Molecular Ecology

As heatwaves increase in intensity and frequency, more birds are exposed to sublethal heat, which can affect many elements of the phenotype, from growth to cognition to reproduction. These widespread performance-related effects of heat, coupled with the rapid declines seen in many bird populations in recent decades, underscore the urgency of detecting recent heat exposure and its downstream physiological effects in the wild. To develop minimally invasive biomarkers of past heat, we experimentally elevated nest temperatures for free-living nestling Tree Swallows (Tachycineta bicolor) for four hours on their twelfth day of life. Twenty-four hours later, we returned to collect a small blood sample and quantify carryover effects of prior sublethal heat on the blood transcriptome. By comparing these carryover effects to those that occur in the immediate aftermath of heat, we identify biomarkers of heat that reflect distinct and time-dependent processes. Candidate biomarkers include four upregulated genes with connections to stress and disease (LAMA3, ATP1B1, RASGEF1A, TMEM181) and two additional down-regulated genes. By incorporating the sex of each nestling into our analyses, we also unveiled marked sexual dimorphism in the blood transcriptome, even among autosomal genes and including pathways that imply inherent sex differences in heat tolerance. When these sex differences are controlled, we see that the sexes respond to heat with overwhelming similarity, further grounding the utility of our suggested transcriptomic biomarkers. Though these biomarkers will require further validation to be used across bird species, our collective results uncover temporally calibrated targets can be measured with just one drop of blood, improving our understanding of climate impacts on wild birds. Lay summaryO_LIAs global temperatures rise, many birds experience bouts of heat stress, but we do not have simple biomarkers that reliably reflect this past exposure in the wild. C_LIO_LIWe tested whether a small blood sample could reveal recent heat stress through changes in gene activity. C_LIO_LIOur experiment exposed nestling Tree Swallows to a non-lethal heat stressor and measured how their gene activity changed during and after the heat event. C_LIO_LISome genes reacted quickly but returned to normal within a day, while others showed longer-lasting effects. C_LIO_LIMales and females responded to heat in similar ways, even though their baseline gene activity differed substantially. C_LIO_LISix genes responded consistently across the sexes and in relation to temperature, making them promising biomarkers of past heat. C_LIO_LIThese results can help scientists better track heat exposure in wild birds and improve predictions on how populations respond to continued climate change. C_LI

Free-living nematodes are among the most abundant animals on Earth and play critical ecological roles in soil ecosystems. However, the global population structure and evolutionary history of most species remain poorly understood. Here, we analyzed genome-wide variation in Oscheius tipulae using whole-genome sequence data from 31 isolates, including 28 publicly available genomes and three newly collected strains from Korea. Population structure analyses, phylogenomic inference, and ancestry estimation consistently identified three deeply divergent lineages. These analyses did not detect admixture among lineages and collectively supported a predominantly tree-like evolutionary history. Notably, the lineages were structured by latitude rather than geographic proximity. Isolates from similar latitudinal zones clustered together regardless of continental origin, forming three major groups: northern mid-latitude (NML), low-latitude (LL), and southern mid-latitude (SML). This pattern indicates that the lineages have maintained largely independent evolutionary trajectories over extended timescales despite the potential for long-distance dispersal. Furthermore, environmentally associated variants showed significant differentiation among lineages, indicating that environmental selection may contribute to the maintenance of this latitudinally structured diversity. Our results reveal unexpectedly deep global divergence within O. tipulae, and highlight the importance of ecological divergence and long-term lineage retention in shaping the global diversity of this group.

Evolutionary and demographic processes such as selection, drift and migration shape the genetic variation of populations. Genetic diversity is often lower in populations toward higher latitudes. This decrease potentially threatens their survival as several factors are putting more pressure on the populations, including the spread of infectious diseases. In this study, we combined whole-genome re-sequencing with MHC class II genotyping and skin microbiome profiling in Bufo bufo and B. spinosus, two closely related European toad species. We investigated the underlying immunogenetic and microbial variation resulting from different demographic histories and environmental conditions to identify their potential impact on infection outcomes in these two species. We found lower immunogenetic diversity in B. bufo compared to B. spinosus, with highly significant differences in genes related to adaptive and innate immunity. We found lower overall MHC class II diversity and skin microbiome diversity at the species level in B. bufo, compared with B. spinosus. In contrast, at the individual level, B. bufo showed higher MHC allelic diversity and greater diversity in the core skin microbiota than B. spinosus. Together, our findings suggest that divergence in immunogenetic background and host-associated microbial communities may underlie differences in susceptibility to emerging infectious diseases. This integrative framework provides new insight into how host genetics and microbial communities jointly influence disease outcomes across environmental gradients.

