Browsing by Subject "POPULATIONS"

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  • Fountain, Toby; Ravinet, Mark; Naylor, Richard; Reinhardt, Klaus; Butlin, Roger K. (2016)
    The rapid evolution of insecticide resistance remains one of the biggest challenges in the control of medically and economically important pests. Insects have evolved a diverse range of mechanisms to reduce the efficacy of the commonly used classes of insecticides, and finding the genetic basis of resistance is a major aid to management. In a previously unstudied population, we performed an F-2 resistance mapping cross for the common bed bug, Cimex lectularius, for which insecticide resistance is increasingly widespread. Using 334 SNP markers obtained through RAD-sequencing, we constructed the first linkage map for the species, consisting of 14 putative linkage groups (LG), with a length of 407 cM and an average marker spacing of 1.3 cM. The linkage map was used to reassemble the recently published reference genome, facilitating refinement and validation of the current genome assembly. We detected a major QTL on LG12 associated with insecticide resistance, occurring in close proximity (1.2 Mb) to a carboxylesterase encoding candidate gene for pyrethroid resistance. This provides another example of this candidate gene playing a major role in determining survival in a bed bug population following pesticide resistance evolution. The recent availability of the bed bug genome, complete with a full list of potential candidate genes related to insecticide resistance, in addition to the linkage map generated here, provides an excellent resource for future research on the development and spread of insecticide resistance in this resurging pest species.
  • Saarinen, Kati; Laakso, Jouni; Lindström, Leena; Ketola, Tarmo (2018)
    Rapid environmental fluctuations are ubiquitous in the wild, yet majority of experimental studies mostly consider effects of slow fluctuations on organism. To test the evolutionary consequences of fast fluctuations, we conducted nine independent experimental evolution experiments with bacteria. Experimental conditions were same for all species, and we allowed them to evolve either in fluctuating temperature alternating rapidly between 20°C and 40°C or at constant 30°C temperature. After experimental evolution, we tested the performance of the clones in both rapid fluctuation and in constant environments (20°C, 30°C and 40°C). Results from experiments on these nine species were combined meta-analytically. We found that overall the clones evolved in the fluctuating environment had evolved better efficiency in tolerating fluctuations (i.e., they had higher yield in fluctuating conditions) than the clones evolved in the constant environment. However, we did not find any evidence that fluctuation-adapted clones would have evolved better tolerance to any measured constant environments (20°C, 30°C, and 40°C). Our results back up recent empirical findings reporting that it is hard to predict adaptations to fast fluctuations using tolerance curves.
  • Lamnidis, Thiseas C.; Majander, Kerttu; Jeong, Choongwon; Salmela, Elina; Wessman, Anna; Moiseyev, Vyacheslav; Khartanovich, Valery; Balanovsky, Oleg; Ongyerth, Matthias; Weihmann, Antje; Sajantila, Antti; Kelso, Janet; Pääbo, Svante; Onkamo, Päivi; Haak, Wolfgang; Krause, Johannes; Schiffels, Stephan (2018)
    European population history has been shaped by migrations of people, and their subsequent admixture. Recently, ancient DNA has brought new insights into European migration events linked to the advent of agriculture, and possibly to the spread of Indo-European languages. However, little is known about the ancient population history of north-eastern Europe, in particular about populations speaking Uralic languages, such as Finns and Saami. Here we analyse ancient genomic data from 11 individuals from Finland and north-western Russia. We show that the genetic makeup of northern Europe was shaped by migrations from Siberia that began at least 3500 years ago. This Siberian ancestry was subsequently admixed into many modern populations in the region, particularly into populations speaking Uralic languages today. Additionally, we show that ancestors of modern Saami inhabited a larger territory during the Iron Age, which adds to the historical and linguistic information about the population history of Finland.
