Take-off flight performance in the butterfly Pararge aegeria relative to sex and morphology: a quantitative genetic assessment

Adult fitness components may strongly depend on variation in locomotory performance such as flight; this variation can be sex specific. Fast take-off to intercept females and competing males is an essential behavioral component of the territorial perching behavior in male speckled wood butterflies (Pararge aegeria L.). Females on the other hand avoid frequent take-offs particularly under suboptimal temperatures, typically showing fewer but longer flights than males. We estimated the heritability of take-off acceleration performance under suboptimal body temperatures by a restricted maximum-likelihood model. We calculated genetic correlations between this performance and a selection of morphological traits: size (body mass), flight muscle investment (relative thorax mass), and wing shape (forewing aspect ratio). Our results show significant additive genetic variation for mean acceleration performance and a similar but nonsignificant trend (P= 0.08) for maximal acceleration performance during take-off in males (h(2)= 0.15). In females, heritability was not significantly different from zero for either of the acceleration performance measures. Morphological traits and take-off performance were genetically linked in a sex-specific way. In males, relative thorax mass and forewing aspect ratio were positively genetically correlated with acceleration performance. In females, there was a negative genetic correlation between acceleration performance and abdomen mass, but not with residual abdomen mass (i.e., regressed on total body mass). To fully understand the evolution of sexual differences in flight performances and morphology, several other flight performances will have to be included. This multifunctional nature of flight and its consequences for the evolutionary study of flight has not yet been fully appreciated in the literature.     

Flight endurance in relation to adult age in the green‐veined white butterfly Pieris napi

• 1 The flight apparatus in butterflies, as well as in other insects, is costly to manufacture. Since most animals live in a world where resources are limited, trade‐offs are expected and available resources must thus be allocated between flight and other functions, such as reproduction.
• 2 To mitigate this trade‐off, previous studies have shown that butterflies can break down flight muscles in the thorax as they age in order to use muscle nutrients for reproduction.
• 3 Although breakdown of flight muscles is expected to reduce flight ability, relative flight muscle mass (thorax mass/body mass) in many butterfly species does not decrease with age. The aim of the present study was to test the relationship between flight endurance and adult age in the green‐veined white butterfly Pieris napi (L.). The tests were performed in the laboratory at five different temperatures.
• 4 The results showed that age has a significant influence on butterfly flight endurance; older butterflies showed reduced flight endurance. Male butterflies fly for a longer time than females and flight endurance increases with temperature in both sexes.

     

Age-related changes in thoracic mass: possible reallocation of resources to reproduction in butterflies

In nectar-feeding butterflies, reproductive potential is usually thought to depend on the size of the reproductive reserves in the abdomen, the adult food quality and, for females, the amount of resources received in the spermatophores at mating. Recent findings show that thorax mass and nitrogen content decrease with age in some butterfly species, and that thorax resources may be used for reproduction in the butterfly Pieris napi , just as in some other insects. In order to determine whether this is a general pattern and ascertain how it relates to the investment of resources in reproduction we studied the dynamics of thorax and abdomen mass changes in 11 Swedish butterfly species. By regressing thorax and abdomen mass on age of field-collected specimens, we show that loss of mass from both the thorax and the abdomen is a common phenomenon among nectar-feeding temperate zone butterflies under natural conditions. We argue that our results indicate that resources from flight muscles can be reallocated to reproduction by these butterflies, thus increasing their reproductive potential. Within species, females use proportionately more resources from the thorax than do males, as expected from the difference in investment of resources in reproduction. Among males we expect species with a higher reproductive investment to have a larger decrease in thorax and abdomen mass, and our data indicate that this is the case. Looking at the change in relative thorax mass, our results suggest that the use of resources from the thorax does not affect flight performance negatively, something that could constrain the use of muscle resources.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 86 , 363–380.     

