Anders Herland

• Lindsø, Lars; Rivrud, Inger Maren; König, Emilie A.; Herland, Anders & Mysterud, Atle (2025). Diel Niche of Sympatric Small Mammals Revealed by Year-Round Camera Trapping. Ecology and Evolution. 15(6). doi: https:/onlinelibrary.wiley.com/doi/10.1002/ece3.71590. Full text in Research Archive Show summary

  At northern latitudes, small mammals are of key importance for ecosystem dynamics. Yet, few have monitored the small mammal community to accurately investigate activity of sympatric small mammals at finer temporal resolutions, and consequently their temporal niche partitioning that may provide novel insights into how they interact with their environment and each other. Here, we deployed 12 tunnel-based camera traps to continuously monitor a forest community of small mammals in South-East Norway (2018–2020). We statistically determined the diel period selection (cathemeral, nocturnal, diurnal, crepuscular) in the wood mouse (Apodemus sylvaticus), bank vole (Myodes glareolus), common shrew (Sorex araneus) and pygmy shrew (S. minutus). We analyzed how temperature and snow cover influenced small mammal occurrence in winter and whether camera trap observations correlated with numbers from ordinary trapping in spring and fall. In both winter and summer, wood mice were nocturnal, while common shrews were cathemeral. Diel period selection in bank voles and pygmy shrews varied seasonally, and both were cathemeral in summer and nocturnal in winter. The occurrence of both rodents and shrews developed from a low year in 2018, to an increase in 2019, and to a peak year in 2020, albeit at lower amplitudes for the pygmy shrew. Small mammal occurrence in winter was positively influenced by temperature, but the relationship was dependent on snow cover and was only significant at low snow levels. Camera trap occurrence correlated moderately with spatially and temporally coinciding ordinary trapping indices in spring and fall. Thus, tunnel-based camera traps captured a new level of detail in species synchrony of common small mammals in northern Europe at annual, seasonal, and diel scales, yielding a better understanding of their ecology.

• Lindsø, Lars; Anders, Jason Lee; Viljugrein, Hildegunn; Herland, Anders; Stigum, Vetle Malmer & Easterday, William Ryan [Show all 7 contributors for this article] (2023). Individual heterogeneity in ixodid tick infestation and prevalence of Borrelia burgdorferi sensu lato in a northern community of small mammalian hosts. Oecologia. ISSN 0029-8549. 203(3), p. 421–433. doi: 10.1007/s00442-023-05476-w. Full text in Research Archive Show summary

  Abstract Heterogeneous aggregation of parasites between individual hosts is common and regarded as an important factor in understanding transmission dynamics of vector-borne diseases. Lyme disease is vectored by generalist tick species, yet we have a limited understanding of how individual heterogeneities within small mammal host populations affect the aggregation of ticks and likelihood of infection. Male hosts often have higher parasite and infection levels than females, but whether this is linked to sexual body size dimorphism remains uncertain. Here, we analysed how host species, sex, and body mass influenced Ixodes ricinus tick infestations and the infection prevalence of Borrelia burgdorferi sensu lato (s.l.) in three species of small mammals involved in the enzootic transmission cycle of Lyme disease in Norway from 2018 to 2022. Larval and nymphal ticks were found on 98% and 34% of all individual hosts, respectively. In bank voles and wood mice, both larval and nymphal tick infestation and infection probability increased with body mass, and it increased more with mass for males than for females. Tick infestation in the common shrew increased with body mass and was higher in males, while pathogen infection was higher in females. Sex-biases in infestation did not correspond with level of sexual body mass dimorphism across species. This study contributes to our understanding of how individual heterogeneity among small mammalian hosts influences I. ricinus tick aggregation and prevalence of B. burgdorferi s.l. at northern latitudes.

