Anais Rivas-Torres

Intensive forestry, particularly the establishment of monospecific plantations with exotic species, can deeply impact the ecological functioning of forest streams, where riparian leaf litter is the primary source of energy. In this study, we investigated the effects of Eucalyptus globulus afforestation on macroinvertebrate communities in 20 streams in Galicia (NW Spain) with varying levels of accumulated eucalypt leaf litter. Sampling was done in autumn 2020 and spring 2021. In autumn, six streams had leaf litter composed of >50% of eucalypt leaves, a proportion that increased to 12 streams in spring. A total of 24,705 individuals were found in autumn and 12,529 in spring, belonging to 125 taxa. Although some taxa decreased their abundance with an increase in the proportion of eucalypt litter, variability in overall macroinvertebrate abundance was mainly explained by season, stream flow, and water temperature. However, species richness and diversity were significantly lower in streams mainly subsided by Eucalyptus litter compared to those dominated by native riparian vegetation. Macroinvertebrate abundance, richness, and diversity peaked in autumn, coinciding with the influx of deciduous litterfall and lower proportion of eucalypt litter. The lower quality, low-nutrient content, and presence of feeding deterrents in Eucalyptus leaf litter compared to native deciduous tree species likely drive these observed patterns, underscoring the importance of preserving native riparian forests to sustain stream biodiversity, even in managed landscapes dominated by Eucalyptus plantations.

Intensive forestry, particularly the establishment of monospecific plantations with exotic species, can deeply impact the ecological functioning of forest streams, where riparian leaf litter is the primary source of energy. In this study we investigated the effects of Eucalyptus globulus afforestation on macroinvertebrate communities in 20 streams in Galicia (NW Spain) with varying levels of accumulated eucalypt leaf litter. Sampling was done in autumn 2020 and spring 2021. In autumn, six streams had leaf litter composed of >50% of eucalypt leaves, a proportion that increased to 12 streams in spring. A total of 24,705 individuals were found in autumn and 12,529 in spring, belonging to 125 taxa. Although some taxa decreased their abundance with the increase of the proportion of eucalypt litter, variability in overall macroinvertebrate abundance was mainly explained by season, stream flow and water temperature. However, species richness and diversity were significantly lower in streams mainly subsided by Eucalyptus litter compared to those dominated by native riparian vegetation. Macroinvertebrate abundance, richness and diversity peaked in autumn, coinciding with the influx of deciduous litterfall and lower proportion of eucalypt litter. The lower quality, low-nutrient content, and the presence of feeding deterrents in Eucalyptus leaf litter compared to native deciduous tree species, likely drive these observed patterns, underscoring the importance of preserving native riparian forests to sustain stream biodiversity, even in managed landscapes dominated by Eucalyptus plantations.

Behavioural diversity is a level of biodiversity that focuses on the existence of alternative behaviours, either linked to different ecological functions or with similar functional significance. Here, we tested whether libellulid dragonflies from species-poor communities of Isabela island (Galapagos) show high diversity in their egg-laying strategies, which is the expectation if the behavioural niche is not completely filled by the relatively few species present in the community. Our results indicate that the community of odonates of these island ponds shows very high diversity of oviposition strategies, with four modes for Tramea darwini (more than any other studied population of the genus) and two for the other common libellulids, Brachymesia herbida and Erythemis vesiculosa. The most frequent oviposition strategy of T. darwini (‘tandem–oviposition–tandem’) was clearly less efficient than oviposition by females alone or under non-contact guarding, and a similar result was found for B. herbida and E. vesiculosa, whose females were more efficient when alone in comparison to oviposition under male non-contact guarding. We suggest that this paradox is attributable to sexual conflict, which favours a different behaviour in males and females.

Freshwater insects are highly significant as ecosystem service providers, contributing to provisioning services, supporting services, and cultural services. Odonates are dominant predators in many freshwater systems, becoming top predators in fishless ecosystems. One service that odonates provide is the export of matter and energy from aquatic to terrestrial ecosystems. In this study, we provide a review of the literature aiming to estimate the density, biomass, and secondary production of odonates and discuss to what extent this order of insects is relevant for the fertilization of terrestrial ecosystems. We found published data on 109 species belonging to 17 families of odonates from 44 papers. Odonata larvae are abundant in freshwater systems, with a mean density of 240.04 ± 48.01 individuals m⁻² (±SE). Lentic habitats show much higher densities (104.40 ± 55.31 individuals m⁻², N = 118) than lotic systems (27.12 ± 5.09, N = 70). The biomass estimations for odonates indicate values of 488.56 ± 134.51 mg m⁻² y⁻¹, with similar values in lentic and lotic habitats, which correspond to annual secondary productions of 3558.02 ± 2146.80 mg m⁻² y⁻¹. The highest biomass is found in dragonflies of the Aeshnidae, Corduliidae, and Gomphidae families. The available evidence suggests a significant potential contribution of Odonata to the exportation of material from water bodies to land. This is further strengthened by the ability of adult odonates to migrate and to colonize different types of water bodies.

