Incipient reproductive isolation between two morphs of Drosophila elegans (Diptera: Drosophilidae)

Drosophila elegans is a flower-breeding species occurring in tropical and subtropical regions of Asia. Two morphs, brown and black, are known in this species. The brown morph is recorded from southern China, Philippines, Indonesia and New Guinea, while the black morph is from the Okinawa islands and Taiwan. The present crossing experiment suggests that the difference of body colour between them was due to alleles on a single locus or closely linked loci on an autosome; F₁ hybrids exhibited intermediate body colour. Female choice tests revealed asymmetrical premating isolation between the brown and black morphs; isolation indices ranged from 0.55 to 0.83 in the tests using females of the black morph (deviation from random mating was significant), but from — 0.03 to 0.50 in the tests using females of the brown morph (deviation from random mating was insignificant). However, body colour was not used as a criterion of mate choice by females. A weak and asymmetrical postmating isolation was also observed between the brown and black morphs; viability was lowered in F₂ progenies of crosses between females of the brown morph and males of the black morph. No premating or postmating isolation was observed between geographic strains of each morph. Under irradiation, body temperature was higher in the black morph than in the brown morph. On the other hand, no significant difference was observed in tolerance to cold, heat and desiccation between the brown and black morphs.     

Oxygen consumption in offspring tawny owls Strix aluco is associated with colour morph of foster mother

In several colour polymorphic species, morphs differ in thermoregulation either because dark and pale surfaces absorb solar radiation to a different extent and/or because morphs differ in key metabolic processes. Morph-specific thermoregulation may potentially account for the observation that differently coloured individuals are frequently not randomly distributed among habitats, and differ in many respects, including behaviour, morphology, survival and reproductive success. In a wild population of the colour polymorphic tawny owl Strix aluco, a recent cross-fostering experiment showed that offspring raised and born from red mothers were heavier than those from grey mothers. In the present study, we tested in the same individuals whether these morph-specific offspring growth patterns were associated with a difference in metabolic rate between offspring of red and grey mothers. For this purpose, we measured nestling oxygen consumption under two different temperatures (laboratory measurements: 4 and 20°C), and examined the relationships between these data sets and the colour morph of foster and biological mothers. After controlling for nestling body mass, oxygen consumption at 20°C was greater in foster offspring raised by grey foster mothers. No relationship was found between nestling oxygen consumption and coloration of their biological mother. Therefore, our study indicates that in our experiment offspring raised by grey foster mothers showed not only a lower body mass than offspring raised by red foster mothers, but also consumed more oxygen under warm temperature. This further indicates that rearing conditions in nests of grey mothers were more stressful than in nests of red mothers.     

Immune function, parasitization and extended phenotypes in colour polymorphic pygmy grasshoppers

Ecological and evolutionary consequences of host–parasite interactions have attracted considerable attention from evolutionary biologists. Previous studies have suggested that immune responsiveness may be genetically or developmentally linked with colour pattern, such that the evolution of animal colour patterns may be influenced by correlated responses to selection for parasite resistance. We studied interactions between the endoparasitic fly Leiophora innoxia (Meigen) (Diptera: Tachinidae) and its colour polymorphic pygmy grasshopper host Tetrix undulata (Sow.) (Orthoptera: Tetrigidae) to test for morph‐specific differences in parasitization and immune defence, and host‐induced variation in parasite phenotypes. Our results revealed that c. 2 and 30% of adult grasshoppers collected from the same natural population in two subsequent years, respectively were parasitized. Parasite prevalence was independent of host sex and colour morph. Pupae were larger if the parasite had developed in a female than in a male host, possibly reflecting host resource value or a physical constraint on larval growth imposed by host body size. Pupal size was also associated with host colour morph, with individuals that had developed in dark morphs being smaller at pupation compared to those that developed in paler morphs. However, immune defence, measured as the encapsulation response to a novel antigen, did not differ among individuals belonging to alternative colour morphs or sexes. Darker morphs warm up more quickly and prefer higher body temperatures than paler ones. Encapsulation was not influenced by maintenance temperature (15 vs. 30 °C), however, suggesting that indirect effects of coloration on parasite resistance mediated via differential body temperature are unlikely. The dependence of parasite body size on host colour morph may thus reflect plasticity of growth and development of the larvae in response to differential host body temperature, rather than variable host immune defence. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 373–383.     

