Browsing by Subject "ecology and Evolutionary Biology"

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  • Howlader, Mohammad Sajid Ali (Helsingin yliopisto, 2016)
    Amphibians are the most threatened class of vertebrates. About 48% of the known amphibian species are threatened by extinction, and many species still remain undescribed, especially from tropical and sub-tropical countries such as Bangladesh. In contrast to India and Sri Lanka, amphibian diversity in Bangladesh is poorly known, and little effort has been put towards documenting the species diversity and resolving evolutionary affinities among amphibian taxa in this country. Hence, the actual diversity of amphibians in Bangladesh remains unknown. The aim of this dissertation work was to improve our knowledge of amphibian diversity in Bangladesh by identifying and describing new amphibian species and investigating their evolutionary relationships with closely related taxa. I used morphological and molecular phylogenetic methods to identify and describe one new genus and five new species from different genera. In addition to using traditional morphological comparisons, I also utilized mitochondrial gene fragments to estimate phylogenetic affinities among the studied taxa, with Maximum-likelihood and Bayesian methods. The first two chapters of the thesis focus on the amphibian genera Fejervarya and Zakerana, the latter which was previously embedded within Fejervarya. These chapters also include descriptions of two new species Fejervarya asmati sp. nov. (now Zakerana asmati), as well as Fejervarya burigangaensis sp. nov. , respectively. In the third chapter, a new species (Zakerana dhaka sp. nov.) is described from the urban core of Dhaka, the capital of Bangladesh and one of the most densely populated mega cities in the world. In the fourth chapter, I describe Euphlyctis kalasgramensis sp. nov., which was earlier recognized as E. cyanophlyctis, and show that it is genetically highly divergent from the E. cyanophlyctis described from southern India. In the last and fifth chapter, I describe Microhyla nilphamariensis sp. nov. as a new species. It is a member of a highly genetically heterogeneous group of frogs that have been recognized as M. ornata for the past 173 years. In general, the results of the studies included in this dissertation advance our understanding of amphibian diversity in Bangladesh and adjacent regions, and show that discovery and description of new amphibian species from this region is still fairly easy. Consequently, it seems likely that more thorough sampling and further investigations in this region can uncover additional new amphibian species to science. Such studies, together with the discoveries described in this thesis, should also provide useful information for understanding and conserving the amphibian biodiversity in this poorly studied region.
  • Gruber, Christina (Helsingin yliopisto, 2015)
    Both the ability to gain a high dominance status and having an efficient immune defence are favourable qualities that typically increase fitness in social and host-parasite interactions. Individuals with a high dominance status are predicted to gain fitness-related benefits from prior access to limited, defensible resources, such as food and matings. Immune defence mechanisms, on the other hand, have evolved to minimize the fitness costs of parasitic infections. The relative significance of a high dominance status and strong immune defence for individual fitness is, however, affected by the quality of the environment. The aim of this thesis is to improve the understanding of environmentally determined variation in dominance status, immune defence and their consequences for individual fitness. I use the native noble crayfish (Astacus astacus), the invasive signal crayfish (Pacifastacus leniusculus) and the highly virulent, invasive Aphanomyces astaci, the causative agent of the crayfish plague, as my study models. I first experimentally test theoretical predictions on how major ecological factors, including food availability, predation risk and population density, influence behavioural decision-making in fight contests, especially with regard to the maintenance of dominance hierarchies between size-matched crayfish. Using natural noble crayfish subpopulations with different crayfish plague history, I then explore whether variation in immune defence and crayfish plague resistance is potentially explained by local adaptation to the disease, or alternatively by geographical divergence. By keeping noble crayfish experimentally under constant environmental conditions, I finally determine whether seasonal variation in immune defence is endogenously regulated. My results show that individuals that had achieved dominant status in non-resource fight contests have an advantage in monopolising a limited, defendable food resource in a future contest. Furthermore, I find evidence that as population density increases, the division of the resource between dominants and subdominants becomes more unequal. Generally, my results suggest that due to ecological factors the dominance status of individuals can be more dynamic than theory predicts, especially when the contestants have similar fighting ability. For example, in line with the asset-protection principle, individuals having achieved dominant status in a non-predation risk contest increase their submissive behaviours in the presence of a predation threat, giving subdominants the opportunity to win a larger percentage of bouts in the predation risk contest. My results also reveal evidence for geographical variation in resistance to the crayfish plague and immune defence that is, however, independent of historical disease outbreaks in the study subpopulations. Furthermore, for the first time in invertebrates, my results demonstrate reproduction-related endogenous seasonal variation in the immune defence of noble crayfish. Overall, my results suggest that ecological factors, such as population density, predation risk and disease history, have to be taken in to account to better understand the causes and consequences of dominance status and immune defence in any individual species.
