Biology subjects

Stefanescu, C.

Publications and source records attributed to Stefanescu, C..

8 recordsLinked to original sources

bioRxiv2025

The interplay of climate change, urbanization, and species traits shapes European butterfly population trends

Species populations naturally fluctuate, yet long-term trend analysis can reveal patterns of success, decline, or stability under global change pressures. While responses to climate change are well-documented, its synergy with another major global driver, urbanization, remains understudied. Here, we analyzed long-term monitoring data from over 8,400 populations of 145 butterfly species across Europe, representing a high diversity of species traits, to assess population trends in response to climate change and urbanization. We examined how population responses vary between urban and rural contexts, providing insights into the influence of site-specific conditions. Climate warming was associated with population declines, which were more pronounced in urban areas. The effect of precipitation varied between environments: increases in precipitation generally benefited populations in rural areas but had detrimental effects in urban ones. Aridity consistently drove population declines across environments, with slightly stronger effects in urban areas. Species with colder climatic niches declined the most in response to warming, increased aridity, and reduced precipitation, while trophic specialists were particularly vulnerable to aridity and precipitation changes in urban environments. Although increasing urbanization did not explain overall population trends, its effects became evident when considering species traits, with certain traits being more vulnerable to urbanization. Specifically, species with narrow climatic niches declined the most in response to urbanization in rural areas, while those and larger body sizes decline the most in urban environments. Our findings highlight the complex interplay between environmental change, landscape context, and species traits in shaping biodiversity outcomes. Importantly, our results suggest that urbanization generally amplifies the impact of climate change on insect population trends.

ecology↗

bioRxiv2024

Beyond community-weighted means: quantifying trait distributions for detecting community assembly patterns

The distributions of ecological traits are commonly used to infer the processess structuring ecological communities, as these processes (either deterministic or stochastic) select and filter species, leading to distint trait patterns across communities. Trait distributions are frequently characterised by their average, the community-weighted mean, but increasing evidence exists for non-gaussian trait distributions in empirical communities. In such situations, community-weighted means are insufficient to capture the patterns of community traits and to infer the implied ecological processes. Here we analyse the empirical distributions of 6 functional traits of butterflies from a natural community and a filtered community from a urban area across a period of six years. First, we show that to adequately describe trait distributions, statistical descriptors beyond community-weighted means are needed, as distributions were in all cases clearly non-gaussian. In particular, besides distribution averages and standard deviations, we compute the skewness, kurtosis, the range of trait values, and a multimodality index. Second, we compare this set of descriptors between our natural and filtered communities. We find clear differences between communities, detected in particular by combining the relationships between the skewness, kurtosis, and range of the distributions. These analyses allow us to infer that the filtered community is mostly shaped by deterministic filtering processes, through a mixture of directional and stabilizing assembly filters. These patterns are furthermore consistent across the six years of data, providing further evidence of deterministic processes shaping the assembly of our urban butterfly community. Overall, we provide evidence of the ubiquity of non-gaussian trait distributions across natural and filtered communities, propose key descriptors for understanding and comparing such distributions, and identify filtering process structuring these communities.

ecology↗

bioRxiv2022

Spatial variation in relative abundances of two butterfly species sharing both host plant and natural enemies

The decline of insect populations is of great concern because they play an essential part in several services that are key for ecosystem functioning and human well-being. Therefore, full understanding of the processes and factors shaping spatial variation in insects is required for their effective conservation. Here, we study a system comprising two congeneric butterfly species (Brimstone Gonepteryx rhamni and Cleopatra G. cleopatra) that share both host plants and natural enemies and analyse whether biotic and/or abiotic factors explain their relative abundances. The two species coexist in continental Spain but not on a nearby archipelago, where only the Cleopatra occurs. The hypotheses tested were based on (H1) dispersal behaviour; (H2) apparent competition mediated via shared parasitoids; and (H3) environmental conditions (overwintering habitat availability, abundance of host plants and temperature). H1 explained differences in Brimstone abundance between climate regions on the mainland since in warmer summers populations increased in cooler areas but decreased in warmer areas. Cleopatra did not show the same pattern but was found to have twice the number of summer adults on one island than on the mainland. It is unlikely that H2 can explain this result because, although richer parasitoid communities were found on the mainland, larval mortality rates were similar. H3 was important in explaining variation in abundances between sites within each climate region even though similar environmental conditions were found on the mainland and on the islands. Our study demonstrates the complexity of any attempt to understand insect population dynamics in space due to the number of factors that are potentially involved. We argue thus that a more comprehensive approach taking into account landscape topography and resource connectivity on a broader scale is required to unravel the factors shaping the relative abundance of insects in island systems.

