Insect thermal limits in warm and perturbed habitats: Dragonflies and damselflies as study cases

Physiological traits explain the response of dung beetles to land use at local and regional scales

Physiological traits in insects are useful to understand their distribution at different spatial scales, their presence and abundance, and the use of different habitats. This study explored physiological parameters of dung beetles in two contrasting ecoregions of Argentina: Paranaense Forest and Dry Chaco. We capture dung beetles from both regions and habitats with different degrees of disturbance within each region, and performed lab experiments on metabolic rate and thermal tolerance. This study revealed that dung beetles inhabiting regions or habitats with higher temperatures (Dry Chaco and open pastures) showed greater temperature tolerance compared to those inhabiting regions or habitats with lower temperatures (Paranaense Forest and habitats preserving tree canopy). Furthermore, in the Dry Chaco, more species exploit open disturbed habitats, indicating less physiological sensitivity to temperature changes than dung beetles in the Paranaense Forest. This study is the first to compare dung beetle assemblages at both regional and local scales. The findings highlight the importance of preserving tree canopy in land use planning to mitigate microclimatic changes, especially in humid forests, to support dung beetle populations and their crucial ecosystem roles in the face of climate change.

Microhabitat selection and thermoregulation in amazonian dragonflies

Insect eco-physiological traits are important for understanding their distribution and habitat selection, especially in the face of land use change. We estimated the average temperature of the thoracic surface of 20 Odonata (Insecta) species and classified them into thermoregulation categories according to their preferences for sunny or shaded habitats to assess their temperature variation. We tested the influence of air temperature and six morphological metrics related to thorax and abdomen size. We expected that: (i) heliothermic species would have higher thoracic temperatures compared to thermoconformer species; (ii) Zygopterans, due to their smaller body size, are less efficient at maintaining a constant body temperature relative to the air when compared to anisopterans; (iii) thorax volume would cause an increase in Odonata thoracic temperature, and abdomen length would cause a decrease. The study was conducted at 18 Amazonian streams in Eastern Amazonia. We observed differences of 2.5 °C in thoracic temperature between heliothermic and thermoconformer species, as predicted in the first hypothesis. Both suborders, Zygoptera and Anisoptera, use different morphological and environmental variables to control temperature. While Zygoptera thoracic temperature oscillated near and below air temperature (-1.28 ± 0.62), Anisoptera maintained temperatures above air temperature (1.81 ± 1.96). Air temperature influenced only the increase in Zygoptera thoracic temperature, supporting our second hypothesis. The third hypothesis was corroborated for order Odonata, but partially for its suborders. Zygoptera thoracic temperature was only related to abdomen length, which was proportional to a temperature decrease. Anisoptera temperature showed a relationship only with thoracic metrics, especially thorax volume, which had a significant contribution to temperature increase. Despite the observed differences, which varied according to size, we noted exceptions in the thermal characteristics of some species that deviated from these predictions. Therefore, we emphasize the importance of considering the interaction of other eco-physiological aspects in dragonfly temperature regulation.

Amazonian Odonata Trait Bank

Discussion regarding the gaps of knowledge on Odonata is common in the literature. Such gaps are even greater when dealing with basic biological data for biodiverse environments like the Amazon Rainforest. Therefore, studies that address, classify, and standardize functional traits allow the elaboration of a wide range of ecological and evolutionary hypotheses. Moreover, such endeavors aid conservation and management planning by providing a better understanding of which functional traits are filtered or favored under environmental changes. Here, our main goal was to produce a database with 68 functional traits of 218 Odonata species that occur in the Brazilian Amazon. We extracted data on behavior, habit/habitat (larvae and adults), thermoregulation, and geographic distribution from 419 literature sources classified into different research areas. Moreover, we measured 22 morphological traits of approximately 2500 adults and categorized species distributions based on approximately 40,000 geographic records for the Americas. As a result, we provided a functional matrix and identified different functional patterns for the Odonata suborders, as well as a strong relationship between the different trait categories. For this reason, we recommend the selection of key traits that represent a set of functional variables, reducing the sampling effort. In conclusion, we detect and discuss gaps in the literature and suggest research to be developed with the present Amazonian Odonata Trait Bank (AMO-TB).

