17 research outputs found
Evolution of insect life histories in relation to time constraints in seasonal environments:polymorphism and clinal variation
Abstract
Both the length of the season that is favourable for insect growth and reproduction and the number of generations emerging per season (voltinism) increase with decreasing latitude. Thus, time constraints on reproduction and juvenile development decrease with decreasing latitude, except where voltinism changes and time constraints suddenly increase as the season must be shared with one more generation.
I studied the evolution of insect life histories in relation to time constraints from two perspectives: polymorphism and clinal variation. Life history polymorphism in seasonal environments was studied with the butterfly Pieris napi that has discrete life history strategies, and polymorphic natural populations. Experimental studies showed that asymmetric intraspecific larval competition and divergent timing of reproduction between the strategies may promote the maintenance of polymorphism. A simulation model showed that the divergent timing of reproduction between the strategies is sufficient to maintain polymorphism even in the absence of intraspecific competition.
Clinal variation was studied empirically with four geometrid moths (Cabera exanthemata, Cabera pusaria, Chiasmia clathrata and Lomaspilis marginata) and generally in theory. Due to latitudinal saw-tooth variation in time constraints, traditional theory predicts a saw-tooth cline in body size and development time. A common garden experiment with the four geometrid moths did not support the traditional theory even when a saw-tooth cline in body size was found, suggesting that the theory is based on unrealistic assumptions. A theoretical analysis showed that reproductive effort should be high in populations under intense time constraints and low in populations experiencing no time constraints, resulting in a saw-tooth cline. In the four geometrid moths, support for these predictions was found, although the observed clinal variation deviated from the predicted pattern.
The results imply that clinal variation is expected in almost any continuous life history trait, whereas polymorphism of different strategies may emerge when life histories fall into discrete categories. When inferring the evolution of a single trait, complex interdependencies among several traits should be considered, as well as the possibility that the time constraints are not similar for each generation in multivoltine populations.TiivistelmÀ
Hyönteisten kasvu ja kehitys ovat pÀÀsÀÀntöisesti mahdollisia vain kesÀn aikana. EtelÀÀn pÀin mentÀessÀ kesÀ pitenee, ja saman kesÀn aikana kehittyvien hyönteissukupolvien mÀÀrÀ kasvaa. KesÀn pituus aiheuttaa lisÀÀntymiseen ja toukkien kasvuun kohdistuvan aikarajoitteen, joka heikkenee etelÀÀn pÀin siirryttÀessÀ. Aikarajoite kuitenkin tiukkenee siellÀ, missÀ yksi uusi sukupolvi ehtii juuri kehittymÀÀn saman kesÀn aikana, sillÀ kesÀ on nyt jaettava useamman sukupolven kesken.
VÀitöstyössÀ tarkastelin hyönteisten elinkierto-ominaisuuksien evoluutiota suhteessa aikarajoitteisiin sekÀ diskreetin ettÀ jatkuvan muuntelun nÀkökulmista. DiskreettiÀ muuntelua tutkin lanttuperhosella (Pieris napi), jolla esiintyy diskreettejÀ elinkiertostrategioita. Kokeellisesti osoitin, ettÀ toukkien vÀlinen kilpailu on epÀsymmetristÀ, mikÀ yhdessÀ eri elinkiertostrategioiden erilaisen lisÀÀntymisen ajoittumisen kanssa voi yllÀpitÀÀ diskreettiÀ muuntelua. Simulaatiomalli osoitti, ettÀ erilaiset elinkiertostrategiat voivat sÀilyÀ populaatiossa pelkÀstÀÀn niiden erilaisen lisÀÀntymisen ajoittumisen ansiosta.
Elinkierto-ominaisuuksien jatkuvaa muuntelua tutkin neljÀn mittariperhosen (Cabera exanthemata, Cabera pusaria, Chiasmia clathrata ja Lomaspilis marginata) avulla ja teoreettisesti yleisellÀ tasolla. Aikaisempi teoria ennustaa ruumiinkoon ja kehitysajan muuntelevan sahalaitakuvion mukaisesti siirryttÀessÀ pohjoisesta etelÀÀn, koska aikarajoitteet muuntelevat samalla tavalla. TÀmÀ teoria perustunee epÀrealistisiin oletuksiin, koska kokeelliset tulokset eivÀt tukeneet teoriaa silloinkaan, kun mittariperhosten ruumiinkoko muunteli ennustetulla tavalla. Teoreettinen tutkimus osoitti, ettÀ myös lisÀÀntymispanostuksen tulisi muunnella sahalaitakuvion mukaisesti suhteessa kesÀn pituuteen siten, ettÀ se on korkeimmillaan siellÀ, missÀ aikarajoitteet ovat tiukat. Mittariperhosten tutkiminen antoi jossain mÀÀrin tukea tÀlle ennusteelle.