ecology↗

bioRxiv2020

Timing of mating, reproductive status and resource availability in relation to migration in the painted lady butterfly, Vanessa cardui

In many migratory insects, migration occurs during the pre-reproductive phase of the life cycle. This trait probably arises from a trade-off between migration and reproduction and in females has been termed as the oogenesis-flight syndrome. However, the generality of this syndrome has been questioned, especially for monomorphic insects. We studied the relationship between migration and reproduction in the highly cosmopolitan painted lady butterfly, which in the Palaearctic undertakes the longest known multi-generational migration circuit of any insect. We tested for the oogenesis-flight syndrome in both spring and autumn migrants in two regions linked by migration, North Africa and northern Spain. Field observations were combined with laboratory experiments to determine the lifespan and the age at first mating to unravel the reproductive strategy observed in individuals captured in the wild. Females and males wait on average around 5-6 days before mating, and field data revealed that mating frequencies increase rapidly once females reach a medium wing wear category. There were seasonal differences in mating frequencies in the study regions depending on whether the region acted as a source or as a destination for migrants, and in the latter case there were almost twice as many mated females. Moreover, about 80% of females collected during migratory flights were unmated, the remaining females having mated only very recently. Our results thus strongly indicate that the painted lady fulfils the oogenesis-flight syndrome, as migration is concentrated in its relatively short pre-reproductive period. Field data also showed a high positive correlation between mating frequency and host plant abundance, which suggests that mated females have the ability to locate potential breeding areas. This, together with the very high fecundity estimated from over 1000 eggs in laboratory trials, makes the painted lady one of the most successful migratory insects on Earth.

animal behavior and cognition↗

bioRxiv2020

Spatio-temporal responses of butterflies to global warming on a Mediterranean island over two decades

In recent decades, efforts have been made to understand how global warming affects biodiversity and in this regard butterflies have emerged as a model group. The most conspicuous sign that warming is affecting the ecology of butterflies are the phenological advances occurring in many species. Moreover, rising temperatures are having a notable impact - both negative and positive - on population abundances. To date, patterns have generally been analysed at species level without taking into account possible differences between populations, which, when they are noted, are mostly attributed to large-scale climate differences across a latitudinal gradient. In this work, we use a long-term database of butterflies from the island of Menorca (Balearic Islands, Spain) to investigate how phenology and population dynamics have been affected by climate warming during the past two decades. In addition, we assess how responses are modulated by habitat characteristics and by species biological cycles. Our results show that species respond differently to warming at a local scale depending on season and habitat, and that coastal habitats in the Mediterranean region are particularly sensitive to the effects of climate change. Furthermore, our findings suggest that the effects of temperature could be partially offset in more inland habitats such as forests and deep ravines. The positive effect of temperature on ravine populations during the summer suggests that butterflies disperse across habitats as a response to rising temperatures during the season. This type of dispersal behaviour as a response to warming could be especially important in island ecosystems where the possibilities of modifying altitudinal or latitudinal distributions are often severely limited.

ecology↗

bioRxiv2020

Altered parasitism of a butterfly assemblage associated with a range-expanding species

