EVOLUTION OF LEAF ARCHITECTURE IN THE CHAPARRAL SPECIES FREMONTODENDRON CALIFORNICUM SSP. CALIFORNICUM (STERCULIACEAE)

The chaparral species Fremontodendron californicum ssp. californicum and the cloud forest species Cheirostemon platanoides arose from a common mesophytic stock. The leaf of C. platanoides is proposed as a model for the ancestral leaf and provides an architectural baseline allowing identification of the types and relative magnitudes of morphological and anatomical modifications which have occurred in the leaf of F. californicum. The leaf of F. californicum reflects intense selection for reduced surface area; however, both deletion and addition of lobes has occurred. Vein density has increased due to a greater number of more highly branched terminal veinlets. Mechanical structures, i.e., sclerenchyma, cuticle, show a quantitative reduction; whereas, water storage tissue, i.e., mucilage cells, has been augmented at the expense of spongy mesophyll. The leaf has become weakly isolateral and the number of palisade strata has increased. No increase in the volume of palisade tissue per unit volume of mesophyll is apparent due to a reduction in palisade cell length and palisade packing density. Total leaf thickness has not increased. The indumentum shows selection for non-living, pedestalled stellate trichomes which form a transpiration-limiting canopy above the stomata. Stomatal density has decreased while guard cell dimensions have become larger. Some structural modifications in F. californicum appear to have evolved directly in response to long-term water stress, others seem more directly related to leaf diminution. Xeroplastic changes in foliar structure are in some cases unreliable indicators of ultimate xeromorphic modifications arising in an evolutionary context.     

LIFE HISTORY AND SEED DISPERSAL OF THE SHORT-LIVED CHAPARRAL SHRUB DENDROMECON RIGIDA (PAPAVERACEAE)

The natural history of the short-lived, fire-following shrub Dendromecon rigida Benth. was studied with emphasis on reproductive output and the consequences of seed dispersal, by intensive study of one population and comparisons with several others.

1. In 16 populations throughout California, mean seed weight ranged from 10 to 16 mg, and was not correlated with rainfall, elevation or latitude. Seed number per fruit ranged from 3 to 11. Adult populations ranged in size up to several million, but each was probably even-aged, established after recent disturbance. Seed-dispersing ants were found at all localities.
2. Reproduction began one year after establishment. Precocious reproduction did not increase mortality; rather, longer-lived plants were more fecund at all ages.
3. The percentage of the population reproducing and fruit number in the most fecund plants were directly related to rainfall in the preceding six months, regardless of plant age. Reproduction also differed according to topographic position.
4. Mean life expectancy of one-year-old plants was about six years, and only 5% survived to age 10 years. Intraspecific density effects were not apparent. Seed longevity probably exceeds adult longevity by a factor of five or ten.
5. The fruits are explosive and secondary dispersal is by gravity and ants. The ants are attracted to a caruncle which represents 14% of the propagule's caloric content. In the intensive study area ants removed more seeds from more sites than did vertebrate seed predators. Pogonomyrmex subnitidus developed large nests on open sites on ridges, and thus provided uphill (even interdrainage) dispersal; it discarded seeds on the soil surface, free to roll but open to predation. Camponotus species had fewer foragers but many small nests in well-covered sites, and discarded the seeds in underground refuse galleries. Dispersal thus affects exposure to predation, the microsite of germination, conspecific aggregation, and position in the mosaic patterns of topography and fire.

     

SEX-RATIO VARIATION IN THE GYNODIOECIOUS SHRUB HEBE STRICTISSIMA (SCROPHULARIACEAE)

The frequency of females was determined for eight populations of the gynodioecious shrub, Hebe strictissima (Scrophulariaceae) and related to plant vigor among populations, as indicated by the average number of leaves per shoot. The purpose was to test the idea that females should be more prevalent in relatively poor sites where plant vigor is low. This hypothesis was based on sex-ratio theory, coupled with the idea that fruit-set in the polleniferous morph (i.e., in “males”) is more dependent on vigor than it is in females. I found that, within populations, females produced significantly more fruit than males and that plant vigor did not differ significantly between the sexes. Fruit-set on males was positively and significantly correlated with the number of leaves per shoot within plants, among plants within populations, and among populations. No such correlations were found for females. The greater plasticity of the males altered the relative seed fitnesses of the two morphs among the eight populations, resulting in a negative correlation between female frequency and average plant vigor. I suggest, in general, that such plasticity may be an important factor in sex-ratio variation among populations and that it should be incorporated into models of sex-ratio evolution.     