On the sex-specific mechanisms of butterfly flight: flight performance relative to flight morphology, wing kinematics, and sex in Pararge aegeria

Many evolutionary ecological studies have documented sexual dimorphism in morphology or behaviour. However, to what extent a sex-specific morphology is used differently to realize a certain level of behavioural performance is only rarely tested. We experimentally quantified flight performance and wing kinematics (wing beat frequency and wing stroke amplitude) and flight morphology (thorax mass, body mass, forewing aspect ratio, and distance to centre of forewing area) in the butterfly Pararge aegeria (L.) using a tethered tarsal reflex induced flight set-up under laboratory conditions. On average, females showed higher flight performance than males, but frequency and amplitude did not differ. In both sexes, higher flight performance was partly determined by wing beat frequency but not by wing stroke amplitude. Dry body mass, thorax mass, and distance to centre of forewing area were negatively related to wing beat frequency. The relationship between aspect ratio and wing stroke amplitude was sex-specific: females with narrower wings produced higher amplitude whereas males show the opposite pattern. The results are discussed in relation to sexual differences in flight behaviour.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 675–687.     

Thermal biology of flight in a butterfly: genotype,flight metabolism,and environmental conditions

Knowledge of the effects of thermal conditions on animal movement and dispersal is necessary for a mechanistic understanding of the consequences of climate change and habitat fragmentation. In particular, the flight of ectothermic insects such as small butterflies is greatly influenced by ambient temperature. Here, variation in body temperature during flight is investigated in an ecological model species, the Glanville fritillary butterfly (Melitaea cinxia). Attention is paid on the effects of flight metabolism, genotypes at candidate loci, and environmental conditions. Measurements were made under a natural range of conditions using infrared thermal imaging. Heating of flight muscles by flight metabolism has been presumed to be negligible in small butterflies. However, the results demonstrate that Glanville fritillary males with high flight metabolic rate maintain elevated body temperature better during flight than males with a low rate of flight metabolism. This effect is likely to have a significant influence on the dispersal performance and fitness of butterflies and demonstrates the possible importance of intraspecific physiological variation on dispersal in other similar ectothermic insects. The results also suggest that individuals having an advantage in low ambient temperatures can be susceptible to overheating at high temperatures. Further, tolerance of high temperatures may be important for flight performance, as indicated by an association of heat‐shock protein (Hsp70) genotype with flight metabolic rate and body temperature at takeoff. The dynamics of body temperature at flight and factors affecting it also differed significantly between female and male butterflies, indicating that thermal dynamics are governed by different mechanisms in the two sexes. This study contributes to knowledge about factors affecting intraspecific variation in dispersal‐related thermal performance in butterflies and other insects. Such information is needed for predictive models of the evolution of dispersal in the face of habitat fragmentation and climate change.     

Thermal physiological ecology of Colias butterflies in flight

Summary As a comparison to the many studies of larger flying insects, we carried out an initial study of heat balance and thermal dependence of flight of a small butterfly (Colias) in a wind tunnel and in the wild.Unlike many larger, or facultatively endothermic insects, Colias do not regulate heat loss by altering hemolymph circulation between thorax and abdomen as a function of body temperature. During flight, thermal excess of the abdomen above ambient temperature is weakly but consistently coupled to that of the thorax. Total heat loss is best expressed as the sum of heat loss from the head and thorex combined plus heat loss from the abdomen because the whole body is not isothermal. Convective cooling is a simple linear function of the square root of air speed from 0.2 to 2.0 m/s in the wind tunnel. Solar heat flux is the main source of heat gain in flight, just as it is the exclusive source for warmup at rest. The balance of heat gain from sunlight versus heat loss from convection and radiation does not appear to change by more than a few percent between the wings-closed basking posture and the variable opening of wings in flight, although several aspects require further study. Heat generation by action of the flight muscles is small (on the order of 100 m W/g tissue) compared to values reported for other strongly flying insects. Colias appears to have only very limited capacity to modulate flight performance. Wing beat frequency varies from 12–19 Hz depending on body mass, air speed, and thoracic temperature. At suboptimal flight temperatures, wing beat frequency increases significantly with thoracic temperature and body mass but is independent of air speed. Within the reported thermal optimum of 35–39°C, wing beat frequency is negatively dependent on air speed at values above 1.5 m/s, but independent of mass and body temperature. Flight preference of butterflies in the wind tunnel is for air speeds of 0.5–1.5 m/s, and no flight occurs at or above 2.5 m/s. Voluntary flight initiation in the wild occurs only at air speeds 1.4 m/s.In the field, Colias fly just above the vegetation at body temperatures of 1–2°C greater than when basking at the top of the vegetation. These measurements are consistent with our findings on low heat gain from muscular activity during flight. Basking temperatures of butterflies sheltered from the wind within the vegetation were 1–2°C greater than flight temperatures at vegetation height.     

