QTL analysis and candidate gene mapping for skin and flesh color in sweet cherry fruit (<Emphasis Type="Italic">Prunus avium</Emphasis> L.)

Sweet cherry (Prunus avium L.) skin and fruit colors vary widely due to differences in red and yellow pigment profiles. The two major market classes of sweet cherry represent the two color extremes, i.e., yellow skin with red blush and yellow flesh and dark mahogany skin with mahogany flesh. Yet, within these extremes, there is a continuum of skin and flesh color types. The genetic control of skin and flesh color in sweet cherry was investigated using a quantitative trait locus (QTL) approach with progeny derived from a cross between cherry parents representing the two color extremes. Skin and flesh colors were measured using a qualitative color-card rating over three consecutive years and also evaluated quantitatively for darkness/lightness (L*), red/green (a*), and yellow/blue (b*). Segregations for the color measurements (card, L*, a*, and b*) did not fit normal distributions; instead, the distributions were skewed towards the color of the dark-fruited parent. A major QTL for skin and flesh color was identified on linkage group (LG) 3. Two QTLs for skin and flesh color were also identified on LG 6 and LG 8, respectively, indicating segregation for minor genes. The significance and magnitude of the QTL identified on LG 3 suggests the presence of a major regulatory gene within this QTL interval. A candidate gene PavMYB10, homologous to apple MdMYB10 and Arabidopsis AtPAP1, is within the interval of the major QTL on LG 3, suggesting that PavMYB10 could be the major determinant of fruit skin and flesh coloration in sweet cherry.     

The dark side of coloration: Ecogeographical evidence supports Gloger's rule in American marsupials

Geographical distribution of color phenotypes and associations with ecological predictors remains poorly understood. An important geographic pattern concerning this topic is Gloger's rule, which predicts the increase of pigmentation in endothermic animals from cold and dry to warm and wet environments. Didelphid marsupials exhibit a variety of color patterns, ranging from light and dark uniform to more complex colorations. However, surprisingly little is known about the adaptive significance of dark coloration in this singular group of mammals. Using a phylogenetic comparative approach, we investigated whether coloration in different body regions of didelphids (i.e., dorsum and face) is associated with variables representing heat and humidity of the environment, as predicted by Gloger's rule. We demonstrated that Gloger's rule explains the interspecific color variation in American marsupials, especially when considering the facial region. Thus, dark coloration was more frequent among didelphid species occupying warm and wet environments than cold and dry environments. We also discuss the selective forces that can potentially explain coat color variation in didelphid marsupials, including camouflage, pathogen resistance, and pleiotropy hypotheses.     

Development of a codominant CAPS marker for allelic selection between canary yellow and red watermelon based on SNP in lycopene β-cyclase (<Emphasis Type="Italic">LCYB</Emphasis>) gene

Flesh color of watermelon is an agronomically important trait that is predominantly determined by a network of the carotenoid biosynthetic pathway, which also contributes to the nutritional value of the fruit through the health-promoting function of carotenoids. We have identified a key gene, lycopene β-cyclase (LCYB) that may determine canary yellow and red flesh color of watermelon and developed a zero-distance molecular marker that identifies a critical single nucleotide polymorphism (SNP) that distinguishes different alleles of the LCYB gene. Analysis of the flesh color inheritance in segregating populations indicated that a single gene determines the color difference between canary yellow and red flesh in watermelon. The sequence comparison of full-length cDNA of LCYB, which was isolated using degenerate PCR and RACE, identified three SNPs in the coding region of LCYB between canary yellow and red. These SNPs showed perfect co-segregation with flesh color phenotypes. One of the SNPs introduces an amino acid replacement of evolutionarily conserved Phe226 to Val, which may impair the catalytic function of LCYB. This SNP was used to develop a cleaved amplified polymorphic sequence (CAPS) marker, which perfectly cosegregated with flesh color phenotype. Our results strongly suggest that LCYB may be the genetic determinant for canary yellow or red flesh color and our CAPS marker will allow breeders to economically distinguish between canary yellow and red watermelon fruit color at the seedling stage.     