AimBiotic interactions are an important factor structuring ecological communities but data scarcity limits our understanding of the impact of their response to climate and land use changes on communities. We studied the impact of a change in species assemblage on biotic interactions in a community of closely-related butterflies. Specifically, we examined the impact of the recent range expansion of Araschnia levana on the resident species, with a particular focus on natural enemies, parasitoids, shared with other butterfly species in the assemblage. LocationSweden. Time periodTwo years (2017-2018). Major taxa studiedNettle-feeding butterflies (Aglais urticae, Aglais io, Araschnia levana, and Vanessa atalanta) and their parasitoids. MethodsWe assessed parasitism in 6777 butterfly larvae sampled in the field from 19 sites distributed along a 500 km latitudinal gradient, and every two weeks throughout species reproductive seasons. We identified the parasitoid complex of each butterfly species and their overlap, and analysed how parasitism rates were affected by species assemblage, variations in abundance, time, and the arrival of A. levana. ResultsParasitoids caused high mortality, with substantial overlap across the four host species. The composition of the host community influenced parasitism rates and this effect was specific to each species. In particular, the rate of parasitism in resident species was comparatively higher at sites where A. levana has been established for longer. Main conclusionsParasitoid pressure is a significant source of mortality in the nettle-feeding butterfly community studied. Variations in butterfly species assemblages are associated with substantial variations in rates of parasitism. This is likely to affect the population dynamics of their butterfly host species, and, potentially, the larger number of species with which they interact.

ecology↗

bioRxiv2020

Varying thermal exposure, host-plant traits and oviposition behaviour across vegetation ecotones

Vegetation cover generates local microclimatic gradients in the understorey, being especially pronounced at narrow ecotones linking open and forested habitats (open-closed ecotones). They provide key habitats for multiple insect communities and may largely determine the exposure of herbivorous insects to the increasing impacts of climate change. We report parallel measurements of microclimatic variables, multiple host-plant traits, and oviposition behaviour in Mediterranean populations of two Pieris butterflies across ecotones of vegetation cover. Open microhabitats were significantly warmer, drier, and more exposed to thermal amplification, which increased temperatures to values affecting insect larval survival. Host plants advanced their reproductive phenology and were shorter. Open microhabitats also inhibited the development of shade-adapted plants (e.g. Alliaria petiolata), decreasing fruit production. In contrast, the reproduction of sun-adapted host plants (e.g. Lepidium draba) was vigorous in the open microhabitats and completely inhibited in closed microhabitats, which were exclusively inhabited by non-reproductive ramets. Key plant traits for the selection of oviposition sites by butterflies, such as foliar water and chlorophyll contents, varied significantly across the open- closed ecotones. Foliar water content was always lower in the open microhabitats, whereas foliar chlorophyll gradients differed between sun- and shade-adapted plants. The oviposition behavior of Pieris butterflies across the ecotones differed significantly between the thermotolerant species (P. rapae, preferentially selecting open microhabitats) and the thermosensitive species (P. napi, selecting microhabitats protected by vegetation cover), matching the values of thermal susceptibility estimated from parallel heat tolerance assays of the populations. The larvae of the thermotolerant Pieris species grew under completely different thermal conditions due to differential microhabitat selection, indicating marked interspecific differences in thermal exposure (5-10 {degrees}C). These results suggest that the impacts of global warming in these communities will likely be mediated by open-closed ecotones, which determine pronounced local variability in thermal exposure, oviposition placement, and host-plant traits affecting larval performance in summer.

ecology↗

bioRxiv2018

A female alternative life-history strategy arose via novel recruitment of homeobox gene, BarH-1

Tradeoffs affect resource allocation during development and result in fitness consequences that drive the evolution of life history strategies. Yet despite their importance, we know little about the mechanisms underlying life history tradeoffs in wild populations. Many species of Colias butterflies exhibit an alternative life history strategy (ALHS) where females divert resources from wing pigment synthesis to reproductive and somatic development. Due to this reallocation, a wing color polymorphism is associated with the ALHS: individuals have either yellow/orange or white wings. Here we map the genetic basis of the ALHS switch in Colias crocea to a transposable element insertion downstream of the Colias homolog of BarH-1, a homeobox transcription factor. Using CRISPR/Cas9 gene editing, antibody staining, and electron microscopy we find morph-specific specific expression of BarH-1 suppresses the formation of pigment granules in wing scales. Lipid and transcriptome analyses reveal physiological differences associated with the ALHS. These findings characterize a novel mechanism for a female-limited ALHS and show that the switch arises via recruitment of a transcription factor previously known for its function in cell fate determination in pigment cells of the retina.

genomics↗