Pararge Aegeria Research Articles

Testing for variation in photoperiodic plasticity in a butterfly: Inconsistent effects of circadian genes between geographic scales.

The genetic components of the circadian clock have been implicated as involved in photoperiodic regulation of winter diapause across various insect groups, thereby contributing to adaptation to adverse seasonal conditions. So far, the effects of within-population variation in these genes have not been well explored. Here, we present an experimental test of the effects of within-population variation at two circadian genes, timeless and period, on photoperiodic responses in the butterfly Pararge aegeria. While nonsynonymous candidate SNPs in both of these genes have previously shown to be associated with diapause induction on a between-population level, in the present experiment no such effect was found on a within-population level. In trying to reconcile these results, we examine sequence data, revealing considerable, previously unknown protein-level variation at both timeless and period across Scandinavian populations, including variants unique to the population studied here. Hence, we hypothesize that these variants may counteract the previously observed diapause-averting effect of the candidate SNPs, possibly explaining the difference in results between the experiments. Whatever the cause, these results highlight how the effects of candidate SNPs may sometimes vary across genetic backgrounds, which complicates evolutionary interpretations of geographic patterns of genetic variation.

Microclimatic buffering in forest, agricultural, and urban landscapes through the lens of a grass‐feeding insect

AbstractFor small ectotherm species, dealing with microclimatic variation during sensitive stages of their development is a critical component of their ecological interactions within and among different landscape settings. However, it is often unknown whether the use of habitats in different landscape settings may affect microclimatic conditions at the level of microhabitats (e.g., at host plants for herbivorous insects). As opposed to standard ecological monitoring experiments, we aim to identify the microclimatic variables that accurately represent the environment in which a small arthropod spends most of its life. As a case study, we selected grassy sites that corresponded to the microhabitat of grass‐feeding insects in general, and larvae of the butterfly Pararge aegeria in particular, as this insect recently expanded its habitat use from forest (edges) to agricultural and urban environments. We tested the extent to which local microclimates and microclimatic buffering capacity differed between tufts of grass in forest and in two anthropogenic (i.e., agricultural and urban) landscape settings by measuring microclimatic variables with sensors at the level of the grasses. We compared temperature, relative humidity, and vapor pressure deficit (VPD) during an exceptionally warm and dry summer period with parallel data from weather stations and tested for differences between microclimatic profiles among the three landscape settings. Microclimatic conditions correspond only partly to variables based on weather station data. Differences are particularly significant for relative humidity and VPD, but not for day and night temperatures. Effects of canopy openness on the variability of microclimatic variables are landscape‐specific. Host plants in agricultural settings experience strong microclimatic fluctuations and low short‐term variability in VPD. In urban settings, urban heat island effects increase night temperature but also show microclimatic buffering effects similar to the ones in forest settings. Our findings stress the functional implications of landscape‐specific microclimatic profiles at the appropriate organism‐centered scale. We discuss the significance of such microclimatic profiles for ecological studies dealing with ectotherms under climate and land use change.

Larval and adult experience and ecotype affect oviposition behavior in a niche-expanding butterfly

AbstractLocal adaptation, early-developmental and behavioral plasticity have all been suggested to be underlying mechanisms of behavioral variation. They allow organisms to cope with resource heterogeneity in time and space. However, the relative contribution of each of these drivers on niche-expansion success is still unclear. We addressed this issue by studying oviposition behavior in a butterfly (Pararge aegeria) that used to be confined to forest, but recently colonized anthropogenic areas too. We caught females of either forest or agricultural ecotype and allowed their larval offspring to experience early-habitat cues in either open field or woodland conditions. For 110 females of this transplant experiment, we monitored all oviposition-related behaviors (i.e., site selection, searching, motivation, learning) using repeated trials in outdoor flight cages with naturally occurring host grasses. We observed changes in oviposition site preference, with increasing preference for semi-shaded host grass (by vegetation or vertical structures) over consecutive egg-lays. Motivation to oviposit was most affected by larval experience (in interaction with cage environment). We also show evidence for ecotypic differentiation with the agricultural ecotype showing reduced search effort during the first trial compared to the forest ecotype. We argue that females of agricultural landscapes with fragmented resource distributions adopt a more risk-aversive oviposition strategy. Our detailed behavioral tracking under ecologically relevant conditions, stresses the importance of considering different types of behavioral plasticity to unravel a species’ success during niche expansion.

