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Large freshwater mussels (Unionida) are long-lived, have large bodies, and produce thousands to millions of larvae (glochidia) that usually must attach to host fish tissue to complete their life cycle. This is an obligate parasitic stage of mussel larvae. However, less than one in onemillion find a suitable host and survive. The degree of host specificity varies among unionid species, from specialists that can successfully parasitize only one or a few closely related fish species to generalists that can complete development on a taxonomically broad range of fish species. In addition, freshwater mussels are among the most threatened groups of animals. This is due to habitat destruction, the introduction of non-native species, and the loss of host fish on which their larvae (glochidia) are obligate parasites. Glochidiosis harms fish by affecting their growth; on the other hand, freshwater mussels play an important role in freshwaters by improving water quality and ridding the water of bacteria, algae, and pollutants, they are an indicator species of water quality. During our parasitological survey of fish from the Macedonian part of Lake Prespa in April 2022, many glochidia were found on the gills, skin, and fins of two endemic fishes, Prespa roach (Rutilus prespensis) and Prespa nase (Chondrostoma prespense), in the range of tens to thousands on one host. We thus recorded these two endemic species as new hosts of A. cygnea.

Co-infections are common in host-parasite interactions, but studies about their impact on the virulence of parasites/diseases are still scarce. The present study compared mortality induced by a fatal bacterial pathogen, Flavobacterium columnare between brown trout infected with glochidia from the endangered freshwater pearl mussel, Margaritifera margaritifera, and uninfected control fish during the parasitic period and after the parasitic period (i.e. glochidia detached) in a laboratory experiment. We hypothesised that glochidial infection would increase host susceptibility to and/or pathogenicity of the bacterial infection. We found that the highly virulent strain of F. columnare caused an intense disease outbreak, with mortality reaching 100% within 29 h. Opposite to the study hypothesis, both fresh ongoing and past infection (14 months post-infection) with glochidia prolonged the fish host’s survival statistically significantly by 1 h compared to the control fish (two-way ANOVA: fresh-infection, F1, 82 = 7.144, p = 0.009 and post-infection, F1, 51 = 4.227, p = 0.044). Furthermore, fish survival time increased with glochidia abundance (MLR: post-infection, t = 2.103, p = 0.045). The mechanism could be connected to an enhanced non-specific immunity or changed gill structure of the fish, as F. columnare enters the fish body mainly via the gills, which is also the glochidia’s attachment site. The results increase current knowledge about the interactions between freshwater mussels and their (commercially important) fish hosts and fish pathogens and also emphasise the importance of (unknown) ecosystem services (e.g., protection against pathogens) potentially associated with imperilled freshwater mussels.

Amphibian larvae typically inhabit relatively shallow freshwater environments, and within these boundaries there is considerable diversity in the structure of the habitats exploited by different species. This diversity in habitat structure is usually taken into account in relation to aspects such as locomotion and feeding, and plays a fundamental role in the classification of tadpoles into ecomorphological guilds. However, its impact in shaping the sensory worlds of different species is rarely addressed, including the optical qualities of each of these types of water bodies and the challenges and limitations that they impose on the repertoire of visual abilities available for a typical vertebrate eye. In this Perspective article, we identify gaps in knowledge on (1) the role of turbidity and light-limited environments in shaping the larval visual system; and (2) the possible behavioral and phenotypic responses of larvae to such environments. We also identify relevant unaddressed study systems paying special attention to phytotelmata, whose small size allows for extensive quantification and manipulation providing a rich and relatively unexplored research model. Furthermore, we generate hypotheses ranging from proximate shifts (i.e., red-shifted spectral sensitivity peaks driven by deviations in chromophore ratios) to ultimate changes in tadpole behavior and phenotype, such as reduced foraging efficiency and the loss of antipredator signaling. Overall, amphibians provide an exciting opportunity to understand adaptations to visually limited environments, and this framework will provide novel experimental considerations and interpretations to kickstart future research based on understanding the evolution and diversity of strategies used to cope with limited visibility.

1. The freshwater pearl mussel Margaritifera margaritifera (FPM) is an endangered unionid which has a glochidium larva that attaches to the gills of Atlantic salmon Salmo salar or brown trout S. trutta, although some FPM populations have been shown to exclusively attach to only one of these species. The origin of host fish populations may be crucial for conservation actions for this mussel species, but the relative suitability of local (sympatric) and non- local (allopatric) salmonid populations as the hosts for FPM has been studied only rarely. We hypothesised that FPM glochidia would show adaptation to local salmonid strains and, there-fore, that they would be more successful (abundant, larger) attached to sympat-ric than to allopatric fish. 2. Here, we investigated the infection success (abundance and growth of encysted larvae in fish) of FPM in local versus non- local fish by caging different strains of brown trout and Atlantic salmon in rivers where FPM populations are present. 3. Higher abundances of glochidia in local fish were observed in three brown trout streams, and larger glochidia were found in sympatric hosts in one brown trout stream and in one salmon river. Furthermore, non- local allopatric fish were not better hosts than local fish in any of the FPM populations tested, neither in brown trout or salmon rivers and neither in abundance nor size of larvae. Therefore, the results supported the hypothesis that glochidia show local adap-tation by being more successful when attached to local fish strains. 4. Thus, the local, sympatric fish strain should be preferred in FPM conservation programmes that involve captive breeding of juvenile mussels and introduction of host fish, but the regional assessment of local host dependency of FPM also would be important outside the current study area. 5. The results also indicate the importance of restoration of original salmonid pop-ulations in FPM rivers to enable the natural, effective reproduction cycle of FPM in their original, sympatric hosts, and thus to promote the recovery of endan-gered FPM populations. peerReviewed

