SEED PRODUCTION AND DISPERSAL IN DALECHAMPIA (EUPHORBIACEAE): DIVERGENT PATTERNS AND ECOLOGICAL CONSEQUENCES

Patterns of capsule development and methods of seed dispersal are described and compared for 16 neotropical species of Dalechampia. In 15 species all the capsules in a single inflorescence develop simultaneously. In one species, D. spathulata, the capsules develop sequentially. I suggest that the difference between D. spathulata and the other species is the result of the fact that D. spathulata occurs in a low-light, rainforest environment, whereas the other species grow in high-light environments. Sequential development of capsules appears to reduce the loss of seeds to seed predators in species that occur in light-limited environments. The seeds of all 16 species of Dalechampia are dispersed by explosive dehiscence of the capsules. Within the genus there are several different adaptations that increase the average dispersal distance for the seed crop.     

Host plant-mediated variation in overwintering site quality: implications for the size and composition of populations of Acanthoscelides alboscutellatus (Coleoptera: Bruchidae)

This study provides an example of how variation in the quality of overwintering sites provided by the host plant of an insect seed predator can influence both the probability of overwintering survival and the size and composition of postwintering populations. Thus, the concept of host plant quality is extended to include variation in the suitability of the overwintering site of temperate region insects that overwinter within, or in habitats created by, their host plant. Adult Acanthoscelides alboscutellatus (Horn) (Coleoptera: Bruchidae) overwinter inside the fruit of Ludwigia alternifolia (L.) (Onagraceae). In early winter, however, fruits begin to dehisce, i.e., one or more of the fruit's four sides and/or top are shed. Variation in the onset and extent of dehiscence creates a range of overwintering habitats that vary in exposure to ambient conditions. In this study the frequency of possible overwintering sites in natural populations of L. alternifolia was determined by monitoring the phenology of fruit dehiscence from October through May in two populations for four years and for a third population for three years. Winter survivorship of adult A. alboscutellatus was assessed experimentally in eight environments representative of the conditions created by variation in dehiscence. These environments were produced by crossing four levels of exposure (degree of dehiscence) with two locations of the overwintering site, i.e., above or on the ground surface. The onset, phenology, and overall frequency of fruit dehiscence varied markedly among populations and years. Exposure, location, and their interaction had strong effects on survival and accounted for 80% of the observed variation in winter survival. Survivorship was higher on than above the ground, and in both locations decreased with increasing exposure. Thus, variation in fruit dehiscence among L. alternifolia populations will influence the size of postwintering A. alboscutellatus populations by dictating the quality of overwintering sites. Adult beetles that over-winter inside indehiscent fruit experience selection for small body size, associated with high mortality, when they attempt to exit the fruit at eclosion. As a consequence, the frequency of fruit dehiscence at eclosion coupled with the relative survival rates of adults within indehiscent fruit will determine the body size composition of postwintering populations and hence the response to selection for small body size in this species.     

ENCAPSULATION OF EGGS BY MARINE GASTROPODS: EFFECT OF VARIATION IN CAPSULE FORM ON THE VULNERABILITY OF EMBRYOS TO PREDATION

Representatives of many plant and animal taxa enclose their embryos within some form of protective structure. Inter- and intraspecific differences in the morphology of these egg coverings may have profound effects on the development and survival of encapsulated embryos, yet in many taxa little is known about the causes or potential consequences of this variation. Comparisons of capsule morphology among populations of the rocky shore gastropod, Nucella emarginata, revealed significant variation in the thickness of capsule walls, the only barrier separating developing embryos from the external environment. Laboratory experiments demonstrated that thicker-walled capsules were more resistant to predation by a co-occurring isopod, Gnorimosphaeroma oregonense, than were thinner-walled capsules. Control experiments confirmed that these differences in vulnerability were not caused by differences in the palatability of the capsule wall or attractiveness of the capsule contents. The actual mechanism by which thick-walled capsules differentially protect developing embryos remains unclear, although decreased vulnerability of thick-walled capsules to these isopods may simply result from increased handling time by predators. Subtle differences in capsule morphology thus appear to have substantial effects on the survival of encapsulated embryos. Hence, predators may have played an important role in selecting for the production of thick-walled capsules among populations of N. emarginata.     

