THE EFFECT OF TEMPERATURE AND PHOTOPERIOD ON THE DEVELOPMENT OF GEOGRAPHICALLY ISOLATED POPULATIONS OF FUNARIA HYGROMETRICA AND WEISSIA CONTROVERSA

Geographically isolated populations of Funaria hygrometrica Hedw. and Weissia controversa Hedw. were cultured under controlled axenic conditions in the laboratory to determine the developmental variability found between and within two species of widespread distribution. Funaria plants were found to grow more rapidly than those of Weissia; the latter could not be induced to complete the life cycle in culture, and generally had a less broad tolerance to environmental extremes than did Funaria. Optimum temperatures of 30 C for spore germination and 25 C for protonematal growth and gametophore formation were observed in all populations of Funaria. Gametangial formation required cooler temperatures in all populations; however, optimal temperature requirements and sporophytic growth characteristics were population-dependent. The temperature responses of the various stages of the life cycle correlate well with seasonal temperature fluctuations that might be expected in nature. The presence of ecological races in Funaria hygrometrica is demonstrated in the behavior of the reproductive stages of the life cycle.     

Life history variation in gametophyte populations of the moss Ceratodon purpureus (Ditrichaceae)

The life cycles of mosses and other bryophytes are unique among land plants in that the haploid gametophyte stage is free-living and the diploid sporophyte stage is ephemeral and completes its development attached to the maternal gametophyte. Despite predictions that populations of haploids might contain low levels of genetic variation, moss populations are characterized by substantial variation at isozyme loci. The extent to which this is indicative of ecologically important life history variation is, however, largely unknown. Gametophyte plants from two populations of the moss Ceratodon purpureus were grown from single-spore isolates in order to assess variation in growth rates, biomass accumulation, and reproductive output. The data were analyzed using a nested analysis of variance, with haploid sib families (gametophytes derived from the same sporophyte) nested within populations. High levels of life history variation were observed within both populations, and the populations differed significantly in both growth and reproductive characteristics. Overall gametophytic sex ratios did not depart significantly from 1:1 within either population, but there was significant variation among families in both populations for progeny sex ratio. Some families produced predominantly male gametophytes, while others yielded predominantly females. Because C. purpureus has a chromosomal mechanism of sex determination, these observations suggest differential (but unpredictable) germination of male and female spores. Life history observations showed that male and female gametophytes are dimorphic in size, maturation rates, and reproductive output.     

ECOLOGICAL GENETICS OF SERPENTINE TOLERANCE IN THE MOSS,FUNARIA FLAVICANS: VARIATION WITHIN AND AMONG HAPLOID SIB FAMILIES

Many mosses occur both on and off serpentine soils, but experiments designed to test whether serpentine populations of widespread species display genetic adaptations for growth on serpentines have not been reported. Toward that end, two populations of the moss, Funaria flavicans, were grown on nutrient media varying in nickel and chromium concentration and in the ratio of magnesium to calcium. Three haploid siblings from each of five sporophytic families from the two populations were grown on five experimental media. There was no evidence that serpentine plants were more tolerant of nickel, chromium, high magnesium/calcium, or high nickel combined with high magnesium/calcium. In fact, plants from the nonserpentine population produced more protonemal growth than the serpentine plants on every medium except the control, on which plants from the two populations were indistinguishable. Large differences in nickel tolerance among haploid sib families (families of meiotic progeny derived from the same sporophyte) from the nonserpentine site provided evidence of genetic polymorphism in that population.     