Many specialist herbivores have evolved strategies to cope with plant defences, with gut microbiota potentially participating to such adaptations. In this study, we assessed whether the history of plant use (population origin) and microbiota may interact with plant defence adaptation. We tested whether microbiota enhance the performance of Melitaea cinxia larvae on their host plant, Plantago lanceolata and increase their ability to cope the defensive compounds, iridoid glycosides (IGs). The gut microbiota were significantly affected by both larval population origin and host plant IG level. Contrary to our prediction, impoverishing the microbiota with antibiotic treatment did not reduce larval performance. As expected for this specialized insect herbivore, sequestration of one of IGs was higher in larvae fed with plants producing higher concentration of IGs. These larvae also showed metabolic signature of intoxication (i.e. decrease in Lysine levels). However, intoxication on highly defended plants was only observed when larvae with a history of poorly defended plants were simultaneously treated with antibiotics. Our results suggest that both adaptation and microbiota contribute to the metabolic response of herbivores to plant defence though complex interactions. Read the free Plain Language Summary for this article on the Journal blog.

Juveniles of the endangered freshwater pearl mussel (FPM,Margaritifera margaritifera) live burrowed in stream substrate for the first years of their life. Fine sediments block water exchange within substrate and may cause juvenile mortality and recruitment failure. To better understand the connection between success of juvenile FPM and substrate particle size, it would be important to understand behavioural responses of FPM to varying substrate sizes at this critical life stage. We placed newly detached FPM juveniles in a 7-mm layer of sieved sand sorted into five sizes (

Correction Frontiers in Ecology and Evolution Volume 9 Article Number 737651 DOI 10.3389/fevo.2021.737651 Published JUL 29 2021 Predator-induced plasticity in life-history and antipredator traits during the larval period has been extensively studied in organisms with complex life-histories. However, it is unclear whether different levels of predation could induce warning signals in aposematic organisms. Here, we investigated whether predator-simulated handling affects warning coloration and life-history traits in the aposematic wood tiger moth larva, Arctia plantaginis. As juveniles, a larger orange patch on an otherwise black body signifies a more efficient warning signal against predators but this comes at the costs of conspicuousness and thermoregulation. Given this, one would expect that an increase in predation risk would induce flexible expression of the orange patch. Prior research in this system points to plastic effects being important as a response to environmental changes for life history traits, but we had yet to assess whether this was the case for predation risk, a key driver of this species evolution. Using a full-sib rearing design, in which individuals were reared in the presence and absence of a non-lethal simulated bird attack, we evaluated flexible responses of warning signal size (number of orange segments), growth, molting events, and development time in wood tiger moths. All measured traits except development time showed a significant response to predation. Larvae from the predation treatment developed a more melanized warning signal (smaller orange patch), reached a smaller body size, and molted more often. Our results suggest plasticity is indeed important in aposematic organisms, but in this case may be complicated by the trade-off between costly pigmentation and other life-history traits.

Sulfate occurs naturally in the aquatic environment but its elevated levels can be toxic to aquatic life in freshwater environments. We investigated the toxicity of sulfate in humic, soft freshwater to whitefish (Coregonus lavaretus) from fertilization of eggs to hatching i.e. during the critical phases of whitefish early development. Anadromous Kokemäenjoki whitefish eggs and sperm during fertilization, embryos and larvae were exposed in the long-term 175-day incubation to seven different sodium sulfate (Na2SO4) concentrations from 44 to 2 000 mg SO4 L−1. Endpoint variables were the fertilization success, offspring survival and larval growth. Egg fertilization and early embryonic development were the most sensitive developmental stages of whitefish to sulfate, although the fertilization success and survival of embryos decreased only in the highest concentration of 2 000 mg SO4 L−1. The survival during late embryonic period, hatching and the 5-day larval period was high and no difference between the control and sulfate treatments were observed. LC50-values of sulfate for early embryonic period and for the entire embryonic and larval period was 1 413 and 1 161 mg L−1, respectively. The NOEC (No-observed Effect Concentration) of sulfate for the both periods was 1 207 mg L−1. The tolerance of whitefish early stages to sulfate toxicity seems to be on the same level as the tolerance of other salmonids’ early stages. peerReviewed

