Phenotypic variation in adult morphology and pupal colour within and among families of the speckled wood butterfly Pararge aegeria

Abstract .1. Larvae from eggs of fifteen wild-caught speckled wood females were reared individually under common conditions (LD 18:6 h and 17 °C) in the laboratory.
2. Pupal colour (green or brown) and the following adult morphological variables that are known or assumed to be related to behavioural variation (thermoregulation, flight, crypsis) were studied: size, relative thorax mass, area of yellow patches on the dorsal forewing, size of submarginal eyespots on the dorsal hindwing, colour of the dorsal thorax, dorsal basal wing, and dorsal distal wing.
3. The results of the breeding experiment indicate significant differences in adult morphological traits among families, sexes, and pupal colour types.
4. All adult morphological variables (except spot size and thorax colouration) differed significantly among families, suggesting genetic variation underlying the phenotypic variation. Heritabilities for these features were intermediate (0.38) to high (> 1).
5. Apart from known aspects (e.g. size), novel aspects of the sexual dimorphism were found: females had paler thoraxes than males, which relates to higher abundance of fur on the thorax and hence to thermoregulatory differences.
6. Green pupae produced larger individuals with a larger relative thorax mass than brown pupae. Green pupae produced adults with a paler basal wing colour in females, but not in males. These relationships are novel and suggest a trade-off between juvenile and adult investment.     

Active background choice facilitates crypsis in a tropical crab

Animals can evade predators in multiple ways, one of the most effective of which is to avoid detection in the first place. We know much about the evolution of color patterns that match the visual background to avoid detection (i.e., crypsis), yet we know surprisingly less about the specific behaviors that have co‐evolved with these morphological traits to enhance or maintain crypsis. We here explore whether the match between body color and background in a seemingly well‐camouflaged tropical shore crab is a result of active background choice. Taking advantage of a coastal area in the Solomon Islands with variable sand color and a population of the pallid ghost crab Ocypode pallidula with varying carapace color, we experimentally tested whether individuals actively choose specific substrate that best matches their color patterns. We found that individuals taken from extreme sand colors chose substrate that maintained crypsis, with relatively darker crabs typically choosing dark sand and lighter crabs choosing light sand. Crabs of intermediate color pattern, in contrast, showed no clear preference for dark or light sand. Our results suggest that potential prey can actively choose specific backgrounds to enhance and maintain crypsis, providing insights into how behavior interacts with morphological traits to avoid predator detection.     

The red and the black: bioluminescence and the color of animals in the deep sea

The colors of deep-sea species are generally assumed to be cryptic,but it is not known how cryptic they are and under what conditions.This study measured the color of approximately 70 deep-sea species,both pelagic and benthic, and compared the results with twosets of predictions: 1) optimal crypsis under ambient light,2) optimal crypsis when viewed by bioluminescent "searchlights."The reflectances of the pelagic species at the blue-green wavelengthsimportant for deep-sea vision were far lower than the predictedreflectances for crypsis under ambient light and closer to thezero reflectance prediction for crypsis under searchlights.This suggests that bioluminescence is more important than ambientlight for the visual detection of pelagic species at mesopelagicdepths. The reflectances of the benthic species were highlyvariable and a relatively poor match to the substrates on whichthey were found. However, estimates of the contrast sensitivityof deep-sea visual systems suggest that even approximate matchesmay be sufficient for crypsis in visually complex benthic habitats.Body coloration was generally uniform, but many crabs had strikingpatterns that may serve to disrupt the outlines of their bodies.     

Predation and cryptic coloration in a managed landscape

Protective forms of animal color, such as crypsis, are thought to reduce the probability of detection by visual predators. However, because crypsis is ostensibly intuitive, the working hypothesis of cryptic coloration is seldom tested. Additionally because crypsis is a background-specific adaptation, events which alter habitat structure and substrate composition are likely to affect rates of predation on cryptic animals; animal colors that are cryptic against one visual background may be conspicuous against different visual backgrounds. Populations of Sceloporus woodi, a cryptic diurnal lizard, occupy clear-cut stands of sand pine scrub and prescribe-burned longleaf pine habitat within the Ocala National Forest. Here, we used a combination of clay models resembling S. woodi, and spectral analysis, to examine the effects of spatial heterogeneity and model-substrate contrast on rates of predation. The rate of attack on clay models differed between substrate types and habitats, and was highest when clay models were conspicuous against the local visual background. The dorsal color of models greatly contrasted open sand and dead wood, but had similar reflectance values to leaf litter, suggesting that models were most cryptic on leaf litter. We conclude that crypsis is adaptive in this species, and that variation in rates of attack between sampling locations is related to changes in substrate composition due to management history. For instance, the data suggest that the rate of attack on clay models would decrease in response to succession in sand pine scrub, because aging in sand pine scrub results in increased amounts of leaf litter and decreased amounts of open sand. Overall, the results of this study support the theory of protective coloration.     

