Spatial genetic structure of Simarouba amara Aubl. (Simaroubaceae), a dioecious, animal-dispersed Neotropical tree, on Barro Colorado Island, Panama

Simarouba amara (Simaroubaceae) is a vertebrate-dispersed, insect-pollinated Neotropical tree found in lowland moist forest from upper Mesoamerica to the Amazon basin. We assessed the spatial genetic structure of S. amara within the 50-ha Forest Dynamics Plot on Barro Colorado Island in the Republic of Panama. A total of 300 individuals were genotyped using five microsatellite loci, representing 100 individuals with a dbh>or=10 cm, 100 individuals of 1-10 cm dbh, and 100 individuals of <1 cm dbh. The 200 individuals in the two larger size classes were also genotyped with 155 AFLP loci. Spatial autocorrelation analysis using Moran's Index detected significant genotypic association at the smallest distance classes for 1-10 cm dbh (0-20 m) and >10 cm dbh (0-40 m) size categories. Significant spatial autocorrelations were detected over larger scales (0-140 m) in <1 cm dbh individuals. The relatively weak genetic structure of S. amara, in comparison to other recent studies, may be explained by pollen and seed dispersal over the 50 ha plot, overlapping seed shadows, and postrecruitment mortality.     

Roles of nectar robbers in reproduction of the tropical treelet Quassia amara (Simaroubaceae)

Summary Different subsets of mainland nectarivores visited Quassia amara (Simaroubaceae), a self-compatible, predominately bird-pollinated treelet, at three islands and the mainland in Panamá. Factors correlated with reproductive success, defined as seed to ovule ratio, included the species pollinating and robbing flowers, visitor activity, pollinator response to nectar robbing, and internal regulation of fruit production. The absence of robbers and former pollinators on an island separated from the mainland during the holocene was associated with shifts in flower size, nectar production, and 3–4fold increases in population reproductive success and pollinator efficiency (=seeds produced per visit). Exclusion of robbers at three sites resulted in seed production 4–12 times greater than control flowers, at which robbers accounted for 52–98% of all visits. Although 36% of buds and over 83% of all flowers were robbed, this had no direct influence on the recorded 36–61% respective abortion rates of buds and flowers. Opportunistic avian robbers appeared where normal robbers were absent; three avian robbers extensively used floral perforations made by Trigona bees, and all ancillary pollinators also robbed. Selection pressures from nectar robbers are discussed that may relate to plant reproductive fitness.     

Picrasin K,a new quassinoid from Quassia amara L. (Simaroubaceae)

A new quassinoid Picrasin K 1 was isolated from a decoction made of Quassia amara leaves, traditionally used in French Guyana to treat malaria. The structure and relative stereochemistry of 1 was determined through extensive NMR analysis. Picrasin K showed a low activity against Plasmodium falciparum in vitro (IC₅₀ = 8 μM), and a similar low activity on human cancerous cells line (IC₅₀ = 7 μM on MCF-7 cells line).     

Phagodeterrence by Quassia amara (Simaroubaceae) wood extract fractions on Hypsipyla grandella (Lepidoptera: Pyralidae) larvae

In Latin America and the Caribbean, precious wood species like mahoganies (Swietenia spp.) and cedars (Cedrela spp.) are seriously injured by the mahogany shootborer, Hypsipyla grandella (Zeller) (Lepidoptera: Pyralidae) larva, which bores into the main shoot of trees. In previous experiments focused on searching for a preventive method for managing this pest, a wood extract of bitterwood, Quassia amara L. ex Blom (Simaroubaceae) had been shown to cause phagodeterrence to larvae. Therefore, three fractions (water, methanol and diethyl ether) of a wood extract were tested for their phagodeterrence to larvae, by means of laboratory and greenhouse trials. Phagodeterrence was assessed by determining their effect on foliage consumption, mortality and signs of damage (number of orifices, sawdust piles, fallen shoots, number of tunnels and tunnel length) caused by larvae on Spanish cedar (C. odorata). Both the methanol and diethyl ether fractions caused phagodeterrence, by strongly reducing foliage consumption and signs of damage, while not causing larval mortality. The lowest concentration at which phagodeterrence was detected for the methanol fraction corresponded to 0.0625%, which is equivalent to a 1.0% of the bitterwood crude extract. However, results with the diethyl ether fraction were unsatisfactory, as none of the treatments differed from the solvent, possibly because of an adverse effect of the solvent on foliar tissues. Phagodeterrent principles from Q. amara derivatives may play an important role in dealing with H. grandella if they are complemented with other integrated pest management preventative tactics.     

