Frontiers in Ecology and Evolution

Riparian environments are characterised by a high diversity of arthropod species, linking the aquatic with the terrestrial ecosystem. One of the dominant arthropod predators in this ecotone, carabid beetles are of particular interest as they may also act as facultative scavengers, feeding on carrion deposited along the shoreline. To test whether carabids feed on carrion, we examined the feeding preferences of the abundant riparian carabid Bembidion elongatum in a laboratory feeding trial, offering freshly killed and 24 hours post mortem Drosophila melanogaster. We subsequently assessed the detection probability of ribosomal prey RNA and DNA in predator gut contents using Drosophila-specific RT-PCR and PCR assays, and quantified nucleotide abundance by quantitative real-time PCR at 0, 3, 6, and 12 hours post-feeding. In the feeding experiment, B. elongatum showed a significant preference for fresh over carrion prey. Following consumption, the quantities of prey DNA and RNA in the predators gut declined over a 12-hour post-feeding period. However, no differences were detected in prey DNA or RNA quantities between individuals fed fresh prey and those fed carrion. Only immediately after consumption was the DNA:RNA ratio significantly lower in individuals fed fresh prey compared to those fed carrion while this difference was not observed at later time points. Overall, our results indicate that ingested ribosomal prey RNA in predators is present in high quantities, and that the DNA:RNA ratio is not a suitable indicator for distinguishing between consumption of carrion and fresh prey.

Color polymorphism can facilitate local adaptation, maintain intraspecific diversity, or reflect early stages of speciation. Clownfishes (Amphiprion spp.) typically display a simple black, orange, and white pattern, but the saddleback clownfish (Amphiprion polymnus) shows striking variation in melanism and the number of vertical bars, which are thought to play a role in species recognition. In 2024, a revision on iNaturalist split A. polymnus into multiple species based solely on color pattern and geographic range. This raises the question of whether these morphs represent true species or intraspecific polymorphism, which we tested using genomic and image-based data. We sampled 97 individuals from seven populations across the species range and quantified color patterns from standardized photographs. Phenotypic and genomic analyses reveal a complex pattern of divergence. Image analysis identified three distinct phenotypic clusters, with A. polymnus, A. annamensis, and A. laticlavius each showing consistent differences in saddle shape and vertical bar extent. ADMIXTURE resolved three distinct genetic groups corresponding to the morphs. Pairwise FST (0.54-0.71) and dxy indicate extremely high differentiation between A. polymnus and A. annamensis, consistent with species-level divergence, whereas A. laticlavius shows much lower differentiation from A. polymnus (FST 0.09-0.18) and higher differentiation from A. annamensis (FST 0.64-0.66). Overall, phenotypic and genomic data show structured variation, but the status of A. laticlavius remains ambiguous. Our study reveals clear and structured divergence across the full range, yet the taxonomic interpretation of this variation remains inherently challenging. The key question remains: do these patterns reflect a single polymorphic species or a complex of closely related species?

The introduction of alien species into new habitats stands as a pressing economic and ecological challenge but it is also essential for unveiling evolutionary processes. The introduction of the Argentine ant (Linepithema humile) led to the spread of a single supercolony through different continents and thousands of kilometres like in Europe, from Northwest Spain to Greece. It was assumed that the high invasiveness of the species mainly relied on the lack of agonism among colonies, an effect derived from its introduction. However, recent studies suggest that local adaptations and evolutionary divergence could involve the disruption of the Argentine ant "empire" into a mosaic of competitive colonies. We investigated how isolation affects population divergence by comparing mainland and island populations in two distant regions colonized in Spain and in Greece with morphology, agonism, cuticular hydrocarbons, and genetic diversity of ant workers. Our results showed that all colonies sampled belonged to the most spread supercolony in Europe (main supercolony) except one sampled in Crete (Heraklion; Greece), which resulted to be a supercolony not registered in Europe. The Heraklian supercolony showed a different chemical and genetic profile and hostile agonism towards the other Greek colonies. Differences between islands and mainland colonies belonging to the main supercolony were higher in Galiza than in Greece. Surprisingly, the chemical profile of the Cretan colony belonging to the main supercolony showed more similarity with the Galizan colonies than with the Greek mainland, suggesting that L. humile may have been introduced into Greece through this island instead of the mainland. Our study suggests that local adaptations in Argentine ant colonies can trigger competition between colonies. Our data strongly support the existence of a candidate supercolony which highlights either ongoing introductions of L. humile in Europe or gaps in our understanding of its metapopulation dynamics.

