Anthropogenic land-use change decreases pollination and male and female fitness in terrestrial flowering plants.

BACKGROUND AND AIMS: The majority of the earth's land area is currently occupied by humans. Measuring how terrestrial plants reproduce in these pervasive environments is essential for understanding their long-term viability and their ability to adapt to changing environments. METHODS: We conducted hierarchical and phylogenetically-independent meta-analyses to assess the overall effects of anthropogenic land-use changes on pollination, and male and female fitness in terrestrial plants. KEY RESULTS: We found negative global effects of land use change (i.e., mainly habitat loss and fragmentation) on pollination and on female and male fitness of terrestrial flowering plants. Negative effects were stronger in plants with self-incompatibility (SI) systems and pollinated by invertebrates, regardless of life form and sexual expression. Pollination and female fitness of pollination generalist and specialist plants were similarly negatively affected by land-use change, whereas male fitness of specialist plants showed no effects. CONCLUSIONS: Our findings indicate that angiosperm populations remaining in fragmented habitats negatively affect pollination, and female and male fitness, which will likely decrease the recruitment, survival, and long-term viability of plant populations remaining in fragmented landscapes. We underline the main current gaps of knowledge for future research agendas and call out not only for a decrease in the current rates of land-use changes across the world but also to embark on active restoration efforts to increase the area and connectivity of remaining natural habitats.

The International Oryza Map Alignment Project (IOMAP): the Americas-past achievements and future directions.

The wild relatives of rice hold unexplored genetic diversity that can be employed to feed an estimated population of 10 billion by 2050. The Oryza Map Alignment Project (OMAP) initiated in 2003 has provided comprehensive genomic resources for comparative, evolutionary, and functional characterization of the wild relatives of rice, facilitating the cloning of >600 rice genes, including those for grain width (GW5) and submergence tolerance (SUB1A). Following in the footsteps of the original project, the goal of 'IOMAP: the Americas' is to investigate the present and historic genetic diversity of wild Oryza species endemic to the Americas through the sequencing of herbaria and in situ specimens. The generation of a large diversity panel describing past and current genetic status and potential erosion of genetic variation in the populations will provide useful knowledge for the conservation of the biodiversity in these species. The wild relatives of rice in the Americas present a wide range of resistance traits useful for crop improvement and neodomestication approaches. In the race against time for a sustainable food future, the neodomestication of the first cereal species recently accomplished in O. alta opens the door to the potential neodomestication of the other wild Oryza species in Americas.

Gone with the wind: Negative genetic and progeny fitness consequences of habitat fragmentation in the wind pollinated dioecious tree Brosimum alicastrum.

PREMISE: Habitat fragmentation negatively affects population size and mating patterns that directly affect progeny fitness and genetic diversity; however, little is known about the effects of habitat fragmentation on dioecious, wind pollinated trees. We assessed the effects of habitat fragmentation on population sex ratios, genetic diversity, gene flow, mating patterns, and early progeny vigor in the tropical dioecious tree, Brosimum alicastrum. METHODS: We conducted our study in three continuous and three fragmented forest sites in a Mexican tropical dry forest. We used eight microsatellite loci to characterize the genetic diversity, gene flow via pollen distances, and mean relatedness of progeny. We compared early progeny vigor parameters of seedlings growing under greenhouse conditions. RESULTS: Sex ratios did not deviate from 1:1 between habitat conditions except for one population in a fragmented habitat, which was female biased. The genetic diversity of adult trees and their offspring was similar in both habitat conditions. Pollen gene flow distances were similar across habitat types; however, paternity correlations were greater in fragmented than in continuous habitats. Germination rates did not differ between habitat conditions; however, progeny from fragmented habitats produced fewer leaves and had a lower foliar area, total height, and total dry biomass than progeny from continuous habitats. CONCLUSIONS: Changes in mating patterns because of habitat fragmentation have negative effects on early progeny vigor. We conclude that negative habitat fragmentation effects on mating patterns and early progeny vigor may be a serious threat to the long-term persistence of tropical dioecious trees.

Isolation and characterization of microsatellites for the neotropical dioecious palm Chamaedorea tepejilote (Arecaceae) and cross-amplification in other Chamaedorea species.

