The structure and genetics of a montane population of the checkerspot butterfly,Chlosyne palla

Summary The population structure, genetics and ecology of the checkerspot butterfly, Chlosyne palla, in an area of Gunnison County, Colorado were investigated. The population structure was found to be quite different from that of most butterflies and from all of those aspects known for its thoroughly studied relative, Euphydryas editha. The population unit of Chlosyne palla may cover an area some five to eight times the size of the largest known Euphydryas population and twice the size of an Erebia epipsodea population in the same county of Colorado.Genetic variation at eleven loci of Chlosyne palla was examined by electrophoresis. Three samples of Chlosyne palla separated by 1.6, 4.7, and 12.0 km were not significantly different. Comparison with Euphydryas editha yields a genetic similarity of 0.186, about the same level as found by Ayala (1975) for different genera of Drosophila. Euphydryas editha from the same Colorado location were more similar to California E. editha than to C. palla, showing concordance with the phenetic classification. Decreased heterozygosity was observed for the Colorado E. editha and C. palla compared to California populations of E. editha and E. chalcedona.     

Population biology of the checkerspot butterfly,Euphydryas chalcedona structure of the Jasper Ridge colony

Summary Euphydryas chalcedona at Jasper Ridge consists of two independently varying major demographic units, similar in scale but not in structure to those of Euphydryas editha. In contrast, however, Jasper Ridge E. chalcedona represent just a portion of a deme-while E. editha occurs as two partially connected demes. The life history and general ecology of E. chalcedona is described and compared with those of its intensively-studied congener. Various problems of mark-release-recapture estimation of population size are discussed     

Diet divergence in two sympatric congeneric butterflies: Community or species level phenomenon?

Summary Two species ofEuphydryas butterflies were studied in California, USA, and showed considerable diet overlap at the species level. They utilize many of the same plant genera for oviposition. However,E. editha is less likely to use woody perennials than isE. chalcedona.Both butterfly species are known to specialize on different host plants in different populations, so species level divergence may not be a good predictor of community level divergence. Within five communities,E. editha andE. chalcedona showed no dietary overlap. A major component of the niche ofE. editha in one community was occupied byE. chalcedona in a second community, even though both butterfly species occupied both communities. These resource use patterns indicate that community level interactions may affect diet divergence. The degree to which divergence within communities is greater (or less) than expected from a species level comparison may be used to provide a measure of community organization. Equations are given in the Appendix for calculating overlap probabilities from presence/absence types of data; in this study, presence is oviposition on a particular plant species, absence is no oviposition on that plant species. Given the various assumptions of the model,E. editha andE. chalcedona show significant community level components of their dietary divergence in the areas studied. However, in some other communitiesE. editha andE. chalcedona do share host plant species. Therefore, we could not demonstrate community level divergence conclusively, nor has this been demonstrated for any other pair of insect herbivore species. We do not know whether this is because the phenomenon is truly rare or just very hard to demonstrate.     

INCORPORATION OF A EUROPEAN WEED INTO THE DIET OF A NORTH AMERICAN HERBIVORE

Populations of the butterfly Euphydryas editha living within a 30 times 100–km region on the eastern slope of the Sierra Nevada range were compared for oviposition preference and ability of larvae to grow and survive on two host plants, Collinsia parviflora and Plantago lanceolata. Since its introduction approximately 100 years ago, P. lanceolata has been incorporated in the diet of E. editha in one of the study populations. The populations differed in oviposition preference; only the population that uses P. lanceolata contains some individuals that prefer P. lanceolata. Larvae from two populations, one using both P. lanceolata and C. parviflora, the other using only C. parviflora, were not found to differ in relative abilities to grow or survive on P. lanceolata. The potential for E. editha to use P. lanceolata appears in populations that have had no prior exposure to this plant, while oviposition preference for this plant has evolved in the population in which the plant now grows.     