Climate‐related genetic variation in drought‐resistance of Douglas‐fir (Pseudotsuga menziesii)

There is a general assumption that intraspecific populations originating from relatively arid climates will be better adapted to cope with the expected increase in drought from climate change. For ecologically and economically important species, more comprehensive, genecological studies that utilize large distributions of populations and direct measures of traits associated with drought‐resistance are needed to empirically support this assumption because of the implications for the natural or assisted regeneration of species. We conducted a space‐for‐time substitution, common garden experiment with 35 populations of coast Douglas‐fir (Pseudotsuga menziesii var. menziesii) growing at three test sites with distinct summer temperature and precipitation (referred to as ‘cool/moist’, ‘moderate’, or ‘warm/dry’) to test the hypotheses that (i) there is large genetic variation among populations and regions in traits associated with drought‐resistance, (ii) the patterns of genetic variation are related to the native source‐climate of each population, in particular with summer temperature and precipitation, (iii) the differences among populations and relationships with climate are stronger at the warm/dry test site owing to greater expression of drought‐resistance traits (i.e., a genotype × environment interaction). During midsummer 2012, we measured the rate of water loss after stomatal closure (transpiration_min), water deficit (% below turgid saturation), and specific leaf area (SLA, cm² g^?1) on new growth of sapling branches. There was significant genetic variation in all plant traits, with populations originating from warmer and drier climates having greater drought‐resistance (i.e., lower transpiration_min, water deficit and SLA), but these trends were most clearly expressed only at the warm/dry test site. Contrary to expectations, populations from cooler climates also had greater drought‐resistance across all test sites. Multiple regression analysis indicated that Douglas‐fir populations from regions with relatively cool winters and arid summers may be most adapted to cope with drought conditions that are expected in the future.     

Sexual selection and trichromatic color vision in primates: statistical support for the preexisting-bias hypothesis

The evolution of trichromatic color vision in primates may improve foraging performance as well as intraspecific communication; however, the context in which color vision initially evolved is unknown. We statistically examined the hypothesis that trichromatic color vision in primates represents a preexisting bias for the evolution of red coloration (pelage and/or skin) through sexual selection. Our analyses show that trichromatic color vision evolved before red pelage and red skin, as well as before gregarious mating systems that would promote sexual selection for visual traits and other forms of intraspecific communication via red traits. We also determined that both red pelage and red skin were more likely to evolve in the presence of color vision and mating systems that promote sexual selection. These results provide statistical support for the hypothesis that trichromatic color vision in primates evolved in a context other than intraspecific communication with red traits, most likely foraging performance, but, once evolved, represented a preexisting bias that promoted the evolution of red traits through sexual selection.     

Phylogenetic Correlation Between Male Nuptial Color and Behavioral Responses to Color Across a Diverse and Colorful Genus of Freshwater Fish (Etheostoma spp., Teleostei: Percidae)

Sexual selection theory predicts that preferences in both sexes select for the elaboration of male nuptial coloration, with empirical evidence supporting these predictions. Empirical studies are often limited in their taxonomic inclusiveness, however, and typically do not examine how male and female preferences contribute to macroevolutionary patterns of male color variation across multiple lineages in a clade. This study examined color preferences in a group of dichromatic freshwater fishes known as darters (genus Etheostoma) that vary in the presence of male coloration. The strengths of attraction to black, blue, gray, and red models were tested in females of 18 species, in addition to males of five species. We found a positive association between the presence of red or orange on the body and the amount of time associating with red models, suggesting color variation is at least in part due to variation in female preferences between species. Males also spent more time associating with colors that most closely resembled conspecifics, suggesting that preferential responses to color in males also can contribute to the diversity of nuptial coloration in darters.     

Geographic proximity not a prerequisite for invasion: Hawaii not the source of California invasion by light brown apple moth (Epiphyas postvittana)

Background

The light brown apple moth (LBAM), Epiphyas postvittana (Walker), is native to Australia but invaded England, New Zealand, and Hawaii more than 100 years ago. In temperate climates, LBAM can be a major agricultural pest. In 2006 LBAM was discovered in California, instigating eradication efforts and quarantine against Hawaiian agriculture, the assumption being that Hawaii was the source of the California infestation. Genetic relationships among populations in Hawaii, California, and New Zealand are crucial to understanding LBAM invasion dynamics across the Pacific.

Methodology/Principal Findings

We sequenced mitochondrial DNA (mtDNA) from 1293 LBAM individuals from California (695), Hawaii (448), New Zealand (147), and Australia (3) to examine haplotype diversity and structure among introduced populations, and evaluate the null hypothesis that invasive populations are from a single panmictic source. However, invasive populations in California and New Zealand harbor deep genetic diversity, whereas Hawaii shows low level, shallow diversity.