Mitochondrial genomes encode for the proteins and RNAs that serve as the basis for aerobic respiration and energy production. Yet mitochondria depend on the nuclear genome for hundreds of additional genes whose products engage in core metabolic processes (N-mt genes). Despite strong selective pressure for coevolved mitonuclear interactions, there are numerous examples of mitochondrial introgression across species barriers. Mitonuclear co-introgression, a process whereby alleles at N-mt genes move across species boundaries in concert with mitochondrial genomes, has been suggested as a mechanism whereby species could capture heterospecific mitochondria while avoiding mitonuclear incompatibilities, but evidence for this phenomenon is sparse. We test for evidence of mitonuclear co-introgression in two discordant populations of North American red-backed voles (Clethrionomys gapperi nuclear genomes, C. rutilus mitochondrial genomes) using whole genome resequencing. We find that N-mt genes in both populations are significantly enriched for C. rutilus ancestry, with evidence of co-introgression at eighteen N-mt genes. Notably, two N-mt genes directly associated with mitochondrial translation are fixed or nearly fixed for C. rutilus ancestry in both discordant populations and analyses of genetic variation at these genes suggest recent selective sweeps. We pair these findings with mitochondrial phylogenies, recent demographic histories, and recombination maps, which support a scenario of ongoing introgression in British Columbia but cessation of gene flow in Southeast Alaska. Together, our results show that mitochondrial introgression in North American red-backed voles is adaptive and that mitonuclear incompatibilities are avoided through mitonuclear co-introgression.

Infection can substantially reduce host fitness and influence population dynamics, yet it is often difficult to detect and quantify in wild animal populations. Molecular tools offer a valuable means of identifying cryptic infection in natural systems. Using whole-genome bisulfite sequencing, we examined whether infection with the parasitic leech Ozobranchus margoi is associated with DNA methylation variation in loggerhead sea turtles (Caretta caretta), while also assessing the potential value of this variation as a biomarker of parasite infection. In nesting females, we identified infection-associated differentially methylated CpG sites associated with genes implicated in immune signalling and cellular regulation. Offspring of infected females also showed infection-associated methylation patterns, despite not being directly exposed to the parasite themselves. Differential methylation analyses identified genes involved in immunity, neurodevelopment and metabolic activity, with limited overlap in associated genes and no overlap in differentially methylated sites between generations. Maternal and offspring genome-wide methylation levels showed a non-linear association that differed subtly with maternal infection status, indicating that infection modifies intergenerational methylation associations. Finally, methylation profiles showed strong discriminatory power for maternal infection status in both maternal and hatchling samples using machine learning models, supporting their potential as candidate biomarkers of cryptic infection. Together, these results show that parasite infection is associated with distinct, generation-specific DNA methylation signatures, and highlight the potential value of epigenetic data for monitoring cryptic infection states in conservation-relevant systems.

Thermal history provenancing can guide the choice of parental broodstock for selective breeding of corals from distinct reefs and has been proposed as an intervention for enhancing climate resilience. However, the genetic and molecular mechanisms underlying resultant offspring responses to heat stress, particularly during early life stages, remain poorly understood. Here, we generated Acropora tersa larvae and recruits by crossing parental colonies from the historically warmer Martin Reef and cooler Davies Reef and assessed the effects of within- and between-reef crosses on genetic diversity and transcriptional responses to heat stress. Genome-wide single nucleotide polymorphism analyses showed that broodstock from Martin and Davies Reefs were weakly differentiated (FST = 0.008) and exhibited comparable heterozygosity, as did all larval offspring groups. Transcriptomic analyses of recruits exposed to heat stress (32 {degrees}C for 36 days) revealed that both within- and between-reef offspring groups activated conserved stress-response pathways, with seven genotype-independent heat-responsive genes detected across all offspring groups. Differential expression and enrichment analyses showed induction of defence, protein homeostasis, intracellular transport, and metabolic processes alongside repression of growth- and signalling-related functions, consistent with the Type A General Coral Stress Response. Taken together, these findings suggest that the benefits of thermal history provenancing-informed selective breeding may be limited in low-differentiation systems and that targeted pre-screening of broodstock may help capture functional genetic variation relevant to restoration applications.

