Biology subjects

Laurila, A.

Publications and source records attributed to Laurila, A..

11 recordsLinked to original sources

bioRxiv2026

Latitudinal Patterns in Immunogenetic and Microbiome Diversity in two anuran species: Bufo bufo and Bufo spinosus

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.

evolutionary biology↗

bioRxiv2026

Assessing local adaptation and divergence at early life stages within Eastern Baltic cod

Many commercially exploited fish stocks have declined over the last few decades. It is therefore essential to identify natural populations and understand local adaptation for sustainable management. Salinity is a key environmental factor shaping local adaptation, and adaptive trait divergence often occurs at the egg and larval stages. The strong salinity gradient in the brackish Baltic Sea has driven rapid adaptation in multiple taxa. The Eastern Baltic cod (Gadus morhua) has adapted to low salinity with buoyant and tolerant eggs and larvae, but the stock has declined both in abundance and geographical range during the last decades. The main reproduction area of this stock is in the Bornholm Basin (ICES subdivision (SD) 25) in the southern Baltic Proper. Cod in this area, however, exhibit stunted growth and small body sizes. In contrast, large and healthy cod in reproductive condition have been observed in the [A]land Sea in the northern Baltic Proper (SD 29), raising the question of whether these fish represent a locally adapted population capable of successful reproduction in the lower salinities (5-10 psu in the northern Baltic Proper (SD 27, 29 and 32). Here, we experimentally assessed egg and yolk-sac larvae survival across salinities, egg size, egg and larval neutral buoyancy and egg survival on sediment, to test whether northern ([A]land) cod show adaptation to low salinity at early life stages as compared to southern cod. Mortality of larvae increased with decreasing salinity in cod from both areas, with the lowest survival at 7 psu. At 9 psu, more than 50% of northern cod larvae survived, suggesting that development could occur in SD29. Egg size and buoyancy were similar between northern and southern cod, and eggs and larvae were negatively buoyant, sinking under local salinity conditions. Nevertheless, the eggs survived and hatched well on sediment, indicating potential for demersal spawning. Our findings show no strong evidence of adaptive divergence to lower salinity in northern cod; however, their ability to tolerate sediment contact at early life stages suggests that Eastern Baltic cod may reproduce outside their historical spawning grounds.

ecology↗

bioRxiv2025

Eastern Baltic cod larvae in a salinity gradient: choice of salinity and the role of neutral buoyancy

Fish rely on multiple sensory systems to navigate in the aquatic environment, yet these mechanisms are often scarcely known during their early life history stages. Salinity is an important environmental parameter affecting the performance of fish larvae, and recent studies have shown that some larval fish use it as an environmental cue to position, orientate and navigate. Further, fish larvae are often visual feeders, and light has been suggested to be a crucial environmental cue for visual orientation and feeding. In this study, we investigate whether first-feeding larvae of eastern Baltic cod (Gadus morhua callarias) are driven by light and salinity. We examine this in the context of their natural vertical distribution and movement; from deeper, darker and more saline (13-17 psu) water layers towards the more light-exposed and less saline (7 psu) surface water. Further, we investigate the relationship between this movement and the neutral buoyancy measured both in active and passive larvae. We found that the larvae remain in a saline environment close to the salinity which supports their neutral buoyancy. They show negative phototaxis, suggesting an active avoidance of the lighter and less saline upper water layers. These results improve our understanding of the ecophysiology and behaviour of eastern Baltic cod larvae during the first-feeding stage and serve as an important input for restocking efforts of eastern Baltic cod and potential future production of hatchery rearing of eastern Baltic cod. HighlightsO_LIFirst-feeding larvae had no preference for a low-salinity environment. C_LIO_LIVertical distribution of eastern Baltic cod larvae was mainly driven by negative phototaxis. C_LIO_LILarval neutral buoyancy played a larger role in their behaviour than light. C_LI

ecology↗

bioRxiv2025

First occurrence of Ranavirus in Scandinavian peninsula

Emerging infectious diseases (EIDs) pose a major threat to global amphibian populations, contributing to widespread mortality and species extinctions. Among EIDs, those caused by fungal infection pathogens Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal), and viral infections of the genus Ranavirus (Rv), represent the most significant threats to amphibian biodiversity. Here, we test for occurrence of Rv infection in three different locations in southeastern Sweden. Using a quantitative PCR (qPCR) assay, complemented by a secondary PCR-based validation method targeting the viral major capsid protein gene (MCP) and additional five partial sequences, we detected Rv infection in two of three locations and in five out of 43 individuals tested. This is the first confirmed record of Rv occurrence reported at such high latitudes in north Europe and the first one from Scandinavian peninsula, contributing important insights into infection prevalence in northern amphibian populations. These findings establish a basis for further research for the conservation of these vulnerable populations.