Many insect populations are experiencing thermal stress as a result of global change, making it imperative to investigate how their relationship with other organisms will be impacted by heat disturbances. Microbial symbionts, such as bacteria, have the potential to enhance or inhibit an insect's thermal tolerance. Solitary bee larvae host bacteria within their food stores ("pollen provisions"), which have been shown to benefit survival and development; however, it is unclear how heatwaves brought about by climate change will impact their relationships with these bacterial partners. In this study, we subjected blue orchard bee (Osmia lignaria) eggs and larvae to a 4-day heatwave (35 {degrees}C daytime:22 {degrees}C nighttime) or kept them at control temperatures (25 {degrees}C daytime:15 {degrees}C nighttime), then returned all bees to control temperatures for a 5-day recovery period. We assessed bacterial communities within pollen provisions and larval development stage pre-heatwave (Day 0), immediately post-heatwave (Day 4), and following the recovery period (Day 9). Bacterial community composition, diversity, and abundance were resilient to heat stress, but larval bees developed faster when subjected to a heatwave. This finding refutes the hypothesis that bacteria within pollen provisions modulate blue orchard bee responses to heat, suggesting instead that developmental effects could be more largely shaped by bee physiology or interactions with microorganisms other than bacteria.

O_LIInformation on diet composition at both individual and population levels is fundamental to understanding resource use and availability, which influence individual fitness and the population dynamics of both predators and their prey. DNA diet metabarcoding offers a powerful molecular approach to diet analysis, but its application can be limited by methodological biases, particularly in generalist species with highly diverse diets. C_LIO_LIHere, we evaluate the performance of DNA metabarcoding for diet analysis in the lesser black-backed gull (Larus fuscus), a highly generalist mesopredator whose populations have shown complex responses to changes in natural and anthropogenic food resources over the past half-century. We collected faecal and regurgitate samples from pre-fledging chicks at two coastal and inland breeding colonies in northwest England, alongside pharyngeal, stomach, intestinal, and cloacal swabs from adult gull carcasses. Samples were analysed using COI (targeting animal DNA) and 12S (targeting vertebrate DNA) metabarcoding markers, and three blocking primers were developed to reduce host amplification in 12S libraries. C_LIO_LIMetabarcoding performance varied substantially among sample types and primer combinations. Without blocking primers, usable dietary information was recovered from regurgitate and stomach samples but not from intestinal or faecal samples. Blocking primers improved recovery of dietary DNA from faecal samples, but also increased the amplification of contaminants, elevating the risk of false-positive detections. C_LIO_LIAcross all sample types, metabarcoding identified 71 unique species belonging to 61 genera, including earthworms, small mammals, commercial and non-commercial fish species, lapwing, and urban-derived food products originating from livestock species. Dietary profiles revealed distinct clusters of consumed species associated with urban, agricultural, and marine foraging strategies, and demonstrated differences in dietary niche between age and colony cohorts. C_LIO_LIOverall, DNA metabarcoding enabled the detection of a highly diverse diet and revealed differences in resource use among colonies and age cohorts. These findings demonstrate the potential of DNA metabarcoding to advance our understanding of diet in highly generalist species and contribute to ongoing efforts to understand how dietary variation may shape demographic processes in highly dynamic populations. C_LI

Globally, nocturnal lightscapes are now determined by both moonlight and light pollution, or artificial light at night (ALAN). Organisms respond both to changes in moonlight across lunar cycles and to alterations in light conditions due to artificial light. The interaction of natural and artificial light is a critical aspect to incorporate into our understanding of how crepuscular and nocturnal ecology is altered in anthropogenically-modified landscapes. In this manuscript we review the rapidly expanding body of research on ecological impacts of ALAN to (1) assess patterns of lunar data inclusion and (2) summarize documented interactions of moonlight and ALAN. Three-fourths (72%) of 379 papers reviewed did not incorporate moonlight into their statistical analyses and experimental design. Only 12% directly investigated interaction effects of moonlight and ALAN. However, 70% of these studies reported an interactive effect. Considering this stark contrast, as a precursor to our literature review, we present an overview of moonlight and the lunar cycle for biologists. The overarching trend emerging from the literature is that biological impacts of ALAN decrease with increasing moonlight, although the opposite is true in some cases. After summarizing the literature, we present general hypotheses regarding the interaction of the lunar cycle and ALAN. These hypotheses consider the different forms of ALAN encountered by organisms (i.e. skyglow and light sources) and account for the influence of cloud cover. Finally, we suggest best practices for incorporating moonlight into future research on biological impacts of ALAN.

