Morphs In Populations Research Articles

Purging of inbreeding depression within a population of Oxalis alpina (Oxalidaceae)

Variation among individuals in levels of inbreeding depression associated with selfing levels could influence mating system evolution by purging deleterious alleles, but empirical evidence for this association is limited. We investigated the association of family-level inbreeding depression and presumed inbreeding history in a tristylous population of Oxalis alpina (Oxalidaceae). Mid-styled individuals possessed the greatest degree of self-compatibility (SC) and produced more autogamous capsules than short- or long-styled individuals. Offspring of highly self-compatible mid-styled individuals showed reduced inbreeding depression. Mid-styled plants that produced capsules autogamously exhibited reduced stigma-anther separation compared to mid-styled plants that produced no capsules autogamously. Reduced inbreeding depression was not correlated with stigma-anther separation, suggesting that self-compatibility and autogamy evolve before morphological changes in stigma-anther separation. Purging of inbreeding depression occurred in SC mid-styled maternal families. Low inbreeding depression in SC mid-styled plants may lead to retention of the mid-styled morph in populations, despite the occurrence of higher selfing rates in mid-styled relative to short- or long-styled morphs. Variation among individuals in levels of self-fertilization within populations may lead to associations between inbreeding lineages and lower levels of inbreeding depression, influencing the evolution of mating systems.

Genetic diversity and population structure of North America’s rarest heron, the reddish egret (Egretta rufescens)

The global distribution of the reddish egret is characterized by disjunct colonies occurring from the Pacific side of Northwest Mexico to the Caribbean. We examined distantly isolated colonies of reddish egret to determine global population genetic structure. We used seven polymorphic microsatellites to accomplish five goals: (1) to assess range wide population differentiation among reddish egret (Egretta rufescens) populations, (2) identify extent of gene flow, (3) determine any historical occurrence of bottlenecks, (4) assess genetic differentiation between color morphs, (5) clarify subspecies status of E. r. dickeyi, a completely dark morph population located in and around the Baja California peninsula, Mexico. Genetic differentiation was dramatic (global Fst = 0.161) throughout the reddish egrets range extending from Baja California, Mexico to Great Inagua, Bahamas. Differentiation occurred among three distinct regions (Fst = 0.238) but not among colonies/islands within regions suggesting regional philopatry. Genetic diversity (alleles per locus, and heterozygosity) in Baja California Sur, Mexico and Great Inagua, Bahamas populations is lower than in the Texas/Mexico population due to minimal dispersal between regions and smaller population sizes. Dark and white color morphs when present within the same region showed no differentiation. Patterns of recent population bottlenecks are not evident in each of the three regional populations. With evidence of limited gene flow in addition to low genetic diversity and prospects of habitat loss we recommend that reddish egrets be managed as three distinct or evolutionary significant units.

Fruit color, chemical and genetic diversity and structure of Myrtus communis L. var. italica Mill. morph populations

Abstract Myrtus communis presents two morphologies based on fruit color. Both morphs are present in some region of Tunisia, with the white morph being rare. In the present study, essential oil composition and AFLP markers were used to assess the chemical and genetic diversity and structure of four myrtle populations from each morph. A chemical polymorphism attributed to the morphs and the origin of populations was detected. The genetic diversity within population varied according to morphs. Variation in the dark blue morph populations was higher than that observed for the white ones. For each morph, a high genetic differentiation among populations was observed. Population structure based on AFLP markers is in accordance with that based on oil composition. Furthermore, a significant correlation between chemical and genetic data was observed. The conservation strategies of populations should be made for each morph according to its level of diversity and bioclimate.

Range limits, large-scale biogeographic variation, and localized evolutionary dynamics in a polymorphic damselfly

Studies of heritable colour polymorphisms allow investigators to track the genetic dynamics of natural populations. By comparing polymorphic populations over large geographic areas and across generations, issues about both morph stability and evolutionary dynamics can be addressed, increasing our understanding of the potential mechanisms maintaining genetic polymorphisms. In the present study, we investigated population morph frequencies in a sex-limited heritable colour polymorphic damselfly (Ischnura elegans, Vander Linden), with three discrete female morphs. We compared the frequencies of these three female morphs in 120 different populations from ten European countries at differing latitudes and longitudes. There were pronounced differences in morph frequencies both across the entire European biogeographic range, as well as at a smaller scale within regions. We also found considerable between-population variation at the local scale within regions, particularly at the edges of the range of this species. We discuss these findings in the context of recent models of adaptive population divergence along the range of a species. This polymorphism is thus highly dynamic, with stable morph frequencies at the core of the species range but fluctuating morph dynamics at the range limits. We finish with a discussion of how local interactions and climatic factors can be expected to have a strong influence on the biogeographic patterns in this species and other sexually selected polymorphisms.