New findings on Simalikalactone D, an antimalarial compound from Quassia amara L. (Simaroubaceae)

Quassia amara L. (Simaroubaceae) is a species widely used as tonic and is claimed to be an efficient antimalarial all over the Northern part of the Amazon basin. Quassinoid compound Simalikalactone D (SkD) has been shown to be one of the molecules responsible for the antiplasmodial activity of a watery preparation made out of juvenile fresh leaves of this plant. Because of its strong antimalarial activity, we decided to have a further insight of SkD pharmacological properties, alone or in association with classical antimalarials. At concentrations of up to 200μM, we showed herein that SkD did not exert any apoptotic or necrotic activities in vitro on lymphoblastic cells. However, an antiproliferative effect was evident at concentrations higher than 45nM. SkD was inefficient at inhibiting heme biomineralization and the new permeability pathways induced by the parasite in the host erythrocyte membrane. With respect to Plasmodium falciparum erythrocytic stages, SkD was almost inactive on earlier and later parasite stages, but potently active at the 30th h of parasite cycle when DNA replicates in mature trophozoites. In vitro combination studies with conventional antimalarial drugs showed that SkD synergizes with atovaquone (ATO). The activity of ATO on the Plasmodium mitochondrial membrane potential was enhanced by SkD, which on its own had a poor effect on this cellular parameter.     

Invertebrates Colonization on Native Tree Leaves in a Neotropical Stream (Brazil)

We evaluate the composition and structure of invertebrate assemblages during leaf breakdown of five native tree species (Myrcia guyanensis, Ocotea sp., Miconia chartacea, Protium brasiliense and Protium heptaphyllum) and a mixture of them in a headwater stream, Southeastern Brazil. Coarse mesh litter bags were used over a 120‐day period. P. heptaphyllum showed the slowest breakdown rate, while Myrcia showed the fastest. Total densities and biomass values of associated invertebrates were different among leaf types and incubation periods. The highest values of total abundance were found in P. heptaphyllum, while Ocotea sp. and Miconia were few colonized. Gathering‐collectors feeding group dominated all leaf types, followed by predators and shredders. Shredders were more abundant in Myrcia than in Miconia and the mixed pack. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Population Genetic Structure of Neotropical Mangrove Species on the Colombian Pacific Coast: Avicennia germinans (Avicenniaceae)1

We investigated the genetic variation of Avicennia germinans using 172 AFLP (Amplified Fragment Length Polymorphism) bands of 45 plants from four localities on the Colombian Pacific coast: 11 from Virudó (Chocó), 10 from La Plata (Valle), 12 from Tumaco (Nariño), and 12 from Chontal (Nariño). AFLP variation among localities (16.2%) was highly significant (AMOVA; P < 0.0001). All the analyses showed that Tumaco was the most genetically distinct locality of the four under study. The other three localities, La Plata, Virudó, and Chontal, apparently form a large single subpopulation with high‐to‐moderate gene flow among localities. We also found the genetic diversity of A. germinans on the Colombian Pacific coast (H_E= 0.251) higher than that estimated by others over the broad geographic range of A. germinans. All these results together show that mangroves on the Colombian Pacific coast deserve a strong investigative effort to improve our ecological, evolutionary, and biogeographic knowledge of this important tropical forest type.     