Conclusions/Significance

LBAM recently has established itself in California, but was in Hawaii and New Zealand for hundreds of generations, yet California and New Zealand show similar levels of genetic diversity relative to Hawaii. Thus, there is no clear relationship between duration of invasion and genetic structure. Demographic statistics suggest rapid expansion occurring in California and past expansions in New Zealand; multiple introductions of diverse, genetically fragmented lineages could contribute to these patterns. Hawaii and California share no haplotypes, therefore, Hawaii is not the source of the California introduction. Paradoxically, Hawaii and California share multiple haplotypes with New Zealand. New Zealand may be the source for the California and Hawaii infestations, but the introductions were independent, and Hawaii was invaded only once. This has significant implications for quarantine, and suggests that probability of invasion is not directly related to geographic distance. Surprisingly, Hawaiian LBAM populations have much lower genetic diversity than California, despite being older.     

Population-Specific Covariation between Immune Function and Color of Nesting Male Threespine Stickleback

Multiple biological processes can generate sexual selection on male visual signals such as color. For example, females may prefer colorful males because those males are more readily detected (perceptual bias), or because male color conveys information about male quality and associated direct or indirect benefits to females. For example, male threespine stickleback often exhibit red throat coloration, which females prefer both because red is more visible in certain environments, and red color is correlated with male immune function and parasite load. However, not all light environments favor red nuptial coloration: more tannin-stained water tends to favor the evolution of a melanic male phenotype. Do such population differences in stickleback male color, driven by divergent light environments, lead to changes in the relationship between color and immunity? Here, we show that, within stickleback populations, multiple components of male color (brightness and hue of four body parts) are correlated with multiple immune variables (ROS production, phagocytosis rates, and lymphocyte:leukocyte ratios). Some of these color-immune associations persist across stickleback populations with very different male color patterns, whereas other color-immune associations are population-specific. Overall, lakes with red males exhibit stronger color-immune covariance while melanic male populations exhibit weak if any color-immune associations. Our finding that color-immunity relationships are labile implies that any evolution of male color traits (e.g., due to female perceptual bias in a given light environment), can alter the utility of color as an indicator of male quality.     

Is Brightest Best? Testing the Hamilton-Zuk Hypothesis in Mandrills

Although many primates exhibit striking coloration, including brightly colored pelage and bare areas of skin, our understanding of the function and evolution of these traits pales in the face of knowledge about color in other taxa. However, recent years have seen an increase in the number of studies of individual variation in primate color and evidence is accumulating that these traits can act as important signals to conspecifics. Mandrills are arguably the most colorful of all primates. Here, we review what we have discovered about the signal function of coloration in male and female mandrills from our long-term studies of a semi-free-ranging colony in Franceville, Gabon and test the predictions of the Hamilton-Zuk hypothesis—that bright coloration is condition dependent, and that only individuals of superior quality will be able to express color fully—in this species. We compare measures of facial coloration in both sexes with parasite load (using fecal analysis over 1 annual cycle), immune status (hematological parameters), neutral genetic diversity (microsatellite heterozygosity), and major histocompatability (MHC) genotype to examine whether red coloration acts as an honest signal of individual quality in mandrills. We found that red coloration was unrelated to parasitism and hematological parameters. Red was also unrelated to genome-wide heterozygosity and MHC diversity, although specific MHC genotypes were significantly related to red. The healthy, provisioned nature of the colony and problems associated with observational, correlational studies restrict interpretation of our data, and it would be premature to draw conclusions as to whether color signals individual quality in mandrills. We conclude with some suggestions for future studies on the signal content of color in mandrills and other primates.     

Foliage color contrasts and adaptive fruit color variation in a bird-dispersed plant community

The color of vertebrate-dispersed fruits has been a source of inquiry for over 150 years, yet the ecological and evolutionary processes responsible for fruit color diversity remain elusive. We tested the hypothesis that fruit color varies temporally, to maximize conspicuousness against seasonal changes in foliage coloration, in a bird-dispersed plant community in western North America. Field observations showed that while red fruits predominate during summer periods of green foliage coloration, black fruits are produced during flushes of red-orange foliage coloration in autumn. Although two species did not conform to this pattern, one produced its own contrasting background color, via colored bracts. We conducted experimental manipulations of both fruit color and the color of artificial backgrounds to test whether both factors had a synergistic effect on fruit removal rates. Interactions between fruit and background color explained most of the variation in experimental fruit removal rates. Although red fruits were removed rapidly on green backgrounds, preference for black fruits on red-orange backgrounds was less pronounced. Consequently, the temporal pattern in fruit color appears to result from elevated fruit conspicuousness against seasonal changes in foliage coloration. Support for this hypothesis suggests a temporal connection between fruit color diversity, foliage color contrasts and avian color preferences.     

