RESUMO
So far, six species of Oxeoschistus Butler, including its junior synonym Dioriste Thieme, were listed from Central America, with five of them from Costa Rica alone, which appears to represent the highest regional diversity of this Neotropical montane butterfly genus. Our research based on field work, morphological studies and barcode analysis proved that one record is a misunderstanding perpetuated in scientific literature for over a century: Oxeoschistus cothonides Grose-Smith is identified here as an individual form of the female of O. cothon Salvin. The presence of Oxeoschistus tauropolis (Westwood) in Costa Rica, subject to some controversy, is confirmed, and a new local subspecies is described from Costa Rica, O. tauropolis mitsuko Pyrcz & Nakamura n. ssp. Specific status of O. euriphyle Butler is reinstated based on morphological and molecular data. A new subspecies O. hilara lempira Pyrcz n. ssp. is described from Honduras. O. puerta submaculatus Butler is reported for the first time from the Darién region on the Panama-Colombia border. Species relationships are preliminarily evaluated based on COI data concluding, among others, that O. hilara and O. euriphyle are less closely related than previously assumed. Altitudinal and distributional data are revised, and ecological and behavioural information of all the species of Central American Oxeoschistus is provided.
Assuntos
Distribuição Animal , Borboletas/classificação , Floresta Úmida , Animais , Borboletas/anatomia & histologia , Colômbia , Costa Rica , Feminino , Masculino , Panamá , FilogeniaRESUMO
Arhuaco Adams & Bernard (1977) is one of the least known genera of Neotropical Satyrinae. It comprises two species and presents an unusual disjunct distribution, with A. ica Adams & Bernard (1977), endemic to the isolated Colombian Sierra Nevada de Santa Marta, and A. dryadina (Schaus 1913) found in the mountains of Costa Rica and Panama. Here, the female of A. dryadina is described, and a new generic diagnosis is presented. Affinities with other genera of the subtribe Pronophilina, in particular the potential closest relatives, such as Pronophila Doubleday (1849), are investigated based on morphological, molecular, ecological, and behavioral data. Results from molecular and morphological sources are incongruent. Molecular data indicate that Arhuaco is paraphyletic, with A. dryadina segregating within the Pronophila clade. Morphological data, by contrast, indicate a closer affinity between the two species currently placed in Arhuaco, favoring the monophyly of the genus, and show no consistent synapomorphies for Arhuaco + Pronophila. A vicariance biogeographical scenario is evaluated.
Assuntos
Borboletas/anatomia & histologia , Borboletas/classificação , Filogenia , Animais , Colômbia , Costa Rica , DNA Mitocondrial/genética , Ecossistema , Feminino , Masculino , PanamáRESUMO
The genus Praepedaliodes Forster, 1964, the only representative of the mega-diverse mostly Andean Pedaliodes complex lineage in the Brazilian Atlantic Forest, is revised. Prior to this study, four species were known, P. phanias (Hewitson, 1862), P. granulata (Butler, 1868), P. amussis (Thieme, 1905) and P. exul (Thieme, 1905). Here, a further six are described, all from SE Brazil, expanding to 10 the number of species in this genus. Lectotypes are designated for P. phanias, P. granulata and P. amussis. The genus is most diverse in the Serra da Mantiqueira (São Paulo, Rio de Janeiro, Minas Gerais) and in the Serra Geral (Paraná, Santa Catarina) with seven species occurring in both ranges. Praepedaliodes phanias is the most widespread species and the only one found in the western part of the Atlantic Forest; only this species and P. duartei Dias, Dolibaina & Pyrcz n. sp. occurring to near sea level. Other species, P. zaccae Dolibaina, Dias & Pyrcz n. sp., P. francinii Freitas & Pyrcz n. sp., P. sequeirae Pyrcz, Dias & Dolbaina n. sp., P. landryi Pyrcz & Freitas n. sp. and P. pawlaki Pyrcz & Boyer n. sp. are strictly montane and the highest species richness is reached at 1400-1800 m. One species, P. sequeirae n. sp., is a narrow endemic found only at timberline in the Agulhas Negras massif above 2300 m. Immature stages are described for two species, P. phanias and P. landryi n. sp. Molecular data (barcode region of cytochrome oxidase, subunit I) and adult morphology, including male and female genitalia, support the genus as monophyletic, belonging to a predominantly Andean clade of the Pedaliodes Butler, 1867 complex. Morphological evidences, in particular female genitalia comparative analysis, indicate the genera Physcopedaliodes Forster, 1964 and Panyapedaliodes Forster, 1964 as possibly the closest relatives to Praepedaliodes. Molecular data are inconclusive in this respect.
