Showing papers by "University of Costa Rica published in 1995"

Environmental and physiological regulation of transpiration in tropical forest gap species: the influence of boundary layer and hydraulic properties.

Abstract: Environmental and physiological regulation of transpiration were examined in several gap-colonizing shrub and tree species during two consecutive dry seasons in a moist, lowland tropical forest on Barro Colorado Island, Panama. Whole plant transpiration, stomatal and total vapor phase (stomatal + boundary layer) conductance, plant water potential and environmental variables were measured concurrently. This allowed control of transpiration (E) to be partitioned quantitatively between stomatal (gs) and boundary layer (gb) conductance and permitted the impact of invividual environmental and physiological variables on stomatal behavior and E to be assessed. Wind speed in treefall gap sites was often below the 0.25 m s−1 stalling speed of the anemometer used and was rarely above 0.5 m s−1, resulting in uniformly low gb (c. 200–300 mmol m−2 s−1) among all species studied regardless of leaf size. Stomatal conductance was typically equal to or somewhat greater than gb. This strongly decoupled E from control by stomata, so that in Miconia argentea a 10% change in gs when gs was near its mean value was predicted to yield only a 2.5% change in E. Porometric estimates of E, obtained as the product of gs and the leaf-bulk air vapor pressure difference (VPD) without taking gb into account, were up to 300% higher than actual E determined from sap flow measurements. Porometry was thus inadequate as a means of assessing the physiological consequences of stomatal behavior in different gap colonizing species. Stomatal responses to humidity strongly limited the increase in E with increasing evaporative demand. Stomata of all species studied appeared to respond to increasing evaporative demand in the same manner when the leaf surface was selected as the reference point for determination of external vapor pressure and when simultaneous variation of light and leaf-air VPD was taken into account. This result suggests that contrasting stomatal responses to similar leaf-bulk air VPD may be governed as much by the external boundary layer as by intrinsic physiological differences among species. Both E and gs initially increased sharply with increasing leaf area-specific total hydraulic conductance of the soil/root/leaf pathway (Gt), becoming asymptotic at higher values of Gt. For both E and gs a unique relationship appeared to describe the response of all species to variations in Gt. The relatively weak correlation observed between gs and midday leaf water potential suggested that stomatal adjustment to variations in water availability coordinated E with water transport efficiency rather than bulk leaf water status.

Mitochondrial DNA diversity in the Kuna Amerinds of Panamá

Abstract: Mitochondrial DNA (mtDNA) haplotype diversity was determined for 63 Chlbcha-speaking Kuna Amerinds sampled widely across their geographic range in eastern Panama^ The Kuna data were compared with mtDNA control region I sequences from two neighboring Chibchan groups, the Ngdb6 and the Huetar; two Amerind groups located at the northern and southern extremes of Amerind distribution, the Nuu-ChahNulth of the Pacific Northwest and the Chilean Mapuche; and with a single Na-Dene group, the Haida of the Pacific Northwest. The Kuna exhibited low levels of mitochondrial diversity as had been reported for the other two Chibchan groups and, furthermore, carried only two of the four Amerind founding lineages first reported by Schurr and coworkers (4m. J. Hum. Genet. 1990; 46: 613-623). We posit that speakers of modern Chibchan languages (henceforth referred to as the Chibcha) passed through a population bottleneck caused either by ethnogenesls from a small founding population and/or subsequent European conquest and colonization. Using the approach of Harpending etal. (Curr. Anthropol. 1993; 34: 483-496), we estimated a Chibchan population bottleneck and subsequent expansion approximately 10 000 years before present, a date consistent with a bottleneck at the time of Chibchan ethnogenesis. The low mtDNA diversity of Kuna Amerinds, as opposed to the generally high levels of mtDNA variation detected in other Amerind groups, demonstrates the need for adequate sampling of cultural or racial groups when attempting to genetically characterize human populations.

Acute-phase reactions, including cytokines, in patients bitten by bothrops and crotalus snakes in brazil

Abstract: Thirty-one patients bitten by venomous snakes in Botucatu area (State of Sao Paulo - Brazil), sixteen by Bothrops spp. and fifteen by Crotalus durissus terrificus, were studied. The group comprised twenty-nine males and two females, ranging from fourteen to sixty-three years of age (mean 33 ± 15). Leukocytosis with neutrophilia and lymphopenia, increase of mucoproteins and C-reactive protein, decrease of total serum protein and albumin, were observed on the first day after the accident. In addition, increased serum levels of the cytokines IL-6 and IL-8, but not of IL-1b and TNF-a, were observed. The alterations were generally more intense in patients bitten by Crotalus durissus terrificus than by Bothrops spp. It is concluded that these snakebite envenomations closely resemble an acute trauma, inducing a typical acute-phase response.