BackgroundSynonymous mutations, once considered neutral, can affect translation efficiency through mRNA folding and splicing, generating codon usage bias. This bias is often linked to genomic GC content, which also influences gene regulation. In the parasitoid wasp Lysiphlebus fabarum, GC content was previously shown to shift between developmental stages, with larvae showing higher GC than adults. Whether this phenomenon is widespread among insects remains unknown. ResultsTranscriptomic data from six insect species spanning Diptera, Hymenoptera, and Lepidoptera was used to compare GC content between expressed genes in larvae and adults. In five species, larval transcripts exhibited higher GC content than adult transcripts. Differential expression analysis revealed that stage-biased genes displayed consistent GC shifts, and orthologous gene families with representatives across species showed particularly GC-rich larval-biased genes in Hymenoptera and Diptera. At the genome scale, modeling in 317 insect species demonstrated an association between parasitic lifestyle and reduced mean GC content in Hymenoptera and Diptera, providing a possible ecological explanation for AT-rich genomes. ConclusionsOur results show that GC content is dynamic across developmental stages, independent of overall genome composition. Stage-specific GC enrichment may reflect adaptive codon usage optimizing translation during energetically demanding life-history stages such as larval development. Furthermore, the association between parasitism and reduced genomic GC highlights how ecological lifestyle might with genome content and evolution. Lastly, this work identifies candidate genes underlying stage-specific GC bias and provides new insights into the interplay between molecular evolution, development, and parasitic adaptation in insects.

The sperm whale is an emblematic species of the Azores archipelago. After a century of intensive whaling, the species has become a focal point for ecotourism since the late 1980s, enabling collaborative research during tourism activities. This study assessed the feasibility of using a citizen science based non-invasive sampling approach to evaluate the genetic diversity of local sperm whales. Seven local whale-watching companies contributed to collect 70 fecal samples and 34 sloughed skin fragments between 2019 and 2024. A 588-bp fragment of mitochondrial DNA Control Region (MCR) was successfully sequenced from 56 fecal samples and all skin fragments, yielding 90 MCR sequences assigned to 79 individual sperm whales. MCR sequences from both sources of the same individuals were in perfect agreement, validating the use of fecal samples for mitochondrial haplotype analysis - the first study to do so in sperm whales. Four MCR haplotypes, including a newly determined one, evidenced different maternal lineages within the Macaronesia population. Haplotypes showed a clear geographic pattern around Sao Miguel Island: one was restricted almost exclusively to the south coast, while the other three occurred predominantly on the north. This contrasted distribution is likely correlated to different matrilineal groups.

A central goal when assessing patterns of population structure for conservation is to identify populations with unique genetic compositions. The use of genomic sequencing to identify distinct populations has become an increasingly popular method of delineating conservation units. Reduced costs associated with sequencing make it possible to generate larger, more informative datasets to assess genetic diversity within and among populations. In species that exhibit nest-site philopatry, genetic population structure can emerge on much finer scales, particularly in maternally inherited mitochondrial genomes. We demonstrate the feasibility and insight gained by using whole mitochondrial genome sequencing for evaluating population genetic structure and comparing to previous single marker studies in a vulnerable turtle. We used whole mitochondrial genome sequences from diamond-backed terrapin (Malaclemys terrapin) to evaluate whether nest-site philopatry generates fine-scale genetic structure among M. terrapin nesting beaches in western Mobile Bay (Alabama, USA). We then compared haplotype diversity between the Alabama population and M. terrapin populations from the Atlantic and Gulf coasts and evaluated the utility of using whole mitochondrial genomes rather than a subset of loci to characterize unique haplotypic diversity. We found no genetic structure associated with nest-site philopatry within Alabama, but none of the haplotypes in this region were shared with other Gulf Coast sites. This genetic structure is consistent with strong female natal philopatry within western Mobile Bay relative to the Gulf of Mexico and suggests that the Mobile Bay population is genetically unique relative to other M. terrapin populations and merits a unique conservation and management plan.

