Ecogeographical Differentiation in Nectandra (Lauraceae), and its Historical Implications

Following a taxonomic revision of Nectandra, a genus of about 114 species of neotropical trees, character gradients are compared against geographical distribution, habitat preferences, and reproductive phenology of individual species, with the aim of reconstructing the spatial and temporal diversification of the genus. It is shown that Nectandra, together with Ocotea, Persea, and other genera of the Lauraceae, originated from a northern hemisphere matrix that immigrated into South America, perhaps as late as after the closure of the Central American land bridge in the Pliocene. The dramatic diversification of the genus within South America was facilitated by its ornithochorous dispersal system, implying ample processes of allopatric speciation. At present, speciation seems to take place preferably by processes of ecotypic (mostly edaphic) specialization, by which widely distributed, ecologically polymorphic species give rise to swarms of ecologically narrowly specialized satellite species.     

Mating system dynamics of Ocotea tenera (Lauraceae), a gynodioecious tropical tree

Progeny arrays of Ocotea tenera (Lauraceae), a gynodioecious tree endemic to Costa Rica, were electrophoretically surveyed for allozyme variation to estimate the outcrossing rate in the overall population and to test for differences in outcrossing rates between hermaphroditic and female trees. Multilocus outcrossing rate estimates across 3 yr indicated O. tenera predominantly outcrosses. However, significant heterogeneity in single-locus outcrossing rates was found among loci. Two loci (Fe1, Fe2) gave high outcrossing estimates, and a third locus (Gdh) gave much lower outcrossing estimates. Heterogeneity in Gdh pollen allele frequencies, consanguineous matings, and selection against homozygous zygote genotypes at the Fe1 and Fe2 loci are factors contributing to the discrepancy in outcrossing rate estimates among loci. There were no differences in the mating systems of hermaphroditic and female trees, which suggests that factors beyond prevention of self-fertilization may have also promoted the evolution of gynodioecy in O. tenera.     

Population genetic structure of the tropical tree species Aegiphila sellowiana (Lamiaceae)

The Tibagi River, located in southern Brazil, is associated with a significant degree of environmental heterogeneity, along its 550 km extension. There is concern about the integrity of this river's ecosystem, as human interference has been increasing. Aegiphila sellowiana (Lamiaceae) is an important pioneer tree species, commonly found near rivers; the fruit is consumed by avifauna. We studied this species along three ecological gradients, comprising the upper, middle, and lower regions of the Tibagi River basin. The genetic structure of nine subpopulations of A. sellowiana distributed along these gradients was investigated using RAPDs. Moderate levels of gene diversity (ranging from 0.091 to 0.132) were identified, inferred by a traditional approach and a Bayesian model-based method. The F-statistic, G(ST) parameters and molecular variance analysis showed high genetic differentiation among the three regions (39.5 to 50.26%). Analysis of molecular variance revealed high levels of genetic variation between populations (50.26%), while lower values of genetic variation (ranging from 9.56 to 16.35%) were seen between subpopulations within the upper, middle, and lower regions of the Tibagi River basin. The validity of these results was confirmed by principal coordinate analysis. Linear regression analysis showed significant correlations (r = 0.621, P = 0.0001) between the genetic and geographical distances. The differences observed in genetic variation between regions are probably due to habitat fragmentation; for conservation purposes, we recommend that at least one subpopulation from each region of the Tibagi River should be maintained.     

Population structure and genetic diversity in four tropical tree species in Costa Rica

Despite intensified interest in conservation of tropical forests, knowledge of the population genetics of tropical forest trees remains limited. We used random amplified polymorphic DNA (RAPD) data to evaluate trends in genetic diversity and differentiation for four tropical tree species, Alchornea latifolia, Dendropanax arboreus, Inga thibaudiana and Protium glabrum . These species occur at contrasting population densities along an elevational gradient and we use RAPD and ecological data to examine natural levels of genetic diversity of each species, trends in genetic variability with population density and structure, genetic differentiation along the elevation gradient, and the relationship between genetic diversity and such factors as seed dispersal and pollination syndrome. At the distances we examined (plot distances ranging from 0.8 to 8.6 km) there was very little genetic structuring at any distance along the gradient. All four species exhibited levels of variation expected for spatial distribution, mating system and pollinator syndrome; greater than 96% of the genetic variation occurred within plots for Inga thibaudiana, Protium glabrum and Dendropanax arboreus. Alchornea latifolia only occurred in a single plot. The results of this study contribute to a growing database of genetic diversity data that can be utilized to make predictions about the effect of disturbance and subsequent reductions in population size on genetic variation and structure in tropical tree species.     