Pollen competitive ability in maize: within population variability and response to selection

Summary Male gametophytic selection can play a special role in the evolution of higher plant populations. The main assumption — gametophytic-sporophytic gene expression of a large portion of a plant's genes — has been proven by a number of studies. Population analyses have revealed a large amount of variability for male gametophytic fitness. However, the data available do not prove that at least a portion of this variability is due to postmeiotic gene expression. This paper reports the analysis of a synthetic population of maize based on a gametophytic selection experiment, carried out according to a recurrent scheme. After two cycles of selection, the response was evaluated for gametophytic and sporophytic traits. A parameter representing pollen viability and time to germination, although showing a large amount of genetic variability, was not affected by gametophytic selection, indicating that this variability is largely sporophytically controlled. Pollen tube growth rate was significantly affected by gametophytic selection: 21.6% of the genetical variability was released by selection. Correlated response for sporophytic traits was observed for mean kernel weight: 15.67% of the variability was released. The results are a direct demonstration that pollen competitive ability due to pollen tube growth rate and kernel development are controlled, to a considerable extent, by genes expressed in both tissues. They also indicate that gametophytic selection in higher plants can produce a higher evolution rate than sporophytic selection; it can thus serve to regulate the amount of genetic variability in the populations by removing a large amount of the genetic load produced by recombination.     

Effects of Competition and Temporal Variation on the Evolutionary Potential of Two Native Bunchgrass Species

The capacity of restored plant populations to adapt to new environmental challenges depends on within‐population genetic variation. We examined how much genetic and environmentally based variation for fitness‐associated traits exists within populations of two native grasses commonly used for restoration in California. We were also interested in understanding how phenotypic expression of genetic variation for these traits varies with growth environment. Thirty maternal families of Elymus glaucus (Blue wild rye) and Nassella pulchra (Purple needlegrass) were sampled from both coastal and interior populations and reciprocally transplanted into three replicated common gardens with and without interspecific competition at each site. Reproductive output of families differed both among years and with competition treatments. Phenotypic expression of genetic variation in culm production differed among populations and was very low when families were grown with interspecific competition. Without interspecific competition, the degree of genetic determination peaked in year two in both species (8.4 and 15.1% in E. glaucus and N. pulchra, respectively). Significant genetic differences in reproduction and phenotypic plasticity were found among N. pulchra subpopulations sampled less than 3 km apart, further highlighting the importance of thoroughly sampling available genetic variation in populations used for restoration. The variable and generally low expression of genetic variation indicates that rates of adaptation in restored populations of these native grasses may vary temporally and may be especially slow within competitive environments.     

GAMETOPHYTIC SELF-FERTILIZATION IN HOMOSPOROUS PLANTS: DEVELOPMENT,EVALUATION, AND APPLICATION OF A STATISTICAL METHOD FOR EVALUATING ITS IMPORTANCE

The methods described here make it possible to use data on sporophytic genotype frequencies to estimate the frequency of gametophytic self-fertilization in populations of homosporous plants. Bootstrap bias reduction is effective in reducing or eliminating the bias of the maximum likelihood estimate of the gametophytic selfing rate. The bias-corrected percentile method provides the most reliable confidence intervals for allele frequencies. The percentile method gives the most reliable confidence intervals for the gametophytic selfing rate when selfing is common. The maximum likelihood intervals, the percentile intervals, the bias-corrected percentile intervals, and the bootstrap t intervals are all overly conservative in their construction of confidence intervals for the gametophytic selfing rate when self-fertilization is rare. Application of the recommended methods indicates that gametophytic self-fertilization is quite rare in two sexually reproducing populations of Pellaea andromedifolia studied by Gastony and Gottlieb (1985).     

EFFECTS OF WOUNDING BY THE HERBIVOROUS SNAILS LITTORINA SITKANA AND L. SCUTULATA (MOLLUSCA) ON GROWTH AND REPRODUCTION OF THE INTERTIDAL ALGA FUCUS DISTICHUS (PHAEOPHYTA)1

Small (3–7 cm long) Fucus distichus ssp. edentatus (de la Pyl.) Pow. Plants were tagged at three sites in which densities of the herbivorous snails Littorina sitkana and L. scutulata ranged from 367–4690 animals · M^-2. From April–August 1986, the growth rate, degree of wounding, and reproductive status of individual thalli were monitored at 2–4 week intervals. Grazer-inflicted damage to the thalli varied within and among sites. Mean growth rates at the site with low densities of littorines were about twice those at the site with intermediate densities and about four times those at the high density site. At the site with high densities of littorines, F. distichus growth rates were negatively correlated with the degree to which the plants were wounded. There appeared to be no correlation of grazer density with F. distichus survivorship. Thalli at the site with few herbivores tended to reproduce earlier and at a larger size than did those at the other two sites. In all three areas, only thalli that had received little damage from herbivores became reproductive. By lowering growth rates and delaying reproduction in F. distichus, grazing by littorine snails can potentially cause variation in reproductive output among individual thalli.     

