Browsing by Subject "METAPOPULATION"

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  • Tollenaere, C.; Pernechele, B.; Mäkinen, H. S.; Parratt, S. R.; Nemeth, M. Z.; Kovacs, G. M.; Kiss, L.; Tack, A. J. M.; Laine, A. -L. (2014)
  • Booksmythe, Isobel; Gerber, Nina; Ebert, Dieter; Kokko, Hanna (2018)
    Cyclical parthenogenesis presents an interesting challenge for the study of sex allocation, as individuals' allocation decisions involve both the choice between sexual and asexual reproduction, and the choice between sons and daughters. Male production is therefore expected to depend on ecological and evolutionary drivers of overall investment in sex, and those influencing male reproductive value during sexual periods. We manipulated experimental populations, and made repeated observations of natural populations over their growing season, to disentangle effects of population density and the timing of sex from effects of adult sex ratio on sex allocation in cyclically parthenogenetic Daphnia magna. Male production increased with population density, the major ecological driver of sexual reproduction; however, this response was dampened when the population sex ratio was more male-biased. Thus, in line with sex ratio theory, we show that D.magna adjust offspring sex allocation in response to the current population sex ratio.
  • Duplouy, Anne; Wong, Swee C.; Corander, Jukka; Lehtonen, Rainer; Hanski, Ilkka (2017)
    Background: Adaptation to local habitat conditions may lead to the natural divergence of populations in life-history traits such as body size, time of reproduction, mate signaling or dispersal capacity. Given enough time and strong enough selection pressures, populations may experience local genetic differentiation. The genetic basis of many life-history traits, and their evolution according to different environmental conditions remain however poorly understood. Methods: We conducted an association study on the Glanville fritillary butterfly, using material from five populations along a latitudinal gradient within the Baltic Sea region, which show different degrees of habitat fragmentation. We investigated variation in 10 principal components, cofounding in total 21 life-history traits, according to two environmental types, and 33 genetic SNP markers from 15 candidate genes. Results: We found that nine SNPs from five genes showed strong trend for trait associations (p-values under 0.001 before correction). These associations, yet nonsignificant after multiple test corrections, with a total number of 1,086 tests, were consistent across the study populations. Additionally, these nine genes also showed an allele frequency difference between the populations from the northern fragmented versus the southern continuous landscape. Discussion: Our study provides further support for previously described trait associations within the Glanville fritillary butterfly species across different spatial scales. Although our results alone are inconclusive, they are concordant with previous studies that identified these associations to be related to climatic changes or habitat fragmentation within the angstrom land population.
  • Fountain, Toby; Husby, Arild; Nonaka, Etsuko; DiLeo, Michelle; Korhonen, Janne H.; Rastas, Pasi; Schulz, Torsti Michael; Saastamoinen, Marjo Anna Kaarina; Hanski, Ilkka Aulis (2018)
    Dispersal is important for determining both species ecological processes, such as population viability, and its evolutionary processes, like gene flow and local adaptation. Yet obtaining accurate estimates in the wild through direct observation can be challenging or even impossible, particularly over large spatial and temporal scales. Genotyping many individuals from wild populations can provide detailed inferences about dispersal. We therefore utilized genomewide marker data to estimate dispersal in the classic metapopulation of the Glanville fritillary butterfly (Melitaea cinxia L.), in the Aland Islands in SW Finland. This is an ideal system to test the effectiveness of this approach due to the wealth of information already available covering dispersal across small spatial and temporal scales, but lack of information at larger spatial and temporal scales. We sampled three larvae per larval family group from 3732 groups over a six-year period and genotyped for 272 SNPs across the genome. We used this empirical data set to reconstruct cases where full-sibs were detected in different local populations to infer female effective dispersal distance, that is, dispersal events directly contributing to gene flow. On average this was one kilometre, closely matching previous dispersal estimates made using direct observation. To evaluate our power to detect full-sib families, we performed forward simulations using an individual-based model constructed and parameterized for the Glanville fritillary metapopulation. Using these simulations, 100% of predicted full-sibs were correct and over 98% of all true full-sib pairs were detected. We therefore demonstrate that even in a highly dynamic system with a relatively small number of markers, we can accurately reconstruct full-sib families and for the first time make inferences on female effective dispersal. This highlights the utility of this approach in systems where it has previously been impossible to obtain accurate estimates of dispersal over both ecological and evolutionary scales.