Flight morphology of Neotropical butterflies: palatability and distribution of mass to the thorax and abdomen

Summary We test whether palatability of Neotropical butterflies is associated with distribution of mass to the thorax and abdomen. Thoracic mass is predominantly muscle mass, whereas abdominal mass includes organs of digestion, food storage, and reproduction. To escape from predation, butterflies palatable to the rufous-tailed jacamar (Galbula ruficauda) use fast, erratic flight, whereas unpalatable butterflies have defensive chemicals and slow, regular flight patterns. We adjusted for effects of phylogeny and report partial correlations for two levels of analysis: 1) comparisons among-lineage means, which test for correlations between traits of distantly related lineages, and 2) comparisons among deviations from lineage means (or within lineages), which test for correlations between traits of more closely related species.Among lineages for both males (n=10 lineages) and females (n=9), palatability and thoracic mass were positively correlated, whereas palatability and abdominal mass were negatively correlated. An inverse correlation between thoracic and abdominal mass is a consequence of the two segments composing 75% of the total body mass. Predation, indexed by palatability, may select for increased flight speed and thoracic mass at the expense of the abdomen, but relative flight speed and thoracic mass were not significantly correlated.Within lineages (n=45 species for each sex), thoracic mass was uncorrelated with palatability in both sexes. Relative flight speed correlated positively with thoracic mass and negatively with body mass. Palatability and abdominal mass were negatively correlated for males but not females. Hence differences between the sexes in mass distribution suggest differences in reproductive constraints and predation stress.     

Coevolution between flight morphology,vertical stratification and sexual dimorphism: what can we learn from tropical butterflies?

Occurrence patterns are partly shaped by the affinity of species with habitat conditions. For winged organisms, flight‐related attributes are vital for ecological performance. However, due to the different reproductive roles of each sex, we expect divergence in flight energy budget, and consequently different selection responses between sexes. We used tropical frugivorous butterflies as models to investigate coevolution between flight morphology, sex dimorphism and vertical stratification. We studied 94 species of Amazonian fruit‐feeding butterflies sampled in seven sites across 3341 ha. We used wing–thorax ratio as a proxy for flight capacity and hierarchical Bayesian modelling to estimate stratum preference. We detected a strong phylogenetic signal in wing–thorax ratio in both sexes. Stouter fast‐flying species preferred the canopy, whereas more slender slow‐flying species preferred the understorey. However, this relationship was stronger in females than in males, suggesting that female phenotype associates more intimately with habitat conditions. Within species, males were stouter than females and sexual dimorphism was sharper in understorey species. Because trait–habitat relationships were independent from phylogeny, the matching between flight morphology and stratum preference is more likely to reflect adaptive radiation than shared ancestry. This study sheds light on the impact of flight and sexual dimorphism on the evolution and ecological adaptation of flying organisms.     