QUANTITATIVE GENETICS OF BRYOZOAN PHENOTYPIC EVOLUTION. III. PHENOTYPIC PLASTICITY AND THE MAINTENANCE OF GENETIC VARIATION

Cheilostome bryozoan species show long-term morphologic stasis, implying stabilizing selection sustained for millions of years, but nevertheless retain significant heritable variation in traits of skeletal morphology. The possible role of within-genotype (within-colony) phenotypic variability in preserving genetic diversity was analyzed using breeding data for two species of Stylopoma from sites along 110 km of the Caribbean coast of Panama. Variation among zooids within colonies accounts for nearly two-thirds of the phenotypic variance on average, increases with environmental heterogeneity, and includes significant genotype-environment interaction. Thus, within-colony variability apparently represents phenotypic plasticity, at least some of which is heritable, rather than random “developmental noise.” Almost all of the among-colonies component of phenotypic variance is accounted for by additive genetic differences in trait means, suggesting that within-colony plasticity includes virtually all of the environmental component of phenotypic variance in these populations of Stylopoma. Thus, heritable within-colony plasticity could play a significant part in maintaining genetic diversity in cheilostomes, but it is also possible that rates of polygenic mutation alone are sufficient to balance the effects of selection.     

AN ELECTRON MICROSCOPIC STUDY OF THE SPOROPHYTIC AND GAMETOPHYTIC PLANTS OF PADINA VICKERSIAE HOYT1

An electron microscopic comparison was made of the “isomorphic” sporophytic and gametophytic plants of Padina vickersiae. Light microscopic studies of the 2 generations showed few differences. This observation was also supported by studies at the ultrastructural level. However, minor differences in the gametophytic plant have been noted: (1) a well-defined nucleolus in the nucleus of the non-meristematic cell; (2) a general lack of osmiophilic globules in the chloroplasts; and (3) a clumping of chloroplasts in the maturing oogonium. The first and second differences are considered in terms of growth activity.     

Gene expression during the male gametophytic phase

Abstract

In recent years a number of experimental findings have indicated that in higher plants the gametophytic phase is able to express its own genetic information, a large part of which it shares with the sporophytic generation. Quantitative estimates of haploid and haplodiploid gene expression have been obtained by mRNA and isozyme analysis in several plant species: 60-70% of the genes are expressed in both pollen and plant, about 10% are pollen-specific, and 20% represent the sporophytic domain. Moreover, it has been demonstrated that stage-specific genes are expressed in the gametophytic generation: at least two sets of genes are activated during pollen development, others are expressed only in the postshedding period, during germination and tube growth. Studies have been made to ascertain the role played by gametophyte-expressed genes in pollen development; the in vivo and in vitro pollen tube growth rate has been revealed to be controlled by the gametophyte genome itself. Differential effects of specific chromosomal deficiencies on the development of maize pollen grains have indicated that components of normal microspore development are controlled by genes located in specific parts of the genome. For single gene analysis, gene transfer can be used; on the contrary, for traits with a multifactorial genetic control, direct proof of gene expression both in the gametophytic and the sporophytic generation can be obtained when selection is applied to the pollen population of a hybrid plant, and response to selection is observed in the resulting sporophytic progeny. Response to selection, applied at different stages of the gametophytic phase, has been described in the sporophytic progeny and this with regard to many adaptive traits; thus the phenomenon can have an important bearing on the genetic structure of natural populations and on higher plant evolution, it can also be used as a breeding tool to increase the efficiency of conventional selection methods.     

