Browsing by study line "ei opintosuuntaa"

Global surface temperature is increasing at an alarming rate. Local populations can cope with the change, if they have adaptive potential to face the new thermal regime. Hybridization with a closely related lineage is one potential source of adaptive genetic variability. My thesis aimed to investigate thermal adaptation by looking into thermal tolerance differences between two mound-building wood ants Formica polyctena and Formica aquilonia and their hybrids. The two parental species have distinct distributions: F. aquilonia can be found in Northern Europe while F. polyctena is distributed from Central Europe to Fennoscandia. The samples for this thesis were collected from a relatively small area in southern Finland and Åland Islands. Aim of my thesis was to clarify whether the two parental species have distinct thermal tolerances, which would reflect the differences in their distributions. I also tested whether hybrid individuals have wider thermal limits since they have alleles from both northern and southern parental species and could therefore show adaptive potential. I tested thermal tolerance differences with two temperature assays: heat-knockdown resistance and chill-coma recovery. I hypothesized that F. aquilonia would express more cold-tolerant thermal limits whereas F. polyctena would express more heat-tolerant limits. My results showed that the parental species differed in their thermal tolerance and expressed thermal limits which reflected their distribution. These results support the thermal adaptation hypothesis: parental species expressed thermal limits that reflected the thermal environment in their native habitat. The results also showed that hybrids could not combine the thermal tolerance of both parental species as they did not have wider thermal tolerance than parental species. Intriguingly, dry weight had a significant role in thermal tolerance, bigger ants coping better with higher temperatures. These results contribute to building up knowledge on the outcomes of hybridization and the potential that species possess in coping with the environmental change. Wood ants are keystone species in boreal forests and the findings of my thesis shed a light on the changes in population dynamics for these species in the face of global climate change.

Trace element analysis is a useful tool for the study of migration and migratory connectivity in birds. Trace elements are present in the environment and, through the food chain, can be incorporated into tissues such as growing feathers. Since the concentrations of elements remain stable after the feather has stopped growing, and trace element abundances can vary at very small geographical scales, the concentration of trace elements in feathers can provide information on the location where a feather was moulted. Trace element analysis is still rarely used and there are important gaps in our understanding of how trace elements can vary at different organizational levels such as within a feather, between individuals or even between species. It is also not clear if large-scale geographical patterns can be detected by the method, as trace element concentrations can vary a lot even at small scales, which could make it impossible to see larger-scale patterns. To address that, my objectives were (1) analysing the variability of trace element concentrations within feathers, between individuals and between species and (2) determining whether trace element levels differed in feathers grown in Africa compared to feathers grown in Europe. This would shed insight on the suitability of trace element analysis for the study of migration and migratory connectivity. I analysed the concentration of 18 trace elements in the rachis of feathers from willow warblers (Phylloscopus trochilus) and barn swallows (Hirundo rustica) collected in Finland. I plucked three belly feathers from willow warblers collected in spring, whose feathers had grown in Africa. These feathers were used to analyse variability of trace element concentrations within feathers and between individuals. They were also compared to feathers plucked from barn swallows collected in spring (two feathers per bird) to analyse variability between the feathers of two species that winter in the same region. Finally, African-grown feathers of willow warblers were compared to European-grown feathers of willow warblers collected in autumn (two feathers per bird) to look for differences in trace element concentrations in feathers grown on two different continents. Trace element concentrations were analysed using Laser-Ablation Inductively-Coupled-Plasma Mass-Spectrometry (LA-ICP-MS), which allowed to measure concentration at hundreds to thousands of points along the feather rachis. The concentration of each of the 18 elements was used as the response variable in linear mixed models (LMM). To model variation in concentration within the feather I used location along the feather rachis as the explanatory variable and explored how well it predicted concentration of each element. To compare variation between feathers and individuals I fit models including and excluding the feather and individual that each measurement belonged to as random effects and compared them using AIC. To compare between willow warbler and barn swallow feathers grown in Africa I included species identity as the explanatory variable and looked at how the concentration of the 18 elements differed between them. Finally, I followed the same approach to compare willow warbler feathers moulted in Africa and in Europe. For most elements there was little variation along the feather rachis, with concentration remaining stable from feather base to tip. Zn and S showed an increase in concentration starting at the feather base until the central part of the feather and then remained constant toward the tip. Feathers belonging to the same individual showed mostly similar trace element concentrations, although there were exceptions and differences between feathers of different willow warbler individuals were also little. 10 out of 18 elements showed significant differences in feathers of willow warblers and barn swallows grown in Africa. Eight of those elements were more abundant in willow warbler feathers, while only two were more abundant in barn swallow feathers.12 out of 18 elements showed significant differences between their level in African-grown feathers and European-grown feathers. Of those, 10 elements showed higher levels in African-grown feathers, while only two were higher in European-grown feathers. My results suggest that trace elements can show variation at different organizational levels. Variability within feathers was important in at least two elements, which could be caused by physiological processes. This means that when designing sample collection for trace element analysis, unless we know that an element does not vary along a feather, it is important to consider which part of feathers we are sampling. Variability between feathers and individuals was lower than within feather variability, but still significant. Future studies should account for possible within and between individual differences in their design. Differences between barn swallows and willow warblers were large, which was expected based on the literature. It is still unknown what drives these differences between species: some explanations suggested have been physiological and dietary differences or differences in their habitats. I also found clear differences between feathers of willow warblers grown in Europe and Africa. While the exact cause is still not known, this means that at least in willow warbler feathers it is possible to study large scale geographical patterns by trace element analysis. LA-ICP-MS has potential to be a powerful tool to study migration and migratory connectivity in birds. It allows to detect variation in trace elements at continental scales while also allowing to control for different levels of variability in the study design. I encourage researchers to adopt its use in their research.