Effects of weight loading on flight performance and survival of palatable Neotropical Anartia fatima butterflies

Previous studies show that the position of centre of body mass ( cm_body ) and the ratio of flight muscle to total body mass (flight muscle ratio, FMR) are good predictors of flight speed and manoeuvrability in butterflies. However, cm_body , FMR, and related morphometric traits are strongly correlated phcnotypically, making it difficult to identify the causal determinants of flight performance. By experimentally gluing weights that amounted to 15% body weight to a palatable Neotropical butterfly species (Anartia fatima) , we tested the effects of altering FMR and repositioning cm_body on two measures of flight performance: flight speed and the ability to evade capture. We then tested their effects on survival in a natural setting. Flight performance studies detected no significant differences in airspeed or evasive flight ability among unweighted controls, weighted-loaded butterflies (WL), and those with cm_body positioned further posterior (CM). In two mark-release-recapture experiments, survival of treatment groups did not differ, but males survived longer than females. In one experiment, WL and CM butterflies were recaptured more frequently than controls, whereas the probability of recapture for females was higher than that for males in the second experiment. When significant, results for recapture were consistent with a causal relationship between FMR and flight speed. Presumably, a decrease in flight speed was due to a reduction in muscle mass-specific power output in the weighted butterflies. However, the results did not support a relationship between manoeuvrability and cm_body     

Sexual differences rather than flight performance underlie movement and exploration in a tropical butterfly

1. Individual movement behaviour governs several routine processes, and may scale up to important ecological processes, including dispersal. However, movement is affected by a wealth of factors, including abiotic conditions, flight performance, and behavioural traits. Although it has been historically assumed that insect flight is in the first place ruled by physiology and morphology, researchers have only recently begun to understand the potentially important role of behavioural traits. 2. This study aims to disentangle the relative importance of thermal conditions during development, and especially flight performance (capacity), versus behaviour (intrinsic motivation) in relation to movement attributes (i.e. time until take‐off, number of positions visited) under controlled laboratory conditions in the tropical butterfly Bicyclus anynana. 3. As predicted, links were found between flight performance (forced flight) and morphological traits (body size). However, this link was less pronounced for movement and exploratory behaviour, suggesting a more pronounced role of intrinsic motivation on the actual decision to move, or not. Thus, flight performance and movement may not be intimately associated. 4. Flight behaviour was mainly determined by sexual differences, with males showing better flight performance, higher mobility, and enhanced exploration than females. 5. Lower developmental temperatures increased thorax–abdomen ratio, thorax mass, and exploratory behaviour, and decreased wing loading. This may potentially aid flight capacity under thermally challenging conditions. 6. This study adds to the growing evidence that behavioural traits should not be neglected when investigating movement and dispersal, as they may well play a crucially important role.     

Landscape structure and phenotypic plasticity in flight morphology in the butterfly Pararge aegeria

In evolutionary time, varying environments may lead to different morphs as a result of genetic adaptation and divergence or phenotypic plasticity. Landscapes that differ in the extent of habitat fragmentation may provide different selection regimes for dispersal, but also for other ecological functions. Several studies on flying insects have shown differences in flight morphology between landscapes, but whether such differences result from plastic responses have rarely been tested. We did a reciprocal transplant experiment with offspring of speckled wood butterfly females (Parargeaegeria) from three types of landscape differing in fragmentation: woodland landscape, landscape with woodland fragments and agricultural landscape with only hedgerows. Young caterpillars were allowed to grow individually on potted host grasses in small enclosures under the three landscape conditions (split‐brood design). Mortality in caterpillars was much higher in agricultural landscape compared to the other landscapes. Additive to the effect of landscape of development, landscape of origin also affected mortality rate in a similar way. Flight morphology of the adults resulting from the experiment differed significantly with landscape. Independent of the landscape of origin, males and females that developed in agricultural landscape were the heaviest and had the greatest wing loadings. Females that developed in agricultural landscape had higher relative thorax mass (i.e. greater flight muscle allocation) in line with adaptive predictions on altered dispersal behaviour with type of landscape. In males, relative thorax mass did not respond significantly relative to landscape of development, but males originating from landscape with woodland fragments allocated more into their thorax compared to males from the other types. We found significant G×E interactions for total dry mass and wing loading. Our results suggest the existence of phenotypic plasticity in butterfly flight morphology associated with landscape structure.     