Palms are important components of tropical and subtropical ecosystems and have even been considered keystone plant resources that can support a large array of pollinators and frugivores. Palms are also economically important. Chamaedorea tepejilote Liebm. is a widely distributed palm with important bioeconomic potential for food, traditional medicine and ornamental purposes. Eighteen microsatellite primers were developed for C. tepejilote. Polymorphism and genetic diversity were evaluated in 71 individuals from four populations in Costa Rica. Thirteen loci were polymorphic and the number of alleles in the pooled sample ranged between 5 and 20, the average number of alleles was 10.61. Average observed heterozygosity was Ho = 0.607 ± 0.04 (SD) and the average expected heterozygosity was He = 0.600 ± 0.03. The exclusion probability of the combined 13 loci, was PE = 0.998. We tested transferability of the markers in the congeneric C. costaricana, C. pinnantifrons and C. macrospadix. Dioecious species are common in tropical forests; however, few studies have analyzed gene flow patterns in these species. The markers developed for C. tepejilote are an important tool to quantify gene flow patterns and the distribution of genetic diversity within populations. This information will be useful for the development of conservation and management practices of this dioecious tropical palm species.

Habitat fragmentation reduces plant progeny quality: a global synthesis.

Most of the world's land surface is currently under human use and natural habitats remain as fragmented samples of the original landscapes. Measuring the quality of plant progeny sired in these pervasive environments represents a fundamental endeavour for predicting the evolutionary potential of plant populations remaining in fragmented habitats and thus their ability to adapt to changing environments. By means of hierarchical and phylogenetically independent meta-analyses we reviewed habitat fragmentation effects on the genetic and biological characteristics of progenies across 179 plant species. Progeny sired in fragmented habitats showed overall genetic erosion in contrast with progeny sired in continuous habitats, with the exception of plants pollinated by vertebrates. Similarly, plant progeny in fragmented habitats showed reduced germination, survival and growth. Habitat fragmentation had stronger negative effects on the progeny vigour of outcrossing- than mixed-mating plant species, except for vertebrate-pollinated species. Finally, we observed that increased inbreeding coefficients due to fragmentation correlated negatively with progeny vigour. Our findings reveal a gloomy future for angiosperms remaining in fragmented habitats as fewer sired progeny of lower quality may decrease recruitment of plant populations, thereby increasing their probability of extinction.

Isolation and characterization of microsatellites loci in Spondias purpurea (Anacardiaceae) and cross amplification in congeneric species.

Microsatellite markers provide high polymorphism levels, useful to study genetic diversity and gene flow patterns in plant populations. Here we develop and characterize microsatellite primers to evaluate patterns of genetic structure and diversity, and gene flow levels in the dioecious tropical tree Spondias purpurea (Anacardiaceae). Twenty-four microsatellite primers were developed for Spondias purpurea. Polymorphism was evaluated in 139 individuals from three localities in Mexico. Ten loci were polymorphic. The number of alleles ranged between two and 21, the average number of alleles was 5.88. Cross-amplification trials on S. mombin, S. radlkoferi, Astronium graveolens and Amphipterygium adstringens achieved successful amplification for only six microsatellites in S. mombin and S. radlkoferi. Microsatellites developed for S. purpurea will be a useful tool to estimate genetic diversity within and among populations, as well as to assess the consequences of habitat fragmentation on gene flow patterns of this species.

Contrasting Patterns of Population History and Seed-mediated Gene Flow in Two Endemic Costa Rican Oak Species.

