| 1. |
- Kivelä, Sami M., et al.
(författare)
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Adaptive developmental plasticity in a butterfly : mechanisms for size and time at pupation differ between diapause and direct development
- 2017
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Ingår i: Biological Journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4066 .- 1095-8312. ; 122:1, s. 46-57
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Tidskriftsartikel (refereegranskat)abstract
- Diapause (overwintering) and direct development are alternative developmental pathways in temperate insects. Diapause necessitates physiological preparations for dormancy, while direct development is associated with strong time constraints, resulting in selection for fast development under the direct development pathway. Physiological and behavioural preparations for pupation contribute to development time, so divergent selection in them is expected between the alternative developmental pathways. Critical mass for pupation induction is a central physiological parameter for the pupation process. Here, we compare the critical masses and the characteristics of the wandering stage - wandering taking place after the cessation of growth and before pupation - between diapausing and directly developing larvae in the butterfly Pieris napi. Critical mass estimation succeeded only for diapausing individuals, among which it was lower in females than in males, indicating an inter-pathway difference in the physiology of critical mass. Directly developing individuals wandered for a shorter time and distance and lost less mass before pupation than diapausing individuals. These physiological and behavioural differences represent adaptive phenotypic plasticity and contribute to fast development under direct development. Thus, the observed developmental plasticity in physiology offers a mechanistic explanation for adaptive life-history variation between alternative developmental pathways and sexual dimorphism.
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| 2. |
- Kivelä, Sami M., et al.
(författare)
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Comparative analysis of larval growth in Lepidoptera reveals instar-level constraints
- 2020
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Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 34:7, s. 1391-1403
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Tidskriftsartikel (refereegranskat)abstract
- Juvenile growth trajectories evolve via the interplay of selective pressures on age and size at maturity, and developmental constraints. In insects, the moulting cycle is a major constraint on larval growth trajectories. Surface area to volume ratio of a larva decreases during growth, so renewal of certain surfaces by moulting is likely needed for the maintenance of physiological efficiency. A null hypothesis of isometry, implied by Dyar's Rule, would mean that the relative measures of growth remain constant across moults and instars. We studied ontogenetic changes and allometry in instar-specific characteristics of larval growth in 30 lepidopteran species in a phylogenetic comparative framework. Relative instar-specific mass increments (RMI) typically, but not invariably, decreased across instars. Ontogenetic change in RMIs varied among families with little within-family variation. End-of-instar growth deceleration (GD) became stronger with increasing body size across instars. Across-instar change in GD was conserved across taxa. Ontogenetic allometry was generally non-isometric in both RMI and GD. Results indicate that detailed studies on multiple species are needed for generalizations concerning growth trajectory evolution. Developmental and physiological mechanisms affecting growth trajectory evolution show different degrees of evolutionary conservatism, which must be incorporated into models of age and size at maturation.
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| 3. |
- Kivelä, Sami M., et al.
(författare)
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Developmental plasticity in metabolism but not in energy reserve accumulation in a seasonally polyphenic butterfly
- 2019
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 0022-0949 .- 1477-9145. ; 222:13
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of seasonal polyphenisms (discrete phenotypes in different annual generations) associated with alternative developmental pathways of diapause (overwintering) and direct development is favoured in temperate insects. Seasonal life history polyphenisms are common and include faster growth and development under direct development than in diapause. However, the physiological underpinnings of this difference remain poorly known despite its significance for understanding the evolution of polyphenisms. We measured respiration and metabolic rates through the penultimate and final larval instars in the butterfly Pieris napi and show that directly developing larvae grew and developed faster and had a higher metabolic rate than larvae entering pupal diapause. The metabolic divergence appeared only in the final instar, that is, after induction of the developmental pathway that takes place in the penultimate instar in P. napi. The accumulation of fat reserves during the final larval instar was similar under diapause and direct development, which was unexpected as diapause is predicted to select for exaggerated reserve accumulation. This suggests that overwinter survival in diapause does not require larger energy reserves than direct development, likely because of metabolic suppression in diapause pupae. The results, nevertheless, demonstrate that physiological changes coincide with the divergence of life histories between the alternative developmental pathways, thus elucidating the proximate basis of seasonal life history polyphenisms.