Animals are often difficult to distinguish at an individual level, but being able to identify individuals can be crucial in ecological or behavioral studies. In response to this challenge, biologists have developed a range of marking (tattoos, brands, toe-clips) and tagging (PIT, VIA, VIE) methods to identify individuals and cohorts. Animals with complex life cycles are notoriously hard to mark because of the distortion or loss of the tag across metamorphosis. In frogs, few studies have attempted larval tagging and none have been conducted on a tropical species. Here, we present the first successful account of VIE tagging in early larval stages (Gosner stage 25) of the dyeing poison frog (Dendrobates tinctorius) coupled with a novel anaesthetic (2-PHE) application for tadpoles that does not require buffering. Mean weight of individuals at time of tagging was 0.12g, which is the smallest and developmentally youngest anuran larvae tagged to date. We report 81% tag detection over the first month of development, as well as the persistence of tags across metamorphosis in this species. Cumulative tag retention versus tag observation differed by approximately 15% across larval development demonstrating that “lost” tags can be found later in development. Tagging had no effect on tadpole growth rate or survival. Successful application of VIE tags on D. tinctorius tadpoles introduces a new method that can be applied to better understand early life development and dispersal in various tropical species.

Global pollution of mercury (Hg) threatens ecosystem and human health. We measured total Hg (THg) and monomethylmercury (MMHg) concentrations in filter-feeding blackfly (Simulium spp.) larvae in the inflows and the outflows of six boreal lakes with no Hg point source pollution. THg in the larvae ranged from 0.03 to 0.31 mg kg−1 dw and MMHg between 0.02 and 0.25 mg kg−1 dw. The proportion of MMHg in the larvae was 74 ± 0.16% and ranged from 43 to 98% of THg, the highest proportions being comparable to those typically found in aquatic predatory insects and fish. We compared the larvae MMHg concentrations to river water quality, catchment land-use, and to size-adjusted lake pike THg data. Two of the investigated catchments have been affected by a multimetal biomine since 2008 and were characterized by higher conductivity and higher urban land-use activity. Larvae THg and MMHg concentrations were higher in the lake inflows than in outflows and associated with water conductivity and catchment land-use activity. Lake pike THg concentrations were highly correlated to lake outflow blackfly larvae MMHg concentrations. Our data illustrate that blackfly larvae take up high percentage of THg that is MMHg, which in turn is available for higher consumers in aquatic and terrestrial food webs.

Antipredator strategies of the pupal stage in insects have received little attention in comparison to larval or adult stages. This is despite the fact that predation risk can be high during the pupal stage, making it a critical stage for subsequent fitness. The immobile pupae are not, however, defenceless; a wide range of antipredator strategies have evolved against invertebrate and vertebrate predators. The most common strategy seems to be ‘avoiding encounters with predators' by actively hiding in vegetation and soil or via cryptic coloration and masquerade. Pupae have also evolved behavioural and secondary defences such as defensive toxins, physical defences or deimatic movements and sounds. Interestingly, warning coloration used to advertise unprofitability has evolved very rarely, even though the pupal stage often contains defensive toxins in chemically defended species. In some species, pupae gain protection from conspecifics or mimic chemical and auditory signals and thereby manipulate other species to protect them. Our literature survey highlights the importance of studying selection pressures across an individual's life stages to predict how ontogenetic variation in selective environments shapes individual fitness and population dynamics in insects. Finally, we also suggest interesting avenues for future research to pursue. This article is part of the theme issue ‘The evolution of complete metamorphosis’.

Removal of parasite free-living stages by predators has previously been suggested an important factor controlling parasite transmission in aquatic habitats. Experimental studies of zooplankton predation on macroparasite larvae are, however, scarce. We tested whether trematode cercariae, which are often numerous in shallow waters, are suitable prey for syntopic zooplankters. Feeding rates and survival of freshwater cyclopoids (Megacyclops viridis, Macrocyclops distinctus), calanoids (Arctodiaptomus paulseni), cladocerans (Sida crystallina) and rotifers Asplanchna spp., fed with cercariae of Diplostomum pseudospathaceum, a common fish trematode, were studied. In additional long-term experiments, we studied reproduction of cyclopoids fed with cercariae. All tested zooplankton species consumed cercariae. The highest feeding rates were observed for cyclopoids (33 ± 12 cercariae ind−1 h−1), which actively reproduced (up to one egg clutch day−1) when fed ad libitum with cercariae. Their reproductive characteristics did not change significantly with time, indicating that cercariae supported cyclopoids’ dietary needs. Mortality of rotifers and cladocerans was high (25–28% individuals) when exposed to cercariae in contrast to cyclopoids and calanoids (