Lower Central America is an important area to study recent population history and diversification of Neotropical species due to its complex and dynamic geology and climate. Phylogeographic studies in this region are few in comparison with other regions and even less for tree species. The aim of the present study was to characterize the phylogeographic structure in 2 partially co-distributed endemic oak species (Quercus costaricensis and Q. bumelioides) of the Costa Rican mountains using chloroplast short sequence repeats (cpSSRs), and to test for the effect of geological and palaeoclimatic processes on their population history. Genetic diversity and structure, haplotype networks, patterns of seed-mediated gene flow and historical demography were estimated for both species. Results suggested contrasting patterns. Quercus costaricensis exhibited high values of genetic diversity, a marked phylogeographic structure, a north-to-south genetic diversity gradient and evidence of a demographic expansion during the Quaternary. Quercus bumelioides did not show significant genetic structure and the haplotype network and historical demography estimates suggested a recent population expansion probably during the Pleistocene-Holocene transition. The phylogeographic structure of Q. costaricensis seems to be related to Pleistocene altitudinal migration due to its higher altitudinal distribution. Meanwhile, historical seed-mediated gene flow through the lower altitudinal distribution of Q. bumelioides may have promoted the homogenization of genetic variation. Population expansion and stable availability of suitable climatic areas in both species probably indicate that palaeoclimatic changes promoted downwards altitudinal migration and formation of continuous forests allowing oak species to expand their distribution into the Panamanian mountains during glacial stages.

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.

Elevational and seasonal patterns of plant pollinator networks in two highland tropical ecosystems in Costa Rica.

Many plant species in high montane ecosystems rely on animal pollination for sexual reproduction, however, our understanding of plant-pollinator interactions in tropical montane habitats is still limited. We compared species diversity and composition of blooming plants and floral visitors, and the structure of plant-floral visitor networks between the Montane Forest and Paramo ecosystems in Costa Rica. We also studied the influence of seasonality on species composition and interaction structure. Given the severe climatic conditions experienced by organisms in habitats above treeline, we expected lower plant and insect richness, as well as less specialized and smaller pollination networks in the Paramo than in Montane Forest where climatic conditions are milder and understory plants are better protected. Accordingly, we found that blooming plants and floral visitor species richness was higher in the Montane Forest than in the Paramo, and in both ecosystems species richness of blooming plants and floral visitors was higher in the rainy season than in the dry season. Interaction networks in the Paramo were smaller and more nested, with lower levels of specialization and modularity than those in the Montane Forest, but there were no seasonal differences within either ecosystem. Beta diversity analyses indicate that differences between ecosystems are likely explained by species turnover, whereas within the Montane Forest differences between seasons are more likely explained by the rewiring of interactions. Results indicate that the decrease in species diversity with elevation affects network structure, increasing nestedness and reducing specialization and modularity.

Spatial distribution of Guaiacum sanctum (Zygophyllaceae) seedlings and saplings relative to canopy cover in Palo Verde National Park, Costa Rica.

The spatial distribution of individuals is a fundamental property of most species and constitutes essential information for the development of restoration and conservation strategies, especially for endangered plant species. In this paper we describe the spatial distribution of different size classes of the endangered tropical tree Guaiacum sanctum and the effect of canopy cover on spatial aggregation. Adult G. sanctum were located and mapped in a 50 ha plot in Palo Verde National Park, Costa Rica. Seedlings, saplings and juveniles were mapped to the nearest centimetre and permanently marked in three 50 x 50 m subplots. Within each subplot spatial aggregation was assessed using Ripley's K statistic and canopy opening readings were performed every 5 m using a densitometer. Kriging spatial interpolation and Monte Carlo simulations were used to determine if average canopy cover differed among size classes. Individuals of G. sanctum were spatially aggregated at all size classes with seedlings being the most frequent size class in all subplots. Seedlings were found predominantly in areas with significantly higher canopy cover. In contrast, juveniles were more likely found in areas with higher light availability. The high number of seedlings, saplings, and juveniles relative to adults suggests that populations of G. sanctum in PVNP are expanding. Light availability and canopy structure are important factors shaping the spatial distribution of this species. The contemporary demographic structure of G. sanctum is dependent on forest gap dynamics and changes in human disturbance during the past 25 years.

Genetic diversity and phylogeographic patterns of the dioecious palm Chamaedorea tepejilote (Arecaceae) in Costa Rica: the role of mountain ranges and possible refugia.