Female Colour Polymorphism: Gender and the Eye of the Beholder in Damselflies

Damselflies provide a classic example of female colour polymorphism. Usually, one female morph resembles the blue male colour (andromorph) while one, or more, female morphs are seen as typically female (gynomorph). Damselfly species fall in two distinct groups with respect to recent developments in mimicry theory: in some species females are perfect, they match male colouration and black patterning, and in other species they are supposed to be imperfect mimics, only matching male colouration. However, the underlying assumption of one female morph looking male-like is mostly based on human vision. Therefore we investigated the black patterning and colour of the three female morphs in Coenagrion puella, an imperfect mimic, using image analysis. In C. puella the blue female morph is perceived as male-like. We found that the black patterning of such females cannot be distinguished from the other female morphs, and is clearly different from males. Furthermore, the blue colour of andromorph females differs from the blue colour of males. Intriguingly, however, the red content did not differ between blue males and females.     

Influence of shell colour on the mortality rate of the land snail Arianta arbustorum under different microclimatic regimes

The mortality of phenotypic shell colour morphs and age classes of the snail Arianta arbustorum in several microclimatic conditions was recorded. An analysis of variance was performed on five factors: adaptation temperature, relative humidity, shell colour, age class and test temperature. There were no significant differences in the mortality between different adaptation temperatures or relative humidities, but the interaction of these two factors was highly significant. There were significant differences in mortality rate between test temperature and age class. The mortality of the brown morph was higher than the yellow one at all adaptation temperatures (overall, P < 0.05). There were no significant differences between the mortality rates of the two morphs at different relative humidities. The mortality of the brown morph was higher than that of the yellow at six out of seven test temperatures. Juvenile snails survived significantly better than adults at all test temperatures.     

Reproductive success and risk of predation in normal and melanistic colour morphs of the adder, Vipera berus

In a population of adders (Vipera berus) in Southwest Sweden, melanistic males were heavier than normal coloured males of the same length. Victory in male-male sexual combats was positively related to size. Higher risk of predation in the black morph was inferred from experiments showing a high predator attack rate on models of the black morph. Even the bright colour in newly moulted basking males of the normal morph gives cryptic protection. In females, melanism probably also affects body size and risk of predation by visually searching predators. The thermoregulatory influence of black colour, the reproductive success and the maintenance of two colour morphs in the population are discussed.     

Colour-associated foraging success and population genetic structure in a sit-and-wait predator Nephila maculata (Araneae: Tetragnathidae)

Giant wood spiders, Nephila maculata (Fabricius 1793), typically have a greenish cephalothorax and a dark abdomen decorated with striking yellow bands and spots. However, in Taiwan and neighbouring coastal islands we also found some morphologically indistinguishable individuals that were totally dark. As insects are attracted to ultraviolet (UV) light, we compared the UV reflectance property and insect-catching ability of the two morphs to see whether variation in colour affected foraging success. We also examined the population genetic structure to estimate indirectly the level of gene flow between these two colour morphs. Body surface UV reflection rate was measured from six areas of the spider with a spectrometer. To compare the insect-catching ability of different morphs, we recorded the spiders' body colour, orb size and insect-interception rates. The typical morph of N. maculata reflected significantly more UV in four of the six areas examined and caught significantly more insects than the melanic morph. We estimated population genetic structure by allozyme electrophoresis, using 20 loci from 17 enzymes. The population differentiation index (F_ST) derived from all eight polymorphic loci was 0.023, indicating a minimum level of genetic differentiation. These results indicate that the two morphs ofN. maculata may be members of an interbreeding population, and melanics have lower foraging success because of a lower body surface reflectance.     