Beta diversity (total dissimilarity) can be partitioned into two components: dissimilarity attributed to turnover and nestedness-resultant dissimilarity. Turnover refers to the variation in species identities among sites and implies the replacement of some species by others. In contrast, nestedness occurs when species-poor sites have a subset of the biota present in species-richer sites. Although disentangling the relative contribution of these two antithetic components from beta diversity can characterize species assemblages, the dissimilarity indices do not provide information on the processes generating the patterns. Conversely, Hierarchical Modelling of Species Communities (HMSC), which unifies many of the recent advantages of Joint Species Distribution Models, has proved to be the one of the best performing frameworks for unravelling the underlying mechanisms structuring ecological communities. The aim of this research is to explore the relationship between the outputs of the HMSC model and the dissimilarity indices in different communities with a wide range of parameterizations. As the observed patterns measured by the beta-diversity indices result from the underlying processes which HMSC attempts to capture, I hypothesized that both frameworks are at least partially linked to each other. To achieve this aim, I simulated the community data by following the structure of the HMSC model. For simplicity, only one environmental covariate was considered, which was scaled to 0 mean. The intercept of the HMSC model accounted for the baseline occurrence probability of the species, while the slope modeled the species responses to the environmental covariate. The HMSC-intercept and the HMSC-slope, which represent the species multivariate niches, were summarized in terms of center and spread. Simultaneously, the beta diversity indices (total, turnover and nestedness dissimilarity) were calculated from the community data. Finally, the outputs of both frameworks were related in terms of linear modelling and variation partitioning. As hypothesized, the results of this study suggest that outputs of the HMSC model are able to explain most of the variation in the beta-diversity indices, indicating that both frameworks are strongly related. By plotting the species niches (intercept and slope coefficients of the HMSC model) it is possible to determine the main axes of niche variation producing the nestedness and turnover patterns. While nestedness is generated by a shared response of the species to the environmental covariate(s), turnover is produced by variation in the species responses. Finally, the total dissimilarity index is driven by species rarity. In conclusion, the most comprehensive evaluation of the structure of ecological communities and the processes determining the diversity patterns can be achieved by combining the outputs of beta-diversity indices and the HMSC model.