Biology subjects

Vesterinen, E. J.

Publications and source records attributed to Vesterinen, E. J..

5 recordsLinked to original sources

bioRxiv2026

Temporal variation and drivers of Ixodiphagus hookeri parasitisation in Ixodes ricinus ticks in northern Europe

Ixodiphagus hookeri (Hymenoptera: Encyrtidae) is a highly specialized koinobiont endoparasitoid of hard ticks (Acari: Ixodidae). While it is considered a prime target for biological control of ticks, longitudinal data on natural parasitisation of tick populations is scarce, consequently leading to a lack of understanding regarding the effects of global warming on wasp populations and factors impacting natural parasitisation rates of ticks. To fill in these gaps, we present a longitudinal time series on natural I. hookeri parasitisation of Ixodes ricinus from the northernmost limits of their occurrence. In total, 2,111 I. ricinus nymphs collected between 2014-2021 from Seili Island in southwestern Finland were screened for I. hookeri DNA utilizing an in-house qPCR assay. Samples had previously been screened for several tick-borne pathogens and larval blood meal sources. Generalized linear mixed models were fitted to determine factors influencing the probability of parasitisation of questing nymphs, whether parasitisation influences tick densities, and if differences in parasitisation can be identified between early (May to mid-July) and late (mid-July to October) season. Log odds ratios were calculated to assess parasitisation-pathogen and parasitisation-host associations. An artificial tick feeding system was used to feed nymphs collected from the island. An increase in I. hookeri parasitisation was observed on the island between 2014-2021. The overall parasitisation prevalence was 8.2 %, with year and study site specific values ranging from 0 to 38 %. Larvae densities, July mean temperatures and parasitisation rates at t-1 were observed to increase probability of parasitisation. Parasitisation was more likely if the nymphs had fed on deer as larvae or carried Babesia spp. protozoa, and less likely if they carried Borrelia spp. Twelve wasps emerged from an artificially fed nymph, immediately starting oviposition and expiring within seven days. We present here the longest time series of natural I. hookeri parasitisation of I. ricinus ticks. An increasing trend in parasitisation was observed, indicating increases in the wasp population likely linked to global warming. Our results regarding associations between parasitisation and tick-borne pathogens - and directly linking parasitisation events to deer - support findings from previous research, which have indicated that parasitisation of ticks is more likely to occur on large host animals than on small hosts or ticks questing on the ground. The results suggest that larvae may be more important parasitisation targets for the wasps than previously accredited.

ecology↗

bioRxiv2024

Opportunistic partner choice among arctic plants and root-associated fungi is driven by environmental conditions.

Interactions between plants and soil microbes play an important role in structuring plant communities. Yet, little is known about how fungal networks are structured on the one hand by fungal responses to their environment (including their host plant) and on the other by responses to each other. We quantified changes in plant-fungus networks along geographic and environmental gradients across the Arctic, assessing the degree to which plants and fungi showed preference for specific interaction partners and how specificity varies along environmental gradients. To this aim, we sampled roots of 12 widely distributed plant taxa: Saxifraga oppositifolia; Bistorta vivipara; Dryas spp.; Vaccinium tis-idaea; Vaccinium uliginosum; Vaccinium myrtillus; Empetrum nigrum; Betula nana; alix arctica; Salix polaris; Cassiope tetragona; and Silene acaulis. To quantify the pool of fungi from which plant roots may recruit association partners, we also sampled fungi in the surrounding soil. Identifying fungaI communities by DNA metabarcoding, we used Hierarchical Modelling of Species Communities (HMSC) to assess how fungal communities change along environmental gradients, and whether plants actively select their root-associated fungi from the pool of fungi present in the bulk soil. We found that although the fungal communities within the soil and rhizosphere share 85% of genera, their composition differs significantly from each other. The two community types show similar responses to the environment and taxa show low partner fidelity. Thus, the structure of fungal communities on plant rhizosphere is mainly driven by abiotic rather than biotic conditions. Overall, in comparison with null models, networks of plants and rhizosphere-associated fungi showed a distinctly non-random structure, responding strongly to pH and temperature gradients. Our findings suggest that the dynamics and structure of plant-root associated interactions might be severely altered by abiotic changes in the rapidly changing arctic environment. Open Research statementData are privately provided for peer review. The raw sequences for the soil and root samples generated during the current study will be available in the Sequence Read Archive repository, in the BioProject PRJNA1094865 upon acceptance. For review purposes, the code and datasets used for the analyses of this study are temporarily available in Figshare open access repository at https://figshare.com/s/1b074f1751682d3487cf upon acceptance.