Recent speckled wood (Pararge aegeria) butterfly observations in Lanarkshire (VC77), Scotland

Recent speckled wood (Pararge aegeria) butterfly observations in Lanarkshire (VC77), Scotland

Local adaptation of life cycles in a butterfly is associated with variation in several circadian clock genes

Many insects exhibit geographical variation in voltinism, the number of generations produced per year. This includes high-latitude species in previously glaciated areas, meaning that divergent selection on life cycle traits has taken place during or shortly after recent colonization. Here, we use a population genomics approach to compare a set of nine Scandinavian populations of the butterfly Pararge aegeria that differ in life cycle traits (diapause thresholds and voltinism) along both north-south and east-west clines. Using a de novo-assembled genome, we reconstruct colonization histories and demographic relationships. Based on the inferred population structure, we then scan the genome for candidate loci showing signs of divergent selection potentially associated with population differences in life cycle traits. The identified candidate genes include a number of components of the insect circadian clock (timeless, timeless2, period, cryptochrome and clockwork orange). Most notably, the gene timeless, which has previously been experimentally linked to life cycle regulation in P.aegeria, is here found to contain a novel 97-amino acid deletion unique to, and fixed in, a single population. These results add to a growing body of research framing circadian gene variation as a potential mechanism for generating local adaptation of life cycles.

Seeing the world through the eyes of a butterfly: visual ecology of the territorial males of Pararge aegeria (Lepidoptera: Nymphalidae)

Combining studies of animal visual systems with exact imaging of their visual environment can get us a step closer to understand how animals see their “Umwelt”. Here, we have combined both methods to better understand how males of the speckled wood butterfly, Pararge aegeria, see the surroundings of their perches. These males are well known to sit and wait for a chance to mate with a passing females, in sunspot territories in European forests. We provide a detailed description of the males' body and head posture, viewing direction, visual field and spatial resolution, as well as the visual environment. Pararge aegeria has sexually dimorphic eyes, the smallest interommatidial angles of males are around 1°, those of females 1.5°. Perching males face the antisolar direction with their retinal region of the highest resolution pointing at an angle of about 45° above the horizon; thus, looking at a rather even and dark background in front of which they likely have the best chance to detect a sunlit female passing through the sunspot.

The genome sequence of the speckled wood butterfly, Pararge aegeria (Linnaeus, 1758)

We present a genome assembly from an individual female Pararge aegeria (the speckled wood butterfly; Arthropoda; Insecta; Lepidoptera; Nymphalidae). The genome sequence is 517 megabases in span. The majority of the assembly (99.68%) is scaffolded into 29 chromosomal pseudomolecules, with the W and Z sex chromosome assembled. Gene annotation of this assembly on Ensembl has identified 12,288 protein coding genes.

Oviposition site selection and learning in a butterfly under niche expansion: an experimental test

Organisms that colonize new habitats may gain fitness advantages from changes in habitat selection including oviposition behaviour. Variation in oviposition site selection may contribute to ecological differentiation in response to novel ecological conditions. Both inherited and environmentally induced or learned differences may contribute to variation in preoviposition search behaviour and oviposition site selection. We addressed this issue with the speckled wood butterfly, Pararge aegeria . Over recent decades, this species has expanded its habitat use by colonizing anthropogenic environments with populations that show differences in several phenotypic traits (i.e. ecotypes). Here we tested whether preoviposition search behaviour and oviposition site selection differ between field-derived females from forested and agricultural ecotypes, and whether prior experience would change their behaviour differently. We used F 1 -offspring reared under common garden laboratory conditions and observed individuals of both ecotypes repeatedly in an indoor experimental arena. The arena offered compartments with host plants under simulated open and woody landscape conditions, as well as control compartments. In contrast with predictions, ecotypic differences in preference were found not for a particular microhabitat, but rather for oviposition site versus control compartment. Nevertheless, exploration and microhabitat use differed between females of agricultural and forest ecotypes. Furthermore, we provide evidence of short-term (i.e. a few hours after initial exposure) learning in the context of preoviposition search behaviour, pointing at the often ignored role of habitat familiarization. Our study sheds new light on behavioural changes that relate to habitat use in novel environments for a species that thrives successfully in landscapes under rapid human-induced environmental change. • Butterfly oviposition behaviour was studied in an experimental arena. • We compared innate and altered behaviour of two ecotypes in repeated trials. • In first trials agricultural ecotype females occurred more near oviposition sites. • Behavioural plasticity was greater in the agricultural than the woodland ecotype. • Microhabitat familiarization plays a role in oviposition search behaviour.