Males display phenotypic characteristics that may be associated with their quality, allowing non-random mating and post-copulatory female choice. In the damselfly Calopteryx haemorrhoidalis asturica , males have a conspicuous pink colouration in the underside of abdominal segments 8–10, which they exhibit during pre- and post-copulatory courtship. We hypothesized that this colouration functions to increase male mating success and/or to elicit females to oviposit. We estimated mating and oviposition success of 27 males, and on the following day, treated males had their segments 8–10 painted black and control males the seventh segment. We recorded the number of male–male fights and courtships, whether the courtship ended in copulation, and whether the female remained in the territory and laid eggs. Our results indicate that the mating success of male C. h. asturica was not significantly affected by the removal of the pink colouration of the abdominal tip, but this colouration clearly affected their success in enticing females to oviposit. Courtship frequency, fat content and muscle mass were positively correlated to male mating rate, and the number of aggressive encounters was negatively correlated. Our study yields experimental evidence for the function of pink colouration of male C. h. asturica , in the context of post-copulatory sexual selection.

Theoretical work suggests that reinforcement can cause the strengthening of prezygotic isolation in sympatry by mitigating the costs of maladaptive hybridization. However, only a handful of studies have tested all predictions of this theory in natural populations. We investigated reinforcement in a mosaic hybrid zone of the damselflies Ischnura elegans and I. graellsii. Firstly, we tested if the conditions of reinforcement were fulfilled by quantifying whether hybridization was costly, and prezygotic isolation was strengthening in sympatry compared with in allopatry. Secondly, we investigated three specific predictions of reinforcement: rarer female effect, presence of concordant prezygotic and postzygotic isolation asymmetries in sympatry, and greater premating asymmetries associated with weaker postzygotic isolation in sympatry. We found that reinforcement has strengthened mechanical isolation in one cross direction between species in sympatry. Our study details a case of reinforcement and heterospecific gene flow causing opposite effects between reciprocal heterospecific crosses and describes a natural model in which reproductive isolation is built by the simultaneous effects of reinforcement, the lock-and-key model, Bateson-Dobzhansky-Müller incompatibilities and Haldane’s rule.

In some species males use weapons to harm females, increasing their short-term fitness. Here we show that females can use genital adaptations against males. Females of the damselfly Enallagma cyathigerum have a conspicuous vulvar spine on the 8 ^th abdominal segment, which contacts with the male during copulation. We tested three hypotheses for its function: it (i) inflicts damage to the male during copulation; (ii) facilitates endophytic oviposition; (iii) stimulates males during copulation to increase their investment. We found that males mated on average for 54 min with control females, but increased copulation to 99 min with females without spine. There was no evidence of physical harm of the spine on the male’s seminal vesicle, which shows 8-18 folds, exactly where the spine contacts during copulation. Females with and without spine exhibited the same egg-laying rates and showed similar fecundity and fertility. Longevity was also similar in males mated to control and spineless females. In contrast to many species where females resist male harassment by behavioral responses, the morphological adaptation observed in E. cyathigerum appears to act as a sexual weapon, allowing females to control copulation duration. We suggest that the spine has evolved because of sexual conflict over mating duration.

Sexual selection favours the evolution and maintenance of polygamy, which is the dominant reproductive strategy in insects. Monogamy can evolve in very short‐lived species due to time constraints. Here we study adult activity and mating behaviour of a population of the damselfly Ischnura hastata , a species rarely seen mating, and which has been suggested to be monandric, in wetlands of Isabela Island, Galápagos. By means of mark‐recapture methods, we estimated that the daily survival rate was low, ranging from 0.385 to 0.876, yielding average life expectancies of mature individuals of only 1.2–3.2 days. Adults showed very low activity before 7:00, indicating that mating does not occur early. The number of male–female interactions and mating attempts was extremely low, with only 44 copulations recorded on over 230 h of observations. Copulations were brief, with a mean duration of 11 min (but only two were observed from the start). Males showed clear preference to attempt to grasp in tandem females of intermediate age (in 94.3% of cases), rather than young (31.3%) or mature females (24.0%). Males were very persistent once a tandem was achieved, retaining females for up to 139 min, but most females resisted and did not copulate. We conclude that females of I. hastata show a very short time window to mate, exactly when they change colour from juvenile to mature, and live only enough to mate once. Short lifespan has selected for female monandry in I. hastata , creating an intense sexual conflict over mating rates.

Nesobasis rito sp. nov. (Holotype ♂, Fiji, Vanua Levu, Drawa, 31 v 2018, A. Rivas-Torres leg.) from the comosa group is here described, illustrated, diagnosed, and compared with morphologically close species of the genus. Nesobasis rito can be distinguished from its related congeners by the shape of the caudal appendages and the ligula. The most similar species are N. comosa and N. heteroneura, which, like N. rito, have the caudal appendages covered by dense setae (especially the first species), but the shape differs clearly in lateral view, with N. rito having longer and more slender appendages, and a basal tooth clearly seen in dorsal view, absent in other members of the comosa group. The specific status of the collected specimens is also supported by the results of genetic analyses, where N. rito appears as a well-supported monophyletic clade. Nesobasis rito also has a distinct distribution from its most similar congeners: it is found on Vanua Levu, while N. comosa is found on Viti Levu and the closely related N. heteroneura is found on Viti Levu and Ovalau. All species of this group are found in streams with native forest riparian vegetation on their respective islands.