| 1. |
- Erkenstam, Nina Hellström, 1976, et al.
(författare)
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Temporal Characterization of Microglia/Macrophage Phenotypes in a Mouse Model of Neonatal Hypoxic-Ischemic Brain Injury.
- 2016
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Ingår i: Frontiers in cellular neuroscience. - : Frontiers Media SA. - 1662-5102. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Immune cells display a high degree of phenotypic plasticity, which may facilitate their participation in both the progression and resolution of injury-induced inflammation. The purpose of this study was to investigate the temporal expression of genes associated with classical and alternative polarization phenotypes described for macrophages and to identify related cell populations in the brain following neonatal hypoxia-ischemia (HI). HI was induced in 9-day old mice and brain tissue was collected up to 7 days post-insult to investigate expression of genes associated with macrophage activation. Using cell-markers, CD86 (classic activation) and CD206 (alternative activation), we assessed temporal changes of CD11b(+) cell populations in the brain and studied the protein expression of the immunomodulatory factor galectin-3 in these cells. HI induced a rapid regulation (6 h) of genes associated with both classical and alternative polarization phenotypes in the injured hemisphere. FACS analysis showed a marked increase in the number of CD11b(+)CD86(+) cells at 24 h after HI (+3667%), which was coupled with a relative suppression of CD11b(+)CD206(+) cells and cells that did not express neither CD86 nor CD206. The CD11b(+)CD206(+) population was mixed with some cells also expressing CD86. Confocal microscopy confirmed that a subset of cells expressed both CD86 and CD206, particularly in injured gray and white matter. Protein concentration of galectin-3 was markedly increased mainly in the cell population lacking CD86 or CD206 in the injured hemisphere. These cells were predominantly resident microglia as very few galectin-3 positive cells co-localized with infiltrating myeloid cells in Lys-EGFP-ki mice after HI. In summary, HI was characterized by an early mixed gene response, but with a large expansion of mainly the CD86 positive population during the first day. However, the injured hemisphere also contained a subset of cells expressing both CD86 and CD206 and a large population that expressed neither activation marker CD86 nor CD206. Interestingly, these cells expressed the highest levels of galectin-3 and were found to be predominantly resident microglia. Galectin-3 is a protein involved in chemotaxis and macrophage polarization suggesting a novel role in cell infiltration and immunomodulation for this cell population after neonatal injury.
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| 5. |
- Qvarnström, Anna, et al.
(författare)
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Life-history divergence facilitates regional coexistence of competing Ficedula flycatchers
- 2009
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 90:7, s. 1948-1957
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Tidskriftsartikel (refereegranskat)abstract
- Regional coexistence of ecologically similar species is facilitated when fluctuations in environmental conditions favor different species at different times or places. However, why species with similar ecology should vary in their response to environmental change is unclear. In this study, we explore the role of a life-history divergence in causing changes in relative fitness across environmental conditions experienced by populations of two closely related Ficedula flycatchers on the Baltic island of Oland, Sweden. We compared patterns of nestling survival between Pied (Ficedula hypoleuca) and Collared (F. albicollis) Flycatchers in relation to two factors known to influence the environment experienced by nestlings: natural variation in their parents' onset of breeding and artificial manipulation of the brood size. Possible differences in the location of the nests (i.e., microhabitat differences) or in habitat use (i.e., feeding patterns) by the adult birds were controlled for by partial cross-fostering of young between the two species. We found that nestling mortality was relatively higher among Collared Flycatchers and that this difference increased with later breeding. Mass gain, which predicted survival probability, of nestling Collared Flycatchers did not respond to the seasonal decline in environmental conditions when they were raised in nests with reduced brood size (i.e., where sibling competition was experimentally reduced). This latter result suggests that the smaller clutch size of Collared Flycatchers reflects an adaptive adjustment to their offspring's higher sensitivity to environmental change. We discuss the possibility that the divergence in life-history traits between the two species represents adaptation to different environments experienced during their recent evolutionary history. We conclude that the survival of nestling Collared Flycatchers is more sensitive to harsh environment and that this is likely to limit where and when the more aggressive Collared Flycatchers are able to displace Pied Flycatchers. Our results provide support for models of species coexistence that emphasize the importance of spatial or temporal heterogeneity in relative fitness or life-history divergence. More precisely, our results demonstrate that variation in life-history adaptations may result in changes in relative fitness of species across environments despite their use of similar resources.
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| 6. |
- Qvarnström, Anna, et al.
(författare)
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Species divergence in offspring begging intensity : Difference in need or manipulation of parents?
- 2007
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 274:1612, s. 1003-1008
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Tidskriftsartikel (refereegranskat)abstract
- Conflicts over the delivery and sharing of food among family members are expected to lead to evolution of exaggerated offspring begging for food. Coevolution between offspring begging intensity and parent response depends on the genetic architecture of the traits involved. Given a genetic correlation between offspring begging intensity and parental response, there may be fast and arbitrary divergence in these behaviours between populations. However, there is limited knowledge about the genetic basis of offspring solicitation and parental response and whether these traits are genetically correlated. In this study, we performed a partial cross-fostering experiment of young between pied and collared flycatchers (Ficedula hypoleuca and Ficedula albicollis) and recorded the behaviour of individual offspring and their (foster)parents. We found that nestling collared flycatchers reached a higher phenotypic quality, estimated both as mass at fledging and as intensity of their T-lymphocyte-mediated immune response when raised by heterospecific foster parents. However, although collared flycatchers begged relatively more intensively, we found no evidence of corresponding higher resistance (i.e. lower feeding rate) of adult collared flycatchers than of adult pied flycatchers. Thus, the difference in offspring begging intensity between the two species seems not to be a result of a difference in escalation of the parent–offspring conflict. Instead, the species' divergence in exaggeration of offspring begging intensity ‘honestly’ matches a difference between the species in offspring need. This interpretation is strengthened by the fact that the difference in begging intensity between the two species increased as the season progressed, coinciding with the higher sensitivity of nestling collared flycatchers to the seasonal decline in food availability. Thus, the behavioural differentiation appears to be a direct consequence of a life-history differentiation (offspring growth patterns).