Developmental instability and immune function in colour polymorphic pygmy grasshoppers

Random left minus right deviations from symmetry in otherwise bilaterally symmetric traits may arise due to developmental instability in response to environmental stress. Here we test for variation in developmental instability, measured as asymmetry of (femur) size, among individuals belonging to four different genetically encoded colour morphs of the pygmy grasshopper Tetrix undulata (Sow.) (Orthoptera: Tetrigidae). Such a difference is expected under the hypotheses that perturbed growth and development and concomitant morphological asymmetry may result from exposure to unfavourable temperatures or costs associated with melanization, or reflect a by-product of past disease in individuals with poor immune responsiveness. Results from mixed model two-way ANOVAs uncovered no statistically significant directional asymmetry in femur size, whereas non-directional asymmetry was significant in each of the four different colour morphs. The degree of intraindividual, interlateral variance in femur size varied significantly among individuals belonging to different colour morphs, being considerably higher in the black morph, which also suffers the greatest risk of overheating, compared to the brown, striped and grey morphs. Asymmetry in femur size was not associated with one measure of immune responsiveness, the encapsulation response of individuals experimentally implanted with a novel antigen consisting of a nylon mono-filament. These results are consistent with the notion that individual pigmentation pattern may indirectly influence developmental instability and morphological asymmetry, via the effects of coloration on body temperature.Co-ordinating editor: Hurst     

Colour polymorphism in relation to population dynamics of the leaf beetle, Chrysomela lapponica

We studied colour morph diversity and frequencies of light and dark morphs in non-fluctuating and fluctuating populations of willow feeding leaf beetle Chrysomela lapponica in the Kola Peninsula, NW Russia. Population-specific Shannon–Weaver diversity index positively correlated with dark morph frequencies, indicating that the larger part of colour polymorphism is related with numbers and diversity of dark morphs. Among-population variation in studied characters was not explained by pollution load or predation rates, but depended on the type of the population and the stage of density change in the fluctuating populations: both colour morph diversity and frequency of dark morphs were low in declining post-outbreak populations but equally high in non-fluctuating populations and in fluctuating populations at peak densities. In time-series, both diversity index and frequency of dark morphs decreased with post-outbreak density decline in the fluctuating population, but did not change in the non-fluctuating population. In the experiment, when adults received low quality food (plants from post-outbreak site), mortality of dark morphs during the hibernation was almost doubled relative to the mortality of light morphs, whereas on high quality food the colour morphs demonstrated similar mortality. This may indicate, that decrease in colour polymorphism extent and dark morph frequencies in the declining populations is due to selective mortality of dark morphs imposed by density dependent (induced by heavy herbivore damage during an outbreak) decrease in host-plant quality (delayed inducible resistance, DIR). DIR is known as one of the factors driving herbivore populations, but our result is the first evidence that DIR may act as a factor of natural selection. Dark morphs are not only susceptible to low food quality, but also have smaller size compared to light morphs, and therefore the dark females are presumably less fecund. Thus, decrease in frequency of low-fitness (dark) individuals in post-outbreak populations and accumulation of low-fitness phenotypes at the popu-lation peak may create feedbacks contributing to regulation of density fluctuations in Ch. lapponica.     

Mitochondrial genetic structure reflects the geographical variation of elytral polymorphism frequency in Cheilomenes sexmaculata (Coleoptera: Coccinellidae)

Many ladybird species are known to have an elytral colour polymorphism, which indicates geographical variation. The ladybird beetle Cheilomenes sexmaculata (Fabricius) exhibits elytral colour polymorphism and has expanded its distribution from 33°N to 36°N in Japan over 100 years since 1900. The mitochondrial COI gene haplotypes were integrated into two haplotype groups, with one group existing at higher frequencies in lower latitudes, the other group appearing at higher frequencies in higher latitudes. In addition, the dark morph types of this species increase with latitude, whereas the light types appear at higher relative frequencies in lower latitudes.In the present study, we first determined the morph types of individuals and examined the mitochondrial DNA COI gene. Second, we investigated the relationship between the genetic population structure based on the mitochondrial DNA COI gene and the morph types’ geographical variation. Results indicated that the mtCOI genetic structure was associated with the morph types by latitude; specifically, the haplotype group existing at higher frequencies in lower latitudes tended to be light morph types. In contrast, the haplotype dominant in higher latitudes more frequently exhibited dark morph types, indicating that dark morph types in the higher latitude genetic group may have led the distributional expansion toward higher latitudes since 1900 rather than the lower latitude light morph types.     

