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Jorn P Scharsack - One of the best experts on this subject based on the ideXlab platform.
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early stages of infection of three spined Stickleback gasterosteus aculeatus with the cestode schistocephalus solidus
2018Co-Authors: Anika Marie Wohlleben, Joachim Kurtz, Frederik Franke, Madeleine Hamley, Jorn P ScharsackAbstract:Parasitic helminths have evolved strategies to evade their host's immune systems. Particularly, the early time of interactions between helminths and their hosts might be decisive for their infection success. We used the cestode Schistocephalus solidus, and its highly specific second intermediate host, the three-spined Stickleback (Gasterosteus aculeatus) to investigate parasite infection and host cellular immune responses starting 1 day postexposure (dpe). We recovered live parasites from Stickleback body cavities already 24 hr after exposure. Infection rates increased up to 50% and did not change from 4 dpe onwards. Thus, not all parasites had reached the body cavity at the early time points and clearance of the parasite at later time points did not occur. Stickleback head kidney leucocytes (HKLs) did not show distinct signs of activation and lymphocyte proliferation, granulocyte-to-lymphocyte ratios and respiratory burst activity of infected Sticklebacks did not deviate from controls significantly. The immune system was activated only late, as indicated by an increase in the total count of HKL relative to Stickleback weight (HKL per mg fish), which was significantly elevated in infected fish 32 dpe. S. solidus seems to evade leucocyte activity early during infection facilitating its establishment in the hosts' body cavity.
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specific manipulation or systemic impairment behavioural changes of three spined Sticklebacks gasterosteus aculeatus infected with the tapeworm schistocephalus solidus
2017Co-Authors: Manuel Talarico, Joachim Kurtz, Franziska Seifert, Josef Lange, Norbert Sachser, Jorn P ScharsackAbstract:Manipulation of host behaviour by parasites to enhance transmission to the next host is a fascinating yet controversial phenomenon. This is because it is often hard to discriminate specific manipulation from unspecific side effects of the infection, i.e. a systemic impairment that could be due to a weakened general body condition. When infected with the tapeworm Schistocephalus solidus, Stickleback fish swim closer to the water surface and exhibit reduced predation avoidance behaviour, which facilitates transmission of the tapeworm to the final host, most often a fish-eating bird. We here tested whether the behavioural changes of infected Sticklebacks are specific to contexts where they would indeed enhance transmission, or rather more general. Therefore, we compared the behaviour of Sticklebacks that were experimentally infected with S. solidus or left uninfected, in settings where the behaviour would influence parasite transmission to a high degree (response to a bird predator stimulus) or to a lesser extent (exploration of a new environment, activity while foraging). As expected, infected Sticklebacks returned much faster to foraging after the bird predator stimulus and spent more time close to the water surface, compared to non-infected Sticklebacks. By contrast, exploration of a new environment and activity while foraging did not differ between infected and non-infected Sticklebacks. This suggests that alteration of the Sticklebacks’ behaviour when infected with S. solidus is indeed due to specific manipulation of the predator avoidance behaviour and not a general, systemic impairment of infected Sticklebacks. Manipulation of host behaviour by parasites is a fascinating but controversial phenomenon, since it is often difficult to disentangle if they are specifically induced or just a side effect of the infection. Stickleback fish, when infected with a tapeworm, change their behaviour dramatically; they swim closer to the water surface and reduce their escape behaviour, which exposes them to predation by birds, the final hosts of the parasite. We observed that Sticklebacks infected with the tapeworm perform equally well as non-infected conspecifics in contexts with low relevance for parasite transmission, such as exploration of a new environment and foraging activity. However, the same infected Sticklebacks exhibited the expected reduced escape behaviour when tested with a simulated bird attack. Our study suggests that the parasite specifically induces the Sticklebacks’ behavioural changes and does not simply cause a systemic impairment.
