with substrate moisture in the field experiment, and for U. telytokous in the lab experiment. We discarded any non-linear responses. Our results demonstrate the importance of substrate moisture as an ecological niche dimension for litter crickets. This work bolsters knowledge of litter cricket life history association with moisture, and suggests that litter crickets may be particularly threatened by changes in climate that favor habitat drying.
Highlights
The distribution of organisms in an environment is influenced simultaneously by top-down and bottom-up control mechanisms [1, 2], synthesized in the concepts of the ecological niche
Through manipulative experiments in field and lab, the preference of cricket oviposition in relation to substrate moisture, testing two alternative hypotheses: (i) oviposition preference shows a non-linear response to substrate moisture, following classical niche theory/norm of reaction predictions; or (ii) oviposition increases linearly with substrate moisture, following available evidence found for other cricket species
The three highest moisture levels accumulated 33 eggs (80%), while the highest three moisture levels accumulated seven eggs (17%); the four substrates with lowest moisture levels contained only a single egg (2%), which was deposited on the substrate treatment with the second-lowest moisture level
Summary
The distribution of organisms in an environment is influenced simultaneously by top-down and bottom-up control mechanisms [1, 2], synthesized in the concepts of the ecological niche. Females should prefer to oviposit in sites where egg predation risk [8], desiccation, and freezing [9, 10] is low, sites with temperatures within the optimal range for egg hatching of that species [8], and sites with adequate resource availability for the developing eggs and emerged juveniles [11]. These habitat features positively influence eclosion rates [12] and offspring survival probability [5, 13] and net reproductive rates [14]
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