Despite being two of the most commercially important flatfish (order Pleuronectiformes) in Europe, little is known of the population structure of common sole Solea solea and European plaice Pleuronectes platessa. To address this gap, we generated full-genome resequencing data for 244 sole and 189 plaice in the Celtic Sea and western English Channel region to analyse both neutral and adaptive loci and quantify population processes, such as reproductive isolation or adaptive differentiation in each species. For sole, there was no evidence of reproductive isolation or population structure at neutral loci. There was, however, adaptive differentiation as adaptive loci indicated two subpopulations, with separation in the western English Channel. This is consistent with previous studies using RAD-seq and gene-linked SNPs. For plaice, there was no evidence of population structure at either neutral or adaptive loci in the Celtic Seas and Western English Channel region. However, when considering a larger geographical area and utilising previously published genomic data, three distinct populations of plaice were identified (Iceland; North Sea, Kattegat and Western Baltic; Celtic Sea and western English Channel), with clear reproductive isolation indicated by neutral loci and adaptive differentiation indicated by adaptive loci. Moreover, three large chromosomal inversions were identified, which differed in their frequency between regions. These large structural variants represent putative key regions for adaptive differentiation. This study shows the benefit from quantifying neutral and adaptive loci to better understand population structure and genetic diversity of commercially important fish.

Bird migration evolved as an adaptation to seasonally changing habitats. Migratory behaviour can vary within the same species in case of partial migratory behaviour, i.e. one population (or individual) is migratory and another one is resident. Species that exhibit a wide variety of migratory phenotypes provide valuable systems to understand the evolutionary drivers behind different phenotypes and how populations adapt to habitats with distinct seasonality. The European robin (Erithacus rubecula) expresses migratory behaviour in central and northern areas of the species distribution range, whereas populations in the South and on the Macaronesian islands are predominantly resident, providing a suitable system to investigate these questions. We use high coverage whole genome re-sequencing data of 125 European robins to investigate how migration behaviour affects population structure and demography, and how it affects the selection landscape in the genome. Genetic structure in European robins coincides with migratory phenotype and geography and populations are characterised by distinct demographic histories. Our results suggest that both the continental resident population as well as the Macaronesian island populations have derived independently from an ancestral migratory population. Unexpectedly, tests for differential selection revealed extensive positive selection pressure acting across all chromosomes in the resident populations, while selective sweeps are largely absent from migrants. We speculate that this might be an analytical artifact due to mismatching timescales between what population genomics methods can detect and the scale on which migration behaviour likely evolved in the robin. We suggest that future studies on the genomics of migration should more focally account for different time scales on which these processes happen, such as including the wider phylogenomic background of the target species, to capture the full evolutionary history of migratory traits.

Mining pollution is an important stressor of freshwater communities worldwide. Persistence in these environments requires adaptation, yet identifying the mechanisms responsible in wild systems remains challenging due to differing water chemistries and genetic backgrounds. Parallel evolution presents a powerful framework for identifying adaptive mechanisms through repeated directional change. Here, we seek to understand the mechanisms that enable brown trout (Salmo trutta) to survive in metal-polluted rivers. Using low-coverage Whole Genome Resequencing (lc-WGS) we analyse paired metal-polluted and non-polluted brown trout populations across the British Isles. Metal-impacted populations show reduced nucleotide diversity and increased genomic divergence from paired control populations. We observe strong signatures of parallel adaptation in populations with shared geography, emphasising the importance of standing genetic variation in rapid adaptation to pollution. We identify a candidate region of 0.5 Mb on chr25 that shows strong parallel adaptation across multiple pairwise comparisons, including a shared signal among populations experiencing highly divergent water chemistries. The chr25 region contains the genes oestrogen receptor (esr2b) and a potassium-gated ion channel (kcnh5b), both of which are linked to developmental and osmoregulatory functions known to be disrupted by metals. Using population branch statistics (PBS) and scans for selective sweeps, we also identify population-specific candidate loci, yet putatively selected regions repeatedly converge on shared gene families and functional pathways. Our findings reveal both parallel and unique evolutionary responses to anthropogenic pollution in wild fish, highlighting convergent adaptive pathways to diverse pollutants in teleosts.