Mapping quantitative trait loci associated with blush in peach [Prunus persica (L.) Batsch]

Blush is an important trait for marketing peaches. The red skin pigmentation develops through the flavonoid and anthocyanin pathways, and both genetic and environmental stimuli, and their interaction, control the regulation of these pathways. The molecular basis of blush development in peach is yet to be understood. An F₂ blush population (ZC²) derived from a cross between two peach cultivars with contrasting phenotypes for blush, “Zin Dai” (～30 % red) and “Crimson Lady” (～100 % red), was used for linkage map construction and quantitative trait loci (QTLs) mapping. The segregating population was phenotyped for blush for 4 years using a visual rating scale and quantified using a colorimeter (L*, a*, and b*) 1 year. The ZC² population was genotyped with the IPSC 9 K peach single-nucleotide polymorphism (SNP) array v1, and a high-density ZC² genetic linkage map was constructed. The map covers genetic a distance of ～452.51 cM with an average marker spacing of 2.38 cM/marker. Four QTLs were detected: one major QTL on LG3 (Blush.Pp.ZC-3.1) and three minor QTLs on LG 4 and 7 (Blush.Pp.ZC-4.1; Blush.Pp.ZC-4.2; Blush.Pp.ZC-7.1), indicating the presence of major and minor genes involved in blush development. Candidate genes involved in skin and flesh coloration of peach (PprMYB10), cherry (PavMYB10), and apple (MdMYB1/MdMYBA/MdMYB10) are located within the interval of the major QTL on LG3, suggesting the same genetic control for color development in the Rosaceae family. Marker-assisted selection (MAS) for blush is discussed.     

Countergradient variation and secondary sexual color: phenotypic convergence promotes genetic divergence in carotenoid use between sympatric anadromous and nonanadromous morphs of sockeye salmon (Oncorhynchus nerka)

Genetically distinct anadromous (sockeye) and nonanadromous (kokanee) morphs of the Pacific salmon, Oncorhynchus nerka, develop identical, brilliant red color at maturity during sympatric breeding in freshwater streams. The marine and lacustrine environments they occupy prior to maturity, however, appear to differ in the availability of dietary carotenoid pigments necessary to produce red coloration. We tested the hypothesis that kokanee, which occupy carotenoid-poor lakes, are more efficient at using the dietary pigments than are sockeye, which occupy the more productive North Pacific Ocean. In a 2-year controlled breeding study, flesh and skin color of mature and immature crosses fed a low-carotenoid diet were quantified with both a chromameter and by chemical extraction of carotenoid pigments. Results revealed striking countergradient variation in carotenoid use, with kokanee approximately three times more efficient at sequestering the pigments to the flesh musculature than similar age sockeye. This difference translated into virtually nonoverlapping differences between pure crosses in secondary sexual color at maturity, when the pigments are mobilized and transported to the skin. Kokanee crosses turned pinkish red over most of their body, whereas sockeye turned olive green. The olive green was similar to the breeding color of residuals in the wild, the progeny of anadromous sockeye that remain in fresh water and are believed to have given rise to kokanee on numerous independent occasions. Reciprocal hybrids were similar to each other and intermediate to the pure crosses, indicating additive genetic inheritance. Mate choice trials with sockeye males in the wild showed the ancestral morph strongly preferred red over green models. These results suggest a preference for red mates maintained in nonanadromous breeding populations drove the reevolution of the red phenotype in kokanee via more efficient use of dietary carotenoid pigments. This is a novel, yet hidden, mechanism by which sexual selection promotes the genetic differentiation of these sympatric populations.     

A detailed linkage map around an apple scab resistance gene demonstrates that two disease resistance classes both carry the V f gene

A detailed genetic map has been constructed in apple (Malus x domestica Borkh.) in the region of the v _f gene. This gene confers resistance to the apple scab fungus Venturia inaequalis (Cooke) Wint. Linkage data on four RAPD (random amplified polymorphic DNA) markers and the isoenzyme marker PGM-1, previously reported to be linked to the v _f gene, are integrated using two populations segregating for resistance to apple scab. Two new RAPD markers linked to v _f (identified by bulked segregant analysis) and a third marker previously reported as being present in several cultivars containing v _f are also placed on the map. The map around v _f now contains eight genetic markers spread over approximately 28 cM, with markers on both sides of the resistance gene. The study indicates that RAPD markers in the region of crab apple DNA introgressed with resistance are often transportable between apple clones carrying resistance from the same source. Analysis of co-segregation of the resistance classes 3A (weakly resistant) and 3B (weakly susceptible) with the linked set of genetic markers demonstrates that progeny of both classes carry the resistance gene.This work was supported in part by grants from the New Zealand Foundation for Research Science and Technology (FoRST) Programme 94-HRT-07-366 and ENZA New Zealand (International)     