A Histological Study of the Effect of Feeding bySmicronyxspp. (Coleoptera: Curculionidae) Larvae on Seed Production byStriga hermonthica(Scrophulariaceae)

Experiments were conducted in Burkina Faso to determine the effect of feeding bySmicronyxspp. (Coleoptera: Curculionidae) larvae on the development of fruit capsule and seed production inStriga hermonthica(Scrophulariaceae). In treated plotsSmicronyxadults were released in the cages while in untreated plots (= control) noSmicronyxwere released. TheStrigacapsules were collected, fixed, and prepared for histological examination. UninfestedStrigacapsules developed normally. In infested capsules, three types of galls were distinguished: they reflected the development of capsule and the seeds. There was a synchrony between seed development and larval development in the same capsule. In most instances, one egg or larva was found per gall.Smicronyxlarvae completely destroyedStrigaseeds in the developing capsule by two mechanisms: (1) by directly eating most of the seeds and (2) by eating the placenta that normally feed the seeds.     

Primula persimilis sp. nov. (Primulaceae) from Sichuan,China

A new species of Primulaceae, Primula persimilis G. Hao, C.M. Hu & Y. Xu, from Sichuan, China, is described and illustrated. In general morphology it is allied to the species of P. sect. Monocarpicae, characterized by the presence of multi‐cellular hairs, the distinctly petiolate leaves, a campanulate calyx, and a globose or cylindrical capsule with valvate dehiscence. The new species superficially resembles P. tsiangii W.W. Smith, but can be distinguished by its white flowers, longer calyx lobes, and cylindrical capsules.     

Temporal variation in egg-capsule deposition by Nassarius vibex (Gastropoda: Nassariidae)

The morphology and the deposition periods of egg capsules by the bruised nassa Nassarius vibex were investigated on two beaches located on the southeast coast of Brazil. The nassariids were associated with the charru mussel Mytella charruana, which forms beds on soft mud-bottoms. A total of 1558 capsules were collected, only from the fronds of the green alga Ulva lactuca, 859 for Camaroeiro Beach and 699 for Cidade Beach. The mean sizes of the egg capsules and numbers of eggs or larvae per capsule were similar on the two beaches, as were the periods of capsule deposition. At Camaroeiro Beach, capsules first appeared in May 2006, reached a peak in August 2006, and disappeared in December 2006. At Cidade Beach, the first capsules were recorded in July 2006, with a peak in August 2006. A second peak was also observed at this beach between January 2007 and April 2007. The two periods of deposition recorded at the latter beach may indicate two periods of recruitment in the same year for N. vibex. Regarding the influence of intertidal level on capsule deposition, there was a significant difference in the number of capsules between the levels at Camaroeiro Beach (F?=?7.445, p?<?0.05), and for the second capsule-deposition peak at Cidade Beach (F?=?6.382, p?<?0.05). This study revealed a selective pattern of capsule deposition, with individuals of N. vibex using only fronds of U. lactuca. This process was influenced by the morphodynamics of the two beaches, with the nassariids maximizing the survival of embryos by depositing more capsules and more eggs per capsule in better-protected parts of the mytilid beds.     