Pigmentation has emerged as a premier model for understanding the genetic basis of phenotypic evolution, and a growing catalog of color loci is starting to reveal biases in the mutations, genes, and genetic architectures underlying color variation in the wild. However, existing studies have sampled a limited subset of taxa, color traits, and developmental stages. To expand the existing sample of color loci, we performed QTL mapping analyses on two types of larval pigmentation traits that vary among populations of the redheaded pine sawfly (Neodiprion lecontei): carotenoid-based yellow body color and melanin-based spotting pattern. For both traits, our QTL models explained a substantial proportion of phenotypic variation and suggested a genetic architecture that is neither monogenic nor highly polygenic. Additionally, we used our linkage map to anchor the current N. lecontei genome assembly. With these data, we identified promising candidate genes underlying (1) a loss of yellow pigmentation in populations in the mid-Atlantic/northeastern United States [C locus-associated membrane protein homologous to a mammalian HDL receptor-2 gene (Cameo2) and lipid transfer particle apolipoproteins II and I gene (apoLTP-II/I)], and (2) a pronounced reduction in black spotting in Great Lakes populations [members of the yellow gene family, tyrosine hydroxylase gene (pale), and dopamine N-acetyltransferase gene (Dat)]. Several of these genes also contribute to color variation in other wild and domesticated taxa. Overall, our findings are consistent with the hypothesis that predictable genes of large effect contribute to color evolution in nature.

Even for parasitoids with a wide host range, not all host species are equally suitable, and host qualityoften depends on the plant the host feeds on. We compared oviposition choice and offspring perfor-mance of a generalist pupal parasitoid,Pteromalus apum(Retzius) (Hymenoptera: Pteromalidae), ontwo congeneric hosts reared on two plant species under field and laboratory conditions. The plantscontain defensive iridoid glycosides that are sequestered by the hosts. Sequestration at the pupal stagediffered little between host species and, although the concentrations of iridoid glycosides in the twoplant species differ, there was no effect of diet on the sequestration by host pupae. The rate of success-ful parasitism differed between host species, depending on the conditions they were presented in. Inthe field, where plant-associated cues are present, the parasitoid usedMelitaea cinxia(L.) overMeli-taea athalia(Rottemburg) (Lepidoptera: Nymphalidae), whereas moreM. athaliawere parasitisedin simplified laboratory conditions. In the field, brood size, which is partially determined by rate ofsuperparasitism, depended on both host and plant species. There was little variation in other aspectsof offspring performance related to host or plant species, indicating that the two host plants are ofequal quality for the hosts, and the hosts are of equal quality for the parasitoids. Corresponding tothis, we found no evidence for associative learning by the parasitoid based on their natal host, so withrespect to these host species they are truly generalist in their foraging behaviour. peerReviewed

The applicability of spectral analysis in detection of freshwater metal contamination was assessed by developing and testing a novel hyperspectral imaging (HSI) application for aquatic insect larvae (Trichoptera: Hydropsychidae). Larvae were first exposed to four different cadmium (Cd) concentrations: 0, 1, 10, and 100 μg L−1 for 96 h. Individual larvae were then preserved in ethanol, inspected with microscopy for the number of anomalies in larval gills, and imaged by hyperspectral camera operating with wavebands between 500 and 850 nm. Three additional larvae from each exposure were analyzed for tissue Cd concentration. Although the larval tissue Cd concentrations correlated positively with actual water concentrations, the toxicity response of larvae, i.e., frequency of gill abnormalities, did not differ among the Cd concentrations. In contrast, hyperspectral imaging data indicated some concentration-response relationship of larval spectral properties to the Cd exposure, but it was too weak for reliable automatic distinction between exposed and unexposed larvae. In this pilot study a workflow for data processing for a novel application of hyperspectral imaging was developed. Based on the results of this preliminary study, the workflow in the imaging process will be optimized and its potential for detecting metal contamination of aquatic environments reassessed. peerReviewed

Diet is one of the major factors directly and indirectly influencing insect’s life history traits and risk of getting infected. Additionally the insect’s fitness is severely affected by the broad diversity of parasites they are exposed to. As a consequence insects have developed well-evolved defences. Behavioural responses include self-medication, the ability of insects to change dietary intake in response to an infection. When studying this ability it is of major importance to consider the insects natural diet range. In this thesis I investigated the effect of different host plants on fitness and immunocompetence of polyphagous Arctia plantaginis larvae and whether the larvae can therapeutically and prophylactically self-medicate by optimising their diet intake. Additionally I examined the long-term effect of prophylactic treatment on lab-reared larvae from the same species. Feeding experiments reveal that the host plants plantain (high in biologically active compounds) and dandelion (high nutritional value) have different effect on the larval development and survival. Results show that a monotonous plantain diet provides lowest protection against an infection, whereas a diet switch from plantain to dandelion increases survival. Immunocompetence seems to be not differently affected by the two host plants. When given the choice, all larvae choose to ingest a mixture of both plants. The ratio of both plants differed depending on the infection status or infection risk in their environment compared to control larvae. This highlights the importance of a mixed diet for some polyphagous species and that dietary variety should be considered when studying insects’ ability to therapeutically and prophylactically medicate. A prophylactic medication applied to laboratory- reared insects showed negative effects on life-history traits and reproductive success, and thus should be carefully considered. In conclusion these findings provide insights in the crucial importance of diet mixing for polyphagous larvae and show evidence for the larvae ability to therapeutically and prophylactically medicate by mixing their diet.