  • Loikkanen, Emil; Oristo, Satu; Hämäläinen, Natalia; Jokelainen, Pikka; Kantala, Tuija; Sukura, Antti; Maunula, Leena (2020)
    The main animal reservoirs of zoonotic hepatitis E virus (HEV) are domestic pigs and wild boars, but HEV also infects cervids. In this study, we estimated the prevalence of HEV in Finnish cervid species that are commonly hunted for human consumption. We investigated sera from 342 European moose (Alces alces), 70 white-tailed deer (Odocoileus virginianus), and 12 European roe deer (Capreolus capreolus). The samples had been collected from legally hunted animals from different districts of Finland during 2008–2009. We analysed the samples for total anti-HEV antibodies using a double-sandwich ELISA assay. Seropositive sera were analysed with RT-qPCR for HEV RNA. HEV seroprevalence was 9.1% (31/342) in moose and 1.4% (1/70) in white-tailed deer. None of the European roe deer were HEV seropositive (0/12). No HEV RNA was detected from samples of seropositive animals. HEV seropositive moose were detected in all districts. Statistically, HEV seroprevalence in moose was significantly higher (p 
  • Camarena-Gomez, Maria Teresa; Ruiz-Gonzalez, Clara; Piiparinen, Jonna; Lipsewers, Tobias; Sobrino, Cristina; Logares, Ramiro; Spilling, Kristian (2021)
    In parts of the Baltic Sea, the phytoplankton spring bloom communities, commonly dominated by diatoms, are shifting toward the co-occurrence of diatoms and dinoflagellates. Although phytoplankton are known to shape the composition and function of associated bacterioplankton communities, the potential bacterial responses to such a decrease of diatoms are unknown. Here we explored the changes in bacterial communities and heterotrophic production during the spring bloom in four consecutive spring blooms across several sub-basins of the Baltic Sea and related them to changes in environmental variables and in phytoplankton community structure. The taxonomic structure of bacterioplankton assemblages was partially explained by salinity and temperature but also linked to the phytoplankton community. Higher carbon biomass of the diatomsAchnanthes taeniata,Skeletonema marinoi,Thalassiosira levanderi, andChaetocerosspp. was associated with more diverse bacterial communities dominated by copiotrophic bacteria (Flavobacteriia, Gammaproteobacteria, and Betaproteobacteria) and higher bacterial production. During dinoflagellate dominance, bacterial production was low and bacterial communities were dominated by Alphaproteobacteria, mainly SAR11. Our results suggest that increases in dinoflagellate abundance during the spring bloom will largely affect the structuring and functioning of the associated bacterial communities. This could decrease pelagic remineralization of organic matter and possibly affect the bacterial grazers communities.
  • Cheng, Lu; Connor, Thomas R.; Aanensen, David M.; Spratt, Brian G.; Corander, Jukka (2011)
  • Verta, Jukka-Pekka; Debes, Paul; Piavchenko, Nikolai; Ruokolainen, Annukka; Ovaskainen, Outi Sinikka; Moustakas-Verho, Jacqueline; Tillanen, Seija Iiris; Parre, Noora; Aykanat, Tutku; Erkinaro, Jaakko; Primmer, Craig (2020)
    A major goal in biology is to understand how evolution shapes variation in individual life histories. Genome-wide association studies have been successful in uncovering genome regions linked with traits underlying life history variation in a range of species. However, lack of functional studies of the discovered genotype-phenotype associations severely restrains our understanding how alternative life history traits evolved and are mediated at the molecular level. Here, we report acis-regulatory mechanism whereby expression of alternative isoforms of the transcription co-factorvestigial-like 3(vgll3) associate with variation in a key life history trait, age at maturity, in Atlantic salmon (Salmo salar). Using a common-garden experiment, we first show thatvgll3genotype associates with puberty timing in one-year-old salmon males. By way of temporal sampling ofvgll3expression in ten tissues across the first year of salmon development, we identify a pubertal transition invgll3expression where maturation coincided with a 66% reduction in testicularvgll3expression. Thelatematuration allele was not only associated with a tendency to delay puberty, but also with expression of a rare transcript isoform ofvgll3pre-puberty. By comparing absolutevgll3mRNA copies in heterozygotes we show that the expression difference between theearlyandlatematurity alleles is largelycis-regulatory. We propose a model whereby expression of a rare isoform from thelateallele shifts the liability of its carriers towards delaying puberty. These results exemplify the potential importance of regulatory differences as a mechanism for the evolution of life history traits. Author summary Alternative life history strategies are an important source of diversity within populations and promote the maintenance of adaptive capacity and population resilience. However, in many cases the molecular basis of different life history strategies remains elusive. Age at maturity is a key adaptive life history trait in Atlantic salmon and has a relatively simple genetic basis. Using salmon age at maturity as a model, we report a mechanism whereby different transcript isoforms of the key age at maturity gene,vestigial-like 3(vgll3), associate with variation in the timing of male puberty. Our results show how gene regulatory differences in conjunction with variation in gene transcript structure can encode for complex alternative life histories.