Seasonal phenotypic plasticity of wing melanisation in the cabbage white butterfly, Pieris rapae L. (Lepidoptera: Pieridae)

Abstract.  1. Effective thermoregulation is crucial for the fitness of small flying insects. Phenotypic plasticity of the ventral hindwing of pierid butterflies is widely recognised as adaptive for effective thermoregulation. Butterflies eclosing in cooler environments have more heavily melanised wings that absorb solar radiation, thus allowing flight under these cool conditions.
2. Many pierids also exhibit phenotypic plasticity of dorsal forewing melanisation but in this case, cooler environments reduce melanisation. It has been hypothesised that this plasticity is also adaptive because it increases solar reflection from the wing surfaces onto the body in certain basking postures.
3. The degree of seasonal variation in ventral hindwing and dorsal forewing melanisation of wild-caught Pieris rapae was quantified to determine if it shows patterns of plasticity similar to that documented for other Pieris species.
4. Male wing melanisation on both wing surfaces shows the characteristic seasonal, adaptive plasticity. However, only some dorsal forewing pattern elements of females conformed to the predictions of the hypothesis of adaptive dorsal forewing melanisation. Sexual dimorphism of wing pattern plasticity may result from, and/or affect, sexual dimorphism of behaviour and physiology of these butterflies.     

The pay-off from superparasitism in the egg parasitoid Trissolcus basalis, in relation to patch defence

1. In species such as quasi-gregarious egg parasitoids, which exploit defendable patches, the fitness pay-off from superparasitism is an important factor in considering the evolution of patch defence and optimal patch defence strategies.
2. When oviposition in a previously parasitized host has a non-zero fitness pay-off, competing parasitoids are not only able to diminish the future value of a patch to other females by depleting unparasitized hosts, but also devalue the previous investment of other females in the patch by superparasitizing.
3. In Trissolcus basalis , an egg parasitoid of pentatomid bugs, the fitness pay-off from superparasitism is higher than 0.5 when the time interval between ovipositions is less than 3 h, suggesting that defending a previous investment will be an important component of patch defence behaviour.
4. The data suggest a mechanism for the high early pay-off, which involves the superparasitizing female adjusting the sex ratio of its offspring in favour of males. Males develop more quickly than females and thus may have a competitive advantage.     

The bright incubate at night: sexual dichromatism and adaptive incubation division in an open-nesting shorebird

Ornamentation of parents poses a high risk for offspring because it reduces cryptic nest defence. Over a century ago, Wallace proposed that sexual dichromatism enhances crypsis of open-nesting females although subsequent studies found that dichromatism per se is not necessarily adaptive. We tested whether reduced female ornamentation in a sexually dichromatic species reduces the risk of clutch depredation and leads to adaptive parental roles in the red-capped plover Charadrius ruficapillus, a species with biparental incubation. Males had significantly brighter and redder head coloration than females. During daytime, when visually foraging predators are active, colour-matched model males incurred a higher risk of clutch depredation than females, whereas at night there was no difference in depredation risk between sexes. In turn, red-capped plovers maintained a strongly diurnal/nocturnal division of parental care during incubation, with males attending the nest largely at night when visual predators were inactive and females incubating during the day. We found support for Wallace''s conclusion that reduced female ornamentation provides a selective advantage when reproductive success is threatened by visually foraging predators. We conclude that predators may alter their prey''s parental care patterns and therefore may affect parental cooperation during care.     

Changes in egg colour, egg weight and oviposition rate with the number of eggs laid by wild females of the small heath butterfly, Coenonympha pamphilus

ABSTRACT. 1. The colour of eggs laid by individual Coenonympha pamphilus (L.) (Lep., Satyridae) females changed over their lifespan. The first laid eggs were green, but after having laid about 100 eggs, females laid only yellow eggs.
2. By following females in the field, or by capturing wild females, and noting the colour of their eggs, it was established that younger females showed higher oviposition rates and laid heavier eggs than older females.
3. Hence, wild C.pamphilus females are unable to sustain a constant egg production by extracting amino acids or any other nutrients from nectar. We hypothesize that this is a general phenomenon in nectar feeding butterflies.
4. The egg colour did not seem to match the colour of the substrate on which the female chose to deposit the egg.     

