| 1. |
- Ittonen, Mats, 1989-
(författare)
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Life history evolution during a climate-driven butterfly range expansion
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate change pushes species polewards and upwards – as temperatures rise, species move to areas that were previously too cold for them. During range expansions, species encounter unfamiliar environmental conditions, which may require evolutionary adaptation, but expanding populations may often be hampered by their genetic and demographic properties. Whether range-expanding populations can adapt may greatly affect species distributions, but the question is largely unexplored for native species expanding in response to climate change. In seasonal environments, organisms must endure harsh conditions and synchronise growth and reproduction with the presence of food and mates. To time their life cycles, many animals and plants use seasonal changes in daylength. Insects typically overwinter in diapause (dormancy with paused development and suppressed metabolism), which is induced by short days well before winter. But across-latitude differences in daylength pose challenges for latitudinal range expansions. I focus on whether traits related to seasonal timing and winter survival have evolved during range expansion of the wall brown butterfly (Lasiommata megera) in Sweden.In Chapter I, I confirmed that the wall brown has, in 2000–2020, expanded northwards along the eastern and western coasts of Sweden, and in Chapter II, I demonstrated that these parallel expansions have proceeded independently from the south, in isolation from each other. Laboratory experiments in Chapter I revealed that caterpillars from northern populations have evolved to correctly interpret their local daylength cues. This rapid evolution, repeated along two range expansions, indicates that latitudinal differences in daylength may seldom hinder insect range expansions. In Chapter II, I found that northern range margin populations have lower genetic variation than southern ones but are unlikely to have received much locally maladaptive gene flow from the south. Further, a genomic scan suggested that the parallel phenotypic changes have evolved through non-parallel genetic changes. In Chapter III, a laboratory experiment showed lack of local adaptation to different winters, in contrast to the rapid evolution of diapause timing. Overall winter survival was low in the coldest treatment, indicating that winter temperatures limit the range.In Chapter IV, I studied diapause induction, growth rate, and winter survival in a field setting. Almost all individuals entered diapause, with only minimal impact from the among-population differences found in Chapter I. These evolved differences could stem from natural selection on earlier parts of the generation, which experience longer days than our experiment captured. Further, individuals of northern descent grew faster than those from the south. This could help them grow large enough before winter, yet pre-winter mass did not affect winter survival. This time, natural selection may favour high growth rates in late-hatching individuals with less time to grow before winter. Like in Chapter III, there was no evidence for evolution of improved winter survival, and survival dropped markedly when transplanting individuals outside of the current range.Despite rapid evolution in two traits, cold winters limit the wall brown’s expansion. To predict range expansions, we must pinpoint their drivers, study trait evolution relevant to these drivers, and recognize that traits that are crucial in different seasons may vary in evolvability.
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| 2. |
- Posledovich, Diana, 1984-
(författare)
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Effects of climate on phenological synchrony between butterflies and their host plants
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Shifts in species’ phenologies and phenological asynchronies between the interacting organisms have received a lot of attention in the context of climate change. Changes in temporal overlap between species, caused by phenological asynchrony, make species depending on one another become so separated in time that they can no longer interact. This may have important consequences both for single species, like fluctuations in abundances, and for the functioning of whole communities by creating mismatches between trophic levels and rearrangements of community structure. This thesis focuses on the impact of temperatures on spring timing and phenological synchrony in a herbivorous insect – host plant system, consisting of the orange tipbutterfly Anthocharis cardamines and five of its Brassicaceae host plant species. Paper I demonstrates that diapause duration and winter thermal conditions can determine the timing of spring emergence in the herbivore, and these traits may differ between species with different feeding strategies. In paper II we show that thermal reaction norms of post-winterdevelopment of A. cardamines display cogradient latitudinal variation.Paper III shows that temperature-mediated phenological plasticity of A. cardamines butterflies and a majority of the most used host plant species is similar within populations originating from different latitudes. Thus, the species’ timing appeared well conserved in response to thermal variation. In paper IV we explored the importance of the butterfly’s adult emergence and thermal conditions on the succeeding part of the butterfly’s life-cycle – larval development. The outcome from the interaction was examined for both the insect and the plant side. The degree in phenological overlap between the female butterflies and host plants as well as temperatures during larval development were found to influence larval development but had no effect on plant reproductive fitness. The four papers of the presented thesis demonstrate that developmental preadaptations, evolvedin a herbivore to maintain phenological synchrony with host plants across yearly variation of spring conditions, can prevent disruption of the interaction under a wide range of temperatures. This indicates that temporary constrained interactions are not always vulnerable to decoupling, particularly if they involve generalist strategy.