  • Susi, Hanna; Sallinen, Suvi; Laine, Anna-Liisa (2022)
    The trade-off between within-host infection rate and transmission to new hosts is predicted to constrain pathogen evolution, and to maintain polymorphism in pathogen populations. Pathogen life-history stages and their correlations that underpin infection development may change under coinfection with other parasites as they compete for the same limited host resources. Cross-kingdom interactions are common among pathogens in both natural and cultivated systems, yet their impacts on disease ecology and evolution are rarely studied. The host plant Plantago lanceolata is naturally infected by both Phomopsis subordinaria, a seed killing fungus, as well as Plantago lanceolata latent virus (PlLV) in the angstrom land Islands, SW Finland. We performed an inoculation assay to test whether coinfection with PlLV affects performance of two P. subordinaria strains, and the correlation between within-host infection rate and transmission potential. The strains differed in the measured life-history traits and their correlations. Moreover, we found that under virus coinfection, within-host infection rate of P. subordinaria was smaller but transmission potential was higher compared to strains under single infection. The negative correlation between within-host infection rate and transmission potential detected under single infection became positive under coinfection with PlLV. To understand whether within-host and between-host dynamics are correlated in wild populations, we surveyed 260 natural populations of P. lanceolata for P. subordinaria infection occurrence. When infections were found, we estimated between-hosts dynamics by determining pathogen population size as the proportion of infected individuals, and within-host dynamics by counting the proportion of infected flower stalks in 10 infected plants. In wild populations, the proportion of infected flower stalks was positively associated with pathogen population size. Jointly, our results suggest that the trade-off between within-host infection load and transmission may be strain specific, and that the pathogen life-history that underpin epidemics may change depending on the diversity of infection, generating variation in disease dynamics.
  • Hällfors, Maria H.; Pöyry, Juha; Heliölä, Janne; Kohonen, Ilmari; Kuussaari, Mikko; Leinonen, Reima; Schmucki, Reto; Sihvonen, Pasi; Saastamoinen, Marjo (2021)
    Species can adapt to climate change by adjusting in situ or by dispersing to new areas, and these strategies may complement or enhance each other. Here, we investigate temporal shifts in phenology and spatial shifts in northern range boundaries for 289 Lepidoptera species by using long-term data sampled over two decades. While 40% of the species neither advanced phenology nor moved northward, nearly half (45%) used one of the two strategies. The strongest positive population trends were observed for the minority of species (15%) that both advanced flight phenology and shifted their northern range boundaries northward. We show that, for boreal Lepidoptera, a combination of phenology and range shifts is the most viable strategy under a changing climate. Effectively, this may divide species into winners and losers based on their propensity to capitalize on this combination, with potentially large consequences on future community composition.