Watching the days go by: Asymmetric regulation of caterpillar development by changes in photoperiod.

Many insects possess the plastic ability to either develop directly to adulthood, or enter diapause and postpone reproduction until the next year, depending on environmental cues (primarily photoperiod) that signal the amount of time remaining until the end of the growth season. These two alternative pathways often differ in co‐adapted life‐history traits, for example, with slower development and larger size in individuals headed for diapause. The developmental timing of these differences may be of adaptive importance: If traits diverge early, the potential for phenotypic differences between the pathways is greater, whereas if traits diverge late, the risk may be lower of expressing a maladaptive phenotype if the selective environment changes during development. Here, we explore the effects of changes in photoperiodic information during life on pupal diapause and associated life‐history traits in the butterfly Pararge aegeria. We find that both pupal diapause and larval development rate are asymmetrically regulated: While exposure to long days late in life (regardless of earlier experiences) was sufficient to produce nondiapause development and accelerate larval development accordingly, more prolonged exposure to short days was required to induce diapause and slow down prediapause larval development. While the two developmental pathways diverged early in development, development rates could be partially reversed by altered environmental cues. Meanwhile, pathway differences in body size were more inflexible, despite emerging late in development. These results show how several traits may be shaped by the same environmental cue (photoperiod), but along subtly different ontogenies, into an integrated phenotype.

On the role of direct sunlight for egg‐laying behaviour: lessons and ideas from the Speckled wood

1. Butterflies rely on suitable weather conditions for thermoregulation during active behaviour. While non‐sunny conditions are known to reduce time spent in active flight, detailed behavioural data on how variable microclimatic conditions affect decision making in specific behavioural contexts (e.g. habitat exploration, dispersal, mating, basking, oviposition) is often lacking.2. We addressed the influence of direct sunlight on females of the Speckled wood butterfly (Pararge aegeria) that were motivated to oviposit. To test this, we observed gravid butterflies one by one in (1) a cage within a greenhouse, where temperature was kept high all the time, and (2) an outdoor cage under uncontrolled weather conditions.3. Our results show that butterflies almost exclusively oviposit under direct sunlight. Surprisingly, results were similar in the warm within‐greenhouse cage, where activity remained high but oviposition never occurred during fully clouded conditions.4. These results suggest that ovipositing butterflies require sunlight not only for thermoregulation. We hypothesise that direct sunlight benefits the ovipositing female by exposing more clearly the microclimatic variation of potential oviposition sites in the herbaceous layer of the vegetation. Heliophily during oviposition and pre‐oviposition exploration may apply to a range of microclimate‐sensitive species, particularly those living in microclimatically heterogeneous habitats. This warrants novel sensory ecological research, which will further improve our understanding of insect functional habitats.

Ecological Analysis of Butterflies and Day-Flying Moths Diversity of the Gouraya National Park (Algeria)

This work represents an initial analysis of butterflies and day-flying moths of the Gouraya National Park (Algeria). Forty-eight field-surveys were made between February 2011 and January 2012, in three stations (the cliff, the low matorral and the high matorral). It allowed us to identify 38 species, belonging to 6 families: Lycaenidae (13 species), Nymphalidae (10 species), Pieridae (9 species), Papilionidae (2 species), Hesperiidae (2 species), Zygaenidae (1 species) and Sphingidae (1 species). The low matorral and cliff were the richest stations, with 33 species for the first one and 23 species for the latter. Only seven species were observed in the high matorral where the highest centesimal frequency was recorded for the Pararge aegeria (47.83 %). This species records the highest frequency of occurrences in all 3 stations. The low matorral (H' = 4.25 bits, E = 0.84) proved to be the most diversified and balanced station.

