Eric J. Fuchs

Factors affecting phenological patterns of bombacaceous trees in seasonal forests in Costa Rica and Mexico

We compared phenological patterns of tree species of the family Bombacaceae in three seasonal forests in Mexico and Costa Rica whose dry seasons vary in duration and intensity. The objectives were to (1) determine intraspecific variation in phenology between sites in different geographic locations with different precipitation regimes, (2) compare interspecific phenological patterns within sites during one year, and (3) document seasonal pollinator use of floral resources at one site in relation to the flowering phenology of these species. To determine the sequence of phenological events in trees of the family Bombacaceae across three study sites, phenology of marked individuals was recorded every 2 wk from September 2000 through August 2001 for six species. To estimate the importance of bombacaceous species in the diet of nectarivorous bats, pollen samples were collected from the bodies or feces of bats once every 2 wk during flowering. Our study suggests that phenological patterns of the Bombacaceae family in Neotropical dry forests are mainly constrained by phylogenetic membership and adaptive selective pressures associated with competition for pollinators. Abiotic factors related to precipitation and soil water content appear to be regulating leaf flushing and abscission, but the principal causes of flowering are related to ultimate factors associated with competition for pollinators. This study is the first that evaluates the phenological pattern of species and genera of the same family at different latitudes in a similar life zone.

Pollen load size, reproductive success, and progeny kinship of naturally pollinated flowers of the tropical dry forest tree Pachira quinata (Bombacaceae)

Several studies have demonstrated, using controlled pollinations, that the number and identity of pollen grains deposited onto a flowers stigma affect the reproductive success of plants. However, few studies have shown this relationship under conditions of natural pollination. Using the tropical dry forest tree Pachira quinata, we evaluated the relationship between the number of microgametophytes per pistil and the number of sires with respect to the production of fruits and seeds in a natural population of Pachira quinata. Our study demonstrates that fruit and seed production are directly related to the number of microgametophytes per pistil in natural populations of P. quinata. Only 6% of the marked flowers developed into mature fruits and 10% of the marked flowers initiated fruits but later aborted them. A mean of 23 pollen grains were required to produce a seed. Flowers with >400 pollen grains on the stigma always developed into mature fruits, whereas flowers that received <200 grains never matured fruits. Half of the pollen grains transferred to a flower stigma germinated and developed pollen tubes to the base of the style. The number of pollen grains on a stigma explained 34% of the variation in seed number per fruit, and the number of seeds produced per fruit is positively correlated with the size of the seeds. The population of P. quinata studied is predominantly outcrossing, and seeds within fruits are sired by one or a few donors. The total seed crop within trees was sired by three to five donors. Our study examined the implications of the variation in size of microgametophyte loads per pistil with respect to the breeding system and the paternity of progeny under natural conditions. The competitive ability of pollen and pollen tube attrition are important factors regulating fruit production in P. quinata.

Spatial genetic structure within size classes of the endangered tropical tree Guaiacum sanctum (Zygophyllaceae)

UNLABELLED PREMISE OF THE STUDY Patterns of spatial genetic structure (SGS) were analyzed within a population of the endangered tropical tree Guaiacum sanctum located in northwestern Costa Rica. Documentation of these patterns provides insights into the gene dispersal mechanisms that play a central role in the maintenance and structure of genetic diversity within plant populations. • METHODS Allozyme analyses were used to examine SGS in Palo Verde National Park, Costa Rica. The SGS was compared among three plots and different age classes. • KEY RESULTS High levels of genetic diversity were found overall with a pooled genetic diversity of H(e) = 0.302 (±0.02). Selfing was proposed as the proximate cause for significant levels of heterozygote deficiency observed across size classes and plots. An unexpected lack of SGS (r(j) < 0.02) was observed for all size classes, suggesting the mixing of seeds from several adults. A parent-pair parentage analysis indicated that at least 48% of the smaller individuals within a plot were produced by parents located at distances of at least 150 m. • CONCLUSIONS Populations of G. sanctum are established and maintained by bird-mediated, moderate- to long-distance seed dispersal, which results in a mixture of seeds from unrelated maternal individuals, effectively eliminating SGS. Proximity between individuals is, therefore, a poor predictor of family structure in this species. Long-distance seed dispersal, coupled with estimates of high genetic diversity, suggests that this endangered species has the potential for natural regeneration and restoration given the availability of suitable habitats.