Assuntos
Borboletas/anatomia & histologia , Borboletas/classificação , Animais , Brasil , Feminino , Florestas , Masculino , FilogeniaRESUMO
The butterfly genus Forsterinaria Gray is the only strictly montane representative of the diverse Neotropical subtribe Euptychiina (Nymphalidae, Satyrinae), with 24 described species. Recent research in some of the most isolated and highly diverse Andean regions, such as central Peru, show that its total species richness is still underestimated. An example is the new species described here, Forsterinaria emo n. sp., which is particularly interesting because of an unusual structure discovered in its male genitalia which consists of a bunch of bristle-like processes, composing a fringe-like formation on the dorsum of the tegumen. No similar, homologous structure was found in any congener, nor indeed, in any species of diurnal Lepidoptera. Scanning electron microscope studies revealed that the microstructure of the processes resembles a membrane lining the tegumen. Its function is unknown but two hypotheses are discussed based on a comparative study with other genital structures of butterflies. We argue that it may help stabilizing the partners in the process of mating or it may serve as a 'mating plug', preventing the female from multiple copulations.
Assuntos
Borboletas/classificação , Animais , Borboletas/anatomia & histologia , Copulação , Feminino , Genitália Masculina , MasculinoRESUMO
Protein restriction impairs the salivary flow rate and composition in human and rats. The aim of the present work was to establish the effect of low protein (casein 5%) and protein free (casein 0%) isocaloric diets on sympathetic activity and salivary evoked secretion in the submandibular gland (SMG) of the rat. After 21 days, rats fed casein 0% presented: (a) a significant shift to the left of the dose-response curves (DRC) to the autonomic agonists-norepinephrine (NE), methoxamine, isoproterenol (ISO) and methacholine; (b) increased food consumption (p<0.001); (c) decreased body (p<0.001) and SMG (p<0.001) weights maintaining SMG/body (w/w) relation; (d) enhanced submandibular alpha1-adrenoceptor number without changes in the apparent dissociation constant (Kd); (e) increased submandibular NE content (p<0.05) and phosphoinositoside hydrolysis (p<0.001); (f) decreased submandibular tyrosine hydroxylase activity (TH) (p<0.01). Casein 5% feeding increased food consumption (p<0.01) and reduced body weight (p<0.05). This protein restriction increased metacholine-evoked salivation, but it altered neither submandibular sympathetic activity nor sympathetic-induced salivary secretion as compared to the Control group (C) fed a similar diet containing 25.5% protein. Present results suggest that in the adult rat, a protein free diet during 21 days lowers SMG sympathetic and cholinergic activity leading to supersensitivity as revealed by up-regulation of alpha1-adrenergic receptor number and increased autonomic-evoked salivation.
Assuntos
Caseínas/administração & dosagem , Dieta com Restrição de Proteínas , Desnutrição Proteico-Calórica/metabolismo , Salivação/efeitos dos fármacos , Glândula Submandibular/metabolismo , Sistema Nervoso Simpático/fisiologia , Agonistas alfa-Adrenérgicos/farmacologia , Agonistas Adrenérgicos beta/farmacologia , Animais , Biomarcadores/análise , Caseínas/metabolismo , Agonistas Colinérgicos/farmacologia , Isoproterenol/farmacologia , Masculino , Cloreto de Metacolina/farmacologia , Metoxamina/farmacologia , Modelos Animais , Fosfatidilinositóis/metabolismo , Distribuição Aleatória , Ratos , Ratos Wistar , Glândula Submandibular/efeitos dos fármacos , Sistema Nervoso Simpático/efeitos dos fármacos , Tirosina 3-Mono-Oxigenase/análise , Tirosina 3-Mono-Oxigenase/metabolismoRESUMO
Nutritional status as well as energy and protein intake are critical regulators of IGF-1 and IGFBP-3 and contribute to the modulation of bone remodeling and formation. The purpose of this study was to investigate on an experimental model with nutritional dwarfing (ND), whether the alterations on body growth velocity, energy metabolism and body composition could affect serum concentrations of IGF-1 and IGFBP-3 and bone (tibiae and mandible) histology and histomorphometry. Twenty-one male weanling Wistar rats (body weight = 38.20 +/- 0.94 g) were randomized to three groups: seven of them were killed at day = 0 (CO, n = 7); control (C, n = 7); and experimental 80 (E80, n = 7). During 4 weeks, C was fed ad libitum with a 1:1 carbohydrate to fat diet. E80 was being underfed with the same diet by 80% and the following parameters were measured: weight (Wt) for length (L) ratio z-score; oxygen consumption (VO2); body composition (BC) by EM-SCAN SA 3000. At t = 28, E80 and C were killed. Serum IGF-1 and IGFBP-3 and bone histology and histomorphometry were performed on C0, E80 and C. E80 showed Wt for L z-score between lean and adequate, a decrease in VO2 according to body proportions, a BC of a delayed puberty individual, IGF-1 and IGFBP-3 decreased by 56 and 53%, respectively. Tibiae's hematopoyetic and adipose bone marrow areas were combined, with sealing trabeculae on metaphyseal areas. This study suggests that there is a relationship among growth deceleration in ND rats and structural alterations on tibiae.