  • Höckerstedt, Layla (Helsingin yliopisto, 2020)
    Infectious diseases have a major influence on the demography of human, animal and agricultural populations. However, we rarely see extensive disease epidemics in the nature, where pathogens play an important role in maintaining biodiversity. Coevolution has the potential to drive the genetic composition of hosts and pathogens by linking their genomes through adaptation and counteradaptation, often leading to evolutionary arms race dynamics. Moreover, predicting the emergence, spread and evolution of pathogens within and among host populations requires understanding of how resistance diversity is maintained through varying migration rates in spatially structured systems. The main goal of this thesis is to understand how pathogen-imposed natural selection maintains diversity in host resistance, from genes to metapopulation. Theoretical and experimental evolution studies predict that migration influences coevolution between hosts and their pathogens, yet evidence of this phenomenon occurring in natural populations is scarce. Using the Plantago lanceolata – Podosphaera plantaginis model system, I revealed the evolutionary trajectories of resistance in spatially isolated and well-connected populations within a metapopulation framework. I then asked if pathogens may also shape host fitness and resistance traits through transgenerationally induced maternal priming mechanism. Finally, we characterized the resistance gene repertoire in P. lanceolata and tested whether any particular genes show signs of pathogen-imposed selection. I found that well-connected host populations support higher resistance and phenotypic resistance diversity than isolated host populations. In contrast to isolated populations, hosts in well- connected populations do not show local adaption to their own pathogens. Local adaptation patterns varied considerably among well-connected host populations, and resistance levels fluctuated over years. These fluctuations may result from either pathogen-imposed selection or from transgenerational maternal effects, as results suggest that pathogen infection may transcend to subsequent generation and hence create an additional layer determining phenotypic resistance. Finally, we found that different host genotypes activate unique genetic defense mechanisms in response to the same pathogen. Jointly, these results highlight that maintaining high levels of diversity in resistance is the key for hosts to cope with their pathogens. Once pathogens have successfully established, they have the upper hand in the coevolutionary arms race, especially in isolated host populations. In well-connected populations hosts may be better able to respond to pathogen-imposed selection. Altogether, this study brings the new perception into how landscape fragmentation and biodiversity loss may dramatically change host survival and the intensity of selection for host resistance in nature and offers insights for resistance studies in both natural and managed plant populations.
  • Burgas, Daniel (Helsingin yliopisto, 2014)
    Under the current biodiversity crisis, there is the need to improve the conservation action. More areas need to be protected to curb biodiversity loss. Also, the methods for selection of both protected areas and management practices have to be well-informed in order to maximise the benefits from the limited resources allocated for conservation. However, because of limited information, decision making procedures are forced to use environmental variables and different species as surrogates of general biodiversity. Moreover, there is a bias towards charismatic and better known species like top predators. It is therefore important to forecast the consequences that favouring certain species might have on other organisms and to evaluate the effectiveness of preserving a subset of species. In this thesis I use empirical data to investigate how avian predators (the Northern Goshawk Accipiter gentilis and the Ural Owl Strix uralensis) associate to biodiversity. The focus is two-fold; First, I investigate the role of species interactions in dictating biodiversity patterns. I show that interactions within the predator assembly can have stronger effect on prey distribution (the Siberian Flying Squirrel Pteromys volans) than landscape attributes. This finding points out that individuals may be able to respond to changes in the structure of the predator assemblage. Additionally, I examine the impact of the Goshawk altering the structure of the forest bird community. I found that not only the raptor conditioned species distribution across space, but that this effect persisted over the years after the Goshawk abandoned the breeding site. Second, I evaluate the potential use of raptors as surrogates to indicate areas of relevant conservation value. On the one hand, I address how the two focal raptor species associate to different biodiversity metrics for birds and polypores (i.e. wood decaying fungi) over a landscape gradient. I found that, while both predator species indicated high biodiversity levels as compared to reference sites, the dominant Goshawk was superior to the Ural Owl. Interestingly, the surrogacy properties remained the same even if the environmental setting changed. On the other hand, I assess the value of preserving raptor nest sites in the context of the existing network of protected areas in the study region. I show that using goshawk nest sites is the most cost-efficient approach if considering only single species. However, combining both predator species further enhanced the conservation output. Concluding, this thesis highlights the idea that avian top predators have a key role on species distributions and shaping community heterogeneity in space and time. Given this disproportionate influence in ecosystems, apex predators might also merit extra conservation commitment. Furthermore, information on the spatial distribution of raptors can indicate, over large areas, locations of disproportional biodiversity value. I show that setting aside raptor nest sites is more cost-effective than other conservation approaches. Additionally, one has to consider that national-wide monitoring schemes already provide raptor nest locations at no extra cost. In the light of these results it is advisable to consider the use of raptors to complement existing and future reserve selection methods.