Seasonal changes in abundance and shifts in dominance of life history stages of the carrageenophyte Sarcothalia crispata (Rhodophyta, Gigartinales) in south central Chile

The population dynamics of the carrageenophyte Sarcothalia crispatais described from subtidal beds at two localities in south-central Chile. Seasonal fluctuations in total density and biomass were not evident. Frondswere identified to phase by the presence of reproductive structures and theresorcinol reaction. The monthly changes in abundance of each kind offrond were determined. Permanent gametophytic or sporophyticdominance was not evident: the more exposed site showed a seasonal shiftfrom sporophytic dominance in summer to gametophytic dominance inwinter, whereas the more protected site showed an interannual shift fromgametophytic to sporophytic dominance. The differences between localitiesand years suggest a very local population dynamics with large contributionof self-seeding to the maintenance of the S. crispata beds.     

INTER- AND INTRASPECIFIC VARIATION OF MOSSES IN TOLERANCE TO COPPER AND ZINC

Bryophytes are often viewed as slowly evolving with little genetic variation within and among populations. A study of heavy-metal tolerance was initiated to test the capacity of bryophytes to undergo genetic differentiation in response to natural selection. Tolerance of Funaria hygrometrica to copper and zinc was greater in populations that originated on soil with high concentrations of these metals. Protonemal growth was more inhibited by the metals than was germination, and copper was more toxic than zinc. Zinc and copper tolerances were correlated, but so were the zinc and copper concentrations of native substrates. The pattern of population differentiation for heavy-metal tolerance in this species is much like that of flowering plants. Five populations of Physcomitrium pyriforme, which does not occur on metal-contaminated soil, were all highly tolerant of zinc but extremely intolerant of copper. This species seems to have an inherent tolerance to the former. Significant variation in tolerance to copper and zinc occurred among populations, but tolerance did not correlate with metal contents in native substrates. This pattern differs from that of flowering plants. Normal populations of species that colonize contaminated sites tended to be more tolerant than populations of species that do not colonize such sites. The extensive population differentiation in Funaria hygrometrica augments the evidence from electrophoretic data that there is genetic variation among populations of mosses and liverworts.     

Basi molecolari dell'interazione polline-stilo

Abstract

Molecular basis of pollen-style interaction - Pollen interaction with sporophytic “female” tissues leads to a block on tube growth within the style in the Angiosperm families under gametophytic control of self-incompatibility (SI). Primary events of the interaction may be described in terms of a signal-receptor model. Alternatively, a cytotoxic enzyme activity (RNase), located in the transmitting tract of the style, should be responsible for inhibition of the incompatible tubes, through degradation of pollen RNA and interference with protein synthesis. In several systems, the expression of the SI-controlling gene has been clarified on the female side (S-glycoproteins); by contrast, no conclusive evidence has been provided for the nature of the S-products in the male gametophyte.     

Water availability and population origin affect the expression of the tradeoff between reproduction and growth in Plantago coronopus

Investment in reproduction and growth represent a classic tradeoff with implication for life history evolution. The local environment can play a major role in the magnitude and evolutionary consequences of such a tradeoff. Here, we examined the investment in reproductive and vegetative tissue in 40 maternal half‐sib families from four different populations of the herb Plantago coronopus growing in either a dry or wet greenhouse environment. Plants originated from populations with an annual or a perennial life form, with annuals prevailing in drier habitats with greater seasonal variation in both temperature and precipitation. We found that water availability affected the expression of the tradeoff (both phenotypic and genetic) between reproduction and growth, being most accentuated under dry condition. However, populations responded very differently to water treatments. Plants from annual populations showed a similar response to drought condition with little variation among maternal families, suggesting a history of selection favouring genotypes with high allocation to reproduction when water availability is low. Plants from annual populations also expressed the highest level of plasticity. For the perennial populations, one showed a large variation among maternal families in resource allocation and expressed significant negative genetic correlations between reproductive and vegetative biomass under drought. The other perennial population showed less variation in response to treatment and had trait values similar to those of the annuals, although it was significantly less plastic. We stress the importance of considering intraspecific variation in response to environmental change such as drought, as conspecific plants exhibited very different abilities and strategies to respond to high versus low water availability even among geographically close populations.     