Climate Change Is Driving Shifts in Dragonfly Species Richness across Europe via Differential Dynamics of Taxonomic and Biogeographic Groups

Understanding how changes in species richness pattern correlate with range changes in different taxonomic and biogeographic groups is important for conservation because it allows for generalizations about which species are at greatest risk. Here, we assessed whether changes in species richness patterns result from generalized range shifts across taxonomic and biogeographic groups or from changes in specific subsets of species. Using data from 1988 and from 2010, we studied changes in distributional range of European dragonfly species, using outline distribution maps for all dragonflies combined and separately for taxonomic suborders (Zygoptera and Anisoptera) and biogeographic groups (Boreo-alpine, Eurasian, Mediterranean, and Tropical). The results demonstrated differing range dynamics for Zygoptera and Anisoptera, with Anisoptera driving local turnover in species richness to a greater extent than Zygoptera. The distributional range of Tropical and Mediterranean species had expanded to a much greater extent than that of Eurasian and Boreo-alpine species. Large-scale changes in species richness arose from several divergent, group-specific processes. Overall, local diversity especially declined in parts of southern and south-eastern Europe, reflecting local losses in multiple species rather than major range contractions among Mediterranean or Eurasian species. In fact, among the biogeographic groups, overall range declines were most prominent among Boreo-alpine species, highlighting the particular threat from climate change to this group.

Climate change will redefine taxonomic, functional, and phylogenetic diversity of Odonata in space and time

Climate change is rearranging the mosaic of biodiversity worldwide. These broad-scale species re-distributions affect the structure and composition of communities with a ripple effect on multiple biodiversity facets. Using European Odonata, we asked: i) how climate change will redefine taxonomic, phylogenetic, and functional diversity at European scales; ii) which traits will mediate species' response to global change; iii) whether this response will be phylogenetically conserved. Using stacked species distribution models, we forecast widespread latitudinal and altitudinal rearrangements in Odonata community composition determining broad turnovers in traits and evolutionary lineages. According to our phylogenetic regression models, only body size and flight period can be partly correlated with observed range shifts. In considering all primary facets of biodiversity, our results support the design of inclusive conservation strategies able to account for the diversity of species, the ecosystem services they provide, and the phylogenetic heritage they carry in a target ecosystem.

Environmental thresholds of dragonflies and damselflies from a Cerrado-Caatinga ecotone

Aquatic ecosystems are affected by different land uses that modify gradients of environmental conditions. These impacts act directly on the community structure, especially the most sensitive ones, such as aquatic insects. Thus, dragonflies have been used as good models to assess these changes, since their suborders Anisoptera and Zygoptera have different ecophysiological and behavioral requirements. This study aimed to evaluate the following hypotheses: (1) dragonfly species composition differs along the environmental gradients of streams; therefore, we expect a higher proportion of species of the suborder Anisoptera in environments with a higher degree of disturbance, since these environmental conditions select heliothermic species with exophytic oviposition; (2) the reduction of habitat integrity and canopy cover will lead to a lower richness of the Zygoptera suborder, due to the restrictions of its thermoregulation and oviposition behavior in relation to Anisoptera, since the higher light input would favor heliothermic and exophytic species; (3) alterations in habitat integrity create ecological thresholds and points of change in the abundance and frequency of Odonata species, generating gradients in the environmental integrity conditions. Specimens were collected from 24 streams (first to third order), in a gradient of land uses. Canopy cover and stream width were predictors of taxonomic richness and abundance of the suborders Anisoptera and Zygoptera, with greater coverage and smaller width, positively affecting Zygoptera and negatively Anisoptera. The turning points were determined by a habitat integrity index, where below 0.38 there is an increase in generalist taxa and a decline in sensitive taxa. On the other hand, above 0.79, there was a sensitive taxa increase in detriment of generalists. Four individual taxa indicators were selected, two of which associated with a negative response (Perithemis tenera and Acanthagrion aepiolum) and two with positive responses (Epipleoneura metallica and Zenithoptera lanei) for habitat integrity. Our results are important to guide management strategies, recovery, and protection policies for areas of permanent protection, aiming to conserving biodiversity and natural resources essential to life quality maintenance.