| 1. |
- Alström, Per, et al.
(författare)
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The Arctic Warbler Phylloscopus borealis - three anciently separated cryptic species revealed
- 2011
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Ingår i: Ibis. - 0019-1019 .- 1474-919X. ; 153:2, s. 395-410
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Tidskriftsartikel (refereegranskat)abstract
- The Arctic Warbler Phylloscopus borealis breeds across the northern Palaearctic and northwestern-most Nearctic, from northern Scandinavia to Alaska, extending south to southern Japan, and winters in Southeast Asia, the Philippines and Indonesia. Several subspecies have been described based on subtle morphological characteristics, although the taxonomy varies considerably among different authors. A recent study (T. Saitoh et al. (2010) BMC Evol. Biol. 10: 35) identified three main mitochondrial DNA clades, corresponding to: (1) continental Eurasia and Alaska, (2) south Kamchatka, Sakhalin and northeast Hokkaido, and (3) most of Japan (Honshu, Shikoku, Kyushu). These three clades were estimated to have diverged during the late Pliocene to early Pleistocene (border at c. 2.6 million years ago). Differences in morphometrics have also been reported among members of the three clades (T. Saitoh et al. (2008) Ornithol. Sci. 7: 135-142). Here we analyse songs and calls from throughout the range of the Arctic Warbler, and conclude that these differ markedly and consistently among the populations representing the three mitochondrial clades. Kurile populations, for which no sequence data are available, are shown to belong to the second clade. To determine the correct application of available scientific names, mitochondrial DNA was sequenced from three name-bearing type specimens collected on migration or in the winter quarters. Based on the congruent variation in mitochondrial DNA, morphology and vocalizations, we propose that three species be recognized: Arctic Warbler Phylloscopus borealis (sensu stricto) (continental Eurasia and Alaska), Kamchatka Leaf Warbler Phylloscopus examinandus (Kamchatka (at least the southern part), Sakhalin, Hokkaido and Kurile Islands), and Japanese Leaf Warbler Phylloscopus xanthodryas (Japan except Hokkaido).
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| 2. |
- Bergek, Sara, 1979-
(författare)
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Population divergence at small spatial scales : – theoretical and empirical investigations in perch
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Genetically structured populations arise when gene flow between groups of individuals is hindered by geographical, behavioural or temporal barriers. The identification of such groups is important for understanding evolution and has large implications for conservation concern. The field of population subdivision has received a lot of interest throughout the years and gained empirical support from a number of species. However, very little is known about population structure at small spatial scales, especially in a highly mobile species such as fish. The main object for my thesis was to further investigate population differentiation, explicitly at small spatial scales in the Eurasian perch. My results show that in this species, genetic differentiation occurs, even at very small spatial scales, both within lakes and in the Baltic Sea. Additionally, the differentiation can be stable over years and thus have a large impact in the evolution of adaptation to different environments. I also found barriers to gene flow that overlapped with the largest change in spring temperature, suggesting a temporal difference in spawning. Morphological differences were found at these small scales as well which indicates that a difference in food resources might be an underlying cause of change. My thesis work shows that the aquatic environment might not be as homogenous as widely thought and that there could be barriers or adaptations to different environments that hinder the fish from genetic panmixia. Slight patterns of isolation by distance (IBD) were found in the Baltic Sea, implying that the distance (i.e. currents) effect the level of differentiation via drifting of larvae and/or small fish. However, I have also theoretically investigated the IBD model of and seen that it is no longer correct when differences in population sizes are introduced. The pattern of IBD can mean high levels of gene flow or no gene flow at all, solely dependent on population size differences and fluctuations. My thesis has resulted in new and important findings regarding the existence and cause of genetic differentiation at very small spatial scales and thus added new knowledge into the field of evolution and speciation. In addition, my results also give insights into the contemporary state of the Eurasian perch and future evolutionary potential.
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| 3. |
- Björklund, Mats, et al.