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| 7. |
- Saether, Stein Are, et al.
(författare)
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Sex chromosome-linked species recognition and evolution of reproductive isolation in flycatchers
- 2007
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 318:5847, s. 95-97
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Tidskriftsartikel (refereegranskat)abstract
- Interbreeding between species (hybridization) typically produces unfit offspring. Reduced hybridization should therefore be favored by natural selection. However, this is difficult to accomplish because hybridization also sets the stage for genetic recombination to dissociate species-specific traits from the preferences for them. Here we show that this association is maintained by physical linkage (on the same chromosome) in two hybridizing Ficedula flycatchers. By analyzing the mating patterns of female hybrids and cross-fostered offspring, we demonstrate that species recognition is inherited on the Z chromosome, which is also the known location of species-specific male plumage traits and genes causing low hybrid fitness. Limited recombination on the Z chromosome maintains associations of Z-linked genes despite hybridization, suggesting that the sex chromosomes may be a hotspot for adaptive speciation.
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| 8. |
- Svedin, Nina, et al.
(författare)
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Natural and sexual selection against hybrid flycatchers
- 2008
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 275:1635, s. 735-744
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Tidskriftsartikel (refereegranskat)abstract
- While sexual selection is generally assumed to quickly cause or strengthen prezygotic barriers between sister species, its role in causing postzygotic isolation, through the unattractiveness of intermediate hybrids, is less often examined. Combining 24 years of pedigree data and recently developed species-specific molecular markers from collared (Ficedula albicollis) and pied (Ficedula hypoleuca) flycatchers and their hybrids, we were able to quantify all key components of fitness. To disentangle the relative role of natural and sexual selection acting on F1 hybrid flycatchers, we estimated various fitness components, which when combined represent the total lifetime reproductive success of F1 hybrids, and then compared the different fitness components of F1 hybrids to that of collared flycatchers. Female hybrid flycatchers are sterile, with natural selection being the selective force involved, but male hybrids mainly experienced a reduction in fitness through sexual selection (decreased pairing success and increased rate of being cuckolded). To disentangle the role of sexual selection against male hybrids from a possible effect of genetic incompatibility (on the rate of being cuckolded), we compared male hybrids with pure-bred males expressing intermediate plumage characters. Given that sexual selection against male hybrids is a result of their intermediate plumage, we expect these two groups of males to have a similar fitness reduction. Alternatively, hybrids have reduced fitness owing to genetic incompatibility, in which case their fitness should be lower than that of the intermediate pure-bred males. We conclude that sexual selection against male hybrids accounts for approximately 75% of the reduction in their fitness. We discuss how natural and sexual selection against hybrids may have different implications for speciation and conclude that reinforcement of reproductive barriers may be more likely when there is sexual selection against hybrids.
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| 9. |
- Svedin, Nina, 1971-
(författare)
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Natural and Sexual Selection in a Natural Hybrid Zone of Ficedula Flycatchers
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Speciation can be viewed as the formation of reproductive barriers between different populations. This thesis investigates patterns of natural and sexual selection shaping reproductive barriers between two hybridizing flycatchers (i.e. collared – and pied flycatchers). Behaviorally driven sexual isolation depends on both the availability of conspecific mates and on discrimination ability of individuals. My results demonstrate that these two factors may also interact. Discrimination abilities may change in response to the relative frequency of two interbreeding species. The underlying reason appears to be that male pied flycatchers have a song that incorporates more elements of the song characteristics of male collared flycatchers into their own song repertoires when occurring in areas inhabited predominantly by collared flycatchers. I investigated selection pressures acting on hybrids. In migratory species, hybrid fitness might be reduced as a consequence of intermediate suboptimal migration routes (extrinsic post zygotic isolation). Comparison of stable isotope signatures of revealed that parental species have separate wintering grounds, but hybrids appear to winter at the same location as pied flycatchers. A possible dominance effect in the inheritance of migration direction may hence reduce this potential cost. This interpretation is supported by the absence of a reduction in juvenile to adult survival of hybrids. By further comparing male hybrid fitness to that of the parental species, using lifehistory data, I demonstrate that hybrid males experience a moderate reduction in fitness (mainly through a sexually selected disadvantage). Sexual selection acting on male hybrids can play a major role in the speciation process because when the same characters affect assortative mating as well as hybrid fitness, reinforcement of reproductive barriers becomes more likely. Even when reproductive isolation is completed- the fate of newly formed species may be uncertain since they may strongly compete for ecological space. Long-term persistence of ecologically similar, species requires that there are spatial or temporal variation in their relative fitness. The growth of nestling pied flycatchers is less affected by harsh environmental conditions. We suggest that a regional co-existence of the two flycatcher species is due to a lifehistory trade-off between interference competitive ability and robustness to a harsh conditions. Overall, the studies in this thesis reveal the complexity of the interactions between mate choice and competition in shaping sexual signals. Furthermore, it suggests that natural selection is moderate on hybrid males and that sexual selection may have strong implications for the maintenance of species integrity.
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