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| 4. |
- Kivelä, Sami M., et al.
(författare)
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Evolution of alternative insect life histories in stochastic seasonal environments
- 2016
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 6:16, s. 5596-5613
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Tidskriftsartikel (refereegranskat)abstract
- Deterministic seasonality can explain the evolution of alternative life history phenotypes (i.e., life history polyphenism) expressed in different generations emerging within the same year. However, the influence of stochastic variation on the expression of such life history polyphenisms in seasonal environments is insufficiently understood. Here, we use insects as a model and explore (1) the effects of stochastic variation in seasonality and (2) the life cycle on the degree of life history differentiation among the alternative developmental pathways of direct development and diapause (overwintering), and (3) the evolution of phenology. With numerical simulation, we determine the values of development (growth) time, growth rate, body size, reproductive effort, adult life span, and fecundity in both the overwintering and directly developing generations that maximize geometric mean fitness. The results suggest that natural selection favors the expression of alternative life histories in the alternative developmental pathways even when there is stochastic variation in seasonality, but that trait differentiation is affected by the developmental stage that overwinters. Increasing environmental unpredictability induced a switch to a bet-hedging type of life history strategy, which is consistent with general life history theory. Bet-hedging appeared in our study system as reduced expression of the direct development phenotype, with associated changes in life history phenotypes, because the fitness value of direct development is highly variable in uncertain environments. Our main result is that seasonality itself is a key factor promoting the evolution of seasonally polyphenic life histories but that environmental stochasticity may modulate the expression of life history phenotypes.
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| 5. |
- Kivelä, Sami M., et al.
(författare)
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Thermal plasticity of growth and development varies adaptively among alternative developmental pathways
- 2015
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Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 69:9, s. 2399-2413
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Tidskriftsartikel (refereegranskat)abstract
- Polyphenism, the expression of discrete alternative phenotypes, is often a consequence of a developmental switch. Physiological changes induced by a developmental switch potentially affect reaction norms, but the evolution and existence of alternative reaction norms remains poorly understood. Here, we demonstrate that, in the butterfly Pieris napi (Lepidoptera: Pieridae), thermal reaction norms of several life history traits vary adaptively among switch-induced alternative developmental pathways of diapause and direct development. The switch was affected both by photoperiod and temperature, ambient temperature during late development having the potential to override earlier photoperiodic cues. Directly developing larvae had higher development and growth rates than diapausing ones across the studied thermal gradient. Reaction norm shapes also differed between the alternative developmental pathways, indicating pathway-specific selection on thermal sensitivity. Relative mass increments decreased linearly with increasing temperature and were higher under direct development than diapause. Contrary to predictions, population phenology did not explain trait variation or thermal sensitivity, but our experimental design probably lacks power for finding subtle phenology effects. We demonstrate adaptive differentiation in thermal reaction norms among alternative phenotypes, and suggest that the consequences of an environmentally dependent developmental switch primarily drive the evolution of alternative thermal reaction norms in P. napi.
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| 6. |
- Kivelä, Sami M., et al.
(författare)
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Towards a mechanistic understanding of insect life history evolution : oxygen-dependent induction of moulting explains moulting sizes
- 2016
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Ingår i: Biological Journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4066 .- 1095-8312. ; 117:3, s. 586-600
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Tidskriftsartikel (refereegranskat)abstract
- Moults characterise insect growth trajectories, typically following a consistent pattern known as Dyar's rule; proportional size increments remain constant across inter-instar moults. Empirical work suggests that oxygen limitation triggers moulting. The insect respiratory system, and its oxygen supply capacity, grows primarily at moults. It is hypothesized that the oxygen demand increases with increasing body mass, eventually meeting the oxygen supply capacity at an instar-specific critical mass where moulting is triggered. Deriving from this hypothesis, we develop a novel mathematical model for moulting and growth in insect larvae. Our mechanistic model has great success in predicting moulting sizes in four butterfly species, indirectly supporting a size-dependent mechanism underlying moulting. The results demonstrate that an oxygen-dependent induction of moulting mechanism would be sufficient to explain moulting sizes in the study species. Model predictions deviated slightly from Dyar's rule, the deviations being typically negligible within the present data range. The developmental decisions (e.g. moulting) made by growing larvae significantly affect age and size at maturity, which has important life history implications. The successful modelling of moulting presented here provides a novel framework for the development of realistic insect growth models, which are required for a better understanding of life history evolution.
