Population divergence shaped by natural selection is central to evolutionary ecology research and has been in focus since Darwin formulated “The origin of species”. Still, the process of adaptive divergence among sympatric populations is poorly understood. In this thesis I studied patterns of adaptive divergence among subpopulations of pike (Esox lucius) that are sympatric in the Baltic Sea but become short-term allopatric during spawning and initial juvenile growth in freshwater streams. I also examined causes and consequences of phenotypic variation among individuals within subpopulations to evaluate the contribution of natural selection to population divergence.   I first investigated homing behaviour and population structures of pike to assess the potential for adaptive divergence among sympatric pike that migrate to spawn in different streams. Mark-recapture data suggested that migrating pike displayed homing behaviour and repeatedly returned to the same stream. Analyses of microsatellite data revealed partial reproductive isolation among subpopulations spawning in different streams. These subpopulations, however, were truly sympatric during the life-stage spent in the Baltic Sea.   To address whether short-term allopatry has resulted in adaptive divergence among sympatric subpopulations I combined observational, experimental and molecular approaches. Observational data showed that subpopulations differed in morphological and life-history traits and common-garden experiments suggested that differences were, at least in part, genetically based. Moreover, QST-FST comparisons indicated that genetically based phenotypic differences has been driven by divergent selection, and a reciprocal translocation experiment showed that phenotypic variation represented local adaptations to spawning habitats. Finally, longitudinal and cross-sectional comparisons among individuals revealed associations between phenotypes, performance and fitness components.   In conclusion, my thesis illustrates how short-term allopatry due to migratory behaviour can result in adaptive divergence among sympatric subpopulations. These findings advance the understanding of evolutionary processes at the finest spatiotemporal scale and illustrate that local adaptations can arise in environments with high connectivity.  The results also emphasise that fine spatial scale population structures must be taken into consideration in management and conservation of biodiversity in the Baltic Sea.

A critical step in ecological speciation is the development of reproductive isolation. The processes leading up to reproductive isolation are difficult to study since they often occur over very long time periods. Populations of European whitefish (Coregonus lavaretus) has gone through reticulate divergent evolution in many Scandinavian lakes during the last 10 000 years. Some populations even exhibit morphological and genetic divergence that involves adaptations to different niches during the first 100-200 years after introduction. This observed rapid diversification into different ecological niches makes whitefish a useful model species for studying ecological speciation and early population divergence. By assessing divergence for three traits in recently introduced whitefish populations, this study aims to elucidate the processes that lead to adaptive phenotypic divergence and reproductive isolation. Whitefish populations of known age (71-170 years) were sampled on their spawning grounds and characterized with respect to, 1) length of spawning season, 2) temporal segregation based on body size, and 3) temporal segregation based on the number of gill rakers. I found that the length of the spawning season and body size differences between early and late spawners increased with population age. No such trend was observed for differences in gill rakers between early and late spawners, but significant divergence within some of the older populations was detected. I conclude that these young whitefish populations have taken the first steps toward reproductive isolation between ecotypes that differs in body size (a highly plastic trait) and gill raker numbers (a trait under strong genetic control).