Long-term persistence of managed species will depend, in part, on whether the species harbors the physiological or genetic potential to adjust to warming temperatures, and whether relevant genetic variation is modified by management practices. The critically endangered Delta Smelt (Hypomesus transpacificus) is intensively managed, but little is known about the presence of genetic variation for resistance to elevated temperature, which will be important to maintain for their persistence in a rapidly warming future. Using a pedigree and whole genome sequencing data, we characterized the genetic variation and genomic architecture for CTMax (as a metric of upper thermal tolerance) across control and elevated rearing temperatures, alongside covarying traits (body size, degree of hatchery ancestry). Warmer rearing temperatures increased CTMax through acclimation but also resulted in reduced additive genetic variation for the trait, which could constrain adaptation under thermal stress. We found that larger fish had reduced CTMax, although this effect was diminished at elevated temperatures. We observed modest heritability for CTMax at rearing temperatures of 15{degrees}C and 18{degrees}C (0.26 and 0.16, respectively), but only a limited number of loci were identified that had consistent effects on CTMax across rearing temperatures. Instead, the genomic basis of thermal tolerance was highly dependent on rearing temperature (many loci detected with a GxE effect). The influence of domestication selection was indicated by changes in allele frequency, and divergence in upper thermal tolerance and plasticity, between low and high hatchery ancestry groups. Minimal overlap between loci associated with domestication and CTMax suggests that these traits possess separate genetic underpinnings. Knowledge of genetic variation supporting ecologically relevant physiological variation may be useful for refuge management and may inform supplementation in an ever-warming environment.

True lemmings (genus Lemmus) underwent substantial range shifts during the Late Pleistocene and the Pleistocene-Holocene transition, but the impact of these events on present-day diversity remains poorly understood. Here, we used whole-genome sequencing data from modern and ancient samples across the Palearctic range to address this knowledge gap. Reconstruction of autosomal phylogeny revealed that Palearctic true lemmings exhibit relatively shallow genetic structure, contrasting with the deep divergence inferred from mitochondrial genomes. Genetic variation largely follows an isolation-by-distance pattern, and no elevated nuclear divergence was detected between the major mitochondrial lineages. Window-based phylogenetic analyses identified several peripheral populations with high concordance factors, including Norway and Amur lemmings. The high degree of phylogenetic concordance along the genome in these populations is likely a consequence of postglacial bottlenecks and isolation, as indicated by reduced heterozygosity and the presence of runs of homozygosity in them. Overall, our results indicate that the modern genomic structure of Palearctic lemmings was shaped primarily by range fragmentation and population isolation following the broad distribution of the genus during the Last Glacial Maximum. Thus, the current genetic structure appears to represent only a fraction of the Late Pleistocene true lemming diversity. This is illustrated by a genetically distinct ancient specimen ([~]40 ka BP) from the Indigirka River basin that does not cluster with any modern lineage. From a taxonomic perspective, these findings do not support strong species-level differentiation among the major Palearctic lineages and highlight the discrepancy between mitochondrial and nuclear patterns of diversity within the genus.

Microbial eukaryotes often exhibit large effective population sizes and broad dispersal, yet the extent of population structure and the forces shaping it remain poorly understood. While biogeographic structure is often attributed to limits on dispersal, the role of natural selection in maintaining differentiation has received less attention. We investigated population structure and adaptive evolution in the cosmopolitan soil alga Chlamydomonas reinhardtii. In addition to the 35 available North American genome sequences we have sequenced 38 new isolates from Ontario (Canada). Population genetic structure analyses demonstrate that these new isolates from Ontario represent a second well-sampled genetically distinct cluster, and that this structure persists despite the presence of recent migrants. Using this data set we were able to conduct genome-wide scans for selective sweeps across the species and within each population. Our results conservatively identify 151 species-wide sweeps and 325 population-specific signals, showing that positive selection is widespread and common. The continued presence of the two distinct genetic clusters as well as loci under differential selection, provide evidence that local adaptation persists despite ongoing gene flow. Together, our results demonstrate that selection plays a central role in reinforcing geographic structure in this highly dispersive microbe.