  • Loo, Evelyn Xiu Ling; Zhang, Yuqing; Yap, Qai Ven; Yu, Guoqi; Soh, Shu E.; Loy, See Ling; Lau, Hui Xing; Chan, Shiao-Yng; Shek, Lynette Pei-Chi; Luo, Zhong-Cheng; Yap, Fabian Kok Peng; Tan, Kok Hian; Chong, Yap Seng; Zhang, Jun; Eriksson, Johan Gunnar (2021)
    Background Gestational diabetes mellitus (GDM) has been associated with adverse health outcomes for mothers and offspring. Prevalence of GDM differs by country/region due to ethnicity, lifestyle and diagnostic criteria. We compared GDM rates and risk factors in two Asian cohorts using the 1999 WHO and the International Association of Diabetes and Pregnancy Study Groups (IADPSG) criteria. Methods The Shanghai Birth Cohort (SBC) and the Growing Up in Singapore Towards healthy Outcomes (GUSTO) cohort are prospective birth cohorts. Information on sociodemographic characteristics and medical history were collected from interviewer-administered questionnaires. Participants underwent a 2-h 75-g oral glucose tolerance test at 24-28 weeks gestation. Logistic regressions were performed. Results Using the 1999 WHO criteria, the prevalence of GDM was higher in GUSTO (20.8%) compared to SBC (16.6%) (p = 0.046). Family history of hypertension and alcohol consumption were associated with higher odds of GDM in SBC than in GUSTO cohort while obesity was associated with higher odds of GDM in GUSTO. Using the IADPSG criteria, the prevalence of GDM was 14.3% in SBC versus 12.0% in GUSTO. A history of GDM was associated with higher odds of GDM in GUSTO than in SBC, while being overweight, alcohol consumption and family history of diabetes were associated with higher odds of GDM in SBC. Conclusions We observed several differential risk factors of GDM among ethnic Chinese women living in Shanghai and Singapore. These findings might be due to heterogeneity of GDM reflected in diagnostic criteria as well as in unmeasured genetic, lifestyle and environmental factors.
  • Budria, Alexandre; De Faveri, Jacquelin; Merilä, Juha (2015)
    Minnow traps are commonly used in the stickleback (Gasterostidae) fishery, but the potential differences in catch per unit effort (CPUE) among different minnow trap models are little studied. We compared the CPUE of four different minnow trap models in field experiments conducted with threespined sticklebacks (Gasterosteus aculeatus). Marked (up to 26 fold) differences in median CPUE among different trap models were observed. Metallic uncoated traps yielded the largest CPUE (2.8 fish/h), followed by metallic black nylon-coated traps (1.3 fish/h). Collapsible canvas traps yielded substantially lower CPUEs (black: 0.7 fish/h; red: 0.1 fish/h) than the metallic traps. Laboratory trials further revealed significant differences in escape probabilities among the different trap models. While the differences in escape probability can explain at least part of the differences in CPUE among the trap models (e. g. high escape rate and low CPUE in red canvas traps), discrepancies between model-specific CPUEs and escape rates suggests that variation in entrance rate also contributes to the differences in CPUE. In general, and in accordance with earlier data on nine-spined stickleback (Pungitius pungitius) trapping, the results suggest that uncoated metallic (Gee-type) traps are superior to the other commonly used minnow trap models in stickleback fisheries.