SEXUAL SELECTION AND BUTTERFLY DESIGN—A COMPARATIVE STUDY

Temperate butterflies of 44 species were examined to determine if their mating system (perching and patrolling) affected flight design. To control for spurious effects due to ancestry, 25 of these species were assigned to eight contrasts within which a change in mating system had occurred. In perching species sexual selection was predicted to favor traits associated with high acceleration ability and speed, while in patrolling species traits associated with flight endurance were predicted. In conformance with these expectations males of perching species had larger thorax/body mass ratios, higher wing loadings, and higher aspect ratios than patrolling species. The male mating system affected females in the same direction in the same variables as males. This could be explained by a genetic correlation with males. When removing the covariance between the sexes, only male design was explained by the mating system. The mating system was also associated with different degrees of sexual dimorphism in wing size. This supported the hypothesis that male design was affected by the mating system.     

Effects of Light Intensity on the Flight Behaviour of Adult <Emphasis Type="Italic">Tirumala limniace</Emphasis> (Cramer) (Lepidoptera: Nymphalidae: Danainae)

Light intensity significantly affects insect flight behaviour. Mating of butterflies is significantly associated with flight frequency. However, no research has elucidated the effects of light intensity on butterfly flight. Thus, a clear understanding of the effects of light intensity on flight has significant theoretical implications for the cultivation and utilization of butterflies. We observed the flight behaviour of adult Tirumala limniace (Cramer) exposed to light intensities from 243 to 2240 lx and measured the frequency of flight, take-off rhythm, thoracic temperature excess (△T) when perching and flying, and the tendency for thoracic temperature to increase. Results showed that high-intensity light significantly increased flight activity, and males were more active than females under similar light intensities; strong light (1280–2240 lx) resulted in female and male butterflies taking flight earlier compared with weak light (243–864 lx); and a similar pattern was observed for flight duration, with flights by males being significantly longer than those by females at 864–2240 lx; △T of adults flying in strong light was significantly higher than in weak light, whereas the thoracic temperature of perching adults was similar to the air temperature. Compared with other light intensities, the equilibrium thoracic temperature of adults exposed to 2240 lx was higher, and the time to reach it was shorter; in addition, the △T and rate of thoracic temperature increase were higher and achieved more quickly, respectively. Thus, of the 243–2240 lx range, 2240 lx was the most optimal light intensity for adult T. limniace flight and captive rearing.     

Weight Loading and Reproductive Status Affect the Flight Performance of Pieris napi Butterflies

Weight-induced mobility reductions can have dramatic fitness consequences and winged animals are especially sensitive to the trade-off between mass and locomotion. Data on how natural weight fluctuations influence a flying insect’s ability to take off are scarce. We therefore quantified take-off flight ability in Pieris napi butterflies in relation to reproductive status. Take-off flight ability (velocity and take-off angle) under suboptimal temperature conditions was recorded with a 3D-tracking camera system and was predicted to decrease with relatively larger weight loads. Our results show that relatively larger weight loads generally reduce flight speed in male butterflies and lower take-off angles in females. However, despite having a lower wing loading, mated male butterflies flew slower than unmated males. Our study suggests that retention of weight loads associated with reproduction impairs insect flight performance.     