Long-term effects of prey-availability, partnering and temperature on overall egg capsule output of 'New Zealand flatworms', Arthurdendyus triangulates

Arthurdendyus triangulatus is an invasive terrestrial flatworm that preys on earthworms. To assess A. triangulatus egg capsule production, flatworms were maintained in ventilated polypropylene tubs (7.5 L) kept in controlled environment (CE) chambers or outdoors in the ground. Controlled environment chambers were maintained at 8°C or 14°C, flatworms kept singly or paired within tubs and offered Eisenia fetida according to a weight equalling one‐eighth or one‐half of the mean flatworm weight, or left unfed. The tubs were a successful method for keeping flatworms, with some surviving for over one year. The greatest number of egg capsules produced by an individual A. triangulatus was nine over a 16 week period for a flatworm kept at 14°C and fed at the one‐half regime (0.56 egg capsules flatworm^‐1 week^‐1). Although the effects of treatments varied with CE chambers, there was some evidence from flatworms kept outdoors, that feeding affected egg capsule output, with those flatworms fed at the one‐half regime tending to produce more egg capsules (P= 0.057). Flatworms at the one‐eighth regime or that were unfed produced progressively lighter egg capsules and substantially declined in weight themselves. Nevertheless, even unfed flatworms continued to produce egg capsules for 18 weeks. The lightest egg capsule weighed 8 mg, whilst the heaviest was 180 mg. In the CE chambers at 14°C, there was evidence for two different reproductive/survival strategies. Some flatworms produced cumulatively more egg capsules the longer they survived, whereas others lived longer but produced fewer egg capsules. Flatworms kept without a partner still produced egg capsules up to 35 weeks later. Egg capsules contained a mean of 4.14 (CE chambers) or 4.62 (outdoors) juveniles, with a maximum of 11. Overall, juveniles were 45% of the weight of egg capsules, although larger egg capsules had more juveniles, which comprised a greater proportion of the egg capsule. The conversion of earthworm prey to egg capsule production was estimated at 13%.     

VARIATIONS IN MICROSPORANGIA AND MICROSPORE DISPERSAL IN SELAGINELLA

Fifty-three species of Selaginella were examined for variations in microsporangium anatomy and microspore dispersal strategies. Five anatomically different kinds of microsporangia were observed, displaying three different strategies for microspore dispersal. Xeric species, including all isophyllous species, have microsporangia that only dry and shrink as they dehisce, resulting in microspores being passively dispersed. Among anisophyllous species from tropical and subtropical habitats some species actively eject their microspores, while others of the series Articulatae eject the entire microsporangium. These two types of active ejection both utilize a mechanism similar to that found in fern leptosporangia.     

COMPARATIVE FLOWER AND FRUIT MORPHOGENESIS IN COLUBRINA (RHAMNACEAE) WITH SPECIAL REFERENCE TO C. ASIATICA

Flower and fruit morphogenesis of Colubrina asiatica, including aspects of fruit dehiscence and seed morphology, were studied by scanning electron microscopy and serial sectioning. Material from 13 additional species representing most intrageneric diversity was also examined. Organ initiation is simultaneous within each floral whorl and proceeds centripetally. Each petal/stamen pair apparently arises by tangential splitting of an individual primordium. The ontogeny of the three-locular, semi-inferior gynoecium follows a pattern common to many Rhamnaceae. At anthesis each uniovulated carpel has an almost independent pollen-tube pathway, with a subbasal compitum allowing for interconnection between carpels. Protandry, herkogamy, and a tendency to polygamy seemed to occur in C. asiatica. Fruit growth results mainly from postfloral promotion of the previously negligible superior part of the ovary. The explosively to tardily dehiscent capsules include three thin-walled, dehiscent stones (endocarpids) of inner dermal origin. At maturity, xerochastic (i.e., caused by desiccation), oblique bending of the endocarpids generates a complex dehiscence pattern involving thorough breaking of epicarp and mesocarp. The Colubrina type of fruit may be considered basic within the Rhamnaceae, which is consistent with the putative primitiveness of the genus. A limited potential for specialization is, however, expressed in such traits as explosive dehiscence, persistent arils on the seeds, and dispersal by sea currents (thalassochory).     