Population Genetic Structure of Neotropical Mangrove Species on the Colombian Pacific Coast: Pelliciera rhizophorae (Pellicieraceae)1

Pelliciera rhizophorae is a Neotropical mangrove species whose distribution is mostly restricted to the Pacific Coast, between the Gulf of Nicoya (Costa Rica) and the Esmeraldas River (Ecuador). In the Caribbean, patches of Pelliciera have been found in Nicaragua, Panama, and Colombia. The genetic variation and the population structure of P. rhizophorae were evaluated in six zones of the Colombian Pacific, using AFLP molecular markers. Of the 225 amplified fragments produced, 155 (69%) were polymorphic in 57 individuals of P. rhizophorae collected in the localities of Virudó, Charambirá, La Plata Island, Tumaco, Milagros, and Chontal. Genetic diversity within populations varied significantly, with the lowest levels of within‐population variation (H_ep= 0.081 and 0.090, respectively) in La Plata Island and Tumaco; and the highest level of variation (H_ep= 0.187) in Chontal. In the Colombian Pacific, P. rhizophorae was significantly structured, with 26.5 percent of the variation found among populations, which was an evidence of substructure within populations. Genetic differentiation was not related to the geographic distance between zones. This suggests that the population dynamics of P. rhizophorae could be associated with historic processes influenced by ecological and environmental factors such as the movement of pollen by birds, the displacement of propagules by marine currents, and the spatial distribution of favorable habitats.     

Biogeography and Genetic Structure in Populations of a Widespread Lichen (Parmelina tiliacea,Parmeliaceae, Ascomycota)

The genetic diversity and population structure of the foliose lichenized fungus Parmelina tiliacea has been analyzed through its geographical range, including samples from Macaronesia (Canary Islands), the Mediterranean, and Eurosiberia. DNA sequences from the nuclear ribosomal internal transcribed spacer, the mitochondrial large subunit ribosomal RNA gene, and the translation elongation factor 1-α were used as molecular markers. The haplotypes of the three markers and the molecular variance analyses of multilocus haplotypes showed the highest diversity in the Canary Islands, while restricted haplotypes occurred at high frequencies in Mediterranean coastal samples. The multilocus haplotypes formed three unevenly distributed clusters (clusters 1-3). In the Canary Islands all the haplotypes were present in a similar proportion, while the coastal Mediterranean sites had almost exclusively haplotypes of cluster 3; cluster 2 predominated in inland Mediterranean sites; and cluster 1 was more abundant in central and northern Europe (Eurosiberian area). The distribution of clusters is partially explained by climatic factors, and its interaction with local spatial structure, but much of the variation remains unexplained. The high frequency of individuals in the Canary Islands with haplotypes shared with other areas suggests that could be a refugium of genetic diversity, and the high frequency of individuals of the Mediterranean coastal sites with restricted haplotypes indicates that gene flow to contiguous areas may be restricted. This is significant for the selection of areas for conservation purposes, as those with most genetic variation may reflect historical factors and biological properties of the species.     

中国大鲵四种群的遗传结构和地理分化

为了确定栖息地的破碎化和片断化引起中国大鲵的地理分化和遗传结构变异,本文测定了来自广西、河南、陕西和湖南4个地理种群的28条大鲵的mtDNAD loop基因全序列。根据这4个地理种群的地理分布,分成珠江单元(广西种群)、黄河单元(河南种群)和长江单元(湖南和陕西种群)。通过ClustalX、MEGA2.0、DnaSP4.0、Arlequin1.1分析发现,全序列长度为771bp,其中64个多态性核苷酸变异位点,占全部碱基数的8.26%。转换和颠换分别为6和2个,插入/缺失11个。27个单倍型间的序列差异平均为1.32%。3个单元的单倍型多样性指数和核苷酸多样性指数值都偏低,而且珠江单元的这两个指数值都低于长江和黄河两个单元。珠江单元和黄河、长江单元之间分化程度显著(P<0.001),而长江和黄河单元之间差异不显著(P>0.05)。地理单元内分化程度占99.31%,而单元间只有0.69%,表明遗传差异主要发生在单元内,而且各地理单元之间的基因流较频繁。构建的NJ树和MP树显示,27个单倍型呈现一种混杂的分布格局,并未分成代表3个地理单元的聚合群。     