  • Noreika, Norbertas (Helsingin yliopisto, 2016)
    Negative anthropogenic disturbances (e.g., drainage and urbanization) are causing biotic homogenization through the replacement of specialist species with generalists. The identification and conservation of biodiversity hotspots within degraded (e.g., highly urbanized) landscapes, and ecological restoration (i.e., positive anthropogenic disturbance) have the potential to be important tools to counteract these negative effects. Mires are suitable targets for the investigation of these homogenization-reducing activities since they host many mire specialist species of, e.g. invertebrates. The main aim of this PhD thesis was to investigate the effects of negative anthropogenic disturbances [urbanization (Chapter I) and drainage for forestry (Chapters II-IV)] on the invertebrate communities of boreal mires and how effective efforts are to reverse these negative effects through ecological restoration [i.e. positive anthropogenic disturbance (Chapters II-IV)]. In addition, the purpose was to determine which environmental variables are key in supporting mire specialist invertebrate species and communities. Therefore, this thesis started by reviewing current knowledge on the responses of mire invertebrate species and communities to anthropogenic disturbances. The effects of urbanization were studied on spiders and carabid beetles (Chapter I), while the effects of drainage for forestry and subsequent restoration were investigated on five solitary invertebrate groups (Chapter II) and social insects, i.e. ants (Chapter III). Finally, a powerful Before-After Control-Impact (BACI) design was used to reveal the effects of drainage and restoration on butterflies (Chapter IV). Generally, both high levels of urbanization (Chapter I) and mire drainage for forestry (Chapters II-IV) had negative effects on mire specialist species (lower abundances) and invertebrate communities (homogenized and very different in structure from pristine mire communities). However, these detrimental effects can be reduced or even reversed through appropriate urban mire conservation and ecological restoration. Local habitat conditions were shown to be particularly important for the survival of specialist invertebrate species in urban mires (Chapter I) and for the successful recovery of restored mire invertebrates (Chapters II-IV). Individual mire specialist species responded negatively to environmental variables associated with deteriorated (i.e. drained or highly urbanized) mire conditions [number of high (> 3m) trees for carabid beetles, crane flies, micromoths (Chapter II), ants (Chapter III) and butterflies (Chapter IV)] and positively to pristine mire-associated variables [Sphagnum cover for carabid beetles and spiders (Chapters I-II), crane flies (Chapter II) and suggestively for ants (Chapter III); larval food plant cover and number of lower (1.5 - 3m) trees for butterflies (Chapter IV)]. The more specialized the mire species were, the more negatively they were affected by deteriorated-mire-associated variables and the more positively they responded to pristine-mire-associated variables. I conclude that the restoration actions taken (removing tall trees but leaving smaller trees, and raising the water table level) are appropriate in creating suitable habitat conditions for mire invertebrates, as both individual specialist species and communities showed positive responses already 1-3 years since restoration (Chapters II-IV). Finally, the appropriate restoration actions in well-prioritized locations as well as urban mire conservation should reverse the trend of biotic homogenization.
