| 1. |
- Lane, Jeffrey E., et al.
(författare)
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Phenological shifts in North American red squirrels : disentangling the roles of phenotypic plasticity and microevolution
- 2018
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Ingår i: Journal of Evolutionary Biology. - : WILEY. - 1010-061X .- 1420-9101. ; 31:6, s. 810-821
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Tidskriftsartikel (refereegranskat)abstract
- Phenological shifts are the most widely reported ecological responses to climate change, but the requirements to distinguish their causes (i.e. phenotypic plasticity vs. microevolution) are rarely met. To do so, we analysed almost two decades of parturition data from a wild population of North American red squirrels (Tamiasciurus hudsonicus). Although an observed advance in parturition date during the first decade provided putative support for climate change-driven microevolution, a closer look revealed a more complex pattern. Parturition date was heritable [h(2)=0.14 (0.07-0.21 (HPD interval)] and under phenotypic selection [=-0.14 +/- 0.06 (SE)] across the full study duration. However, the early advance reversed in the second decade. Further, selection did not act on the genetic contribution to variation in parturition date, and observed changes in predicted breeding values did not exceed those expected due to genetic drift. Instead, individuals responded plastically to environmental variation, and high food [white spruce (Picea glauca) seed] production in the first decade appears to have produced a plastic advance. In addition, there was little evidence of climate change affecting the advance, as there was neither a significant influence of spring temperature on parturition date or evidence of a change in spring temperatures across the study duration. Heritable traits not responding to selection in accordance with quantitative genetic predictions have long presented a puzzle to evolutionary ecologists. Our results on red squirrels provide empirical support for one potential solution: phenotypic selection arising from an environmental, as opposed to genetic, covariance between the phenotypic trait and annual fitness.
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| 2. |
- McFarlane, S. Eryn, et al.
(författare)
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Difference in plasticity of resting metabolic rate - the proximate explanation to different niche breadth in sympatric Ficedula flycatchers
- 2018
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 8:9, s. 4575-4586
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Tidskriftsartikel (refereegranskat)abstract
- Variation in relative fitness of competing recently formed species across heterogeneous environments promotes coexistence. However, the physiological traits mediating such variation in relative fitness have rarely been identified. Resting metabolic rate (RMR) is tightly associated with life history strategies, thermoregulation, diet use, and inhabited latitude and could therefore moderate differences in fitness responses to fluctuations in local environments, particularly when species have adapted to different climates in allopatry. We work in a long‐term study of collared (Ficedula albicollis) and pied flycatchers (Ficedula hypoleuca) in a recent hybrid zone located on the Swedish island of Öland in the Baltic Sea. Here, we explore whether differences in RMR match changes in relative performance of growing flycatcher nestlings across environmental conditions using an experimental approach. The fitness of pied flycatchers has previously been shown to be less sensitive to the mismatch between the peak in food abundance and nestling growth among late breeders. Here, we find that pied flycatcher nestlings have lower RMR in response to higher ambient temperatures (associated with low food availability). We also find that experimentally relaxed nestling competition is associated with an increased RMR in this species. In contrast, collared flycatcher nestlings did not vary their RMR in response to these environmental factors. Our results suggest that a more flexible nestling RMR in pied flycatchers is responsible for the better adaptation of pied flycatchers to the typical seasonal changes in food availability experienced in this hybrid zone. Generally, subtle physiological differences that have evolved when species were in allopatry may play an important role to patterns of competition, coexistence, or displacements between closely related species in secondary contact.
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| 3. |
- Sirkiä, Päivi M, et al.
(författare)
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Climate-driven build-up of temporal isolation within a recently formed avian hybrid zone.
- 2018
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Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 72:2, s. 363-374
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Tidskriftsartikel (refereegranskat)abstract
- Divergence in the onset of reproduction can act as an important source of reproductive isolation (i.e., allochronic isolation) between co-occurring young species, but evidence for the evolutionary processes leading to such divergence is often indirect. While advancing spring seasons strongly affect the onset of reproduction in many taxa, it remains largely unexplored whether contemporary spring advancement directly affects allochronic isolation between young species. We examined how increasing spring temperatures affected onset of reproduction and thereby hybridization between pied and collared flycatchers (Ficedula spp.) across habitat types in a young secondary contact zone. We found that both species have advanced their timing of breeding in 14 years. However, selection on pied flycatchers to breed earlier was weaker, resulting in a slower response to advancing springs compared to collared flycatchers and thereby build-up of allochronic isolation between the species. We argue that a preadaptation to a broader niche use (diet) of pied flycatchers explains the slower response to raising spring temperature, but that reduced risk to hybridize may contribute to further divergence in the onset of breeding in the future. Our results show that minor differences in the response to environmental change of co-occurring closely related species can quickly cause allochronic isolation.
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| 4. |
- Ålund, Murielle, et al.
(författare)
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Optimal sperm length for high siring success depends on forehead patch size in collared flycatchers
- 2018
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Ingår i: Behavioral Ecology. - : OXFORD UNIV PRESS INC. - 1045-2249 .- 1465-7279. ; 29:6, s. 1436-1443
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Tidskriftsartikel (refereegranskat)abstract
- Dominance over rivals, sexual attractiveness, and highly efficient ejaculates are 3 important contributors of male fertilization success but theories about how primary and secondary sexual characters may co-evolve largely remain to be tested. We investigated how variation in a sexual signal (forehead patch size) and sperm morphology jointly affected siring success of 70 males in a natural population of collared flycatchers. We show that the optimal sperm length to attain high relative fertilization success depended on the size of a male's secondary sexual character. Males with small forehead patches sired more offspring in their nest when they produced long sperm and vice-versa. These results are not compatible with theories based on simple relationships between display traits and sperm "quality" but imply that the optimal fertilization strategy (and hence optimal sperm traits) differs between males even in a predominantly socially monogamous population with moderate extra-pair paternity rates. Thus, a better knowledge of the complex chain of behavioural interactions between the sexes and their gametes is needed for a complete understanding of how sexual selection operates in nature.
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