• Evangelista, Charlotte; Dupeu, Julia; Sandkjenn, Joakim; Pauli, Beatriz Diaz; Herland, Anders & Meriguet, Jacques [Show all 8 contributors for this article] (2021). Ecological ramifications of adaptation to size-selective mortality. Royal Society Open Science. 8(10). doi: 10.1098/rsos.210842. Full text in Research Archive Show summary

  Size-selective mortality due to harvesting is a threat to numerous exploited species, but how it affects the ecosystem remains largely unexplored. Here, we used a pond mesocosm experiment to assess how evolutionary responses to opposite size-selective mortality interacted with the environment (fish density and light intensity used as a proxy of resource availability) to modulate fish populations, prey community composition and ecosystem functions. We used medaka (Oryzias latipes) previously selected over 10 generations for small size (harvest-like selection; small-breeder line) or large size (large-breeder line), which displayed slow somatic growth and early maturity or fast somatic growth and late maturity, respectively. Large-breeder medaka produced more juveniles, which seemed to grow faster than small-breeder ones but only under high fish density. Additionally, large-breeder medaka had an increased impact on some benthic prey, suggesting expanded diet breadth and/or enhanced foraging abilities. As a consequence, increased light stimulated benthic algae biomass only in presence of large-breeder medaka, which were presumably better at controlling benthic grazers. Aggregated effect sizes at the community and ecosystem levels revealed that the ecological effects of medaka evolution were of similar magnitude to those induced by the environment and fish introduction. These findings indicate the important environmental dependency of evolutionary response to opposite size-selective mortality on higher levels of biological organizations.

• Mysterud, Atle; Stigum, Vetle Malmer; Linløkken, Harald Kolstad; Herland, Anders & Viljugrein, Hildegunn (2019). How general are generalist parasites? The small mammal part of the Lyme disease transmission cycle in two ecosystems in northern Europe. Oecologia. ISSN 0029-8549. 190(1), p. 115–126. doi: 10.1007/s00442-019-04411-2. Full text in Research Archive Show summary

  The pathogens causing Lyme disease are all vectored by generalist tick species found on a wide range of vertebrates, but spatial and annual variation in host use has rarely been quantified. We here compare the load of Ixodes ricinus (the vector) on small mammals and investigate the infection prevalence of Borrelia burgdorferi s.l. (the pathogen) involved in the enzootic transmission cycle of Lyme disease in two contrasting ecosystems in Norway from 2014 to 2016. The most common larval tick host in the eastern region was the bank vole, while the common shrew dominated in the western region of Norway. However, the wood mouse and the bank vole had consistently higher larval tick loads than the common shrew in both ecosystems. Hence, the evidence indicated that species are differently suitable as hosts, regardless of their abundances. The pathogen infection prevalence was similar among small mammal species, but markedly higher in the region with larger small mammal populations and higher tick loads, while the seasonal and annual variation was less marked. Our study indicated that the generalist I. ricinus shows consistent patterns of load on species of small vertebrate hosts, while B. burgdorferi s.l. (B. afzelii) was a true generalist. The similar roles of host species across regions suggest that disease dynamics can be predicted from host community composition, but predicting the role of host community composition for disease dynamics requires a detailed understanding of the different species population limitations under global change.

• Mysterud, Atle; Stigum, Vetle Malmer; Seland, Ingrid Vikingsdal; Herland, Anders; Easterday, William Ryan & Jore, Solveig [Show all 8 contributors for this article] (2018). Tick abundance, pathogen prevalence, and disease incidence in two contrasting regions at the northern distribution range of Europe. Parasites & Vectors. 11(309). doi: 10.1186/s13071-018-2890-9. Full text in Research Archive Show summary

  Background Emergence of tick-borne diseases is impacting humans and livestock across the Northern Hemisphere. There are, however, large regional variations in number of cases of tick-borne diseases. Some areas have surprisingly few cases of disease compared to other regions. The aim here is to provide a first step towards a better understanding of such contrasting regional patterns of disease emergences at the northern distribution range of Ixodes ricinus in Europe. Methods We compare disease incidence, vector abundance and pathogen prevalence in eastern and western Norway differing in the number of tick-borne disease cases. First, we analysed the incidence of Lyme borreliosis in humans, tick-borne fever (anaplasmosis) in sheep and anaplasmosis and babesiosis in cattle to verify if incidence differed. Secondly, we analysed extensive field data on questing tick density, pathogen prevalence, as well as the broad spatial pattern of human and livestock distribution as it may relate to tick exposure. Results The incidences of all diseases were lower in eastern, compared to western, Norway, but this was most marked for the livestock diseases. While the prevalence of Borrelia burgdorferi (sensu lato) in ticks was similar in the two regions, the prevalence of Anaplasma phagocytophilum was markedly lower in eastern, compared to western, Norway. We found overall a lower abundance of questing nymphs in the east. In the east, there were cases of babesiosis in cattle where anaplasmosis was absent, suggesting absence of the pathogen rather than differences in exposure to ticks as part of the explanation for the much lower incidence of anaplasmosis in eastern Norway. Conclusions Many factors contribute to different disease incidence across ecosystems. We found that regional variation in tick-borne disease incidence may be partly linked to vector abundance and pathogen prevalence, but differently for human and livestock diseases. Further studies are needed to determine if there is also regional variation in specific genospecies and strain frequencies differing in pathogenicity.

