THE INFLUENCE OF FLOWER COLOR ON OUTCROSSING RATE AND MALE REPRODUCTIVE SUCCESS IN IPOMOEA PURPUREA

Experimental populations of the annual plant, Ipomoea purpurea, composed of individuals belonging to two flower color morphs were studied to determine the effect of flower color on outcrossing rate and reproductive success as a male parent. Analyses of parent and offspring genotypes show that the pigmented and white morphs outcross at similar rates, but that the white morph is favored as a pollen donor. The result suggests that the dynamics of selection occurring at the locus coding for white versus pigmented flowers are more complex than previously believed. Factors such as frequency-dependent outcrossing rates and epistatic effects of the white allele may be operating. The results also suggest that pollinator observations are unreliable indicators of the actual mating system.     

Gudgeon fish with and without genetically determined countershading coexist in heterogeneous littoral environments of an ancient lake

Countershading, characterized by a darker dorsal surface and lighter ventral surface, is common among many animals. This dorsoventral pigment polarity is often thought to be adaptive coloration for camouflage. By contrast, noncountershaded (melanistic) morphs often occur within a species due to genetic color polymorphism in terrestrial animals. However, the polymorphism with either countershaded or melanistic morphs is poorly known in wild aquatic animals. This study explored the genetic nature of diverged color morphs of a lineage of gudgeon fish (genus Sarcocheilichthys) in the ancient Lake Biwa and propose this system as a novel model for testing hypotheses of functional aspects of countershading and its loss in aquatic environments. This system harbors two color morphs that have been treated taxonomically as separate species; Sarcocheilichthys variegatus microoculus which occurs throughout the littoral zone and Sarcocheilichthys biwaensis which occurs in and around rocky areas. First, we confirmed that the divergence of dorsoventral color patterns between the two morphs is under strict genetic control at the levels of chromatophore distribution and melanin‐related gene expression under common garden rearing. The former morph displayed sharp countershading coloration, whereas the latter morph exhibited a strong tendency toward its loss. The crossing results indicated that this divergence was likely controlled by a single locus in a two‐allele Mendelian inheritance pattern. Furthermore, our population genomic and genome‐wide association study analyses detected no genome‐wide divergence between the two morphs, except for one region near a locus that may be associated with the color divergence. Thus, these morphs are either in a state of intraspecific color polymorphism or two incipient species. Evolutionary forces underlying this polymorphism appear to be associated with heterogeneous littoral environments in this lake. Future ecological genomic research will provide insight into adaptive functions of this widespread coloration, including the eco‐evolutionary drivers of its loss, in the aquatic world.     

Pollinator response to flower color polymorphism and floral display in a plant with a single-locus floral color polymorphism: consequences for plant reproduction

Variation in flower color, particularly polymorphism, in which two or more different flower color phenotypes occur in the same population or species, may be affected or maintained by mechanisms that depend on pollinators. Furthermore, variation in floral display may affect pollinator response and plant reproductive success through changes in pollinator visitation and availability of compatible pollen. To asses if flower color polymorphism and floral display influences pollinator preferences and movements within and among plants and fitness-related variables we used the self-incompatible species Cosmos bipinnatus Cav. (Asteraceae), a model system with single-locus flower color polymorphism that comprises three morphs: white (recessive homozygous), pink (heterozygous co-dominate), and purple (dominant homozygous) flowers. We measured the preferences of pollinators for each morph and constancy index for each pollinator species, pollination visitation rate, floral traits, and female fitness measures. Flower color morphs differed in floral trait measures and seed production. Pollinators foraged nonrandomly with respect to flower color. The most frequent morph, the pink morph, was the most visited and pollinators exhibited the highest constancy for this morph. Moreover, this morph exhibited the highest female fitness. Pollinators responded strongly to floral display size, while probed more capitulums from plants with large total display sizes, they left a great proportion of them unvisited. Furthermore, total pollinator visitation showed a positive relation with female fitness. Results suggest that although pollinators preferred the heterozygous morph, they alternate indiscriminately among morphs making this polymorphism stable.     

