Mosquito alert: leveraging citizen science to create a GBIF mosquito occurrence dataset.

The Mosquito Alert dataset includes occurrence records of adult mosquitoes collected worldwide in 2014-2020 through Mosquito Alert, a citizen science system for investigating and managing disease-carrying mosquitoes. Records are linked to citizen science-submitted photographs and validated by entomologists to determine the presence of five targeted European mosquito vectors: Aedes albopictus, Ae. aegypti, Ae. japonicus, Ae. koreicus, and Culex pipiens. Most records are from Spain, reflecting Spanish national and regional funding, but since autumn 2020 substantial records from other European countries are included, thanks to volunteer entomologists coordinated by the AIM-COST Action, and to technological developments to increase scalability. Among other applications, the Mosquito Alert dataset will help develop citizen science-based early warning systems for mosquito-borne disease risk. It can also be reused for modelling vector exposure risk, or to train machine-learning detection and classification routines on the linked images, to assist with data validation and establishing automated alert systems.

The effects of drift and selection on latitudinal genetic variation in Scandinavian common toads (Bufo bufo) following postglacial recolonisation.

Clinal variation is paramount for understanding the factors shaping genetic diversity in space and time. During the last glacial maximum, northern Europe was covered by glacial ice that rendered the region uninhabitable for most taxa. Different evolutionary processes during and after the recolonisation of this area from different glacial refugia have affected the genetic landscape of the present day European flora and fauna. In this study, we focus on the common toad (Bufo bufo) in Sweden and present evidence suggesting that these processes have resulted in two separate lineages of common toad, which colonised Sweden from two directions. Using ddRAD sequencing data for demographic modelling, structure analyses, and analysis of molecular variance (AMOVA), we provide evidence of a contact zone located between Uppland and Västerbotten in central Sweden. Genetic diversity was significantly higher in southern Sweden compared to the north, in accordance with a pattern of decreased genetic diversity with increasing distance from glacial refugia. Candidate genes under putative selection are identified through outlier detection and gene-environment association methods. We provide evidence of divergent selection related to stress response and developmental processes in these candidate genes. The colonisation of Sweden by two separate lineages may have implications for how future conservation efforts should be directed by identifying management units and putative local adaptations.

Genetic response to human-induced habitat changes in the marine environment: A century of evolution of European sprat in Landvikvannet, Norway.

Habitat changes represent one of the five most pervasive threats to biodiversity. However, anthropogenic activities also have the capacity to create novel niche spaces to which species respond differently. In 1880, one such habitat alterations occurred in Landvikvannet, a freshwater lake on the Norwegian coast of Skagerrak, which became brackish after being artificially connected to the sea. This lake is now home to the European sprat, a pelagic marine fish that managed to develop a self-recruiting population in barely few decades. Landvikvannet sprat proved to be genetically isolated from the three main populations described for this species; that is, Norwegian fjords, Baltic Sea, and the combination of North Sea, Kattegat, and Skagerrak. This distinctness was depicted by an accuracy self-assignment of 89% and a highly significant F ST between the lake sprat and each of the remaining samples (average of ≈0.105). The correlation between genetic and environmental variation indicated that salinity could be an important environmental driver of selection (3.3% of the 91 SNPs showed strong associations). Likewise, Isolation by Environment was detected for salinity, although not for temperature, in samples not adhering to an Isolation by Distance pattern. Neighbor-joining tree analysis suggested that the source of the lake sprat is in the Norwegian fjords, rather than in the Baltic Sea despite a similar salinity profile. Strongly drifted allele frequencies and lower genetic diversity in Landvikvannet compared with the Norwegian fjords concur with a founder effect potentially associated with local adaptation to low salinity. Genetic differentiation (F ST) between marine and brackish sprat is larger in the comparison Norway-Landvikvannet than in Norway-Baltic, which suggests that the observed divergence was achieved in Landvikvannet in some 65 generations, that is, 132 years, rather than gradually over thousands of years (the age of the Baltic Sea), thus highlighting the pace at which human-driven evolution can happen.

Small-scale population divergence is driven by local larval environment in a temperate amphibian.