High Levels of Diversity Uncovered in a Widespread Nominal Taxon: Continental Phylogeography of the Neotropical Tree Frog Dendropsophus minutus

Species distributed across vast continental areas and across major biomes provide unique model systems for studies of biotic diversification, yet also constitute daunting financial, logistic and political challenges for data collection across such regions. The tree frog Dendropsophus minutus (Anura: Hylidae) is a nominal species, continentally distributed in South America, that may represent a complex of multiple species, each with a more limited distribution. To understand the spatial pattern of molecular diversity throughout the range of this species complex, we obtained DNA sequence data from two mitochondrial genes, cytochrome oxidase I (COI) and the 16S rhibosomal gene (16S) for 407 samples of D. minutus and closely related species distributed across eleven countries, effectively comprising the entire range of the group. We performed phylogenetic and spatially explicit phylogeographic analyses to assess the genetic structure of lineages and infer ancestral areas. We found 43 statistically supported, deep mitochondrial lineages, several of which may represent currently unrecognized distinct species. One major clade, containing 25 divergent lineages, includes samples from the type locality of D. minutus. We defined that clade as the D. minutus complex. The remaining lineages together with the D. minutus complex constitute the D. minutus species group. Historical analyses support an Amazonian origin for the D. minutus species group with a subsequent dispersal to eastern Brazil where the D. minutus complex originated. According to our dataset, a total of eight mtDNA lineages have ranges >100,000 km². One of them occupies an area of almost one million km² encompassing multiple biomes. Our results, at a spatial scale and resolution unprecedented for a Neotropical vertebrate, confirm that widespread amphibian species occur in lowland South America, yet at the same time a large proportion of cryptic diversity still remains to be discovered.     

Spatial Genetic Structure of the Abundant and Widespread Peatmoss Sphagnum magellanicum Brid.

Spore-producing organisms have small dispersal units enabling them to become widespread across continents. However, barriers to gene flow and cryptic speciation may exist. The common, haploid peatmoss Sphagnum magellanicum occurs in both the Northern and Southern hemisphere, and is commonly used as a model in studies of peatland ecology and peatmoss physiology. Even though it will likely act as a rich source in functional genomics studies in years to come, surprisingly little is known about levels of genetic variability and structuring in this species. Here, we assess for the first time how genetic variation in S. magellanicum is spatially structured across its full distribution range (Northern Hemisphere and South America). The morphologically similar species S. alaskense was included for comparison. In total, 195 plants were genotyped at 15 microsatellite loci. Sequences from two plastid loci (trnG and trnL) were obtained from 30 samples. Our results show that S. alaskense and almost all plants of S. magellanicum in the northern Pacific area are diploids and share the same gene pool. Haploid plants occur in South America, Europe, eastern North America, western North America, and southern Asia, and five genetically differentiated groups with different distribution ranges were found. Our results indicate that S. magellanicum consists of several distinct genetic groups, seemingly with little or no gene flow among them. Noteworthy, the geographical separation of diploids and haploids is strikingly similar to patterns found within other haploid Sphagnum species spanning the Northern Hemisphere. Our results confirm a genetic division between the Beringian and the Atlantic that seems to be a general pattern in Sphagnum taxa. The pattern of strong genetic population structuring throughout the distribution range of morphologically similar plants need to be considered in future functional genomic studies of S. magellanicum.     

