INBREEDING DEPRESSION IN SCHIEDEA GLOBOSA AND S. SALICARIA (CARYOPHYLLACEAE), SUBDIOECIOUS AND GYNODIOECIOUS HAWAIIAN SPECIES

Progeny produced by inbreeding were compared to progeny derived from outcrosses for gynodioecious Schiedea salicaria and subdioecious S. globosa to assess fitness consequences of breeding system on parental fecundity (seeds per capsule) and progeny measures of fitness (germination, survival, biomass, and number of flowers). Results from both species indicated that inbreeding depression occurred at all measured stages of the life history. In both species, different females showed different levels of inbreeding depression. Multiplicative fitness functions of the ratio of values for selfed and outcrossed progeny in S. salicaria resulted in inbreeding depression values of 0.62–0.94. Within- vs. between-family crosses of S. globosa also resulted in inbreeding depression values as high as 0.49. These values suggest that inbreeding depression may promote the evolution of dioecy within S. globosa and S. salicaria, depending on the levels of natural outcrossing.     

INBREEDING DEPRESSION IN MORPHOLOGICAL AND PHYSIOLOGICAL TRAITS OF SCHIEDEA LYDGATEI (CARYOPHYLLACEAE) IN TWO ENVIRONMENTS

We compared inbreeding depression in hermaphroditic Schiedea lydgatei and its gynodioecious sister species, S. salicaria, to infer the level of inbreeding depression in their common ancestor. With measurements of selfing rates, this information can be used to assess the importance of inbreeding depression in the evolution of breeding systems in S. lydgatei and S. salicaria. Morphological and physiological characters related to fitness were compared for inbred and outcrossed S. lydgatei in high- and low-fertilizer environments in the greenhouse. Seed mass, number of seeds per capsule, germination, survival, biomass, number of flowers, and age at first flowering were compared for inbred versus outcrossed progeny. We also measured inbreeding depression in maximal rates of photosynthetic carbon assimilation and stomatal conductance to water vapor, traits that affect fitness through their influence on plant carbon balance and water-use efficiency (ratio of carbon gain to water loss). All traits except number of seeds per capsule in parents and survival showed inbreeding depression, with the magnitude depending on family and environment. High inbreeding depression is likely in the ancestor of S. lydgatei and S. salicaria, indicating that, with sufficiently high selfing rates, females could spread in populations. Hermaphroditism in S. lydgatei is probably favored by low selfing rates. In contrast, the evolution of gynodioecy in S. salicaria apparently has been favored by relatively high selfing rates in combination with high inbreeding depression.     

EFFECT OF DENSITY ON SECONDARY SEX CHARACTERISTICS AND SEX RATIO IN SILENE ALBA (CARYOPHYLLACEAE)

A field survey of plant and flower sex ratio and secondary sex characteristics was made in Silene alba. Female-biased plant sex ratios were found, as seems typical for the species. Sex ratio distribution correlated with a gradient of soil moisture (with the more moist area having a more female-biased ratio) and with changes in the density of Silene (intermediate and higher density areas having greater female bias). The floral sex ratio was significantly female-biased only at the site that was most female-biased in terms of plant sex ratio. Otherwise the population of flowers was significantly male-biased. Male and female plants harvested from the field differed in secondary sexual characteristics. Males had more flowers and invested proportionately more biomass in leaf, but less in root, stem and reproductive tissue than did females. Although both males and females were larger in terms of total dry weight at the moist site, males produced more flowers at the driest (high density) site. Here the female bias in plant sex ratio was intermediate, but the floral sex ratio was significantly male-biased. A glasshouse experiment was performed in which plants were grown at four densities. Density significantly influenced plant survivorship and the probability of flowering, and increased female bias in the pots, but it did not affect patterns of biomass allocation in flowering plants. Patterns of male and female biomass allocation did not differ in the experiment, except in terms of reproductive allocation (greater in females) and allocation to leaf, greater in males, but only at the lowest density. This work urges caution in interpreting differences between males and females in the field as secondary sex characteristics, since we find such properties to be overlapping under experimental conditions. It supports the idea that males and females of a species may sustain different reproductive output under differing conditions.     