Tulosten perusteella jatkuvaa maantieteellistÀ muuntelua ennustetaan elinkierto-ominaisuuksille, jotka muuntelevat jatkuvalla asteikolla. Erilaiset elinkiertostrategiat voivat sen sijaan sÀilyÀ populaatiossa, jos elinkierto-ominaisuuksien muuntelu on diskreettiÀ. Eri ominaisuuksien monimutkaiset vuorovaikutukset sekÀ eri sukupolvien mahdollisesti kokemat erilaiset aikarajoitteet olisi syytÀ tuntea, kun tarkastelun kohteena on yksittÀisen ominaisuuden evoluutio
Evolution of searching effort for resources:a missing piece of the puzzle in the ideal free distribution paradigm
Abstract
Animals commonly search for information about available resources to select a breeding or foraging site or a mate. Searching can be costly, which is why even random selection of resources may pay off. However, the evolution of searching effort in relation to key ecological factors and its ecological consequences remain insufficiently understood. We build a model to analyze the evolution of searching effort for resources in relation to key ecological factors; the cost of information acquisition, the cost of competition and the distribution of resource qualities. Evolutionarily stable searching effort decreased with increasing cost of information acquisition, eventually resulting in a random choice of resources. With a very low cost of information acquisition, evolutionarily stable searching effort increased with increasing proportion of low-quality resources in the available resource distribution, while the opposite was predicted with a higher cost of information acquisition. Cost of competition had only a negligible effect on the evolution of searching effort, except that increasing cost of competition increased investment in information acquisition when a resource distribution was biased towards high-quality resources. Informed resource selection (above-zero investment in information acquisition) resulted in skewed distribution of individuals across resources. Consequently, expected fitness became more similar across resources with decreasing cost of information acquisition and associated increase in searching effort, thus approaching the prediction of the classical ideal free distribution (IFD) model stating that individuals distribute themselves so that fitness is invariant across resources. However, we predict a positive correlation between fitness and resource quality with biologically more realistic parameter values, contradicting the IFD model. Costly information acquisition may, thus, explain why IFD is not always found in empirical studies. Generally, our results imply that avoidance of poor choices is more important for the evolution of information acquisition strategies than making the very best choices
Developmental plasticity in metabolism but not in energy reserve accumulation in a seasonally polyphenic butterfly
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
Conceptual preferences can be transmitted via selective social information use between competing wild bird species
Abstract
Concept learning is considered a high-level adaptive ability. Thus far, it has been studied in laboratory via asocial trial and error learning. Yet, social information use is common among animals but it remains unknown whether concept learning by observing others occurs. We tested whether pied flycatchers (Ficedula hypoleuca) form conceptual relationships from the apparent choices of nest-site characteristics (geometric symbol attached to the nest-box) of great tits (Parus major). Each wild flycatcher female (n = 124) observed one tit pair that exhibited an apparent preference for either a large or a small symbol and was then allowed to choose between two nest-boxes with a large and a small symbol, but the symbol shape was different to that on the tit nest. Older flycatcher females were more likely to copy the symbol size preference of tits than yearling flycatcher females when there was a high number of visible eggs or a few partially visible eggs in the tit nest. However, this depended on the phenotype, copying switched to rejection as a function of increasing body size. Possibly the quality of and overlap in resource use with the tits affected flycatchersâ decisions. Hence, our results suggest that conceptual preferences can be horizontally transmitted across coexisting animals, which may increase the performance of individuals that use concept learning abilities in their decision-making
Elucidating mechanisms for insect body size:partial support for the oxygen-dependent induction of moulting hypothesis
Abstract
Body size is a key life history trait, and knowledge of its mechanistic basis is crucial in life history biology. Such knowledge is accumulating for holometabolous insects, whose growth is characterised and body size affected by moulting. According to the oxygen-dependent induction of moulting (ODIM) hypothesis, moult is induced at a critical mass at which oxygen demand of growing tissues overrides the supply from the tracheal respiratory system, which principally grows only at moults. Support for the ODIM hypothesis is controversial, partly because of a lack of proper data to explicitly test the hypothesis. The ODIM hypothesis predicts that the critical mass is positively correlated with oxygen partial pressure (PO2) and negatively with temperature. To resolve the controversy that surrounds the ODIM hypothesis, we rigorously test these predictions by exposing penultimate-instar Orthosia gothica (Lepidoptera: Noctuidae) larvae to temperature and moderate PO2 manipulations in a factorial experiment. The relative mass increment in the focal instar increased along with increasing PO2, as predicted, but there was only weak suggestive evidence of the temperature effect. Probably owing to a high measurement error in the trait, the effect of PO2 on the critical mass was sex specific; high PO2 had a positive effect only in females, whereas low PO2 had a negative effect only in males. Critical mass was independent of temperature. Support for the ODIM hypothesis is partial because of only suggestive evidence of a temperature effect on moulting, but the role of oxygen in moult induction seems unambiguous. The ODIM mechanism thus seems worth considering in body size analyses
Dim light pollution prevents diapause induction in urban and rural moths
Abstract
1. Light pollution is increasingly affecting biodiversity and may also disrupt seasonal adaptations. Even dim artificial light, such as skyglowâwhich can spread far beyond urban areasâcan interfere with using photoperiod as a seasonal cue.