Evidence for reproductive isolation between two colour morphs of cavity nesting honey bees (Apis) in south India

In south India there are two distinct colour morphs of cavity nesting honey bees: the yellow ‘Plain’ morph and the black ‘Hill’ morph which are collectively known as Apis cerana. We show that the Hill morph is associated with a widely distributed mitochondrial haplotype that is present throughout mainland populations of south east Asian A. cerana. In contrast, the Plain morph, which is apparently confined to low to moderate elevations in India and Sri Lanka, is associated with a unique mitochondrial haplotype that is not present in other cavity nesting honey bees. We further show that in a region of sympatry (Bangalore, Karnataka State) the drone mating flight times of the two colour morphs barely overlap. Combined, drone flight data and the complete separation of mitochondrial haplotypes suggest that the two morphs are reproductively isolated. The Plain morph is distinguished from the Hill morph by the first three abdominal tergites of the worker, which are completely yellow in the Plain morph, whereas in the Hill morph they are black or black with yellow patches. Although the two morphs are generally distinguishable in the field by overall colouration, microscopic examination of the first 3 abdominal tergites is preferred. Received 16 February 2006; revised 11 May 2006; accepted 23 May 2006.     

AFLP genome scans suggest divergent selection on colour patterning in allopatric colour morphs of a cichlid fish

Genome scan-based tests for selection are directly applicable to natural populations to study the genetic and evolutionary mechanisms behind phenotypic differentiation. We conducted AFLP genome scans in three distinct geographic colour morphs of the cichlid fish Tropheus moorii to assess whether the extant, allopatric colour pattern differentiation can be explained by drift and to identify markers mapping to genomic regions possibly involved in colour patterning. The tested morphs occupy adjacent shore sections in southern Lake Tanganyika and are separated from each other by major habitat barriers. The genome scans revealed significant genetic structure between morphs, but a very low proportion of loci fixed for alternative AFLP alleles in different morphs. This high level of polymorphism within morphs suggested that colour pattern differentiation did not result exclusively from neutral processes. Outlier detection methods identified six loci with excess differentiation in the comparison between a bluish and a yellow-blotch morph and five different outlier loci in comparisons of each of these morphs with a red morph. As population expansions and the genetic structure of Tropheus make the outlier approach prone to false-positive signals of selection, we examined the correlation between outlier locus alleles and colour phenotypes in a genetic and phenotypic cline between two morphs. Distributions of allele frequencies at one outlier locus were indeed consistent with linkage to a colour locus. Despite the challenges posed by population structure and demography, our results encourage the cautious application of genome scans to studies of divergent selection in subdivided and recently expanded populations.     

Adaptive coat colour polymorphism in the Kermode bear of coastal British Columbia

We investigated potential ecological attributes of the striking coat colour polymorphism in the black bear ( Ursus americanus kermodei Hornaday) occurring on several small islands off the mid-coast of British Columbia, where a white morph (Kermode), fully recessive to the black morph, reaches 10–25% of the population. During three autumn field seasons (2000–2002; 697 h of observation time), we monitored salmon capture behaviour of individual bears (black, N  = 37; white, N  = 4). Both colour morphs foraged on salmon throughout daylight and darkness but with twice the rate during darkness. Log-linear analysis of capture efficiency (success/attempts) and average capture success per bout of the white morph was marginally lower than the black morph during darkness (22.8%, N  = 158 versus 25.8%, N  = 279 respectively; P  < 0.04), although it was significantly higher during daylight (34.1%, N  = 132 versus 25.3%, N  = 896, respectively, P  < 0.02), with similar trends in three different pursuit modes. Replicated ( N  = 10–14) field experiments involving a colour dimorphic simulated predator (i.e. human in a black or white cloak) showed that salmon were one-half as evasive during darkness than during daylight, with no differences ( P  > 0.4) in response to either the white or black models; however, during daylight, salmon were twice as evasive to the black compared to the white model ( P  < 0.001). The persistence of this coat colour polymorphism may be facilitated by increased salmon accessibility to the Kermode bear and diel foraging differences between morphs. These results are consistent with multi-niche models of adaptive variability.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 479–488.     