  • Karisto, Petteri; Kisdi, Èva (2019)
    Functional connectivity, the realized flow of individuals between the suitable sites of a heterogeneous landscape, is a prime determinant of the maintenance and evolution of populations in fragmented habitats. While a large body of literature examines the evolution of dispersal propensity, it is less known how evolution shapes functional connectivity via traits that influence the distribution of the dispersers. Here, we use a simple model to demonstrate that, in a heterogeneous environment with clustered and solitary sites (i.e., with variable structural connectivity), the evolutionarily stable population contains strains that are strongly differentiated in their pattern of connectivity (local vs. global dispersal), but not necessarily in the fraction of dispersed individuals. Also during evolutionary branching, selection is disruptive predominantly on the pattern of connectivity rather than on dispersal propensity itself. Our model predicts diversification along a hitherto neglected axis of dispersal strategies and highlights the role of the solitary sites-the more isolated and therefore seemingly less important patches of habitat-in maintaining global dispersal that keeps all sites connected.
  • DiLeo, Michelle F.; Husby, Arild; Saastamoinen, Marjo (2018)
    There is now clear evidence that species across a broad range of taxa harbor extensive heritable variation in dispersal. While studies suggest that this variation can facilitate demographic outcomes such as range expansion and invasions, few have considered the consequences of intraspecific variation in dispersal for the maintenance and distribution of genetic variation across fragmented landscapes. Here, we examine how landscape characteristics and individual variation in dispersal combine to predict genetic structure using genomic and spatial data from the Glanville fritillary butterfly. We used linear and latent factor mixed models to identify the landscape features that best predict spatial sorting of alleles in the dispersal-related gene phosphoglucose isomerase (Pgi). We next used structural equation modeling to test if variation in Pgi mediated gene flow as measured by F-st at putatively neutral loci. In a year when the population was recovering following a large decline, individuals with a genotype associated with greater dispersal ability were found at significantly higher frequencies in populations isolated by water and forest, and these populations showed lower levels of genetic differentiation at neutral loci. These relationships disappeared in the next year when metapopulation density was high, suggesting that the effects of individual variation are context dependent. Together our results highlight that (1) more complex aspects of landscape structure beyond just the configuration of habitat can be important for maintaining spatial variation in dispersal traits and (2) that individual variation in dispersal plays a key role in maintaining genetic variation across fragmented landscapes.
  • Laine, Anna-Liisa; Makinen, Hannu (2018)
    The ability of a parasite strain to establish and grow on its host may be drastically altered by simultaneous infection by other parasite strains. However, we still lack an understanding of how life-history allocations may change under coinfection, although life-history correlations are a critical mechanism restricting the evolutionary potential and epidemiological dynamics of pathogens. Here, we study how life-history stages and their correlations change in the obligate fungal pathogen Podosphaera plantaginis under single infection and coinfection scenarios. We find increased pathogen loads under coinfection, but this is not explained by an enhanced performance at any of the life-history stages that constitute infections. Instead, we show that under coinfection the correlation between timing of sporulation and final pathogen load becomes positive. The changes in pathogen life-history allocations leading to more severe infections under coinfection can have far-reaching epidemiological consequences, as well as implication for our understanding of the evolution of virulence.
  • Duplouy, Anne; Nair, Abhilash; Nyman, Toshka; van Nouhuys, Saskya (2021)
    Population bottlenecks associated with founder events strongly impact the establishment and genetic makeup of populations. In addition to their genotype, founding individuals also bring along parasites, as well as symbionts that can manipulate the phenotype of their host, affecting the host population establishment, dynamics and evolution. Thus, to understand introduction, invasion, and spread, we should identify the roles played by accompanying symbionts. In 1991, the parasitoid wasp, Hyposoter horticola, and its associated hyperparasitoid were accidentally introduced from the main angstrom land islands, Finland, to an isolated island in the archipelago, along with their host, the Glanville fritillary butterfly. Though the receiving island was unoccupied, the butterfly was present on some of the small islands in the vicinity. The three introduced species have persisted locally ever since. A strain of the endosymbiotic bacterium Wolbachia has an intermediate prevalence in the parasitoid H. horticola across the main angstrom land population. The infection increases its susceptibility of to hyperparasitism. We investigated the establishment and spread of the parasitoid, along with patterns of prevalence of its symbiont using 323 specimens collected between 1992 and 2013, from five localities across angstrom land, including the source and introduced populations. Using 14 microsatellites and one mitochondrial marker, we suggest that the relatively diverse founding population and occasional migration between islands might have facilitated the persistence of all isolated populations, despite multiple local population crashes. We also show that where the hyperparasitoid is absent, and thus selection against infected wasp genotypes is relaxed, there is near-fixation of Wolbachia.