Preference for Male Traits Differ in Two Female Morphs of the Tree Lizard,Urosaurus ornatus

Non-random female mating preferences may contribute to the maintenance of phenotypic variation in color polymorphic species. However, the effect of female preference depends on the types of male traits used as signals by receptive females. If preference signals derive from discrete male traits (i.e., morph-specific), female preferences may rapidly fix to a morph. However, female preference signals may also include condition-dependent male traits. In this scenario, female preference may differ depending on the social context (i.e., male morph availability). Male tree lizards (Urosaurus ornatus) exhibit a dewlap color polymorphism that covaries with mating behavior. Blue morph males are aggressive and defend territories, yellow males are less aggressive and defend smaller territories, and orange males are typically nomadic. Female U. ornatus are also polymorphic in dewlap color, but the covariation between dewlap color and female behavior is unknown. We performed an experiment to determine how female mate choice depends on the visual and chemical signals produced by males. We also tested whether female morphs differ in their preferences for these signals. Female preferences involved both male dewlap color and size of the ventral color patch. However, the female morphs responded to these signals differently and depended on the choice between the types of male morphs. Our experiment revealed that females may be capable of distinguishing among the male morphs using chemical signals alone. Yellow females exhibit preferences based on both chemical and visual signals, which may be a strategy to avoid ultra-dominant males. In contrast, orange females may prefer dominant males. We conclude that female U. ornatus morphs differ in mating behavior. Our findings also provide evidence for a chemical polymorphism among male lizards in femoral pore secretions.     

POSTZYGOTIC GENETIC INCOMPATIBILITY BETWEEN SYMPATRIC COLOR MORPHS

Alternative genetically determined color morphs within a population or species are believed to successfully interbreed within a population. However, the occurrence of prezygotic or ecological selection in a number of polymorphic systems may lead to nonrandom mating and prevent genetic morphs from fully interbreeding. Here we show that postzygotic incompatibility significantly limits gene flow between the sympatric red and black color morphs of the Gouldian finch ( Erythrura gouldiae ). Using a balanced within-female experimental design, in which individuals were forced to breed in pure and mixed morph crosses, we found large inviability effects (>30%) in offspring resulting from genetically mixed genotypes. The consistent mortality effects across different stages of development (e.g., prehatching, juvenile, adulthood), unconfounded by environmentally derived parental effects or social environments, reveal an underlying genetic incompatibility between different genotypes. Furthermore, mortality in mixed morph genotypes was particularly severe (43.6%) for the heterogametic sex (daughters), which is consistent with Haldane's rule predicted for postzygotic incompatibilities between hybridizing species. This significant, but incomplete, postzygotic isolation suggests that the sympatric morphs may represent transient stages in the speciation–hybridization process.     

Differences in Bacterial Community Structure in Two Color Morphs of the Hawaiian Reef Coral Montipora capitata

Corals harbor diverse bacterial associations that contribute to the health of the host. Using 16S rRNA pyrosequencing, we compared the bacterial communities of red and orange morphs of the Hawaiian coral Montipora capitata. Although both color morphs shared dominant bacterial genera, weighted and unweighted UniFrac analyses showed distinct bacterial communities. A single operational taxonomic unit (OTU), classified as Vibrio, represented the largest driver of differences between the color morphs. This OTU comprised 35.4% (±5.5%) of the orange morph bacterial community yet comprised 1.1% (±0.6%) of the red morph bacterial community. Cultivable bacteria from the two color morphs were also compared and tested for antibacterial activity. Cultured isolates represented 14 genera (7% of the total genera identified from sequencing data), and all but two cultured isolates had a matching OTU from the sequencing data. Half of the isolates tested (8 out of 16) displayed antibacterial activity against other cultured isolates but not against two known bacterial pathogens of M. capitata. The results from this study demonstrate that the specificity of coral-bacterial associations extends beyond the level of coral species. In addition, culture-dependent methods captured bacterial diversity that was representative of both rare and abundant members of the associated bacterial community, as characterized by culture-independent methods.     

Direct and indirect selection on floral pigmentation by pollinators and seed predators in a color polymorphic South African shrub

The coexistence of different color morphs is often attributed to variable selection pressures across space, time, morph frequencies, or selection agents, but the routes by which each morph is favored are rarely identified. In this study we investigated factors that influence floral color polymorphisms on a local scale in Protea, within which approximately 40% of species are polymorphic. Previous work shows that seed predators and reproductive differences likely contribute to maintaining polymorphism in four Protea species. We explored whether selection acts directly or indirectly on floral color in two populations of Protea aurea, using path analysis of pollinator behavior, nectar production, seed predation, color, morphology, and maternal fecundity fitness components. We found that avian pollinators spent more time on white morphs, likely due to nectar differences, but that this had no apparent consequences for fecundity. Instead, the number of flowers per inflorescence underpinned many of the reproductively important differences between color morphs. White morphs had more flowers per inflorescence, which itself was positively correlated with nectar production, seed predator occurrence, and total long-term seed production. The number of seeds per plant to survive predation, in contrast, was not directly associated with color or any other floral trait. Thus, although color differences may be associated with conflicting selection pressures, the selection appears to be associated with the number of flowers per inflorescence and its unmeasured correlates, rather than with inflorescence color itself.     

