Asymmetry in pollen flow promotes gender specialization in morphs of the distylous neotropical herb <Emphasis Type="Italic">Arcytophyllum lavarum</Emphasis> (Rubiaceae)

Distyly is a floral polymorphism, characterized by a reciprocal positioning between stigmas and anthers in different flowers, where two floral morphs, long-styled (pin) and short-styled (thrum) occur within the population. Distyly is suggested as one of the routes leading to the evolution of separate sexes in plants. In this evolutionary pathway, pollinators may disrupt the complementarity of pollen transfer between morphs. Consequently, the floral morphs gradually specialize as either male or female. A key process required for gender specialization in distylous plants is a deviation of the realized functional gender (i.e. the proportion of genes transmitted to the next generation via pollen donation and seed production) from the potential functional gender (i.e. the expected contribution of male and female function to reproductive success from the number of ovules or pollen grains produced by each morph). I selected the distylous herb Arcytophyllum lavarum (Rubiaceae) to determine if asymmetry in pollen flow promotes differences in seed production, pollen donation and a discrepancy between the potential and the realized functional genders in pin and thrum floral morphs. Pollen flow in A. lavarum is asymmetric and the pin morph is more efficient at performing cross-pollination than the thrum morph. Conversely, the thrum morph produced two times more seeds than the pin morph. Male and female contributions to the potential functional gender were equivalent in both morphs. However, the pin morph transmitted more genes through pollen donation and the thrum morph more through seed production than expected from their potential functional genders. These results support the hypothesis that if pollinators consistently promote asymmetric pollen flow between morphs over generations, it is possible that gender specialization may evolve to the extreme of dioecism from an original distylous condition.     

Phenotypic plasticity in the Antarctic fish <Emphasis Type="Italic">Trematomus newnesi</Emphasis> (Nototheniidae) from the South Shetland Islands

The presence of the two morphs, “typical” and “large mouth”, in the Antarctic fish species Trematomus newnesi (Perciformes, Notothenioidei) was recorded for the first time in nearshore waters of the South Shetland Islands (Potter Cove) and western Antarctic Peninsula (Petermann Island). The two morphs were distinguishable in specimens of 60–241 mm total length (TL); about 30% of the specimens constituted intermediate forms. In addition to the previously known characters separating the morphs, we found that the “relative size of the eye” can also be used to identify smaller and larger fish of the typical morph. The ecological significance of the two morphs remains unclear. Ratios of diagnostic characters for identification of the species at two size ranges (60–131 and 132–241 mm TL) are provided.     

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

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

Molecular basis and evolutionary origins of color diversity in great star coral Montastraea cavernosa (Scleractinia: Faviida)

Natural pigments are normally products of complex biosynthesis pathways where many different enzymes are involved. Corals and related organisms of class Anthozoa represent the only known exception: in these organisms, each of the host-tissue colors is essentially determined by a sequence of a single protein, homologous to the green fluorescent protein (GFP) from Aequorea victoria. This direct sequence-color linkage provides unique opportunity for color evolution studies. We previously reported the general phylogenetic analysis of GFP-like proteins, which suggested that the present-day diversity of reef colors originated relatively recently and independently within several lineages. The present work was done to get insight into the mechanisms that gave rise to this diversity. Three colonies of the great star coral Montastraea cavernosa (Scleractinia, Faviida) were studied, representing distinct color morphs. Unexpectedly, these specimens were found to express the same collection of GFP-like proteins, produced by at least four, and possibly up to seven, different genetic loci. These genes code for three basic colors-cyan, green, and red-and are expressed differently relative to one another in different morphs. Phylogenetic analysis of the new sequences indicated that the three major gene lineages diverged before separation of some coral families. Our results suggest that color variation in M. cavernosa is not a true polymorphism, but rather a manifestation of phenotypic plasticity (polyphenism). The family level depth of its evolutionary roots indicates that the color diversity is adaptively significant. Relative roles of gene duplication, gene conversion, and point mutations in its evolution are discussed.     

FREQUENCY‐DEPENDENT SOCIAL DOMINANCE IN A COLOR POLYMORPHIC CICHLID FISH

A mechanism commonly suggested to explain the persistence of color polymorphisms in animals is negative frequency‐dependent selection. It could result from a social dominance advantage to rare morphs. We tested for this in males of red and blue color morphs of the Lake Victoria cichlid, Pundamilia. Earlier work has shown that males preferentially attack the males of their own morph, while red males are more likely to win dyadic contests with blue males. In order to study the potential contribution of both factors to the morph co‐existence, we manipulated the proportion of red and blue males in experimental assemblages and studied its effect on social dominance. We then tried to disentangle the effects of the own‐morph attack bias and social dominance of red using simulations. In the experiment, we found that red males were indeed socially dominant to the blue ones, but only when rare. However, blue males were not socially dominant when rare. The simulation results suggest that an own‐morph attack bias reduces the social dominance of red males when they are more abundant. Thus, there is no evidence of symmetric negative frequency‐dependent selection acting on social dominance, suggesting that additional fitness costs to the red morph must explain their co‐existence.     