Wing morphological responses to latitude and colonisation in a range expanding butterfly.

Populations undergoing rapid climate-driven range expansion experience distinct selection regimes dominated both by increased dispersal at the leading edges and steep environmental gradients. Characterisation of traits associated with such expansions provides insight into the selection pressures and evolutionary constraints that shape demographic and evolutionary responses. Here we investigate patterns in three components of wing morphology (size, shape, colour) often linked to dispersal ability and thermoregulation, along latitudinal gradients of range expansion in the Speckled Wood butterfly (Pararge aegeria) in Britain (two regions of expansion in England and Scotland). We measured 774 males from 54 sites spanning 799 km with a 10-year mean average temperature gradient of 4 °C. A geometric morphometric method was used to investigate variation in size and shape of forewings and hindwings; colour, pattern, and contrast of the wings were examined using a measure of lightness (inverse degree of melanism). Overall, wing size increased with latitude by ∼2% per 100 km, consistent with Bergmann’s rule. Forewings became more rounded and hindwings more elongated with history of colonisation, possibly reflecting selection for increased dispersal ability. Contrary to thermal melanism expectations, wing colour was lighter where larvae developed at cooler temperatures and unrelated to long-term temperature. Changes in wing spot pattern were also detected. High heterogeneity in variance among sites for all of the traits studied may reflect evolutionary time-lags and genetic drift due to colonisation of new habitats. Our study suggests that temperature-sensitive plastic responses for size and colour interact with selection for dispersal traits (wing size and shape). Whilst the plastic and evolutionary responses may in some cases act antagonistically, the rapid expansion of P. aegeria implies an overall reinforcing effect between these two mechanisms.

Individual plasticity drives boldness senescence in a territorial butterfly

AbstractMost behavioural traits show plastic responses to changes in internal or external conditions. Similarly, animal personality is not necessarily fixed during an individual's lifetime, leading to age‐related changes. Both individual plasticity (i.e., within‐individual effect) and non‐random selective (dis)appearance of behavioural types (i.e., between‐individual effect) may contribute to age‐related changes observed at the population level. Here, we investigated how boldness changes with age in a woodland population of the Speckled wood butterfly (Pararge aegeria L.) using a capture–mark–recapture approach. We used wing wear as an index for age and we show that fresh individuals are bolder than worn individuals. Using the subsample of recaptured butterflies, we found that this pattern is most likely driven by individual plasticity. Our design also allowed us to explore some aspects of the species' spatial ecology and how it relates to personality. We found no relationship between boldness and net displacement between successive captures, a finding which we discuss within a movement ecology framework.

An experimental test of changed personality in butterflies from anthropogenic landscapes

During the last century, the human footprint on natural ecosystems has increased strongly and human-altered habitats such as urban and agricultural areas have extended globally. Despite their negative impacts on biodiversity, these habitats offer unique opportunities to study how native species respond to novel environmental conditions. Here, we studied phenotypic divergence associated with colonization of human-altered habitats in the Speckled wood (Pararge aegeria). We reared butterflies of woodland, urban and agricultural origins under common garden conditions and we measured boldness and activity at the adult stage. Both behavioural traits were repeatable at the individual level (i.e. personality traits), but we found weak evidence for ecotype-related differences in mean boldness and activity. In line with urban areas being stressful habitats, we found that boldness and activity traits correlate in urban butterflies, while we found no such syndrome in woodland and agricultural butterflies. Our results show that urbanization can alter some aspects of personality in an insect species, but they do not support the prediction that anthropogenic habitats favour boldness. Human activities such as urbanization and intensive agriculture strongly alter terrestrial ecosystems and they are among the most significant threats to biodiversity. To tolerate human-dominated landscapes, many vertebrate species show behavioural shifts towards bold personalities, but similar responses remain rather overlooked in invertebrate taxa. Here, we studied the progeny of woodland, agricultural and urban Speckled woods reared under common garden conditions and we assessed their personality. We found little evidence for differences in personality traits among landscape types, but the behavioural syndrome linking boldness and activity was detected only in urban butterflies. This shows that urbanization can indeed shape some aspects of personality in invertebrates.