Polymorphic populations of Dactylorhiza incarnata s.l. (Orchidaceae) on the Baltic island of Gotland: morphology, habitat preference and genetic differentiation

Background and Aims

Organisms may be polymorphic within natural populations, but often the significance and genetic background to such polymorphism is not known. To understand the colour polymorphism expressed in the diploid marsh-orchids Dactylorhiza incarnata, morphological, habitat and genetic differentiation was studied in mixed populations on the island of Gotland, supplemented with genetic marker data from adjacent areas.

Methods

A total of 398 accessions was investigated for plastid haplotype and three nuclear microsatellites. Morphometric data and vegetation data were obtained from a subset of 104 plants.

Key Results

No clear pattern of habitat differentiation was found among the colour morphs. Within sites, the yellow-flowered morph (ochroleuca) was slightly larger than the others in some flower characters, whereas the purple-flowered morph with spotted leaves (cruenta) was on average smaller. However, populations of the same colour morph differed considerably between sites, and there was also considerable overlap between morphs. Morphs were often genetically differentiated but imperfectly separated within sites. Most populations were characterized by significant levels of inbreeding. The ochroleuca morph constitutes a coherent, highly homozygous sublineage, although introgression from purple-flowered morphs occurs at some sites. The cruenta morph was genetically variable, although Gotland populations formed a coherent group. Purple-flowered plants with unspotted leaves (incarnata in the strict sense) were even more variable and spanned the entire genetic diversity seen in the other morphs.

Conclusions

Colour polymorphism in D. incarnata is maintained by inbreeding, but possibly also by other ecological factors. The yellow-flowered morph may best be recognized as a variety of D. incarnata, var. ochroleuca, and the lack of anthocyanins is probably due to a particular recessive allele in homozygous form. Presence of spotted leaves is an uncertain taxonomic character, and genetic differentiation within D. incarnata would be better described by other morphological characters such as leaf shape and stature and size and shape of lip and spur.Key words: Dactylorhiza incarnata, cruenta, ecology, genetic differentiation, Gotland, microsatellites, ochroleuca, plastid DNA, polymorphism     

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.     

Variation of Freckled Goatfish <Emphasis Type="Italic">Upeneus tragula</Emphasis> (Mullidae): Color Morphs off Hon Thom (Gulf of Thailand,South China Sea)

Two color morphs of freckled goatfish Upeneus tragula with different Vietnamese names and mainly black and red body coloration of fresh dead exemplars are found off Hon Thóm (Thom Island), the largest island of An Thoi Archipelago located to the south of Phu Quoc Island, Gulf of Thailand, South China Sea. The presence of the morphs may be connected with the occurrence of two sympatric stocks or with color variation within a single stock. To test these hypotheses, red color content on the body (based on digital analysis of images) and gonadal condition is compared in both morphs. Body coloration does not depend on the sex of the fish. The black morph differs from the red morph in a smaller body size (12.7 vs. 16.4 cm FL on average), and it is represented by mainly immature individuals of both sexes (mean gonadosomatic index of the females 0.5 vs. 2.0%). It is proposed that the change of body coloration is associated with sexual maturation, and it occurs in the ontogeny within a single stock.     

Phenotypic plasticity in insects: the effects of substrate color on the coloration of two ground-hopper species

SUMMARY The question of how phenotypic variation is maintained within populations has long been a central issue in evolutionary biology. Most of these studies focused on the maintenance of genetic variability, but the phenotype of organisms may also be influenced by environmental cues experienced during ontogeny. Color polymorphism has received particular attention in evolutionary studies as it has strong fitness consequences. However, if body coloration is influenced by the environment, any conclusions on evolutionary consequences of fitness trade-offs can be misleading. Here we present data from a laboratory experiment on the influence of substrate color on three aspects of the coloration of two ground-hopper species, Tetrix subulata and Tetrix ceperoi . We reared hatchlings either on dark or on light substrates, using a split-brood design. Although the type of pronotal pattern changed mainly in response to nymphal development, the basic color was strongly influenced by the substrate color. In both species, black and dark olive color morphs were found more frequently on the dark substrate, whereas the gray color morph dominated on the light substrate. These findings have considerable implications for our understanding of color morph evolution as they show that color polymorphism may not only be maintained by natural selection acting on discrete color morphs, but also by phenotypic plasticity, which enables organisms to adjust to the environmental conditions experienced during ontogeny. This facultative morphology is opposing to the prevailing view of color morph adaptation, which assumes a purely genetic determination and co-evolution of discrete color morphs with life history traits.     