Evidence for coloration plasticity in the yellow‐bellied toad,Bombina variegata

Phenotypic adaptation in terms of background color matching to the local habitat is an important mechanism for survival in prey species. Thus, intraspecific variation in cryptic coloration is expected among localities with dissimilar habitat features (e.g., soil, vegetation). Yellow‐bellied toads (Bombina variegata) display a dark dorsal coloration that varies between populations, assumed to convey crypsis. In this study, we explored I) geographic variation in dorsal coloration and II) coloration plasticity in B. variegata from three localities differing in substrate coloration. Using avian visual modeling, we found that the brightness contrasts of the cryptic dorsa were significantly lower on the local substrates than substrates of other localities. In experiments, individuals from one population were able to quickly change the dorsal coloration to match a lighter substrate. We conclude that the environment mediates an adaptation in cryptic dorsal coloration. We suggest further studies to test the mechanisms by which the color change occurs and explore the adaptive potential of coloration plasticity on substrates of varying brightness in B. variegata and other species.     

Lack of trade-off between direct and indirect defence against grape powdery mildew in riverbank grape

Abstract.  1. The hypothesis that plants that invest more in an indirect defence will invest less in direct mechanisms was tested using genotypes of the riverbank grape Vitis riparia that varied in expression of acarodomatia, tufts of non-glandular trichomes on underside of leaves that are frequently occupied by mycophagous mites. Mycophagous mites in this system have been shown to protect vines from grape powdery mildew caused by the fungus Uncinula necator .
2. Multiple cane cuttings from 24 genotypes of V. riparia , a species native to North America, were obtained from the USDA grape genetics repository and planted out in a common garden.
3. Genotypes varied in size of acarodomatia by threefold and varied in density of mycophagous mites by over 10-fold. Genotypes originating from the western part of the distribution had smaller acarodomatia and fewer mycophagous mites than genotypes from the eastern part of the distribution. There was a positive genetic correlation between acarodomatia size and mite density.
4. In a separate experiment, where vines were kept free of mycophagous mites, genotypes showed 10-fold variation in percentage leaf surface colonised by mildew. There was, however, no relationship between mildew on leaves and size of acarodomatia. Mildew did not vary depending on origin of genotype, although female vines tended to have greater levels than males.
5. No evidence was found for a trade-off between investment in an indirect defence mediated through acarodomatia and investment in direct defence against grape powdery mildew. Mite/plant defence mutualisms are contrasted with ant/plant defence mutualisms where there is better evidence for trade-offs under field conditions.     

Colour, shape and defence in aphidophagous syrphid larvae (Diptera)

Colour patterns, shape and behaviour are analysed in 22 species of aphidophagous syrphid larvae in relation to their possible role in defence against visually hunting predators. Crypsis is the most important method of primary defence. There is much variation in colour pattern. Some species are translucent, others green, brown or otherwise coloured. Most have disruptive stripes, bars or other markings that break up the body outline at short range. There is one example of a bird dropping resemblance. Behavioural requirements for effective crypsis include diurnal immobility, resting in sites that provide maximum concealment, and slow interrupted locomotion. Secondary defences are less variable and involve catalepsis, attack with saliva, and rolling and dropping from the plant.     

Aposematism: what should our starting point be?

The evolution of aposematism is considered to be a major evolutionary problem because if new aposematic forms emerged in defended cryptic populations, they would face the dual problems of rarity and conspicuousness. We argue that this commonly assumed starting point might not have wide validity. We describe a novel evolutionary computer model in which prey evolve secondary defences and become conspicuous by moving widely over a visually heterogeneous habitat. Unless crypsis imposes high opportunity costs (for instance, preventing prey from efficient foraging, thermoregulation and communication), costly secondary defences are not predicted to evolve at all. However, when crypsis imposes opportunity costs, prey evolve secondary defences that facilitate raised behavioural conspicuousness as prey exploit opportunities within their environment. Optimal levels of secondary defence and of behavioural conspicuousness increase with population sizes and the costs imposed by crypsis. When prey are already conspicuous by virtue of their behaviours, the evolution of aposematic appearances (bright coloration, etc.) is much easier to explain because aposematic traits add little further costs of conspicuousness, but can bring large benefits.     

