Hormonal control of seasonal morphs by the timing of ecdysteroid release in Araschnia levana L. (Nymphalidae: Lepidoptera)

Araschnia levana L. occurs in two seasonal morphs. Larvae reared under short-day conditions become diapause pupae and emerge as red spring-morph butterflies. Long-day larvae become non-diapause pupae, which emerge as black and white summer morphs. Pupae reared under these different conditions were joined in parabiosis. Both underwent adult development without diapause and the long-day animals developed into the summer morph as normal. The morph of short-day animals depended on the time of parabiosis. When they were joined to fresh long-day pupae 1 day after their own pupation, summer morphs resulted. When parabiosis began 4 days after pupation or later, spring morphs resulted. Extirpation of the brain-corpora cardiaca-allata complex from long-day pupae affected neither non-diapause development nor the summer morph. Adult development could be prevented by removal of head and prothorax. When adult development was initiated in the remaining bodies by 20-hydroxyecdysone 14 days after pupation, the spring morph resulted.—Injection of 20-dydroxyecdysone into 3-day-old short-day pupae initiated adult development and led to the summer morph. Injections into 10-day-old short-day pupae led to the spring morph. The same was true in diapause pupae deprived of their brain-corpora cardiaca-allata complex. These results indicate that seasonal diphenism in A. levana is controlled only by the timing of ecdysteroid release, which initiates adult development. There is no direct influence of the brain on wing coloration.     

Effects of changing photoperiods in the life cycle regulation of the comma butterfly, Polygonia c-album (Nymphalidae)

Abstract. 1. Regulation of adult reproductive diapause and seasonal polyphenism was studied in two populations of the comma butterfly, Polygonia c-album (L.) (Nymphalidae), from Stockholm, Sweden, and Oxford, England.
2. In the univoltine Stockholm population short and long constant day-lengths (in the range 12–22 h) at 20°C were ineffective in averting the production of the dark, generally diapausing, morph, but the non-diapausing light morph could be produced if daylengths were increased during larval development. The procedure was especially effective with increases from 12 to 22 h, but the tendency was the same with a more realistic increase, from 18 to 20 h.
3. In the partially bivoltine English population a critical constant day-length for morph and diapause induction was found between 12 and 18 h. Decreasing daylengths above the critical daylength early or late in larval development resulted in production of the diapausing morph.
4. These results suggest a system for environmental control where day-lengths which increase throughout the larval period indicate an early date before summer solstice, meaning that there is sufficient time for a second generation of offspring to reach the hibernating adult stage before winter. The ecological significance of the results is discussed.     

Museomics Dissects the Genetic Basis for Adaptive Seasonal Coloration in the Least Weasel

Dissecting the link between genetic variation and adaptive phenotypes provides outstanding opportunities to understand fundamental evolutionary processes. Here, we use a museomics approach to investigate the genetic basis and evolution of winter coat coloration morphs in least weasels (Mustela nivalis), a repeated adaptation for camouflage in mammals with seasonal pelage color moults across regions with varying winter snow. Whole-genome sequence data were obtained from biological collections and mapped onto a newly assembled reference genome for the species. Sampling represented two replicate transition zones between nivalis and vulgaris coloration morphs in Europe, which typically develop white or brown winter coats, respectively. Population analyses showed that the morph distribution across transition zones is not a by-product of historical structure. Association scans linked a 200-kb genomic region to coloration morph, which was validated by genotyping museum specimens from intermorph experimental crosses. Genotyping the wild populations narrowed down the association to pigmentation gene MC1R and pinpointed a candidate amino acid change cosegregating with coloration morph. This polymorphism replaces an ancestral leucine residue by lysine at the start of the first extracellular loop of the protein in the vulgaris morph. A selective sweep signature overlapped the association region in vulgaris, suggesting that past adaptation favored winter-brown morphs and can anchor future adaptive responses to decreasing winter snow. Using biological collections as valuable resources to study natural adaptations, our study showed a new evolutionary route generating winter color variation in mammals and that seasonal camouflage can be modulated by changes at single key genes.     

