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Intraspecific diversity of pike (Esox lucius) in the Baltic Sea and new insights on thermoregulation in fish
Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. (EEMiS)ORCID iD: 0000-0001-9667-1228
2018 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Inomartsvariation hos gädda (Esox lucius) i Östersjön och nya insikter om temperaturreglering hos fisk (Swedish)
Abstract [en]

Fish display a fascinating variation in behavior, morphology and physiology among species, among individuals within species, and within individuals over time. A central quest in ecology and evolution is to understand causes and consequences of such variation. This thesis aims to contribute to this knowledge by: (1) investigating the evolutionary processes that shape intraspecific variation among sympatric subpopulations of pike in coastal areas of the Baltic Sea; and (2) exploring whether fish can utilize sun-basking to regulate body temperature and whether this has any consequences for fitness.

Identifying barriers that delineate populations is a first step towards evaluating the evolutionary origin of intraspecific variation. This thesis reports on genetic population structures among co-existing pike in the coastal Baltic Sea separated by homing behavior, different spawning strategies and geographic barriers. Field studies revealed that these subpopulations also show phenotypic divergence in reproductive and meristic traits. Experimental studies suggested that differentiation among subpopulations likely was a result of divergent selection and local adaptations to spawning grounds. These adaptations that may further reinforce barriers among subpopulations due to a reduced success of immigrant genotypes.

For the second aim of the thesis, we first studied seasonal and diel patterns of activity and vertical migration among the Baltic Sea pike. The results suggested that pike exposed themselves to sunlight during spring and summer, and that body temperatures were positively correlated with sun exposure during these basking events. This was followed by experimental studies on inanimate physical models and a field study on carp which demonstrated that fish can become warmer than ambient water when exposed to sun light, a previously overlooked mechanism for fish thermoregulation, and that the heat gain was positively correlated with growth.

This thesis contributes to our understanding of the origin and maintenance of intraspecific variation among coexisting populations with direct implications for management of pike. It also establishes sun-basking as a novel mechanism for fish to obtain body temperatures in excess of ambient water which could motivate adaptations, both evolutionary and plastic, that optimize heat gain, affect spatiotemporal distributions and biotic interaction within and among species.

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2018. , p. 39
Series
Linnaeus University Dissertations ; 340
Keywords [en]
adaptive divergence, Cyprinus carpio, ecology, Esox lucius, evolution, local adaptation, management, thermoregulation, sun-basking, vertical migration
National Category
Evolutionary Biology Ecology
Research subject
Ecology, Aquatic Ecology; Ecology, Evolutionary Biology
Identifiers
URN: urn:nbn:se:lnu:diva-78842ISBN: 978-91-88898-24-1 (print)ISBN: 978-91-88898-25-8 (electronic)OAI: oai:DiVA.org:lnu-78842DiVA, id: diva2:1263592
Public defence
2018-12-07, Fullriggaren, Landgången 4, Kalmar, 09:30 (English)
Opponent
Supervisors
Available from: 2018-11-16 Created: 2018-11-16 Last updated: 2018-11-16Bibliographically approved
List of papers
1. Causes and consequences of intra-specific variation in vertebral number
Open this publication in new window or tab >>Causes and consequences of intra-specific variation in vertebral number
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2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 26372Article in journal (Refereed) Published
Abstract [en]

Intraspecific variation in vertebral number is taxonomically widespread. Much scientific attention hasbeen directed towards understanding patterns of variation in vertebral number among individualsand between populations, particularly across large spatial scales and in structured environments.However, the relative role of genes, plasticity, selection, and drift as drivers of individual variation andpopulation differentiation remains unknown for most systems. Here, we report on patterns, causesand consequences of variation in vertebral number among and within sympatric subpopulations ofpike (Esox lucius). Vertebral number differed among subpopulations, and common garden experimentsindicated that this reflected genetic differences. A QST-FST comparison suggested that populationdifferences represented local adaptations driven by divergent selection. Associations with fitness traitsfurther indicated that vertebral counts were influenced both by stabilizing and directional selectionwithin populations. Overall, our study enhances the understanding of adaptive variation, which iscritical for the maintenance of intraspecific diversity and species conservation.