REPEATED REVERSALS OF HOST-PREFERENCE EVOLUTION IN A SPECIALIST INSECT HERBIVORE

A tree of mitochondrial DNA (mtDNA) haplotypes was constructed to estimate the number of evolutionary changes of host-plant preference needed to account for variation among 24 populations of the butterfly Euphydryas editha. Using 17 restriction endonucleases, 22 mtDNA haplotypes were found among 24 populations of this butterfly species. We allowed for the possibility of haplotypes to acquire particular preferences either from evolutionary change at their local sites or from migration to populations where those preferences occurred. After we had taken these estimates of migration into account, a minimum of 10 evolutionary changes of host preference (reduced from 22) was needed to explain the pattern of use of five host-plant genera among these populations. Analysis of allozyme variation among a partially overlapping set of populations also suggested multiple host shifts. Although genetic variation of host preference is largely responsible for interpopulation variation of diet, repeated reversals of preference evolution have occurred. However, host preferences were not distributed randomly with respect to phylogeny, and some tendency toward evolutionary conservation of preference also was indicated. The haplotype of E. editha most closely related to the sister species, E. chalcedona, used a principal host of E. chalcedona. Our results suggest that host shifts occur frequently in E. editha, are a result of both migration and local evolution, and have not been associated with speciation in these insects.     

Long range dispersal in checkerspot butterflies: Transplant experiments with Euphydryas gillettii

Summary Transfers of eggs and larvae from montane Wyoming populations of Euphydryas gillettii south to locations in the central Colorado mountains have resulted in the establishment of at least one Colorado population. This result shows that the previous absence of the species from Colorado was the result of its inability to cross the barrier of the Wyoming Basin, not the ecological unsuitability of Colorado habitats. This, in turn, supports the contention that Euphydryas do not easily disperse long distances.Dedicated to Dr. Konrad F. Springer     

Host‐associated genomic differentiation in congeneric butterflies: now you see it,now you do not

Ecotypic variation among populations may become associated with widespread genomic differentiation, but theory predicts that this should happen only under particular conditions of gene flow, selection and population size. In closely related species, we might expect the strength of host‐associated genomic differentiation (HAD) to be correlated with the degree of phenotypic differentiation in host‐adaptive traits. Using microsatellite and Amplified Fragment Length Polymorphism (AFLP) markers, and controlling for isolation by distance between populations, we sought HAD in two congeneric species of butterflies with different degrees of host plant specialization. Prior work on Euphydryas editha had shown strong interpopulation differentiation in host‐adapted traits, resulting in incipient reproductive isolation among host‐associated ecotypes. We show here that Euphydryas aurinia had much weaker host‐associated phenotypic differentiation. Contrary to our expectations, we detected HAD in Euphydryas aurinia, but not in E. editha. Even within an E. aurinia population that fed on both hosts, we found weak but significant sympatric HAD that persisted in samples taken 9 years apart. The finding of significantly stronger HAD in the system with less phenotypic differentiation may seem paradoxical. Our findings can be explained by multiple factors, ranging from differences in dispersal or effective population size, to spatial variation in genomic or phenotypic traits and to structure induced by past histories of host‐adapted populations. Other infrequently measured factors, such as differences in recombination rates, may also play a role. Our result adds to recent work as a further caution against assumptions of simple relationships between genomic and adaptive phenotypic differentiation.     

Protandry and postandry in two related butterflies: conflicting evidence about sex-specific trade-offs between adult size and emergence time

Natural selection acting on timing of metamorphosis can be sex-specific, resulting in differences in timing between males and females. Insects with discrete generations frequently show protandry: males usually mature before females. Both Euphydryas editha and E. aurinia butterflies followed this trend. The present study was motivated by the unusual observation of consistent postandry in addition to protandry. In a single E. editha population observed over 20 years the emergence period of males was longer than that of females, both the first and last emerging individuals being males. Variance of timing among individual E. editha larvae is imposed by spatial patchiness of the snowmelt that releases them from winter diapause. If individual larvae released late from diapause were to compensate for their lateness by shortening their development times, they would be small at maturity. If such compensation were only partial, they would be both late and small. Size and timing would become associated. If females were more prone to such partial compensation than males, the observations of postandry could be explained and the prediction made that any tendency for late individuals to be small should be stronger in females than in males. This was the case: in 1 year late males were the same size as early males, in a second year they were larger. Late females were significantly smaller than early females in both years. In E. aurinia, results were opposite both to theoretical prediction and to the observations from E. editha: although the male emergence period was longer than that of females exactly as in E. editha, late males were smaller than early ones, while late females were not small. The data from E. editha support the hypothesis of a sex-specific trade-off between size and emergence time, the data from E. aurinia do not.     