Gene flow connects populations and is necessary to sustain effective population sizes, and genetic diversity. In the Lower Central American (LCA) region, the complex topographic and climatic history have produced a wide variety of habitats resulting in high biodiversity. Phylogeographic studies of plants from this area are scarce, and to date none have been conducted on palms. We used SSR and chloroplast DNA (cpDNA) markers to study the genetic diversity and structure of populations of the understory palm Chamaedorea tepejilote in Costa Rica. We found that populations of C. tepejilote have moderate to high nuclear simple sequence repeat (SSR) genetic diversity, likely due to large population sizes and its outcrossing mating system. Habitat loss and fragmentation may have contributed to increased genetic structure within slopes. High-elevation mountain ranges appeared to be a significant barrier for gene flow among populations in the Caribbean and Pacific slopes; however, ranges are permeable through low-elevation passes. In contrast, most populations had a single distinct cpDNA haplotype, supporting the hypothesis of several isolated populations that experienced decline that likely resulted in eroded cytoplasmic genetic diversity within populations. The haplotype network and Bayesian analysis linked populations in the Caribbean and the southern Pacific coast, suggesting that gene flow between Pacific and Caribbean populations may have occurred through the southern extreme of the Talamanca Mountain range in Panama, a colonization pathway not previously suggested for LCA plants. This is one of the first phylogeographic studies conducted on tropical palms in the LCA region and the first in the genus Chamaedorea, which sheds light on possible gene flow and dispersal patterns of C. tepejilote in Costa Rica. Our results also highlight the importance of mountain ranges on shaping gene flow patterns of Neotropical plants.

Blooming plant species diversity patterns in two adjacent Costa Rican highland ecosystems.

The Costa Rican Paramo is a unique ecosystem with high levels of endemism that is geographically isolated from the Andean Paramos. Paramo ecosystems occur above Montane Forests, below the permanent snow level, and their vegetation differs notably from that of adjacent Montane Forests. We compared the composition and beta diversity of blooming plant species using phenological data from functional plant groups (i.e., insect-visited, bird-visited and insect + bird-visited plants) between a Paramo and a Montane Forest site in Costa Rica and analyzed seasonal changes in blooming plant diversity between the rainy and dry seasons. Species richness was higher in the Montane Forest for all plant categories, except for insect-visited plants, which was higher in the Paramo. Beta diversity and blooming plant composition differed between both ecosystems and seasons. Differences in species richness and beta diversity between Paramo and the adjacent Montane Forest are likely the result of dispersal events that occurred during the last glacial period and subsequent isolation, as climate turned to tropical conditions after the Pleistocene, and to stressful abiotic conditions in the Paramo ecosystem that limit species establishment. Differences in blooming plant composition between both ecosystems and seasons are likely attributed to differential effects of climatic cues triggering the flowering events in each ecosystem, but phylogenetic conservatism cannot be discarded. Analyses of species composition and richness based on flowering phenology data are useful to evaluate potential floral resources for floral visitors (insects and birds) and how these resources change spatially and temporarily in endangered ecosystems such as the Paramo.

Genetic diversity, asexual reproduction and conservation of the edible fruit tree Spondias purpurea L. (Anacardiaceae) in the Costa Rican tropical dry forest.

The term circa situm has been used to describe different conservation strategies within agricultural landscapes. Circa situm conserves planted or remnant species in farmlands, where natural vegetation has been modified through anthropogenic intervention. It has been proposed that trees planted or retained under circa situm conditions may contribute to maintaining genetic diversity, however information on the role of this strategy in preserving genetic diversity is scarce. The aim of this study was to determine the levels of genetic diversity and structure, and mating patterns in planted and unmanaged stands of the tropical fruit tree Spondias purpurea L. in north western Costa Rica. In three localities, we used seven polymorphic microsatellite loci and genotyped 201 adults and 648 seeds from planted and wild stands. We found no differences in genetic diversity among planted and wild stands. Genetic structure analysis revealed that gene flow occurs among planted and wild stands within localities. Clones were present and their diversity and evenness were both high and similar between planted and wild stands. The number of pollen donors per progeny array was low (Nep = 1.01) which resulted in high levels of correlated paternity (rp = 0.9). Asexual seeds were found in 4.6% of the progeny arrays, which had multilocus genotypes that were identical to the maternal trees. Our results show that although planted stands under circa situm conditions can maintain similar levels of genetic diversity than wild stands, the low number of sires and asexual seed formation could threaten the long term persistence of populations.