Encapsulation of Trichoderma harzianum conidia as a method of conidia preservation at room temperature and propagation in submerged culture

The objective of the present work was to develop a method for the preservation of T. harzianum conidia at room temperature and the immobilised conidia propagation in submerged culture. This was accomplished by immobilising the strain in sodium alginate capsules (white capsules) and subsequently propagating them in a column bubble reactor (green capsules). Three capsule diameters were tested (micro, medium and large capsules), which were produced by emulsion internal gelation and dripping methods. Tested variables were the immobilised conidia propagation in submerged culture for free conidia production, the immobilised conidia viability throughout the time (two years), the resistance of the encapsulated conidia to the UV irradiation of short and long wavelength, and the antagonistic effect of the encapsulated T. harzianum against four phytopathogenic fungi. It was found that the medium capsules (1.5?±?0.3?mm) favoured the massive production of released conidia in submerged culture and that the higher the density of conidia per capsule, the greater the protection against the ultraviolet irradiation. Regarding the conidia preservation in calcium alginate, a viability loss of around 30% was observed two years after storage at environmental temperature in both white and green capsules; along the two years that the viability of conidia was analyzed, the purity of the formulation was corroborated. The results presented here show the efficacy of the green and white capsules for T. harzianum preservation at room temperature for a long period of time.     

Temporal and spatial patterns of seed dispersal in two Cistus species (Cistaceae)

Cistus species are obligate seeding, early colonizers that follow disturbance, particularly fire, in Mediterranean ecosystems. We studied seed release, seed dispersal and soil seed populations in stands of Cistus ladanifer and C. libanotis. Seed release started in mid- to late summer (C. ladanifer) or in early autumn (C libanotis), and continued for a very extended period: 8-10 months in C. ladanifer, and for a mean of 16 months in C. libanotis. The xerochastic capsules of both species released seeds by successive dehiscence of the locules. All capsules begin to dehisce simultaneously at the start of the seed release period, but in C. libanotis capsule fragmentation replaced dehiscence early in the seed release period. In plants of both species, seed shadows were characterized by a peak of density beneath the plant canopy and a very short tail of much lower densities, indicating that seeds are concentrated beneath mother plants when dispersed. Nevertheless, in late May, at the onset of the fire season, soil seed densities beneath plant canopies were low compared with densities expected from seed shadows, but were apparently high enough to allow recovery of the stands if a disturbance, such as fire, had taken place. Seed-eating Bruchidae in summer and granivorous ants during the seed release period were apparently the main causes of seed losses. Results suggest that in both Cistus species, the staggered seed release could constitute an efficient risk-reducing trait. The plant pool of seeds existing throughout most of the year could be a relevant component of Cistus seed banks.     

Ethylene: Response of Fruit Dehiscence to CO(2) and Reduced Pressure

These studies were conducted to determine whether ethylene serves as a natural regulator of fruit wall dehiscence, a major visible feature of ripening in some fruits. We employed treatments to inhibit ethylene action or remove ethylene and observed their effect on fruit dehiscence. CO₂ (13%), a competitive inhibitor of ethylene action in many systems, readily delayed dehiscence of detached fruits of cotton (Gossypium hirsutum L.), pecan (Carya illinoensis [Wang.] K. Koch), and okra (Hibiscus esculentus L.). The CO₂ effect was duplicated by placing fruits under reduced pressure (200 millimeters mercury), to promote the escape of ethylene from the tissue. Dehiscence of detached fruits of these species as well as attached cotton fruits was delayed. The delay of dehiscence of cotton and okra by both treatments was achieved with fruit harvested at intervals from shortly after anthesis until shortly before natural dehiscence. Pecan fruits would not dehisce until approximately 1 month before natural dehiscence, and during that time, CO₂ and reduced pressure delayed dehiscence. CO₂ and ethylene were competitive in their effects on cotton fruit dehiscence. All of the results are compatible with a hypothetical role of ethylene as a natural regulator of dehiscence, a dominant aspect of ripening of cotton, pecan, and some other fruits.     

