Sami Aikio

Do dominants have higher heterozygosity? Social status and genetic variation in brown trout, Salmo trutta

A key question of evolutionary importance is what factors influence who becomes dominant. Individual genetic variation has been found to be associated with several fitness traits, including behaviour. Could it also be a factor influencing social dominance? We investigated the association between social status and the amount of intra-individual genetic variation in juvenile brown trout (Salmo trutta). Genetic variation was estimated using 12 microsatellite loci. Dominant individuals had higher mean heterozygosity than subordinates in populations with the longest hatchery background. Heterozygosity–heterozygosity correlations did not find any evidence of inbreeding; however, single-locus analysis revealed four loci that each individually differed significantly between dominant and subordinate fish, thus giving more support to local than general effect as the mechanism behind the observed association between genetic diversity and a fitness-associated trait. We did not find any significant relation between mean d2 and social status, or internal relatedness and social status. Our results suggest that individual genetic variation can influence dominance relations, but manifestation of this phenomenon may depend on the genetic background of the population.

Optimality and phenotypic plasticity of shoot-to-root ratio under variable light and nutrient availabilities

We studied the phenotypic plasticity of shoot-to-root ratio with a model of plant growth in different availabilities of light and nutrients. Optimal shoot-to-root ratio was defined as the equal limitation of growth by light and nutrients. An optimally growing plant had a curved relative growth rate (RGR) isoclines and a faster growth rate than a fixed-allocation plant having right-angled RGR isoclines. We assumed the plant be exposed to a unit standard deviation of bivariate normally distributed resources. Plants were more plastic in a low than in a high resource availability. Negative correlation between resources increased and positive correlation decreased plasticity. Plasticity was high in plants that saturate at low resource availabilities but independent of maximum growth rate. A trade-off between the maximum growth rate and plasticity of shoot-to-root allocation may rise indirectly from the tendency of fast-growing plants to have high resource requirements.

Moth Outbreaks Alter Root-Associated Fungal Communities in Subarctic Mountain Birch Forests

Climate change has important implications on the abundance and range of insect pests in forest ecosystems. We studied responses of root-associated fungal communities to defoliation of mountain birch hosts by a massive geometrid moth outbreak through 454 pyrosequencing of tagged amplicons of the ITS2 rDNA region. We compared fungal diversity and community composition at three levels of moth defoliation (intact control, full defoliation in one season, full defoliation in two or more seasons), replicated in three localities. Defoliation caused dramatic shifts in functional and taxonomic community composition of root-associated fungi. Differentially defoliated mountain birch roots harbored distinct fungal communities, which correlated with increasing soil nutrients and decreasing amount of host trees with green foliar mass. Ectomycorrhizal fungi (EMF) abundance and richness declined by 70–80xa0% with increasing defoliation intensity, while saprotrophic and endophytic fungi seemed to benefit from defoliation. Moth herbivory also reduced dominance of Basidiomycota in the roots due to loss of basidiomycete EMF and increases in functionally unknown Ascomycota. Our results demonstrate the top-down control of belowground fungal communities by aboveground herbivory and suggest a marked reduction in the carbon flow from plants to soil fungi following defoliation. These results are among the first to provide evidence on cascading effects of natural herbivory on tree root-associated fungi at an ecosystem scale.

The modelled growth of mycorrhizal and non-mycorrhizal plants under constant versus variable soil nutrient concentration