Knowledge regarding variation in habitat use among individuals is crucial for understanding population dynamics and for management and conservation measures. This is especially important for diadromous fishes that shift between habitats, being affected by external pressures and environmental change in different habitats over ontogeny. Herer, we assessed individual variation in habitat use of European eel along a salinity gradient, ranging from fully marine to freshwater in northern Europe, using otolith microchemistry data from >3600 eel together with established time-series segmentation and clustering methods. We show that eel display high degree of individual variation in habitat use. Assigned life-histories included coastal resident, freshwater resident, and coastal and freshwater habitat shifting individuals. Coastal resident eels were observed in a large range of salinities. Given the widespread occurrence of migration barriers in freshwater, it is unknown whether the coastal resident eel preferred that habitat, or if it was the only available habitat for them. Our findings nonetheless highlight the need to include coastal habitats when assessing population development and silver eel production of the critically endangered European eel.

The charismatic migratory monarch butterfly population has declined dramatically, likely precipitated by loss of its breeding host plants (milkweed). Whether restoring milkweed would allow monarch recovery depends on whether additional factors currently limit the population. We investigated road mortality as one such factor. Monarchs cross thousands of roads during fall migration, and traffic volume has increased sharply while the population has plummeted. Using estimates of pre-migration distribution, flight patterns, and road traffic, we estimate that at least 61% (range 61% to 99.99%) of migrating monarchs are road-killed each fall. Although there is high uncertainty in our estimate, its magnitude suggests that roadkill could inhibit recovery of the population. Recovery planning should not only consider increasing the monarchs host plants, but must also address the reality of roadkill.

The red fox, Vulpes vulpes, is abundant in England and can exert limiting effects on their avian and mammalian prey. Large-scale gamebird releases in the UK may be sustaining high predator numbers, leading to greater predation on other prey species, especially once gamebird stocks are depleted. However, little is known how gamebird release affects the broader diet of the red fox. Here we used DNA metabarcoding to assess the diet of foxes from 18 agricultural estates in Southern England, 10 of which released large numbers of gamebirds (red-legged partridges - Alectoris rufus, and common pheasants - Phasianus colchicus) and 8 which did not. Scats were collected over one year, allowing for seasonal investigation of the foxes' diet. We investigated the vertebrate species consumed and compared the non-gamebird dietary diversity and composition between release and non-release estates and across seasons. The field vole (Microtus agrestis) was found to be the most frequently predated species overall. Brown hares and field voles were detected more on release sites, while bank voles and dog faeces were detected more on non-release sites. We found little evidence that foxes predate ground nesting birds or other species of concern. The dietary diversity was significantly lower on estates that released gamebirds, and this difference was most notable during the post-shoot, spring months (February to April). On both estate types, diversity was highest in the summer months. The altered predatory behaviour due to gamebird release is likely to affect the populations of the non-game prey of the red fox and this should be considered when designing policies regarding gamebird management and biodiversity conservation. Alternative predation combined with predator control may be reducing predation pressure on non-game prey where gamebirds are released, but high fox density elsewhere likely results in higher predation pressure on a wide range of species.

Benthic algae integrate catchment-and reach-scale pressures in streams. We assessed land-use effects on benthic algal assemblage structure, chlorophyll-a, ash-free dry mass (AFDM), and autotrophic index across 24 headwater streams in the Sondu-Miriu River basin, Kenya, and explored wet-dry patterns in two monitoring streams. We sampled across four land-use categories: natural forest (NF), tea and tree plantations (TTP), smallholder agriculture (SHA), and smallholder tea (SHT). Synoptic sampling occurred in August 2025, and one NF stream and one SHA stream were sampled five times between November 2024 and May 2025. Shannon and Simpson diversity were highest in NF streams and lowest in SHT streams. Chlorophyll-a and AFDM were highest in SHA streams; chlorophyll-a was lowest in SHT, while AFDM and autotrophic index were lowest in NF. Relative abundance patterns showed that SHA streams were dominated by Lyngbya and Stigeoclonium, whereas SHT streams were dominated mainly by Stigeoclonium; NF streams supported persistent diatom-rich assemblages. Non-metric multidimensional scaling showed land-use separation of benthic algal assemblages, while redundancy analysis indicated weak, non-significant evidence of environmental associations in the synoptic dataset. Composition and biomass metrics tracked land-use gradients and wet-dry patterns, supporting periphyton-based bioassessment for monitoring disturbance in Afrotropical headwater streams.