Mating in nature is rarely random, and most fish species have refined mating systems. The vendace (Coregonus albula) is a short‐lived, small‐sized, cold‐water‐adapted pelagic schooling species that is known to spawn in groups, but the actual mating system of this species, like many other group‐spawning fishes, has not been described in detail. Vendace typically spawn in the littoral or sublittoral zones of lakes in late autumn, and the hatching of larvae occurs close to icebreak in the following spring. In our large study lake, vendace larvae were caught in 93% of 1,149 random sampling locations lake‐wide. We examined the courtship and mating of vendace under experimental conditions by nonintrusive observation of the natural behaviour, to clarify whether spawning activity is associated with illumination and to assess the postspawning mortality of vendace. Here, we describe and document in detail for the first time the spawning behaviour of vendace: they spawn in the dark, and females release a small portion of their eggs (on average 1% of mean total individual fecundity) when the female and male, side by side, dart from near the bottom up towards the surface, that is perform a spawning rise. Males and females had several spawning rises (on average 1,200). Our results showed high postspawning mortality (56%). The spawning stress seems to be a potential component of mortality regulating the lifespan duration of vendace. peerReviewed

The incidence of morphological deformities of chironomid larvae as an indicator of sediment toxicity has been studied for decades. However, standards for deformity analysis are lacking. The authors evaluated whether 25 experts diagnosed larval deformities in a similar manner. Based on high-quality digital images, the experts rated 211 menta of Chironomus spp. larvae as normal or deformed. The larvae were from a site with polluted sediments or from a reference site. The authors revealed this to a random half of the experts, and the rest conducted the assessment blind. The authors quantified the interrater agreement by kappa coefficient, tested whether open and blind assessments differed in deformity incidence and in differentiation between the sites, and identified those deformity types rated most consistently or inconsistently. The total deformity incidence varied greatly, from 10.9% to 66.4% among experts. Kappa coefficient across rater pairs averaged 0.52, indicating insufficient agreement. The deformity types rated most consistently were those missing teeth or with extra teeth. The open and blind assessments did not differ, but differentiation between sites was clearest for raters who counted primarily absolute deformities such as missing and extra teeth and excluded apparent mechanical aberrations or deviations in tooth size or symmetry. The highly differing criteria in deformity assignment have likely led to inconsistent results in midge larval deformity studies and indicate an urgent need for standardization of the analysis. Environ Toxicol Chem 2015;34:1891–1898. © 2015 SETAC

The abundance of freshwater pearl mussels (Margaritifera margaritifera) has declined widely during the past century, and new conservation initiatives are needed. This thesis focused on the relationship between M. margaritifera and its salmonid host required for reproduction of this species. First, by exposing fish experimentally to glochidium larvae of M. margaritifera, different M. margaritifera populations were shown to demonstrate strong differences in their ability to parasitize different salmonid species. Atlantic salmon was clearly a better host for mussels in large river channels, whereas in small headwater tributaries brown trout was the best, or the only suitable, host. These findings provide a previously unrecognised explanation for the collapse and the lack of recruitment especially of the salmon-specific M. margaritifera populations; a high proportion of large salmon rivers were dammed for hydropower production in the 1960s, which prevented the migration of salmon and thus left M. margaritifera without the appropriate host in these rivers. Furthermore, an invasive salmonid, brook trout, was widely introduced to small tributaries above the dams in the past, but in this study was shown to be an unsuitable host for M. margaritifera. Thus, and due to the tendency of brook trout to replace native brown trout, the spread of brook trout is an additional threat to M. margaritifera. An indication of local adaptation of M. margaritifera, i.e. higher infectivity in sympatric salmonid host strain than in allopatric populations of the same species, was also detected. Finally, a new, non- destructive approach to search for M. margaritifera populations, involving electrofishing and quick visual examination of the gills of captured salmonids, revealed the occurrence of 3 previously unknown populations. The results of this thesis highlight the importance of taking into account the roles of salmonid fish in future efforts to search, protect and restore freshwater pearl mussel populations.

