TRIVALENT FORMATION IN MULTIPLE TRISOMICS OF CLARKIA UNGUICULATA

Vasek, F. C. (U. California, Riverside.) Trivalent formation in multiple trisomics of Clarkia unguiculata. Amer. Jour. Bot. 50(3): 244–247. 1963.—A series of multiple trisomics, ranging from 2n + 1 to 2m + 7, was scored for univalents and trivalents at first metaphase. The mean number of trivalents per cell per extra chromosome was 0.43, 0.46, 0.46, 0.56, 0.54, 0.55 and 0.59 for plants with 1, 2, 3, 4, 5, 6 and 7 extra chromosomes respectively. These trivalent frequencies are interpreted to fall into 2 classes, indicating that the cytological differences between triploids and single trisomies may be based on a threshold effect. The results are compared with available data from other genera, and it is suggested that the observed increase in trivalent formation per extra chromosome may be associated with an increase in chiasma frequency.     

TRISOMIC TRANSMISSION IN CLARKIA UNGUICULATA

Vasek , F. C. (U. California, Riverside.) Trisomic transmission in Clarkia unguiculata. Amer. Jour. Bot. 48(9): 829–833. 1961.—Seven primary trisomic plants derived from a triploid-diploid cross were self-pollinated. The 7 progenies included diploids and trisomics, the latter varying in frequency from 16 to 30%. In addition, 2 of the progenies included tetrasomic plants. Crosses were made between diploids and either trisomics or tetrasomics. The extra chromosome of 1 progeny was readily transmitted through the pollen of trisomic and tetrasomic plants. When a trisomic of the same progeny was used as a seed parent, only diploids and tetrasomics were found among the offspring, indicating a duplication of the extra chromosome. The extra chromosomes of other progenies were not transmitted through either pollen or eggs in controlled diploid-trisomic crosses but trisomics of these progenies were recovered after self-pollination. It is suggested that differential pollen-tube growth precluded transmission to diploid-trisomic hybrids and that under conditions of reduced pollen competition the extra chromosome normally would be transmitted through pollen. The extra chromosomes generally occur as univalents at metaphase and are ordinarily included in telophase nuclei.     

EFFECTS OF ENVIRONMENTAL STRESS ON COMPONENTS OF REPRODUCTION IN CLARKIA UNGUICULATA

The effects of stress on reproduction in Clarkia unguiculata were investigated by monitoring flower number, seed number and seed wt after subjecting plants to drought and heavy fruit loads, and by monitoring seed number after pollinating overage flowers. Fewer main-stem flowers were produced in drought stressed plants than in non-stressed plants. Drought stress did not affect overall seed numbers and seed wt in 1981, but did significantly affect seed number and wt in different flower age classes. Overall seed numbers were not affected by drought stress in 1982, but seed wt was significantly lower in plants with stressed ovules. Fewer flowers but more seeds per pollination were produced by plants in which all or ½ the flowers were pollinated than by plants in which ¼ or 1/6 of the flowers were pollinated. Seed wts were lowest in plants with a full fruit load and in fruits produced late in the growth cycle. Seed number was variable but high following pollination of flowers with 1–7 day old stigmas, and much lower in flowers with older stigmas.     

PHENOTYPIC VARIATION OF GROWTH TRAJECTORIES IN FINCHES

Evolution cannot proceed without phenotypic variation for selection to act on. This is particularly true of ontogenetic parameters because it is changes in these parameters that give rise to new phenotypes. I analyzed the amount and dimensionality of phenotypic variation on growth trajectories in early ontogeny in three species of finches (Fringillidae) using the recently developed infinite-dimensional model. For two species, eight traits were analyzed, and for a third, six traits. Growth data were analyzed only up to 6 d of age in two species and 8 d of age in the third. The results were very similar for all species and traits. A very large proportion of the phenotypic variation in growth trajectories was confined to a single dimension. This dimension corresponded to a simultaneous increase/decrease at all ages in early ontogeny. The eigenfunctions, each describing a family of similar-shaped growth trajectories, were highly collinear among traits. A high covariance existed among traits at the same and different ages. If some part of the phenotypic variation has an additive genetic basis, then any selection for a change in size at one age in one trait will lead to a response in a size at subsequent ages and in the other traits. This in turn suggests that morphological evolution frequently will move along a multivariate size axis, as has indeed been found in several taxa.     

EXPERIMENTAL NON-STIGMATIC POLLINATIONS IN CLARKIA UNGUICULATA LINDL. (ONAGRACEAE)

Within angiosperms, the stigma-style apparatus provides a barrier to direct contact between ovules and the external environment. In traversing this barrier, male gametophytes presumably are subject to intense competition and natural selection. Successful fertilizations and resultant seed set can be accomplished following surgical decapitation of the stigma and style, provided that these normally receptive sites are replaced with an optimal environment suitable for pollen germination and growth. Unlike other methodologies, these in situ-in vitro pollinations are comparatively easily accomplished, and provide a means for circumventing natural fertility barriers; additionally, they may provide a simple means of artificially selecting pollen genomes. In Clarkia unguiculata 23.0% of attempted non-stigmatic pollinations produced outcrossed F₁ progeny.     