Development of microsatellites in Machilus thunbergii (Lauraceae), a warm-temperate coastal tree species in Japan

? Premise of the study: Microsatellite markers were developed and characterized in a typically coastal, widespread, and dominant tree species of the evergreen broadleaf forests, Machilus thunbergii, for comparison of the genetic diversity and structure of inland populations surrounding the ancient Lake Biwa and coastal populations in Japan. ? Methods and Results: Eighteen polymorphic microsatellites of this species were isolated using an improved technique for isolating codominant compound microsatellite markers. These isolated loci provided compound simple sequence repeat (SSR) markers with polymorphisms of three to 19 alleles per locus, with an average of 10.9. The expected and observed within-population heterozygosities ranged from 0.16 to 0.86 and from 0.13 to 0.72, respectively. ? Conclusions: These markers may be useful tools for further investigation of the population genetic structure and biogeographic history of M. thunbergii in the warm-temperate zone of East Asia.     

Population structure and ecology of a tropical rare rhizomatous species of teosinte Zea diploperennis (Gramineae).

One of the objectives of the Sierra de Manantlán Biosphere Reserve (Jalisco, México) is the conservation in situ of the teosinte Zea diploperennis Iltis, Doebley, Guzman & Pazzi. Zea diploperennis is perennial, shade intolerant and its 1-3 m shoots are architecturally similar to maize. Clonal growth is of the phalanx type. Genets are iteroparous (modules semelparous). The demography of seven module and genet populations was studied in seven sites representing three stages of old-field succession. Seven permanent one-meter-square plots were randomly established in each site. All genets initially present and those that became established during our study were mapped and labeled according to year of establishment. The magnitude of demographic fluctuations was greater in module populations. Genet population dynamics followed a seasonal rhythm with a maximum population size obtained at the onset of the rainy season. A relation was documented between percent annual mortality of a cohort and its age: the younger the cohort, the greater the mortality. This was a statistically significant relationship, Y = [sin(-0.288x + 1.657)]2 (r = 0.92, p < 0.01), where is proportion annual mortality of genets and is the age of the cohort. The maximum rates of genet mortality occurred during the rainy season when population densities were greatest. As a consequence, we postulate that competition occurs principally during the rainy season. Linear relationships were observed between rate of population increase of genets versus old-field successional stage and soil type. Those areas with poor soil (Ultisol), degraded soil or soils with similar physical characteristics could be rehabilitated by introducing Z. diploperennis. Such rehabilitation would achieve two distinct objectives, promote propagation of this rare endemic and reclaim areas that are susceptible to erosion and further degradation.     

Salvia tonaticensis (Lamiaceae), a rare new species from Mexico

Salvia tonaticensis is described and illustrated as a new species to science. It is known from the extreme southern portion of the Estado de Mexico and northern Guerrero, Mexico. It belongs to section Polystachyae; however, unlike the species of the section hitherto known, it possesses simple, bifurcate and trifurcate multicellular hairs on the stems, abaxial leaf surface, petioles, and inflorescence rachis. The flowers are also larger than those of other species of the section, and the calyces are densely tomentose with purple or white multicellular hairs that vary from simple to dendriform. Within the section this species shows some morphological similarities to S. connivens.     

Pinus georginae (Pinaceae), a new species from western Jalisco, Mexico

Pinus georginae is described and illustrated as a new endemic species from the valleys in the southern basin of Río Ameca, Jalisco, western Mexico. It is closely related to Pinus praetermissa; however, after studying the cones and anatomy of the leaves in detail, characteristics were revealed that identify P. georginae as a distinct species.