Variation of Morphology and Elemental Concentrations in the California Nickel Hyperaccumulator Streptanthus polygaloides (Brassicaceae)

The Ni hyperaccumulator Strepthanthus polygaloides (Brassicaceae) is one of a handful of Ni hyperaccumulators known from continental North America. Surveys have revealed four distinctive morphs of this species, relying primarily on floral traits (sepal color and shape): a purple sepal morph (P), a yellow sepal morph (Y), a morph in which sepals start yellow and mature to purple (Y/P), and a morph with light yellow undulate sepals (U). In this study, we raised plants from ten populations (five Y, three P, one Y/P, and one U) under uniform greenhouse conditions to determine if morphs varied in morphology and elemental concentrations when grown on Ni-amended potting soil in a common garden. Morphological data included measurements of leaf form (length, width, and degree of lobing) and plant size (height to first flower as they bolted in summer). Phenology was documented by noting flowering timing of plants. Elemental concentrations of plants were also determined for nine elements (Ca, Cu, Fe, K, Mg, Mn, Ni, P, and Zn). All morphological/phenological traits measured varied significantly between at least some morphs. The U and Y/P morphs were larger than Y and P morphs, with larger leaves as well. Leaves of U morph plants had wide sinuses and shallow lobes, whereas Y/P plants had narrow sinuses and long narrow lobes. P morph plants were shortest in stature, with the smallest leaves. Morphs also varied significantly in concentrations of all elements except Fe. All populations hyperaccumulated Ni, but the P morph contained significantly greater Ni levels than the other three morphs. The P morph also had more Mg, and less Mn and P, than the other morphs. The U morph had more K and Zn, but less Ca, than the other morphs. Principal components analysis revealed all four morphs to be distinctive from one another, and also suggested both morphological/phenological and elemental differences between Y morph populations along a north—south gradient. We conclude that there is considerable genetic divergence between morphs. If additional information shows that morphs are reproductively isolated, then these morphs may require taxonomic subdivision.

Variation in female morph frequencies and mating frequencies: random, frequency-dependent harassment or male mimicry?

Female-limited colour polymorphisms occur in a variety of species, where often one female morph (androchrome) resembles the body coloration of the conspecific male, whereas the other (gynochrome) does not. We tested predictions of two frequency-dependent hypotheses that are commonly invoked to explain the maintenance of these polymorphisms for multiple populations of the damselfly Ischnura elegans: (1) that males prefer mating with the most abundant female morph (LMR) or (2) that androchromes are functional male mimics (MM). We also asked whether variation in social and abiotic environments account for interpopulation variation in female morph frequencies. Contrary to predictions of the LMR hypothesis, morph mating frequency was not lower than expected based on morph frequency when a morph was uncommon or higher when a morph was most common. In support of the MM hypothesis, androchrome mating frequency was lower than predicted based on population morph frequency. In addition, as predicted, androchrome mating frequency increased with increasing ratio of androchromes to males, but we could not disentangle whether this was a consequence of the changing mimic/model ratio or because of rising androchrome frequency. Although variation in female morph frequencies between populations was not random across our study area, this could not be explained by geographical variation in frequencies and densities of males and females. Androchrome frequencies were higher in populations to the north and west where ambient temperatures were lower. Abiotic conditions such as temperature may need to be considered for understanding the maintenance of female-limited polymorphisms.

Disassortative pollen transfer in distylous Palicourea padifolia (Rubiaceae), a hummingbird-pollinated shrub

Distylous polymorphisms represent a useful model system for studying the functioning of flower morphology because floral morphs have reciprocal flower developmental pathways and co-occur in the same environment such that they share the same pollinators. Distylous plants typically display both reciprocal herkogamy and a heteromorphic incompatibility system, which allows mating only between morphs. In this paper, we document morph-specific patterns in floral morphology and pollen receipt of Palicourea padifolia, a hummingbird-pollinated shrub. Floral traits typically associated with the functioning of distyly, reciprocal herkogamy, and population morph ratios of flowering individuals from 10 populations were measured and quantified. Pollen receipt on stigmas of the same measured flowers was then used to determine the effectiveness of distyly in promoting disassortative pollen transfer. Pollen of long-styled flowers was more effective in reaching legitimate stigmas, while short-styled morphs were more successful in the reception of legitimate pollen across populations. Variation in pollen receipt across populations was not explained by reciprocal herkogamy, which typically promotes legitimate pollination. Natural pollination resulting in a higher proportion of legitimate pollen in short-styled flowers increased with stigma-anther separation (promotion of outcross pollination) and width of corolla entrance (avoidance of self-pollination).