THE INFLUENCE OF DISPERSAL PATTERNS AND MATING SYSTEM ON GENETIC DIFFERENTIATION WITHIN AND BETWEEN POPULATIONS OF THE RED HOWLER MONKEY (ALOUATTA SENICULUS)

The relationship between social structure and partitioning of genetic variance was examined in two red howler monkey populations (W and G) in Venezuela, one of which (G) was undergoing rapid growth through colonization by new troops. Rates and patterns of gene flow had been determined through radiotelemetry and direct observation data on solitary migrants, and 10 years of troop censusing. Standard electrophoresis techniques were used to examine 29 loci in blood samples taken from 137 of the study animals. Analysis of genetic variance demonstrated: (1) a significantly high level of genetic variation among troops within populations (F_ST = 0.225 for W and 0.142 for G), and (2) a significant excess of heterozygosity within troops relative to expected (F_IS = -0.136 for W and -0.064 for G), despite relatively high levels of observed and inferred inbreeding in W. Differences between the populations in F_ST values conformed to those predicted based on differences in colonization rate. Comparison of partitioning of genetic variance among different genealogical subsets of troops demonstrated that the pattern of genetic differentiation observed among troops within populations was promoted by an essentially single-male harem breeding structure, a very low rate of random exchange of breeding males among troops, and a high degree of relatedness among troop females. Between-troop genetic differentiation (F_ST) was thereby increased relative to that expected from other types of social organization, while the correlation between uniting gametes within troops (F_IS) was decreased. Genetic differentiation between populations (2%) corresponded to that predicted from migration rates. Such a mosaic of genetic variation, combined with differences in reproductive success observed among troops and a high troop failure rate, create conditions in which interdemic selection could result in more rapid spread of advantageous gene combinations than would be expected in a panmictic population, particularly in a colonizing situation in which the founder population is small.     

INTERPOPULATIONAL VARIATION IN THE GAMETOPHYTES OF PELLAEA ANDROMEDAEFOLIA

The development and mature morphology of the gametophytes from both sexual and apogamous populations of the fern Pellaea andromedaefolia were investigated. While most sexual examples were indistinguishable, some differences were noted. An insular collection was distinctive in its variability and irregularity of form. Although the latter was a representative of var. pubescens, other collections of the variety could not be distinguished from var. andromedaefolia on the basis of gametophytic characteristics. The apogamous gametophytes were decidedly more variable in development and often very different from sexual thalli. The mature asexual thalli tended to be more irregular in form and usually sharply divergent from the typical cordate type characteristic of the sexual populations. Each of the five apogamous samples was unique with respect to gametophyte development. The differences among the gametophytes of the various populations do not correlate with the sporophytic characteristics which differentiate the two varieties of the species.     

QUANTITATIVE GENETICS OF SIZE,SHAPE, LIFE-HISTORY,AND FRUIT CHARACTERISTICS OF THE SEED-HETEROMORPHIC COMPOSITE HETEROSPERMA PINNATUM. I. VARIATION WITHIN AND AMONG POPULATIONS

We document phenotypic and genetic variation within and among populations of the seed heteromorphic species Heterosperma pinnatum Cav. (Compositae) in the production of seed morphs and in a variety of life-history and morphological characteristics that might be correlated with seed and head traits. Each trait is found to have significant genetic variance in most or, usually, all populations. Significant among-population genetic variation exists for all traits except number of achenes per head and seedling shape, although some traits have much less genetic variation among than within populations. Number and percentage of intermediate achenes per head, total number of achenes per head, and lengths of central and peripheral achenes had little among-population genetic variation compared to within-population variation. Most traits had slightly less genetic variation among than within populations; however, some traits (percentage of central achenes, length of awns, date that the first flowering head opened, date that the first fruiting head opened, and death date) had more among-population genetic variation. The proportions of achene morphs produced had high broad-sense heritabilities and high among-population genetic variance, except in the case of intermediate achenes. All phenological variables had high among-population genetic variation. Within-population heritabilities were high for dates of first flowering head and fruiting head but low for death date and reproductive interval. Family and population means measured in the greenhouse for traits having high broad-sense heritability or among-population genetic variance were closely correlated with field means for the corresponding families or populations. The amounts of phenotypic variation were similar for traits that were measured in both the field and the greenhouse. These lines of evidence suggest that greenhouse results provide reasonable estimates of genetic variation in the field for this species. Numerous studies have reported variation in the proportion of seed morphs for different heteromorphic-seeded species and have discussed adaptive scenarios for the evolution of seed proportions; however, our investigation is one of only a few that have documented the amount of phenotypic and genetic variation within and among populations.     