同口牙齿的磨耗级比较

本文比较和分析了同口同侧牙齿的相应的磨耗级,提供了除臼齿以外的牙齿磨耗年龄变化依据。同时还对上下对应牙、两侧对称牙的磨耗级作了比较和分析。     

梧桐科翅子树属的亲缘关系

翅子树属传统上均作为梧桐科山芝麻族的成员,但也有少数人将它归到Dombeyeae族中。本文根据对翅子树属的外部形态及花粉形态特征的研究,并结合其解剖、染色体和胚胎发育的资料,对翅子树属的亲缘关系进行了分析。翅子树属与山芝麻族在外部形态上比较接近,但在解剖、花粉形态和染色体基数等特征上则差异显著;与Dombeyeae族在花粉形态上一致,但在外部形态(花结构)、染色体基数和瓦形细胞等特征方面则明显不同,反映了翅子树属在这两个族之间的过渡状态,不宜作为任何一族的成员,应该作为一个独立的族存在,其在梧桐科中的位置在Dombeyeae附近。     

REPRODUCTIVE PLASTICITY IN THE KELP ALARIA NANA (PHAEOPHYCEAE)1

Unlike terrestrial plants, reproductive control in algae has not been attributed to biotic factors or internal chemical signals. However, experimental removal of reproductive structures (sporophylls) from the kelp Alaria nana Shrader resulted in the development of functional reproducing structures on the vegetative frond in 45% (10/22) of the experimental plants but not on the control plants where sporophylls were left intact (n = 35). In naturally occurring Alaria nana, this compensatory reproductive response occurred at a low incidence and was restricted primarily to larger individuals in the population. Thus, compensation and developmental plasticity, mediated In plant size, may play an important role in how algae respond to reproductive tissue loss.     

ANDROMONOECY IN THE NEW ZEALAND MONTANE SHRUB MANUKA,LEPTOSPERMUM SCOPARIUM (MYRTACEAE)

The ecological and evolutionary advantages of andromonoecy are considered by examining populations of a montane grasslands shrub. Manuka plants (Leptospermum scoparium, Myrtaceae) produce two kinds of flowers: male flowers having functional stamens and a nonfunctional pistil, and hermaphrodite flowers in which both the stamens and pistil are functional. Factors affecting the ratio of the two flower types were investigated at Cass, Canterbury, New Zealand. Stamens mature at the same rate in the two flower types. Individual plants within one population vary from having predominantly hermaphrodite flowers to having no hermaphrodite flowers. Individual variation within a population in the percentage of hermaphrodite flowers is correlated between seasons, indicating some stability in this character. In a particular season, variation among plants within a population in the percentage of hermaphrodite flowers is negatively correlated with date of flowering, but it is not correlated with either the number of flowers or vegetative growth per plant. The hermaphrodite flowers tend to open in the first flush of flowering, and the proportion of hermaphrodite flowers subsequently declines in individual plants and in the population as a whole. The earlier anthesis of hermaphrodite flowers probably increases the frequency of outcrossing; it also provides more time for fruit to mature. The percentage of hermaphrodite flowers is greater toward the top of the plant and among terminal flowers on branchlets than among proximal flowers. The percentage of hermaphrodite flowers on a plant was progressively increased with increasing nutrient treatments. The flowers are visited by a wide range of insects. Fruit set was not increased by hand pollinations of flowers exposed to natural insect visits, indicating that pollinator activity does not limit natural fruit production. A considerable fraction of the variation between individuals in the proportions of male and hermaphrodite flowers is environmentally induced. Andromonoecy may have been selected for in manuka because it is advantageous for pollen to be presented in more flowers than the number of ovule- and seed-bearing flowers. Alternatively, andromonoecy may allow an individual plant to adjust its reproductive output to its immediate physiological condition. However, andromonoecy by itself is not an out-breeding mechanism.     