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Resumen  Se describe e ilustra Pinus georginae como una especie nueva, endémica de algunos valles intermontanos al sur del Río Ameca, Jalisco, en el Occidente de México. Los árboles se parecen a Pinus praetermissa; sin embargo, al estudiar con detalle los conos y la anatomía de las acículas lo ubican a Pinus georginae como una entidad biológica con categoría específica independiente.

     

Wood anatomy and uses of 7 tropical tree species from Mexico

The wood anatomy of Coccoloba cozumelensis Hemsl., Coccoloba spicata Lundell, Gymnanthes lucida Sw., Blomia cupanioides Miranda, Canella winterana (L.) Gaertn., Aspidosperma megalocarpon Müell Arg. and Ehretia tinifolia L., is described. One tree per species was collected in the tropical rain forest of Quintana Roo, Mexico. Their wood has important traditional uses in furniture, tools, rural buildings, posts, fences, railroads and firewood. Macroscopic and microscopic characteristics were described and measured in wood samples, permanent slides and macerated material. These species have diffuse porosity, alternate vessel pits, simple perforation plates, numerous and small rays; libriform fibres are common, as well as ergastic material in gum forms, calcium carbonate and silica crystals. These characteristics explain aesthetical, weight, hardness and resistance (to mechanical and biological damage) characters that fit traditional use by the Maya.     

Genetic structure in a population of a tropical tree Ocotea tenera (Lauraceae): influence of avian seed dispersal

We studied the influence of avian seed dispersal on the structuring of genetic diversity in a population of a tropical tree, Ocotea tenera (Lauraceae). The seeds of O. tenera are principally dispersed by four, relatively specialized, fruit-eating bird species (emerald toucanets, keel-billed toucans, resplendent quetzals, and three-wattled bellbirds). We found high genetic diversity within the overall population and significant, nonrandom structuring of that diversity among subpopulations. Subpopulations contained members of several sibling groups, and most saplings within subpopulations were shown not to be the progeny of adult trees within the same subpopulation. Our data indicate that O. tenera subpopulations are founded with several seeds from few maternal families, and that this mode of establishment is an important determinant of population genetic architecture.     

Phenology of five tree species of a tropical dry forest in Yucatan, Mexico: effects of environmental and physiological factors

In order to relate phenological responses of trees to environmental variables we recorded the phenological patterns and select morphological and physiological traits (wood density and water potentials) of five tree species (Acacia gaumeri, Apoplanesia paniculata, Bursera simaruba, Gymnopodium floribundum, and Diospyros cuneata) in the tropical dry deciduous forest of the National Park of Dzibilchaltún, Yucatan, Mexico, over a period of 2 years (2004 and 2005). We chose two sites: one close to a permanent water source, locally known as ‘cenote’ (the CC site, ground water table was found at 2 m) and the other far from the cenote (FC site ground water table was at a depth of 10 m). Sites mainly differed in soil depth (FC site having greater soil depth) and soil nutrient characteristics (FC site more potassium, CC site more phosphorous). Our results indicated significant differences in phenology within species between sites and years, with leaf, flower and fruit production tending to be higher at the CC site and in the year 2004. Wood density and xylem water potentials were negatively related to each other, and midday water potentials were higher at the CC site. Differences in phenology found among years suggest that the timing of rainfall as well as the duration of periods without rain may play a more important role in phenology than total annual precipitation. Also differences inter-sites suggest a strong effect of site on tree phenology. Proximity to superficial bodies of water, such as cenotes, coupled with a greater concentration of available phosphorus in the soil may modify the effect of drought in this tropical dry deciduous forest.     