  • Culina, Antica; Adriaensen, Frank; Bailey, Liam D.; Burgess, Malcolm D.; Charmantier, Anne; Cole, Ella F.; Eeva, Tapio; Matthysen, Erik; Nater, Chloe R.; Sheldon, Ben C.; Saether, Bernt-Erik; Vriend, Stefan J. G.; Zajkova, Zuzana; Adamik, Peter; Aplin, Lucy M.; Angulo, Elena; Artemyev, Alexandr; Barba, Emilio; Barisic, Sanja; Belda, Eduardo; Bilgin, Cemal Can; Bleu, Josefa; Both, Christiaan; Bouwhuis, Sandra; Branston, Claire J.; Broggi, Juli; Burke, Terry; Bushuev, Andrey; Camacho, Carlos; Campobello, Daniela; Canal, David; Cantarero, Alejandro; Caro, Samuel P.; Cauchoix, Maxime; Chaine, Alexis; Cichon, Mariusz; Cikovic, Davor; Cusimano, Camillo A.; Deimel, Caroline; Dhondt, Andre A.; Dingemanse, Niels J.; Doligez, Blandine; Dominoni, Davide M.; Doutrelant, Claire; Drobniak, Szymon M.; Dubiec, Anna; Eens, Marcel; Erikstad, Kjell Einar; Espin, Silvia; Farine, Damien R.; Figuerola, Jordi; Gulbeyaz, Pinar Kavak; Gregoire, Arnaud; Hartley, Ian R.; Hau, Michaela; Hegyi, Gergely; Hille, Sabine; Hinde, Camilla A.; Holtmann, Benedikt; Ilyina, Tatyana; Isaksson, Caroline; Iserbyt, Arne; Ivankina, Elena; Kania, Wojciech; Kempenaers, Bart; Kerimov, Anvar; Komdeur, Jan; Korsten, Peter; Kral, Miroslav; Krist, Milos; Lambrechts, Marcel; Lara, Carlos E.; Leivits, Agu; Liker, Andras; Lodjak, Jaanis; Magi, Marko; Mainwaring, Mark C.; Mand, Raivo; Massa, Bruno; Massemin, Sylvie; Martinez-Padilla, Jesus; Mazgajski, Tomasz D.; Mennerat, Adele; Moreno, Juan; Mouchet, Alexia; Nakagawa, Shinichi; Nilsson, Jan-Ake; Nilsson, Johan F.; Norte, Ana Claudia; van Oers, Kees; Orell, Markku; Potti, Jaime; Quinn, John L.; Reale, Denis; Reiertsen, Tone Kristin; Rosivall, Balazs; Russell, Andrew F.; Rytkonen, Seppo; Sanchez-Virosta, Pablo; Santos, Eduardo S. A.; Schroeder, Julia; Senar, Juan Carlos; Seress, Gabor; Slagsvold, Tore; Szulkin, Marta; Teplitsky, Celine; Tilgar, Vallo; Tolstoguzov, Andrey; Torok, Janos; Valcu, Mihai; Vatka, Emma; Verhulst, Simon; Watson, Hannah; Yuta, Teru; Zamora-Marin, Jose M.; Visser, Marcel E. (2021)
    The integration and synthesis of the data in different areas of science is drastically slowed and hindered by a lack of standards and networking programmes. Long-term studies of individually marked animals are not an exception. These studies are especially important as instrumental for understanding evolutionary and ecological processes in the wild. Furthermore, their number and global distribution provides a unique opportunity to assess the generality of patterns and to address broad-scale global issues (e.g. climate change). To solve data integration issues and enable a new scale of ecological and evolutionary research based on long-term studies of birds, we have created the SPI-Birds Network and Database ()-a large-scale initiative that connects data from, and researchers working on, studies of wild populations of individually recognizable (usually ringed) birds. Within year and a half since the establishment, SPI-Birds has recruited over 120 members, and currently hosts data on almost 1.5 million individual birds collected in 80 populations over 2,000 cumulative years, and counting. SPI-Birds acts as a data hub and a catalogue of studied populations. It prevents data loss, secures easy data finding, use and integration and thus facilitates collaboration and synthesis. We provide community-derived data and meta-data standards and improve data integrity guided by the principles of Findable, Accessible, Interoperable and Reusable (FAIR), and aligned with the existing metadata languages (e.g. ecological meta-data language). The encouraging community involvement stems from SPI-Bird's decentralized approach: research groups retain full control over data use and their way of data management, while SPI-Birds creates tailored pipelines to convert each unique data format into a standard format. We outline the lessons learned, so that other communities (e.g. those working on other taxa) can adapt our successful model. Creating community-specific hubs (such as ours, COMADRE for animal demography, etc.) will aid much-needed large-scale ecological data integration.