A CYTOGENETIC STUDY OF CLARKIA UNGUICULATA II. SUPERNUMERARY CHROMOSOMES

Mooring , John S. (Washington State U., Pullman.) A cytogenetic study of Clarkia unguiculata. II. Supernumerary chromosomes. Amer. Jour. Bot. 47(10): 847–854. Illus. 1960.—Supernumerary chromosomes morphologically comparable to those of the basic complement occur in high frequency in wild populations of this onagraceous annual plant. This paper evaluates the role that these supernumerary chromosomes play in the population dynamics of this species. The results of crossing plants with various numbers of supernumeraries showed that these chromosomes often increased in number in the seed parent. Examination of microsporocytes showed that almost 30% of the 491 plants determined had 1 or more supernumerary chromosomes. Studies of natural populations revealed that the frequency of individuals with supernumeraries varied from 0 to 79% in different populations, and also that in 1 population their frequency varied significantly in different years. It is concluded that supernumerary chromosomes in this species are adaptive under at least certain conditions. It is speculated that they are components of polygenic systems which increase tolerance to environmental extremes.     

ONTOGENETIC VARIATION IN PATTERNS OF PHENOTYPIC INTEGRATION IN THE LABORATORY RAT

I used confirmatory factor analysis to evaluate the ability of causal developmental models to predict observed phenotypic integration in limb and skull measures at five stages of postnatal ontogeny in the laboratory rat. To analyze the dynamics of phenotypic integration, I fit successive age-classes simultaneously to a common model. Growth was the principal developmental explanation of observed phenotypic covariation in the limb and skull. No complex morphogenetic model more adequately reconstructed observed covariance structure. Models that could not be interpreted in embryological terms, coupled with a growth component, provide the best models for observed phenotypic integration. During postnatal growth, some aspects of integration vary in both the skull and limb. The covariance between factors and the proportion of variance unique to each character differ between some sequential age-classes. The factor-pattern is invariant in the limb; however, repatterning in the skull occurs in the interval between eye-opening and weaning. The temporal variation in the structure of covariation suggests that functional interactions among characters may create observed patterns of phenotypic integration. The developmental constraints responsible for evolutionary modification of phenotypes might be equally dynamic and responsive to embryonic functional interactions.     

CRYPTIC SELF-INCOMPATIBILITY AND THE BREEDING SYSTEM OF CLARKIA UNGUICULATA (ONAGRACEAE)

Analysis of 2,117 segregating progeny from competitive pollinations involving self and foreign pollen reveals that Clarkia unguiculata possesses a cryptic self-incompatibility mechanism. This mechanism promotes outcrossing when foreign pollen is available, yet allows for high fecundity through selling in marginal or catastrophically reduced populations. Competitively based self-incompatibility in the species suggests that discrimination against genetically similar siblings may also be possible. The preferential self-exclusion system insures that a seed crop of maximal size and genetic heterogeneity will be produced despite unpredictable environmental perturbations.     

ANDROMONOECY AND VARIATION IN PHENOTYPIC GENDER OF PASSIFLORA INCARNATA (PASSIFLORACEAE)

We studied the perennial vine Passiflora incarnata Linnaeus (Passifloraceae) in Alachua County, Florida, from May to August 1983 to determine the breeding system and investigate seasonal changes in phenotypic gender of individual plants. Passiflora incarnata is an obligate outcrosser, incapable of self-fertilization. The major pollinators were carpenter bees (Xylocopa sp.). The proportion of flowers setting fruit was not limited by pollinator service, but the weight of individual fruits and number of seeds/fruit was increased over naturally pollinated flowers by manually performing cross-pollination. Morphological differences in style position among flowers caused some flowers to function primarily as males and others to function as hermaphrodites. Although some of the flowers that functioned as males set fruit when manually cross-pollinated, the proportion of these male flowers capable of setting fruit was lower than the proportion of hermaphroditic flowers setting fruit when manually cross-pollinated. Further, some male flowers had atrophied ovary and styles and were completely incapable of setting fruit. Passiflora incarnata is thus functionally andromonoecious. The relative production of male versus hermaphroditic flowers varied among individuals and over the course of the flowering season. Unmanipulated plants in the population became increasingly male-biased in floral sex ratios as the reproductive season progressed. We attempted to modify phenotypic gender in experimental plants by limiting the ability of plants in some treatment groups to set fruit. Treatment groups significantly affected production of hermaphroditic flowers, but production of male flowers was not affected by treatment. Treatment did not significantly affect fruit weight, number of seeds per fruit or the percentage of hermaphroditic flowers that successfully matured fruit. These results suggest that andromonoecy in P. incarnata is a mechanism for adjusting allocation of reproductive effort to male and female function, and that maternal investment in this species is regulated primarily by varying production of hermaphroditic flowers.     