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effects of environmental variation on host parasite interaction in three spined Sticklebacks gasterosteus aculeatus
2016Co-Authors: Jorn P Scharsack, Frederik Franke, Noemi I Erin, Andra Kuske, Janine Buscher, Hendrik Stolz, Irene E Samonte, Joachim Kurtz, Martin KalbeAbstract:Abstract Recent research provides accumulating evidence that the evolutionary dynamics of host–parasite adaptations strongly depend on environmental variation. In this context, the three-spined Stickleback ( Gasterosteus aculeatus ) has become an important research model since it is distributed all over the northern hemisphere and lives in very different habitat types, ranging from marine to freshwater, were it is exposed to a huge diversity of parasites. While a majority of studies start from explorations of Sticklebacks in the wild, only relatively few investigations have continued under laboratory conditions. Accordingly, it has often been described that Sticklebacks differ in parasite burden between habitats, but the underlying co-evolutionary trajectories are often not well understood. With the present review, we give an overview of the most striking examples of Stickleback–parasite–environment interactions discovered in the wild and discuss two model parasites which have received some attention in laboratory studies: the eye fluke Diplostomum pseudospathacaeum , for which host fish show habitat-specific levels of resistance, and the tapeworm Schistocephalus solidus , which manipulates immunity and behavior of its Stickleback host to its advantage. Finally, we will concentrate on an important environmental variable, namely temperature, which has prominent effects on the activity of the immune system of ectothermic hosts and on parasite growth rates.
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reciprocal cross infection of Sticklebacks with the diphyllobothriidean cestode schistocephalus solidus reveals consistent population differences in parasite growth and host resistance
2016Co-Authors: Martin Kalbe, Jorn P Scharsack, Christophe Eizaguirre, Per Johan JakobsenAbstract:In host-parasite evolutionary arms races, parasites are generally expected to adapt more rapidly, due to their large population sizes and short generation times. There exist systems, though, where parasites cannot outpace their hosts because of similar generation times in both antagonists. In those cases concomitant adaptation is expected. We tested this hypothesis in the three-spined Stickleback-Schistocephalus solidus tapeworm system, where generation times are comparable in both organisms. We chose two populations of Sticklebacks which differ prominently in the prevalence of S. solidus and consequently in its level of selective pressure. We performed a full factorial common garden experiment. Particularly, Norwegian (NO) and German (DE) Sticklebacks, as well as hybrids between both Stickleback populations and in both parental combinations, were exposed each to a single S. solidus originating from the same two host populations. We found the infection phenotype to depend on the host population, the parasite population, but not their interaction. NO-parasites showed higher infectivity than DE-parasites, with NO-Sticklebacks also being more resistant to DE-parasites than to the sympatric NO-parasite. Reciprocally, DE-hosts were more susceptible to the allopatric NO-parasite while DE-parasites grew less than NO-parasites in all Stickleback groups. Despite this asymmetry, the ratio of worm to host weight, an indicator of parasite virulence, was identical in both sympatric combinations, suggesting an optimal virulence as a common outcome of parallel coevolved systems. In hybrid Sticklebacks, intermediate infection rates and growth of S. solidus from either origin suggests a simple genetic basis of resistance. However, comparison of infection phenotypes in NO-maternal and DE-maternal hybrid Sticklebacks indicates local adaptation to the sympatric counterpart in both the host and the parasite. Host-parasite systems with similar generation time show evidence for concomitant reciprocal adaptation resulting in parasite optimal virulence and host parasite specific resistance.
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differences in susceptibility and immune responses of three spined Sticklebacks gasterosteus aculeatus from lake and river ecotypes to sequential infections with the eye fluke diplostomum pseudospathaceum
2014Co-Authors: Jorn P Scharsack, Martin KalbeAbstract:Background: The eye fluke Diplostomum pseudospathaceum is a frequent parasite of many fresh-water fish species, among those three-spined Sticklebacks, particularly in lakes with lymnaeid snails, its first intermediate hosts. Cercariae released from host-snails, penetrate the skin of their fish hosts and within 24 h migrate to the immunologically inert eye lenses. Thus, individual D. pseudospathaceum are exposed to the fish immune system only for a short time, suggesting that only innate immunity can be active against the parasite. However, in nature Sticklebacks are exposed to D. pseudospathaceum repeatedly since snails are shedding cercariae from late spring to autumn. Therefore, acquired immunity after initial infection would be advantageous against subsequent parasite encounters. Methods: We investigated if Sticklebacks originating from a lake with high and from a river with low prevalence of D. pseudospathaceum differ in susceptibility to repeated exposure to the parasite. We compared infection success and immune functions in laboratory-bred Sticklebacks from both habitats in naive fish with fish that had been pre-exposed to eye flukes. Head kidney leukocytes (HKL) from experimental Sticklebacks were investigated for respiratory burst activity and the proliferation of lymphocytes and monocytes 1.5, 5 and 15 days after infection. Results: Lake Sticklebacks were less susceptible than river Sticklebacks, however, in both populations pre-exposure led to a similar relative reduction in infection success. The respiratory burst activity was higher with HKL from lake Sticklebacks and was up-regulated in pre-exposed fish but dropped 1.5d after an additional exposure, suggesting that activation of phagocytic cells is crucial for the defense against D. pseudospathaceum. Changes in lymphocyte proliferation were only detectable 1.5d after the last exposure in lake Sticklebacks, but not 5 and 15d post exposure, indicating that a lymphocyte mediated acquired immune response was not induced. Proliferation of monocytes was significantly increased 1.5d after the last exposure with HKL from both Stickleback populations. Conclusions: Increased resistance to D. pseudospathaceum in Sticklebacks from both populations upon pre-exposure cannot be explained by a prominent adaptive immune response. Monocytic leukocytes were more responsive, suggesting that rather cells of the innate than the adaptive immune system are active in the defense of D. pseudospathaceum.