Distylic Hottonia palustris shows high reproductive success in small populations despite low genetic variability

Hottonia palustris L. (Primulaceae) is characterized by a heteromorphic incompatibility system. The strategy of distylic ramets is believed to promote outcrossing, to maintain overall genetic diversity and to prevent inbreeding depression. In spite of this distyly, an extremely low amount of allozymic diversity was observed in 545 individual ramets from 14 populations in Flanders (Belgium). A possible explanation for such low genetic variation is discussed in relation to the vegetative propagating abilities and the ecological niche width of the species. In contrast to the uniformity in allozymes as well as to the feature of single morph populations, there was a high variability in reproductive success between populations such as the number of seeds per ramet (425–2633), the number of flowers per ramet (9–36) and the mean weight of seeds (0.03–0.17 mg). Small populations and even those consisting of only one style morph may show a high reproductive success. As a whole, H. palustris showed a negative relationship of reproductive success with the surface area of its populations.

Plumage polymorphism of red‐footed boobies (Sula sula) in the western Indian Ocean: an indicator of biogeographic isolation

AbstractThe pantropical red‐footed booby Sula sula is one of the most polymorphic seabirds. In the Indian Ocean most extant colonies hold white morph adults except on Europa Island (southern Mozambique Channel), where adults are of the white‐tailed brown morph and on Tromelin Island (western Indian Ocean), where one‐third of the birds are of the white‐tailed brown morph and two‐thirds are of the white morph. On Tromelin, the morph ratio has remained constant over the last 40 years. An extinct colony (Glorieuses Islands, northern Mozambique Channel) once supported a white‐tailed brown morph population. These results suggest that the colonies of the western Indian ocean do not constitute one great gene pool where exchanges occur, but are isolated at various degree from each other. Particularly, the population of Europa is the only current population of the Indian Ocean constituted almost entirely of white‐tailed brown morph, suggesting that it is isolated from other nearby colonies. Possible causes of isolation are discussed in the light of oceanic features of the Mozambique Channel. Although further studies are needed to understand the adaptive significance of plumage coloration in red‐footed boobies, I suggest that white‐tailed brown morph at Europa may act as a defensive camouflage against kleptoparasitism by great frigatebirds Fregata minor and brown skuas Catharacta antarctica.

Plumage polymorphism of red-footed boobies (Sula sula) in the western Indian Ocean: an indicator of biogeographic isolation

The pantropical red-footed booby Sula sula is one of the most polymorphic seabirds. In the Indian Ocean most extant colonies hold white morph adults except on Europa Island (southern Mozambique Channel), where adults are of the white-tailed brown morph and on Tromelin Island (western Indian Ocean), where one-third of the birds are of the white-tailed brown morph and two-thirds are of the white morph. On Tromelin, the morph ratio has remained constant over the last 40 years. An extinct colony (Glorieuses Islands, northern Mozambique Channel) once supported a white-tailed brown morph population. These results suggest that the colonies of the western Indian ocean do not constitute one great gene pool where exchanges occur, but are isolated at various degree from each other. Particularly, the population of Europa is the only current population of the Indian Ocean constituted almost entirely of white-tailed brown morph, suggesting that it is isolated from other nearby colonies. Possible causes of isolation are discussed in the light of oceanic features of the Mozambique Channel. Although further studies are needed to understand the adaptive significance of plumage coloration in red-footed boobies, I suggest that white-tailed brown morph at Europa may act as a defensive camouflage against kleptoparasitism by great frigatebirds Fregata minor and brown skuas Catharacta antarctica.

POLLEN DISCOUNTING AND THE SPREAD OF A SELFING VARIANT IN TRISTYLOUS EICHHORNIA PANICULATA: EVIDENCE FROM EXPERIMENTAL POPULATIONS.