Seasonal polyphenism in larval type: rearing environment influences the development mode expressed by adults in the sea slug Alderia willowi

Dimorphisms occur when alternative developmental pathways produce discrete phenotypes within a species, and may promote evolutionary novelty in morphology, life history, and behavior. Among marine invertebrates, intra-specific dimorphism in larval type (poecilogony) is notably rare, but should provide insight into the selective forces acting on larval strategies. Most established cases of poecilogony appear to be allelic polymorphisms, with local expression regulated by population-genetic processes. Here, we present evidence that dimorphic larval development in the sea slug Alderia willowi is a seasonal polyphenism; the type of larvae produced by an adult slug depends on the rearing environment in which that slug matured. In field surveys of 1996-1999 and 2007-2009, the population in Mission Bay, San Diego (California, USA) produced only short-lived lecithotrophic larvae in summer and early fall, but a varying proportion of slugs expressed planktotrophy in winter and spring. In laboratory experiments, slugs reared under summer conditions (high temperature, high salinity) produced the highest proportion of lecithotrophic offspring, whereas winter conditions (low temperature, low salinity) induced the lowest proportion of lecithotrophy. The shift to a nondispersive morph under summer conditions may be an adaptive response to historical closure of coastal wetlands during the dry season in southern California, which would inhibit dispersal by larvae of back-bay taxa. In most animal polyphenisms, a single larval type is produced and the rearing environment determines which adult phenotype develops. In contrast, alternative larval morphs are produced by A. willowi in response to seasonal cues experienced by the adult stage, varying the phenotype and dispersal potential of offspring. As the only known case of polyphenism in mode of larval development, A. willowi should become a model organism for mechanistic studies of dimorphism and the evolution of alternative life histories.     

Pupal colour dimorphism in a desert swallowtail (Lepidoptera: Papilionidae) is driven by changes in food availability,not photoperiod

1. The swallowtail butterfly Battus polydamas archidamas Boisduval, 1936, exhibits polyphenism for pupal coloration (green and brown). It is distributed across arid regions with winter rains and is monophagous on Aristolochia plants, which emerge after the winter rains and dry out the during summer. Thus, day length does not covary positively with host plant productivity. It was hypothesised that pupal colour was driven by food availability, not photoperiod. The benefits of pupal coloration matching the colour of pupation sites in terms of field survival were also investigated to evaluate the adaptive value of pupa colour. 2. Larvae were reared under a factorial array of two photoperiods (LD 10:14 h and LD 14:10 h) and two food availability regimes (leaves ad libitum and available every other day) to assess the frequency of green and brown pupae. Field survival of green and brown pupae was quantified in three commonly used habitats that differ in background coloration (cacti, rocks and shrubs). 3. Food availability determined pupal colour. Larvae in the ad libitum regime resulted mostly in green pupae, while those with restricted food were mostly brown. In contrast, photoperiod did not influence pupal colour. Survival probability of pupae placed on cacti was higher than those placed on rocks and shrubs, and the lowest predation risk across habitats was for green pupae on cacti. 4. Food availability plays a major role in the seasonal polyphenism for pupal colour of specialist butterflies inhabiting arid environments with winter rains.     

PHYSIOLOGICAL STRESS AND COLOR POLYMORPHISM IN THE INTERTIDAL SNAIL NUCELLA LAPILLUS

The intertidal snail Nucella lapillus exhibits considerable variation in shell color both within and between populations differentially exposed to wave action. Populations from high-wave-energy shores tended to be highly polymorphic and were dominated by pigmented morphs (especially brown), while those at more sheltered locations exhibited less polymorphism and were predominantly white. Field and laboratory experiments were conducted to determine the role of physiological stress and selective predation in maintaining the observed distribution of color morphs. The results demonstrated that 1) physiological stress from high temperature and desiccation during periods of tidal emersion was greater on protected shores, 2) under similar natural conditions, brown morphs heated up faster, attained higher temperatures, desiccated more rapidly, and suffered greater mortality than did white morphs, and 3) when pairs of brown and white morphs were tethered intertidally there was virtually no mortality of either morph on the exposed shore or in shaded microhabitats on the protected shore, but brown morphs suffered much greater mortality in sunny microhabitats on the protected shore. These findings demonstrate that the interpopulation variation in shell color of N. lapillus is in part a response to a selective gradient in physiological stress. Selection for crypsis by visually hunting predators did not appear to play a prominent role; however, only adults were considered, and the predation experiments were conducted in the fall before shorebirds that prey on whelks had arrived from their summer feeding grounds. Further experimentation to quantify the effects of visual predators such as birds and fish, particularly on juvenile snails, is necessary to assess adequately the importance of predation.     