Geographical variations in freshwater populations of the three-spined stickleback,Gasterosteus aculeatus,in Japan

This paper describes an investigation of morphological variation among six freshwater populations (dominantly low-plated morph) of the three-spined stickleback,Gasterosteus aculeatus, in Japan. Such populations are mainly distributed in restricted water areas within a band from Ise to Wakasa Bays, the most constricted part of Honshu Island. According to some differences in morphological variation, i.e. plate morph, number of lateral plates, body size, body shape and body colour, they were classified into two types corresponding to occurrence in the Ibi River and Lake Biwa water systems. The former type was monomorphic dominated by lowplated morphs in spring-fed water, whereas the latter was a dimorphic population consisting of low- and partially-plated morphs. My results suggest that the plate morph type is not correlated with climate nor predation but is related to geological isolation patterns during the course of the landlocking process. Conversely, variations in meristic (number of dorsal and anal fin rays and gill rakers) and morphometric (body shape and body colour) characteristics may have been related to different environmental conditions. This study also provides supporting evidence that the freshwater three-spined stickleback is a distinct species from the anadromous stickleback,G. aculeatus.     

Male dimorphism, territoriality and mating success in the tropical damselfly, Paraphlebia zoe Selys (Odonata: Megapodagrionidae)

The tropical damselfly Paraphlebia zoe has two male morphs: a black-winged (BW) male which is associated with territorial defense of oviposition sites; and a hyaline-winged (HW) male similar in appearance to females, and, compared to the black morph, less frequently found defending territories. In a wild population of this species, we first assessed the relationship between phenotypic traits [male morph, size and territorial status (being territorial or non-territorial)], their role on mating success, and the degree to which a particular territory may contribute to male mating success. Second, to relate a physiological basis of being territorial we compared both morphs in terms of muscular fat reserves and thoracic muscle, two key traits related to territory defense ability. Males of both morphs defended territories although the BW males were more commonly found doing this. BW males were larger than HW males and size predicted being territorial but only within HW males (territorial males were larger) but not in BW males. Male mating success was related to territorial status (territorial males achieved a higher mating success), but not to morph or size. Furthermore, territory identity also explained mating success with some territories producing more matings than others. The BW morph stored more fat reserves which may explain why this morph was more likely to secure and defend a place than the HW morph. However, the HW morph showed higher relative muscle mass which we have interpreted as a flexible strategy to enable males to defend a territory. These results are distant to what has been found in another male dimorphic damselfly, Mnais pruinosa, where the advantage of the non-territorial morph relies on its longevity to compensate in mating benefits compared to the territorial morph.     

An exuberant, undescribed colour polymorphism in Theridion californicum (Araneae, Theridiidae): implications for a theridiid pattern ground plan and the convergent evolution of visible morphs

An opisthosomal (abdominal) colour polymorphism is described in the North American spider, Theridion californicum , comprising a plain Yellow morph and (at least) ten patterned morphs, which exhibit areas of red or black pigments superimposed on the yellow background, or no pigment (white). The polymorphism appears to be present throughout the species' range. The Yellow morph is the most frequent in populations, with patterned morphs all, individually, being rather rare. Progeny from known mothers were reared and indicate that the polymorphism is genetic and that Yellow is probably recessive to patterned morphs. Similar to other theridiids with well-studied colour polymorphisms, T. californicum occupies an under-leaf habitat and the variation in all these cases might be maintained by sight-hunting predators exerting negative frequency-dependent (apostatic) selection. In T. californicum , blocks of guanine underlying the pigmented hypodermis indicate a segmental patterning, which is not usually apparent in adult spiders. These segments, plus dorso-lateral divisions, permit the dorsal surface of the opisthosoma to be divided up into two mirror-image halves, each comprising 12 compartments. Each compartment can either lack pigment (thus appearing white as a result of underlying guanine) or be yellow, red, or black. All patterns in T. californicum can be derived from this ground plan, as can the morphs of other colour-polymorphic theridiids. It is suggested that selection for polymorphism, combined with constraints imposed by this theridiid ground plan, may have led to the convergent evolution of colour patterns across the family.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 23–34.     