SEASONAL LIGHT AND TEMPERATURE INTERACTION EFFECTS ON DEVELOPMENT OF LAMINARIA SACCHARINA (PHAEOPHYTA) GAMETOPHYTES AND JUVENILE SPOROPHYTES1

In previous studies, Laminaria saccharina L. (Lamour.) sporophytes were found to exhibit two major peaks of sporogenesis and an annual life cycle in Long Island Sound, New York. Young sporophytes were observed shortly after the sporogenesis peaks in early autumn and spring, but most of the mature sporophytes decayed during summer. A new study was conducted to determine if the spring sporogenesis activity contributed to the recruitment observed in autumn through oversummering of gametophytic and juvenile sporophytic stages, as previously suggested. Reproduction and growth in gametophytes and growth in juvenile sporophytes were studied under crossed gradients of light and temperature. Periodic outplantings of substrata seeded with gametophytic and sporophytic stages to the field were conducted to assess actual survival. The optimum temperature and light conditions for gametophyte development, growth and reproduction varied with the time of year meiospores were obtained. Most of this variation was attributable to temperature. A seasonal adaptation to temperature in most developmental stages was observed. Higher temperatures resulted in greater numbers of male gametophytes. Gametophytic stages could develop at all times, suggesting that oversummering in this stage was possible. Juvenile sporophytes had a narrower optimum temperature range and again photon fluence rate contributed little to observed variances. Out planting of sporophytic stages at various times during the year indicated only sporophytes prepared from autumn and winter could survive summer conditions. The thalli of these plants grew rapidly in spring and eroded back to the meristematic region in summer. Most of these plants then quickly became reproductive, resulting in another autumn sporogenesis peak. Gametophytic and sporophytic outplantings prepared from spring meiospores did not survive the summer. Thus, the recruitment observed in autumn can only be the result of the previous autumn's sporogenesis activity. The sporogenous activities of spring and early summer appear to be unimportant, despite the fact that all reproductive indices are superior at those times.     

THE INFLUENCE OF SELF-FERTILIZATION AND POPULATION DYNAMICS ON THE GENETIC STRUCTURE OF SUBDIVIDED POPULATIONS: A CASE STUDY USING MICROSATELLITE MARKERS IN THE FRESHWATER SNAIL BULINUS TRUNCATUS

The distribution of neutral genetic variability within and among sets of populations results from the combined actions of genetic drift, migration, extinction and recolonization processes, mutation, and the mating system. We here analyzed these factors in 38 populations of the hermaphroditic snail Bulinus truncatus. The sampling area covered a large part of the species range. The variability was analyzed using four polymorphic microsatellite loci. A very large number of alleles (up to 55) was found at the level of the whole study. Observed heterozygote deficiencies within populations are consistent with very high selfing rates, generally above 0.80, in all populations. These should depress the variability within populations, because of low effective size, genetic hitchhiking, and background selection, whatever the model of mutation assumed. However, that some populations exhibit much more variability than others suggests that historical demographic processes (e.g., population size variation, bottlenecks, or founding events) may play a significant role. A hierarchical analysis of the distribution of the variability across populations indicates a strong pattern of isolation by distance, whatever the geographical scale considered. Our analysis also illustrates how the mutation rate may affect population differentiation, as different mutation rates result in different levels of homoplasy at microsatellite loci. The effects of both genetic drift and gene flow vary with the temporal and spatial scales considered in B. truncatus populations.