• Mysterud, Atle; Madslien, Knut; Herland, Anders; Viljugrein, Hildegunn & Ytrehus, Bjørnar (2016). Phenology of deer ked (Lipoptena cervi) host-seeking flight activity and its relationship with prevailing autumn weather. Parasites & Vectors. 9(95), p. 1–6. doi: 10.1186/s13071-016-1387-7. Full text in Research Archive Show summary

  Background: The deer ked (Lipoptena cervi) is an ectoparasite on cervids that has invaded large parts of Norway, Sweden and Finland during recent decades. During their host-seeking flight activity, the adult deer keds constitute a considerable nuisance to people and limit human outdoor recreation. The bites of the deer ked can cause long-lasting dermatitis in humans. Determining the pattern of flight activity during autumn is hence important. Methods: Data on flight phenology was gathered by walking along transects in the forest in two counties of Norway during 2009–2013, counting the number of host-seeking keds. We analysed how the flight activity of deer keds varied depending on date and prevailing weather during autumn. Results: The best model of flight activity included both date and temperature, both as nonlinear terms. Host-seeking deer keds were observed from early August to mid-November with a marked peak in late September. Number of host-seeking keds declined with temperatures falling below the mean, but did not increase much at above mean temperatures. The pattern of flight phenology was similar across the two counties and five years. Conclusions: Parasitic arthropods may be strongly affected by prevailing weather during off-host periods. Our study shows an estimated positive effect of temperature on deer ked flight activity mainly for below mean temperatures in late autumn, while the effect of temperature on flight activity in early autumn was weak. The pattern of host-seeking flight activity during late, rather than early autumn, is hence more likely to change with ongoing climate change, with a predicted increase in duration of the host-seeking period. Keywords: Deer ked, Invading parasites, Climate, Temperature, Moose, Phenology

• Taugbøl, Annette; Junge, Claudia; Quinn, Thomas P.; Herland, Anders & Vøllestad, Leif Asbjørn (2014). Genetic and morphometric divergence in threespine stickleback in the Chignik catchment, Alaska. Ecology and Evolution. 4(2), p. 144–156. doi: 10.1002/ece3.918. Full text in Research Archive Show summary

  Divergent selection pressures induced by different environmental conditions typically lead to variation in life history, behavior, and morphology. When populations are locally adapted to their current environment, selection may limit movement into novel sites, leading to neutral and adaptive genetic divergence in allopatric populations. Subsequently, divergence can be reinforced by development of pre- or postzygotic barriers to gene flow. The threespine stickleback, Gasterosteus aculeatus, is a primarily marine fish that has invaded freshwater repeatedly in postglacial times. After invasion, the established freshwater populations typically show rapid diversification of several traits as they become reproductively isolated from their ancestral marine population. In this study, we examine the genetic and morphometric differentiation between sticklebacks living in an open system comprising a brackish water lagoon, two freshwater lakes, and connecting rivers. By applying a set of microsatellite markers, we disentangled the genetic relationship of the individuals across the diverse environments and identified two genetic populations: one associated with brackish and the other with the freshwater environments. The “brackish” sticklebacks were larger and had a different body shape than those in freshwater. However, we found evidence for upstream migration from the brackish lagoon into the freshwater environments, as fish that were genetically and morphometrically similar to the lagoon fish were found in all freshwater sampling sites. Regardless, few F1-hybrids were identified, and it therefore appears that some pre- and/or postzygotic barriers to gene flow rather than geographic distance are causing the divergence in this system.

• Voje, Kjetil Lysne; Mazzarella, Anna Virginia Black; Hansen, Thomas F; Østbye, Kjartan; Klepaker, Tom Olav & Bass, Arthur [Show all 10 contributors for this article] (2013). Adaptation and constraint in a stickleback radiation. Journal of Evolutionary Biology. ISSN 1010-061X. 26(11), p. 2396–2414. doi: 10.1111/jeb.12240. Full text in Research Archive

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