Ecological and evolutionary consequences of the trophic polymorphism in Cichlasoma citrinellum (Pisces: Cichlidae)

The neotropical cichlid fish Cichlasoma citrinellum is polymorphic in the structure of its pharyngeal jaw apparatus and external morphology. The pharyngeal jaws are either gracile and bear slender, pointed teeth (papilliform) or robust with strong, rounded teeth (molariform). Molariform morphs have a ‘benthic’, and papilliform morphs a ‘limnetic’ body form. Furthermore, this species is also polychromatic, with yellow and black morphs. The molariform morphology of the pharyngeal jaw apparatus adapts the fish for cracking and feeding on snails. Based on analysis of stomach contents, 94% of the molariform morph ate snails whereas only 19%, of the papilliform morph did so. This result suggests that the morphs occupy different ecological niches. The morphology of the pharyngeal jaw apparatus does not correlate significantly with sex, but it does with body colouration (P<0.005). Cichlasoma citrinellum mate assortatively with their own colour; therefore a mating preference for colour may lead to genetic isolation of trophic morphs. The frequency of the molariform morph differs strikingly among populations of five Nicaraguan lakes and its abundance is correlated with the abundance of snails, the fishes' principal prey item. Among populations the frequency of molariform morphs decreases in the dry season. Morphology possibly changes reversibly within particular individuals between seasons. These results suggest that phenotypic plasticity and polymorphisms may be an adaptive characteristic of cichlid fishes. Patterns of intraspecific morphological variation match patterns of interspecific morphological diversification which suggests that universal developmental mechanisms canalize the possible expressions of morphology. The ability to respond morphologically to environmental shifts, in conjunction with genetically determined trophic polymorphisms and sexual selection via mate choice, could be the basis for speciation through intermediate stages of polymorphism of the impressive adaptive radiation of cichlid fishes.     

Rice water weevil females of different elytral color morphs: comparisons of locomotor activity, mating success, and reproductive capacity

Females and males of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Erirhinidae), have two elytral color morphs in Texas: the central pattern of their elytra is black (dark morph) or gray (light morph). In southeast Texas, the dark and light females exhibited similar proportions (28.6 and 32.0%, respectively) in populations collected during the spring. In this study, females of the two morphs were collected near rice fields in southeast Texas during April and May 2005. In the laboratory, light females were more active than dark ones. They mated equally successfully with males, irrespective of morph. For females supplied with males for 2 d or kept solitary, and then reared on rice seedlings for 48 d, no significant differences were found between the two morphs in oviposition period, number of eggs deposited, and survival rate. In both morphs, a proportion of mated females did not oviposit throughout the rearing period, implying that a mating experience might be necessary before reproductive development can be initiated. However, oviposition occurred in a proportion of females in which no mating experience could be detected, and their eggs produced larvae, which suggests the probability of existing parthenogenetic females in southeast Texas.     

Comparative life history and parasitism of a new colour morph of the walnut aphid in California

1 The walnut aphid Chromaphis juglandicola is a yellow aphid. In 2003, however, a white colour morph was discovered in the Sacramento Valley of California. The colour dimorphism occurs between clone lines and, when white morphs are present, they occur in mixed colour morph colonies on the underside of walnut leaves. 2 Laboratory experiments were undertaken to evaluate the thermal requirements for development, adult longevity and progeny production of the two colour morphs. Host instar preference of Trioxys pallidus, a parasitoid responsible for the successful biological control of the walnut aphid in California, was examined separately for each colour morph, and host colour preference was investigated for the preferred instar. 3 No differences in thermal requirements for development, adult size or mean longevity were detected between yellow and white colour morphs. A small difference in early reproduction was detected: white colour morphs produced more progeny on each of the two first days of adult reproduction than yellow colour morphs. 4 Trioxys pallidus showed a slight preference for the fourth instar of the yellow morph over the second‐ and third‐, but equal preference for second, third and fourth instars of the white morph. When offered equal numbers of fourth instars of the two colour morphs, T. pallidus did not show any colour preference. 5 The differences in early aphid reproduction and host instar preference by T. pallidus were combined in a stage‐structured matrix model. Model analysis showed a greater potential for population growth of the white morph over the yellow morph, with early reproduction having a greater influence than host instar preference.