Dolph Schluter - One of the best experts on this subject based on the ideXlab platform.
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dna fragility in the parallel evolution of pelvic reduction in Stickleback fish
2019Co-Authors: Kathleen T Xie, Dolph Schluter, Michael A Bell, T E Reimchen, Guliang Wang, Abbey Thompson, Julia I Wucherpfennig, Andrew D C Maccoll, Karen M Vasquez, David M. KingsleyAbstract:Evolution generates a remarkable breadth of living forms, but many traits evolve repeatedly, by mechanisms that are still poorly understood. A classic example of repeated evolution is the loss of pelvic hindfins in Stickleback fish (Gasterosteus aculeatus). Repeated pelvic loss maps to recurrent deletions of a pelvic enhancer of the Pitx1 gene. Here, we identify molecular features contributing to these recurrent deletions. Pitx1 enhancer sequences form alternative DNA structures in vitro and increase double-strand breaks and deletions in vivo. Enhancer mutability depends on DNA replication direction and is caused by TG-dinucleotide repeats. Modeling shows that elevated mutation rates can influence evolution under demographic conditions relevant for Sticklebacks and humans. DNA fragility may thus help explain why the same loci are often used repeatedly during parallel adaptive evolution.
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the temporal window of ecological adaptation in postglacial lakes a comparison of head morphology trophic position and habitat use in norwegian threespine Stickleback populations
2016Co-Authors: Kjartan Ostbye, Dolph Schluter, Chris Harrod, F Gregersen, Tom Klepaker, Michael Schulz, Leif Asbjorn VollestadAbstract:Studying how trophic traits and niche use are related in natural populations is important in order to understand adaptation and specialization. Here, we describe trophic trait diversity in twenty-five Norwegian freshwater threespine Stickleback populations and their putative marine ancestor, and relate trait differences to postglacial lake age. By studying lakes of different ages, depths and distance to the sea we examine key environmental variables that may predict adaptation in trophic position and habitat use. We measured trophic traits including geometric landmarks that integrated variation in head shape as well as gillraker length and number. Trophic position (Tpos) and niche use (α) were estimated from stable isotopes (δ13C, δ15N). A comparison of head shape was also made with two North American benthic-limnetic species pairs. We found that head shape differed between marine and freshwater Sticklebacks, with marine Sticklebacks having more upturned mouths, smaller eyes, larger opercula and deeper heads. Size-adjusted gillraker lengths were larger in marine than in freshwater Stickleback. Norwegian Sticklebacks were compared on the same head shape axis as the one differentiating the benthic-limnetic North American threespine Stickleback species pairs. Here, Norwegian freshwater Sticklebacks with a more “limnetic head shape” had more and longer gillrakers than Sticklebacks with “benthic head shape”. The “limnetic morph” was positively associated with deeper lakes. Populations differed in α (mean ± sd: 0.76 ± 0.29) and Tpos (3.47 ± 0.27), where α increased with gillraker length. Larger fish had a higher Tpos than smaller fish. Compared to the ecologically divergent Stickleback species pairs and solitary lake populations in North America, Norwegian freshwater Sticklebacks had similar range in Tpos and α values, but much less trait divergences. Our results showed trait divergences between threespine Stickleback in marine and freshwater environments. Freshwater populations diverged in trophic ecology and trophic traits, but trophic ecology was not related to the elapsed time in freshwater. Norwegian Sticklebacks used the same niches as the ecologically divergent North American Stickleback species pairs. However, as trophic trait divergences were smaller, and not strongly associated with the ecological niche, ecological adaptations along the benthic-limnetic axis were less developed in Norwegian Sticklebacks.