Developmental Changes in Direct and Indirect Defenses in the Young Leaves of the Neotropical Tree Genus Inga (Fabaceae)

Plant fitness is affected by herbivory, and in moist tropical forests, 70 percent of herbivore damage occurs on young leaves. Thus, to understand the effects of herbivory on tropical plant fitness, it is necessary to understand how tropical young leaves survive the brief, but critical, period of susceptibility. In this study, we surveyed three species of Inga during young leaf expansion. Three classes of toxic secondary metabolites (phenolics, saponins, and tyrosine), extrafloral nectar production, leaf area, and extrafloral nectary area were measured at randomly assigned young leaf sizes. In addition, all defenses were compared for potential trade‐offs during leaf expansion. No trade‐offs among defenses were found, and the concentration of all defenses, except tyrosine, decreased during leaf expansion. We suggest that plants continued to increase phenolic and saponin content, but at a rate that resulted in decreasing concentrations. In contrast, tyrosine content per leaf steadily increased such that a constant concentration was maintained regardless of young leaf size. Nectar production remained constant during leaf expansion, but, because young leaf area increased by tenfold, the investment in extrafloral nectar per leaf area significantly decreased. In addition, nectary area did not change during leaf expansion and therefore the relative size of the nectary significantly decreased during young leaf expansion. These results support the predictions of the optimal defense hypothesis and demonstrate that the youngest leaves have the highest investment in multiple defenses, most likely because they have the highest nitrogen content and are most susceptible to a diversity of herbivores.     

臭椿花器官分化的初步研究

利用扫描电镜(SEM)和光镜(LM)对臭椿花序及花器官的分化和发育进行了初步研究,表明:1)臭椿花器官分化于当年的4月初,为圆锥花序;2)分化顺序为花萼原基、花冠原基、雄蕊原基和雌蕊原基。5个萼片原基的发生不同步,并且呈螺旋状发生;5个花瓣原基几乎同步发生且其生长要比雄蕊原基缓慢;雄蕊10枚,两轮排列,每轮5个原基的分化基本是同步的;雌蕊5,其分化速度较快;3)在两性花植株中,5个心皮顶端粘合形成柱头和花柱,而在雄株中,5个心皮退化,只有雄蕊原基分化出花药和花丝。本研究着重观察了臭椿中雄花及两性花发育的过程中两性花向单性花的转变。结果表明,臭椿两性花及单性花的形成在花器官的各原基上是一致的(尽管时间上有差异),雌雄蕊原基同时出现在每一个花器官分化过程中,但是,可育性结构部分的形成取决于其原基是否分化成所应有的结构:雄蕊原基分化形成花药与花丝,雌蕊原基分化形成花柱、柱头和子房。臭椿单性花的形成是由于两性花中雌蕊原基的退化所造成,其机理有待于进一步研究。     

Genetic characterization of the Neotropical catfish Pimelodus maculatus (Pimelodidae,Siluriformes) in the Upper Uruguay River

Freshwater fish present unique challenges when one attempts to understand the factors that determine the structure of their populations. Habitat fragmentation is a leading cause of population decline that threatens ecosystems worldwide. In this study, we investigated the conservation status of genetic variability in the Neotropical catfish (Pimelodus maculatus). Specifically, we examined the structure and genetic diversity of this species in a region of the Upper Uruguay River fragmented by natural barriers and dams. There was no genetic structure among the four sites analyzed, indicating the existence of only one population group. A combination of environmental management and genetic monitoring should be used to minimize the impact of impoundment on panmitic populations of migratory fish species.     

Genetic structure of Partamona helleri (Apidae, Meliponini) from Neotropical Atlantic rainforest

Stingless bees of the genus Partamona are distributed from southern Mexico to southern Brazil. This genus has been subject to different approaches to solve questions concerning general biology, taxonomy, systematics and biogeography, but population studies applying molecular techniques are inexistent. We analyzed the genetic structure of P. helleri across its geographic distribution along the coastal Atlantic tropical rainforest in Brazil. Ten mtDNA haplotypes were observed in 47 colonies of P. helleri of which some were exclusive and others shared among geographic sub-groups. Statistical analysis showed high genetic differentiation between geographic areas sampled. Fragmentation of the Atlantic forest during Pleistocene glaciations is discussed as a possible cause of the present haplotype distribution and frequency.