Genomic variation within and among populations is shaped by the interplay between natural selection and the effects of genetic drift and gene flow. Adaptive divergence can be found in small-scale natural systems even when population sizes are small, and the potential for gene flow is high, suggesting that local environments exert selection pressures strong enough to counteract the opposing effects of drift and gene flow. Here, we investigated genomic differentiation in nine moor frog (Rana arvalis) populations in a small-scale network of local wetlands using 16,707 ddRAD-seq SNPs, relating levels of differentiation with local environments, as well as with properties of the surrounding landscape. We characterized population structure and differentiation, and partitioned the effects of geographic distance, local larval environment, and landscape features on total genomic variation. We also conducted gene-environment association studies using univariate and multivariate approaches. We found small-scale population structure corresponding to 6-8 clusters. Local larval environment was the most influential component explaining 2.3% of the total genetic variation followed by landscape features (1.8%) and geographic distance (0.8%), indicative of isolation-by-environment, -by-landscape, and -by-distance, respectively. We identified 1000 potential candidate SNPs putatively under divergent selection mediated by the local larval environment. The candidate SNPs were involved in, among other biological functions, immune system function and development. Our results suggest that small-scale environmental differences can exert selection pressures strong enough to counteract homogenizing effects of gene flow and drift in this small-scale system, leading to observable population differentiation.

Antimicrobial peptide and sequence variation along a latitudinal gradient in two anurans.

BACKGROUND: While there is evidence of both purifying and balancing selection in immune defense genes, large-scale genetic diversity in antimicrobial peptides (AMPs), an important part of the innate immune system released from dermal glands in the skin, has remained uninvestigated. Here we describe genetic diversity at three AMP loci (Temporin, Brevinin and Palustrin) in two ranid frogs (Rana arvalis and R. temporaria) along a 2000 km latitudinal gradient. We amplified and sequenced part of the Acidic Propiece domain and the hypervariable Mature Peptide domain (~ 150-200 bp) in the three genes using Illumina Miseq and expected to find decreased AMP genetic variation towards the northern distribution limit of the species similarly to studies on MHC genetic patterns. RESULTS: We found multiple loci for each AMP and relatively high gene diversity, but no clear pattern of geographic genetic structure along the latitudinal gradient. We found evidence of trans-specific polymorphism in the two species, indicating a common evolutionary origin of the alleles. Temporin and Brevinin did not form monophyletic clades suggesting that they belong to the same gene family. By implementing codon evolution models we found evidence of strong positive selection acting on the Mature Peptide. We also found evidence of diversifying selection as indicated by divergent allele frequencies among populations and high Theta k values. CONCLUSION: Our results suggest that AMPs are an important source of adaptive diversity, minimizing the chance of microorganisms developing resistance to individual peptides.

Parental effects influence life history traits and covary with an environmental cline in common frog populations.

Across latitudinal clines, the juvenile developmental rates of ectotherms often covary with the length of the growing season, due to life-history trade-offs imposed by the time-constrained environments. However, as the start of the growing season often varies substantially across years, adaptive parental effects on juvenile developmental rates may mediate the costs of a delayed season. By employing a meta-analysis, we tested whether larval developmental rates across a latitudinal cline of the common frog (Rana temporaria) are affected by fluctuating onsets of breeding, across years. We predicted that larval developmental rate will be inversely related to the onset of breeding, and that northern populations will be more prone to shorten their developmental rate in response to late breeding, as the costs of delayed metamorphosis should be highest in areas with a shorter growing season. We found that the larval period of both northern and southern populations responded to parental environmental conditions to a similar degree in absolute terms, but in different directions. In northern populations, a late season start correlated with decreased development time, suggesting that the evolution of parental effects aids population persistence in time-constrained environments. In southern populations, late season start correlated with increased development time, which could potentially be explained as a predator avoidance strategy. Our findings suggest that local ecological variables can induce adaptive parental effects, but responses are complex, and likely trade-off with other ecological factors.

Latitudinal divergence in a widespread amphibian: Contrasting patterns of neutral and adaptive genomic variation.

Stochastic effects from demographic processes and selection are expected to shape the distribution of genetic variation in spatially heterogeneous environments. As the amount of genetic variation is central for long-term persistence of populations, understanding how these processes affect variation over large-scale geographical gradients is pivotal. We investigated the distribution of neutral and putatively adaptive genetic variation, and reconstructed demographic history in the moor frog (Rana arvalis) using 136 individuals from 15 populations along a 1,700-km latitudinal gradient from northern Germany to northern Sweden. Using double digest restriction-site associated DNA sequencing we obtained 27,590 single nucleotide polymorphisms (SNPs), and identified differentiation outliers and SNPs associated with growing season length. The populations grouped into a southern and a northern cluster, representing two phylogeographical lineages from different post-glacial colonization routes. Hybrid index estimation and demographic model selection showed strong support for a southern and northern lineage and evidence of gene flow between regions located on each side of a contact zone. However, patterns of past gene flow over the contact zone differed between neutral and putatively adaptive SNPs. While neutral nucleotide diversity was higher along the southern than the northern part of the gradient, nucleotide diversity in differentiation outliers showed the opposite pattern, suggesting differences in the relative strength of selection and drift along the gradient. Variation associated with growing season length decreased with latitude along the southern part of the gradient, but not along the northern part where variation was lower, suggesting stronger climate-mediated selection in the north. Outlier SNPs included loci involved in immunity and developmental processes.