Genetic diversity in Oryza glumaepatula wild rice populations in Costa Rica and possible gene flow from O. sativa

Wild crop relatives are an important source of genetic diversity for crop improvement. Diversity estimates are generally lacking for many wild crop relatives. The objective of the present study was to analyze how genetic diversity is distributed within and among populations of the wild rice species Oryza glumaepatula in Costa Rica. We also evaluated the likelihood of gene flow between wild and commercial rice species because the latter is commonly sympatric with wild rice populations. Introgression may change wild species by incorporating alleles from domesticated species, increasing the risk of losing original variation. Specimens from all known O. glumaepatula populations in Costa Rica were analyzed with 444 AFLP markers to characterize genetic diversity and structure. We also compared genetic diversity estimates between O. glumaepatula specimens and O. sativa commercial rice. Our results showed that O. glumaepatula populations in Costa Rica have moderately high levels of genetic diversity, comparable to those found in South American populations. Despite the restricted distribution of this species in Costa Rica, populations are fairly large, reducing the effects of drift on genetic diversity. We found a dismissible but significant structure (θ = 0.02 ± 0.001) among populations. A Bayesian structure analysis suggested that some individuals share a significant proportion of their genomes with O. sativa. These results suggest that gene flow from cultivated O. sativa populations may have occurred in the recent past. These results expose an important biohazard: recurrent hybridization may reduce the genetic diversity of this wild rice species. Introgression may transfer commercial traits into O. glumaepatula, which in turn could alter genetic diversity and increase the likelihood of local extinction. These results have important implications for in situ conservation strategies of the only wild populations of O. glumaepatula in Costa Rica.

Neither insects nor wind: ambophily in dioecious Chamaedorea palms (Arecaceae).

Abstract Pollination of Neotropical dioecious trees is commonly related to generalist insects. Similar data for non‐tree species with separated genders are inconclusive. Recent studies on pollination of dioecious Chamaedorea palms (Arecaceae) suggest that species are either insect‐ or wind‐pollinated. However, the wide variety of inflorescence and floral attributes within the genus suggests mixed pollination mode involving entomophily and anemophily. To evaluate this hypothesis, we studied the pollination of Chamaedorea costaricana,C. macrospadix,C. pinnatifrons and C. tepejilote in two montane forests in Costa Rica. A complementary morphological analysis of floral traits was carried out to distinguish species groups within the genus according to their most probable pollination mechanism. We conducted pollinator exclusion experiments, field observations on visitors to pistillate and staminate inflorescences, and trapped airborne pollen. A cluster analysis using 18 floral traits selected for their association with wind and insect pollination syndromes was carried out using 52 Chamaedorea species. Exclusion experiments showed that both wind and insects, mostly thrips (Thysanoptera), pollinated the studied species. Thrips used staminate inflorescences as brood sites and pollinated pistillate flowers by deception. Insects caught on pistillate inflorescences transported pollen, while traps proved that pollen is wind‐borne. Our empirical findings clearly suggest that pollination of dioecious Chamaedorea palms is likely to involve both insects and wind. A cluster analysis showed that the majority of studied species have a combination of floral traits that allow for both pollination modes. Our pollination experiments and morphological analysis both suggest that while some species may be completely entomophilous or anemophilous, ambophily might be a common condition within Chamaedorea. Our results propose a higher diversity of pollination mechanisms of Neotropical dioecious species than previously suggested.

Complex phylogeographic patterns indicate Central American origin of two widespread Mesoamerican Quercus (Fagaceae) species

The northern Neotropical region is characterized by a heterogeneous geological and climatic history. Recent studies have shown contrasting patterns regarding the role of geographic elements as barriers that could have determined phylogeographic structure in various species. Recently, the phylogeography and biogeography of Quercus species have been studied intensively, and the patterns observed so far suggest contrasting evolutionary histories for Neotropical species in comparison with their Holarctic relatives. The goal of this study was to describe the phylogeographic structure of two Neotropical oak species (Quercus insignis and Quercus sapotifolia) in the context of the geological and palaeoclimatic history of the northern Neotropics. Populations through the distribution range of both species were collected and characterized using nine chloroplast DNA microsatellite loci. Both oak species showed high levels of genetic diversity and strong phylogeographic structure. The distribution of genetic variation in Q. insignis suggested an influence of two major barriers, the Isthmus of Tehuantepec and the Nicaraguan Depression, while Q. sapotifolia exhibited a genetic structure defined by the heterogeneity of the Chortis highlands. The haplotype networks of both species indicated complex histories, suggesting that colonization from the Sierra Madre de Chiapas to central Mexico and from the north of the Nicaraguan Depression to the Costa Rican mountains may have occurred during different stages, and apparently more than one time. In conclusion, the phylogeographic structure of Neotropical oak species seems to be defined by a combination of geological and climatic events.