REPRODUCTIVE SUCCESS OF FUCUS VESICULOSUS (PHAEOPHYCEAE) IN THE BALTIC SEA

Marine organisms colonizing brackish habitats such as the Baltic Sea must cope with the negative effects of low salinities on reproductive success because these may reduce gamete viability and/or increase polyspermy. Reproductive characteristics of the marine seaweed Fucus vesiculosus L. were studied in several brackish habitats, particularly in the northern Baltic Sea, to understand its ability to reproduce where few other marine species survive. Polyspermy and fertilization success were variable at the boundary of the continuous distribution of F. vesiculosus in the Baltic Sea, and polyspermy was high (10%–30%) when fertilization was successful. A strong female bias (80%–86%, ca. 5.5:1) was found at the northernmost limit of Baltic F. vesiculosus. Electrophysiological studies showed that many eggs have a high input resistance (519 ± 150 MΩ[mean ± SE, n = 14] at Drivan, 1995), which may be helpful in preventing polyspermy in this brackish habitat. The polyspermy block remains sodium-dependent in the northern Baltic. Sperm bound quickly to northern Baltic eggs in natural water, but fertilization was delayed compared to marine F. vesiculosus. A subset of northern Baltic eggs studied during an optimal reproductive period (7–11 July 1995) had a membrane potential (E_m) of ca. −100 mV and an effective fertilization potential (FP) of ca. 2 min with a plateau of −25 mV, but repolarized too rapidly for the FP to be protective. Pronuclear migration and cell wall secretion occurred more slowly in Baltic than in marine zygotes. The reproductive success of theseboundary populations may be dependent upon windows of opportunity when there are favorable combinations of the levels of salinity, water motion, population density, and sex ratio. These factors and the short duration of the reproductive season in the northern Baltic Sea may result in reproductive failure in some years.     

塔里木河叶尔羌高原鳅繁殖生物学研究

2010年7月至2011年12月,在塔里木河阿拉尔段采集叶尔羌高原鳅Triplophysa (Hedinichthys) yar-kandensis (Day)940尾(除性别未辨个体外)用于繁殖生物学研究。种群雌雄比为0.85︰1,最小性成熟,雌性个体体长为8.2 cm,体重为7.4 g,年龄为3龄;雄性个体体长为6.5 cm,体重为3.4 g,年龄为2龄。叶尔羌高原鳅卵径分布呈单峰形,推测应属于同步产卵类型。计算了88尾Ⅳ-Ⅴ期雌鱼的怀卵量,其体长范围30-195 mm,体重范围3.59-114.04 g,绝对繁殖力为1101-56320(9944±5487)粒,相对繁殖力为824-1140(982±158);塔里木河阿拉尔段叶尔羌高原鳅种群繁殖力(Fp)为403.46万粒。     

SEX-RATIO AND REPRODUCTIVE VARIATION IN THE MISTLETOE PHORADENDRON JUNIPERINUM (VISCACEAE)

Despite the fact that many parasitic and hemiparasitic plant species such as mistletoes are dioecious and occur in both the new and the old world, few data exist on variation in the sex ratio and allocation to reproduction in these taxa. We investigated 1) the sex-ratio of the xylem-tapping mistletoe Phoradendron juniperinum in relation to its age and position within the canopy of its host tree Juniperus osteosperma, and 2) reproductive effort in relation to the gender and age of mistletoe plants. Our surveys showed that P. juniperinum has a male-biased sex ratio. Despite this predominance of male individuals, females lived longer and had a greater reproductive effort than did males. A statistical analysis of the age distribution data indicated that the peak in the frequency of reproductively mature individuals was later in females than in males. These gender-specific distributions may have resulted 1) from sequential hermaphroditism (age-specific sex switching), or 2) because the average age of peak reproduction is later in female individuals. Because sex is genetically determined in a closely related genus of mistletoe and because we have no data to indicate sex switching in this species, we feel that our data support the interpretation that female individuals, on average, show a peak in reproductive vigor at an older age relative to males. While delayed reproduction in females may be favored because reproductive effort and success appear to be age-dependent in females of this species, both sexes can become reproductively mature relatively early in life. Further, because 1) allocation to reproduction as a function of age increases more rapidly for females of this species relative to males, and 2) because there may be a higher resource cost associated with reproduction in females, we hypothesized that female individuals would be more abundant in the best quality locations within the host tree so as to maximize the opportunity to meet those costs. In spite of the association between gender and some host characteristics, there was no indication that female plants were located in sites most favorable to either their carbon or water balance. We discuss reasons why this may be the case.     