Assuntos
Osso e Ossos/metabolismo , Nanismo/etiologia , Distúrbios Nutricionais/complicações , Animais , Composição Corporal , Nanismo/metabolismo , Nanismo/patologia , Metabolismo Energético , Proteína 3 de Ligação a Fator de Crescimento Semelhante à Insulina/sangue , Fator de Crescimento Insulin-Like I/análise , Masculino , Mandíbula/metabolismo , Mandíbula/patologia , Distúrbios Nutricionais/metabolismo , Distúrbios Nutricionais/patologia , Ratos , Ratos Wistar , Tíbia/metabolismo , Tíbia/patologiaRESUMO
Since no data are available to characterize mandibular growth in nonorganic nutritional dwarfing (ND), the purpose of the present study was to describe the effects of a diet on mandible and femur growth in a nutritional dwarfish animal model. Male Wistar rats were divided into two groups of 10 animals each: Control (C) and Experimental (E80: diet-restricted group). C rats were fed a standard diet ad libitum. E80 rats received 80% of the amount of standard diet eaten by group C. Food intake and body weight (Wt) and length (Lt) were recorded periodically. Growth data (Wt and Lt) were expressed as a Z-score of weight-for-length (WLZ) ratio, an index of body size. Five animals of each group were selected at random at 4 and 8 weeks and sacrificed. Additionally at t = 0, 5 animals were sacrificed for baseline measurements. Mandibular growth was estimated directly on the right mandible by measuring ten dimensions. Femur growth was estimated from Wt and Lt measurements of the bone. Mandibular weight, area, length and height were negatively affected by dietary restriction during the first 4 weeks of the experimental period. Mandibular growth ceased after this point. Dimensions corresponding to the alveolar unit did not change with time. However, all other dimensions were negatively influenced but not to the same extent. Femur rather than mandibular weight was severely affected. Therefore, the negative effects of the nutritional stress that occurs after weaning would be stronger for the femur, than for the mandible. Femur length was also negatively affected by suboptimal nutrition. In summary, the results of the present study showed that mandible and femur growth respond differently to mild chronic food restriction. These observations could be explained in terms of the different critical bone growth periods and of the time at which nutritional stress was imposed.
Assuntos
Desenvolvimento Ósseo , Mandíbula/crescimento & desenvolvimento , Desnutrição Proteico-Calórica/fisiopatologia , Animais , Nanismo/fisiopatologia , Ingestão de Energia , Fêmur/crescimento & desenvolvimento , Masculino , Ratos , Ratos Wistar , DesmameRESUMO
Since no data are available to characterize mandibular growth in nonorganic nutritional dwarfing (ND), the purpose of the present study was to describe the effects of a diet on mandible and femur growth in a nutritional dwarfish animal model. Male Wistar rats were divided into two groups of 10 animals each: Control (C) and Experimental (E80: diet-restricted group). C rats were fed a standard diet ad libitum. E80 rats received 80
of the amount of standard diet eaten by group C. Food intake and body weight (Wt) and length (Lt) were recorded periodically. Growth data (Wt and Lt) were expressed as a Z-score of weight-for-length (WLZ) ratio, an index of body size. Five animals of each group were selected at random at 4 and 8 weeks and sacrificed. Additionally at t = 0, 5 animals were sacrificed for baseline measurements. Mandibular growth was estimated directly on the right mandible by measuring ten dimensions. Femur growth was estimated from Wt and Lt measurements of the bone. Mandibular weight, area, length and height were negatively affected by dietary restriction during the first 4 weeks of the experimental period. Mandibular growth ceased after this point. Dimensions corresponding to the alveolar unit did not change with time. However, all other dimensions were negatively influenced but not to the same extent. Femur rather than mandibular weight was severely affected. Therefore, the negative effects of the nutritional stress that occurs after weaning would be stronger for the femur, than for the mandible. Femur length was also negatively affected by suboptimal nutrition. In summary, the results of the present study showed that mandible and femur growth respond differently to mild chronic food restriction. These observations could be explained in terms of the different critical bone growth periods and of the time at which nutritional stress was imposed.