Variation in wing pattern and palatability in a female‐limited polymorphic mimicry system

Checkerspot butterflies in the genera Euphydryas and Chlosyne exhibit phenotypic polymorphisms along a well‐defined latitudinal and elevational gradient in California. The patterns of phenotypic variation in Euphydryas chalcedona, Chlosyne palla, and Chlosyne hoffmanni suggest a mimetic relationship; in addition, the specific patterns of variation in C. palla suggest a female‐limited polymorphic mimicry system (FPM). However, the existence of polymorphic models runs counter to predictions of mimicry theory. Palatability trials were undertaken to assess whether or not the different color morphs of each species were distasteful or toxic to a generalized avian predator, the European starling (Sturnus vulgaris). Results indicate that the black morph of E. chalcedona is distasteful, but not toxic, to predators, while the red morph is palatable. C. hoffmanni and both color morphs of C. palla are palatable to predators. Predators that learn to reject black E. chalcedona also reject black C. palla, suggesting that the latter is a FPM of the former. C. hoffmanni does not appear to be involved in this mimetic relationship.     

Ecological determinants of food plant choice in the checkerspot butterfly Euphydryas editha in Colorado

Summary The larvae of Euphydryas editha in Gunnison County, Colorado, feed on Castilleja linariifolia. Two related plants, C. chromosa and Penstemon strictus, occur in the same area and are equally nutritious, but are not eaten. Restriction to C. linariifolia appears to be a case of ecological monophagy — survival on the other two species is less likely not because of their biochemical make-up but because of their ecological characteristics, primarily their phenologies.     

Geographic and genetic variation in the leaf surface resin components of Mimulus aurantiacus from southern California

Nearly 30% of the dry weight of leaves of the chaparral subshrub Mimulus aurantiacus comprise leaf surface resins. This resin provides some defense against the insect herbivore, Euphydryas chalcedona and may also protect plants from desiccation and UV light injury. The resin is composed of several components and the different components may contribute differentially to the resin's multiple protective roles. The quantities of each of seven resin components from field-grown plants, from six southern California populations of M. aurantiacus spanning a range of water availability and differing in attack by E. chalcedona, and clones from these plants grown in a common garden, were determined. Two predictions were tested: (1) E. chalcedona will attack plant populations with relatively low quantities of total resins and/or concentrations of the ortho dihydroxy resins, and (2) plant populations in drier environments will produce resin that is relatively richer in the methoxylated components than plant populations in more mesic environments. Although resin composition differed genetically among plant populations, the pattern of variation was not as predicted. Insect attack was not associated with lower levels of ortho dihydroxy compounds, and populations with higher proportions of methoxylated flavonoids were not found in the drier sites. The pattern of genetic variation among populations in resin composition therefore was not explained by the differences in chemical structure that were predicted to influence the role of the components as herbivore protectants or antidesiccants.     

Changing demography and dispersal behaviour: ecological adaptations in an alpine butterfly

High mountain ecosystems are extreme habitats for all organisms and therefore demand specific adaptations. In this context, we studied the ecology of the butterfly Euphydryas aurinia debilis in the High Tauern (Austria) and compared the obtained data against the ecology of the species in lower elevation habitats. We performed mark-release-recapture studies over the entire flight periods (end of June to end of July) in 2007 and 2008 to analyse the fundamental ecological parameters of a population. The demography of males and females was similar in both years, and no indication of typical protandry was detected. We observed a generally low dispersal of the individuals in both years, but males dispersed significantly more than females in 2008; this finding of low vagility was supported by allozyme analyses. Furthermore, butterflies survived periods of several days of continuously closed snow cover without any indication of increased mortality rates. In these three traits, this alpine population of E. aurinia apparently has ecological and physiological adaptations to the extreme requirements of high-altitude habitats and strongly deviates from the lower elevation populations.     