GENETIC EVIDENCE FOR MULTIPLE ORIGINS OF DIOECY IN THE HAWAIIAN SHRUB WIKSTROEMIA (THYMELAEACEAE)

Dioecy is unusually common in the Hawaiian Islands, yet little is known about the evolutionary biology of this breeding system. A native shrub, Wikstroemia, has an unusually diverse array of breeding systems: two forms of dioecy, cryptic and morphological dioecy, as well as hermaphroditism (perfect flowers). The existence of two forms of dioecy is significant for three reasons: 1) the presence of cryptic unisexuals that are functionally unisexual, but retain the appearance of hermaphroditism in both sexes, is strong evidence for the ancestral status of hermaphroditism; 2) the production of nonfunctional pollen, by female cryptic unisexuals, is a new instance of a phenomenon which has previously been reported for a few other species; 3) the two forms of dioecy are morphological markers which are useful in hybridization studies for tracing the genetic basis of their inheritance. Crosses were made between cryptically unisexual individuals (C), between morphologically unisexual individuals (M), and between the two types of unisexuality. The offspring of crosses between individuals with the same sex type usually resulted in offspring with that sex type, but most of the progeny of between-sex type crosses were, unexpectedly, perfect-flowered hermaphrodites. These results show that genetic control of sex determination is not homologous in all populations, suggesting that dioecy has evolved at least twice in Hawaiian Wikstroemia. The genetic data further suggest that males are the heterozygous sex.     

梧桐科一些属的分类位置探讨

梧桐科（Ｓｔｅｒｃｕｌｉａｃｅａｅ）是锦葵目中的一个多型科,科的特征比较比样化。自从Ｅ．Ｐ．Ｖｅｎｔｅｎａｔ（１８３０）建立该科以来,对于该科范围和包含的属种数目,各国学者至今尚存在各种不同的看法。作者认为,火桐属（Ｅｒｙｔｈｒｏｐｓｉｓ）应当从梧桐属（Ｆｉｒｍｉａｎａ）中分出成为单独的属;午时花属（Ｐｅｎｔａｐｅｔｅｓ）不应归入锦葵科（Ｍａｌｖａｃｅａｅ）,应当置于梧桐科;田麻属（Ｃｏｒｃｈｏｒ     

REPRODUCTIVE SYSTEM AND SPERMATOGENESIS IN THE OPISTHOBRANCH GASTROPOD RETUSA OBTUSA (MONTAGU)

The cephalaspidean opisthobranch Retusa obtusa has an ovotestissimultaneously producing eggs and spermatozoa. Reproductiveorgans are characterized by the hermaphrodite duct and seminalreceptacle together joining the pallial glandular duct whichis differentiated anteriorly to form the ‘albumen’gland, membrane or capsule gland, and mucus gland. The ductof a copulatory bursa joins the common central chamber of thiscomplex. Eggs presumably pass through extended tracts in the3 glands to emerge at a hermaphrodite aperture in the rightside of the mantle cavity. Spermatozoa also emerge at this apertureto a ciliated seminal groove along the right side of the headwhich, in turn, joins copulatory organs folded within the headand opening close behind the right cephalic tentacle: a muscularpenial sac receives 4 elements of prostate gland. Spermatophoreswere never seen. Oocytes, surrounded by several thin folliclecells, reach 150–330 µ, m diameter in larger wintersnails, mostly in the periphery of theovotestis. Spermatocytesand spermatids develop as clusters in association with accessory(Sertoli) cells. The acrosome appears in the centre of a denseanterior plaque, develops as a domed acrosome vesicle on a shortpeduncle and eventually becomes a terminal spike on the nucleustip. The Golgi complex is seen sometimes near the early acrosomebut more often behind the nucleus. Mitochondria aggregate firstahead of the nucleus but then form a mitochondrial derivative,with a glycogen helix, spiralled around the axoneme throughoutthe mid-piece of the tail. This region is marked off from theend-piece of the tail by the annulus. The nucleus becomes long,spiralled with a strong keel, and surrounds the centriolar derivativeat the base of the axoneme.     