  • Di Minin, Enrico; Clements, Hayley Susan; Correia, Ricardo A.; Cortes Capano, Gonzalo; Fink, Christoph; Haukka, Anna; Hausmann, Anna; Kulkarni, Ritwik; Bradshaw, Corey (2021)
    The widespread activity of recreational hunting is proposed as a means of conserving nature and supporting livelihoods. However, recreational hunting-especially trophy hunting-has come under increasing scrutiny based on ethical concerns and the arguments that it can threaten species and fail to contribute meaningfully to local livelihoods. We provide an overview of the peer-reviewed literature on recreational hunting of terrestrial birds and mammals between 1953 and 2020 (> 1,000 papers). The most-studied species are large mammals from North America, Europe, and Africa. While there is extensive research on species' ecology to inform sustainable hunting practices, there is comparably little research on the role of local perceptions and institutions in determining socioeconomic and conservation outcomes. Evidence is lacking to answer the pressing questions of where and how hunting contributes to just and sustainable conservation efforts. We outline an agenda to build this evidence base through research that recognizes diverse social-ecological contexts.
  • Paakkanen, Riitta; Vauhkonen, Hanna; Eronen, Katja T.; Järvinen, Asko; Seppanen, Mikko; Lokki, Marja-Liisa (2012)
  • Toivonen, H T T; Onkamo, P; Vasko, K; Ollikainen, V; Sevon, P; Mannila, H; Herr, M; Kere, J (2000)
  • Acanski, Jelena; Vujic, Ante; Djan, Mihajla; Obreht Vidakovic, Dragana; Ståhls, Gunilla; Radenkovic, Snezana (2016)
    Several recent studies have detected and described complexes of cryptic and sibling species in the genus Merodon (Diptera, Syrphidae). One representative of these complexes is the Merodon avidus complex that contains four sibling species, which have proven difficult to distinguish using traditional morphological characters. In the present study, we use two geometric morphometric approaches, as well as molecular characters of the 5' -end of the mtDNA COI gene, to delimit sibling taxa. Analyses based on these data were used to strengthen species boundaries within the complex, and to validate the status of a previously-recognized cryptic taxon from Lesvos Island (Greece), here described as Merodon megavidus Vujic & Radenkovic sp. nov. Geometric morphometric results of both wing and surstylus shape confirm the present classification for three sibling species-M. avidus (Rossi, 1790), M. moenium Wiedemann in Meigen, 1822 and M. ibericus Vujic, 2015-and, importantly, clearly discriminate the newly-described taxon Merodon megavidus sp. nov. In addition to our geometric morphometric results, supporting characters were obtained from molecular analyses of mtDNA COI sequences, which clearly differentiated M. megavidus sp. nov. from the other members of the M. avidus complex. Molecular analyses revealed that the earliest divergence of M. ibericus occurred around 800 ky BP, while the most recent separation happened between M. avidus and M. moenium around 87 ky BP.
  • Candolin, Ulrika; Goncalves, Sara; Pant, Pankaj (2022)
    Early life conditions can have a decisive influence on viability later in life. However, the influence of embryo density within a nest or body cavity on subsequent viability has received little attention within an ecological setting. This is surprising given that embryos often compete for limited resources, such as nutrients and oxygen, and this could influence their viability later in life through carry-over and compensatory effects. We show that the density of fertilized eggs within the nests of threespine stickleback males (Gasterosteus aculeatus) influences their viability after hatching. Embryos from larger broods hatch earlier and at a smaller size than those from smaller broods, which reduces their survival until the age of four weeks. This indicates a trade-off between the number and viability of offspring that males can raise to the hatching stage, which could explain the high incidence of partial egg cannibalism in nest-brooding fishes-as a strategy to improve the survival of remaining offspring. These results highlight the importance of considering conditions at the embryonic stage when evaluating the impact of early life conditions on viability and the adaptive value of reproductive decisions.