(författare)
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Rapid spatial genetic differentiation in an invasive species, the round goby Neogobius melanostomus in the Baltic Sea
- 2010
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Ingår i: Biological Invasions. - : Springer Science and Business Media LLC. - 1387-3547 .- 1573-1464. ; 12:8, s. 2609-2618
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Tidskriftsartikel (refereegranskat)abstract
- We analysed the pattern of genetic differentiation among six newly established (around 10 generations) sites of the round goby (Neogobius melanostomus) in the southern Baltic Sea by means of nine microsatellite loci and in total 183 individuals. All but one site were within 30 km from each other. We found statistically significant genetic differentiation in ten out of 15 comparisons after Bonferroni correction, and since the species is newly introduced this has happened in less than ten generations. The largest genetic differentiation was found between the two most divergent habitats, while sites with a similar habitat were not significantly differentiated. Estimates of gene flow (Nm) were low and ranged from 1.5 to 5.5. A large proportion of individuals were assigned to one site (Puck), suggesting that this site has acted as a source to the other sites.
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| 4. |
- Mats, Björklund, et al.
(författare)
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Assortative mating and the cost of inbreeding : A simulation approach
- 2012
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Ingår i: Ecological Informatics. - : Elsevier BV. - 1574-9541 .- 1878-0512. ; 9, s. 59-63
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Tidskriftsartikel (refereegranskat)abstract
- Assortative mating is an important factor in the process of speciation. Models of speciation frequently deal with small founder populations often with mating preferences based on ecological traits or habitat preferences. Small populations, on the other hand might suffer from inbreeding. However, few studies have explored the combined effects of assortative mating and inbreeding in such populations. Can they speciate, or are they doomed to eventually go extinct? With this simulation we show that assortative mating based on similarities increases the possibility for change in a population, as long as the population does not suffer from inbreeding depression. Inbred populations seem not to be able to cope with strong assortative mating, as this is likely to elevate the level of inbreeding, increasing the risks of inbreeding depression and as a result decreasing population mean fitness. This in turn hinders the possibility of change, and instead might drive the population to extinction.
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| 5. |
- Rova, Emma, 1978-, et al.
(författare)
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An experimental study on the interaction between inbreeding and assortative mating in the process of speciation : Assortative mating and inbreeding
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In the process of speciation, assortative mating and its costs in terms of possible inbreeding depression play a central and sometimes critical role. Despite this fact, given the numerous models on assortative mating, and the rich theory and empirical data on inbreeding at hand, studies of the interaction between the two are essentially missing. This study experimentally explores the interaction of inbreeding and assortative mating in the process of speciation. We show that in small populations of the bean weevil, Callosobruchus maculatus, signs of inbreeding depression, such as reduced female fecundity, decreased juvenile hatching success, changed hatched offspring sex ratio, and extinction develop in relation to assortative mating. We also show that in these inbred populations, the mating system changes in terms of a reduced tendency to mate assortatively.
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| 6. |
- Rova, Emma, 1978-, et al.
(författare)
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Can preference for oviposition sites initiate reproductive isolation in Callosobruchus maculatus?
- 2011
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:1, s. e14628-
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Tidskriftsartikel (refereegranskat)abstract
- Theory has identified a variety of evolutionary processes that may lead to speciation. Our study includes selection experiments using different host plants and test key predictions concerning models of speciation based on host plant choice, such as the evolution of host use (preference and performance) and assortative mating. This study shows that after only ten generations of selection on different resources/hosts in allopatry, strains of the seed beetle Callosobruchus maculatus develop new resource preferences and show resource-dependent assortative mating when given the possibility to choose mates and resources during secondary contact. The resulting reduced gene flow between the different strains remained for two generations after contact before being overrun by disassortative mating. We show that reduced gene flow can evolve in a population due to a link between host preference and assortative mating, although this result was not found in all lines. However, consistent with models of speciation, assortative mating alone is not sufficient to maintain reproductive isolation when individuals disperse freely between hosts. We conclude that the evolution of reproductive isolation in this system cannot proceed without selection against hybrids. Other possible factors facilitating the evolution of isolation would be longer periods of allopatry, the build up of local adaptation or reduced migration upon secondary contact.
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| 7. |
- Rova, Emma, 1978-, et al.