Abstract. We studied the response of mycorrhizal and non-mycorrhizal plants to variation in soil nutrient concentration. A model for the relative growth rate (RGR) of plant biomass was constructed with soil nutrients as an explanatory variable. A literature survey was carried out to find the relative magnitudes of parameter values for mycorrhizal and non-mycorrhizal plants. Mycorrhizal plants had higher RGR at low nutrient concentrations and non-mycorrhizal plants at high nutrient concentrations. The RGR of mycorrhizal and non-mycorrhizal plants at constant versus log-normally distributed soil nutrient concentration were compared to see the effect of mycorrhizal status on responses to variation. Variation in nutrient concentration generally reduced RGR, especially in mycorrhizal plants. The RGR of a non-mycorrhizal plant may increase with variation where a growth function threshold exists, i.e. a soil nutrient concentration that must be exceeded to allow growth. Mycorrhizal plants appeared more sensitive to variation in nutrient concentration than non-mycorrhizal plants due to the higher affinity of mycorrhizal roots at low nutrient levels. However, this prediction may be reversed if mycorrhizal symbiosis considerably stabilises flow of nutrients to plant physiological processes, such that mycorrhizal plants experience less variation in soil nutrient concentration than non-mycorrhizal plants. Our results also attain broader significance by suggesting a general trade-off between competitive ability in a constant versus variable resource availability.

Male mating strategy and the introgression of a growth hormone transgene

Escaped transgenic organisms (GMO’s) may threaten the populations of their wild relatives if able to hybridize with each other. The introgression of a growth enhancement transgene into a wild Atlantic salmon population may be affected by the transgene’s effects not only on fitness parameters, but also on mating behaviour. Large anadromous GMO males are most preferred in mating, but a transgene can also give the large sneakers a reproductive advantage over the smaller wild individuals. With a simulation model, we studied whether the increase in the proportion and mating success of sneakers in transgenic and hybrid genotypes could facilitate the introgression of a transgene into wild population after the release of GMOs. The model combines population dynamics and Mendelian inheritance of a transgenic trait. We found that the introgression of the transgene is strongly affected by the greater mating preference of large GMO males. Furthermore, the difference in reproductive success between the anadromous versus sneaker strategy defines how much GMO’s have to be preferred to be able to invade. These results emphasize the importance of detailed knowledge of reproductive systems and the effect of a transgene on the phenotype and behaviour of GMOs when assessing the consequences of their release or escape to the wild.

Invasion under a trade-off between density dependence and maximum growth rate

The invasion of alien species and genotypes is an increasing concern in contemporary ecology. A central question is, what life-history traits enable invasion amidst populations of wild species and conventional cultivars? In order to invade, the initially rare species must perform better than their resident competitors. We conducted a mathematical analysis and simulation of a two-species extension of the Maynard Smith and Slatkin model for population dynamics in discrete time to study the role of density dependence as different types of competition in the invasion of new species. The type of density dependence ranged from scramble to contest competition. This led to intrinsic dynamics of the species range from point equilibrium to cycles and chaos. The traits were treated either as free parameters or constrained by a trade-off resulting from a common fixed strength of density dependence or equilibrium density. Resident and intruder traits had up to ten-fold differences in all of the parameters investigated. Higher equilibrium density of the intruder allowed invasion. Under constrained equilibrium density, an intrinsically stable intruder could invade an unstable resident population. Scramble competition made a population more susceptible to invasion than contest competition (e.g., limitation by light or territory availability). This predicts that a population which is mainly limited by food (or nutrients in plants) is more likely to be invaded than a population limited by a hierarchical competition, such as light among plants. The intruder population may have an effect on the resident population’s dynamics, which makes the traditional invasion analysis unable to predict invasion outcome.

Quantitative tools and simultaneous actions needed for species conservation under climate change–reply to Shoo et al. (2013)

We identify four issues in the decision framework for species conservation management under climate change proposed by Shoo et al. (2013) Clim Chan 119:239–246 and suggest ways to address them. First, binary-decision flow charts require Yes/No answers, which are not appropriate in most conservation decisions. A quantitative framework is preferable and action-guidance should be obtained even when the realistic answer to some questions remains “we simply do not know”. Second, the proposed flow chart imposes an a priori order of precedence and does not explicitly allow simultaneous actions. A workable framework should enable optimal allocation between multiple kinds of conservation efforts and permit complementary actions. Third, the probability of success, co-benefit to non-target species, and cost are unlikely to have a simple, consistent relationship across taxa. These variables need to be assessed case-by-case for each conservation measure and species. Finally, the decision framework disregards the legal, social, and ethical aspects pertaining to decision-making.