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Rapid evolution of cold tolerance in Stickleback
2010Co-Authors: Rowan D. H. Barrett, Dolph Schluter, Antoine Paccard, Timothy M. Healy, Sara Bergek, Patricia M. Schulte, Sean M. RogersAbstract:Climate change is predicted to lead to increased average temperatures and greater intensity and frequency of high and low temperature extremes, but the evolutionary consequences for biological communities are not well understood. Studies of adaptive evolution of temperature tolerance have typically involved correlative analyses of natural populations or artificial selection experiments in the laboratory. Field experiments are required to provide estimates of the timing and strength of natural selection, enhance understanding of the genetics of adaptation and yield insights into the mechanisms driving evolutionary change. Here, we report the experimental evolution of cold tolerance in natural populations of threespine Stickleback fish (Gasterosteus aculeatus). We show that freshwater Sticklebacks are able to tolerate lower minimum temperatures than marine Sticklebacks and that this difference is heritable. We transplanted marine Sticklebacks to freshwater ponds and measured the rate of evolution after three generations in this environment. Cold tolerance evolved at a rate of 0.63 haldanes to a value 2.58C lower than that of the ancestral population, matching values found in wild freshwater populations. Our results suggest that cold tolerance is under strong selection and that marine Sticklebacks carry sufficient genetic variation to adapt to changes in temperature over remarkably short time scales.
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natural selection on a major armor gene in threespine Stickleback
2008Co-Authors: Rowan D. H. Barrett, Sean M. Rogers, Dolph SchluterAbstract:Experimental estimates of the effects of selection on genes determining adaptive traits add to our understanding of the mechanisms of evolution. We measured selection on genotypes of the Ectodysplasin locus, which underlie differences in lateral plates in threespine Stickleback fish. A derived allele (low) causing reduced plate number has been fixed repeatedly after marine Stickleback colonized freshwater from the sea, where the ancestral allele (complete) predominates. We transplanted marine Sticklebacks carrying both alleles to freshwater ponds and tracked genotype frequencies over a generation. The low allele increased in frequency once lateral plates developed, most likely via a growth advantage. Opposing selection at the larval stage and changing dominance for fitness throughout life suggest either that the gene affects additional traits undergoing selection or that linked loci also are affecting fitness.
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strong assortative mating between allopatric Sticklebacks as a by product of adaptation to different environments
2006Co-Authors: Timothy H Vines, Dolph SchluterAbstract:Speciation involves the evolution of reproductive isolation between populations. One potentially important mechanism is the evolution of pre- or postzygotic isolation between populations as a by-product of adaptation to different environments. In this paper, we tested for assortative mating between allopatric Stickleback populations adapted to different ecological niches. Our experimental design controlled for interpopulation interactions and non-adaptive explanations for assortative mating. We found that prezygotic isolation was surprisingly strong: when given a choice, the majority of matings occurred between individuals from similar environments. Our results indicate that the by-product mechanism is a potent source of reproductive isolation, and likely contributed to the origin of sympatric species of Sticklebacks.
Leif Asbjorn Vollestad - One of the best experts on this subject based on the ideXlab platform.
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ongoing niche differentiation under high gene flow in a polymorphic brackish water threespine Stickleback gasterosteus aculeatus population
2018Co-Authors: Kjartan Ostbye, Annette Taugbol, Mark Ravinet, Chris Harrod, Ruben Alexander Pettersen, Louis Bernatchez, Leif Asbjorn VollestadAbstract:Marine threespine Sticklebacks colonized and adapted to brackish and freshwater environments since the last Pleistocene glacial. Throughout the Holarctic, three lateral plate morphs are observed; the low, partial and completely plated morph. We test if the three plate morphs in the brackish water Lake Engervann, Norway, differ in body size, trophic morphology (gill raker number and length), niche (stable isotopes; δ15N, δ13C, and parasites (Theristina gasterostei, Trematoda spp.)), genetic structure (microsatellites) and the lateral-plate encoding Stn382 (Ectodysplasin) gene. We examine differences temporally (autumn 2006/spring 2007) and spatially (upper/lower sections of the lake – reflecting low versus high salinity). All morphs belonged to one gene pool. The complete morph was larger than the low plated, with the partial morph intermediate. The number of lateral plates ranged 8–71, with means of 64.2 for complete, 40.3 for partial, and 14.9 for low plated morph. Stickleback δ15N was higher in the lower lake section, while δ13C was higher in the upper section. Stickleback isotopic values were greater in autumn. The low plated morph had larger variances in δ15N and δ13C than the other morphs. Sticklebacks in the upper section had more T. gasterostei than in the lower section which had more Trematoda spp. Sticklebacks had less T. gasterostei, but more Trematoda spp. in autumn than spring. Sticklebacks with few and short rakers had more T. gasterostei, while Sticklebacks with longer rakers had more Trematoda. spp. Stickleback with higher δ15N values had more T. gasterostei, while Sticklebacks with higher δ15N and δ13C values had more Trematoda spp. The low plated morph had fewer Trematoda spp. than other morphs. Trait-ecology associations may imply that the three lateral plate morphs in the brackish water lagoon of Lake Engervann are experiencing ongoing divergent selection for niche and migratory life history strategies under high gene flow. As such, the brackish water zone may generally act as a generator of genomic diversity to be selected upon in the different environments where threespine Sticklebacks can live.