Roost site selection by Little Owls Athene noctua in relation to environmental conditions and life‐history stages

Roost site selection is a state‐dependent process, affected by the individual's costs and benefits of roosting at a specific site in the available environment. Costs and benefits of different roost sites vary in relation to intrinsic factors and environmental conditions. Thus, the cost–benefit functions of roost sites are expected to differ between seasons and life‐history stages, resulting in adjustments in roost site selection. Studying roost site selection throughout the year therefore provides information about year‐round habitat requirements at different life‐history stages. However, little is known about the roosting behaviour of birds. Here, the roost site selection of Little Owls Athene noctua was studied by repeated daytime location of 24 adult and 75 juvenile radiotagged individuals from July to November. Little Owls preferred sheltered roost sites such as tree cavities with multiple entrances. They increasingly used sheltered sites from summer to winter and preferentially used sheltered roost sites with low ambient temperatures. Juveniles used significantly less sheltered sites during dispersal than before and afterwards, and used less sheltered sites than adults within their home‐range. The survival probability of birds roosting frequently at exposed sites was reduced. Roost site selection is probably driven by the two mechanisms of predator avoidance and thermoregulation, and the costs of natal dispersal may include increased predation threat and higher energy expenditure for thermoregulation. We suggest that adequate roost sites, such as multi‐entrance tree cavities, are an important habitat requirement for Little Owls and that habitat quality can be affected by manipulating their availability.     

The conceptual and practical implications of interpreting diet breadth mechanistically in generalist predatory insects

Seasonal polyphenism in animal colour patterns indicates that temporal variation in selection pressures maintains phenotypic plasticity. Spring generation of the polyphenic European map butterfly Araschnia levana has an orange–black fritillary‐like pattern whilst individuals of the summer generation are black with white bands across the wings. What selects for the colour difference is unknown. Because predation is a major selection pressure for insect coloration, we first tested whether map butterfly coloration could have a warning function (i.e. whether the butterflies are unpalatable to birds). In a following field experiment with butterfly dummies we tested whether the spring form is better protected than the summer form from predators in the spring, and vice versa in the summer. The butterflies were palatable to birds (blue tits Cyanistes caeruleus) and in the field the spring and summer form dummies were attacked equally irrespective of season. Therefore, we found no evidence that the map butterfly is warning‐coloured or that seasonal polyphenism is an adaptation to avian predation. Because insect coloration has multiple functions and map butterfly coloration is linked to morphology, life history and development it is likely that the interplay of several selection pressures explains the evolution of colour polyphenism. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Does colour polymorphism enhance survival of prey populations?

That colour polymorphism may protect prey populations from predation is an old but rarely tested hypothesis. We examine whether colour polymorphic populations of prey exposed to avian predators in an ecologically valid visual context were exposed to increased extinction risk compared with monomorphic populations. We made 2976 artificial pastry prey, resembling Lepidoptera larvae, in four different colours and presented them in 124 monomorphic and 124 tetramorphic populations on tree trunks and branches such that they would be exposed to predation by free-living birds, and monitored their ‘survival’. Among monomorphic populations, there was a significant effect of prey coloration on survival, confirming that coloration influenced susceptibility to visually oriented predators. Survival of polymorphic populations was inferior to that of monomorphic green populations, but did not differ significantly from monomorphic brown, yellow or red populations. Differences in survival within polymorphic populations paralleled those seen among monomorphic populations; the red morph most frequently went extinct first and the green morph most frequently survived the longest. Our findings do not support the traditional protective polymorphism hypothesis and are in conflict with those of earlier studies. As a possible explanation to our findings, we offer a competing ‘giveaway cue’ hypothesis: that polymorphic populations may include one morph that attracts the attention of predators and that polymorphic populations therefore may suffer increased predation compared with some monomorphic populations.     