Fistulobalanus albicostatus Pilsbry, 1916 (Thoracica: Balanidae) is a tropical to temperate species distributed in the NW Pacific. The previously known northernmost record of this species in Japan was from Aomori Prefecture, at the northern end of Honshu Island, Japan. However, field surveys conducted in 2023 and 2026 confirmed the occurrence of F. albicostatus in Hakodate Bay, the southern end of Hokkaido, Japan, across the Tsugaru Strait, thereby extending the northern limit of its known distribution. A line transect survey conducted in May 2026 recorded seven living individuals within an area of 128 m. F. albicostatus was rare on the mid-high shores, accounting for only 2% of all barnacle individuals in a quadrat survey. The basal diameter of the living individuals ranged from 0.76 to 1.23 cm, and all individuals possessed ovaries. Based on characteristics of both morphological and COI gene, the specimens were identified as F. albicostatus, and belonged to the same haplotype of populations that are present in Honshu Island. The establishment of F. albicostatus in Hokkaido suggests an ongoing northward range shift of this warm-water species, with the potential for further expansion under continued ocean warming.

Predator satiation is an understudied topic among vertebrate organisms, especially avian species. In Anderson, South Carolina, a species of migratory black bird, Euphagus carolinus (Rusty Blackbird) was observed roosting seasonally in a patch of Phyllostachys aurea (Golden bamboo) in large numbers. A resident avian predator, Buteo lineatus (Red-shouldered Hawk was seen preying on these roosting blackbirds; however, when this hawk would attack, pin down, and eat a blackbird, the rest of the flock would not react or fly away. Upon initial observation, we questioned if these roosting blackbirds exhibited predator satiation as a protection mechanism against avian predation. When E. carolinus flocked to roost, their numbers were visually counted and compared between at least two members of the research team. After allowing the birds to settle between fifteen seconds and one minute, a B. lineatus call was played with speakers to the flock. Simultaneously, a regulation-sized football was tossed to simulate the hawk attacking a member of the flock. The number of birds that flew away was recorded. Results between roosting numbers and flight numbers upon disturbance were analyzed to see if roosting group size correlates with evasiveness in birds. Results indicated that as blackbird group size increased, the total percentage of escaping birds decreased. Statistical analysis showed the leaving percentage versus the natural logarithm of group size was highly statistically significant (p < 0.001) and had a moderately negative overall correlation (rs = -0.62). Our results suggest that these blackbirds feel safer in large groups instead of small groups during predation events when roosting in dense brush. LAY SUMMARYO_LIThere is little research involving predator satiation tendencies in birds. C_LIO_LIPredator satiation is a strategy developed by prey animals to cope with predators, relying on sheer numbers to avoid predation instead of fight or flight. C_LIO_LIWe observed roosting Rusty Blackbirds in Anderson, SC displaying predator satiation-linked tendencies under avian predation stress when in large groups. C_LIO_LIWe tested the behavior of Rusty Blackbirds by simulating a hawk attack, noting the group size and the number of birds escaping. C_LIO_LIOur results showed that as group size increased, flight percentage decreased under a simulated predator attack. C_LIO_LIRusty Blackbirds seem to use the predator satiation strategy when roosting. C_LI

Machine learning models can be used to analyze large bioacoustics datasets and explore variation due to geography or habitat. We find that in the monotypic Lark Sparrow (Chondestes grammacus), both environmental variables and geographic distance influence song variation in this species. Bird song is an important method of communication within avian species. The variation in bird song within a species can be due to a variety of factors, including genetic drift and isolation by distance. However, it remains unclear in species with wide ranges how environmental factors in particular can cause changes to the song. In this study, the song C. grammacus was analyzed via machine learning to determine if it had significant variation based on multiple geographical metrics. We trained a convolutional neural network to segment individual syllables of 91 C. grammacus recordings, then extracted song characteristics. We found that ecoregion and state explain variation in C. grammacus songs. Our results demonstrate the efficacy of using machine learning models to analyze large datasets, as well as the impact that ecogeographic variation has on song variance.

Smoke from spring boreal wildfires increasingly impacts eastern North America, exposing breeding birds to hazardous air pollution that may impact reproductive outcomes. Using data collected in 2018-2025 from 70,979 monitored nests of four widespread cavity-nesting songbirds, we found strong evidence that smoke greatly delays egg laying and can extend incubation and nestling duration. We further found that while smoke is associated with increased clutch sizes, in some species smoke exposure strongly decreases hatching or fledging success. Our results demonstrate that extreme smoke can have wide-ranging impacts on breeding birds, from altering phenology to impacting fitness. While the exact mechanisms underlying these results remain elusive, the full suite of effects suggests that modifications to adult behavior under smoky conditions is the most likely cause. As fire regimes shift, birds and other wildlife are at greater risk of exposure to toxic smoke during the breeding season, which may further exacerbate the biodiversity crisis.

