SIZE-DEPENDENT GENDER CHANGE IN GREEN DRAGON (ARISAEMA DRACONTIUM; ARACEAE)

Green dragon (Arisaema dracontium; Araceae) is a perennial woodland herb capable of switching gender from year to year. Small flowering plants produce only male flowers but when larger they produce male and female flowers simultaneously. Distinct male and monoecious phenotypes (referred to hereafter as plants) share a single underlying cosexual genotype. Four populations in southern Louisiana were sampled to determine frequencies and size distributions of male and monoecious plants, and to determine the relationship of plant size with male and female flower production in monoecious plants. Male plants were significantly smaller than monoecious plants and made up 34%–78% of flowering plants within populations. Flower number (average = 120) was weakly positively correlated with size. Monoecious plants produced an average of 169 flowers (90 female) and had 100% fruit set, with individual berries containing an average of 2.5 ovules and 1.3 filled seeds. Male flower number was negatively correlated, and female flower number positively correlated, with basal stem diameter. Extrapolation of regression slopes suggested that green dragon should become completely female at a size 20% larger than the largest plant observed in this study. A simple model of inflorescence development is presented to illustrate how the reproductive system of green dragon is related to that of jack-in-the-pulpit (A. tnphyllum), which exhibits a more distinct switch between male and female phenotypes.     

PATHOGEN IMPACT ON SEXUAL VS. ASEXUAL REPRODUCTIVE SUCCESS IN ARISAEMA TRIPHYLLUM

Populations of Arisaema triphyllum commonly harbor a systemic fungal pathogen, Uromyces ari-triphylli, which reduces leaf area and leaf longevity. Infected plants produced 42% fewer asexual progeny (cormlets). Furthermore, all asexual progeny from infected parents were themselves infected with Uromyces. Mean seed production of infected plants was only 21% of that among healthy plants. A hand pollination experiment demonstrated that 1) infected male plants can produce viable pollen, 2) the low seed production of naturally pollinated infected females was not due to inadequate pollination, and 3) seed production among healthy female plants was strongly pollinator limited. Seeds from infected and healthy parents had similar viability, and all seeds germinating from both types of parents were uninfected. The contrast in disease transmission to sexual vs. asexual progeny suggests that pathogen attack may be one selective factor favoring sexual reproduction in A. triphyllum populations.     

THE RELATIONSHIPS BETWEEN SEASONAL VARIATION IN LIGHT INTENSITY,RAMET SIZE,AND SEXUAL REPRODUCTION IN NATURAL AND EXPERIMENTAL POPULATIONS OF ASTER ACUMINATUS (COMPOSITAE)

We conducted experiments to evaluate the effects of different patterns of seasonal light availability on ramet size and sexual reproduction in the understory herb, Aster acuminatus. In April 1982, 200 potted rhizomes were divided equally between a high light and a shaded site. Twice during the growing season subsets of pots were reciprocally transferred between the sites, resulting in eight different light treatments. There was significant variation among treatments in mean ramet weight (0.41–1.21 g), height (15.0–23.4 cm), number of flowers (0.4–7.9) and percentage of ramets flowering (14–95). Periods of high light increased ramet height, weight, rhizome production and flowering, but high light earlier in the season increased ramet height more than did high light later in the season, while high light later had pronounced effects on the other three traits. Measurements taken in nine natural patches experiencing different patterns of seasonal light availability are consistent with the experimental results. The results provide new insights into the general phenomenon of size-dependent reproduction in herbs and illustrate how the phenology of biomass allocation can affect growth and reproduction.     

CYCLIC HETEROPHYLLY IN SYNGONIUM (ARACEAE)

Species in the genus Syngonium germinate on the ground and mature on the trunks of the trees. These vines consist of relatively unbranched shoots which grow through the forest for considerable distances both horizontally and vertically. In the three species of this study, the shape of the segment, measured as internode diam/length, falls into two distinct classes, leafy and elongate, and varies cyclicly along single shoots. Two cycles are recognized. One cycle occurs in small diam terrestrial shoots in which cycling seems to be controlled by endogenous factors, and occurs with a period of a few tens of segments. The other cycle occurs in shoots of larger diam which climb and descend from trees. In this cycle, alternation between the two forms is controlled by gain or loss of contact with trees, and shoots may remain within a phase of the cycle for hundreds of segments, as long as the substrate does not change.     