Floral traits that increase self-fertilization are expected to spread unless countered by the effects of inbreeding depression, pollen discounting (reduced outcross pollen success by individuals with increased rates of self-fertilization), or both. Few studies have attempted to measure pollen discounting because to do so requires estimating the male outcrossing success of plants that differ in selfing rate. In natural populations of tristylous Eichhornia paniculata, selfing variants of the mid-styled morph are usually absent from populations containing all three style morphs but often predominate in nontrimorphic populations. We used experimental garden populations of genetically marked plants to investigate whether the effects of population morph structure on relative gamete transmission by unmodified (M) and selfing variants (M') of the mid-styled morph could explain their observed distribution. Transmission through ovules and self and outcross pollen by plants of the M and M' morphs were compared under trimorphic, dimorphic (S morph absent), and monomorphic (L and S morphs absent) population structures. Neither population structure nor floral morphology affected female reproductive success, but both had strong effects on the relative transmission of male gametes. The frequency of self-fertilization in the M' morph was consistently higher than that of the M morph under all morph structures, and the frequency of self-fertilization by both morphs increased as morph diversity of experimental populations declined. In trimorphic populations, total transmission by the M and M' morphs did not differ. The small, nonsignificant increase in selfing by the M' relative to the M morph was balanced by decreased outcross siring success, particularly on the S morph. In populations lacking the S morph, male gamete transmission by the M' morph was approximately 1.5 times greater than that by the M morph because of both increased selfing and increased success through outcross pollen donation. Therefore, gamete transmission strongly favored the M' morph only in the absence of the S morph, a result consistent with the distribution of the M' morph in nature. This study indicates that floral traits that alter the selfing rate can have large and context-dependent influences on outcross pollen donation.

Genetic divergence between colour morphs in populations of the common intertidal sea anemones Actinia equina and A. prasina (Anthozoa: Actiniaria) in the Isle of Man

A distinctive morph ofActinia equina (L.) is found at low frequency among populations on intertidal hard substrata on some shores on the Isle of Man. This morph is red with rows of green oval spots or elongate markings running longitudinally down the column. Starch gel electrophoresis of 21 allozyme loci was used to compare samples of this morph from two localities with other sympatricActinia spp. Collections were made in early summer 1986. For one sampling site the comparison was with redA. equina and greenA. prasina Gosse, whilst at the other site with redA. equina only. At both sites significant genetic differences in allele frequencies at several loci were found between the new morph and sympatricA. equina andA. prasina. The results also confirm the reproductive isolation ofA. prasina. As with much previous work on sea anemones, levels of mean heterozygosity per locus (H) were found to be high (H=0.157 to 0.342). A surprising feature of the results, although bearing out earlier unpublished data, is that high levels of genetic differentiation are found between populations of what appear to be the same morphs collected from shores only a few km apart. Among theActinia spp. studied, differentiation between populations of the same morph on different shores was of the same order as between sympatric, reproductively isolated populations.

Pollinator visitation in populations of tristylous Eichhornia paniculata in northeastern Brazil.

The frequencies of floral morphs in populations of tristylous Eichhornia paniculata often deviate from the theoretical expectation of equality. This variation is associated with the breakdown of tristyly and the evolution of self-fertilization. Differences in morph frequencies could result from selection pressures due to variable levels of insect visitation to populations and contrasting foraging behavior among the floral morphs. We estimated pollinator densities in 16 populations and quantified visitation sequences to morphs in five populations of E. paniculata in northeastern Brazil. Foraging behavior among floral morphs was measured as the frequency of visits to morphs relative to their frequency in the population (preference) and number of flights between inflorescences of the same versus different morphs (constancy). Pollinator density (number/m2/minute) was not correlated with population size, plant density or morph diversity. Pollinator densities varied most among populations of less than 200 plants. Whether pollinators discriminated among the morphs, depended on whether they primarily collected nectar or pollen. In four populations, nectar-feeding bees (Ancyloscelis and Florilegus spp.) and butterflies showed no consistent preference or constancy among the morphs. In contrast, pollen-collecting bees (Trigona sp.) visited a lower proportion of longstyled inflorescences than expected and tended to visit more mid-and short-styled inflorescences in succession, once they were encountered. Pollinator constancy for morphs did not result from differences in inflorescence production or spatial patchiness among the morphs. Although non-random pollinator visitation to morphs in heterostylous populations could potentially affect mating and hence morph frequencies, the observed visitation patterns in this study do not provide evidence that pollinators play a major role in influencing floral morph frequencies.

Geographical Variation of the Plumage Polymorphism in the Eastern Reef Heron (Egretta sacra)

I investigated the distribution of white and dark morphs of the Eastern Reef Heron (Egretta sacra) on several coasts and islands in central to southwestern Japan, eastern Australia, and French Polynesia. Both morphs preferred white beaches to dark beaches. Every local population contained some dark herons, however, the range of the white morph was restricted. The white morph population increased in proportion to the distance from the equator in Japan. It was plentiful in the Great Barrier Reef in Australia and was common in Polynesian islands. The distribution of the white morph coincides with the presence of coral reefs, from which white beaches are derived. Only the dark morph was seen outside this range. None of several hypotheses proposed so far explains the observed polymorphism and its geographic variation.