The effect of habitat amount on flight-related traits in the butterfly Hamadryas februa is sex-dependent

1. Mobility in flying animals can be assessed by variations in morpho–ecological traits such as body, thorax and wing sizes, wing shape and the proportion between body mass and wing area. Habitat loss and fragmentation can promote phenotypic plasticity and microevolutionary divergencies in natural populations. In this context, sexual differences in physiology and behaviour can impose different selection pressure on morphological aspects related to flight.
2. We evaluated the relative impact of forest patch area and habitat amount in shaping flight-related morpho–ecological traits of the tropical butterfly Hamadryas februa. We find a marked sexual dimorphism in the species, with females being larger, having larger thorax, higher wing loadings and larger wing total area than males. These trait values indicate females as the more dispersive sex. We show that habitat amount modulates body mass allocations in both sexes, leading to an increase in thorax mass with decreasing habitat amount. The effect of habitat amount was more pronounced in females, which increased total mass and wing loading while decreasing thorax allocation with decreasing habitat amount. This outcome suggests that females increase abdominal mass in response to a reduction in habitat amount. The focal forest patch increasing area was linked to increases in hindwing lengths in both females and males.
3. We advocate that both landscape metrics (i.e., habitat amount and patch area) should be considered in studies evaluating landscapes' impacts on insect mobility. We discuss results in terms of the species' sexual differences in flight behaviour and the relative importance of both landscape metrics.

     

Female butterflies modulate investment in reproduction and flight in response to monsoon‐driven migrations

Migratory species may display striking phenotypic plasticity during individual lifetimes. This may include differential investment in body parts and functions, differential resource use and allocation, and behavioural changes between migratory and non‐migratory phases. While migration‐related phenotypic changes are well‐reported, their underlying mechanisms are usually poorly understood. Here we compare individuals from migratory (reproductive diapause) and non‐migratory (reproductive) phases of closely related aposematic butterfly species to study how sexual dimorphism and migratory behaviour underlie significant morphological tradeoffs, and propose a plausible scenario to explain the migration‐related phenotypic plasticity observed in females of migratory species. We found that female butterflies invested significantly more in their abdominal mass compared to males irrespective of their migratory phase, and underwent a clear shift in their body mass allocation after the switch from the reproductive diapause phase to the reproductive phase. In reproductive phase, females invested much more in reproductive tissue. This switch occurred as a result of increased abdominal mass (i.e. reproductive tissue mass) without significant reduction in the thoracic mass (i.e. flight muscle mass). Migratory males, however, were not significantly different from non‐migratory males in terms of relative investment in flight and reproductive tissues. These patterns were consistent between migratory and non‐migratory aposematic species within and across clades. While migratory habits may influence the physiology and behaviour of both sexes, long‐distance migration affected female morphology much more markedly compared to that of males. These results show the sex‐specific nature of adaptations to migratory behaviour, and suggest that seemingly disparate life‐history traits such as aposematism and migration may have similar influences on the lifetime energetic investments of insects.     

Nuptial gifts and the use of body resources for reproduction in the green-veined white butterfly Pieris napi

Reproduction in butterflies, as in many holometabolous insects, is usually constrained by the amount of nutrients the animals can collect as juveniles. In polyandric species the females can also supplement their larval-derived reserves with protein-rich donations, so-called nuptial gifts, delivered by the males at mating. Recent findings also indicate that females have access to nitrogen from the histolysis of flight muscles in the thorax. This field study examined how butterflies of the polyandric gift-giving species Pieris napi (Lepidoptera: Pieridae) use body resources in their reproduction and how the male donations affect the females use of stored reserves. The results support earlier studies, indicating that females use resources from the breakdown of thorax muscles to increase their reproductive potential and the results also indicate that males also use thorax material in their reproduction. The study also supports recent findings that the male donation increases the breakdown of body resources and thereby boosts the reproductive output of the female.     

Does habitat fragmentation affect temperature-related life-history traits? A laboratory test with a woodland butterfly