The Gulf of Nicoya Estuary, Costa Rica: Past, present, and future cooperative research

Abstract: The Gulf of Nicoya is a tectonic estuary on the Pacific coast of Costa Rica (10°N–85°W), extending about 100 km from the Tempisque river to the 500 m isobath. A dry season (December–April) and a rainy season (May–November) exert a significant impact on its water characteristics. The estuary is the most important fishing ground of Costa Rica, and the main Pacific ports are located within it. Coastal zone development has increased in recent years. In 1979 a research programme to study the Gulf was established at the University of Costa Rica, and foreign scientists were invited to work jointly with local experts to achieve the goals of the evaluation. More than 80 papers have been published to date, making the Gulf one of the best known tropical estuaries. The study of soft-bottom communities is an important component of this research programme. Past benthic research focused on the description of the structure of communities, while future efforts will find an unexplored field in the study of energy flow and community interactions. More than 200 species of fish, and 400 of benthic invertebrates have been identified. Future cooperative research is most welcome in larval ecology, interactions between size groups, and physiological tolerances. Considerable experience has been accumulated in the experimental manipulation of soft-bottom communities of high latitudes. This branch of ecology, however, remains little explored in the tropics. Future cooperative efforts in the Gulf of Nicoya will be established on solid ground, formed by a data base that has been improved since 1979, the existence of a marine research centre and a group of active, local scientists who have experience in working together with foreign expertise.

Purification and characterization of myotoxin IV, a phospholipase A2 variant, from Bothrops asper snake venom

Abstract: A basic myotoxic protein was purified from Bothrops asper venom. Like other basic Bothrops myotoxins, myotoxin IV induces acute muscle damage after intramuscular injection in mice and disrupts negatively charged liposomes but not positively charged ones. Furthermore, this protein exerts a weak anticoagulant effect only at concentrations of 40 micrograms/ml or higher, and is devoid of phospholipase A2 activity. Rabbit polyclonal antibodies to B. asper myotoxin II, a related lysine-49 isoform, cross-react strongly with myotoxin IV by enzyme immunoassay, indicating a high degree of antigenic similarity between these two proteins. The fact that both toxins have similar amino acid compositions and amino-terminal sequences, including leucine-5 and glutamine-11, 2 amino acid residues conserved in all lysine-49 phospholipase A2 variants purified, strongly suggests that B. asper myotoxin IV is a lysine-49 phospholipase A2.

Using the HOME inventory with infants in Costa Rica.

Abstract: It has been established through several decades of research that childrens home environments significantly influence their development. Many researchers have also been interested in expanding research beyond indirect measures of the home environment such as socioeconomic status to help understand the nature of specific environmental mechanisms which influence early behavior and cognitive development. The Home Observation for Measurement of the Environment (HOME) Inventory was developed to meet these needs. Specifically HOME measures the quality of stimulation in a childs early family environment. Almost all studies of the approachs reliability and validity have been conducted with US samples. HOME is however being used in other countries. The authors report their findings from a study of whether the psychometric properties of HOME based upon US samples parallel those found in Costa Rica and whether HOME discriminates between Costa Rican environments with different associations to child health and development. Focus centers upon the infant/toddler version of the HOME Inventory. HOME data for 183 healthy Costa Rican infants were compared to the original HOME standardization sample from Little Rock Arkansas. The study found the HOME Inventory to be helpful in identifying children at risk for delayed development in this Latin American sample. Lower HOME scores related to a shorter duration of breastfeeding and differentiated children with iron deficiency anemia in infancy a condition associated with long-lasting developmental disadvantage.

Morphometric, isozymic and mitochondrial variability of Africanized honeybees in Costa Rica

Abstract: Wing morphometry, isozymic variation and mitochondrial RFLPs were studied in samples of feral Africanized bees collected at three different locations in Costa Rica, two of them in the lowlands (Guanacaste and Golfito regions) and the other in the Central Valley. These data revealed a predominantly African origin at all locations. However, significant heterogeneity was found between the two lowland sites and the Central Valley for some isozyme markers as well as for the RFLPs considered in this study. Both isozymic and mitochondrial DNA European markers were more frequent in the Central Valley. This could be the result of different opportunities for European gene introgression at the beginning of the migration of Africanized honeybees. It is shown that different gene frequencies of mitochondrial and nuclear European genetic markers may exist in Africanized bee populations, and that this may result from different selection pressures among colonies with African and European queens.