Arctic and Boreal raptor communities will continue to be affected by borealization and other climate change related processes, providing a challenge for ecologists predicting future sates. However, by using community assembly theory and species traits, future communities may be predictable. In this study, we analyzed variation in reproduction traits as a consequence of diet specialization for 29 raptors, 2 skuas and 3 corvids. We assessed and implemented foraging traits for specialists and generalists into predator-prey models from which successful invasion conditions were derived. Specialist raptors produced larger clutch sizes, had a higher proportion of fledged per clutch and also expressed more variation compared to generalist raptors. These results suggest a relationship between diet specialization and reproductive traits which was also observed within phylogenetic orders. Specialist owls (Strigiformes) produced higher clutch sizes with a larger clutch range compared to generalist owls. The same pattern was observed for falcons (Falconiformes). No clear difference in reproduction was observed for specialist and generalist hawks, kites and eagles (Accipitriformes). Corvids expressed clutch sizes similar to that of specialist raptors while having the lowest proportion of fledged per clutch. Differences in foraging traits between specialists and generalists could be distinguished using functional response curves. A predator-prey model parameterized with foraging trait data showed that a generalist can coexist with a resident specialist if it has access to prey unavailable to the resident specialist. Otherwise, the native specialist outcompetes the invading generalist due to foraging efficiency. The combined empirical and theoretical findings in this study show how diet specialization affects both reproduction and the potential invasion success of raptors.

Classic foraging models and discounting tasks may oversimplify the decision-makers environment, resulting in a discrepancy between predicted and observed behaviour. In delay discounting tasks, animals typically steeply devalue larger-later (LL) outcomes, choosing smaller-sooner (SS) rewards after short delays. This steep discounting appears to be irreconcilable with natural foraging behaviour, where animals frequently endure long delays when travelling to find food, handling tough items, and storing food for future use. This apparent mismatch in behaviour has led to questions regarding the ecological validity of laboratory discounting tasks. Here, we developed a rich dynamic optimisation model to identify the conditions under which animals should choose LL or SS outcomes. In our model, a food-storing animal encounters food items differing in energy content and handling time and must decide which items to eat immediately and which to cache, so that it has enough stored food to survive winter. We simulated a range of environments, including laboratory conditions where foragers face negligible predation risk when searching for food and have a high probability of finding food, compared to more natural conditions where searching for food is risky, and food is harder to find. In line with preference reversals seen in the discounting literature, our model predicts that LL items should be rejected more often when the handling time for such items is increased, whereas SS items should be rejected more often when the handling time for both items is increased. Importantly, our model only predicts rejection of food items under parameter values that reflect laboratory conditions, supporting the notion that the steep devaluation of rewards seen in animals may be driven by the artificiality of traditional discounting tasks.

Rock surface weathering is a critical element in the process of early soil formation, in which lichens are thought to play a significant role. Crustose lichens, with a large area of rock-surface contact, are generally considered more influential in rock weathering, while foliose and fruticose growth forms, with more developed three-dimensional structure and less rock-surface contact, are rarely considered in this context. Here, we test the extent to which all three growth forms contribute to granitic rock surface weathering in Maritime Antarctic ecosystems, by quantifying rock hardness beneath foliose (n = 2 species), fruticose (n = 2) and crustose lichens (n= 5). Our data confirm that foliose lichens reduced rock surface hardness by 9%, to a lesser extent than crustose and foliose lichens (40% and 31% reduction, respectively). To disentangle whether these effects result from lichen-induced weathering or lichen preference for pre-weathered rock, we also analyzed a dated deglaciation sequence on granitic rocks from the Morteratsch Glacier forefield in the Swiss Alps. At this location, the impact of crustose lichens on rock substrate hardness generally increased with time since exposure from glacial retreat and with lichen thallus size. We conclude that lichen presence on rock surfaces significantly reduces rock hardness, with crustose lichens having a greater impact than foliose and fruticose forms, highlighting the potential role of lichens of all three growth forms in driving substrate breakdown and shaping early-stage ecosystem processes in polar and alpine regions.