MICROCLIMATE VERSUS PREDATION RISK IN ROOST AND COVERT SELECTION BY BOBWHITES

Abstract: Knowledge of factors that influence habitat selection by wildlife leads to better understanding of habitat ecology and management. Therefore, we compared microclimate and predation risk as factors influencing the selection of stopping points (mid-day coverts, nocturnal roosts) by northern bobwhites (Colinus virginianus). Stopping points were located using radiomarked bobwhites in the Texas Panhandle, USA, during 2002–2003. We obtained blackbody temperatures of microclimates and assessed predation risk (angles of obstruction for aerial predators, vegetation profiles for terrestrial predators) at stopping points and paired random points. Summer coverts showed fewer degree-minutes of hyperthermic exposure (blackbody temperatures >39°C; x̄ = 655.0, SE = 4.1 for coverts, x̄ = 2,255.5, SE = 4.9 for random; 1200–1600 hr) and a lower risk to predators (e.g., 95% confidence intervals [CIs] of angles of obstruction = 87.8–90.8° for coverts, 55.9–70.6° for random). Summer roost temperatures were similar to paired random sites (x̄ = −13.9°C, SE = 0.6 for roost, x̄ = 13.9°C, SE = 0.7 for random) as were winter roost temperatures (x̄ = −1.3°C, SE = 0.7 for roosts, x̄ = −1.4°C, SE = 0.8 for random). There were minor issues of habitat selection of winter or summer roosts based on predation risk (e.g., 95% CIs of vegetation profiles of summer roosts and random sites did not overlap at lower strata). We concluded other selection factors likely exist for winter roosts because microclimate and predation risk assessments between winter roosts and random sites showed no difference. Similarly, other selection factors may exist for summer roosts, as they showed only a weak difference in terrestrial predation risk and no difference in microclimate in comparison to random sites. We concluded microclimate was the primary selection factor for coverts because prevention of hyperthermia necessitated that bobwhites select cooler microclimates within the study area.     

Hormonal control of seasonal-morph determination in the small copper butterfly, Lycaena phlaeas daimio Seitz.

Spring and summer morphs of Lycaena phlaeas daimio Seitz. are characterized by a wing colour of red and reddish brown, respectively.When newly ecdysed pupae destined to be summer or intermediate morphs (90 or 10%) by larval exposure to long days (long-day pupae) were decapitated or decerebrated, more than half of the operated pupae developed into intermediate and spring morphs (48 and 7%). But, in pupae destined to be spring, intermediate, or summer morphs (72, 22 or 4%) (short-day pupae) these operations did not produce any significant changes in the seasonal morph.Brains excised from newly ecdysed long-day pupae were transplanted into the abdomen of decapitated short-day pupae of the same age. The implants changed most recipients into summer and intermediate morphs (46 and 36%). However, when the brains of short-day pupae were used, no significant changes occurred in the seasonal morph.When long-day or short-day pupae were treated with 20-hydroxyecdysone just after pupation, they produced more reddish wings than those of the untreated or saline-treated controls. When the application was followed by chilling, already known to induce the reddish morph, the effects of both treatments are cumulative so that more reddish adults developed.The results indicate that the brain of long-day pupae secretes a factor causing the wing to be brownish. In the absence (or low titre) of the factor, most short-day pupae develop into spring or intermediate morphs. Furthermore, ecdysteroids make the wing more reddish, when applied to newly ecdysed pupae.     

Genetic divergence among three morphs of Acentrogobius pflaumii (Gobiidae) around Japan and their identification using multiplex haplotype-specific PCR of mitochondrial DNA

Genetic divergence among three morphs of a goby, Acentrogobius pflaumii, was investigated on the basis of sequence variations in a partial section of the mitochondrial cytochrome oxidase subunit?I gene. A total of 95 specimens, representing the three morphs, collected almost sympatrically from three sites around the Japanese archipelago, were sequenced, the sequence divergences between the morphs (8.62–15.50%) being much greater than within each morph (0.44–0.57%). In addition, each morph formed a distinct cluster in a neighbor-joining tree. Together with an earlier morphological study, such evidence indicated that each morph clearly represented a distinct species. Based on the determined gene sequences, three morph-specific primers were designed for multiplex haplotype-specific polymerase chain reaction (PCR) to enable quick and easy identification of each morph in future studies, especially for early life ecology given morphological similarities at these stages.     