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Ongoing niche differentiation under high gene flow in a polymorphic brackish water threespine Stickleback (Gasterosteus aculeatus) population
2018Co-Authors: Kjartan Ostbye, Annette Taugbol, Mark Ravinet, Chris Harrod, Ruben Alexander Pettersen, Louis Bernatchez, Leif Asbjorn VollestadAbstract:Background Marine threespine Sticklebacks colonized and adapted to brackish and freshwater environments since the last Pleistocene glacial. Throughout the Holarctic, three lateral plate morphs are observed; the low, partial and completely plated morph. We test if the three plate morphs in the brackish water Lake Engervann, Norway, differ in body size, trophic morphology (gill raker number and length), niche (stable isotopes; δ^15N, δ^13C, and parasites ( Theristina gasterostei , Trematoda spp.)), genetic structure (microsatellites) and the lateral-plate encoding Stn382 ( Ectodysplasin ) gene. We examine differences temporally (autumn 2006/spring 2007) and spatially (upper/lower sections of the lake – reflecting low versus high salinity). Results All morphs belonged to one gene pool. The complete morph was larger than the low plated, with the partial morph intermediate. The number of lateral plates ranged 8–71, with means of 64.2 for complete, 40.3 for partial, and 14.9 for low plated morph. Stickleback δ^15N was higher in the lower lake section, while δ^13C was higher in the upper section. Stickleback isotopic values were greater in autumn. The low plated morph had larger variances in δ^15N and δ^13C than the other morphs. Sticklebacks in the upper section had more T. gasterostei than in the lower section which had more Trematoda spp. Sticklebacks had less T. gasterostei , but more Trematoda spp. in autumn than spring. Sticklebacks with few and short rakers had more T. gasterostei , while Sticklebacks with longer rakers had more Trematoda . spp. Stickleback with higher δ^15N values had more T. gasterostei, while Sticklebacks with higher δ^15N and δ^13C values had more Trematoda spp. The low plated morph had fewer Trematoda spp. than other morphs. Conclusions Trait-ecology associations may imply that the three lateral plate morphs in the brackish water lagoon of Lake Engervann are experiencing ongoing divergent selection for niche and migratory life history strategies under high gene flow. As such, the brackish water zone may generally act as a generator of genomic diversity to be selected upon in the different environments where threespine Sticklebacks can live.
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the temporal window of ecological adaptation in postglacial lakes a comparison of head morphology trophic position and habitat use in norwegian threespine Stickleback populations
2016Co-Authors: Kjartan Ostbye, Dolph Schluter, Chris Harrod, F Gregersen, Tom Klepaker, Michael Schulz, Leif Asbjorn VollestadAbstract:Studying how trophic traits and niche use are related in natural populations is important in order to understand adaptation and specialization. Here, we describe trophic trait diversity in twenty-five Norwegian freshwater threespine Stickleback populations and their putative marine ancestor, and relate trait differences to postglacial lake age. By studying lakes of different ages, depths and distance to the sea we examine key environmental variables that may predict adaptation in trophic position and habitat use. We measured trophic traits including geometric landmarks that integrated variation in head shape as well as gillraker length and number. Trophic position (Tpos) and niche use (α) were estimated from stable isotopes (δ13C, δ15N). A comparison of head shape was also made with two North American benthic-limnetic species pairs. We found that head shape differed between marine and freshwater Sticklebacks, with marine Sticklebacks having more upturned mouths, smaller eyes, larger opercula and deeper heads. Size-adjusted gillraker lengths were larger in marine than in freshwater Stickleback. Norwegian Sticklebacks were compared on the same head shape axis as the one differentiating the benthic-limnetic North American threespine Stickleback species pairs. Here, Norwegian freshwater Sticklebacks with a more “limnetic head shape” had more and longer gillrakers than Sticklebacks with “benthic head shape”. The “limnetic morph” was positively associated with deeper lakes. Populations differed in α (mean ± sd: 0.76 ± 0.29) and Tpos (3.47 ± 0.27), where α increased with gillraker length. Larger fish had a higher Tpos than smaller fish. Compared to the ecologically divergent Stickleback species pairs and solitary lake populations in North America, Norwegian freshwater Sticklebacks had similar range in Tpos and α values, but much less trait divergences. Our results showed trait divergences between threespine Stickleback in marine and freshwater environments. Freshwater populations diverged in trophic ecology and trophic traits, but trophic ecology was not related to the elapsed time in freshwater. Norwegian Sticklebacks used the same niches as the ecologically divergent North American Stickleback species pairs. However, as trophic trait divergences were smaller, and not strongly associated with the ecological niche, ecological adaptations along the benthic-limnetic axis were less developed in Norwegian Sticklebacks.