In this thesis, two bucephalid trematode parasites Rhipidocotyle campanula and R. fennica, which use the same first (Anodonta anatina) and second intermediate (Rutilus rutilus) host were studied. The aim was to investigate the effect of temperature on one of the key processes in the transmission of these parasites: 1) the emergence of cercarial larvae from A. anatina over short (1 h) and 2) long (throughout the annual cercarial shedding period, from May to October) time periods as well, as on 3) mussel survival and 4) the seasonal timing of cercarial release. In addition, the aim was to study how the cercarial shedding traits are linked to the 5) geographical occurrence and abundance of the Rhipidocotyle species. In the experimental studies, the cercarial emergence by R. fennica increased significantly with increasing temperature over short and long time periods, while that by R. campanula was unaffected by temperature. R. campanula clearly started seasonal cercarial release earlier and at a lower temperature than R. fennica. Survival of mussels, especially cercariae-shedding mussels, was lower at higher temperature, and the shedding of R. campanula cercariae was associated with higher mussel mortality than the shedding of R. fennica. The average duration of the seasonal cercarial release period of both species was unaffected by temperature at the individual host level, but at the host population level the cercarial shedding period of R. fennica (but not of R. campanula) was longer at higher temperature. The field study showed that the occurrence, mean prevalence and abundance of R. fennica – in accordance with the experimentally observed association of cercarial release with high temperature – decreased from the south (61–64 °N) to the low north (65–66 °N), but this pattern was not detected in R. campanula.

Anthropogenic climate change and habitat loss and deterioration affect populations worldwide. Climate warming has changed phenologies of many species across trophic levels. Some predator populations now experience temporal mismatches with their prey, as timings of peak prey abundance and of the predator’s highest food demands no longer meet. The temporal mismatch hypothesis suggests that the population’s recruitment rate is related to its degree of synchrony with the food resources needed to feed offspring. However, species’ and populations’ responses to climate warming differ. Human land use alters and destroys habitats of countless species. For example, many boreal forest bird populations have declined, presumably due to intensive forestry. It has decreased the amount of dead wood, causing a threat to saproxylic species. Identification of the key characteristics of high-quality habitats is essential for conservation planning and for developing sustainable forestry. As individuals are suspected to settle in habitats that maximize their fitness, analysis of nest site selection can be used to identify the key habitats. My dissertation concerns the impacts of climate change and habitat deterioration on boreal populations. I use hole-nesting passerines as model species. By utilizing long-term data I show that breeding phenologies of Parus major and Poecile montanus, but not of Cyanistes caeruleus, have shifted earlier. Also, the timing of the food peak has advanced, improving the synchrony between P. montanus and caterpillars. In P. major and C. caeruleus, synchrony has remained good. However, the positive effect of good synchrony on breeding success seems to be conditional, arising only in certain circumstances, such as in years of high caterpillar abundance. I suggest that in boreal populations temperature affects timing of breeding mostly as a proximate factor. The availability of standing decaying trees used for nesting sites was the most important habitat characteristic determining the nest site selection of P. montanus. Remote sensing data alone was insufficient to produce reliable models, as the ecologically important small-scale factor can only be determined by direct field surveys. Omission of forest thinning in selected forest sites would ensure the continuous availability of decaying wood with positive influence on biodiversity in managed forests. Tiivistelmä Ihmisen aiheuttama habitaattien katoaminen ja huononeminen sekä ilmastonmuutos vaikuttavat populaatioihin kaikkialla maailmassa. Ilmaston lämpeneminen on muuttanut monien lajien fenologioita eri trofiatasoilla. Osalla saalistajalajien populaatioista suurin ravinnontarve ei enää ajoitu samaan aikaan saaliin runsaushuipun kanssa. Ajoituksen eriaikaisuus -hypoteesin mukaan todennäköisyys populaatioon rekrytoitumiselle riippuu synkronian asteesta saaliin kanssa. Ilmaston lämpenemisen vaikutuksissa lajeihin ja populaatioihin on kuitenkin vaihtelua. Ihmisen maankäyttö muuttaa ja tuhoaa lukuisien lajien elinympäristöjä. Esimerkiksi useiden boreaalisten metsien lintupopulaatioiden pienentymistä on selitetty intensiivisellä metsätaloudella. Lahopuun määrä metsissä on vähentynyt, mikä on uhka lahopuusta riippuvaisille lajeille. Korkealaatuisten habitaattien keskeisten piirteiden tunnistaminen on tärkeää luonnonsuojelun ja kestävän metsätalouden suunnittelulle. Koska yksilöiden oletetaan valitsevan niiden kelpoisuutta maksimoivia elinympäristöjä, pesäpaikanvalinta-analyysiä voidaan käyttää tärkeiden habitaattipiirteiden tunnistamiseen. Tarkastelen väitöskirjassani ilmastonmuutoksen ja habitaattien laadun vaikutuksia boreaalisiin populaatioihin. Mallilajeina käytän koloissa pesiviä varpuslintuja. Hyödyntämällä pitkäaikaisaineistoja osoitan, että lisääntymisen ajoittuminen on aikaistunut tali- ja hömötiaisella, mutta ei sinitiaisella. Myös ravintohuippu on aikaistunut, mikä on parantanut synkroniaa hömötiaisen ja sen pääasiallisen ravinnon eli toukkien välillä. Tali- ja sinitiaisella synkronia on pysynyt hyvänä. Hyvän synkronian myönteinen vaikutus lisääntymismenestykseen vaikuttaa kuitenkin ehdolliselta: se tulee esiin vain tietyissä olosuhteissa, kuten vuosina jolloin toukkia on runsaasti. Kevään lämpötilat näyttävät vaikuttavan pesinnän ajoittumiseen erityisesti proksimaattisena tekijänä. Pesäpaikkoina toimivien seisovien lahopuiden määrä on tärkein hömötiaisen pesäpaikanvalintaa määräävä tekijä. Kaukokartoitusaineisto yksinään ei riitä luotettavien mallien tuottamiseen, sillä ekologisesti tärkeät pienen skaalan tekijät voidaan kartoittaa vain suorin maastomittauksin. Metsien harventamatta jättäminen valituilla laikuilla turvaisi lahopuun jatkuvan saatavuuden, mikä vaikuttaisi myönteisesti talousmetsien biodiversiteettiin.