Predation drives stable coexistence ratios between red and green pea aphid morphs

We conducted field surveys and experiments to evaluate the hypothesis that predation is an important driving factor determining the degree of coexistence between red and green morphs of the pea aphid Acyrthosiphon pisum. Theory suggests that the different colour morphs are differentially susceptible to natural enemies and selection by predation which in turn leads to variable relative abundances of red and green morphs among host plants across landscapes. Our field surveys on pea and alfalfa revealed, however, that the colour morphs tended to coexist closely in a ratio of one red to three green aphids across fields with different host plant monocultures. Experimentation involving manipulation of the relative abundances of the two colour morphs on host plants pea and alfalfa with and without predator presence revealed that red morphs had higher or same fitness (per capita reproduction) than green morphs on both pea and alfalfa only when in the proportion of one red/three green proportion. Moreover, experimentation evaluating predator efficiency revealed that red morphs are safest from predation when in a 1 : 3 ratio with green morphs. These results suggest that in addition to predation selection effects, red morphs may behaviourally choose to associate with green morphs in a narrow 1 : 3 ratio to maximize their fitness. This evidence, along with existing published data on red and green morph anti‐predator behaviour indicates that a 1 : 3 red and green morph coexistence ratio is driven by a balance between predation pressure and behavioural assorting by red morphs across landscapes. In this way predators may have ecological‐evolutionary consequences for traits that affect the colour morphs' proportion and tolerances to selective pressure.     

Survival,behaviour and spatial distribution of shell morphs in a population of the snail Brephulopsis bidens (Pulmonata)

Summary Microspatial variation of banded and unbanded shell morphs frequencies as well as number of individuals per m², mortality, migration and burrowing into the ground were examined in a population of snail Brephulopsis bidens found in South Crimea mountains (USSR). Differential values of relative survival of morphs were determined by their thermotolerance. The relative survival of the banded morph was lower at the west sites of population area (W=0.273), and increased gradually up to 1 at the east sites. Survival of the banded morph was dependent on its burrowing activity. Differences in relative survival of morphs decreased parallel with increasing general mortality of snails.Burrowing activity and intensity of migration of the banded morph were significantly higher than that in unbanded. In experiments with artificial shaded sections, the banded morph preferred shaded sections, whereas unbanded chose illuminated sites. All these differences in behaviour probably form the main factors for microspatial variation of morph frequencies.     

Spatial analyses of two color polymorphisms in an alpine grasshopper reveal a role of small‐scale heterogeneity

Discrete color polymorphisms represent a fascinating aspect of intraspecific diversity. Color morph ratios often vary clinally, but in some cases, there are no marked clines and mixes of different morphs occur at appreciable frequencies in most populations. This poses the questions of how polymorphisms are maintained. We here study the spatial and temporal distribution of a very conspicuous color polymorphism in the club‐legged grasshopper Gomphocerus sibiricus. The species occurs in a green and a nongreen (predominately brown) morph, a green–brown polymorphism that is common among Orthopteran insects. We sampled color morph ratios at 42 sites across the alpine range of the species and related color morph ratios to local habitat parameters and climatic conditions. Green morphs occurred in both sexes, and their morph ratios were highly correlated among sites, suggesting shared control of the polymorphism in females and males. We found that in at least 40 of 42 sites green and brown morphs co‐occurred with proportions of green ranging from 0% to 70% with significant spatial heterogeneity. The proportion of green individuals tended to increase with decreasing summer and winter precipitations. Nongreen individuals can be further distinguished into brown and pied individuals, and again, this polymorphism is shared with other grasshopper species. We found pied individuals at all sites with proportions ranging from 3% to 75%, with slight, but significant variation between years. Pied morphs show a clinal increase in frequency from east to west and decreased with altitude and lower temperatures and were more common on grazed sites. The results suggest that both small‐scale and large‐scale spatial heterogeneity affects color morph ratios. The almost universal co‐occurrence of all three color morphs argues against strong effects of genetic drift. Instead, the data suggest that small‐scale migration–selection balance and/or local balancing selection maintain populations polymorphic.     