PROGENY SEX RATIOS IN DIOECIOUS SILENE LATIFOLIA (CARYOPHYLLACEAE)

Most sex ratios reported for Silene latifolia are female biased. As a result of experiments performed by Correns in the early 1900s, pollen tube competition has generally been accepted as the primary cause of these skewed ratios. We did four sets of hand pollinations in which we varied the size of pollen loads and placement of pollen along the filamentous stigma. The effect of pollen load size on progeny sex ratios was not statistically significant. Of 32 maternal families, 17 contained more females than males (one ratio deviated statistically from 1:1), and 13 contained more males than females. Paternal families exhibited a greater range of sex ratios, including three with a significant female bias and one with a significant male bias. Within experiments, neither the maternal parent nor where pollen was placed had a statistically significant effect on progeny sex ratios; the paternal effect was significant in one experiment. We suggest that sex ratios in Silene latifolia are not necessarily affected by the level of pollen competition. Other factors, including variation among males and sex-linked mortality, may help explain the skewed sex ratios that characterize populations of this species. Further, Correns' observations of excess females may have resulted from his use of interspecific hybrids.     

SEX POLYMORPHISM IN SILENE ACAULIS (CARYOPHYLLACEAE) AND THE POSSIBLE ROLE OF SEXUAL SELECTION IN MAINTAINING FEMALES

Pollen accumulation rates and their relationship to stigma morphology and pollinator visitation behavior were compared between female and hermaphrodite sex morphs of the alpine plant Silene acaulis var. subacaulescens (Caryophyllaceae). Although stigmas of female and perfect flowers collected comparable pollen loads, stigmas of female flowers became receptive earlier in anthesis and therefore recruited a larger number of pollen tubes. Together with early receptivity young female flowers had a larger stigmatic area with longer papillae than did perfect flowers. Pollinator behavior also differed between morphs, with bumble bees spending more time probing female than perfect flowers. Differences in stigma receptivity schedules of female and perfect flowers have consequences for different opportunities for sexual selection in the two sex morphs. Female flowers, by providing a more effective gametophytic screen, have the potential to produce higher quality offspring. This is proposed as a further compensatory advantage maintaining females, with a single fitness function, in populations containing hermaphrodites which have both male and female fitness functions.     

ECOLOGICAL ASPECTS OF ADAPTIVE RADIATION IN BIRDS

1. Relatively few birds feed heavily upon green-plant materials, though a number may take substantial numbers of buds. Birds appear not to possess adequate gut biota to break down cellulose efficiently, and even it they did, this system would not be compatible with efficient flight, on account of the long processing times required. 2. Birds have stronger adaptations toward feeding upon seeds and make a particularly heavy impact upon seeds in trees and on those in widely scattered or unpredictable crops. 3. Several families, mostly of tropical distribution, feed primarily upon fruit. Again, they are most successful in exploiting resources reached only with difficulty by other groups. A similar pattern holds for nectar stores. In the case of fruit and nectar, evolutionary complications result because the plants compete for seed dispersers and pollinators. 4. Most primarily herbivorous species feed their young partially or totally upon insects or other animal foods. Only a few species are able to fledge upon an entirely herbivorous diet, and those that do so often have extremely long fledging periods, which subject their young to high rates of predation unless the parents nest in places inaccessible to predators. 5. In general, herbivorous birds make a heavy impact relative to other animals only when they exploit resources that the other groups have difficulty in obtaining (hard to reach, or widely scattered in space and/or time). 6. Insects are exploited by more families of birds than any other food category. Birds are of greatest relative importance in capturing insects on the wing and in arboreal locations. Other terrestrial invertebrates are probably taken by techniques similar to those used for insects. 7. A variety of species take invertebrate prey along the water's edge or in shallow water. 8. Almost without exception, vertebrate prey is of small size, in part a function of the size of birds. Occasionally predation upon small terrestrial vertebrates may be relatively heavy, generally in outbreak situations. 9. Several families feed exclusively upon fish, crustacea, squid, and other aquatic prey. Some indirect evidence suggests that exploitation of these resources may sometimes be heavy, though there is little evidence that these groups often make an appreciable impact upon this food source. 10. Birds appear to be among the most important scavengers of animal remains. 11. Like the herbivorous birds, carnivorous birds appear to exert their greatest impact upon resources that are hard to reach or are widely scattered in space and/or time. 12. One-third of the avian families feed regularly on a variety of resources, as recognized in Table I. Most of these families specialize upon resources located in certain areas (ground, water's edge, trees, etc.). Only 13% of these families regularly use such a wide range of foods that they transcend both of these considerations (food type, segment of the habitat). In very few cases (5 %) does this designation result from some species of a family specializing upon one category of food and others using a different category. 13. There have been few large (> 20 kg), primarily herbivorous birds, though there have been several large omnivorous species. Large carnivorous species have been even rarer. All of these large species have been flightless, and in most cases they have occurred when or where large mammals were scarce or absent. 14. Birds have made extremely limited use of subterranean areas, caves, or deep water, and adaptations facilitating other types of life appear to be virtually incompatible with success in these situations. All these areas are characterized by a rapidly decreasing food gradient. 15. Bats exploit certain, but not all, of the food resources regularly exploited by birds. The resources not used by bats that are exploited by birds are those that are available over a full 24 h period; thus, bats' nocturnal habits do not provide them with an advantage in exploiting them. 16. Insects also use some of the resources exploited by birds. With few exceptions, insects are smaller than birds or bats. Considerable indirect evidence is consistent with the argument that the segregation in time, resource type, and size of flying animals is at least in part caused by competition. 17. While selection for anti-predatory mechanisms can be surmised, the reciprocal density relationships frequently noticed between birds and other organisms suggest that they arise from competition, rather than predation. 18. Most information suggests that interactions between birds and other animals of the same trophic level are usually, though not invariably, over food. 19. The types of relationship existing between birds and other organisms described above are repeated in a variety of other animal groups, though they clearly are not ubiquitous in the animal kingdom.     