Habitat fragmentation may change local climatic conditions leading to altered selection regimes for life-history traits in small ectotherms, including several insects. We investigated temperature-related performance in terms of fitness among populations of the woodland butterfly Pararge aegeria (L.) originating from populations of a closed, continuous woodland landscape versus populations of an open, highly fragmented agricultural landscape in central Belgium. Female fecundity and longevity were evaluated in a temperature-gradient experiment. As predicted, females of woodland landscape origin reached higher maximum daily fecundity and lifetime number of eggs than did agricultural landscape females at low ambient temperatures, but this reversed at high ambient temperature. Egg weight decreased with temperature, and eggs of woodland butterflies were smaller. Contrary to what is generally assumed, remaining thorax mass was a better predictor of lifetime reproductive output than was abdomen mass. Since we used the F2 generation from wild-caught females reared under common garden conditions, the observed effects are likely to rely on intrinsic, heritable variation. Our results suggest that differential selection regimes associated with different landscapes intervene by intraspecific variation in the response of a butterfly to variation in ambient temperature, and may thus be helpful when making predictions of future impacts on how wild populations respond to environmental conditions under a global change scenario, with increasing temperatures and fragmented landscapes.     

Effects of Increased Flight on the Energetics and Life History of the Butterfly Speyeria mormonia

Movement uses resources that may otherwise be allocated to somatic maintenance or reproduction. How does increased energy expenditure affect resource allocation? Using the butterfly Speyeria mormonia, we tested whether experimentally increased flight affects fecundity, lifespan or flight capacity. We measured body mass (storage), resting metabolic rate and lifespan (repair and maintenance), flight metabolic rate (flight capacity), egg number and composition (reproduction), and food intake across the adult lifespan. The flight treatment did not affect body mass or lifespan. Food intake increased sufficiently to offset the increased energy expenditure. Total egg number did not change, but flown females had higher early-life fecundity and higher egg dry mass than control females. Egg dry mass decreased with age in both treatments. Egg protein, triglyceride or glycogen content did not change with flight or age, but some components tracked egg dry mass. Flight elevated resting metabolic rate, indicating increased maintenance costs. Flight metabolism decreased with age, with a steeper slope for flown females. This may reflect accelerated metabolic senescence from detrimental effects of flight. These effects of a drawdown of nutrients via flight contrast with studies restricting adult nutrient input. There, fecundity was reduced, but flight capacity and lifespan were unchanged. The current study showed that when food resources were abundant, wing-monomorphic butterflies living in a continuous meadow landscape resisted flight-induced stress, exhibiting no evidence of a flight-fecundity or flight-longevity trade-off. Instead, flight changed the dynamics of energy use and reproduction as butterflies adopted a faster lifestyle in early life. High investment in early reproduction may have positive fitness effects in the wild, as long as food is available. Our results help to predict the effect of stressful conditions on the life history of insects living in a changing world.     

Rearing Temperature Influences Adult Response to Changes in Mating Status

Rearing environment can have an impact on adult behavior, but it is less clear how rearing environment influences adult behavior plasticity. Here we explore the effect of rearing temperature on adult mating behavior plasticity in the butterfly Bicyclus anynana, a species that has evolved two seasonal forms in response to seasonal changes in temperature. These seasonal forms differ in both morphology and behavior. Females are the choosy sex in cohorts reared at warm temperatures (WS butterflies), and males are the choosy sex in cohorts reared at cooler temperatures (DS butterflies). Rearing temperature also influences mating benefits and costs. In DS butterflies, mated females live longer than virgin females, and mated males live shorter than virgin males. No such benefits or costs to mating are present in WS butterflies. Given that choosiness and mating costs are rearing temperature dependent in B. anynana, we hypothesized that temperature may also impact male and female incentives to remate in the event that benefits and costs of second matings are similar to those of first matings. We first examined whether lifespan was affected by number of matings. We found that two matings did not significantly increase lifespan for either WS or DS butterflies relative to single matings. However, both sexes of WS but not DS butterflies experienced decreased longevity when mated to a non-virgin relative to a virgin. We next observed pairs of WS and DS butterflies and documented changes in mating behavior in response to changes in the mating status of their partner. WS but not DS butterflies changed their mating behavior in response to the mating status of their partner. These results suggest that rearing temperature influences adult mating behavior plasticity in B. anynana. This developmentally controlled behavioral plasticity may be adaptive, as lifespan depends on the partner’s mating status in one seasonal form, but not in the other.