Variation in butterfly diapause duration in relation to voltinism suggests adaptation to autumn warmth, not winter cold

Abstract The life cycles of animals vary in relation to local climate, as a result of both direct environmental effects and population‐level variation in plastic responses. Insects often respond to the approach of winter by entering diapause, a hormonally programmed resting state where development is suspended and metabolism suppressed. Populations often differ in the duration of diapause, but the adaptive reasons for this are unclear. We performed a common‐garden overwintering experiment with respirometric measurements in order to investigate the progression of diapause in the butterfly Pararge aegeria. Both the duration of diapause and the depth of metabolic suppression were shown to vary between populations. In contrast to previous results from various insects, diapause duration did not correspond to the local length of winter. Instead, the observed pattern was consistent with a scenario in which diapause duration is primarily a product of selection for suppressed metabolism during warm autumn conditions. The relationship between optimal diapause duration and the length of the warm season is complicated by variation in the number of yearly generations (voltinism). These results shed new light on variation in diapause ecophysiology, and highlight voltinism as an integrated product of selection at multiple points in the seasonal cycle. A free Plain Language Summary can be found within the Supporting Information of this article.

On Madeira, the success of the speckled wood butterfly (Pararge aegeria) has coincided with declining populations of the Madeiran speckled wood (Pararge xiphia): is the colonist to blame?

The endemic Madeiran speckled wood butterfly (Pararge xiphia) was once abundant and widely distributed on the island of Madeira. Declining populations and a range contraction have coincided with the colonisation of Madeira by the speckled wood (Pararge aegeria). The colonist has expanded its range and increased in abundance, whereas the opposite is true for P. xiphia, where a decline in occurrence and abundance resulted in its current endangered designation. During 3 weeks in July and August of 2018, we assessed the relative abundance, distribution and habitat preferences of the Pararge species on Madeira on ten transects, at a range of locations and altitudes, recording all individuals of both species. In addition, we scored percentage cover of several habitat variables per 5-min periods of recording on each transect. Our findings support an ongoing decline in relative abundance of P. xiphia, which accounted for 25% of Pararge individuals in 2018 compared with historical date from 1986, when P. xiphia represented 78% of the Pararge population. The endemic species was associated with the native laurel forest and P. aegeria with non-native planted forests and agriculture. In addition, we found evidence for an altitudinal range-shift ‘uphill’ which was particularly evident in P. aegeria. Causal reasons for the decline of P. xiphia are difficult to pinpoint; however, we surmise that one or more, or a combination of factors ranging from interspecific competition, habitat loss and disturbance resulting from recent environmental events and parasitism may be accountable.

Behavioural repeatability is affected by early developmental conditions in a butterfly

For developing organisms, early environmental conditions are critical as they provide cues about their environment and are thus helpful to make decisions for the short and long term. As such, the early environment is known to affect several phenotypic traits, and these can persist after developmental growth. However, the role of these early environmental conditions in shaping personality traits remains largely unknown. Here, we used a reciprocal transplant experiment to explore the effect of landscape of origin versus landscape of development on boldness and activity in a butterfly, Pararge aegeria. Larvae of woodland, agricultural and urban population origins were reared in situ in their landscape of origin or under the two alternative environmental conditions. We then repeatedly quantified boldness and activity in the F1 adults under laboratory conditions. While the landscape of development appeared to have no effect on mean trait values, it affected trait repeatability through changes in among-individual variation. Additionally, males of agricultural origin had higher mean boldness scores than woodland and urban origin males. Also, average boldness declined with testing sequence in individuals of woodland origin, but not in agricultural and urban origin individuals. Overall, our results suggest that (1) conspecifics originating from distinct habitat types differ in some aspects of boldness, and (2) early developmental conditions can affect behavioural consistency without changing mean behavioural phenotypes.