Shell colour polymorphism in a mangrove snail Littorina sp. (Prosobranchia: Littorinidae)

Shell colour polymorphism was examined in populations of a mangrove snail Littorina sp. in Queensland, Australia. Three morphs were recognized, yellow, red and brown, and morph frequencies varied both between widely spaced populations and between islands less than 1 km apart. Morph frequencies also varied with time of year. There was a relationship between shell colour and position on the tree, with yellow snails more often occurring amongst the foliage and brown snails more often on trunks and branches. In some populations yellow snails appeared to survive better than the other morphs, while in other populations there was no difference. The evidence for the maintenance of the polymorphism by natural selection is discussed.     

Differential visual predation on morphs of Timema cristinae (Phasmatodeae:Timemidae) and its consequences for host range

Timema cristinae is a herbivorous insect that exhibits polymorphism for body coloration (green, red and grey morphs) and for pattern (striped, expressed only in the green morph, and unstriped). The striped green morph is associated with ceanothus ( Ceanothus spinosus ) and the unstriped green morph is associated with chamise ( Adenostoma fasciculatum ). This study examines the relative vulnerabilities to predation of the different pattern and colour morphs on their natural backgrounds. The vulnerabilities of the striped and unstriped morphs on their two food plants were tested using uncaged wild birds (Scrub Jays) and captive western fence lizards. Strong differential predation was observed suggesting that each morph is most cryptic on the food plant on which it is most common. Furthermore, in a mark-recapture experiment in a patch of ceanothus the unstriped and red morphs were recaptured in higher proportion than the other morphs. The vulnerabilities of the grey and green morphs on the ground and foliage were tested using lizards. The grey morph was more vulnerable on the plants than the green morph, but the inverse was observed on the ground (where they drop after a disturbance). This may be why the grey morph is not associated with specific food plants. The striped and colour polymorphisms in T. cristinae appear to be an evolutionary consequence of differential predation on different backgrounds. The implications of differential predation to food-plant utilization are discussed.     

Delimitation of a continuous morphological character with unknown prior membership: application of a finite mixture model to classify scapular setae of Abacarus panticis

Unambiguous classification is a prerequisite for the study of polymorphism, but accurate delimitation of continuous morphological characters can be challenging. Finite mixture modeling is a rigorous and flexible approach for delimiting continuous variables with unknown prior membership, but its application to morphological studies remains limited. In this study, the lengths of scapular setae of the eriophyoid mite Abacarus panticis Keifer collected from 18 sites in Taiwan were used as an example to evaluate the eligibility of finite mixture models. We then tested the hypothesis that longer scapular setae can facilitate dispersal. Lastly, we investigate morphological variation in various seta morphs by geometric morphometric techniques. Finite mixture models can satisfactorily classify scapular setae of A. panticis into long and short seta morphs. Abacarus panticis of the long morph only occurred in five sites whereas the short seta morph existed in all study sites. Geometric morphometric analyses revealed a more elongated coxal area in individuals of long morph than in those of short morph. Because the short morph is more widespread in geographical distribution than the long morph, longer scapular setae seem unlikely a specialized adaptation for dispersal. Further studies should capitalize on the finite mixture model in the delimitation of continuous morphological characters.     

On the selective forces acting in the industrial melanism of Biston and Oligia moths (Lepidoptera: Geometridae and Noctuidae)

Melanic and typical morphs of Biston betularius (L.), Oligia latruncula (D. & S.) and 0. strigilis (L.) made choices between vertical trunks and horizontal branches, sprayed with white and black paints, in a transparent plastic cylinder in natural illumination. The moths settled in exposed positions. In neither Biston nor Oligia did the choice for white/black backgrounds differ between the morphs. Biston moths settle on narrow branches (not on twigs) with the body at right angles to the longitudinal axis of the branch. The Oligias showed an asymmetrical light reaction: one eye is kept in shadow so that they settle as a continuation of an irregularity of the surface, often of a lichen.
In nature, Biston betularius probably rests high up in the canopies, on the under surfaces of horizontal branches. The visual selection acting on the morphs is expected to be less intensive than that measured on tree trunks. The mark-release-recapture results of Kettlewell (1955a, 1956) do not show any qualitative change during the self-determination of the moths but the material is too limited for firm conclusions.
Newly-hatched Biston males take off straight from the trunk where they have expanded their wings but the females may climb higher in the tree. A hypothesis is presented to explain the black-and-white coloration of f. carbonaria : the short-winged moths climbing up the trunks might deter bird predation.