  • Couchoux, Christelle (Helsingin yliopisto, 2013)
    In my thesis I investigated the foraging behaviour of the wasp Hyposoter horticola, an egg-larval parasitoid of the Glanville fritillary butterfly Melitaea cinxia, in the Åland islands in Finland. The particularity of this system is that the wasp is resource limited and faces strong intraspecific competition. ---------- I first focused on behaviour at an individual scale. In a series of experiments I tested how H. horticola s host searching behaviour was affected by developmental timing of both the parasitoid and the host, and direct intraspecific competition among foraging females. I found that the wasps visit host egg clusters before the hosts are susceptible to parasitism, presumably to cope with the limited time availability of the hosts. As the unparasitized hosts matured their value increased, competition became more frequent, and the wasps foraged more actively. Competition can also affect the parasitoid at earlier stages in its life. As larvae inside the hosts, the immature H. horticola suffered from competition due to superparasitism. Combining behavioural experiments in the laboratory and genetic analyses of sibship, I found that adult H. horticola deposit a chemical marking after oviposition that deters conspecifics from parasitizing a previously exploited host cluster. This protects parasitized host clusters from further exploitation. I found that the effectiveness of the deterrent persisted under natural conditions, where individual host egg clusters were each primarily parasitized by a single female H. horticola. Even when several females parasitized a cluster, the great majority of the offspring were full-siblings and the parasitism rate did not increase above the average 1/3 observed throughout the population. Considering that H. horticola is resource limited and faces intraspecific competition when foraging for hosts, it is surprising that only they parasitize a fraction of the hosts in each host egg cluster. After testing several physiological and evolutionary hypotheses for what might lead to this sub-maximal rate of host exploitation, I concluded that optimal foraging with avoidance of superparasitism was the most plausible explanation, as long as the search time between host clusters was low. ------ Then, I worked at a larger scale than individual behaviour. In the Åland islands, the butterfly host lives as a classic metapopulation with a high extinction rate of local populations. Due to strong competition, almost all the M. cinxia egg clusters in the population are found and parasitized by H. horticola. This suggests that the wasps must be good dispersers, which could influence the spatial genetic structure of the parasitoid population. I used DNA microsatellite markers and analysed H. horticola individuals sampled from over the entire population. My results indicate that, contrary to theory that higher trophic level species are more affected by habitat fragmentation than the species upon which they depend, the H. horticola population was less strongly genetically structured than the metapopulation of its butterfly host. It seems that H. horticola s dispersal ability allows it to compensate for the fragmented distribution of its host and not suffer from the metapopulation dynamics of the host local populations. Overall, the results of my thesis show that interactions between H. horticola and its host M. cinxia are strongly affected by competition among the adult female wasps. Intraspecific competition has an important role from an evolutionary perspective. Hyposoter horticola s deterrent marking behaviour has evolved in response to competition and the risk of superparasitism faced by immature offspring. Avoidance of superparasitism to limit competition is also the fundamental mechanism that controls H. horticola s optimal foraging strategy. And intraspecific competition modifies individual female host searching behaviour, increasing their foraging activity. -------- Interactions within a multitrophic system are complex and predictions concerning host-parasitoid interactions are difficult to generalise. However, as in this system, competition is factor that should receive more attention in empirical and theoretical studies of host-parasitoid interactions.