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.     

Pollen competition between morphs in a pollen‐color dimorphic herb and the loss of phenotypic polymorphism within populations

Flower color polymorphism is relatively uncommon in natural flowering plants, suggesting that maintenance of different color morphs within populations is difficult. To address the selective mechanisms shaping pollen‐color dimorphism, pollinator preferences and reproductive performance were studied over three years in Epimedium pubescens in which some populations had plants with either green or yellow pollen (and anthers). Visitation rate and pollen removal and receipt by the bee pollinator (Andrena emeishanica) did not differ between the two color morphs. Compared to the green morph, siring success of the yellow morph's pollen was lower, but that of mixtures of pollen from green and yellow morphs was lowest. This difference, corresponding to in vivo and ex vivo experiments on pollen performance, indicated that pollen germination, rather than tube growth, of the green morph was higher than that of the yellow morph and was seriously constrained in both morphs if a pollen competitor was present. A rare green morph may invade a yellow‐morph population, but the coexistence of pollen color variants is complicated by the reduced siring success of mixed pollinations. Potential pollen competition between morphs may have discouraged the maintenance of multiple phenotypes within populations, a cryptic mechanism of competitive exclusion.     

Odour-Mediated Orientation of Beetles Is Influenced by Age,Sex and Morph

The behaviour of insects is dictated by a combination of factors and may vary considerably between individuals, but small insects are often considered en masse and thus these differences can be overlooked. For example, the cowpea bruchid Callosobruchus maculatus F. exists naturally in two adult forms: the active (flight) form for dispersal, and the inactive (flightless), more fecund but shorter-lived form. Given that these morphs show dissimilar biology, it is possible that they differ in odour-mediated orientation and yet studies of this species frequently neglect to distinguish morph type, or are carried out only on the inactive morph. Along with sex and age of individual, adult morph could be an important variable determining the biology of this and similar species, informing studies on evolution, ecology and pest management. We used an olfactometer with motion-tracking to investigate whether the olfactory behaviour and orientation of C. maculatus towards infested and uninfested cowpeas and a plant-derived repellent compound, methyl salicylate, differed between morphs or sexes. We found significant differences between the behaviour of male and female beetles and beetles of different ages, as well as interactive effects of sex, morph and age, in response to both host and repellent odours. This study demonstrates that behavioural experiments on insects should control for sex and age, while also considering differences between adult morphs where present in insect species. This finding has broad implications for fundamental entomological research, particularly when exploring the relationships between physiology, behaviour and evolutionary biology, and the application of crop protection strategies.     

Florivores prefer white versus pink petal color morphs in wild radish, Raphanus sativus

Many hypotheses suggest that pollinators act to maintain or change floral color morph frequencies in nature, although pollinator preferences do not always match color morph frequencies in the field. Therefore, non-pollinating agents may also be responsible for color morph frequencies. To test this hypothesis, we examined whether Raphanus sativus plants with white flowers received different amounts of florivory than plants with pink flowers, and whether florivores preferred one floral color over the other. We found that white-flowered plants received significantly more floral damage than pink-flowered plants in eight populations over 4 years in northern California. Both generalists and specialists on Brassicaceae preferred white petals in choice and short-term no choice tests. In performance tests, generalists gained more weight on white versus pink petals whereas specialists gained similar amounts of weight on pink and white morphs. Because our results suggest that florivores prefer and perform better on white versus pink flowers, these insects may have the opportunity to affect the frequency of color morphs in the field.     

Why are female color polymorphisms rare in territorial damselflies?