Divergence among populations and species commonly occurs across multiple biological levels, yet the extent to which genomic, phenotypic, and ecological dimensions are coupled remains poorly understood. We integrated whole-genome sequencing, multivariate morphology, population-level phylogenetic structure, and gut microbiome composition to evaluate divergence in two allopatric annual killifish species across spatially structured populations in Malawi. Geographic and hydrological structure emerged as the primary axis of divergence, with strong differentiation between species and among populations. Genome-wide analyses revealed consistent clustering among populations in ordination and phylogenetic analyses, indicating pronounced spatial structuring of genomic variation. Although genomic divergence was widespread, exon-level enrichment analyses revealed distinct signatures across evolutionary scales. Divergence within N. kirki was associated primarily with translation-related functions, whereas divergence within N. wattersi involved ATP biosynthesis and physiological homeostasis. Interspecific divergence was enriched for transcription factor activity and transcription factor binding, implicating regulatory evolution as a major component of species differentiation. Morphological variation was likewise strongly structured among populations and aligned with drainage systems and geographic regions but was not correlated with genome-wide genetic differentiation, indicating partial decoupling between genotype and multivariate phenotype. Gut microbiome composition represented a more environmentally responsive layer of divergence, broadly reflecting host species and drainage structure while exhibiting greater overlap among populations. These results support a hierarchical model in which geographic and hydrological structure organize stable genomic divergence, whereas phenotypic and microbiome variation represent increasingly context-dependent and only partially aligned biological layers. Our findings highlight the value of integrating multiple biological levels to understand how evolutionary processes shape divergence in natural populations.

Invasive alien species (IAS) represent a major threat to biodiversity, human health, and economy. Yet the role of host-associated microbiomes in invasion processes remains poorly understood in natural systems. Here, we investigated the bacterial and fungal microbiomes of IAS and native Drosophila species collected along an anthropization gradient in French Guiana. Analyses of Drosophila communities revealed that IAS establishment is limited outside coastal habitats. Using bacterial 16S rRNA and fungal ITS metabarcoding of pooled individuals, we assessed microbial diversity, composition, and structure across host species, host category (invasive vs. native), and locality. Bacterial communities associated with IAS harboured reduced alpha diversity and distinct community structure compared to native Drosophila species, and host phylogenetic relatedness and locality also contributed to bacteriome variation. In contrast, fungal communities were mainly structured by locality and host species. We further identified core and exclusive taxa, compared bacteriome composition between native and IAS hosts using global reference datasets, and integrated information from the microbiome literature. This approach led to the identification of 45 bacterial and fungal candidate taxa potentially associated with host adaptation or competitiveness across coastal and rainforest environments. Overall, our results highlight microbiome variation as a potential component of invasion dynamics in Neotropical Drosophila.

Understanding the genomic basis of early adaptation is a central question in evolutionary biology. Although there is ongoing debate about whether early adaptation is more likely to be driven by polygenic responses or by loci of large effect, few studies of natural populations have been able to address this problem. Furthermore, early adaptation to a novel environment often coincides with founding events, making it difficult to disentangle neutral effects from adaptive genomic changes. Here we take advantage of the unique in situ guppy experimental system, in which we established replicate populations by translocating guppies from a high predation locality to four low predation localities. We present whole genome sequencing from the source population and the four experimental populations, sampled after [~]8-10 generations (first period), and again at [~]18-22 generations (second period). We find signatures of inbreeding only in the first period, despite documented population crashes in the second period. We show genome-wide dynamics of selection as well as selective change at single loci and uncover new targets of selection. Overall, we found signatures of selection at all levels; genome-wide, chromosome, and individual windows are more repeatable among replicates in the first period than in the second period.

Understanding how intraspecific diversity is structured is essential for predicting the eco-evolutionary trajectories of populations, especially under rapid environmental change. While such diversity has been extensively studied from a genetic perspective, much less is known about the distribution and ecological relevance of epigenetic variation within natural populations. To address this question, we focused on two species of reef-building corals belonging to distinct functional groups, Pocillopora acuta and Acropora hyacinthus, sampled across the South Pacific (New Caledonia, Fiji, French Polynesia). Using genome-wide Enzyme-Methyl sequencing, we jointly analyzed genetic (SNPs) and DNA methylation (CpGs) variation, while explicitly disentangling genetically associated from genetically independent epigenetic variation. Genetic and epigenetic structure showed contrasting spatial patterns, reflecting distinct temporal and ecological components of population dynamics. Genetic structure was strongest between archipelagos and followed an isolation-by-distance pattern consistent with long-term evolutionary processes. In contrast, epigenetic variation converged between colonies from different archipelagos. At finer spatial scales within archipelago, genetically independent epigenetic variation exhibited stronger structure than both genetic and genetically associated epigenetic variation, likely reflecting local environmental conditions. Together, our results show that genetic and epigenetic variation provide complementary insights into the eco-evolutionary processes shaping intraspecific diversity.