Keywords
Biodiversity, Evolution, Evolutionary ecology, Ichthyology
National Category
Evolutionary Biology Ecology
Research subject
Natural Science, Ecology; Ecology, Evolutionary Biology; Ecology, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-52632 (URN)10.1038/srep26372 (DOI)000376236300001 ()27210072 (PubMedID)2-s2.0-84971287174 (Scopus ID)
Projects
EcoChange
Available from: 2016-05-23 Created: 2016-05-23 Last updated: 2018-11-16Bibliographically approved
2. Testing for local adaptation to spawning habitat in sympatric subpopulations of northern pike by reciprocal translocation of embryos
Open this publication in new window or tab >>Testing for local adaptation to spawning habitat in sympatric subpopulations of northern pike by reciprocal translocation of embryos
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2016 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 5, article id e0154488Article in journal (Refereed) Published
Abstract [en]

We tested for local adaption in early life-history traits by performing a reciprocal translocation experiment with approximately 2500 embryos of pike (Esox lucius) divided in paired split-family batches. The experiment indicated local adaptation in one of the two subpopulations manifested as enhanced hatching success of eggs in the native habitat, both when compared to siblings transferred to a non-native habitat, and when compared to immigrant genotypes from the other subpopulation. Gene-by-environment effects on viability of eggs and larvae were evident in both subpopulations, showing that there existed genetic variation allowing for evolutionary responses to divergent selection, and indicating a capacity for plastic responses to environmental change. Next, we tested for differences in female life-history traits. Results uncovered that females from one population invested more resources into reproduction and also produced more (but smaller) eggs in relation to their body size compared to females from the other population. We suggest that these females have adjusted their reproductive strategies as a counter-adaptation because a high amount of sedimentation on the eggs in that subpopulations spawning habitat might benefit smaller eggs. Collectively, our findings point to adaptive divergence among sympatric subpopulations that are physically separated only for a short period during reproduction and early development – which is rare. These results illustrate how combinations of translocation experiments and field studies of life-history traits might infer about local adaptation and evolutionary divergence among populations. Local adaptations in subdivided populations are important to consider in management and conservation of biodiversity, because they may otherwise be negatively affected by harvesting, supplementation, and reintroduction efforts targeted at endangered populations.

National Category
Evolutionary Biology Ecology
Research subject
Ecology, Evolutionary Biology
Identifiers
urn:nbn:se:lnu:diva-51999 (URN)10.1371/journal.pone.0154488 (DOI)000375675700036 ()27139695 (PubMedID)2-s2.0-84969850246 (Scopus ID)
Projects
EcoChange
Available from: 2016-04-08 Created: 2016-04-08 Last updated: 2018-11-16Bibliographically approved
3. Sun-basking fish benefit from body temperatures that are higher than ambient water
Open this publication in new window or tab >>Sun-basking fish benefit from body temperatures that are higher than ambient water
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2018 (English)In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 285, no 1879, article id 20180639Article in journal (Refereed) Published
Abstract [en]

In terrestrial environments, cold-blooded animals can attain higher bodytemperatures by sun basking, and thereby potentially benefit from broaderniches, improved performance and higher fitness. The higher heat capacityand thermal conductivity of water compared with air have been universallyassumed to render heat gain from sun basking impossible for aquaticectotherms, such that their opportunities to behaviourally regulate body temperatureare largely limited to choosing warmer or colder habitats. Here wechallenge this paradigm. Using physical modelswe first showthat submergedobjects exposed to natural sunlight attain temperatures in excess of ambientwater. We next demonstrate that free-ranging carp (Cyprinus carpio) canincrease their body temperature during aquatic sun basking close to thesurface. The temperature excess gained by basking was larger in dark thanin pale individuals, increased with behavioural boldness, and was associatedwith faster growth. Overall, our results establish aquatic sun basking as a novelecologically significant mechanism for thermoregulation in fish. The discoveryof this previously overlooked process has practical implications for aquaculture,offers alternative explanations for behavioural and phenotypicadaptations, will spur future research in fish ecology, and calls for modificationsof models concerning climate change impacts on biodiversity inmarine and freshwater environments.

National Category
Ecology Evolutionary Biology
Research subject
Natural Science, Ecology
Identifiers
urn:nbn:se:lnu:diva-75330 (URN)10.1098/rspb.2018.0639 (DOI)000433506100024 ()
Available from: 2018-06-07 Created: 2018-06-07 Last updated: 2018-11-16Bibliographically approved

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Doctoral Thesis (Comprehensive Summary)(3886 kB)12 downloads
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