The roles of history and habitat area in the distribution and composition of avian species assemblages in the highlands of Costa Rica

Bird species assemblages in isolated Neotropical highland mountains have been moulded by the drastic climatic changes that occurred in late Pleistocene. Palynological evidence indicates that after the Pleistocene the highlands of Costa Rica and western Panama became isolated as climate turned gradually more tropical and highland vegetation retreated to the upper elevations of high mountains, forming highland islands. We surveyed birds at 10 representative sites throughout the Costa Rican highlands in order to determine the species composition of highland endemic assemblages. The area of available highland habitat explains 77% of the variance in species richness of the 36 highland endemics across highland islands, and the composition of these species assemblages have a nested distribution, rather than being independent sets of species on each island. The observed nested pattern is more consistent with a differential extinction model of species assemblages, and less likely to be explained by differential migration. We conclude that the reduction of highland vegetation and the avifauna associated with it, and its subsequent confinement to the summit of high mountains, is a possible explanation for the current distribution of highland endemic species in Costa Rican highland islands.

Effect of fragmentation on the Costa Rican dry forest avifauna

Deforestation and changes in land use have reduced the tropical dry forest to isolated forest patches in northwestern Costa Rica. We examined the effect of patch area and length of the dry season on nestedness of the entire avian community, forest fragment assemblages, and species occupancy across fragments for the entire native avifauna, and for a subset of forest dependent species. Species richness was independent of both fragment area and distance between fragments. Similarity in bird community composition between patches was related to habitat structure; fragments with similar forest structure have more similar avian assemblages. Size of forest patches influenced nestedness of the bird community and species occupancy, but not nestedness of assemblages across patches in northwestern Costa Rican avifauna. Forest dependent species (species that require large tracts of mature forest) and assemblages of these species were nested within patches ordered by a gradient of seasonality, and only occupancy of species was nested by area of patches. Thus, forest patches with a shorter dry season include more forest dependent species.

Reproductive biology of Macleania rupestris (Ericaceae), a pollen-limited Neotropical cloud-forest species in Costa Rica.

The reproductive success of hummingbird-pollinated plants often depends on complex interactions between environmental conditions and pollinator biology (Navarro 1999, Stiles 1985, Wolf et al . 1976). The effect of environment on reproductive success of hummingbird-pollinated plants is particularly pronounced at high altitudes, where large daily fluctuations in temperature, relative humidity and solar radiation limit the effective time for photosynthesis (Cavieres et al . 2000) and affect foraging activity (Navarro 1999) and abundance of pollinators (Rahbek 1997). At high altitudes in the tropical cloud forests of Costa Rica these factors may have serious impacts on fruit production.

Lack of early inbreeding depression and distribution of selfing rates in the neotropical emergent tree Ceiba pentandra: Assessment from several reproductive events

PREMISE OF THE STUDY Selfing and mixed mating systems are prevalent in many flowering plants. Purging of genetic load can occur in these species, reducing negative effects of selfing. Long-term studies of the temporal and spatial variation of selfing rates and inbreeding depression at the individual level are necessary to understand the forces that maintain selfing as a mating strategy in these species. METHODOLOGY We used microsatellites to estimate selfing rates in seeds and seedlings over 6 years in a population of Ceiba pentandra in southwestern Costa Rica. We studied the correlation of selfing with early seedling vigor variables to test for inbreeding depression. KEY RESULTS Selfing rates varied widely among maternal trees. However, we found high consistency of selfing rates for individuals among years. Selfing rate did not influence early fitness traits, suggesting a lack of inbreeding depression at this stage. Maternal effects were a predominant source of variation for early vigor variables. CONCLUSIONS Variability in selfing rates among trees may be partly explained by genetic variation in a late-acting self-incompatibility system or low, early-acting genetic load in some individuals. This population did not show evidence of early inbreeding depression in traits related to seed vigor probably from complete or partial purging as a result of repeated selfing of a fraction of the population or from strong maternal effects. Expression of genetic load at later developmental stages or in more stressful natural conditions may explain differences in inbreeding levels between seeds and adults.