Cheek pouch capacity in heteromyid rodents

Summary Diplacus aurantiacus produces a full canopy of leaves during the rainy winter and spring. As the drought begins in summer, all but the terminal leaves are lost. The leaves present during the growth period have a comparatively low specific weight and a high content of water, protein, and non-structural carbohydrate on a weight basis. Leaves of this type have a high carbon-gain per unit dry matter investment.The larvae of Euphydryas chalcedona utilize Diplacus as their principal food source. Following the first winter rains, the shrub starts to grow and the larvae of Euphydryas break diapause and begin actively feeding. Adults are produced which lay eggs that hatch into prediapause larvae. During the end of the growth period of the shrub, as the quality and quantity of Diplacus leaves decline, the prediapause larvae have a brief period of active feeding and growth and then enter diapause. Diplacus produces a leaf surface resin which inhibits the growth of Euphydryas larvae. It is present in the highest amounts on those few leaves that remain on the shrub during the drought period.The type and pattern of herbivore defense in Diplacus fits the model described for apparent plants.     

HERITABILITY OF OVIPOSITION PREFERENCE AND ITS RELATIONSHIP TO OFFSPRING PERFORMANCE WITHIN A SINGLE INSECT POPULATION

Within a population of the butterfly Euphydryas editha that oviposits predominantly on two host species, heritable variation in postalighting oviposition preference was found. In a separate experiment, oviposition preference of adult females was found to be correlated with offspring performance (growth). There was a significant tendency for offspring to perform better on the host species that their female parent preferred. Analysis of the data showed that no single factor, neither maternal preference nor the host species on which the offspring were raised, accounted for any significant variation in larval performance. However, the effect of the interaction between host species and maternal preference on offspring performance was highly significant. These findings imply specialization in both oviposition preference and offspring performance by individuals within a single population. With present evidence, this preference-performance correlation is likely to be genetic. However, as in previous studies, other interpretations cannot be excluded.     

Quantification of host preference by manipulation of oviposition behavior in the butterfly Euphydryas editha

Summary This paper describes a novel method of measuring host specificity and determining host rank order. As applied to oviposition behavior of the butterfly Euphydryas editha, the rank order of preference is the order in which plants become acceptable as the insect searches, while specificity is quantified in terms of the rate at which searching insects become less discriminating. The information obtained is different from that gleaned from other preference testing techniques. It is useful in helping to assess the behavioral bases of interpopulation differences in the degree of host specialization, in understanding the ways in which multiple host use is generated within a population, and in testing hypotheses about the evolution of host specialization.The data presented here show interpopulation variation in both rank order of host species and in the degree of host specificity of E. editha.     

Rainfall and the interaction of microclimate with larval resources in the population dynamics of checkerspot butterflies (Euphydryas editha) inhabiting serpentine grassland

Summary The interaction of host plant phenology and microclimatic heterogeneity was examined to determine its role in the population dynamics of checkerspot butterflies, Euphydryas editha, inhabiting serpentine grassland in California's outer Coast Range.Within the 2–3 hectares inhabited by a population of E. editha (Jasper Ridge Area H), microclimatic differences resulting from topographic heterogeneity largely determine the temporal and spatial pattern of senescence of the larval host plants, Plantago erecta and Orthocarpus densiflorus. Survival of larvae from hatching to diapause is extremely low as a result of unpredictable variation in the timing of larval development relative to the timing of host plant senescence, both of which are mediated by microclimatic patterns. During this study, population H declined to near extinction as a result of two consecutive years of record rainfall that apparently disrupted the tenuous temporal relationship between larval development and plant senescence. Retarded development of post-diapause larvae led to a late and extended flight season and delayed egg production; this in turn resulted in massive mortality of pre-diapause larvae due to starvation because host plant senescence occurred before larvae became large enough to enter diapause. Adult population size the following spring was the smallest in 25 years of study. This work emphasizes the importance of microclimatic heterogeneity for understanding population-level processes in small ectothermic animals and underlines the potential importance of such heterogeneity in the establishment of reserves designed to protect such animals     