Competitive interaction between two leaf morph populations of white clover in relation to soil nitrogen

The pure and mixed stands of the two populations of white clover (Trifolium repens L.) differing in leaf character were raised in the experimental pots using de Wits' replacement series. Of the two populations, one is characterized by having white ‘V’-shaped markings on the leaflets (marked population) and the other does not have any such marking (unmarked population). The competitive interaction between the two populations has been studied at two soil nitrogen regimes. The nitrogen requirement of the marked population seems to be higher than that of the unmarked population. The marked population was found to be more competitive as compared to the other population at high N level as shown by their relative yield. The competitiveness of the former was, however, masked to some extent under low soil nitrogen. This confirmed the differential response of the two populations ofT. repens to soil fertility as observed in nature.

GROWTH AND SHELL VARIATION IN THE TROPICAL EASTERN PACIFIC INTERTIDAL GASTROPOD GENUSPURPURA:ECOLOGICAL AND EVOLUTIONARY IMPLICATIONS

In this study we investigate variation in shell morphology among Purpura pansa Gould, 1853 and P. columellaris Lamarck, 1822; high intertidal predatory gastropods found in the eastern tropical Pacific. Field observations on the high frequency of shells intermediate in apertural characteristics, the occurrence of cross-copulations between distinct morph types, coupled with morphometric analyses and examination of sectioned shells lead us to conclude that these two forms are the same species. Hence, we propose P. pansa as a junior synonym of P. columellaris.Growth studies reveal that the thicker shelled columellaris morph is much slower growing and represents a terminal growth stage of the pansa morph. Unlike some other thaidid species, starvation experiments failed to induce thickening of the apertural lip and apertural tooth formation. The stimulus that cues thickening is unknown.Field experiments indicated that thick-toothed morphs are relatively more resistant to predation and are most common in wave protected, high predation risk environments. Absence of thick-shelled morphs in populations ofthe geminate congener, P. patula in the Caribbean suggests that predation is probably less severe in this region.

Plate morphs in freshwater samples of Gasterosteus aculeatus from Arctic and Atlantic Canada: Complementary comments on a recent contribution

Additional analyses of museum samples for plate morphs in the freshwater threespine stickleback from Arctic and Atlantic Canada confirm the scarcity of the low morph in mainland Atlantic Canada as shown by Hagen and Moodie (D. W. Hagen and G. E. E. Moodie. 1982. Can. J. Zool. 60: 1032–1042). Insular Newfoundland samples show evidence that populations containing the low morph are not uncommon and this agrees well with Hagen and Moodie's climatic explanation for plate morph distribution. This climatic explanation does not, however, account for the high frequencies of low morph populations shown here to occur in Arctic Canada. Two populations are identified which may be monomorphic for the low morph, and a monomorphic partial population is reported from an inland stream. Both these types of populations are rare in eastern North America.

Sex allocation in heterostylous plants

This paper examines the heterostylous breeding system in plants from the perspective of sex allocation theory. Models are used to predict the frequencies of the different floral morphs in populations of heterostylous species and the relative amounts of resources allocated to pollen and seeds in each morph. We note that in natural populations morph ratios may deviate from equality and that the morphs may specialize in the production of either pollen or seeds. Our sex allocation models are an attempt to explain why such patterns exist.

Temporal Phenotypic Heterogeneity as a Substrate for Selection

The interaction of temporal phenotypic heterogeneity with a population level fitness function was explored through the use of a simple model. The model, based upon experimental data, assumes that the exploitation of pollinators, and seed-set within plant populations are dependent upon the frequency of a pink flower morph in populations composed of pink and white morphs. An increase in pink frequency is accompanied by an increase in seed-set for both morphs. The model also assumes that seed-set within a population is the same for pink and white individuals. In perennials and annuals with long-lived seeds, fluctuations in morph balance from one season to another may lead to reproductive pulses or drags, depending upon which morph was in excess. The reproductive differential which stems from different levels of pollinator service leads to an increase in pink frequency and an attendant fitness gain. The perennial habit and long-lived seeds provide a population with a memory which permits the current population image to compete with images of previous years. As a consequence, fitness gains may be achieved in the absence of interplant or interpopulation selection.