Chris Harrod - One of the best experts on this subject based on the ideXlab platform.
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ongoing niche differentiation under high gene flow in a polymorphic brackish water threespine Stickleback gasterosteus aculeatus population
2018Co-Authors: Kjartan Ostbye, Annette Taugbol, Mark Ravinet, Chris Harrod, Ruben Alexander Pettersen, Louis Bernatchez, Leif Asbjorn VollestadAbstract:Marine threespine Sticklebacks colonized and adapted to brackish and freshwater environments since the last Pleistocene glacial. Throughout the Holarctic, three lateral plate morphs are observed; the low, partial and completely plated morph. We test if the three plate morphs in the brackish water Lake Engervann, Norway, differ in body size, trophic morphology (gill raker number and length), niche (stable isotopes; δ15N, δ13C, and parasites (Theristina gasterostei, Trematoda spp.)), genetic structure (microsatellites) and the lateral-plate encoding Stn382 (Ectodysplasin) gene. We examine differences temporally (autumn 2006/spring 2007) and spatially (upper/lower sections of the lake – reflecting low versus high salinity). All morphs belonged to one gene pool. The complete morph was larger than the low plated, with the partial morph intermediate. The number of lateral plates ranged 8–71, with means of 64.2 for complete, 40.3 for partial, and 14.9 for low plated morph. Stickleback δ15N was higher in the lower lake section, while δ13C was higher in the upper section. Stickleback isotopic values were greater in autumn. The low plated morph had larger variances in δ15N and δ13C than the other morphs. Sticklebacks in the upper section had more T. gasterostei than in the lower section which had more Trematoda spp. Sticklebacks had less T. gasterostei, but more Trematoda spp. in autumn than spring. Sticklebacks with few and short rakers had more T. gasterostei, while Sticklebacks with longer rakers had more Trematoda. spp. Stickleback with higher δ15N values had more T. gasterostei, while Sticklebacks with higher δ15N and δ13C values had more Trematoda spp. The low plated morph had fewer Trematoda spp. than other morphs. Trait-ecology associations may imply that the three lateral plate morphs in the brackish water lagoon of Lake Engervann are experiencing ongoing divergent selection for niche and migratory life history strategies under high gene flow. As such, the brackish water zone may generally act as a generator of genomic diversity to be selected upon in the different environments where threespine Sticklebacks can live.
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Ongoing niche differentiation under high gene flow in a polymorphic brackish water threespine Stickleback (Gasterosteus aculeatus) population
2018Co-Authors: Kjartan Ostbye, Annette Taugbol, Mark Ravinet, Chris Harrod, Ruben Alexander Pettersen, Louis Bernatchez, Leif Asbjorn VollestadAbstract:Background Marine threespine Sticklebacks colonized and adapted to brackish and freshwater environments since the last Pleistocene glacial. Throughout the Holarctic, three lateral plate morphs are observed; the low, partial and completely plated morph. We test if the three plate morphs in the brackish water Lake Engervann, Norway, differ in body size, trophic morphology (gill raker number and length), niche (stable isotopes; δ^15N, δ^13C, and parasites ( Theristina gasterostei , Trematoda spp.)), genetic structure (microsatellites) and the lateral-plate encoding Stn382 ( Ectodysplasin ) gene. We examine differences temporally (autumn 2006/spring 2007) and spatially (upper/lower sections of the lake – reflecting low versus high salinity). Results All morphs belonged to one gene pool. The complete morph was larger than the low plated, with the partial morph intermediate. The number of lateral plates ranged 8–71, with means of 64.2 for complete, 40.3 for partial, and 14.9 for low plated morph. Stickleback δ^15N was higher in the lower lake section, while δ^13C was higher in the upper section. Stickleback isotopic values were greater in autumn. The low plated morph had larger variances in δ^15N and δ^13C than the other morphs. Sticklebacks in the upper section had more T. gasterostei than in the lower section which had more Trematoda spp. Sticklebacks had less T. gasterostei , but more Trematoda spp. in autumn than spring. Sticklebacks with few and short rakers had more T. gasterostei , while Sticklebacks with longer rakers had more Trematoda . spp. Stickleback with higher δ^15N values had more T. gasterostei, while Sticklebacks with higher δ^15N and δ^13C values had more Trematoda spp. The low plated morph had fewer Trematoda spp. than other morphs. Conclusions Trait-ecology associations may imply that the three lateral plate morphs in the brackish water lagoon of Lake Engervann are experiencing ongoing divergent selection for niche and migratory life history strategies under high gene flow. As such, the brackish water zone may generally act as a generator of genomic diversity to be selected upon in the different environments where threespine Sticklebacks can live.