BREEDING SYSTEMS AND FECUNDITY IN THE AMERICAN GINSENG,PANAX QUINQUEFOLIUM (ARALIACEAE)

American ginseng is self-compatible with fecundity among bagged inflorescences equivalent to (Missouri) or greater (New York) than that observed for nonbagged inflorescences. Population differences in flowering time and synchrony, protandry, autogamy, xenogamy, and fecundity, imply major genetic divergence in the species.     

CHROMOSOME NUMBERS IN THE GENUS ANTHURIUM (ARACEAE) II

Chromosome numbers were determined for 86 Anthurium species. Fifty-one of these were newly determined with counts ranging from 2n = 24 to 66 and 30 being the most common. All known Anthurium chromosome numbers were summarized, and 43 taxonomic changes were made in the previous reports to reflect current taxonomy. In terms of somatic chromosome numbers, the numbers form four polyploid series of 20–40–60, 24–30–48–84, 28–56 and 30–60–90–ca. 124. Paleoaneuploidy, polyploidy and B-chromosomes are basic features of the genus, but subsequent recent aneuploidy is not. The exact nature of chromosome evolution in Anthurium remains to be elucidated.     

DIVERSITY OF SHOOT MORPHOLOGY IN TYPHONIUM (ARACEAE)

The details of shoot organization, including number of leaves per shoot, position of foliage leaves and cataphylls, position of the lateral continuation shoot, nature of axillary buds and phyllotaxis, and the pattern of shoot extension were observed and compared in five species of Typhonium, Dracunculus vulgaris, Sauromatum venosum, Arum italicum, and Helicodiceros muscivorus, resulting in the recognition of four types of stems. Three of the four types were found in the genus Typhonium. One type was found in Typhonium giganteum and Sauromatum venosum and is presumably the same in Biarum. Another type, found in T. trilobatum, T. blumei, and T. flagelliforme, is distinct in the position of the lateral continuation shoot, which arises from the axil of the n-1 leaf and is adnate to the axis to above the n leaf. Based on the results, two groups, one of which is further subdivided into two subgroups, are recognized in subtribe Arinae (subfam. Aroideae tribe Areae).     

RELATIVE POLLINATOR EFFECTIVENESS AND EVOLUTION OF FLORAL TRAITS IN SPATHIPHYLLUM FRIEDRICHSTHALII (ARACEAE)

We studied the relative effectiveness of different pollinators of Spathiphyllum friedrichsthalii Schott for 15 months on Barro Colorado Island, Panama. Pollen-foraging stingless bees (Apidae: Trigona) made 87% of floral visits. Experiments showed that these bees pollinate flowers, and correlations of fruit- and seed-set with visitation frequencies and floral contact times suggested that they were responsible for the majority of seeds produced. Fifteen species of fragrance-foraging, male euglossine bees (Apidae: Euglossini) collectively accounted for a small portion of seed-set in fewer than 27% of the inflorescences. Neocorynura (Halictidae) were pollen thieves and were unimportant as pollinators. We propose that euglossine and stingless bees differentially influence outcrossing rates and the evolution of floral traits of S. friedrichsthalii. Foraging behavior of male euglossines should allow for more long-distance pollen flow whereas stingless bees are likely to promote near-neighbor and geitonogamous pollinations. We discuss why the prolonged male phase of anthesis in this protogynous species may be maintained through pollination by stingless bees rather than male euglossines. Furthermore, although the floral fragrance is attractive to many species of male euglossines, it attracts few individuals. This condition may represent an intermediate step in the evolution of predominant pollination by male euglossines.     

SIZE VARIABILITY AND SELF-THINNING IN WILD-RICE (ZIZANIA AQUATICA)

Size variability decreases during the course of density-dependent mortality (self-thinning) in dense, naturally-occurring monocultures of wild-rice in a tributary to the Chesapeake Bay. As self-thinning progresses, the size distribution changes from high inequality and positive skewness to become more uniform and equal. This is consistent with the hypothesis that self-thinning is driven by competition for light.     