Genetic structure in neotropical birds with different tolerance to urbanization.

Gene flow in birds can be affected by urbanization depending on natural history traits and adaptability to habitat change. Contrasting results can be expected when comparing species with opposite resilience to urbanization. In this study, we assessed genetic diversity and structure for two bird species, the urban avoider white-eared ground-sparrow, Melozone leucotis, and the urban dweller house wren Troglodytes aedon. We used seven microsatellite loci and sampled five locations with differing levels of urbanization in Costa Rica. We found considerably higher genetic structure in white-eared ground-sparrows than in house wrens. Circuit theory analyses proved a higher isolation from urban resistance for the white-eared ground-sparrow than for house wrens. These results support that urbanization is a significant barrier for gene flow in urban avoiders, in contrast to urban dweller species that showed little to no impact. Differences could be attributed to a higher plasticity in habitat and nesting site preferences in the house wren, and significant dispersal limitation for the white-eared ground-sparrow. These results emphasize the need for conservation strategies towards white-eared ground-sparrows and other urban avoider species whose habitat and connectivity have been reduced by the recent urban expansion.

Genetic diversity in the endangered tropical tree, Guaiacum sanctum (Zygophyllaceae).

Fragmentation of tropical forests has changed continuous tropical landscapes into a network of poorly connected fragments, reducing population sizes and potentially increasing genetic isolation. This study quantifies genetic diversity within and among the 7 extant populations of the endangered tropical tree Guaiacum sanctum in Costa Rica. We describe how genetic diversity differs between populations representing continuous and fragmented habitats. Allozyme analyses were conducted on adult samples from populations representing 2 geographic regions in northwestern Costa Rica. We found high levels of genetic diversity within the species (H(es) = 0.329) and significant but relatively small differences in allele frequencies among populations (G(ST) = 0.101) and between regions (G(ST) = 0.053). We found no differences in genetic diversity between fragmented and continuous populations. Evidence for significant isolation-by-distance (IBD) was seen only when all populations were analyzed. If populations within the 2 regions were analyzed separately, IBD ceased to be significant. Our results suggest that the patterns of genetic diversity observed for G. sanctum may be caused by the ancient separation of populations into 2 disjunct geographic regions with extensive historical rates of gene flow among populations within each region. Recent forest fragmentation has not yet affected patterns of genetic diversity in this species.

Janzen-Connell effects shape gene flow patterns and realized fitness in the tropical dioecious tree Spondias purpurea (ANACARDIACEAE).

Pollination and seed dispersal patterns determine gene flow within plant populations. In tropical forests, a high proportion of trees are dioecious, insect pollinated and dispersed by vertebrates. Dispersal vectors and density dependent factors may modulate realized gene flow and influence the magnitude of Fine Scale Genetic Structure (FSGS), affecting individual fitness. Spondias purpurea is a vertebrate-dispersed, insect-pollinated dioecious tropical tree. We assessed the influence of sex ratio, effective and realized gene flow on genetic diversity, FSGS and individual fitness within a 30 ha plot in the tropical dry forest reserve of Chamela-Cuixmala, Mexico. All individuals within the plot were tagged, geo-referenced and sampled for genetic analysis. We measured dbh and monitored sex expression during two reproductive seasons for all individuals. We collected seeds directly from maternal trees for effective pollen dispersal analysis, and analyzed established seedlings to assess realized pollen and seed dispersal. Nine microsatellite loci were used to describe genetic diversity parameters, FSGS and gene flow patterns among different size classes. A total of 354 individuals were located and classified into three size classes based on their dbh (<10, 10-20, and >20 cm). Population sex ratios were male biased and diametric size distributions differed among sexes, these differences may be the result of precocious male reproduction at early stages. Autocorrelation analyses indicate low FSGS (Fj <0.07) across all size classes. Long realized pollen and seed dispersal and differences among effective and realized gene flow were detected. In our study site low FSGS is associated with high gene flow levels. Effective and realized gene flow indicate a population recruitment curve indicating Janzen-Connell effects and suggesting fitness advantages for long-distance pollen and seed dispersal events.