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| 7. |
- Lee, Kyung Min, et al.
(författare)
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Information Dropout Patterns in Restriction Site Associated DNA Phylogenomics and a Comparison with Multilocus Sanger Data in a Species-Rich Moth Genus
- 2018
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Ingår i: Systematic Biology. - : Oxford University Press (OUP). - 1063-5157 .- 1076-836X. ; 67:6, s. 925-939
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Tidskriftsartikel (refereegranskat)abstract
- A rapid shift from traditional Sanger sequencing-based molecular methods to the phylogenomic approach with large numbers of loci is underway. Among phylogenomic methods, restriction site associated DNA (RAD) sequencing approaches have gained much attention as they enable rapid generation of up to thousands of loci randomly scattered across the genome and are suitable for nonmodel species. RAD data sets however suffer from large amounts of missing data and rapid locus dropout along with decreasing relatedness among taxa. The relationship between locus dropout and the amount of phylogenetic information retained in the data has remained largely uninvestigated. Similarly, phylogenetic hypotheses based on RAD have rarely been compared with phylogenetic hypotheses based on multilocus Sanger sequencing, even less so using exactly the same species and specimens. We compared the Sanger-based phylogenetic hypothesis (8 loci; 6172 bp) of 32 species of the diverse moth genus Eupithecia (Lepidoptera, Geometridae) to that based on double-digest RAD sequencing (3256 loci; 726,658 bp). We observed that topologies were largely congruent, with some notable exceptions that we discuss. The locus dropout effect was strong. We demonstrate that number of loci is not a precise measure of phylogenetic information since the number of single-nucleotide polymorphisms (SNPs) may remain low at very shallow phylogenetic levels despite large numbers of loci. As we hypothesize, the number of SNPs and parsimony informative SNPs (PIS) is low at shallow phylogenetic levels, peaks at intermediate levels and, thereafter, declines again at the deepest levels as a result of decay of available loci. Similarly, we demonstrate with empirical data that the locus dropout affects the type of loci retained, the loci found in many species tending to show lower interspecific distances than those shared among fewer species. We also examine the effects of the numbers of loci, SNPs, and PIS on nodal bootstrap support, but could not demonstrate with our data our expectation of a positive correlation between them. We conclude that RAD methods provide a powerful tool for phylogenomics at an intermediate phylogenetic level as indicated by its broad congruence with an eight-gene Sanger data set in a genus of moths. When assessing the quality of the data for phylogenetic inference, the focus should be on the distribution and number of SNPs and PIS rather than on loci.
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| 8. |
- Merckx, Thomas, et al.
(författare)
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Urbanization extends flight phenology and leads to local adaptation of seasonal plasticity in Lepidoptera
- 2021
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 118:40
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Tidskriftsartikel (refereegranskat)abstract
- Urbanization is gaining force globally, which challenges biodiversity, and it has recently also emerged as an agent of evolutionary change. Seasonal phenology and life cycle regulation are essential processes that urbanization is likely to alter through both the urban heat island effect (UHI) and artificial light at night (ALAN). However, how UHI and ALAN affect the evolution of seasonal adaptations has received little attention. Here, we test for the urban evolution of seasonal life-history plasticity, specifically changes in the photoperiodic induction of diapause in two lepidopterans, Pieris napi (Pieridae) and Chiasmia clathrata (Geometridae). We used long-term data from standardized monitoring and citizen science observation schemes to compare yearly phenological flight curves in six cities in Finland and Sweden to those of adjacent rural populations. This analysis showed for both species that flight seasons are longer and end later in most cities, suggesting a difference in the timing of diapause induction. Then, we used common garden experiments to test whether the evolution of the photoperiodic reaction norm for diapause could explain these phenological changes for a subset of these cities. These experiments demonstrated a genetic shift for both species in urban areas toward a lower daylength threshold for direct development, consistent with predictions based on the UHI but not ALAN. The correspondence of this genetic change to the results of our larger-scale observational analysis of in situ flight phenology indicates that it may be widespread. These findings suggest that seasonal life cycle regulation evolves in urban ectotherms and may contribute to ecoevolutionary dynamics in cities.