GENETICS OF SEX EXPRESSION IN FRAG ARIA SPECIES

Hermaphroditism is the normal mode of sex expression in diploid species of Fragaria (Rosaceae, 2n = 14, x = 7) with one known exception, gynodioecious F. vesca L. ssp. bracteata. The polyploid species of Fragaria are all trioecious. An extensive study involving appropriate hybridization, testcrossing, selling, and backcrossing revealed that the repression of sporangia and the inhibition of sporogenesis are controlled by a single gene (or a gene complex) with at least three alleles in the sporophytes of trioecious octoploid species (2n = 56, x = 7). A male suppressor (allele F) reduces microsporangia and represses microsporogenesis completely, but it allows normal development of the stigma, style, and ovary. A female suppressor (allele M), in the absence of modifier genes, inhibits megasporogenesis and drastically reduces the number of carpels and size of receptacles. The allele H, conferring perfect flowers at an early stage of flower organogenesis, acts as an inducer of microsporogenesis in females, but leaves both microand megasporangial development intact. At the sex locus, the F allele (femaleness) is dominant to H and M and the H allele (hermaphroditism) is dominant to M (maleness). Females are exclusively heterogametic (F/H or F/M), hermaphrodites may be homo- or heterogametic (H/H or H/M), and males are homogametic (M/M). The sex gene is expressed precisely in the genetic background of octoploid × diploid hybrids of Fragaria and their derivatives and in crosses with closely related hermaphroditic diploid Pontentilla glandulosa L. Gene dosage phenomena are absent. First generation progeny of colchi-decaploids (F/F, –/–) are exclusively female, but all generations thereafter segregate in a normal diploidized manner (1:1). Application of phytohormones alters sex expression to a limited extent.     

CERTAIN EMBRYOLOGICAL AND BIOCHEMICAL ASPECTS OF CYTOKININ SD 8339 IN CONVERTING SEX OF A MALE VITIS VINIFERA (SYLVESTRIS)

Certain embryological and biochemical effects of the cytokinin (SD 8339) in converting flower sex from male to hermaphrodite were studied in a clone of Vitis vinifera L. (sylvestris). The cytokinin accelerated the meiotic division of the megaspore mother cell, mitotic divisions of the megaspore and cells of pistillate tissue, and increased the rate of protein synthesis in flower buds. Two working hypotheses for the possible mode of action of the cytokinin in sex conversion are presented.     

ATTRACTIVE STRUCTURES AND THE STABILITY OF HERMAPHRODITIC SEX EXPRESSION IN FLOWERING PLANTS

Plant attributes serving both male and female sex functions are thought to favor hermaphroditic breeding systems over systems where sex expression is separated between individuals. Morphological features used by plants to attract biotic pollinators can be considered in this light, because such “attractive” structures are prerequisite for both pollen donation and receipt. A model involving allocation of a limiting resource between attractive structures benefiting both sex functions, structures benefiting male function only, and structures benefiting female function only, is constructed and analyzed using the evolutionary stable strategy (ESS) approach. Contrary to expectation, conditions resulting in large allocation to attractive structures tend to destabilize hermaphroditism, although the effect is slight. Substantial asymmetry in the benefits accruing to male and female fertility for a given investment in pollinator attraction produces more pronounced effects, reducing the parameter space in which hermaphroditism is expected. Results of this model are used to assess the importance of “accelerating gain” curves previously suggested for the evolution of dioecy in flowering plants. Accelerating gains associated with fruit production and dispersal represent female function only, and can be sufficient to initiate evolution toward dioecy. Accelerating gains associated with pollinator attraction may contribute to the evolution of separate sexes only if male function benefits from increased investment in attractive structures at a disproportionate rate compared to female function. Even in this instance, though, hermaphroditism may be evolutionarily stable.     