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the temporal window of ecological adaptation in postglacial lakes a comparison of head morphology trophic position and habitat use in norwegian threespine Stickleback populations
2016Co-Authors: Kjartan Ostbye, Dolph Schluter, Chris Harrod, F Gregersen, Tom Klepaker, Michael Schulz, Leif Asbjorn VollestadAbstract:Studying how trophic traits and niche use are related in natural populations is important in order to understand adaptation and specialization. Here, we describe trophic trait diversity in twenty-five Norwegian freshwater threespine Stickleback populations and their putative marine ancestor, and relate trait differences to postglacial lake age. By studying lakes of different ages, depths and distance to the sea we examine key environmental variables that may predict adaptation in trophic position and habitat use. We measured trophic traits including geometric landmarks that integrated variation in head shape as well as gillraker length and number. Trophic position (Tpos) and niche use (α) were estimated from stable isotopes (δ13C, δ15N). A comparison of head shape was also made with two North American benthic-limnetic species pairs. We found that head shape differed between marine and freshwater Sticklebacks, with marine Sticklebacks having more upturned mouths, smaller eyes, larger opercula and deeper heads. Size-adjusted gillraker lengths were larger in marine than in freshwater Stickleback. Norwegian Sticklebacks were compared on the same head shape axis as the one differentiating the benthic-limnetic North American threespine Stickleback species pairs. Here, Norwegian freshwater Sticklebacks with a more “limnetic head shape” had more and longer gillrakers than Sticklebacks with “benthic head shape”. The “limnetic morph” was positively associated with deeper lakes. Populations differed in α (mean ± sd: 0.76 ± 0.29) and Tpos (3.47 ± 0.27), where α increased with gillraker length. Larger fish had a higher Tpos than smaller fish. Compared to the ecologically divergent Stickleback species pairs and solitary lake populations in North America, Norwegian freshwater Sticklebacks had similar range in Tpos and α values, but much less trait divergences. Our results showed trait divergences between threespine Stickleback in marine and freshwater environments. Freshwater populations diverged in trophic ecology and trophic traits, but trophic ecology was not related to the elapsed time in freshwater. Norwegian Sticklebacks used the same niches as the ecologically divergent North American Stickleback species pairs. However, as trophic trait divergences were smaller, and not strongly associated with the ecological niche, ecological adaptations along the benthic-limnetic axis were less developed in Norwegian Sticklebacks.
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habitat specific adaptation of immune responses of Stickleback gasterosteus aculeatus lake and river ecotypes
2007Co-Authors: Jorn P Scharsack, Martin Kalbe, Chris Harrod, Gisep RauchAbstract:Freshwater populations of three-spined Sticklebacks (Gasterosteus aculeatus) in northern Germany are found as distinct lake and river ecotypes. Adaptation to habitat-specific parasites might influence immune capabilities of Stickleback ecotypes. Here, naive laboratory-bred Sticklebacks from lake and river populations were exposed reciprocally to parasite environments in a lake and a river habitat. Sticklebacks exposed to lake conditions were infected with higher numbers of parasite species when compared with the river. River Sticklebacks in the lake had higher parasite loads than lake Sticklebacks in the same habitat. Respiratory burst, granulocyte counts and lymphocyte proliferation of head kidney leucocytes were increased in river Sticklebacks exposed to lake when compared with river conditions. Although river Sticklebacks exposed to lake conditions showed elevated activation of their immune system, parasites could not be diminished as effectively as by lake Sticklebacks in their native habitat. River Sticklebacks seem to have reduced their immune-competence potential due to lower parasite diversity in rivers.
Juha Merila - One of the best experts on this subject based on the ideXlab platform.
