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Gall-inducing cynipid community composition differences among seven localities, using the non-metric multidimensional scaling (NMDS). Each point is a two-dimensional (axis 1 and axis 2) representation of gall-inducing cynipid species composition (10 points per locality). Distances between points reflect a dissimilarity matrix created using the Bray–Curtis dissimilarity coefficient (Faith et al. 1987). Points that are close together have arthropod communities that are more similar in composition compared to points that are far apart (Stress values: 0.239. Final instability, 0.0001) were used in this analysis
Source publication
The galls induced by cynipids in host oaks have been proposed as biodiversity hotspots. They constitute support for the development of arthropod communities of great diversity and functional complexity that find in them nutrition and protection from external abiotic and biotic elements which change according to environmental gradients. We character...
Citations
... This means our augmented 'Enemy Guild Hypothesis' cannot be applied to many previously published studies on gall enemy communities [e.g. [66][67][68][69][70][71][72]; however, with the methodology outlined in this work, we hope that data collection moving forward in gall-associated communities can incorporate these crucial elements. ...
The evolution of diverse and novel morphological traits is poorly understood, especially how symbiotic interactions can drive these adaptations. The extreme diversity of external traits in insect-induced galls is currently explained by the Enemy Hypothesis, in which these traits have selective advantage in deterring parasitism. While previous tests of this hypothesis used only taxonomic identity, we argue that ecologically functional traits of enemies (i.e. mode of parasitism, larval development strategy) are a crucial addition. Here, we characterize parasitoid guild composition across four disparate gall systems and find consistent patterns of association between enemy guild and gall morphology. Specifically, galls with a longer average larva-to-surface distance host a significantly higher proportion of enemies with a distinct combination of functional traits (i.e. ectoparasitic, idiobiont, elongate ovipositor). Our results support the Enemy Hypothesis and highlight the importance of species ecology in examining insect communities and the evolution of novel defensive characters.
The action of natural enemies within a model tri‐trophic system, such as oak cynipid communities, can provide valuable insight into the mechanisms underlying the variation in gall inducer diversity across geographic gradients. Two hypotheses were formulated: (1) The diversity and abundance patterns of cynipid gall wasps, their parasitoids and inquilines differ between high‐ and low‐altitude habitats. (2) Parasitoids and inquilines are involved in mechanisms that influence the abundance patterns of gall wasps. In order to test these hypotheses, we established a study site at various altitudes in the northeastern region of Algeria, selecting three localities: Bouzizi, Ghora and Mechrouha. In each of these localities, two distinct habitats were identified: one located at a lower altitude and the other at a higher altitude. Bud and acorn galls on Quercus faginea were collected, and the insects that emerged from these galls were then identified. The study showed that gall wasps had markedly greater abundance, species richness and diversity in low‐altitude habitats. In contrast, parasitoids showed significantly higher abundance, species richness and diversity in high‐altitude habitats. Conversely, there is no significant difference in the abundance and diversity of inquiline species between high and low altitudes. The rates of parasitism and inquilinism escalated at elevated elevations but diminished at lower altitudes. A negative correlation was seen between the parasitism rate and the gall wasp population ( r = 0.87, r ² = 0.77, p < 0.001), as well as between the inquilinism rate and the gall wasp populations ( r = 0.86, r ² = 0.75, p < 0.001). The results presented in this study confirm the involvement of parasitoids and inquilines in the mechanisms that influence the abundance patterns of gall wasps through their varying pressures between high‐ and low‐elevation habitats.
One method to study the impact of climate change on host-parasitoid relationships is to compare populations along geographical gradients in latitude, altitude or longitude. Indeed, temperatures, which vary along geographic gradients directly shape the life traits of parasitoids and indirectly shift their populations through trophic interactions with hosts and plants. We explored the pros and cons of using these comparisons along gradients. We highlighted that the longitudinal gradients, although understudied, are well correlated to winter warming and summer heat waves and we draw attention to the impact of the increase in extreme events, which will probably be the determining parameters of the effect of climate change on host-parasitoid relationships.