LABILE SEX EXPRESSION IN ANDROMONOECIOUS SOLANUM HIRTUM: FLORAL DEVELOPMENT AND SEX DETERMINATION

Sex expression (the proportions of hermaphrodite and staminate flowers produced) of the andromonoecious species Solatium hirtum is labile, and this lability of whole plant sex expression is due to labile sex expression of individual floral buds. In this paper I examine the developmental processes that underlie the differences in floral sex expression of hermaphrodite and staminate flowers of Solarium hirtum, focusing particularly on the processes responsible for the observed lability of floral sex expression. Differences in bud growth rate and relative growth of floral organs in these buds are evident at about the time of megasporocyte meiosis (11–12 days before anthesis). However, gynoecial sterility in staminate buds does not occur until just 6–7 days before anthesis. At this time, abnormalities in ovule development occur in staminate buds: the ovules begin to appear necrotic, the integumentary tapetum collapses, and the megagametophytes of many ovules cease normal development. These observations are consistent with the predictions of labile floral development.     

黄河鲤性别决定时间和相关基因表达研究

鱼类性别决定和分化机制极为复杂,通过性腺组织切片鉴定得出黄河鲤从未分化性腺发育为Ⅱ期精巢、卵巢的时间为受精后第40天到第80天。选取一些可能参与黄河鲤性别决定分化相关的基因（amh、ar、cyp19a、cyp19b、dax1、dmrt1、er、foxl2、nobox、sox9a、sox9b、zp2）进行实时荧光定量PCR分析各个基因在受精后40d、45d、50d、55d、65d和80d的表达情况。结果显示性别决定相关基因在50d都有高表达,推测45-50 d为性别决定的关键时间。ar、amh、dax1、dmrt1、sox9a、sox9b六个基因在80d雄性表达量升高,且雄性明显高于雌性,推测这些基因参与精巢分化发育过程。cyp19a、cyp19b、foxl2、nobox、zp2五个基因在80d雌性表达升高,且高于雄性,推测其可能参与卵巢分化发育。     

DISTANCE-DEPENDENT REGULATION OF STAMEN NUMBER IN CROSSES OF SCLERANTHUS ANNUUS (CARYOPHYLLACEAE) FROM A DISCONTINUOUS POPULATION

Scleranthus annuus is a highly inbreeding annual that has varying numbers of fertile stamens per flower. Two stamen-positions always have fully fertile stamens, whereas the other eight carry staminoids or stamens to varying degrees. I measured male expression in progeny produced by crossing individuals growing in a discontinuous population. Four types of progeny were analyzed: from self-pollinations, from cross-pollinations within a patch, from cross-pollinations between patches, and from cross-pollinations between populations. Selfed progeny showed the lowest total male fertility (25.8), followed by between-population crosses (26.7), between-patch crosses (27.4), and within-patch crosses (27.8). The effect of crossing, as measured by the relative increase in frequency of fully fertile stamens compared to selfed progeny, is highest for within-patch crosses and declines with increasing spatial separation between parents. The increase was strongest for one of the antipetalous stamen positions in progeny produced by between-patch crosses (490%). The response to crossing measured as an increase in stamen fertility was not the same for all ten stamen positions. A strong increase of fertile stamens is noted in all types of crossed progeny for the five stamen positions in the outer whorl (antipetalous stamens), positions that in selfed progeny carry staminoids. The three positions in the inner whorl that are not occupied by fully fertile stamens show varying responses to crossing.     

DROUGHT STRESS AND INBREEDING DEPRESSION IN LYCHNIS FLOS-CUCULI (CARYOPHYLLACEAE)

Interactions between drought stress and inbreeding depression were studied in Lychnis flos-cuculi. Four inbreeding levels (F = 0, 0.25, 0.50 and 0.75), and three watering treatments were used. Performance was scored for germination rate and proportion, survival, plant size, proportion of plants flowering, flowering date, stem height, number of flowers, flower size, anther weight, fruiting proportion and number of capsules. Multiplicative fitness values were estimated from these traits. Inbreeding affected most of the traits studied, and a severe inbreeding depression was found for the combined fitness estimates. The higher inbreeding depression found here relative to the same family groups in a former experiment may reflect greater dominance and suppression in the present experiment at higher density.     