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genetic population structure constrains local adaptation in Sticklebacks
2021Co-Authors: Petri Kemppainen, Baocheng Guo, Juha Merila, Pasi Rastas, Ari Loytynoja, Bohao Fang, Jing Yang, Takahito ShikanoAbstract:Repeated and independent adaptation to specific environmental conditions from standing genetic variation is common. However, if genetic variation is limited, the evolution of similar locally adapted traits may be restricted to genetically different and potentially less optimal solutions or prevented from happening altogether. Using a quantitative trait locus (QTL) mapping approach, we identified the genomic regions responsible for the repeated pelvic reduction (PR) in three crosses between nine-spined Stickleback populations expressing full and reduced pelvic structures. In one cross, PR mapped to linkage group 7 (LG7) containing the gene Pitx1, known to control pelvic reduction also in the three-spined Stickleback. In the two other crosses, PR was polygenic and attributed to 10 novel QTL, of which 90% were unique to specific crosses. When screening the genomes from 27 different populations for deletions in the Pitx1 regulatory element, these were only found in the population in which PR mapped to LG7, even though the morphological data indicated large-effect QTL for PR in several other populations as well. Consistent with the available theory and simulations parameterized on empirical data, we hypothesize that the observed variability in genetic architecture of PR is due to heterogeneity in the spatial distribution of standing genetic variation caused by >2× stronger population structuring among freshwater populations and >10× stronger genetic isolation by distance in the sea in nine-spined Sticklebacks as compared to three-spined Sticklebacks.
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population transcriptomics reveals weak parallel genetic basis in repeated marine and freshwater divergence in nine spined Sticklebacks
2020Co-Authors: Yingnan Wang, Yongxin Zhao, Yu Wang, Baocheng Guo, Juha MerilaAbstract:The degree to which adaptation to similar selection pressures is underlain by parallel versus non-parallel genetic changes is a topic of broad interest in contemporary evolutionary biology. Sticklebacks provide opportunities to characterize and compare the genetic underpinnings of repeated marine-freshwater divergences at both intra- and interspecific levels. While the degree of genetic parallelism in repeated marine-freshwater divergences has been frequently studied in the three-spined Stickleback (Gasterosteus aculeatus), much less is known about this in other Stickleback species. Using a population transcriptomic approach, we identified both genetic and gene expression variations associated with marine-freshwater divergence in the nine-spined Stickleback (Pungitius pungitius). Specifically, we used a genome-wide association study approach, and found that ~1% of the total 173,491 identified SNPs showed marine-freshwater ecotypic differentiation. A total of 861 genes were identified to have SNPs associated with marine-freshwater divergence, but only 12 of these genes have also been reported as candidates associated with marine-freshwater divergence in the three-spined Stickleback. Hence, our results indicate a low degree of interspecific genetic parallelism in marine-freshwater divergence. Moreover, 1,578 genes in the brain and 1,050 genes in the liver were differentially expressed between marine and freshwater nine-spined Sticklebacks, ~5% of which have also been identified as candidates associated with marine-freshwater divergence in the three-spined Stickleback. However, only few of these (e.g., CLDND1) appear to have been involved in repeated marine-freshwater divergence in nine-spined Sticklebacks. Taken together, the results indicate a low degree of genetic parallelism in repeated marine-freshwater divergence both at intra- and interspecific levels.
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predation imposed selection on threespine Stickleback gasterosteus aculeatus morphology a test of the refuge use hypothesis
2011Co-Authors: Tuomas Leinonen, Gabor Herczeg, J M Cano, Juha MerilaAbstract:The transition from marine to freshwater life in the threespine Stickleback (Gasterosteus aculeatus) is accompanied by complex morphological changes-including reduction in bony armor and change in body shape-but experimental evidence for the selective agents behind these evolutionary transitions is sparse. We investigated whether selection by predatory fish affects threespine Stickleback morphology differentially when refuge is absent (pelagic lifestyle-ancestral condition) or present (benthic lifestyle-derived condition). Our results show that selection favors low numbers of lateral plates in habitats with refuge, whereas fully plated individuals have a selective advantage in habitats without refuge. We also found that a decrease in the length of the caudal peduncle increased survival probability, irrespective of habitat. The effect of spine lengths on survival was evident only in a multivariate analysis of selection, implying that it is essential to account for phenotypic and genetic correlations between traits before drawing conclusions about the effects of selection on single traits. Apart from uncovering targets and patterns of predator-induced selection on threespine Stickleback morphology, our results provide direct evidence to support the hypothesis that differences in antipredator strategies in pelagic versus benthic Sticklebacks could play a role in the repeated, independent cases of plate number reduction following freshwater colonization in this species.
