Ecologists are challenged to construct models of the biological consequences of habitat loss and fragmentation. Here, we use a metapopulation model to predict the distribution of the Glanville fritillary butterfly during 22 years across a large heterogeneous landscape with 4,415 small dry meadows. The majority (74%) of the 125 networks into which the meadows were clustered are below the extinction threshold for long-term persistence. Among the 33 networks above the threshold, spatial configuration and habitat quality rather than the pooled habitat area predict metapopulation size and persistence, but additionally allelic variation in a SNP in the gene Phosphoglucose isomerase (Pgi) explains 30% of variation in metapopulation size. The Pgi genotypes are associated with dispersal rate and hence with colonizations and extinctions. Associations between Pgi genotypes, population turnover and metapopulation size reflect eco-evolutionary dynamics, which may be a common feature in species inhabiting patch networks with unstable local dynamics.

Sexual maturation timing is a life‐history trait central to the balance between mortality and reproduction. Maturation may be triggered when an underlying compound trait, called liability, exceeds a threshold. In many different species and especially fishes, this liability is approximated by growth and body condition. However, environmental vs. genetic contributions either directly or via growth and body condition to maturation timing remain unclear. Uncertainty exists also because the maturation process can reverse this causality and itself affect growth and body condition. In addition, disentangling the contributions of polygenic and major loci can be important. In many fishes, males mature before females, enabling the study of associations between male maturation and maturation‐unbiased female liability traits. Using 40 Atlantic salmon families, longitudinal common‐garden experimentation, and quantitative genetic analyses, we disentangled environmental from polygenic and major locus (vgll3) effects on male maturation, and sex‐specific growth and condition. We detected polygenic heritabilities for maturation, growth, and body condition, and vgll3 effects on maturation and body condition but not on growth. Longitudinal patterns for sex‐specific phenotypic liability, and for genetic variances and correlations between sexes suggested that early growth and condition indeed positively affected maturation initiation. However, towards spawning time, causality appeared reversed for males whereby maturation affected growth negatively and condition positively via both the environmental and genetic effects. Altogether, the results indicate that growth and condition are useful traits to study liability for maturation initiation, but only until maturation alters their expression, and that vgll3 contributes to maturation initiation via condition.

A major goal in biology is to understand how evolution shapes variation in individual life histories. Genome-wide association studies have been successful in uncovering genome regions linked with traits underlying life history variation in a range of species. However, lack of functional studies of the discovered genotype-phenotype associations severely restrains our understanding how alternative life history traits evolved and are mediated at the molecular level. Here, we report a cis-regulatory mechanism whereby expression of alternative isoforms of the transcription co-factor vestigial-like 3 (vgll3) associate with variation in a key life history trait, age at maturity, in Atlantic salmon (Salmo salar). Using a common-garden experiment, we first show that vgll3 genotype associates with puberty timing in one-year-old salmon males. By way of temporal sampling of vgll3 expression in ten tissues across the first year of salmon development, we identify a pubertal transition in vgll3 expression where maturation coincided with a 66% reduction in testicular vgll3 expression. The late maturation allele was not only associated with a tendency to delay puberty, but also with expression of a rare transcript isoform of vgll3 pre-puberty. By comparing absolute vgll3 mRNA copies in heterozygotes we show that the expression difference between the early and late maturity alleles is largely cis-regulatory. We propose a model whereby expression of a rare isoform from the late allele shifts the liability of its carriers towards delaying puberty. These results exemplify the potential importance of regulatory differences as a mechanism for the evolution of life history traits.

We characterize allelic and gene expression variation between populations of the Glanville fritillary butterfly (Melitaea cinxia) from two fragmented and two continuous landscapes in northern Europe. The populations exhibit significant differences in their life history traits, e.g. butterflies from fragmented landscapes have higher flight metabolic rate and dispersal rate in the field, and higher larval growth rate, than butterflies from continuous landscapes. In fragmented landscapes, local populations are small and have a high risk of local extinction, and hence the long-term persistence at the landscape level is based on frequent re-colonization of vacant habitat patches, which is predicted to select for increased dispersal rate. Using RNA-seq data and a common garden experiment, we found that a large number of genes (1,841) were differentially expressed between the landscape types. Hexamerin genes, the expression of which has previously been shown to have high heritability and which correlate strongly with larval development time in the Glanville fritillary, had higher expression in fragmented than continuous landscapes. Genes that were more highly expressed in butterflies from newly-established than old local populations within a fragmented landscape were also more highly expressed, at the landscape level, in fragmented than continuous landscapes. This result suggests that recurrent extinctions and re-colonizations in fragmented landscapes select a for specific expression profile. Genes that were significantly up-regulated following an experimental flight treatment had higher basal expression in fragmented landscapes, indicating that these butterflies are genetically primed for frequent flight. Active flight causes oxidative stress, but butterflies from fragmented landscapes were more tolerant of hypoxia. We conclude that differences in gene expression between the landscape types reflect genomic adaptations to landscape fragmentation.