  • Rosa, Elena; Saastamoinen, Marjo (2017)
    Organisms with complex life-cycles acquire essential nutrients as juveniles, and hence even a short-term food stress during development can impose serious fitness costs apparent in adults. We used the Glanville fritillary butterfly to investigate the effects of larval food stress on adult performance under semi-natural conditions in a population enclosure. We were specifically interested in whether the negative effects observed were due to body mass reduction only or whether additional effects unrelated to pupal mass were evident. The two sexes responded differently to the larval food stress. In females, larval food stress reduced pupal mass and reproductive performance. The reduced reproductive performance was partially mediated by pupal mass reduction. Food stressed females also had reduced within-patch mobility, and this effect was not dependent on pupal mass. Conversely, food stress had no effect on male pupal mass, suggesting a full compensation via prolonged development time. Nonetheless, food stressed males were less likely to sire any eggs, potentially due to changes in their territorial behavior, as indicated by food stress also increasing male within-patch mobility (i.e., patrolling behavior). When males did sire eggs, the offspring number and viability were unaffected by male food stress treatment. Viability was in general higher for offspring sired by lighter males. Our study highlights how compensatory mechanisms after larval food stress can act in a sex-specific manner and that the alteration in body mass is only partially responsible for the reduced adult performance observed.
  • Duplouy, Anne; Minard, Guillaume; Lähteenaro, Meri; Rytteri, Susu; Saastamoinen, Marjo (2018)
    All organisms are challenged by encounters with parasites, which strongly select for efficient escape strategies in the host. The threat is especially high for gregarious species entering immobile periods, such as diapause. Larvae of the Glanville fritillary butterfly, Melitaea cinxia, spend the winter in diapause in groups of conspecifics each sheltered in a silk nest. Despite intensive monitoring of the population, we have little understanding of the ecological factors influencing larval survival over the winter in the field. We tested whether qualitative and quantitative properties of the silk nest contribute to larval survival over diapause. We used comparative proteomics, metabarcoding analyses, microscopic imaging, and in vitro experiments to compare protein composition of the silk, community composition of the silk-associated microbiota, and silk density from both wild-collected and laboratory-reared families, which survived or died in the field. Although most traits assessed varied across families, only silk density was correlated with overwinter survival in the field. The silk nest spun by gregarious larvae before the winter acts as an efficient breathable physical shield that positively affects larval survival during diapause. Such benefit may explain how this costly trait is conserved across populations of this butterfly species and potentially across other silk-spinning insect species.
  • Minard, Guillaume; Tikhonov, Gleb; Ovaskainen, Otso; Saastamoinen, Marjo (2019)
    Understanding of the ecological factors that shape intraspecific variation of insect microbiota in natural populations is relatively poor. In Lepidopteran caterpillars, microbiota is assumed to be mainly composed of transient bacterial symbionts acquired from the host plant. We sampled Glanville fritillary (Melitaea cinxia) caterpillars from natural populations to describe their gut microbiome and to identify potential ecological factors that determine its structure. Our results demonstrate high variability of microbiota composition even among caterpillars that shared the same host plant individual and most likely the same genetic background. We observed that the caterpillars harboured microbial classes that varied among individuals and alternated between two distinct communities (one composed of mainly Enterobacteriaceae and another with more variable microbiota community). Even though the general structure of the microbiota was not attributed to the measured ecological factors, we found that phylogenetically similar microbiota showed corresponding responses to the sex and the parasitoid infection of the caterpillar and to those of the host plant's microbial and chemical composition. Our results indicate high among-individual variability in the microbiota of the M. cinxia caterpillar and contradict previous findings that the host plant is the major driver of the microbiota communities of insect herbivores.