  • Wong, Swee Chong (Helsingin yliopisto, 2016)
    In the past decade, advances in next generation sequencing (NGS) and genotyping technology have enabled merging of genetic analyses in ecological field studies of natural populations. The development of transcriptome sequencing such as RNA-seq provides a golden opportunity for researchers studying non-model organisms. In the design of genetic analyses in the context of ecological studies, genetic relationships among individuals are often overlooked, especially when sampling wild populations. In ecological studies, studies of e.g., life-history traits, environmental and ecological factors are often the main issues of interest, and genetic analyses remain a secondary consideration. Samples from ecological studies often represent different types, such as inbred samples, samples with complex family structure, and samples with unknown relationships. These distinctly different experimental setups present a challenge for genetic association studies, as the underlying relationships among samples could affect allele frequency distributions in populations, leading to spurious associations. The primary aim of this thesis is to devise protocols for quantitative genetic studies of samples from experimental designs intended for ecological studies, using a non-model organism, the Glanville fritillary butterfly, as the study species. Strategies and methods were implemented to discover potential genetic factors affecting trait variation in the Glanville fritillary. Interactions between the organism and the environment, such as effects of temperature on flight metabolic rate, on phenotypic plasticity and on larval development were studied. All samples were obtained from a large metapopulation of the Glanville fritillary in the Åland Islands in Finland. Flight metabolic rate, life history, female reproductive traits, and phenotypic plasticity were measured in family-based material, while the study of larval development was implemented using a population-based model. Problems tied to to relatedness of samples in each experimental setting were addressed with various strategies. The key findings of this thesis include discovery of a novel association between a SNP in the sex chromosomal gene triosephosphase isomerase and flight metabolic rate in females. This discovery was confirmed with one additional material: a dataset with 16 population samples. This gene is potentially another candidate gene in regulating the complex flight metabolic pathway. An interaction between temperature treatment preceding flight activity and SNP genotypes in the phosphoglucose isomerase gene was found to influence flight metabolic rate. Individuals with the genotype AC performed better when treated with low temperature, but individuals with genotype AA showed superior performance in high temperature treatments. Moreover, in another experiment, individuals with the AA genotype were more tolerable to heat shock than the AC individuals. Three SNPs in the cytochrome P450 337 gene were associated with the total number of eggs and caterpillars produced by females in their life-time. Further sequencing showed that regions prior to the coding region displayed similar association pattern with the three candidate SNPs, suggesting that causal variants might be located in the 5 regulatory region. Finally, SNPs from the vitellin-degrading protease precursor were associated with the incidence of the extra eighth larval instar (a development stage of insects), though the result was not significant after adjusting for multiple testing. This work contributes to developing procedures for samples originating from ecological studies and which might have sub-optimal experimental design for genetic analyses. Rigorous steps such as relatedness control, confidence interval calculation, and genetic power estimation were performed in this thesis to help interpret results from different chapters. The thesis shows that sound protocols can be developed to address problematic issues related to relationships among the samples.
  • Chernenko, Anton (Helsingin yliopisto, 2012)
    Communication is probably one of the major means of life maintenance. Communication involves the use of signals, which can be visual, audial, olfactory etc. Organisms communicate in many different contexts, ranging from establishing own identity, foraging for food, finding a mate, protecting their territory, to more sophisticated ones such as engaging in social behaviour. Recognition is the action or process of recognizing or being recognized. Recognition based on olfactory cues is perhaps best known from many insect species and is mediated by a wide range of volatile compounds, e.g. esters or terpenes, or non-volatile compounds such as cuticular hydrocarbons. In insects cuticular hydrocarbons are often the main agents involved in species recognition, predator avoidance, fertility and dominance signalling, cues that help parasites intrude their host nests but also those that help hosts to fend off the parasites; and also as cues facilitating sexual selection. In social insects in addition to above mentioned, cuticular hydrocarbons are involved in coordinating division of labour and nest mate recognition. The aim of my thesis was to study recognition system underlining social behaviour in Formica ants such as recognition of con- and hetero-specifics, e.g. nestmates and social parasites, and their brood as well as to examine cuticular hydrocarbon profiles of males and females. The results show that queens of potential social parasites have a very low chance to invade host colonies of Formica ants and become fully integrated. Moreover, social parasitism pressure, beside from affecting how the parasites are discriminated against, may also have an effect on the host kin recognition system and lead to rejection errors of descendant brood. Thus selection mediated by temporary social parasitism may drive enhanced recognition abilities. Colony kin structure does not seem to have any effect on recognition system towards con-specific non-nestmate and nestmate queens as both low- and high-relatedness colonies were as stringent towards unrelated individuals, although colonies with presumably high genetic diversity also showed significantly greater chemical diversity based on chemical profiles of sexuals. Hence nest mate recognition entails more complex interactions between individual genotypes and colony recognition cue phenotype than previously assumed. This thesis provides important insights on host-parasite interactions and highlights the complex interactions between different selection regimes affecting recognition system.