Dispersal, disturbance and the contrasting biogeographies of New Zealand's diadromous and non-diadromous fish species

Aim To examine the relationship between diadromy and dispersal ability in New Zealand’s freshwater fish fauna, and how this affects the current environmental and geographic distributions of both diadromous and non‐diadromous species. Location New Zealand. Methods Capture data for 15 diadromous and 15 non‐diadromous fish species from 13,369 sites throughout New Zealand were analysed to establish features of their geographic ranges. Statistical models were used to determine the main environmental correlates of species’ distributions, and to establish the environmental conditions preferred by each species. Environmental predictors, chosen for their functional relevance, were derived from an extensive GIS database describing New Zealand’s river and stream network. Results In terms of geography, most diadromous species occur in a scattered fashion throughout extensive geographic ranges, and occupy large numbers of catchments of widely varying size. By contrast, most non‐diadromous species show relatively high levels of occupancy of smaller geographic ranges, and most are restricted to a few large catchments, particularly in the eastern South Island. In terms of environment, there is marked separation of diadromous from non‐diadromous species, with diadromous species generally caught most frequently in low‐gradient coastal rivers and streams with warm, maritime climates. With a few notable exceptions, most diadromous species have lower occurrence in river segments that are located above obstacles to upstream migration. Non‐diadromous species are usually caught in inland rivers and streams with cool, strongly seasonal climates, typified by a low frequency of high‐intensity rainfall events. Main conclusions We interpret the contrasting biogeographies of New Zealand’s diadromous and non‐diadromous species as reflecting interaction between their marked differences in dispersal ability and a landscape that is subject to recurrent, often large‐scale, natural disturbance. While both groups are likely to be equally susceptible to local, disturbance‐driven extinction, the much greater dispersal ability of diadromous species has allowed them to persist over wide geographic ranges. By contrast, the distributions of most non‐diadromous species are concentrated in a few large catchments, mostly in regions where less intense natural disturbance regimes are likely to have favoured their survival.     

Experimental Tests for Heritable Morphological Color Plasticity in Non-Native Brown Trout (Salmo trutta) Populations

The success of invasive species is frequently attributed to phenotypic plasticity, which facilitates persistence in novel environments. Here we report on experimental tests to determine whether the intensity of cryptic coloration patterns in a global invader (brown trout, Salmo trutta) was primarily the result of plasticity or heritable variation. Juvenile F₁ offspring were created through experimental crosses of wild-caught parents and reared for 30 days in the laboratory in a split-brood design on either light or dark-colored gravel substrate. Skin and fin coloration quantified with digital photography and image analysis indicated strong plastic effects in response to substrate color; individuals reared on dark substrate had both darker melanin-based skin color and carotenoid-based fin colors than other members of their population reared on light substrate. Slopes of skin and fin color reaction norms were parallel between environments, which is not consistent with heritable population-level plasticity to substrate color. Similarly, we observed weak differences in population-level color within an environment, again suggesting little genetic control on the intensity of skin and fin colors. Taken as whole, our results are consistent with the hypothesis that phenotypic plasticity may have facilitated the success of brown trout invasions and suggests that plasticity is the most likely explanation for the variation in color intensity observed among these populations in nature.     

Color discrimination by the cotton-top tamarin (Saguinus oedipus oedipus) and its relation to fruit coloration

Old World monkeys and apes have been reported to differ from New World monkeys in their abilities to discriminate colors across the visible spectrum. Old World monkeys and apes (Macaca, Pan, Pongo) discriminate colors quite accurately, while some New World monkeys studied (Saimiri, Cebus) have shown lower sensitivity to and poorer discrimination of long wavelength light. This study examined the color discrimination ability of another New World primate, the cotton-top tamarin, Saguinus oedipus oedipus (family Callitrichidae). The tamarins were trained to discriminate a set of Munsell color chips, both within the same hue category and from the 2 hue categories on either side of the training hue. Results indicated that the cotton-top tamarin can make accurate discriminations across the visible spectrum. Human subjects were tested under similar conditions in order to compare their color discrimination abilities to those of the tamarins. The tamarins and human subjects had the most difficulty discriminating the same hues. The discrimination abilities of the monkeys were assessed in relation to the coloration of fruits eaten in a natural environment. A list of the species of fruits commonly eaten by various species of New World monkeys was compiled and the coloration of fruits at maturity was noted. It was found that most New World primate species eat fruits whose mature coloration ranges across most of the spectrum.