REPRODUCTIVE ECOLOGY OF JEFFERSONIA DIPHYLLA (BERBERIDACEAE)

The reproductive ecology of Jeffersonia diphylla (L.) Pers. (Berberidaceae) was investigated by studying its breeding system, ovule production, seed set, seed dispersal by ants and seed predation by rodents. This species flowers early in the spring and is facultatively autogamous. In a typical year fruit and seed set is high (90%), however, freezing temperatures from late spring frosts in 1983 and 1985 resulted in low fruit set (7% and 20%, respectively), and reduced seed set in those flowers that produced fruit. No differences in seed set between selfed and outcrossed flowers were observed over a two-yr period (1983–84). Ovule number per capsule increased with plant size as measured by leaf number. Seed set and seed wt were unaffected by leaf number unless leaves were removed after flowering was initiated. Jeffersonia diphylla is myrmecochorous. Ants removed seeds faster when seeds were placed in areas where J. diphylla plants were absent, suggesting that dispersal within J. diphylla populations is ant limited. Moreover, fresh (1 day old) seeds were removed by ants faster than 3 day old seeds. Seed predation by rodents prior to dehiscence from capsules is heavy in large populations (85–90%), and apparently negligible in small populations. Predation of seeds that are released from capsules is heavy (approx. 66%), particularly at night. Overall, seed predators consume about 96% of the seed crop in well established populations, but probably much less in small young populations. Hence, seedling recruitment is likely to be higher in small populations, whereas ramet production from rhizomes is the primary mode of propagation in large ones. The evolution of autogamy, early flowering, and myrmecochory are discussed in light of the results of this study.     

Deciphering the role of the capsule of Klebsiella pneumoniae during pathogenesis: A cautionary tale

Extracellular capsule polysaccharides increase the cellular fitness under abiotic stresses and during competition with other bacteria. They are best-known for their role in virulence, particularly in human hosts. Specifically, capsules facilitate tissue invasion by enhancing bacterial evasion from phagocytosis and protect cells from biocidal molecules. Klebsiella pneumoniae is a worrisome nosocomial pathogen with few known virulence factors, but the most important one is its capsule. In this issue, Tan et al. assess the fitness advantage of the capsule by competing a wild-type strain against four different mutants where capsule production is interrupted at different stages of the biosynthetic pathway. Strikingly, not all mutants provide a fitness advantage. They suggest that some mutants have secondary defects altering virulence-associated phenotypes and blurring the role of the capsule in pathogenesis. This study indicates that the K1 capsule in K. pneumoniae is not required for gut colonization but that it is critical for bloodstream dissemination to other organs. These results contribute to clarify the contradictory literature on the role of the Klebsiella capsule during infection. Finally, the varying fitness effects of different capsule mutations observed for K. pneumoniae K1 might apply also to other capsulated diderm bacteria that are facultative or emerging pathogens.     

Renalia hueberi, a new plant from the lower Devonian of Gaspé

A new genus and species, Renalia hueberi, is described from the Battery Point Formation, Gaspé Sandstone, Quebec. It consists of 1 mm wide axes, at least 11 cm long, bearing dichotomous lateral branches terminated by round to reniform sporangia. The sporangia dehisce along the distal margin and the line of dehiscence is bordered by thick-walled, rectangular cells. Spores are trilete, curvaturate and smooth to granulose. Renalia hueberi is superficially similar to the genus Cooksonia, but it differs from the presently known cooksonias in having both pseudomonopodial branching and dehiscent sporangia. It is interpreted however as being evolved from Cooksonia-like plants, and exhibits a sporangial position most comparable to that of the rhyniophytes and a mode of dehiscence characteristic of zosterophylls.     