Insect flight is one of the most energetically demanding activities in the animal kingdom, yet for many insects flight is necessary for reproduction and foraging. Moreover, dispersal by flight is essential for the viability of species living in fragmented landscapes. Here, working on the Glanville fritillary butterfly (Melitaea cinxia), we use transcriptome sequencing to investigate gene expression changes caused by 15 min of flight in two contrasting populations and the two sexes. Male butterflies and individuals from a large metapopulation had significantly higher peak flight metabolic rate (FMR) than female butterflies and those from a small inbred population. In the pooled data, FMR was significantly positively correlated with genome-wide heterozygosity, a surrogate of individual inbreeding. The flight experiment changed the expression level of 1513 genes, including genes related to major energy metabolism pathways, ribosome biogenesis and RNA processing, and stress and immune responses. Males and butterflies from the population with high FMR had higher basal expression of genes related to energy metabolism, whereas females and butterflies from the small population with low FMR had higher expression of genes related to ribosome/RNA processing and immune response. Following the flight treatment, genes related to energy metabolism were generally down-regulated, while genes related to ribosome/RNA processing and immune response were up-regulated. These results suggest that common molecular mechanisms respond to flight and can influence differences in flight metabolic capacity between populations and sexes.

The rate of excision of U12-type introns has been reported to be slower than that of U2-type introns, suggesting a rate-limiting bottleneck that could down-regulate genes containing U12-type introns. The mechanistic reasons for this slower rate of intron excision are not known, but lower abundance of the U12-type snRNPs and slower rate of assembly or catalytic activity have been suggested. To investigate snRNP abundance we concentrated on the U4atac snRNA, which is the least abundant of the U12-type snRNAs and is limiting the formation of U4atac/U6atac complex. We identified mouse NIH-3T3 cell line isolates in which the level of both U4atac snRNA and U4atac/U6atac complexes is reduced to 10%-20% of the normal level. We used these cell lines to investigate splicing efficiency by transient transfection of a reporter gene containing a U12-type intron and by quantitative PCR analysis of endogenous genes. The splicing of the reporter U12-type intron was very inefficient, but the activity could be restored by overexpression of U4atac snRNA. Using these U4atac-deficient NIH-3T3 cells, we confirmed the results of previous studies showing that U12-type introns of endogenous genes are, indeed, excised more slowly than U2-type introns, but we found that the rate did not differ from that measured in cells displaying normal levels of U4atac snRNA. Thus our results suggest that the cellular abundance of the snRNPs does not limit U12-type intron splicing under normal conditions.

A better understanding of the genetic and phenotypic architecture underlying life-history variation is a longstanding aim in biology. Theories suggest energy metabolism determines life-history variation by modulating resource acquisition and allocation trade-offs, but the genetic underpinnings of the relationship and its dependence on ecological conditions have rarely been demonstrated. The strong genetic determination of age-at-maturity by two unlinked genomic regions ( vgll3 and six6 ) makes Atlantic salmon ( Salmo salar ) an ideal model to address these questions. Using more than 250 juveniles in common garden conditions, we quantified the covariation between metabolic phenotypes—standard and maximum metabolic rates (SMR and MMR), and aerobic scope (AS)—and the life-history genomic regions, and tested if food availability modulates the relationships. We found that the early maturation genotype in vgll3 was associated with higher MMR and consequently AS. Additionally, MMR exhibited physiological epistasis; it was decreased when late maturation genotypes co-occurred in both genomic regions. Contrary to our expectation, the life-history genotypes had no effects on SMR. Furthermore, food availability had no effect on the genetic covariation, suggesting a lack of genotype-by-environment interactions. Our results provide insights on the key organismal processes that link energy use at the juvenile stage to age-at-maturity, indicating potential mechanisms by which metabolism and life-history can coevolve.

Phone number: +358 2 9415 9537; Email: paul.debes@dal.ca; ORCID: 13 https://orcid.org/0000-0003-4491-9564 14 KeywordsSexual maturation, life-history evolution, lipid reserves, resource allocation trade-15 off, large effect locus 16Abstract 17Sexual maturation is a pivotal life-history trait that balances the probabilities between mortality and 18 reproduction. Environmental vs. genetic contributions to maturation component traits, such as somatic 19 growth and body condition, remain uncertain because of difficulties in determining causality. In Atlantic 20 salmon, maturation timing associates with a large-effect locus around vgll3, which also links with growth, 21 condition, and maturation in mammals. We investigate environmental vs. genetic contributions to 22Maturation timing is a central life-history trait that contributes to maximizing individual survival and 46 reproductive success and, thereby, per capita population growth rate (1-3). Maturation timing is assumed 47