鲫幼鱼游泳运动能力的个体变异与表型关联

为考察鲤科鱼类运动能力的个体变异和表型关联及不同加速度对匀加速游泳能力的影响, 研究在(25±0.5)℃条件下测定鲫(Carassius auratus)幼鱼的静止代谢率(Resting metabolic rate, RMR), 通过临界游泳速度(Critical swimming speed, U_crit)法和过量耗氧(EPOC)法获取实验鱼的最大代谢率(Maximum metabolic rate, MMR)、代谢空间(Aerobic scope, AS=MMR-RMR)、相对代谢空间(Factorial aerobic scope, FAS=MMR/RMR)、U_crit及步法转换速度(Gait transition speed, U_gt), 并在不同加速度(0.083、0.167、0.250、0.333 cm/s2)下测定鲫幼鱼的匀加速游泳能力(Constant accelerated test, U_cat)和U_gt。研究发现: 鲫幼鱼的MMR和AS与U_crit均呈正相关, 但RMR与U_crit不相关; 能量代谢参数(MMR、AS、RMR)与U_gt不相关。U_crit法获取的MMR、AS、FAS与EPOC法均无平均值的显著性差异, 但2种方法获得的上述参数具有较高的个体重复性; 鲫幼鱼的能量代谢参数之间存在表型关联并且关联方向不尽相同。鲫幼鱼的U_crit和U_gt均小于各加速度下的U_cat和U_gt, 加速度对U_cat测定无影响但对U_gt有影响。鲫幼鱼的U_gt与U_crit或U_cat呈正相关, 并且其匀加速游泳能力参数在不同加速度下保持较高的重复性。除0.333 cm/s2外, 其他加速度下鲫幼鱼U_cat的无氧代谢组分(U_cat-U_gt)与U_cat呈正相关; 然而, 鲫幼鱼的有氧代谢组分(U_gt)与无氧代谢组分(U_cat-U_gt)呈负相关。研究表明: U_crit法和EPOC法诱导鲫幼鱼的有氧代谢能力无方法学差异; 鲫幼鱼的能量代谢存在表型关联, 其匀加速游泳能力具有稳定个体差异, 并且该种鱼的有氧代谢与无氧代谢存在权衡。     

CONSISTENCY AND VARIATION IN PHENOTYPIC SELECTION EXERTED BY A COMMUNITY OF SEED PREDATORS

Phenotypic selection that is sustained over time underlies both anagenesis and cladogenesis, but the conditions that lead to such selection and what causes variation in selection are not well known. We measured the selection exerted by three species of predispersal seed predators of lodgepole pine (Pinus contorta latifolia) in the South Hills, Idaho, and found that net selection on different cone and seed traits exerted by red crossbills (Loxia curvirostra) and cone borer moths (Eucosma recissoriana) over 10 years of seed crops was similar to that measured in another mountain range. We also found that the strength of selection increased as seed predation increased, which provides a mechanism for the correlation between the escalation of seed defenses and the density of seed predators. Red crossbills consume the most seeds and selection they exert accounts for much of the selection experienced by lodgepole pine, providing additional support for a coevolutionary arms race between crossbills and lodgepole pine in the South Hills. The third seed predator, hairy woodpeckers (Picoides villosus), consumed less than one‐sixth as many seeds as crossbills. Across the northern Rocky Mountains, woodpecker abundance and therefore selective impact appears limited by the elevated seed defenses of lodgepole pine.     

CAUSES OF VARIATION IN BIOTIC INTERACTION STRENGTH AND PHENOTYPIC SELECTION ALONG AN ALTITUDINAL GRADIENT

Understanding the causes of variation in biotic interaction strength and phenotypic selection remains one of the outstanding goals of evolutionary ecology. Here we examine the variation in strength of interactions between two seed predators, common crossbills (Loxia curvirostra) and European red squirrels (Sciurus vulgaris), and mountain pine (Pinus uncinata) at and below tree limit in the Pyrenees, and how this translates into phenotypic selection. Seed predation by crossbills increased whereas seed predation by squirrels decreased with increasing elevation and as the canopy became more open. Overall, seed predation by crossbills averaged about twice that by squirrels, and the intensity of selection exerted by crossbills averaged between 2.6 and 7.5 times greater than by squirrels. The higher levels of seed predation by crossbills than squirrels were related to the relatively open nature of most of the forests, and the higher intensity of selection exerted by crossbills resulted from their higher levels of seed predation. However, most of the differences in selection intensity between crossbills and squirrels were the result of habitat features having a greater effect on the foraging behavior of squirrels than of crossbills, causing selection to be much lower for squirrels than for crossbills.     

GENETIC VARIATION AND ESTIMATES OF GENE FLOW IN CLARKIA SPECIOSA SUBSP. POLYANTHA (ONAGRACEAE)

Estimates of interpopulational gene flow and the levels and distribution of genetic variation in Clarkia speciosa subsp. polyantha were obtained using enzyme electrophoresis. Eight enzymes encoded by 17 loci were analyzed. Nei's mean genetic identity was 0.96, indicating little genetic divergence among populations. Gene diversity statistics also suggest little heterogeneity among populations. Interpopulational gene flow, estimated according to Slatkin (1985), was fairly high, Nm = 3.9, probably accounting for the lack of differentiation among populations.     

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.