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.     

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.     

Morph‐specific differences in biochemical composition related to flight capability in the wing‐polyphenic Sitobion avenae

Flight performance at various times after emergence in the alate morph and age‐dependent changes in biochemical composition of winged and wingless morphs were evaluated in the wing‐polyphenic aphid Sitobion avenae (Fabricius) (Hemiptera: Aphididae). Alates exhibited the highest flight activity at 18–36 h after adult emergence. Throughout the nymphal and adult development, the whole‐body content of total lipid was significantly higher in the winged vs. wingless morph, whereas the content of water, soluble sugar, glycogen, phospholipid, and soluble protein showed significantly higher levels in the wingless vs. winged morph. There were no significant differences in the content of triglyceride and free fatty acid during nymphal and adult stages in both morphs. However, triglyceride content was significantly higher in the winged vs. wingless morph during adulthood. Differences in biochemical composition between morphs indicate that there is an energetic cost of flight capability. Our results from S. avenae adults showed that total lipid and triglyceride for the winged morph accumulated significantly to a maximum, and water content decreased significantly to a minimum, on days 1 and 2 after the final molt, exactly when the highest flight activity was reached. This study suggests that flight activity is associated with triglyceride and water content.     

Genetic support for random mating between left and right‐mouth morphs in the dimorphic scale‐eating cichlid fish Perissodus microlepis from Lake Tanganyika

Population genetic analyses were conducted to investigate whether random mating occurs between left and right‐mouth morphs of the dimorphic scale‐eating cichlid fish Perissodus microlepis from two geographical sites in southern Lake Tanganyika. The mitochondrial and nuclear DNA markers (13 microsatellite loci) revealed no genetic differentiation between left and right morphs (i.e. widespread interbreeding). The observed lack of genetic divergence between the different morphs allowed for the exclusion of the possibility of assortative mating between same morph types. The microsatellite data showed no significant departures of heterozygosity from Hardy–Weinberg equilibrium, suggesting purely random mating between the morphs. Overall, this study indicated no genetic evidence for either assortative or disassortative mating, but it did provide support for the random mating hypothesis. Highly significant, albeit weak, spatial population structure was also found when samples of different morphs were pooled according to geographical sites. An additional analysis of two microsatellite loci that were recently suggested to be putatively linked to the genetic locus that determines the laterality of these mouth morphs did not show any such association.     

The role of vision and color in the close proximity foraging behavior of four coccinellid species

The role of vision and color in close-proximity foraging behavior was investigated for four species of lady beetles: Coccinella septempunctata, Hippodamia convergens, Harmonia axyridis, and Coleomegilla maculata. The effect of light level and color cues on consumption rates varied among the four predator species. The consumption rates of these predators on the pea aphid Acyrthosiphon pisum (Harris) was measured under light and dark conditions. C. septempunctata,H. convergens, and Ha. axyridis consumed significantly more aphids in the light than in the dark, while the consumption rate of Col. maculata was not affected by light level. Foraging ability was also measured on red and green color morphs of the pea aphid on red, green, and white backgrounds. C. septempunctata consumed significantly more of the aphid morph that contrasted with the background color, and showed no difference between morphs on the white background. H. axyridis consumed significantly more red morph aphids regardless of background. The remaining two species showed no difference in consumption rates on the two color morphs. The variation in the use of visual cues demonstrates how different species of predators can exhibit different foraging behaviors when searching for the same prey. Received: 4 August 1997 / Accepted: 3 February 1998     

Host nest defense against a color-dimorphic brood parasite: great reed warblers (Acrocephalus arundinaceus) versus common cuckoos (Cuculus canorus)

We tested great reed warbler (Acrocephalus arundinaceus) discrimination against two common cuckoo (Cuculus canorus) female color morphs (gray and rufous) in two areas with different parasitism rates and proportions of the two morphs. Hosts recognized the two cuckoo morphs from a control, the feral pigeon (Columba livia), at Apaj, Hungary (where brood parasitism was heavy), whereas no significant differences among the models were recorded at Lužice, Czech Republic (where the parasitism rate was moderate). At Apaj, the hosts discriminated the rufous morph (which is slightly predominant there) better than the gray morph from the control. Between-site comparison (after controlling for background aggression) revealed that great reed warblers were more aggressive towards the rufous morph at Apaj than at Lužice, whereas their responses to the gray morph did not differ, corresponding with much higher between-site difference in the relative abundance of the rufous morph. Our results suggest that both local parasitism pressure and relative abundance of two female color morphs of a brood parasite may significantly influence host nest defenses.     

