Vivian Negrón-Ortiz

Chromosome numbers, nuclear DNA content, and polyploidy in Consolea (Cactaceae), an endemic cactus of the Caribbean Islands

Polyploidy, an important mechanism of plant evolution, was investigated in Consolea, an endemic Caribbean opuntioid genus represented by nine subdioecious species with very narrow distributions, including species classified as rare or threatened. Standard chromosome counting and flow cytometric analyses were used to determine chromosome numbers and ploidy of each taxon. Compared to the base number (x = 11), the mitotic and meiotic counts indicated that there are seven hexaploid (2n = 66) and two octoploid species (2n = 88); no diploids were found. Histograms of intact nuclei confirmed that all species are polyploid, with C-DNA values ranging from 4.88-9.50 pg. The variation of DNA content was significantly higher for the octoploids than for the hexaploids. Male and female sexual morphs had similar DNA content, suggesting that there are no sex chromosomes. Cytomixis between cells and microsporocytes with no chromatin were observed. This provides a mechanism whereby gametes with variable chromosome numbers are produced, influencing reproduction and promoting speciation. In conclusion, C-DNA content and chromosome number separated Consolea species into two groups, which may correspond to two phylogenetic lineages or indicate that polyploidization occurred independently, with comparable effects on C-DNA content.

Effects of Fire Season and Postfire Herbivory on the Cycad Zamia pumila (Zamiaceae) in Slash Pine Savanna, Everglades National Park, Florida

We investigated the effect of prescribed wet‐season fire on the demography of Zamia pumila L. (Zamiaceae) in slash pine savanna of Everglades National Park, Florida. We monitored survival, coning, leaf production, and herbivore damage on two plots burned during the wet season of 1995 and on two unburned plots. Fire killed all leaves and promoted the flushing of new leaves but caused minimal mortality of adults and seedlings. Seeds within cones were killed, but some dispersed seeds survived. Coning, particularly of females, was enhanced in the plot that burned earlier and hotter. Larvae of Seirarctia echo appeared on new leaves within 1 mo postfire and were present at higher density on burned plots. Herbivore damage was significantly greater on burned plots for the first wet season following the fire, with many plants completely defoliated. This defoliation, which was more frequent in the plot burned late in the wet season, resulted in mortality of some adults but promoted greater leaf production in the remainder. Seirarctia echo consumed some Zamia cones, cancelling the positive effect of fire on reproduction. Overall, the combined direct and indirect effects of wet‐season fires on Zamia was positive for the early wet‐season fire but negative for the late wet‐season fire because of reduced coning and increased mortality following herbivory.

Comparative microsporangium development in male‐fertile and male‐sterile flowers of Consolea (Cactaceae): When and how does pollen abortion occur

Anther development, microsporogenesis, and microgametogenesis were studied using both light and TEM microscopy in the six accessible subdioecious/cryptically dioecious species of Consolea (Cactaceae). Anther wall development, microsporogenesis, and microgametogenesis are uniform in staminate flowers of all six species, and are typical for Cactaceae. Breakdown of microsporogenesis in male‐sterile anthers occurs early, at the onset of meiosis, and results in anthers bearing no pollen grains. The abortive process follows a common pattern in all investigated species. The tapetum is the first layer to deviate from normal male‐fertile anther development. Tapetal cells in male‐sterile anthers elongate at an early stage and have abundant rER with atypical configurations. Ultimately, the tapetum becomes hypertrophied and non‐functional. Male‐sterility in pistillate flowers appears to be directly related to these anomalies. In addition, other anther layers and tissues are affected, and normal patterns of programmed cell death (PCD) are disrupted. The relationship between these patterns and the pattern of PCD in normal male‐fertile anthers is discussed. We hypothesize a single origin for the cryptically dioecious/subdioecious breeding system of Consolea based on the uniformity of the anthers abortive processes in pistillate flowers.

Hypotheses for the Colonization of the Caribbean Basin by Two Genera of the Rubiaceae: Erithalis and Ernodea

Abstract Ernodea Swartz (Tribe Spermacoceae) and Erithalis P. Browne (Tribe Chiococceae) are two genera of Rubiaceae that are endemic to the Caribbean, composed of four and nine species, respectively. Molecular phylogenies were analyzed in a biogeographic context using Brooks Parsimony Analysis (BPA) and Fitch Parsimony methods. A geographic association of Cuba and Dominican Republic was supported by area cladograms generated by BPA for Erithalis and by the combined data matrix. Additionally, the two parts of Hispaniola (Dominican Republic and Haiti) appear in two different places on the cladogram suggesting that Hispaniola represents a composite of geological areas. Fitch analyses support a Greater Antillean origin for Erithalis, however, it was ambiguously resolved for Ernodea. Overall, biogeographic analyses explain the present-day distribution of Ernodea as a product of dispersal, whereas a combination of vicariance and dispersal events appears to be involved in Erithalis biogeographical history. In general, the study implies that trans-oceanic seed dispersal plays an important role in the distribution of these genera, in addition to Tertiary vicariance events for Erithalis.

The Genus Ernodea (Rubiaceae) in the Caribbean Basin. II. Morphological Analyses and Systematics

The genus Ernodea, consisting of erect or prostrate shrubs, has been thought to consist of nine species, most of which are endemic to the Bahamian Archipelago. The classification of the genus is difficult because the original species descriptions are incomplete and include characters of great plasticity. Addition- ally, reproductive and genetic studies failed to provide evidence to support recognition of distinct species. We measured 30 floral and vegetative characters from samples representing all taxa and distributed across the entire range of the genus to delimit relationships at the specific level and to delineate morphological gaps within the genus. Phenetic analyses involving Principal Component Analysis and Canonical Discriminant Analysis provided consistent separation of two main clusters; each cluster separated into two subclusters. Vegetative characters provided better discrimination than floral characters. In contrast to the current literature, this study recognizes four morphological species: E. cokeri, E. littoralis, E. taylori and E. millspaughii. The morphological and ecological diversity of Ernodea in these islands suggest that there has been rapid divergence associated with adaptive radiation. A key to the species with descriptions and nomenclature is provided.