Personality traits influence contest outcome, and vice versa, in a territorial butterfly

Holding a territory is often crucial in order to acquire key resources, including mating partners. However, few studies have investigated the role of animal personality in the context of territorial conflicts and how the contest outcome itself may influence personality traits. We studied personality in male Speckled wood butterflies, Pararge aegeria, before and after territorial contests for sunspot territories. Before interactions, boldness decreased with age, while activity and exploration were only influenced by ambient conditions. Neither age nor morphology did influence the probability to win contests, but winners were more active and more explorative than losers and, moreover, males that received a red wing mark were more likely to be winners. Butterflies that lost a contest showed pronounced behavioural changes. Mean boldness increased and its repeatability was disrupted, while no such change was detected in winners. The observed boldness increase in losers may be explained by a ‘desperado effect’, though its implication for successive contests remains unknown. Given that territoriality is expected to have important consequences for reproductive success, our results suggest that personality traits may indirectly contribute to individual fitness by influencing the ability to gain access to mate-location patches.

Local adaptation of photoperiodic plasticity maintains life cycle variation within latitudes in a butterfly

The seasonal cycle varies geographically and organisms are under selection to express life cycles that optimally exploit their spatiotemporal habitats. In insects, this often means producing an annual number of generations (voltinism) appropriate to the local season length. Variation in voltinism may arise from variation in environmental factors (e.g., temperature or photoperiod) acting on a single reaction norm shared across populations, but it may also result from local adaptation of reaction norms. However, such local adaptation is poorly explored at short geographic distances, especially within latitudes. Using a combination of common-garden rearing and life cycle modeling, we have investigated the causal factors behind voltinism variation in Swedish populations of the butterfly Pararge aegeria, focusing on a set of populations that lie within a single degree of latitude but nonetheless differ in season length and voltinism. Despite considerable differences in ambient temperature between populations, modeling suggested that the key determinant of local voltinism was in fact interpopulation differences in photoperiodic response. These include differences in the induction thresholds for winter diapause, as well as differences in photoperiodic regulation of larval development, a widespread but poorly studied phenomenon. Our results demonstrate previously neglected ways that photoperiodism may mediate insect phenological responses to temperature, and emphasize the importance of local adaptation in shaping phenological patterns in general, as well as for predicting the responses of populations to changes in climate.

Urbanisation and sex affect the consistency of butterfly personality across metamorphosis

Animal behaviour may change with age, when young individuals experience different environments from adults. However, the role of ontogeny in personality traits is still open to debate and it is not clear whether individual differences in behaviour are maintained across important ontogenetic changes such as metamorphosis. Here, we repeatedly quantified personality in rural and urban populations of the speckled wood butterfly (Pararge aegeria) at the larval, pupal and adult stages. We detected significant repeatability at all life stages, showing that personality is already present at the immature stages. We found no evidence for landscape-related differences in personality traits, but adult males were bolder and more active than adult females. Adults also became bolder with trial sequence, suggesting habitation to the experimental procedure. Urbanisation, together with sex, affected relationships among larval and adult personality traits. More active larvae with short latencies resulted in more explorative adults. However, this was the case in males of urban origin only, and we detected no such correlation in females or in rural males. We suggest that harsh conditions prevailing in cities may lead to stronger trait integration across metamorphosis but also that these urbanisation-related selective pressures may act differently on males and females. In many taxa, metamorphosis marks the transition between the juvenile and the adult stages. During this crucial developmental step, morphology and physiology are deeply remodelled, which may have important consequences for the behaviour of individuals. Although personality has emerged as a hot topic in behavioural ecology, little is known about the consequences of metamorphosis for personality stability. We studied rural and urban speckled wood butterflies at the immature and adult stages to examine whether insect personality is retained over metamorphosis. Sexes differed regarding boldness and activity, but rural and urban butterflies behaved similarly. Nevertheless, urbanisation affected relationships among larval and adult personality traits. Some larval and adult traits correlated in urban males, whereas this was not the case in females or in rural males. This suggests that urbanisation may alter trait combinations across metamorphosis, but this in a sex-specific manner.