A Comparative Study of Two Corbicula Morphs (Bivalvia,Corbiculidae) Inhabiting River Danube

In Europe, at least two Corbicula morphs (generally referred as C. fluminea and C. fluminalis) are known. However, their taxonomic and systematic position is controversial. In order to ascertain their taxonomy and systematics, we studied their characteristics in River Danube. Morphometric analysis confirmed the existence of two distinguishable morphs. Based on mtCOI sequence, morph‐1 is identical to C. fluminea, while morph‐2 is an undefined species. According to the median joining analysis, morph‐1 belongs to the C. fluminea clade, whereas morph‐2 forms a distinct clade, which is known only from invasive populations. Differences were recorded in population structure and reproductive biology, too. It is probably correct to treat the two morphs as distinct taxa, but as long as the African and western Asian parts of the genus’ range are poorly studied, taxonomic position of morph‐2 remains unclear. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Do genetic structure and landscape heterogeneity impact color morph frequency in a polymorphic salamander?

Landscape heterogeneity plays an important role in population structure and divergence, particularly for species with limited vagility. Here, we used a landscape genetic approach to identify how landscape and environmental variables affect genetic structure and color morph frequency in a polymorphic salamander. The eastern red‐backed salamander, Plethodon cinereus, is widely distributed in northeastern North America and contains two common color morphs, striped and unstriped, that are divergent in ecology, behavior, and physiology. To quantify population structure, rates of gene flow, and genetic drift, we amplified 10 microsatellite loci from 648 individuals across 28 sampling localities. This study was conducted in northern Ohio, where populations of P. cinereus exhibit an unusually wide range of morph frequency variation. To test whether genetic distance was more correlated with morph frequency, elevation, canopy cover, waterways, ecological niche or geographic distance, we used resistance distance and least cost path analyses. We then examined whether landscape and environmental variables, genetic distance or geographic distance were correlated with variation in morph frequency. Tests for population structure revealed three genetic clusters across our sampling range, with one cluster monomorphic for the striped morph. Rates of gene flow and genetic drift were low to moderate across sites. Genetic distance was most correlated with ecological niche, elevation and a combination of landscape and environmental variables. In contrast, morph frequency variation was correlated with waterways and geographic distance. Thus, our results suggest that selection is also an important evolutionary force across our sites, and a balance between gene flow, genetic drift and selection interact to maintain the two color morphs.     

Evolution towards dioecy in heterostylous populations

The effective gender of a plant is defined as the proportion of the plant's genes that are transmitted through pollen (its maleness) or through ovules (its femaleness). Formulae are derived that enable the average effective gender of the morphs of a heterostylous population and the gender of individual plants to be estimated. Estimates require a knowledge of the morph ratio and the seed set that results in each morph from self-fertilization and from legitimate and illegitimate cross-fertilizations. If no illegitimate fertilizations occur, the average gender of the morphs can be estimated from their seed production alone; in this situation the average femaleness of one morph is exactly equal to the average maleness of the other morph. The average gender of long- and short-styled morphs is calculated for populations of fiveCordia species (Boraginaceae) from published data ofOpler & al. (1975). In two species, both morphs transmit their genes equally through pollen and ovules. In the other species, the long-styled morph acts predominantly (or in one species exclusively) as an ovule parent and the short-styled morph succeeds predominantly (or exclusively) as a pollen parent.The features of the evolutionary pathway from heterostyly to dioecy and the selective forces that may be responsible are outlined.     

GENETIC AND COLOR INTERACTIONS AT A CONTACT ZONE OF ACANTHOCHROMIS POLYACANTHUS: A MARINE FISH LACKING PELAGIC LARVAE

Abstract. — Acanthochromis polyacanthus is an unusual tropical marine damselfish that uniquely lacks pelagic larvae and has lost the capacity for broad-scale dispersal among coral reefs. Different color morphs exist in different regions of the Great Barrier Reef, and morphs from northern and southern regions are genetically distinct. In the Hydrographers Passage area, which is a large break through the reef matrix in the central Great Barrier Reef that may have acted as a bottleneck on the migration of these animals during sea level rise, three morphs recognized from other regions were found on neighboring reefs. The transition between them is abrupt with three loci (AAT-2*, GPI-1*, and PGM*) showing allelic frequency patterns close to fixation between opposite alleles within a few kilometers. On two reefs (Hyde, Bebe), a pair of morphs was found to coexist and exhibited a habitat partitioning pattern with each morph restricted to one side on the reef and steep transitions in between. Outside these transition zones, phenotypes and genotypes matched those on surrounding reefs without coexistence and were little changed from reefs several hundred kilometers away. An electrophoretic survey across one transition zone on Hyde Reef showed steep genetic gradients along one kilometer of reef slope. Significant linkage disequilibria in samples collected in Hyde Reef as a result of dispersal of parental combinations of alleles into the center or because parental combinations of alleles confer greater fitness, allowed us to estimate the dispersal rate (189 m/generation) and the selection pressure on the marker loci (0.411). Finally, we investigated models that could lead to such a steep transition in genotypic and phenotypic combinations. Both contact zones on each side of Hyde Reef were associated with geomorphological discontinuities in the reef structure. We suggest that assortative mating may be a proximal mechanism for maintaining isolated each color morph, which could be reinforced by selective predation against hybrids outside the zone of their formation (i.e., the frequency-dependent selection model of Mallet and Barton (1989). Acanthochromis is a midwater planktivore and, when in coexistence, the two morphs forage in different habitats amid multispecific flocks of other damselfishes of matching colors.