Spatial Distribution of Whitefly Species (Hemiptera: Aleyrodidae) and Identification of Secondary Bacterial Endosymbionts in Tomato Fields in Costa Rica.

In Costa Rica, tomato (Solanum lycopersicum Linnaeus) Linnaeus (Solanales: Solanaceae) is one of the crops most severely affected by the whiteflies (Hemiptera: Aleyrodidae) Trialeurodes vaporariorum (Westwood) and the Bemisia tabaci (Gennadius) species complex. The objective of this study was to monitor the spatial distribution and diversity of these species and to detect the presence of secondary bacterial endosymbionts in individuals collected in areas of intensive tomato production. In total, 628 whitefly individuals were identified to the species level using restriction analysis (PCR-RFLP) of a fragment of the mitochondrial cytochrome C oxidase I gene (mtCOI). Trialeurodes vaporariorum was the predominant species, followed by B. tabaci Mediterranean (MED). Bemisia tabaci New World (NW) and B. tabaci Middle East-Asia Minor 1 (MEAM1) were present in lower numbers. The mtCOI fragment was sequenced for 89 individuals and a single haplotype was found for each whitefly species. Using molecular markers, the 628 individuals were analyzed for the presence of four endosymbionts. Arsenophonus Gherna et al. (Enterobacterales: Morganellaceae) was most frequently associated with T. vaporariorum, whereas Wolbachia Hertig (Rickettsiales: Anaplasmataceae) and Rickettsia da Rocha-Lima (Rickettsiales: Rickettsiaceae) were associated with B. tabaci MED. This study confirmed that B. tabaci NW has not been completely displaced by the invasive species B. tabaci MED and B. tabaci MEAM1 present in the country. An association was found between whitefly species present in tomato and certain secondary endosymbionts, elevation was the most likely environmental factor to affect their frequency.

Effect of barriers and distance on song, genetic, and morphological divergence in the highland endemic Timberline Wren (Thryorchilus browni, Troglodytidae).

Populations may become isolated by distance, geographic barriers or both. Isolated populations often diverge in behavioral, morphological and genetic traits as a result of reduced inter-population gene flow. Highland species commonly present naturally fragmented distributions that confine populations to the highest mountain peaks, isolated by mountain passes and distance. The endemic Timberline Wren (Thryorchilus browni) inhabits the highlands of the Talamanca mountain range, including western Panama, and the highest peak in the Central Volcanic mountain range of Costa Rica. Using microsatellites and song recordings we studied the effect of a geographic barrier and distance on song, genetic and morphological divergence among four populations in Costa Rica. A lowland mountain pass resulted in the largest genetic, vocal, and morphological (bill length) differences among populations, likely due to reduce the gene flow. Cultural drift and assortative mating by females selecting songs from their own population likely accentuates the effect of isolation and limited gene flow between populations. This pattern of population divergence has been found in other Neotropical highland birds, but over larger geographical scales. We conclude that mountain passes and distance both reduce gene flow between populations in recently-isolated highland species with restricted distributions.

Molecular characterization and genetic diversity of Jatropha curcas L. in Costa Rica.

We estimated the genetic diversity of 50 Jatropha curcas samples from the Costa Rican germplasm bank using 18 EST-SSR, one G-SSR and nrDNA-ITS markers. We also evaluated the phylogenetic relationships among samples using nuclear ribosomal ITS markers. Non-toxicity was evaluated using G-SSRs and SCARs markers. A Neighbor-Joining (NJ) tree and a Maximum Likelihood (ML) tree were constructed using SSR markers and ITS sequences, respectively. Heterozygosity was moderate (He = 0.346), but considerable compared to worldwide values for J. curcas. The PIC (PIC = 0.274) and inbreeding coefficient (f =  - 0.102) were both low. Clustering was not related to the geographical origin of accessions. International accessions clustered independently of collection sites, suggesting a lack of genetic structure, probably due to the wide distribution of this crop and ample gene flow. Molecular markers identified only one non-toxic accession (JCCR-24) from Mexico. This work is part of a countrywide effort to characterize the genetic diversity of the Jatropha curcas germplasm bank in Costa Rica.

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.