Genetic basis of amphibian larval development along a latitudinal gradient: Gene diversity, selection and links with phenotypic variation in transcription factor C/EBP-1.

Ectotherm development rates often show adaptive divergence along climatic gradients, but the genetic basis for this variation is rarely studied. Here, we investigated the genetic basis for phenotypic variation in larval development in the moor frog Rana arvalis from five regions along a latitudinal gradient from Germany to northern Sweden. We focused on the C/EBP-1 gene, a transcription factor associated with larval development time. Allele frequencies at C/EBP-1 varied strongly among geographical regions. Overall, the distribution of alleles along the gradient was in concordance with the dual post-glacial colonization routes into Scandinavia, with a large number of alleles exclusively present along the southern colonization route. Only three of 38 alleles were shared between the routes. Analysis of contemporary selection on C/EBP-1 showed divergent selection among the regions, probably reflecting adaptation to the local environmental conditions, although this was especially strong between southern and northern regions coinciding also with lineages from different colonization routes. Overall, the C/EBP-1 gene has historically been under purifying selection, but two specific amino acid positions showed significant signals of positive selection. These positions showed divergence between southern and northern regions, and we suggest that they are functionally involved in the climatic adaptation of larval development. Using phenotypic data from a common garden experiment, we found evidence for specific C/EBP-1 alleles being correlated with larval development time, suggesting a functional role in adaptation of larval development to large-scale climatic variation.

Transgenerational effects and impact of compensatory responses to changes in breeding phenology on antipredator defenses.

As organisms living in temperate environments often have only a short time window for growth and reproduction, their life-history strategies are expected to be influenced by these time constraints. Parents may alter the pace of offspring life-history as a response to changes in breeding phenology. However, the responses to changes in time constraints must be balanced with those against other stressors, such as predation, one of the strongest and more ubiquitous selective factors in nature. Here, after experimentally modifying the timing of breeding and hatching in the moor frog (Rana arvalis), we studied how compensatory responses to delayed breeding and hatching affect antipredator strategies in amphibian larvae. We examined the activity patterns, morphology and life-history responses in tadpoles exposed to different combinations of breeding and hatching delays in the presence and absence of predators. We found clear evidence of adaptive transgenerational effects since tadpoles from delayed breeding treatments increased growth and development independently of predation risk. The presence of predators reduced tadpole activity, tadpoles from delayed breeding treatments maintaining lower activity than non-delayed ones also in the absence of predators. Tadpoles reared with predators developed deeper tails and bodies, however, tadpoles from breeding delay treatments had reduced morphological defenses as compared to non-delayed individuals. No significant effects of hatching delay were detected in this study. Our study reveals that amphibian larvae exposed to breeding delay develop compensatory life-history responses even under predation risk, but these responses trade-off with the development of morphological antipredator defenses. These results suggest that under strong time constraints organisms are selected to develop fast growth and development responses, and rely on lower activity rates as their main antipredator defense. Examining how responses to changes in phenology affect species interactions is highly relevant for better understanding ecological responses to climate change.

Local divergence of thermal reaction norms among amphibian populations is affected by pond temperature variation.

Although temperature variation is known to cause large-scale adaptive divergence, its potential role as a selective factor over microgeographic scales is less well-understood. Here, we investigated how variation in breeding pond temperature affects divergence in multiple physiological (thermal performance curve and critical thermal maximum [CTmax]) and life-history (thermal developmental reaction norms) traits in a network of Rana arvalis populations. The results supported adaptive responses to face two main constraints limiting the evolution of thermal adaptation. First, we found support for the faster-slower model, indicating an adaptive response to compensate for the thermodynamic constraint of low temperatures in colder environments. Second, we found evidence for the generalist-specialist trade-off with populations from colder and less thermally variable environments exhibiting a specialist phenotype performing at higher rates but over a narrower range of temperatures. By contrast, the local optimal temperature for locomotor performance and CTmax did not match either mean or maximum pond temperatures. These results highlight the complexity of the adaptive multiple-trait thermal responses in natural populations, and the role of local thermal variation as a selective force driving diversity in life-history and physiological traits in the presence of gene flow.