Jokihelmisimpukan (Margaritifera margaritifera L.) elämänkierron eri vaiheiden ajoitus tunnetaan heikosti, mikä vaikeuttaa mm. suojelutoimien suunnittelua. Tämän tutkimuksen tavoitteena oli havainnoida jokihelmisimpukan glokidium-toukkien kehittymistä ja lukumääriä kahdessa Iijoen alueen taimenpurossa. Erityisesti pyrimme saamaan tietoa siitä, milloin toukat kiinnittyvät kaloihin ja milloin ne irtoavat niistä. Lisäksi tavoitteena oli saada tietoa toukkien kasvunopeudesta loisvaiheessa. Tutkimus kohdistettiin kahteen lämpötiloiltaan erilaiseen puroon Iijoen alueella 9.6. ja 7.9. välisenä aikana. Tutkimuskalana käytettiin purotaimenta (Salmo trutta m. fario L.), joka on puroissa luonnostaan esiintyvä raakun loisvaiheen isäntäkala. Työ on osa pohjoismaista Interreg Raakku -hanketta (2011–2014). Glokidium-toukkien irtoaminen kaloista ajoittui lämpimällä purolla pääasiassa välille 9.6.–28.6. ja kylmällä purolla välille 27.6.–20.7. Uudet toukat eivät olleet tarttuneet kaloihin kylmällä purolla vielä 2.8., mutta 31.8. näytteessä niitä havaittiin ja toukat olivat keskipituudeltaan 80 µm. Lämpimällä purolla uusia toukkia ei havaittu vielä 31.8., mutta 7.9. näytteessä niitä esiintyi keskipituuden ollessa 70 µm. Toukkien pituudesta voidaan päätellä, että kylmällä purolla infektoituminen uusilla glokidium-toukilla on tapahtunut selvästi ennen elokuun loppua, koska aikaisemmat havainnot viittaavat uusien toukkien olevan kooltaan n. 70 µm. Erot toukkien kehittymisessä eri puroissa johtunevat pääasiassa veden lämpötilaerosta. Veden lämpötila oli kylmässä purossa yli 15 °C viiden vuorokauden ajan aikavälillä 29.6.–3.7. Toukkien pudottautuminen kaloista lienee alkanut kyseisenä ajanjaksona, koska aikaisemmissa tutkimuksissa toukkien on havaittu irtoavan kaloista veden lämpötilan ollessa ”pysyvästi” yli 15 °C. Tulokset tukivat tätä kynnyslämpötilan ”pysyvän” ylityksen tarpeellisuutta toukkien parveilun ajoittumiseen. Kylmän puron toukat olivat kesäkuun alussa huomattavasti pienempiä verrattuna lämpimään puroon. Seuraavana tutkimuspäivänä 27./28.6. ero oli lähes tyystin kadonnut. Lämpimällä purolla lämpötila laski 3.9.–5.9 nopeasti alle 13 °C:een, mikä on ehkä toiminut laukaisevana tekijänä uusien glokidium-toukkien parveilulle. Kylmän puron vesi oli alle 13-asteista aikavälillä 5.8.–15.8., joten siellä toukat ovat voineet tarttua kaloihin jo elokuun alkupuoliskolla. Raakun loisvaihe kesti siis kylmällä purolla ehkä 11-11,5 kk ja lämpimällä purolla n. 10,5 kk, jos infektoitumisen oletetaan tapahtuneen molemmilla puroilla myös edellisenä vuonna samoihin aikoihin.