2. Here, we test how light pollution impacts diapause induction and whether urban evolution counteracts it, by using common-garden experiments with a common, widespread geometrid moth (Chiasmia clathrata). We raised offspring from urban and rural populations from North- and Mid-European countries in treatments with and without dim light at night.
3. The dim light treatment strongly increased direct development overallâwith no evidence for urban adaptation to itâbut distinctly more so in Mid- than in North-European populations.
4. Because diapause induction is critical for surviving winter, these results indicate that dim but widespread light pollution may have detrimental effects on insect populations, especially so at mid-latitudes, and may hence explain part of the ongoing, large-scale insect declines globally.
5. Synthesis and applications. Latitudinal variation in sensitivity to light pollution means that its contribution to insect declinesâand its conservation importanceâshould likewise vary among regions. In mid-latitude regions, where populations seem more sensitive to light pollution, mitigating light pollution should be a high priority for insect conservation. Reducing skyglow from cities should benefit both urban populationsâwhich were just as susceptible as rural populations in our studyâand rural populationsâbecause skyglow extends far beyond the geographic boundaries of cities
Comparative analysis of larval growth in Lepidoptera reveals instarâlevel constraints
Abstract
1. 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.
2. 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 Dyarâs Rule, would mean that the relative measures of growth remain constant across moults and instars.
3. We studied ontogenetic changes and allometry in instarâspecific characteristics of larval growth in 30 lepidopteran species in a phylogenetic comparative framework.
4. Relative instarâspecific mass increments (RMI) typically, but not invariably, decreased across instars. Ontogenetic change in RMIs varied among families with little withinâfamily variation. Endâofâinstar growth deceleration (GD) became stronger with increasing body size across instars. Acrossâinstar change in GD was conserved across taxa. Ontogenetic allometry was generally nonâisometric in both RMI and GD.
5. 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
Ecological and evolutionary consequences of selective interspecific information use
Abstract
Recent work has shown that animals frequently use social information from individuals of their own species as well as from other species; however, the ecological and evolutionary consequences of this social information use remain poorly understood. Additionally, information users may be selective in their social information use, deciding from whom and how to use information, but this has been overlooked in an interspecific context. In particular, the intentional decision to reject a behaviour observed via social information has received less attention, although recent work has indicated its presence in various taxa. Based on existing literature, we explore in which circumstances selective interspecific information use may lead to different ecological and coevolutionary outcomes between two species, such as explaining observed co-occurrences of putative competitors. The initial ecological differences and the balance between the costs of competition and the benefits of social information use potentially determine whether selection may lead to trait divergence, convergence or coevolutionary arms race between two species. We propose that selective social information use, including adoption and rejection of behaviours, may have far-reaching fitness consequences, potentially leading to community-level eco-evolutionary outcomes. We argue that these consequences of selective interspecific information use may be much more widespread than has thus far been considered
Rodent host population dynamics drive zoonotic Lyme Borreliosis and Orthohantavirus infections in humans in Northern Europe
Abstract
Zoonotic diseases, caused by pathogens transmitted between other vertebrate animals and humans, pose a major risk to human health. Rodents are important reservoir hosts for many zoonotic pathogens, and rodent population dynamics affect the infection dynamics of rodent-borne diseases, such as diseases caused by hantaviruses. However, the role of rodent population dynamics in determining the infection dynamics of rodent-associated tick-borne diseases, such as Lyme borreliosis (LB), caused by Borrelia burgdorferi sensu lato bacteria, have gained limited attention in Northern Europe, despite the multiannual abundance fluctuations, the so-called vole cycles, that characterise rodent population dynamics in the region. Here, we quantify the associations between rodent abundance and LB human cases and Puumala Orthohantavirus (PUUV) infections by using two time series (25-year and 9-year) in Finland. Both bank vole (Myodes glareolus) abundance as well as LB and PUUV infection incidence in humans showed approximately 3-year cycles. Without vector transmitted PUUV infections followed the bank vole host abundance fluctuations with two-month time lag, whereas tick-transmitted LB was associated with bank vole abundance ca. 12 and 24 months earlier. However, the strength of association between LB incidence and bank vole abundance ca. 12 months before varied over the study years. This study highlights that the human risk to acquire rodent-borne pathogens, as well as rodent-associated tick-borne pathogens is associated with the vole cycles in Northern Fennoscandia, yet with complex time lags
Urbanization extends flight phenology and leads to local adaptation of seasonal plasticity in Lepidoptera
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