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| 9. |
- Morinay, Jennifer, et al.
(författare)
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Heterospecific nest site copying behavior in a wild bird : assessing the influence of genetics and past experience on a joint breeding phenotype
- 2018
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Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media SA. - 2296-701X. ; 5:167
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Tidskriftsartikel (refereegranskat)abstract
- Breeding site selection is often a joint decision of pair members in species with biparental care and the experience of both pair members may influence the use of information for site selection. Nevertheless, quantitative genetics of joint information use for site selection remains unexplored so far. We used an experimental approach to quantify the relative importance of genetics (heritability) and past experience (age, familiarity with the environment, previous breeding success, previous information use) in heterospecific social information use for nest site selection in wild collared flycatchers (Ficedula albicollis). Flycatchers collect social information from resident tits for nest site selection. We created an apparent preference of tits for a novel nest site feature and recorded choices of flycatchers (copying or rejecting the tit preference). Copying behavior was stronger for naive individuals but also differed between years, which could be explained by contrasting seasonality in the demonstrator species. Past experience as reflected by age affected subsequent use of social information: pairs with a yearling male were more likely to copy the heterospecific preference than pairs with older immigrant males. There was no general pattern in successive individual choices over the years. Accordingly, individual repeatability in copying tit preference was very low. At the pair level, we estimated sex-specific direct and indirect genetic effects on the joint nest site decision and found no sex-specific heritability and no cross-sex genetic correlation. Our results confirm the importance of past experience for social information use and suggest that social information use is highly plastic and most likely not genetically inherited in collared flycatchers. Whether individuals use social information should be related to environmentally-induced changes in the quality of information and thus be context-dependent. Selection may therefore act on the ability to optimally use social information in varying environments and on the processes underlying such adjustment, such as learning, rather than the use of information itself.
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| 10. |
- Raitanen, Jani, et al.
(författare)
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Attraction to conspecific eggs may guide oviposition site selection in a solitary insect
- 2014
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Ingår i: Behavioral Ecology. - : Oxford University Press (OUP). - 1045-2249 .- 1465-7279. ; 25:1, s. 110-116
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Tidskriftsartikel (refereegranskat)abstract
- Conspecific attraction is a form of social information use whereby individuals are attracted to the presence of conspecifics because they may indicate high-quality sites or resources. Conspecific attraction results in aggregation of individuals with similar needs and may therefore intensify competition, in particular, at high densities. Thus, the occurrence and strength of conspecific attraction may be dependent on density, but the effects of predicted intensity of future competition for resources on individual decisions have rarely been quantified. We studied realized early fecundity and oviposition site selection in the butterfly Pieris napi in relation to a density gradient of conspecific eggs on available host plants in an explicit laboratory experiment. Relying on conspecific assessment of host quality is expected to select for conspecific attraction, whereas competition avoidance is expected to select for avoidance of high conspecific densities. Presence of conspecific cues did not substantially affect realized fecundity as females exposed to an environment containing conspecific cues laid approximately equal number of eggs as females exposed to an environment lacking such cues. Instead, when females were able to choose among host plants with or without previously laid conspecific eggs, they preferred plants that already carried eggs in relation to egg-free host plants, independently of the initial egg density. Indeed, the maintenance of conspecific attraction, rather than avoidance, in P. napi implies that the possible benefits of conspecific attraction in oviposition site selection may outweigh the costs of competition in the wild.
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