  • Garzon, Marta Benito; Robson, T. Matthew; Hampe, Arndt (2019)
    Improving our understanding of species ranges under rapid climate change requires application of our knowledge of the tolerance and adaptive capacity of populations to changing environmental conditions. Here, we describe an emerging modelling approach, Delta TraitSDM, which attempts to achieve this by explaining species distribution ranges based on phenotypic plasticity and local adaptation of fitness-related traits measured across large geographical gradients. The collection of intraspecific trait data measured in common gardens spanning broad environmental clines has promoted the development of these new models - first in trees but now rapidly expanding to other organisms. We review, explain and harmonize the main findings from this new generation of models that, by including trait variation over geographical scales, are able to provide new insights into future species ranges. Overall, Delta TraitSDM predictions generally deliver a less alarming message than previous models of species distribution under new climates, indicating that phenotypic plasticity should help, to a considerable degree, some plant populations to persist under climate change. The development of Delta TraitSDMs offers a new perspective to analyse intraspecific variation in single and multiple traits, with the rationale that trait (co)variation and consequently fitness can significantly change across geographical gradients and new climates.
  • Saulamo, Kari; Heikinheimo, Outi; Lappalainen, Jyrki (2020)
    In the Archipelago Sea, pikeperch (Sander lucioperca) is an important species in both commercial and recreational fisheries. Pikeperch is caught mainly with small mesh size gillnets, and annual fishing mortality is high. The possible effects of such fisheries, as well as temperature or density on pikeperch growth have not been studied earlier. The first hypothesis of this study was that the effect of temperature on growth is positive and that of density is negative. The second hypothesis was that size selectivity of gillnets causes the fast-growing individuals to be caught at younger ages than the slow growing ones. The results showed that temperature had a significant positive effect on growth, and this was greater than the negative effect of year-class density, which was also significant. The gillnet selectivity caused a difference of up to 60mm in back-calculated lengths in the fully recruited age groups within the same year class, between pikeperch caught at age 6+ and age 9+. Thus, the Rosa Lee phenomenon caused by gillnet size-selectivity led to the removal of faster growing specimens from the population at younger ages. This can potentially cause underestimation of real growth, and thus, poor fishery management.
  • Jakubaviciute, Egle; Candolin, Ulrika (2021)
    The invasion of non-native species into an ecosystem can markedly alter the structure and functioning of the system. Yet, we have limited knowledge of the factors that determine invasion success. Behavioural interactions have been suggested as critical determinants of invasion success in animals, but the exact mechanisms are less well known. We investigated if density-dependent behavioural interactions could have facilitated the invasion of the shrimp Palaemon elegans into the spawning habitat of the threespine stickleback Gasterosteus aculeatus in the Baltic Sea. This was done by manipulating the densities of the two species in mesocosms. We found the stickleback to dominate behaviourally over the shrimp through higher aggression, but that the impact on the shrimp was density-dependent; a high density of sticklebacks increased aggressive interactions, which caused the shrimps to decrease their activity and restrict their habitat use to dense vegetation, while a low density of sticklebacks had no impact on the distribution and activity of the shrimps. The density of the shrimps had no impact on stickleback behaviour. These results suggest that the present density of the stickleback has allowed the invasion of the shrimp into the habitat. However, a current increase in stickleback abundance caused by human-induced ecological disturbances could limit the further expansion of the shrimp. Thus, our results indicate that a behavioural mechanism-density-dependent aggression-can influence invasion success and subsequent population expansion. At a broader level, our results stress the importance of considering density-dependent behavioural interactions when investigating the mechanisms behind invasion success.