In birds, song can evolve quickly through cultural transmission and due to errors in the learning process may result in regional dialects. A lack of dialectal recognition may be a critical component of reproductive isolation through female mate preference. I investigated the role of cultural divergence in reproductive isolation in a widespread Neotropical passerine the rufous-collared sparrow (Zonotrichia capensis). In Chapter II, I investigated, the role of female preference for and male territorial response towards, local and non-local dialects in two allopatric populations. Females in both populations preferred their local dialect to the dialect of an allopatric population only 25 km away. In contrast, males showed similar territorial response to all conspecific dialects. Premating reproductive isolation based on culture may exist among the study populations. In chapter III, I investigated if cultural divergence can drive population divergence by examining dialects and variable microsatellite loci among eight populations of Z. capensis. I investigated the presence of population divergence and then identified the mechanism that may be driving the pattern. Apart from culture, a geographic barrier (the Andean ridge), elevation, and geographic distance were potential mechanisms of population divergence that I considered. All sites exhibited localized dialects, except for two closest neighboring populations. Populations exhibited genetic differentiation with support for the presence of five genetic clusters. Culture does not appear to be driving population divergence because song dialects and genetic population structure were not correlated. Populations separated by an Andean ridge did not display higher genetic or song differences than distance would predict, suggesting that the ridge is not driving population divergence. Elevation was not correlated to song or genetic differentiation. Both song divergence and microsatellite allele frequency differentiation were correlated with geographic distance suggesting a pattern of isolation by distance. Overall, geographic distance is the best predictor of population divergence in this system. Cumulatively, I found that culture might promote assortative mating via female mate choice, perhaps generating partial reproductive isolation; however, song dialect differences among contiguous populations is not currently driving population divergence in this species. / Ph. D.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24310号 / 理博第4880号 / 新制||理||1698(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 曽田 貞滋, 准教授 渡辺 勝敏, 教授 中務 真人 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Evolutionary transitions between the two major predator avoidance strategies aposematism and crypsis are expected to be associated with changes in many important traits of animals. However, empirical studies on populations experiencing ongoing or recent transitions between these strategies are rare. This thesis investigates the co-evolution of traits among populations of the Strawberry poison frog D.pumilio in Bocas del Toro, Panama. I found that all investigated populations were genetically distinct but that colour and pattern did not correlate with genetic or geographic distance, which suggests that selection needs to be invoked to explain the observed variation. Based on the chromatic contrast between frog dorsal colour and the natural habitat substrates used by the frogs, the populations were defined as bright or dull coloured. I found that frogs from bright coloured populations were larger. This is expected if aposematism is enhanced by large signals while crypsis is enhanced by small size. Further, individuals from bright coloured populations had a coarser black dorsal pattern, which is expected if crypsis is impaired by a bold pattern. The importance of pattern coarseness was confirmed by an avian detection experiment showing that coarse patterned dark green prey were more easily detected than dark green prey without pattern or with fine pattern. I put forward the hypothesis that enhanced protection, gained by aposematism, may affect behaviours that influence dispersal and pairing patterns. Indeed, males from bright coloured populations displayed at more exposed sites and showed a tendency to be more explorative and aggressive. In summary, my results show that the bright and dull coloured populations most likely represent an aposematic and a cryptic strategy, respectively. Furthermore, I show that evolutionary changes between aposematism and crypsis can be associated with coevolution of both morphology and behaviour. I argue that this coevolution may increase the likelihood of both pre- and post-zygotic reproductive isolation. This is because greater phenotypic differences between populations increase the likelihood of selection against badly adapted migrants and hybrids with intermediate traits.