ecology↗

bioRxiv2022

Novel frontier in wildlife monitoring: identification of small rodent species from faecal pellets using Near-Infrared Reflectance Spectroscopy (NIRS)

Small rodents are prevalent and functionally important across worlds biomes, making their monitoring salient for ecosystem management, conservation, forestry and agriculture. Yet, there is a dearth of cost-effective and non-invasive methods for large-scale, intensive sampling. As one such method, fecal pellet counts readily provide relative abundance indices. Given available analytical methods, feces could also allow for determination of multiple ecological and physiological variables, including community composition. We developed calibration models for rodent taxonomic determination using fecal near-infrared reflectance spectroscopy (fNIRS). Our results demonstrate fNIRS as an accurate and robust method for predicting genus and species identity of five co-existing subarctic microtine rodent species. We show that sample exposure to weathering did not reduce accuracy, indicating suitability of the method for samples collected from the field. Diet was not a major determinant of species prediction accuracy in our samples, as diet exhibited large variation and overlap between species. While regional calibration models predicted poorly samples from another region, calibration models including samples from two regions provided a good prediction accuracy for both regions. We propose fNIRS as a fast and cost-efficient high-throughoutput method for rodent taxonomic determination, and highlight its potential for cross-regional calibrations and use on field-collected samples. FNIRS can facilitate rodent population censuses at larger spatial extent than before deemed feasible, if combined with pellet-count based abundance indices. Given the versatility of fNIRS analytics, developing such monitoring schemes can support ecosystem- and interaction-based approaches to monitoring.

ecology↗

bioRxiv2020

Body size and tree species composition determine variation in prey consumption in a forest-inhabiting generalist predator

Trophic interactions may strongly depend on body size and environmental variation, but this prediction has been seldom tested in nature. Many spiders are generalist predators that use webs to intercept flying prey. The size and mesh of orb webs increases with spider size, allowing a more efficient predation on larger prey. We studied to this extent the orb-weaving spider Araneus diadematus inhabiting forest fragments differing in edge distance, tree diversity and tree species. These environmental variables are known to correlate to insect composition, richness and abundance. We anticipated these forest characteristics to be a principle driver of prey consumption. We additionally hypothesised them to impact spider size at maturity and expect shifts towards larger prey-size distributions in larger individuals independently from the environmental context. We quantified spider diet by means of metabarcoding of nearly 1000 A. diadematus from a total of 53 forest plots. This approach allowed a massive screening of consumption dynamics in nature, though at the cost of identifying the exact prey identity, as well as their abundance and putative intraspecific variation. Our study confirmed A. diadematus as a generalist predator, with more than 300 prey ZOTUs detected in total. At the individual level, we found large spiders to consume fewer different species, but adding larger species to their diet. Tree species composition affected both prey species richness and size in the spiders diet, although tree diversity per se had no influence on the consumed prey. Edges had an indirect effect on the spider diet as spiders closer to the forest edge were larger and therefore consumed larger prey. We conclude that both intraspecific size variation and tree species composition shape the consumed prey of this generalist predator.

ecology↗

bioRxiv2018

Counting with DNA in metabarcoding studies: how should we convert sequence reads to dietary data?

Advances in DNA sequencing technology have revolutionised the field of molecular analysis of trophic interactions and it is now possible to recover counts of food DNA barcode sequences from a wide range of dietary samples. But what do these counts mean? To obtain an accurate estimate of a consumers diet should we work strictly with datasets summarising the frequency of occurrence of different food taxa, or is it possible to use the relative number of sequences? Both approaches are applied in the dietary metabarcoding literature, but occurrence data is often promoted as a more conservative and reliable option due to taxa-specific biases in recovery of sequences. Here, we point out that diet summaries based on occurrence data overestimate the importance of food consumed in small quantities (potentially including low-level contaminants) and are sensitive to the count threshold used to define an occurrence. Our simulations indicate that even with recovery biases incorporated, using relative read abundance (RRA) information can provide a more accurate view of population-level diet in many scenarios. The ideas presented here highlight the need to consider all sources of bias and to justify the methods used to interpret count data in dietary metabarcoding studies. We encourage researchers to continue to addressing methodological challenges, and acknowledge unanswered questions to help spur future investigations in this rapidly developing area of research.

ecology↗