The unprecedented rate of climate warming threatens many species, and assessing their vulnerability to climate change represents a critical challenge in conservation biology. The Apollo butterfly, an emblematic mountain species, is expected to be impacted by climate change. Here, we analysed thousands of SNPs from 101 localities across Apollo French distribution. We identified 93 SNPs strongly associated with climate variation using five genotype-environment association analyses. We forecasted future climate maladaptation of French Apollo populations using four genomic offset methods and integrated these results with neutral and adaptive genetic diversity, genetic structure and adaptive climatic niches to infer their vulnerability to climate change. Jura and Alps populations exhibited the lowest risk of vulnerability to climate change, with low genomic offsets, high genetic diversity and connectivity, whereas Auvergne populations showed the highest genomic offsets and lowest neutral and adaptive genetic diversity. Only a reduced percentage (<1%) of the current distribution is predicted to face climatic conditions outside the current range, suggesting that adaptive variability required to adapt to future climates may already be present, and that assisted gene flow could represent an effective conservation strategy. Finally, we discuss some of the main challenges of genomic forecasts, particularly for declining non-model species.

Biodiversity losses continue to outpace traditional management, underscoring the need to understand adaptive capacity and the potential for interventions to increase fitness under climate change. We undertook a genome-wide association study on 156 Acropora palmata genets to investigate the genomic basis of areal growth, endosymbiont association, and thermal tolerance. Seven peaks on chromosomes 1, 3 and 14 were associated with endosymbiont shuffling and two peaks on chromosome 4 were associated with areal growth. As variants were located in non-coding regions we incorporated additional data from an independent field-transplant experiment to investigate their relationship with patterns of gene expression. Intersection of these datasets implicated melanocortin-like receptor activity and Ran GTPase activating protein 1 in endosymbiont composition and surface area growth, respectively. Results indicate that growth and endosymbiont associations may represent more viable intervention targets than temperature tolerance and highlight the need to better understand the role of non-coding variation in basic biology and development of restoration interventions.

The coast redwood (Sequoia sempervirens) is a long-lived, hexaploid conifer of high ecological, cultural, and economic value whose range has been greatly reduced by historical logging. Effective restoration and conservation depend on understanding patterns of genetic differentiation across the redwood range to delineate populations for management prioritization. Yet, past range-wide studies provided only a partial picture of population structure in coast redwood as they relied on a limited set of genetic markers or limited sampling, as sequencing was done on the same range-wide provenance collection. Here, we analyze 334,029 SNPs from a new range-wide set of 224 individuals using a dosage-based approach that accounts for polyploidy. Principal coordinates and neighbor-joining analyses reveal clear latitudinal genetic differentiation, with a distinct break south of San Francisco Bay. Outlier SNP analysis indicates new candidate loci involved in salinity tolerance, climate stress response, and nutrient uptake, suggesting potential local adaptation. These results point to the central role of geography in shaping genetic variation in coast redwood and give scientific basis for designing new conservation strategies and future experiments, including assisted migration, provenance trials, and restoration planning aimed at preserving the species into the future.

Remote island systems with small landmasses and reliable estimates of human occupancy are ideal model systems to disentangle the roles of global climatic changes and local human occupation on biota. Here, we used mitochondrial and nuclear genomic data from five endemic Fijian Lasioglossum (Homalictus) bee species to infer changes in effective population size (Ne). These ground-nesting bees are native, with non-specialised floral visitation habits, and distributed across the elevational gradient. All lowland species and populations showed strong signals of increasing Ne that correspond to the timing of human occupation of Fiji, but not Holocene climatic change. Highland populations, with greater isolation and present in regions less affected by anthropogenic impacts, did not show evidence of recent rapid increases in Ne. Population expansion rates across the elevational gradient differed between taxa, with significantly earlier and larger increases in predominantly lowland species than those with more restricted ranges in the highlands. This is consistent with the movement of people inland from coastal regions and into montane elevations of the island, and corresponding landscape changes that benefit the ecology of these bees. Specific life history traits of these bees, combined with substantive clearing of forest cover and floristic changes at lower elevations, has likely increased nesting opportunities and abundance of invasive floral resources. Our findings contrast with recent evidence that human occupation of Fiji has resulted in decreased ant biodiversity and raise the paradoxical possibility that human-mediated environmental changes may benefit some native montane tropical insect faunas.