ecology↗

bioRxiv2023

Metamorphosis reverses the risk-taking behavioral phenotype in moor frog along a latitudinal gradient

O_LIUnderstanding how demographic processes and environmental conditions shape behavioural variation across populations is pivotal in evolutionary ecology. However, the role that such processes play in the link between behaviour and life-history traits across populations remains largely unclear. C_LIO_LIThe moor frog (Rana arvalis) has colonized Sweden via two distinct routes from south via Denmark and from north via Finland. We collected R. arvalis eggs from multiple populations along a 1700 km latitudinal gradient across Northern Europe and raised tadpoles in a common garden experiment. We assessed developmental growth and proactivity levels in ca. 300 individuals at two key stages of anuran larval development: tadpoles (Gosner stage 32) and froglets (Gosner stage 46). C_LIO_LIWe found strong behavioural differences along the latitudinal gradient and between developmental stages. Tadpoles from northernmost populations were bolder (shorter times to leave a shelter) and showed higher activity levels in an open field test compared to those from southern populations. C_LIO_LIHowever, these behavioural patterns reversed at the froglet stage, with individuals from northern populations showing reduced proactivity that those from southern populations. Further analyses indicated significant associations between developmental growth and boldness, with contrasting patterns across developmental stages and colonization routes. C_LIO_LIIn line with recent revisitations of the pace-of-life syndrome theory (POLS) for animal personality, our findings suggest a decoupling of correlations between behaviour and life history traits across ontogeny, likely reflecting adaptive responses to divergent ecological and demographic constraints along the latitudinal gradient. C_LI

animal behavior and cognition↗

bioRxiv2023

Association between the skin microbiome and MHC class II diversity in an amphibian

It has become clear that the microbiome plays an important role in determining host health, diseases, and phenotypic variation. There is increasing evidence that the microbiome influences host fitness and its adaptation to the environment is changing our thinking on host-microbe interactions. However, it remains unclear how a host genotype shapes its microbiome. Here, we explored how genetic background and evolutionary history influence associated microbiome in amphibian populations. We studied how skin bacterial diversity is associated with the Major Histocompatibility Complex (MHC) class II exon 2 diversity in 12 moor frog populations belonging to two geographical clusters that show signatures of past and ongoing differential selection patterns. We found that bacterial alpha-diversity remained similar between the two clusters, while MHC haplotype-supertypes and genetic diversity differed between the clusters. Bacterial alpha-diversity was positively correlated with expected MHC heterozygosity and negatively with MHC nucleotide diversity. We also found that bacterial community composition differed significantly between the two geographic clusters and between specific MHC supertypes. These findings further suggest that population historical demographic events influence hologenomic variation and provide new insights into how immunogenetic host variability and microbial diversity may jointly influence host fitness with consequences for disease susceptibility and population persistence.

evolutionary biology↗

bioRxiv2021

Body size mediates latitudinal population differences in response to Bd infection in two amphibian species.

Populations of the same species may differ in their sensitivity to pathogens but the factors behind this variation are poorly understood. Moreover, infections may cause sub-lethal fitness effects even in species resistant or tolerant to disease. The chytrid fungus Batrachochytrium dendrobatidis (Bd), is a generalist pathogen which has caused amphibian population declines worldwide. In many species, Bd infection causes the disease chytridiomycosis, often leading to high mortality. We investigated how geographical origin affects tolerance to Bd by exposing newly metamorphosed individuals of two North European amphibians (moor frog Rana arvalis, common toad Bufo bufo) from two latitudinal regions to two different BdGPL strains. Bd exposure strongly lowered survival in B. bufo, and in both species survival was lower in the northern region, this difference being much stronger in B. bufo. Northern individuals were smaller in both species, and the survival difference between the regions was size-mediated with smaller individuals being more sensitive to Bd. In both species, Bd exposure led to sub-lethal effects in terms of reduced growth suggesting that even individuals surviving the infection may have reduced fitness mediated by smaller body size. Bd strain affected size-dependent mortality differently in the two regions. We discuss the possible mechanisms how body size and geographical origin can contribute to the present results.

ecology↗

bioRxiv2019

Latitudinal MHC variation and haplotype associated differential survival in response to experimental infection of two strains of Batrachochytrium dendrobatitis (Bd-GPL) in common toads