Abstract The study of speciation has been an area of primary interest in evolutionary biology from Darwin to the present day. Understanding the processes that give rise to new species requires knowledge on how reproductive isolation develops between diverging populations. An irreversible and therefore important component of reproductive isolation is intrinsic postzygotic isolation. Postzygotic incompatibilities often manifest themselves through hybrid inviability or sterility, and distort allelic transmission ratios in hybrid progenies. The genetic basis of such incompatibilities has often been found to be negative interactions between two or more loci, also known as Bateson-Dobzhansky-Muller incompatibilities. During the last decade some genes involved in this type of incompatibilities have been identified, but especially in plants our knowledge remains scarce. In this thesis I examined whether intrinsic postzygotic isolation had developed between allopatric populations of a perennial, outcrossing plant; Arabidopsis lyrata. The studied populations of A. lyrata were found to be genetically highly differentiated. In F2 progenies of crosses between populations many molecular markers reveal non-Mendelian genotype ratios, that is, show transmission ratio distortion (TRD). By contrast, TRD was found to be nearly absent in progenies of within population crosses. The degree of TRD clearly increased with genetic distance between the crossed populations, and origin for TRD was often in F1 gamete formation, instead of F2 zygotic level. The genetic basis of TRD appeared due to interactions between nuclear loci, and between nuclear and cytoplasmic factors. In addition to transmission ratio distortion, reduced male fertility and cytoplasmic male sterility was found in the F2 hybrids between A. lyrata subspecies petraea and lyrata. Quantitative trait loci for reduced male fertility were polymorphic within populations, and dependent on cytoplasm. Thus, the findings in this thesis underline the role of cytonuclear interactions, and the possibility of development of genic incompatibilities through genomic conflicts due to divergence likely unrelated to local adaptation. / Tiivistelmä Lajiutumistutkimus on ollut yksi evoluutiobiologian suurimmista kiinnostuksen kohteista Darwinin ajoista nykypäivään. Jotta voisimme ymmärtää uusien lajien syntymiseen johtavia prosesseja, on ensin ymmärrettävä, miten lisääntymisisolaatio kehittyy erilaistuvien populaatioiden välille. Lajien välisten risteytysten jälkeläiset ovat usein steriilejä tai elinkyvyttömiä. Tämä perustuu kahden erilaistuneen populaation perimän yhteensopimattomuuteen. Tällaiset sisäsyntyiset hedelmöityksen jälkeiset yhteensopimattomuudet ovat tärkeä osa lisääntymisisolaatiota, sillä ne ovat peruuttamattomia. Ne aiheuttavat vääristymiä genotyyppien lukusuhteissa risteytysjälkeläistöissä. Posttsygoottisen yhteensopimattomuuden taustalla on usein kahden tai useamman geenilokuksen välinen negatiivinen interaktio, jota kutsutaan myös Bateson-Dobzhansky-Muller -inkompatibiliteetiksi. Viime vuosikymmenen aikana on tunnistettu muutamia geenejä, jotka ovat mukana negatiivisissa interaktioissa, mutta kasveista tietoa geneettisistä tekijöistä on vielä vähän. Väitöstutkimuksessa selvitettiin onko geneettisiä posttsygoottisia yhteensopimattomuuksia kehittynyt kasvilajin sisällä (Arabidopsis lyrata) allopatristen populaatioiden välille. Tutkitut kasvipopulaatiot olivat geneettisesti hyvin erilaistuneita. Näiden populaatioiden välisten jälkeläistöjen genotyypeissä havaittiin yleisesti paljon mendelistisistä lukusuhteista poikkeavia lukusuhteita. Genotyyppejä tarkasteltiin myös populaation sisäisissä risteytyksissä, joiden jälkeläistöissä periytyminen oli lähes mendelististä. Väitöstutkimuksessa havaittiin, että mitä geneettisesti erilaisemmat populaatiot risteytettiin, sitä suurempi oli ei-mendelistisen periytymisen osuus. Tutkimukset osoittivat lukusuhteiden vääristyvän jo F1-hybridin tuottaessa sukupuolisoluja, eikä niinkään muodostuneissa uusissa F2-tsygooteissa. Taustalla olevien geneettisten yhteensopimattomuuksien havaittiin vaikuttavan tuman geenien välillä, mutta myös tuman ja soluliman geneettisten tekijöiden välillä. Mendelistisistä lukusuhteista poikkeamisen lisäksi tutkimuksessa havaittiin siitepölyn alentunut elinkyky ja solulimaan liittyvä koirassteriliteetti F2-jälkeläistössä A. lyrata alalajien petraea ja lyrata välillä. Lokukset, jotka vaikuttivat siitepölyn alentuneeseen elinkykyyn, olivat polymorfisia populaatioiden sisällä ja vuorovaikutuksessa soluliman geneettisten tekijöiden kanssa. Nämä tutkimustulokset korostavat tuman ja soluliman geenien vuorovaikutuksen tärkeyttä lajien välisten lisääntymisesteiden synnyssä. Ne myös osoittavat, että yhteensopimattomuus voi kehittyä mahdollisesti ilman luonnonvalinnan vaikutusta.

No description available.

Cross-boundary movements of energy and material are ubiquitous. Freshwater ecosystems receive nutrients, dissolved, and particulate organic matter from adjacent terrestrial ecosystems, whereas terrestrial ecosystems mainly receive prey organisms and detritus deposited by physical processes such as floods from freshwater ecosystems. Within lakes, fish are considered as integrators between habitats due to their high mobility, although they often occupy either near-shore littoral or open-water pelagic habitats and develop habitat-specific morphologies. Such intra-population divergence in morphological traits might limit the use of multiple habitats. In this thesis, I first focused on quantity and quality of reciprocal fluxes of particulate organic matter between freshwater and terrestrial ecosystems and responses of recipient consumers. Freshwater ecosystems generally received higher amounts of externally-produced resources than terrestrial ecosystems. Despite this discrepancy, aquatic and terrestrial consumer responses were similar, likely due to the differences in resource quality. Second, I investigated the potential of particulate organic carbon (POC) supporting benthic food webs in lakes; a pathway that has largely been neglected in previous studies. I found that POC can substantially subsidize the benthic food web and that the effects on the benthic food web were transferred to the pelagic habitat, thus emphasizing the importance of benthic pathways for pelagic production. Third, I examined how water transparency can affect intra-population divergence in perch (Perca fluviatilis). I observed that increased water transparency can considerably increase morphological divergence between littoral and pelagic populations likely due to its effects on foraging. Finally, I investigated the effects of such intra-population divergence on littoral-pelagic food web coupling. I found that low morphological divergence corresponded with high overlap in resource use, whereas strong morphological divergence resulted in low overlap in resource use. Here littoral populations mainly utilized littoral resources and pelagic populations primarily utilized pelagic resources, indicating that habitat coupling might be strongly limited when intra-population divergence is high. In conclusion, although different ecosystems seem separated by distinct physical boundaries, these boundaries are often crossed. However, the development of habitat-specific adaptive traits might limit movement between apparently contiguous habitats.