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Map of sampling population of gall-inducing cynipids and their associated arthropod communities on Quercus rugosa located at the Trans-Mexican Vocanic Belt. The localities are represented by numbers, 1 = Coajomulco, 2 = Tlaquetzaltitla, 3 = Mineral del Monte, 4 = Sierra de Guadalupe, 5 = Mineral El Chico, 6 = Calcahualco, and 7 = Omitlán de Juarez
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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
... It is estimated that the host plant Q. rugosa houses at least 52 species of cynipids [37,43,95,96], making it the oak species with the most significant number of gall-inducing species. Therefore, in this study, we documented 46% of the cynipid species recorded for Q. rugosa. ...
Analyzing the nutritional and defensive chemistry of Quercus rugosa provides insight into gall wasp interactions. Quercus rugosa is the most widely distributed white oak species in Mexico. It is the dominant canopy species in its geographic distribution range and has the largest number of associated gall wasp species (Cynipidae: Cynipini). Our main aims were to characterize the nutritional and defensive chemistry of Q. rugosa leaves and determine whether this chemistry differed between leaves with and without galls. We evaluated 60 trees from six populations of Q. rugosa in central Mexico. For each tree, we analyzed the nutritional chemistry (nitrogen, phosphorus, carbon, and carbon/nitrogen ratio) and defensive chemistry (secondary metabolites). Also, we characterized the community of cynipids in the leaf tissue of each tree. We documented 18 cynipid species, and the cynipid communities differed in composition among localities. We recorded the presence of a total of ten phenolics. The composition of nutritional and defensive chemicals differed significantly between leaves with and without galls in each locality. The nutritional and defensive chemical compounds of Q. rugosa were influenced by their associated cynipids. Our results suggest that gall-inducing cynipids influence the production of secondary metabolites in leaves with galls through the reassignment of nutritional compounds by the hosts.
... 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.