(författare)
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Competitive environments induce shifts in host fidelity
- 2010
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Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 23:8, s. 1657-1663
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Tidskriftsartikel (refereegranskat)abstract
- Recent models support the idea of sympatric speciation as a result of the joint effects of disruptive selection and assortative mating. We present experimental data, testing models of speciation through frequency-dependent selection. We show that under high competition on a mixture of resources/hosts, strains of the Seed beetle, Callosobruchus maculatus, change their host fidelity and evolve a more generalistic behaviour in resource utilisation among females. The change in host fidelity did not result in disruptive selection and was not followed by assortative mating. This means that only one out of three fundamental prerequisites for sympatric speciation evolved as a result of the frequency-dependent selection. We conclude that for this process to work, a shift to a novel food resource as a result of selection must also lead to a loss of preference for the original source such that individuals are only able to use either one of the two.
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| 8. |
- Rova, Emma, 1978-, et al.
(författare)
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The influence of migration on the maintanance of assortative mating
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Rapid speciation has been shown plausible without the need for extreme founder events, complete geographic isolation, the existence of distinct adaptive peaks or selection for local adaptation. However, standard theory predicts that extremely low migration rates are enough to hinder divergence between populations, and thus speciation. Our question to be answered is at which migration rates divergence, and hence speciation is still possible. Is it really as strict as theory predicts? We show that assortative mating can be upheld for several generations in populations experiencing immigration rates of up to eight percent, or 13-15 immigrants per generation, despite the lack of adaptive divergence and trade-offs between the exchanging populations. Since assortative mating vanishes after some generations of extensive gene flow without selection against hybrids, we conclude that selection is likely to be an important factor in speciation in the face of gene flow.
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| 9. |
- Rova, Emma, 1978-
(författare)
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The role of Assortative Mating in the Initial Stages of Sympatric and Parapatric Speciation
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Divergence in the face of gene flow is perhaps the most wildly disputed subject among researchers through time. The debate is an old one and we find its origin as far back as the era of Darwin. The theories dealing with sympatric and parapatric speciation, its processes and ecological conditions, are numerous and the empirical data supporting the ideas is constantly growing. However, the reach of a consensus almost seem as distant as ever. Two fundamental prerequisites can be identified for the evolution of divergence with gene flow, the act of disruptive selection, and the development of assortative mating. A set of models in which speciation with gene flow seem particularly likely is when a shift occurs in host preference in phytophagous insects and mating takes place on the host. In the work behind this thesis, the role of assortative mating in the initial stages of sympatric and parapatric speciation has been studied, as has the interaction between assortative mating and inbreeding and how it effects speciation in small sympatric populations, an aspect not much attended to earlier in the literature. My results show that assortative mating based on resource preference, can evolve rapidly upon secondary contact, and even in parapatric populations with a migration rate of 8% (13-15 individuals) per generation. However for assortative mating to be maintained selection against hybrids is needed. My results also suggests that small inbred populations have a hard time coping with strong assortative mating an as a consequence tend to relax their mating preferences to avoid inbreeding depression. Based on these results, I advocate for the importance of considering not only assortative mating in itself, but also the joint effects of assortative mating and inbreeding when dealing with theories of speciation with gene flow.
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| 10. |
- Aho, Teija, et al.
(författare)
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Impacts of effective population size on genetic diversity and relatedness in hatchery reared Brown trout (Salmo trutta L.)
- 2006
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Ingår i: Aquaculture. - : Elsevier BV. - 0044-8486 .- 1873-5622. ; 253:1-4, s. 244-248
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Tidskriftsartikel (refereegranskat)abstract
- Many populations of brown trout are managed by hatchery breeding and supportive release. Using a limited number of individuals as founders creates a bottleneck, which can lead to loss of genetic diversity in a population. In this study 17 populations of hatchery-reared brown trout were examined genetically using microsatellite markers. Genetic variation measured as gene diversity and allelic richness were analysed and the effects of effective population size of founders and time since founding on these parameters were explored. Allelic richness and gene diversity decreased with increasing time since founding of the stock, and there was a negative relationship between current effective population size and time since founding. Allelic richness was positively correlated with effective population size at founding. The results indicate that considerations concerning effective population size in hatcheries must be taken seriously to promote high levels of genetic variation among individuals and minimise loss of genetic diversity.
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