Genetic differentiation within metapopulations of Euphydryas aurinia and Melitaea phoebe in China

We analyzed genetic differentiation within metapopulations of two species of checkerspot butterfly, Euphydryas aurinia and Melitaea phoebe, in China. To generate genetic information, we used a new molecular technique, DALP – direct amplified length polymorphism. AMOVA results showed that most of the variation occurred among individuals within local populations of both E. aurinia and M. phoebe. However, while there was differentiation among local population in E. aurinia (P < 0.001), there was no subdivision in metapopulation of M. phoebe (P = 0.210). This is consistent with the behavior of M. phoebe adults being more dispersive than E. aurinia. Within the M. phoebe metapopulation, three neighboring patches were always occupied during the observation period (1998–2000). In addition, the number of individuals in these three populations accounted for the majority of M. phoebe larvae, and hence we conclude that the M. phoebe metapopulation might exist as a source-sink metapopulation. On the other hand, the E. aurinia metapopulation is an example of a classical metapopulation. Therefore, the conservation management of these two species should reflect these differences.     

Variation among individual butterflies along a generalist–specialist axis: no support for the 'neural constraint' hypothesis

Abstract 1. Degree of host specialisation was a continuous variable in a population of Edith’s checkerspot butterfly (Euphydryas editha). A novel host, Collinsia torreyi, had been added to the diet in response to anthropogenic disturbance, and then abandoned prior to the current study. Butterflies either showed no preference or preferred their traditional host, Pedicularis semibarbata. 2. Strength of preference for Pedicularis over Collinsia was measured in the field and used to estimate host specialisation of individual butterflies. Efficiency was estimated from the times taken by each insect to perform two tasks: (i) identification of a Pedicularis plant as a host, and (ii) successful initiation of oviposition after the decision to do so had been made. 3. There was no clear trend for association between host specialisation and either measure of efficiency. Generalists were not slower than specialists at identifying Pedicularis as a host or at handling it after deciding to oviposit. 4. Prior work indicated that generalists paid no detectable cost in terms of reduced discrimination among individuals of their preferred host species. 5. In contrast to other species, generalist E. editha paid in neither time nor accuracy. Why then does the diet not expand? Behavioural adaptations to the traditional host caused maladaptations to the novel host and generated short‐term constraints to evolutionary expansion of diet breadth. To date, however, no long‐term constraints have been found in this system. In those traits investigated to date, increased adaptation to the novel host has not caused reduced adaptation to the traditional host.     

Genomic inference accurately predicts the timing and severity of a recent bottleneck in a nonmodel insect population

The analysis of molecular data from natural populations has allowed researchers to answer diverse ecological questions that were previously intractable. In particular, ecologists are often interested in the demographic history of populations, information that is rarely available from historical records. Methods have been developed to infer demographic parameters from genomic data, but it is not well understood how inferred parameters compare to true population history or depend on aspects of experimental design. Here, we present and evaluate a method of SNP discovery using RNA sequencing and demographic inference using the program δaδi, which uses a diffusion approximation to the allele frequency spectrum to fit demographic models. We test these methods in a population of the checkerspot butterfly Euphydryas gillettii. This population was intentionally introduced to Gothic, Colorado in 1977 and has as experienced extreme fluctuations including bottlenecks of fewer than 25 adults, as documented by nearly annual field surveys. Using RNA sequencing of eight individuals from Colorado and eight individuals from a native population in Wyoming, we generate the first genomic resources for this system. While demographic inference is commonly used to examine ancient demography, our study demonstrates that our inexpensive, all‐in‐one approach to marker discovery and genotyping provides sufficient data to accurately infer the timing of a recent bottleneck. This demographic scenario is relevant for many species of conservation concern, few of which have sequenced genomes. Our results are remarkably insensitive to sample size or number of genomic markers, which has important implications for applying this method to other nonmodel systems.     

Nectar source distribution as a determinant of oviposition host species in Euphydryas chalcedona

The distribution of nectar sources is shown to affect both the distribution of adult Euphydryas chalcedona and their offspring. We suggest that nectar sources thereby influence the selection of oviposition host plant species in habitats where those species are spacially separated.