Population structure and demographic history of a tropical lowland rainforest tree species Shorea parvifolia (Dipterocarpaceae) from Southeastern Asia

Distribution of tropical rainforests in Southeastern Asia has changed over geo-logical time scale, due to movement of tectonic plates and/or global climatic changes. Shorea parvifolia is one of the most common tropical lowland rainforest tree species in Southeastern Asia. To infer population structure and demographic history of S. parvifolia, as indicators of temporal changes in the distribution and extent of tropical rainforest in this region, we studied levels and patterns of nucleotide polymorphism in the following five nuclear gene regions: GapC, GBSSI, PgiC, SBE2, and SODH. Seven populations from peninsular Malaysia, Sumatra, and eastern Borneo were included in the analyses. STRUCTURE analysis revealed that the investigated populations are divided into two groups: Sumatra-Malay and Borneo. Furthermore, each group contained one admixed population. Under isolation with migration model, divergence of the two groups was estimated to occur between late Pliocene (2.6 MYA) and middle Pleistocene (0.7 MYA). The log-likelihood ratio tests of several demographic models strongly supported model with population expansion and low level of migration after divergence of the Sumatra-Malay and Borneo groups. The inferred demographic history of S. parvifolia suggested the presence of a scarcely forested land bridge on the Sunda Shelf during glacial periods in the Pleistocene and predominance of tropical lowland rainforest at least in Sumatra and eastern Borneo.     

Dion tomasellii (Zamiaceae), a new species with two varieties from western Mexico

Dion tomasellii sp. nov. occurs with an interrupted distribution from Guerrero to central Sonora. It is characterized by falcate to subfalcate leaflets. The populations from Sonora and northern Sinaloa are segregated asD. tomasellii var.sonorense on the basis of their narrower and glaucous leaflets.     

Erigeron astranthioides (Asteraceae: Astereae), a new epappose species from western Mexico

A new species,Erigeron astranthioides, apparently endemic to the Sierra Madre of central Durango, is described and illustrated. It is contrasted withE. forreri (Greene) Greene andAstranthium, both of which are similar, though apparently through convergence. The new species is part of a lineage that includes six other primarily epapposeErigeron species mostly from the western Sierra Madre; within this group its closest relative appears to beE. mimus (S. F. Blake) Nesom, with which it is compared.     

Population genetics of Ryparosa kurrangii (Achariaceae), a rare lowland rainforest tree

Ryparosa kurrangii B.L. Webber (Achariaceae) is a rare lowland rainforest tree found in dense, discrete populations between the Daintree River and Cape Tribulation in Far North Queensland, Australia. It is one of many Australian rainforest trees thought to rely on the Southern Cassowary (Casuarius casuarius johnsonii) for long-distance seed dispersal. A survey of chloroplast non-coding DNA found no genetic variation at any of four non-coding chloroplast loci. Seedlings of three populations separated by a mountain range were then examined for amplified fragment length polymorphisms. High levels of genetic diversity were found within each population. Only two percent of the variation in this study was explained by separation due to the mountain range. This finding of high genetic diversity but minimal distinction between populations accords with general expectations for outcrossing, large-fruited, animal-dispersed trees. Either continuing or historical long-distance gene flow (mediated by cassowaries) could explain these results.     

Population structure, physiology and ecohydrological impacts of dioecious riparian tree species of western North America

The global water cycle is intimately linked to vegetation structure and function. Nowhere is this more apparent than in the arid west where riparian forests serve as ribbons of productivity in otherwise mostly unproductive landscapes. Dioecy is common among tree species that make up western North American riparian forests. There are intrinsic physiological differences between male and female dioecious riparian trees that may influence population structure (i.e., the ratio of male to female trees) and impact ecohydrology at large scales. In this paper, we review the current literature on sex ratio patterns and physiology of dioecious riparian tree species. Then develop a conceptual framework of the mechanisms that underlie population structure of dominant riparian tree species. Finally, we identify linkages between population structure and ecohydrological processes such as evapotranspiration and streamflow. A more thorough understanding of the mechanisms that underlie population structure of dominant riparian tree species will enable us to better predict global change impacts on vegetation and water cycling at multiple scales.     