In nonterritorial damselflies, females often come in multiple color morphs, perhaps because females with rare colors experience reduced sexual harassment, and thus have a frequency‐dependent fitness advantage, compared to females of the most common color morph, but such polymorphisms are rare in territorial species. We consider three hypotheses to explain the rarity of female color polymorphisms in territorial species: (a) misdirected male aggression, (b) poor male mate recognition, and (c) low mating harassment rates. The first hypothesis has some empirical support, and can account for the absence of andromorphs (i.e., females that resemble males), but does not explain the absence of multiple heteromorphs. We tested the second hypothesis by presenting females of two novel color morphs (green‐ or red‐banded abdomens) to territorial male Hetaerina capitalis. Females of both novel color morphs elicited fewer sexual responses than control females, and the red morph occasionally elicited aggressive responses. These results indicate that novel female color morphs would experience reduced mating harassment in this species, contradicting the hypothesis that male mate recognition is too poorly developed to reduce harassment of novel female morphs. By process of elimination, the third hypothesis, that harassment rates are too low in territorial species to provide rare female morphs a fitness advantage, is favored, but remains untested. Our findings also suggest that the common practice of color‐marking odonates for behavioral research is likely to interfere with mate choice, as has long been known to be the case in birds.     

Inheritance of glabrous plants in <Emphasis Type="Italic">Helianthemum oelandicum</Emphasis> var. <Emphasis Type="Italic">oelandicum</Emphasis> and spatial patterns of allele frequencies in local populations

Helianthemum oelandicum var. oelandicum is an endemic taxon on the Baltic island of Öland, SE Sweden. Plants can be classified into two morphs: the bristled morph (with bristles and with or without scattered stellate hairs) and the glabrous morph (without bristles and stellate hairs). In crosses between plants assumed to be homozygous for the trait that characterises the phenotypes of the two morphs, offspring in F1 could not be distinguished from the bristled morph. Segregation in F2 did not deviate from the expected 3:1 ratio (bristled morphs/glabrous morphs), indicating one major gene with a dominant allele for the phenotype of the bristled morph and a recessive allele for the phenotype of the glabrous morph. Besides the Mendelian inheritance of presence/absence of hairs, the density of hairs appeared to be further modified by quantitative genes. The frequency of the recessive allele for the phenotype of the glabrous morph varied among local populations and showed a geographical structure, both on local and regional scales. Possible mechanisms behind the spatial variation in indumentum are discussed.     

Survivorship and fecundity of the radiate and non-radiate morphs of Groundsel,Senecio vulgaris L., raised in pure stand and mixture

British populations of Senecio vulgaris frequently contain two common capitulum morphs (radiate and non-radiate) and one rare intermediate morph. The radiate morph shows a higher maternal rate of intermorph outcrossing than the non-radiate morph and due to the ‘cost of outcrossing’ should decline in frequency, ultimately to be lost from a population. To determine whether the radiate morph exhibits some inherent advantage in fitness to offset the ‘cost of outcrossing’, a comparison was made of the survivorship and fecundity of the radiate and non-radiate morphs raised in pure stands and 1 : 1 mixture at three planting dates (autumn 1983, and spring and autumn 1984). Plants in stands established in spring 1984 were harvested in late August 1984, while plants in stands established in autumn overwintered before being harvested the following summer. In spring planted stands, the two morphs exhibited equivalent survivorships, while the fecundity of the non-radiate morph tended to be greater than the radiate morph. In autumn planted stands, survivorship and Net Reproductive Output (survivorship × fecundity) of the non-radiate morph was greater than that of the radiate morph in mixture, and also in pure stands established in 1983. In no instance was the Net Reproductive Output of either morph significantly greater in mixture than in pure stand. Density had a contrasting effect on morph survivorship and fecundity in the spring and autumn 1984 planted stands. Whereas, in spring stands, fecundity was subject to compensating density dependent regulation while survivorship was density independent, the opposite trend was observed in autumn planted stands. It is concluded that under the conditions of the experiments, the radiate morph exhibited no fitness advantage which might offset the inherent disadvantage it suffers in natural polymorphic populations due to the ‘cost of outcrossing’.     

棕背伯劳羽色多态现象探讨

羽色多态现象的研究对了解物种的遗传、变异和进化有着重要意义。棕背伯劳(Lanius schach)具有典型的羽色多态现象。结合华南濒危动物研究所馆藏标本和2005年4月—2007年1月间的野外调查,分析棕背伯劳棕色型和黑色型在形态和地理分布上的差异性后,得到的结果如下:1)广东可能存在与棕色型、黑色型相区别的一种新色型——黑色白边型,该色型全身以黑色为主,但具多枚白色飞羽;2)棕色型与黑色型各身体量度均无显著性差异(P>0.05);3)野外种群中棕色型为优势色型,黑色型多集中于沿海地区而山区未有发现,黑色白边型仅在沿海的海丰县被发现。据此认为新色型的出现说明沿海可能是黑色型分化的重要地区,且色型的分化仍在进行中。