Effects of habitat patchiness and connectivity on the spatial ecology of the root vole Microtus oeconomus

1. The effect of habitat patchiness and connectivity on dispersal distances and spatial aggregation of individuals is investigated in 12 enclosed populations of the root vole, Microtus oeconomus , employing a factorial experimental design with three different patch configurations and two distinct geographical root vole strains. The three patch configurations, all with an identical total area, were: two large patches, six small patches and six small patches connected by corridors.
2. The populations were followed for three generations (13. weeks) using live-trapping. Matrilineal relationships, time and place of birth, and weekly home ranges were established for the 1155 individuals in the study.
3. Smaller patch sizes enhanced dispersal, but most for one of the strains. The strain difference is, tentatively, explained by inbreeding avoidance which is known to differ between the strains.
4. The effect of habitat configuration on the dispersion pattern was similar for the two strains. Increased patchiness increased the aggregation of individuals. The two sexes diverged in their response, however, females being more aggregated than males.
5. The spatial pattern of matrilinearity was used as an indication of the resulting effect of habitat configuration on the demic structure in space. Patchiness enhanced and connectivity decreased the substructuring.     

Evolution of color variation in dragon lizards: quantitative tests of the role of crypsis and local adaptation

Abstract Many animal species display striking color differences with respect to geographic location, sex, and body region. Traditional adaptive explanations for such complex patterns invoke an interaction between selection for conspicuous signals and natural selection for crypsis. Although there is now a substantial body of evidence supporting the role of sexual selection for signaling functions, quantitative studies of crypsis remain comparatively rare. Here, we combine objective measures of coloration with information on predator visual sensitivities to study the role of crypsis in the evolution of color variation in an Australian lizard species complex (Ctenophorus decresii). We apply a model that allows us to quantify crypsis in terms of the visual contrast of the lizards against their natural backgrounds, as perceived by potential avian predators. We then use these quantitative estimates of crypsis to answer the following questions. Are there significant differences in crypsis conspicuousness among populations? Are there significant differences in crypsis conspicuousness between the sexes? Are body regions “exposed” to visual predators more cryptic than “hidden” body regions? Is there evidence for local adaptation with respect to crypsis against different substrates? In general, our results confirmed that there are real differences in crypsis conspicuousness both between populations and between sexes; that exposed body regions were significantly more cryptic than hidden ones, particularly in females; and that females, but not males, are more cryptic against their own local background than against the background of other populations. Body regions that varied most in contrast between the sexes and between populations were also most conspicuous and are emphasized by males during social and sexual signaling. However, results varied with respect to the aspect of coloration studied. Results based on chromatic contrast (“hue’ of color) provided better support for the crypsis hypothesis than did results based on achromatic contrast (“brightness’ of color). Taken together, these results support the view that crypsis plays a substantial role in the evolution of color variation and that color patterns represent a balance between the need for conspicuousness for signaling and the need for crypsis to avoid predation.     

Evolution of weaponry in female bovids

Weaponry is ubiquitous in male ungulates and is driven by intrasexual selection, but the mystery surrounding its sporadic presence in females remains unsolved. Female horns are often smaller and shaped differently to male horns, suggesting a different function; indeed, hypotheses explaining the presence of female horns include competition for food, male mollification and defence against predators. Here we use comparative phylogenetic analyses to show that females are significantly more likely to bear horns in bovids that are conspicuous due to large body size and living in open habitats than inconspicuous species living in closed habitats or that are small. An inability to rely on crypsis or take refuge in deep vegetation has apparently driven the evolution of horns for defence against predators in female bovids, a finding supported by many field observations. Typically, exceptions are small species where females are territorial (e.g. duikers) and use horns in intrasexual contests. Furthermore, we suggest that conspicuousness and territoriality hypotheses may explain other instances of female cranial weaponry (i.e. antlers and ossicones) in other horned ruminants. Our phylogenetic reconstruction indicates that the primary function of horns in females is linked to antipredator defence in most clades, but occasionally to intrasexual competition in others.     

The role of substrate preparation in the symbiosis between the leaf-cutting ant Acromyrmex octospinosus (Reich) and its food fungus

Abstract. 1. In laboratory nests the ants thoroughly licked leaf fragments by a rasping action of their glossa before inoculating the food fungus. The extent of this licking varied with the substrate and was influenced by the thickness of surface leaf waxes and by the chemical attractiveness of the substrate.
2. Microscopy and wettability studies showed that licking removes the wax layer present on leaves. It also removes or inhibits micro-organisms present.
3. Chemically de-waxed and decontaminated leaves and ant-licked leaves proved the best substrates for artificially culturing the ant fungus.
4. The process of substrate preparation circumvents some of the normal defence mechanisms of green plants against fungal attack. The ant fungus thus utilizes nutritionally richer resources of green leaves normally available only to specialized parasitic fungi, rather than the nutritionally inferior shed leaves normally available to saprophytic fungi.     