VASCULAR PATTERNS IN STEMS OF ARACEAE: SUBFAMILIES COLOCASIOIDEAE,AROIDEAE AND PISTIOIDEAE

The stem vasculature of ten genera of Colocasioideae and three genera of Aroideae was analyzed by films of series of cross sections. The technique was unsuited for the numerous tuberous genera of Aroideae (and Pistia), which have shortened internodes. The Colocasioideae has long been recognized as one of the most natural large assemblages in the Araceae, a concept further supported by information from stem anatomy and vasculature. All species examined have amphivasal axial bundles that undergo frequent anastomosis and bifurcation of a seemingly irregular kind. Syngonium is the only viny genus and is exceptional in a number of anatomical features which are associated with its unusual morphology. One of the principle points of diversity in the Colocasioideae is the presence or absence of a permanent cortical vascular system. All four genera with a permanent cortical system (Caladiopsis, Caladium, Xanthosoma, and Syngonium) are neotropical. In the Aroideae (and Pistioideae) all of the tuberous genera have a highly condensed vascular system. Genera with elongated internodes (Stylochiton, Lagenandra, Cryptocoryne) also have a similar pattern, which makes taxonomic comparisons based on stem vasculature in the Aroideae of little value. Branch trace insertion is much less well developed in Colocasioideae and Aroideae than in most other subfamilies.     

THE RELATIONSHIP BETWEEN AGE,SIZE, AND REPRODUCTION IN TRILLIUM GRANDIFLORUM (LILIACEAE)

The relative importance of age and size as predictors of demographic parameters such as survivorship or reproductive status is generally unknown for herbaceous perennials, due primarily to the difficulty in estimating the age of herbaceous plants. We investigated the relationship between age, size, and reproductive status in Trillium grandiflorum, a rhizomatous perennial herb in which age can be estimated. We measured the leaf area and rhizome volume and estimated the age of plants in a study population that included reproductive and nonreproductive individuals. Reproductive plants were significantly older ( = 22.8 years) than nonreproductive plants ( = 13.3 years). Reproductive plants also had significantly larger total leaf areas and rhizome volumes. Total leaf area, rhizome volume, and age were positively correlated in both groups. Reproduction in this population occurred once plants reached a threshold leaf area or rhizome volume. Both measures of plant size, i.e., total leaf area and rhizome volume, were better predictors of plant reproductive status than was plant age.     

THE EFFECT OF TEMPERATURE ON BODY SIZE AND FECUNDITY IN FEMALE DROSOPHILA MELANOGASTER: EVIDENCE FOR ADAPTIVE PLASTICITY

The reaction norm linking rearing temperature and size in Drosophila melanogaster results in progressively larger flies as the temperature is lowered from 30°C to 18°C, but it has remained unclear whether this phenotypic plasticity is part of an adaptive response to temperature. We found that female D. melanogaster reared to adulthood at 18°C versus 25°C showed a 12% increase in dry weight. Measurements of the fecundity of these two types of fly showed that the size change had no effect on lifetime fecundity, regardless of the adult test temperature. Thus the phenotypic plasticity breaks the usual positive correlation between body size and fecundity. However, at a given temperature, early fecundity (defined as productivity for days 5 through 12 after eclosion at 25°C and days 7 through 17 at 18°C) was highest when the rearing and test temperatures were the same. The early fecundity advantage due to rearing at the test temperature was 25% at 18°C and 16% at 25°C, a result consistent with the overall phenotypic response to temperature being adaptive. This conclusion is further supported by the finding that the temperature treatments resulted in a trade-off between early fecundity and longevity, a trade-off that parallels the known genetic correlation. Another parallel is that both the temperature-induced and genetic effects are independent of total fecundity. By contrast, within the temperature treatments, the phenotypic correlation between early fecundity and longevity was positive, illustrating the danger of assuming that phenotypic and genetic correlations are similar, or even of the same sign.