ADVANTAGES OF BEING A SPECIALIST FEMALE IN NODIOECIOUS SILENE VULGARIS S.L. (CARYOPHYLLACEAE)

According to sex allocation theory, to maintain a mutant male-sterile plant in a population of hermaphrodites such a plant must compensate its loss of fitness caused by inhibition of pollen production with a higher reproductive success through its female function. In the present study of a gynodioecious population of Silene vulgaris (Caryophyllaceae) I show that hermaphrodites not only benefit from outcrossing, in that progeny from outcrossed flowers are more vigorous than those from selfed flowers within an individual plant, but they also suffer heavily from self-pollination between different flowers of the same individuals, which could be demonstrated in experimentally made male-sterile (emasculated) individuals. Seeds from the emasculation period were heavier and germinated better than when the same individual was an intact hermaphrodite. Naturally male-sterile (female) individuals produced more fruits due to flowers staying open longer for pollen to arrive via some vector. However, the higher seed number alone could not provide the fitness advantage needed for females to be maintained in the population, but females also produced heavier seeds as compared to the hermaphrodites. Differences in seed survival and seedling establishment in the field are expected to add the advantages necessary for female plants to be selectively plausible.     

ASPECTS OF CONE AND OVULE ONTOGENY IN CRYPTOMERIA (TAXODIACEAE)

The axillary complex of female cones of Cryptomeria is initiated as a tangentially extended triangular structure with a rounded apex. It is bilaterally symmetrical. Structures interpreted as prophylls are differentiated first, but they become insignificant in later development. They are succeeded by two successive pairs of lobes, each lobe being the common primordium for an adaxial ovule and a tooth. The ovule initially much exceeds the tooth. The apex of the complex has a diversity of fates and may differentiate as an ovule-tooth pair. A one-to-one relation between teeth and ovules may be lost by abortion of ovules. The initial relation between teeth and ovules is obscured in later development due to extension of tissues at the base of the complex associated with considerable enlargement of the teeth. Histogenesis of the various parts is described, together with the vascular system. There is a vascular supply to the tooth but not the ovule. The results support a direct comparison with the extinct transition conifers Pseudovoltzia and Aethophyllum but do not fully support Florin's generalized model for the arrangement of parts in the axillary complex of conifers.     

厦门港球型侧腕水母(Pleurobrachia globosa Moser)的生殖

球型侧腕水母是厦门港最常见、数量最大的栉水母。雌雄同体。主要生殖季节在4—7月,是水产养殖业的重要敌害。精、卵多在下半夜排放。精子和卵子分别由位于两栉毛板之间的输精孔和输卵孔排出。卵子呈圆球状,其外为一层透明的胶质卵膜。平均卵径为319.2±57.5μm。胚胎发育在胶质膜内进行。当膜内幼体的雏形平衡囊、栉毛带、口及口道形成之后,幼体便用口及口道顶破胶质膜而孵出。     

GENETIC AND HORMONAL REGULATION OF GROWTH,FLOWERING, AND SEX EXPRESSION IN PLANTS

The interaction of the genetic and hormonal regulation of growth, flowering, and sex expression in plants is discussed. The genetic control of these processes is characterized, and data on their hormonal regulation are supplied. The interaction of genetic and hormonal regulation is considered with reference to tall-growing and genetic dwarf forms of the pea and wheat plants. It is shown that in the dwarf forms of the pea plant and in many other varieties, growth stimulation in response to treatment with the phytohormone gibberellic acid is clearly manifested and the expression of genetic dwarfism is eliminated, whereas in dwarf wheats it is expressed only slightly, if at all. At the same time both tall-growing and dwarf forms of both pea and wheat show a clearly defined growth retardation response to treatment with the growth inhibitor, abscisic acid, which causes the expression of physiological dwarfism. The short- and long-day characteristics of the photoperiodic response of plants are described as genetically controlled features, and data are given on the induction of flowering of a long-day variety coneflower grown under short-day conditions with the aid of gibberellins extracted from leaves of long-day vegetative plants of short-day Mammoth tobacco. Data are also supplied on the induction of flowering of a short-day variety, red-leaved goosefoot, grown under continuous light with the aid of metabolites extracted from leaves of the same Mammoth tobacco plants flowering under short-day conditions. This demonstrates the possibility of hormonal regulation of the genetically controlled long-day and short-day characteristics in photoperiodically sensitive plants. Genetic and hormonal regulation of sex expression in two dioecious plants, hemp and spinach, is discussed. It is shown that sex expression in these plants is regulated by gibberellins which are synthesized in leaves and cause male sex expression and by cytokinins which are synthesized in the roots and cause female sex expression. These data indicate that sex expression in dioecious plants is the result of interaction between the genetic apparatus and phytohormones.