Root system analysis of seedlings of seven tree species from a tropical dry forest in Mexico

Summary Root attributes of tree seedlings of seven species from the tropical deciduous forest along the Pacific Coast of Mexico are described using morphometirc root system analysis. Mean relative growth rate, root/shoot ratios, specific root length, root density, mean number of roots tips and root length/leaf area ratio were determined in seedlings grown for 35 days inside growth chambers. All the species had low relative growth rates, low root/shoot ratios and low root densities (<0.5 cm/cm³). The species associated with disturbed habitats, in contrast to the species characteristic of undisturbed areas, presented small seeds, a dichotomous root branching pattern and large specific root length. No relationship was found between seed size and mean relative growth rate among the species studied.     

Fire controls population structure in four dominant tree species in a tropical savanna

The persistence of mesic savannas has been theorised as being dependent on disturbances that restrict the number of juveniles growing through the sapling size class to become fire-tolerant trees. We analysed the population structures of four dominant tropical savanna tree species from 30 locations in Kakadu National Park (KNP), northern Australia. We found that across KNP as a whole, the population size structures of these species do not exhibit recruitment bottlenecks. However, individual stands had multimodal size-class distributions and mixtures of tree species consistent with episodic and individualistic recruitment of co-occurring tree species. Using information theory and multimodel inference, we examined the relative importance of fire frequency, stand basal area and elevation difference between a site and permanent water in explaining variations in the proportion of sapling to adult stems in four dominant tree species. This showed that the proportion of the tree population made up of saplings was negatively related to both fire frequencies and stand basal area. Overall, fire frequency has density-dependent effects in the regulation of the transition of saplings to trees in this Australian savanna, due to interactions with stem size, regeneration strategies, growth rates and tree–tree competition. Although stable at the regional scale, the spatiotemporal variability of fire can result in structural and floristic diversity of savanna tree populations.     

Seed reserve translocation and early seedling growth of eight tree species in a tropical deciduous forest in Mexico

Seed reserves play an essential role during germination and seedling establishment and are particularly important for species that grow in seasonal ecosystems with a short growing season. In this study, we examined (a) how and when the seedlings change their dependence from seed resources to external resources, (b) the lipid, nitrogen, and non-structural carbohydrate reserve translocation from seeds to seedlings over time, and (c) whether reserve translocation may be correlated to cotyledon and leaf lifespan of seedlings for eight tree species in a tropical deciduous forest in north-western Mexico. Our results showed that the cotyledon lifespan was not related to the cotyledon type (photosynthetic or reserve) and that the cotyledon biomass did not decrease significantly until germination. In six of the eight studied species, biomass allocation to the leaves was favored; lipids were the first reserve exhausted before the first leaves were totally expanded in seven of the eight study species. Species with the highest N concentration had expanded leaves and lost their cotyledons faster than species with a low N concentration. Our results suggest that tropical deciduous forest species employ different strategies to survive the dry season and re-sprout in the next growing season mediated by seed reserve concentrations, translocation patterns and subsequent biomass allocation.     

Population structure and genetic diversity of Dysosma versipellis (Berberidaceae), a rare endemic from China

Dysosma versipellis (Berberidaceae) is an endangered and endemic species in China. To provide scientific foundation for formulating conservation strategies, we sampled six extant populations of this species and assessed the levels and patterns of genetic diversity using ISSR markers (11 primers). Of 144 bands detected 57.64% were polymorphic, but on average only 20.72% were polymorphic within populations. Our results revealed a low level of intraspecific genetic diversity (at population level: H_pop = 0.082, H_B = 0.177, SI = 0.1194; at species level: H_pop = 0.207, H_B = 0.378, SI = 0.3069). A high level of genetic differentiations among populations was detected based on Nei's genetic diversity analysis (60%), AMOVA analysis (65%), and Bayesian analysis (53%). The low levels of heterozygosity and high genetic differentiation observed in D. versipellis may be the consequence of low rate of natural recruitment, clonal growth, gene drift, and habitat fragmentation. Based on this, we suggest that in situ conservation be an important and practical measure for maintaining the genetic diversity of this species. Ex situ conservation should sample from different populations across the distribution range of the species to conserve high genetic diversity.