While both innate and adaptive immune system mechanisms have been implicated in resistance against the chytrid fungus Batrachochytrium dendrobatitis, studies on the role of specific MHC haplotypes on Bd infection are rare. Here, we studied latitudinal variation in MHC Class IIB loci along a latitudinal gradient from southern to northern Sweden in common toads, Bufo bufo. Swedish toad populations had fewer MHC Class IIB haplotypes compared to a previous study of populations in Britain. Furthermore, we found MHC diversity to decline from south to the north within Sweden. The low diversity may compromise the ability of northern populations to fight emerging disease, such as the chytrid fungus Bd. In a laboratory experiment, we infected newly metamorphosed toads with two strains of the Global Pandemic Lineage of the fungus (Bd-GPL) and compared survival with sham controls. We found Bd-infected toads had lower survival compared to controls. Survival was dependent on Bd-strain and whether experimental toads where collected in the south or the north of Sweden with lower survival in northern individuals. MHC diversity was lower in toads of northern origin, all northern animals being monomorphic for a single MHC haplotype, whereas we found seven different haplotypes in southern animals. Survival of infected animals was dependent on both Bd-strain and MHC haplotype suggesting differential infection dynamics depending on both Bd-strain and host MHC characteristics.

evolutionary biology↗

bioRxiv2018

Adaptive genomic variation associated with environmental gradients along a latitudinal cline in Rana temporaria

Rana temporaria occur across a large geographic and environmental gradient in Scandinavia. Several studies involving common garden experiments have established adaptive divergence across the gradient. The main objective of this study was to determine the extent of neutral and adaptive genetic divergence across the latitudinal gradient. Here we sequence genome-wide markers for 15 populations from six regions sampled from southern Sweden to Finland. Using a multivariate approach we find that 68% of the genomic variation is associated with climate or geographically structured climate. Using outlier scans and environmental association analyses we identify a set of potentially adaptive loci and examine their change in allele frequency associated with different climatic variables. Using a gradient forest analysis we identify points along three of the climate variables where allele frequencies change more rapidly than expected if it were a linear association. We identify a large threshold effect associated with BIO5 (mean temperature during the warmest month) which is seen as a rapid change in southern Sweden. By comparing the change in neutral and adaptive allele frequencies across the whole gradient, we identify southern Sweden as a region with the largest divergence between the datasets. This suggests small changes in the climate may result in a mismatch between the adaptive genotypes and the environment in these populations. Overall this study shows that genomic analyses can provide a powerful complement to common garden experiments to improve our understanding of adaptive divergence across heterogeneous landscapes.

evolutionary biology↗

bioRxiv2018

Effects of host species and environmental factors on the prevalence of Batrachochytrium dendrobatidis in northern Europe

The fungal pathogen Batrachochytrium dendrobatidis (Bd) is a major threat to amphibian populations. Here we asked if the prevalence of Bd differs between amphibian species and whether it is related to local environmental factors in breeding habitats as well as landscape variables measured at three scales (500, 2000 and 5000 m radius) in southernmost Sweden. We sampled 947 anurans from six species in 31 ponds. Canopy cover, pond perimeter, pH and temperature were treated as local scale pond characteristics. Number of surrounding ponds, area of arable land, area of mature forest and number of resident people were treated as landscape variables. Bufo bufo and Rana temporaria had a prevalence of 0.5-1.0% which differed strongly from the other four species (Bombina bombina, Bufotes variabilis, Epidalea calamita, Rana arvalis) showing 13-64% prevalence. Bd prevalence in these four species was higher in ponds with higher pH, surrounded by a landscape with less mature forest and few wetlands. Our results show that the infection dynamics of Bd are complex and depend on local pond characteristics, host community composition and the spatial scale under investigation. Information on environmental factors associated with Bd and species differences in susceptibility may mitigate further spread of the disease through public information and guide conservational action plans, especially for the most threatened species.

ecology↗

bioRxiv2018

Development and worldwide use of a non-lethal and minimal population-level impact protocols for the isolation of chytrids from amphibians

Parasitic chytrid fungi have emerged as a significant threat to amphibian species worldwide, necessitating the development of techniques to isolate these pathogens into sterile culture for research purposes. However, early methods of isolating chytrids from their hosts relied on killing amphibians. We modified a pre-existing protocol for isolating chytrids from infected animals to use toe clips and biopsies from toe webbing rather than euthanizing hosts, and distributed the protocol to interested researchers worldwide as part of the BiodivERsA project RACE - here called the RML protocol. In tandem, we developed a lethal procedure for isolating chytrids from tadpole mouthparts. Reviewing a database of use a decade after their inception, we find that these methods have been widely applied across at least 5 continents, 23 countries and in 62 amphibian species, and have been successfully used to isolate chytrids in remote field locations. Isolation of chytrids by the non-lethal RML protocol occured in 18% of attempts with 207 fungal isolates and three species of chytrid being recovered. Isolation of chytrids from tadpoles occured in 43% of attempts with 334 fungal isolates of one species (Batrachochytrium dendrobatidis) being recovered. Together, these methods have resulted in a significant reduction and refinement of our use of threatened amphibian species and have improved our ability to work with this important group of emerging fungal pathogens.

ecology↗