Comparison of methods for evaluating mineral loss: hardness versus synchrotron microcomputed tomography.

This study analyzed degrees of demineralization in bovine enamel using synchrotron microcomputed tomography (SMCT) and hardness measurements (Knoop hardness number, KHN). For 5 days, 40 bovine enamel blocks were individually subjected to a pH cycling model and treatment with fluoride dentifrices (placebo, 275, 550 and 1,100 microg F/g) diluted in deionized water twice a day. Surface hardness number and cross-sectional profiles of hardness and mineral concentration (by SMCT) were determined. Integrated hardness (KHN x microm) for sound and demineralized specimens was calculated and subtracted to give the integrated loss of hardness (DeltaKHN) for the lesions. Increasing fluoride concentration in the dentifrices led to higher values for surface hardness after pH cycling and mineral concentration (g(HAp) cm(-3)), and lower values for DeltaKHN (p < 0.05). From the present results, it may be concluded that hardness measurements revealed demineralization in all groups, which was lower in groups treated with dentifrice with a higher F concentration. SMCT and hardness measurements gave similar results in areas with higher demineralization, but diverged in areas with lower demineralization.

Tropical nematode diversity: vertical stratification of nematode communities in a Costa Rican humid lowland rainforest.

Comparisons of nematode communities among ecosystems have indicated that, unlike many organisms, nematode communities have less diversity in the tropics than in temperate ecosystems. There are, however, few studies of tropical nematode diversity on which to base conclusions of global patterns of diversity. This study reports an attempt to estimate nematode diversity in the lowland tropical rainforest of La Selva Biological Research Station in Costa Rica. We suggest one reason that previous estimates of tropical nematode diversity were low is because habitats above the mineral soil are seldom sampled. As much as 62% of the overall genetic diversity, measured by an 18S ribosomal barcode, existed in litter and understorey habitats and not in soil. A maximum-likelihood tree of barcodes from 360 individual nematodes indicated most major terrestrial nematode lineages were represented in the samples. Estimated 'species' richness ranged from 464 to 502 within the four 40 x 40 m plots. Directed sampling of insects and their associated nematodes produced a second set of barcodes that were not recovered by habitat sampling, yet may constitute a major class of tropical nematode diversity. While the generation of novel nematode barcodes proved relatively easy, their identity remains obscure due to deficiencies in existing taxonomic databases. Specimens of Criconematina, a monophyletic group of soil-dwelling plant-parasitic nematodes were examined in detail to assess the steps necessary for associating barcodes with nominal species. Our results highlight the difficulties associated with studying poorly understood organisms in an understudied ecosystem using a destructive (i.e. barcode) sampling method.

Heterorhabditis sonorensis n. sp. (Nematoda: Heterorhabditidae), a natural pathogen of the seasonal cicada Diceroprocta ornea (Walker) (Homoptera: Cicadidae) in the Sonoran desert.

A new Heterorhabditis species was isolated from nymphal stages of the seasonal cicada Diceroprocta ornea (Walker) in an asparagus field in the state of Sonora, Mexico. Concomitantly, another isolate of the same nematode species was also collected from an oak woodland habitat in the Chiricahua mountain range in southeastern Arizona. Morphological and molecular studies together with cross-hybridization tests indicate these two isolates are conspecific and represent a new undescribed Heterorhabditis sp. This new species is distinguished from other species in this genus by a combination of several qualitative and quantitative morphological traits. Key diagnostic features include: presence of a pronounced post-anal swelling in the hermaphrodite; male with nine pairs of bursal rays, with pairs 4 and 7 bent outwards and one pair of papillae placed on the cloacal opening, value of D% (average: 79); infective juveniles with a well developed cuticular tooth, long tail (average: 105mum) and values of D% (average: 90) and E% (average: 99). In addition to these diagnostic characters, cross-hybridization tests between the new species with H. bacteriophora and H. mexicana yielded no fertile progeny. Comparison of ITS rDNA sequences with other available sequences of described species depicted the two isolates as a new species. Phylogenetic analysis of these sequence data placed H. sonorensis n. sp. as a member of the indica-group.