THE EVIDENCE OF REPRODUCTIVE MECHANISMS IN FOSSIL DASYCLADS (ALGAE: CHLOROPHYTA)

Dasyclads (members of Order Dasycladales: Algae, Chlorophyta) are reviewed for evidence of reproductive structures in the fossil state, and then compared with what is known of the reproductive processes in living examples. The effects of poor preservation in most of the fossils are shown to result in many uncertainties, and the resulting degree of interpretation required is emphasized. Selected genera of fossil dasyclads considered relevant to this problem are briefly analysed and discussed: Archaeobatophora (Ordovician), Kulikia (Carboniferous), Imperiella (Permian), Stichoporella (Jurassic) and Cympolia (Cretaceous to Recent). The pioneer views of J. Pia on dasyclad reproduction through geological time are seen to need much modification in the light of later work. The fundamental dasyclad nucleus-fragmentation-reproduction mechanism is believed to have operated within the great morphological variety of known dasyclads, giving rise to modification in genera where basic evolution was structural. In this way the variety of dasyclads can be seen to be the result of varied morphological evolution, often modified by the consistently simple basic reproductive mechanism.     

REPRODUCTIVE PROFICIENCY IN PAEONIA CALIFORNICA (PAEONIACEAE)

Study of three populations of geophytic Paeonia californica in southern California revealed considerable variation, within and between populations, in both potential and in realized seed output. Plants are weakly self-compatible, but natural seed set (x = 4.2 seeds per carpel) is closer to seed set produced in hand cross-pollinations (x = 4.5) than in self pollinations (x = 1.4). Flowers are protogynous, nectariferous, and scented; 17 species of bees in four families, and one species of melyrid beetle were found in them and probably account for pollinations at these sites. Counts of reproductive parts show greatest inter-population variation in mean numbers per plant, of flowers (population means ranged from 16.2 to 21.2), ovules (744 to 1142), pollen grains (23 million to 38 million), and % viable pollen (26.6 to 81.4). Seed set also varied significantly, with only 11.4 to 26.8 % of the ovules maturing into seeds. This low reproductive success is probably correlated with the genetic anomalies studied by others—particularly the translocation heterozygosity that causes lowered production of viable gametes. The relatively few seeds produced are heavy (x = 0.184 g per seed), and germination percentages are high (x = 80%). The elongation of cotyledon bases during hypogeal germination seems to permit optimal germination at soil depths of only 2–3 cm, but environmental factors such as drought stress and herbivore pressure promote high seedling mortality.     

准噶尔无叶豆的开花物候与生殖特征

 为了研究沙漠稀有植物准噶尔无叶豆(Eremosparton songoricum)的开花物候特征及其对生殖成功的影响, 2005和2006年连续两年对其自然种群的开花物候和开花过程中的花部表型变化进行了观察, 并运用相对开花振幅、开花强度和开花同步性等开花物候指数研究了开花物候特征。结果表明: 准噶尔无叶豆在5月下旬至6月中下旬开花, 其种群、个体、花序和单花的花期分别历时26~29 d、8~10 d、5~7 d和2~3 d。单花开花进程依其形态和散粉特征可分为散粉前期、散粉初期、散粉盛期和凋谢期4个时期。其个体水平的开花物候进程(开花振幅曲线)呈渐进式单峰曲线, 具有很高的开花同步指数, 表现出一种集中开花的模式。开花物候指数与座果数之间的相关分析结果表明, 始花日期与花期持续时间存在负相关关系, 而与开花数和座果数存在正相关关系; 花期持续时间与开花数和座果数存在显著正相关关系。准噶尔无叶豆个体开花物候在很大程度上是由其遗传因子决定的, 而开花物候在年度间的变异, 可能是由于荒漠气候的差异(主要是水分和温度的差异)所引起的。作为沙漠窄域分布特有种, 准噶尔无叶豆在环境和人为干扰的双重选择压力下, 为了吸引更多的传粉者访问而达到生殖成功, 形成了大量集中开花的模式。     

淀山湖河蚬性腺发育分期的研究

作者研究了河蚬性腺发育并确定了性腺分期标准。雌雄性腺发育皆可分为五个时期:第Ⅰ期增殖期、第Ⅱ期小生长期、第Ⅲ期在雌性为大生长期,在雄性为成形期、第Ⅳ期成熟期、第Ⅴ期在雌性为排卵期,在雄性为耗尽期。此外,还发现河蚬存在雌雄同体现象。     

稀有鮈鲫性别决定类型初探

稀有鮈鲫(Gobiocypris rarus)是中国特有的一种小型鲤科鱼类,属于亚科、鮈鲫属,俗称金白娘、墨线鱼,主要分布于四川省汉源县大渡河支流的流沙河及成都附近的一些小河流中,被中国野生动物红皮书列为濒危鱼类。