Phytophagy in the Genus Monitoriella (Hymenoptera: Braconidae) with Description of New Species

Abstract: Exposures of uninfested plants to mated females were used to confirm data from field collections that suggested the braconid wasp Monitoriella elongata was phytophagous, producing galls on Philodendron radiatum . We predict that all members of the genus Monitoriella are phytophagous. The vast majority of the Braconidae are parasitic on other insects. Only 1 other species in the family Braconidae is known to be phytophagous, as a gall inducer on legumes, but a few others are also suspected. A redeseription of M. elongata is presented based on material from Mexico and Costa Rica, a new species of Monitoriella is described from Trinidad, and a key is provided to the known species of Monitoriella .

Observations on the plankton of some Costa Rican lakes

Abstract: We sampled 30 lakes in Costa Rica in the wet season (July–August) of 1991 for phytoplankton (with integrated and whole water samples), and 17 for zooplankton (with net tows). Taxa of plankton and community richness were poorly related to geography, morphology, chemistry, and other biota. Neither the zooplankton nor the phytoplankton appeared to influence the composition of the other, and neither were apparently influenced by the presence of fish.

Sobre el estudio diacrónico de las lenguas chibchenses y su contribución al conocimiento del pasado de sus hablantes

Abstract: La semejanza entre lenguas puede tener distintos origenes: la herencia de un estado anterior que les haya sido comun (esto es, el parentesco), la difusion de rasgos de unas a otras, las tendencias universales del lenguaje humano y la casualidad.

The influence of leaf characteristics on epiphyllic cover: a test of hypotheses with artificial leaves

Abstract: Studies of epiphyll ecology have been hindered by the biochemical and morphological variability of the leaf substrate. The use of artificial (plastic ribbon tape) leaves solved that problem in a study done at the Braulio Carrillo National Park, Costa Rica. It showed that after nine months of field exposure, relative epiphyll cover was similar in five leaf shapes and two sizes. Driptips do not affect epiphyll cover, which was four times higher under a clearing than in the shaded understory, for all leaf shapes and sizes.

Detection and Isolation of Bovine Immunodeficiency‐like Virus (BIV) in Dairy Herds of Costa Rica

Abstract: Serological (Western blot) detection of bovine immunodeficiency-like virus (BIV) in Holstein dairy herds is reported in Costa Rica for the first time, as well as the isolation of the virus, from a seropositive bovine, by cocultivation of peripheral blood mononuclear cells (PBMC) with embryonic rabbit epithelial (EREp) cells The isolated strain, BIVCR1, reacted similarly in Western blot as the reference strain BIV R29 and is clearly distinguishable from bovine leukaemia virus (BLV) The data suggest an association between BIV infections and BLV infections, as it has been reported elsewhere From these results it can be concluded that BIV is present in Costa Rica and it is suggested that these viral infections will probably follow the epidemiological parameters of BLV infections in Costa Rica, reaching high infection rates in dairy herds

Effects of Calf Removal at Parturition on Postpartum Ovarian Activity in Zebu (Bos indicus) Cows in the Humid Tropics

Abstract: To assess endocrine and morphological responses of ovaries to total weaning at parturition, 6 Zebu (Bos indicus) cows 5 years or older were investigated. Following parturition, blood samples were collected daily during the first month and twice weekly thereafter until day 60 to determine concentrations of progesterone (P4) and prostaglandin F2α metabolite. It took between 25 to 32 days to complete uterine involution.The prostaglandin metabolite remained elevated for a mean period of 14.2 days (range, 4-21) postpartum. Five of the animals resumed cyclicity with a short estrous cycle starting between days 7 to 34 and lasting between 7 and 14 days. No estrous behavior was recorded prior to the short estrous cycles, but subsequent normal-length estrous cycles were all preceded by signs of estrus. In the 1 animal that resumed cyclicity with an estrous cycle of normal length on day 37 (length 20 days), the cycle was preceded by estrous behavior. Progesterone concentrations reached a mean maximum of 4.8 nmol liter−1 during the short estrous cycles, and prostaglandin metabolite concentrations peaked while P4 concentrations were decreasing. P4 concentrations reached a mean maximum of 12.2 nmol liter−1 during the estrous cycles of normal length. The interval from parturition to the first estrous cycle of normal length varied between 16 and 48 days, and the length of the cycle was 18 to 22 days. Starting 2 days postpartum, ovaries from 5 of the cows were scanned by ultrasonography every second day until day 30 postpartum. Medium-sized follicles were detected between days 4 to 7 postpartum in 4 of the scanned cows that later had short estrous cycles. The time between parturition and the appearance of the first dominant follicle was 7.6 days (range 6-10 days). The interval between parturition and the appearance of the first ovulatory-sized follicle was 10.2 days (range 8-13 days). In 3 of the scanned cows this ovulatory-sized follicle ovulated. We conclude that cyclic ovarian activity in Zebu cows can start early in the postpartum period in the absence of offspring, and that short luteal phases, not preceded by estrous behavior, may play an important role in establishing normal postpartum ovarian activity.