SEED SET AND SEED PREDATION IN PEDICULARIS FURBISHIAE,A RARE ENDEMIC OF THE ST. JOHN RIVER,MAINE

We measured seed set and losses due to mammal and insect predation during 1983 in seven northern Maine populations of Furbish's Lousewort (Pedicularis furbishiae S. Wats.; Scrophulariaceae), a perennial herb endemic to the banks of the St. John River. Only about a quarter of initiated flowers developed a capsule with a full complement (mean = 25) of seeds. Secondary (lateral) inflorescences matured a smaller proportion of capsules than primary (terminal) inflorescences. About 58% of the initiated flower primordia were aborted or did not develop mature seeds by early September; this was probably not due to pollinator limitation. Several agents could have reduced seed production. Although spittlebugs infested between 3 and 30% (average 20%) of developing flower scapes by population, they did not depress the number of inflorescences initiated or the number of capsules matured. In contrast, 74% of capsules containing a lepidopteran seed predator (the plume moth Amblyptilia pica [Walsingham], newly discovered as a seed predator on P. furbishiae) had no seeds (mean = 3 seeds). Seed predation affected 39% of the potentially maturable capsules. In 6–30% of all capsules preyed upon, the lepidopteran was parasitized by an ichneumonoid wasp larva; these capsules matured about 7 seeds. Herbivory by rabbits, rodents, and deer also reduced seed set, eliminating 98% of the scapes at one site, and averaging 40% for other populations. Mammals and insects together removed at least 62% of maturable seeds. Populations varied widely in predation and seed set. Predispersal seed loss in P. furbishiae, coupled with slow seedling growth and occasional catastrophic mortality from ice scour and erosion, could limit population growth in this rare endemic.     

星油藤蒴果及种子的性状变异研究

为进行星油藤(Plukenetia volubilis L.)良种选育,对其蒴果和种子的性状变异进行了研究。结果表明,星油藤蒴果中4、5、6裂片果分别为49.71%、37.69%和12.60%,以4和5裂片为主;种子性状变异系数比果实的小,种子性状比果实更稳定。按果裂片类型统计,以4裂片的性状变异系数最小,性状也较为稳定,性状分化变异率有54.19%~95.63%来自蒴果间,而果实和种子性状分化变异率分别有79.81%~95.76%和67.66%~93.0%来源于裂片类型,性状分化变异受裂片数影响大,而相同裂片数不同蒴果间的变异程度低。不同裂片类型的果实与种子大多数性状间均存在显著或极显著差异,果裂数是造成性状差异的主要原因。种子萌发率以6裂片果5裂片果4裂片果,平均萌发率超过91%;种子萌发率与单果重、单果重与果形态指标、种子重与种子形态性状间均存在极显著正相关关系,其中单果重对果厚、种子重对种子宽的影响大于其它性状。综合分析星油藤以4裂片果的生物产量最高,平均果重和种子重均好于其他类型。     

Morphological and Anatomical Studies of Linaria species from South-west Spain: Fruits

A morphological and anatomical study of fruits of 24 taxa ofLinaria Miller from south-west Spain has been made. Followingexamination of these species, by scanning electron and lightmicroscopy, five morphological types are established relatingto hair types, symmetry and dehiscence of capsules. A key tothe different species or groups of species is provided. Finally,dehiscence mechanisms are discussed briefly. Copyright 1999Annals of Botany Company Pericarp, hairs, dehiscence, SEM, Antirrhineae.     

濒危植物长柄双花木的花部综合特征与繁育系统

 通过野外观察,运用杂交指数、花粉-胚珠比、人工授粉和套袋实验及等位酶电泳等方法,对长柄双花木(Disanthus cercidifolius Maxim. var. longipes H. T. Chang)自然种群和人工种群的开花状态、繁育系统进行了研究。结果如下：该种单花花期一般6～7 d,开花过程中柱头始终高于花药的位置,花药散粉具有先后顺序,一般2花药先散粉,其余3花药滞后1～2 d。单花花期依其形态和散粉时间可分为5个时期：即散粉前期、散粉初期、散粉盛期、凋谢期。种群开花一般历时49～55 d,但不同地点、年份之间有所差异,推测开花持续时间不同主要是环境条件所致。由于其杂交指数大于4,花粉-胚珠比等于1 250,结合人工套袋和授粉实验以及等位酶电泳结果可以确定该种的繁育系统属于异交为主,部分自交亲和,传粉过程需要传粉者。花粉竞争可能是导致该种濒危的主要的生殖生物学原因。