Steinernema costaricense n. sp. and S. puntauvense n. sp. (Rhabditida: Steinernematidae), two new entomopathogenic nematodes from Costa Rica.

Steinernema costaricense n. sp. and S. puntauvense n. sp. were recovered during a survey for native entomopathogenic nematodes in Costa Rica. Morphological data, molecular (28S rDNA sequence data) studies and cross-hybridisation tests were used for diagnostic and identification purposes. Additionally, 28S rDNA sequence data were used to assess the evolutionary relationships of the new species with other Steinernema spp. Morphological diagnostic features for S. costaricense n. sp. include: the body size of the infective juvenile (av. 1,696); the presence of protruding 'horn-like' cephalic papillae; the position of the excretory pore in the infective juvenile (av. 77 microm) and the first generation male (av. 117 microm); the D% value of the infective juvenile (av. 53) and the first generation male (av. 56); the E% value of the infective juvenile (av. 85); and the morphology of the spicules and gubernaculum of the first generation male. Diagnostic traits for S. puntauvense n. sp. are: the position of the excretory pore in the infective juveniles (av. 25 microm); the shape and size of the spicules and gubernaculum of the first generation male; and the shape of the tail of the first generation female. In addition to these traits, 28S rDNA sequences analysis and hybridisation tests showed that both new Steinernema species are distinct and unique entities.

First record of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) in Costa Rica.

A survey of entomopathogenic nematodes was conducted in the north Pacific (Guanacaste Conservation Area) and southeast Caribbean (Gandoca-Manzanillo Natural Refuge) regions of Costa Rica. Out of a total of 41 soil samples, 5 were positive for entomopathogenic nematodes (20.5%), with 3 (12.3%) containing Steinernema and 2 (8.2%) Heterorhabditis isolates. Morphological and molecular studies were undertaken to characterize these isolates. The Heterorhabditis isolates were identified as Heterorhabditis indica and the three Steinernema isolates were identified as two new undescribed species. H. indica was recovered from a coastal dry forest. Steinernema n. sp. 1 was isolated from a rainforest valley, between volcanoes. Steinernema sp. n. 2 was isolated from sand dunes in the Caribbean Coast (Punta Uva) near the rainforest strip along the coast. Although limited to two geographic regions, this study suggests entomopathogenic nematodes may be diverse and perhaps widely distributed in Costa Rica. A more intensive survey, covering all geographic regions is currently undergoing.

Thirst and vasopressin secretion counteract dehydration in newborn infants.

OBJECTIVE AND STUDY DESIGN: Our goal was to study the water balance in healthy breast-fed infants (n = 139) during their first 5 days, by cross-sectional measurements of body weight, serum sodium, serum osmolality, and hematocrit. We also investigated infants' capacity to conserve body water by increased secretion of vasopressin, the main antidiuretic hormone in human beings. RESULTS: The maximal body weight reduction was 5.7% +/- 1.7% (mean +/- SD) of birth weight and most infants started to gain weight when they were 3 days old. The serum sodium level at 16 +/- 4 hours (on day of birth) was 142 mmol/L; the level increased after 1 day (p < 0.01) and remained constantly high for the following 2 days (p < 0.05). The serum osmolality was increased at 1 day (p < 0.01) and 2 days (p < 0.05) compared with the value on the day of birth (296 mOsm/kg). The plasma vasopressin level was constant up to 24 hours (1 day), but decreased during the next 2 days (p < 0.01). Infants with body weight reduction exceeding 10% (n = 15) had a further elevation of the serum sodium level (p < 0.0001) and serum osmolality (p < 0.0001), and the plasma vasopressin level was twofold higher (p < 0.0001) compared with corresponding levels in infants with less weight reduction. These infants also had a reduced interval between two subsequent feedings (p < 0.001). The hematocrit remained unchanged irrespective of the degree of weight reduction. CONCLUSIONS: When the reduction of body weight exceeds 10%, the newborn infant releases vasopressin in response to fluid hypertonicity. This state also affects feeding behavior, perhaps as an expression of thirst. It is likely that hormone release is also stimulated in parallel with a weight reduction of less than 10%, because it is also accompanied by a hyperosmotic state.