Energy maximization and foraging strategies in Potamon fluviatile (Decapoda, Brachyura)

SUMMARY. 1 Foraging of the freshwater crab Potamon fluviatile was studied by recording the activity of seventy-eight specimens in a 50 m² pool in a Tuscan stream during early summer. Foraging was related both to the organic content of the substrate and to the crabs' oxygen consumption. During this period, adult females underwent "second vitellogenesis". with abundant deposition of yolk in oocytes.
2. A dispotic distribution (not accompanied by agonistic interactions, but 'peacefully' based on size) was observed within the foraging area. Larger animals (mostly males) fed on the rare patches of vegetable debris, which presented the highest organic content. Conversely, smaller specimens were relegated lo the poorer substrates, such as the stream banks.
3. The females extended and diversified their foraging areas by also venturing into terrestrial habitats, in contrast to the more sedentary and aquatic males. This behaviour (which was not accompanied by a different energetic output) resulted in a more proteinaceous diet (even when the N-content of vegetable debris fell drastically), and in a significant increase in fats and the hepatopancreas index.
4. The reserves of energetic substances are presumed to sustain the highly expensive vitellogenesis, with the production of macrolecithal eggs. The females' behaviour as energy maximizers' seemed to be under a strong selective pressure, since their reproductive success is directly related to the efficient harvesting of food.     

Synchrony in small mammal populations of montane forest patches in southern India

1. Small mammal populations were studied in montane evergreen forests in the Nilgiris, southern India, using live-trapping from January 1994 to September 1996. Two sites were selected, one with a single large forest patch and adjoining plantations, and the other with several small forest patches separated by grassland.
2. Nine species were recorded, of which eight were trapped in the forest patches, two in the grasslands and five in plantations. Rattus rattus was the most abundant species (2–36 individuals ha⁻¹) followed by Suncus montanus (0–11 individuals ha⁻¹). Densities of seven other species recorded were very low.
3. Synchrony in various population variables – density, biomass, mean weight, density of adults and adult females, and proportion of adults, adult females and sub-adults – was examined for Rattus rattus populations in the forest patches and plantations. Density and biomass were studied in seven other species recorded at these sites. Spearman's rank order correlation was used as a measure of synchrony between the population variables.
4. Within-site synchrony was higher than between-site synchrony in population characters. Synchrony was also higher between plots within the unfragmented site than they were between plots in the fragmented site. Relatively high synchrony in proportions of adults, adult females and juveniles in the forest patches implied that breeding is probably influenced by climate and food availability, which are seasonal in this habitat.
5. Given the small patch sizes (≈1–10 ha) and low population sizes, asynchrony is likely to be an outcome of demographic and environmental stochasticity, and low dispersal rates may impede establishment of synchrony.     

Colonization of host patches following long-distance dispersal by a goldenrod beetle, Trirhabda virgata

1. The arrival of the chrysomelid beetle Trirhabda virgata on isolated patches of its host Solidago altissima was closely monitored to determine how conspecific density and host condition influence colonization.
2. Experimental host patches, which were set on the roof of a four-storey building located 0.7 km from the nearest naturally occurring hosts, were frequently colonized by beetles over a 2-week dispersal period.
3. Females preferred lush host patches that were free from simulated Trirhabda chewing damage. Females colonized lush patches more often than defoliated patches at two spatial scales, when patches were 2 m and 25 m apart. Males did not show a strong preference for lush plants.
4. Males aggregated on plants that already contained adult conspecifics, apparently increasing their reproductive success. Females did not respond to the presence of adults on the patch.
5. Ninety-five per cent of the females arriving on the isolated plants had mated before flying, indicating that lone females are able to colonize empty stands.
6. By avoiding heavily defoliated plants, females should dissipate local outbreaks and spread their offspring away from over-exploited areas.     

Feeding strategies in drosophilid parasitoids: the impact of natural food resources on energy reserves in females

1. Adult feeding strongly increases longevity and fecundity in parasitic wasps. Searching for food resources involves costs; therefore, it is advantageous to be able to feed on the breeding substrate.
2. Cohorts of females of four drosophilid parasitoid species were assigned to different food treatments including starvation. Fat contents were measured and compared after 5 days. In this way the nutritional value of breeding substrates to females could be expressed in terms of energy reserves.
3. Three of the four species tested fed on natural breeding substrates. A fourth species did not produce evidence of such feeding. However, this species fed on honey when fat reserves were low.
4. Feeding is related to: (i) the species' natural breeding substrate, (ii) the energy allocation and lifetime expectancy of the female, and (iii) time of the season.
5. Because feeding strongly influences longevity and fecundity, it is argued that the different feeding strategies found may affect competitive relationships between these drosophilid parasitoid species.