Interspecific association of brown trout (Salmo trutta) with non-native brook trout (Salvelinus fontinalis) at the fry stage

The introduction of non-native brook trout (Salvelinus fontinalis) in Europe has led to displacement and decreasing populations of native brown trout (Salmo trutta). Some studies have found that brown trout shift to a diet niche similar to brook trout when the two species live in sympatry, which conflicts with the competitive exclusion principle. A change in feeding niche may be a sign of early interspecific association and social learning, leading to behavioral changes. As a first step to address this possibility, it is essential to assess the interspecific association between the species during the early ontogenetic life stages. In this study, we therefore assess whether juvenile brown trout associate with non-native juvenile brook trout to the same extent as with conspecifics by setting up two experiments: (i) a binomial choice test allowing visual and chemical cues to estimate the species specificity of group preference, and (ii) an association test without physical barriers to estimate the degree of association of a focal brown trout with a group of either conspecifics or heterospecifics. In experiment (1), we found that focal juvenile brown trout preferred to associate with the stimuli groups and did not discriminate either against conspecific or heterospecific groups. Furthermore, more active individuals showed stronger preference for the stimuli group than less active ones, regardless of species. In experiment (2), we found that brook trout groups had a tighter group structure than brown trout groups, and that focal brown trout showed stronger association with brook trout than with brown trout. These results indicate that brown trout may associate with brook trout at an early life stage, which would allow for interspecific social learning to occur. Future studies should look closer into causes and consequences of interspecific association and social learning, including potential effects on the phenotype selection in brown trout populations

Exploring mechanisms regulating the heterogeneity of Tumor-Associated Macrophages

Accumulation of macrophages in the tumor microenvironment is associated to poor prognoses in most human cancers. Tumor-associated macrophages (TAMs) represent a heterogeneous and plastic population of cells that contribute to tumor growth, metastatic dissemination, angiogenesis, and immune suppression. Both recruitment of monocytes from the blood and in situ proliferation contribute to the accumulation of TAMs. During the course of tumor progression, the phenotype of the infiltrating TAMs is changing by influences from other cells, extracellular signal molecules and availability of oxygen and nutrients. Therapeutic targeting of TAMs as a monotherapy has limited success, however, experimental studies show promising results when selectively depleting specific subsets of TAMs or changing the function of the TAM population. Yet, the mechanisms whereby macrophage phenotypes are regulated during tumor growth are still largely unknown. In this thesis, we investigated mechanisms underlying the dynamic changes in the TAM population observed during tumor growth. In our first study, overexpression of semaphorin 3A induced the proliferation of anti-tumoral macrophages and at the same time reduced the proliferation of pro-tumoral TAMs resulting in accumulation and activation of CD8+ T-cells and NK-cells and restricted tumor growth. In study II, we identified translational regulation of gene expression as an important mechanism regulating the TAM phenotype during tumor growth. By selective inhibition of translational activation, pro-tumoral macrophages were skewed towards an anti-tumoral phenotype. In the third study, we demonstrated a functional difference between macrophages of different ontogeny in a mouse model of glioblastoma. M2-polarized microglia, but not bone-marrow derived macrophages induced the expression of platelet-derived growth factor receptor B (PDGFRB) in glioma cells, enhancing their migratory capacity. In study IV, we showed that Zoledronic acid in combination with interleukin-2 induced the expression of interferon-g by monocytes leading to an up-regulation of TNF-related apoptosis-inducing ligand (TRAIL) on NKcells, inducing their cytotoxicity against tumor cells. In summary, we describe several mechanisms whereby the TAM phenotype may be regulated i.e translational control of gene expression, regulation of proliferation and ontogeny

Kiri Peterburi TA-le

Wallerius, Johan Gottschalk, 1709-1785, rootsi keemik ja mineraloog, Peterburi TA auliigeTänukiri Peterburi TA auliikmeks valimise puhu

Laboratory captivity can affect scores of metabolic rates and activity in wild brown trout

Phenotypic scoring of wild animals under standardized laboratory conditions is important as it allows field ecologists and evolutionary biologists to understand the development and maintenance of interindividual differences in plastic traits (e.g. behaviour and physiology). However, captivity is associated with a shift from a natural familiar environment to an unfamiliar and artificial environment, which may affect estimates of plastic phenotypic traits. In this study, we tested how previous experience with laboratory environments and time spent in captivity affects behavioural (i.e. activity) and metabolic (i.e. standard and maximum metabolic rates) scoring of our model species, wild brown trout Salmo trutta. We found that individuals with previous experience of laboratory captivity (10.5 months earlier) showed higher activity in an open field test than individuals with no prior experience of laboratory captivity. Previous experience with captivity had no significant effect on metabolic rates. However, metabolic rates seemed to increase with increasing time spent in captivity prior to the collection of measurements. Although there are benefits of keeping wild animals in captivity prior to scoring, our results suggest that while allowing for sufficient acclimatization researchers should aim at minimizing time in captivity of wild animals to increase accuracy and ecological relevance of the scoring of plastic phenotypic traits

Socially induced stress and behavioural inhibition in response to angling exposure in rainbow trout

It is well known that fish can learn to avoid angling gear after experiencing a catch‐and‐release event, that is, after a private hooking experience. However, the possible importance of social information cues and their influence on an individual's vulnerability to angling remains largely unexplored, that is, social experience of a conspecific capture. The effects of private and social experience of hooking on the stress response of fish and subsequent catch rates were examined. Hatchery‐reared rainbow trout, Oncorhynchus mykiss (Walbaum), were implanted with heart rate loggers and experimentally subjected to private or social experience of hooking. Private and social experience of angling induced an increased heart rate in fish compared with naïve control fish. While private experience of hooking explained most of the reduced vulnerability to capture, no clear evidence was found that social experience of hooking affected angling vulnerability in fish that had never been hooked before. While both private and social experiences of angling constitute significant physiological stressors for rainbow trout, only the private experience reduces an individual's vulnerability to angling and in turn affecting population‐level catchability