Complex life-cycle parasites use their intermediate hosts both as an energy source and as a vessel for transmission to the next host in the life cycle. Parasites that grow rapidly to a large size may have high fitness (e.g. time spent in uninfective stages is limited), yet those that grow too aggressively may reduce host viability and their own probability of successful transmission. I examined aspects of both the growth and transmission strategy of an acanthocephalan (Acanthocephalus lucii) in its isopod intermediate host. In an experimental infection, the relative rate of larval parasite growth slowed over time, and eventually parasites seemed to reach a threshold biomass sustainable by their hosts. Consequently, late during this infection parasite growth depended on the level of resources a given host could provide. The rapid, unconstrained growth of young A. lucii appeared worse for isopod viability than the slow, constrained growth of larger parasites. Female A. lucii grew larger than males and their size was more strongly related to host size, suggesting they invest more in growth and are consequently more limited by resources. Patterns of sexual dimorphism across acanthocephalan species suggest that sexual selection driving adult dimorphism may promote sexual divergence in larval growth strategies. Isopods infected with A. lucii cystacanths spent less time hiding and had darker abdominal coloration than uninfected isopods. The magnitudes of these two altered traits were not correlated, even when both traits were measured somewhat repeatably from individual hosts. Parasite-induced host alteration seemed to increase over time as parasites grew. Refuge use by infected isopods decreased over eight weeks, and, in general, the altered coloration of infected isopods seemed to increase with parasite growth. An increasing probability of host mortality, as well as a decreasing potential for additional parasite growth, could favor increased parasitic manipulation of host phenotype.

Suppealla alueella esiintyvät päiväperhoslajit ovat usein paikallisesti suhteellisen runsaslukuisia. Tämän yllättävän seikan havaitsi filosofian maisteri Jussi Päivinen tutkiessaan väitöskirjaansa varten päiväperhosia. Havainto on maailmanlaajuisesti erittäin harvinainen. Yhtenä syynä voi olla Suomen pohjoinen sijainti, jonka seurauksena monien päiväperhoslajien levinneisyysalue rajoittuu Etelä-Suomeen. - Levinneisyysalueensa reunalla elävät perhoslajit pystyvät asuttamaan ainoastaan suurimmat ja laadultaan parhaimmat elinympäristölaikut, mutta koska laikut ovat korkealaatuisia, niihin voi muodostua erittäin runsaslukuiset päiväperhoskannat. Reuna-alueella elävien päiväperhosten ns. elinympäristölaikut ovat todennäköisesti eristyneempiä kuin niiden lajien, joiden levinneisyysalue kattaa suuren osan tutkittavasta alueesta, Päivinen selvittää. Several mechanisms have been proposed to explain the patterns of species richness, distribution and abundance. Also several mechanisms have been put forward in explaining the generally observed positive relationship between regional distribution and local abundance of species. In this thesis factors affecting distribution, abundance and species richness were studied using butterflies and myrmecophilous beetles as study objects. The data of myrmecophilous beetles are based on the literature and a field survey and data of butterflies is based on the literature. This thesis suggests that ant colonies maintain species rich beetle fauna, and that widespread host ant species and the species with large colony size are able to maintain higher species richness of myrmecophilous beetles. Surprisingly, a strong negative relationship between local abundance and regional distribution was found for the Finnish butterflies. The study suggested that sedentary butterfly species, species at the edge of their distribution range and the most specialized species were locally abundant with restricted distribution. Mobile species, species furthest from the edge of their distribution and generalist butterfly species were locally few in number and widespread, thus, generating the negative relationship. Larval specificity, habitat breadth and resource availability were observed to be in a key role when explaining the mobility of the butterflies. Range position had strong effect both on the mobility and on the length of the flight period of the butterflies. The surprising results emphasize the importance of the study of basic ecology of species. More studies are needed to find out, whether observed negative relationship between distribution and abundance is a more general phenomenon than previously thought.

In a locality in Southern Finland where the white-backed woodpecker, (Bechst.), was previously breeding was found many conical borings excavated during the winter in young aspens ( L.) on average 8.1 cm in diameter. Full-grown larvae of (L.) (Coleoptera, Cerambycidae) hibernated in pupal chambers constructed about 0.5 m above ground level. Below this chamber the larva has usually prepared an exit hole. After the larva has blocked itself in the pupating chamber it is easy to prey for the woodpecker during the whole winter.Dendrocopos leucotosPopulus tremulaSaperda carchariasS. sarcharias

Assimilation of cow liver by Lucilia illustris (Meigen) larvae was studied in the laboratory. The larvae were cultured from hatching to the end of development in the respiration chambers of an infra-red gas analyser (IRGA), and respiration was measured as CO2 production. Assimilation was calculated in both carbon and energy units. In this organism the Cr203 indicator method proved unsuitable for measuring food consumption. In early larval development respiration showed two linear phases, which are suggested to be correlated with the first two instars. Both the cumulative and the instantaneous net production efficiency, K2 (production/assimilation), were calculated. Integration of the latter to the final larval weight produced results similar to those obtained by direct determination. K2 varied both with temperature and with the developmental stage of the larvae (weight). Efficiency was highest during the most intense growth phase, or a little before it, then being 88 % in carbon units (90 % in energy units) at 25 to 300C. At this optimal temperature the cumulative K2 to the end of the feeding period was 82 % (84 %); in changing temperature conditions the corresponding K2 was 77 0 (79 %). The value of instantaneous concepts in bioenergetic research and the application of IRGA to measurements of animal respiration is discussed.