Reproductive Biology ofDalbergia miscolobiumBenth. (Leguminosae-Papilionoideae) in SE Brazil: The Effects of Pistillate Sorting on Fruit-set

The breeding system ofDalbergia miscolobiumBenth. was investigatedby means of controlled pollinations and studies of post-pollinationevents in pistils. This species does not have homomorphic self-incompatibility,but crossed flowers always have higher fruit set than selfs,despite the fact that embryo development may be initiated inselfed pistils. It is suggested that deleterious recessive alleles,which lead to abortion of most selfed seeds, together with somematernal resource limitation, result in low fruiting success.Copyright1998 Annals of Botany Company Dalbergia miscolobiumBenth., Leguminosae, breeding system, pistillate sorting, fruiting success, seed set.     

Recombination indices in species of Erythrina L. (Leguminosae, Papilionoideae)

Darlington's recombination indices were calculated for eight species of Erythina by adding the mean chiasma frequency and the haploid chromosome number of each species. The recombination indices distinguished subgenus Erythraster (two species with greater mean chiasma frequency) from subgenera Micropteryx and Eythrina. This discrimination corroborates literature data on pollen morphology. It was not possible to separate groups at sectional level using recombination index. The recombination indices were also compared with data on breeding system and pollinators, available in literature, to investigate Grant's hypothesis on the occurrence of compensatory mechanisms in the regulation of recombination in plants. The data on breeding systems in Eythrina are very incomplete and it was not possible to correlate values of recombination indices with autogamy or allogamy. Species visited by hummingbirds showed lower recombination indices than species visited by other kind of pollinators.     

Polyethism and nestmate recognition in the alarm reaction of Atta leaf-cutting ants

Abstract.  Ethological studies are conducted under laboratory conditions using workers of Atta sexdens sexdens and Atta opaciceps collected from field colonies to investigate the mechanisms involved in the alarm response and intra-specific recognition in leaf-cutting ants. Hexane extracts from the heads of gardeners and generalist workers elicit higher levels of alarm response in foragers from the same colony than do mandibular gland extracts from foragers and soldiers, indicating that gardeners, generalists and foragers are primarily responsible for the production of alarm pheromone. Foragers subjected to extracts from non-nestmates exhibit significantly greater alarm responses than are induced by similar extracts derived from nestmate workers, suggesting that the alarm pheromone may have a role in nestmate recognition.     

Ultrastructure of Trypanosoma conorhini in the Crithidial Phase*

SYNOPSIS. The ultrastructure of the crithidial phase of T. conorhini culture has been studied. The structure of the plasma membrane is not easy to make out; only at a few points in highly magnified picit is seen as a double osmiophilic membrane with an intermedilayer of low density. Sub-pellicular tubules are present also around the flagellar pocket. The nucleus usually has a single large nucleolus, but sometimes this may be double. The flagellum has the sual 2 central and 9 double peripheral fibers, the latter having lateral arms. The structure of the kinetoplast is similar to that of other rypanosomatids but the division of the organelle seems to be more complex than has been described: the central, DNA-bearing lamellae duplicate, forming a double transverse band; 1 of these bands probably migrates toward the side before invagination of the membrane completes the division. Mitochondria are long tubular structures with few cristae, disposed chiefly along the periphery of the cell. A communication between the kinetoplast and tubular mitochondria is very frequent. The endoplasmic reticulum is poorly developed, represented chiefly by smooth membranes surrounding vesicles, rough-surfaced membranes being scanty in most cells. Several inclusions may be found, some probably lipids, others being of unknown nature.     

Ultrastructural Studies on the Trypanosomatid Phytomonas serpens in the Salivary Glands of a Phytophagous Hemipteran

Electron microscopy of salivary glands of the phytophagous hemipteran Phihia picta infected with Phytomonas serpens revealed the presence of flagellates in the gland periphery beneath the gland envelope, in the gland central lumen, between gland cells in the intercellular space and inside the gland cells. In the latter case, flagellates were found in the cytoplasm whether or not it was surrounded by a vacuolar membrane. Flagellates were always of the promastigote type, sometimes displaying a large twisted body. Morphological peculiarities of flagellates in different gland locations are recorded.     

Out of the Andes: patterns of diversification in clearwing butterflies

Global biodiversity peaks in the tropical forests of the Andes, a striking geological feature that has likely been instrumental in generating biodiversity by providing opportunities for both vicariant and ecological speciation. However, the role of these mountains in the diversification of insects, which dominate biodiversity, has been poorly explored using phylogenetic methods. Here we study the role of the Andes in the evolution of a diverse Neotropical insect group, the clearwing butterflies. We used dated species-level phylogenies to investigate the time course of speciation and to infer ancestral elevation ranges for two diverse genera. We show that both genera likely originated at middle elevations in the Andes in the Middle Miocene, contrasting with most published results in vertebrates that point to a lowland origin. Although we detected a signature of vicariance caused by the uplift of the Andes at the Miocene–Pliocene boundary, most sister species were parapatric without any obvious vicariant barrier. Combined with an overall decelerating speciation rate, these results suggest an important role for ecological speciation and adaptive radiation, rather than simple vicariance.     

Does the disturbance hypothesis explain the biomass increase in basin‐wide Amazon forest plot data?

Positive aboveground biomass trends have been reported from old-growth forests across the Amazon basin and hypothesized to reflect a large-scale response to exterior forcing. The result could, however, be an artefact due to a sampling bias induced by the nature of forest growth dynamics. Here, we characterize statistically the disturbance process in Amazon old-growth forests as recorded in 135 forest plots of the RAINFOR network up to 2006, and other independent research programmes, and explore the consequences of sampling artefacts using a data-based stochastic simulator. Over the observed range of annual aboveground biomass losses, standard statistical tests show that the distribution of biomass losses through mortality follow an exponential or near-identical Weibull probability distribution and not a power law as assumed by others. The simulator was parameterized using both an exponential disturbance probability distribution as well as a mixed exponential–power law distribution to account for potential large-scale blowdown events. In both cases, sampling biases turn out to be too small to explain the gains detected by the extended RAINFOR plot network. This result lends further support to the notion that currently observed biomass gains for intact forests across the Amazon are actually occurring over large scales at the current time, presumably as a response to climate change.