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| 3. |
- Moradinour, Zahra, 1989-
(författare)
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The sensory morphology of insect pollinators : From structure to behaviour and ecology
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Insect pollinators play an important role in balancing our ecosystems and maintaining plant and food diversity. Due to anthropogenic activities such as global warming, habitat loss and degradation, pesticides, and pathogens, many pollinator populations have been undergoing drastic declines in recent decades. Sudden changes in environmental conditions may lead to selection pressures to alter sensory systems, their structures and functions, and, consequently, behaviour. Despite the multitude of studies on insect pollinators and their population declines, these effects are often overlooked. To address this knowledge gap, I studied the morphology of sensory systems in butterflies and bumblebees – two pollinator groups found in temperate regions – from the aspects of development, behaviour, ecology and adaptation. In Chapter I, I used allometry to study how investment into sensory systems varies within and between different sexes of the butterfly Pieris napi. I measured the size and other parameters of sensory traits including eyes, antennae, proboscis, and wings. I showed that sensory system investment varies between sexes and only antennal length and wing size increase allometrically with body size. These findings suggest that not all sensory organs scale with body size and energetic investment between them can vary among sexes of the same species. In Chapter II, I explored the effect of a sub-optimal temperature on the development and morphology of sensory systems in P. napi, an ectothermic solitary insect. I exposed the pupae of P. napi to 23°C (optimal temperature) and 32°C (sub-optimal temperature) and measured their body and sensory organ size after emergence. I found that the mortality rate was higher at the suboptimal temperature and that the eclosion time decreased. Also, body and proboscis size decreased in both sexes, while antennal length decreased only in males. These results show that global warming can have negative consequences for the survival of butterflies and affect the size of their sensory systems potentially by accelerating the developmental process. In Chapter III, we studied the effect of heatwave-like temperatures on the sensory systems and behaviour of another insect pollinator, Bombus terrestris. Our results revealed that development in suboptimal temperatures had a negative impact on behavioural responses of bumblebee workers. Interestingly, the elevated temperature did not have a significant effect on the size of their antennae, eyes and forewings. These findings indicate that an elevated developmental temperature can impair important behavioural responses to sensory stimuli without causing any visible changes in sensory organ morphology. In Chapter IV, I explored how well the qualitative light micro habitat associated with a distribution range of insects, matches with carefully measured quantitative values. I used three butterfly species (P. napi, Pararge aegeria, Vanessa atalanta) that are associated with different light habitats and have different dispersal ranges. The results showed that only P.napi distribution was affected by light intensity. Eye and brain neuropil investment varied among the three species. P. napi had highest eye size investment while V. atalanta had highest optic neuropils investment. These findings suggest that visual and neural investments could only in part be associated with quantitative and/or qualitative light micro habitat and dispersal in these species.
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| 4. |
- Rowiński, Piotr K., 1982-
(författare)
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Evolutionary consequences of maternal effects and stress
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Maternal effects occur when maternal environment or phenotype influence offspring phenotype, in addition to genetic contribution of the mother. As maternal effects often influence phenotypes that are under natural selection, they hence have evolutionary consequences. Further, the expression of both maternal effects and evolutionary potential has been argued to depend on environmental conditions, but the evidence of this dependency for the process of adaptation has been inconclusive. The main objective of this thesis was to investigate evolutionary consequences of maternal effects and stressful or variable environmental conditions.I started by performing a meta-analysis of quantitative genetic studies that investigated expression of additive genetic, maternal, and residual variance under both stressful and benign environmental conditions (Paper I). Data spanning over many animal taxa and stress types revealed that high levels of environmental stress correlated with increased expression of genetic and residual variances. However, against our predictions, maternal effects were relatively unaffected by stress.In Paper II and III, I explored the evolutionary divergences of traits previously shown to be under maternal control. Specifically, in Paper II, I performed a second meta-analysis, that investigated if parents of common frogs (Rana temporaria) influenced offspring development time to mediate the effects of time constraints, across a latitudinal cline. I found that reproductive delay in the parental generation correlated with decreased development time in tadpoles of northern R. temporaria populations, suggesting that parental effects may further decrease development time in populations from time-constrained environments.In Paper III, I used an annual killifish system, to explore if environmental unpredictability, measured by variation in precipitation during rainy season, correlated with maternally mediated variation in embryo development time (bet-hedging). Although I found significant among-species differences in variation in development time, there was no clear linear relationship between variation in development time and precipitation. The results suggest that either bet-hedging is not important for persistence in the unpredictable annual killifish habitats, or that other ecological factors, rather than precipitation unpredictability, influenced evolution of variation in development times.Lastly, I investigated if occurrence of placenta correlated with increased offspring brain size among poeciliid fish (Paper IV). In contrast to our prediction, I did not find any consistent differences in relative brain size between the fry of placental and non-placental species. It is possible that either the poeciliid placental structures do not have a sufficient capacity to transfer resources necessary for increased brain development, or that other factors, such as sexual selection, or differences in food abundance and competition, shaped brain evolution among poeciliids.In conclusion, the results of this thesis suggest that environmental stress may influence evolutionary potential by increasing genetic variation available for selection, that time-constrained habitats may be conducive to evolution of parental effects on offspring development times, and that maternal influence on offspring traits may be difficult to detect, as many ecological factors may potentially influence evolution of life-history and morphology traits.
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| 5. |
- Aalberg Haugen, Inger Marie, 1980-
(författare)
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The diapause switch : Evolution of alternative developmental pathways in a butterfly
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diapause decision is a classic example of a threshold switch mechanism with cascading effects on morphology, behaviour and life-history traits. This thesis addresses the downstream effects of the insect diapause switch, with the main focus on pathway-specific regulation of life-history traits, using the speckled wood butterfly (Pararge aegeria) as a study species. The ultimate pathway decision is made towards the end of larval development and allows the larvae to take into account up-to-date information from the environment about future conditions (Paper I, IV). However, already from an early point in development the larvae are sensitive to environmental cues and continuously adjust their growth trajectory in accordance to current information about the environmental conditions to be expected in future (Paper IV). An asymmetry in the ability to change from one developmental pathway to another at a late point in larval development suggests that the diapause and the direct pathway require different physiological preparations (Paper IV). Pathway-specific regulation of traits downstream of the diapause switch is maintained by ongoing selection. When the direct pathway is not regularly expressed, as with a shift from bivoltinism to univoltinism, relaxed selection on the unexpressed pathway leads to genetic drift and loss of protandry (Paper II, III). Natural populations display local adaptations in the diapause switch with an increase in critical daylengths as there is a gradual shift from bivoltinism to univoltinism (Paper III). This thesis highlights two aspects of the diapause decision, the determination of how and when this decision is made as well as the way the resulting pathways are moulded by selection in order to produce adaptive seasonal polyphenism in life-history traits.
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