RESUMO
Since no data are available to characterize mandibular growth in nonorganic nutritional dwarfing (ND), the purpose of the present study was to describe the effects of a diet on mandible and femur growth in a nutritional dwarfish animal model. Male Wistar rats were divided into two groups of 10 animals each: Control (C) and Experimental (E80: diet-restricted group). C rats were fed a standard diet ad libitum. E80 rats received 80
of the amount of standard diet eaten by group C. Food intake and body weight (Wt) and length (Lt) were recorded periodically. Growth data (Wt and Lt) were expressed as a Z-score of weight-for-length (WLZ) ratio, an index of body size. Five animals of each group were selected at random at 4 and 8 weeks and sacrificed. Additionally at t = 0, 5 animals were sacrificed for baseline measurements. Mandibular growth was estimated directly on the right mandible by measuring ten dimensions. Femur growth was estimated from Wt and Lt measurements of the bone. Mandibular weight, area, length and height were negatively affected by dietary restriction during the first 4 weeks of the experimental period. Mandibular growth ceased after this point. Dimensions corresponding to the alveolar unit did not change with time. However, all other dimensions were negatively influenced but not to the same extent. Femur rather than mandibular weight was severely affected. Therefore, the negative effects of the nutritional stress that occurs after weaning would be stronger for the femur, than for the mandible. Femur length was also negatively affected by suboptimal nutrition. In summary, the results of the present study showed that mandible and femur growth respond differently to mild chronic food restriction. These observations could be explained in terms of the different critical bone growth periods and of the time at which nutritional stress was imposed.
RESUMO
Catch-up growth has been defined as growth with a velocity above the statistical limits of normality for age during a defined period of time which follows a period of impaired growth. Since no data are available on catch-up in mandibular growth, the present study was designed to estimate the dynamics of the mandibular size after short-term dietary protein restriction in rats during the post-weaning period. Weanling male rats, 22 d of age, were divided into two groups, control (C) and experimental (E). E rats were fed a protein-free diet during the first 10 d; from this time on, they were placed on a 20% protein diet, as were C rats during the entire experimental period, which lasted 70 d. Five rats from both groups were randomly selected every 10 d and sacrificed. Mandibular growth was estimated directly on the right mandible by measuring several dimensions (mandibular area, base length, mandibular height, mandibular length, alveolar length and incisor alveolar process length). Alveolar and incisor alveolar process lengths did not change with age or dietary protein. All other dimensions increased with age and were thus negatively affected by protein restriction. After growth restriction ceased, the rate of increase of all affected dimensions was above normal values and deficits were swiftly eliminated. Since age-independent dimensions compose roughly the anterior portion of the mandible, this portion of the bone was not affected by protein restriction. It was, thus, the posterior part of the mandible which stopped growth during the nutritional insult and showed catch-up during nutritional rehabilitation. In summary, the rat mandible has a high potential for catch-up during the post-weaning period, showing the ability to achieve complete catch-up in about 30 d.
Assuntos
Dieta com Restrição de Proteínas , Proteínas Alimentares/administração & dosagem , Mandíbula/crescimento & desenvolvimento , Distúrbios Nutricionais/fisiopatologia , Fatores Etários , Processo Alveolar/anatomia & histologia , Processo Alveolar/crescimento & desenvolvimento , Análise de Variância , Animais , Cefalometria , Proteínas Alimentares/uso terapêutico , Masculino , Mandíbula/anatomia & histologia , Distúrbios Nutricionais/terapia , Distribuição Aleatória , Ratos , Ratos Wistar , Fatores de Tempo , DesmameRESUMO
Malnutrition is one of the most important causes of normal growth disruption. Anthropometric methods are highly valuable in clinic pediatric diagnosis to determine the nutritional status of children and as recovery monitoring. In previous studies, we have demonstrated that the standards weight-age, height-age and weight-height of growing rats had similar distribution to those in normal children. However, to improve the diagnostic effectiveness of anthropometric information, statistical analysis to normally and non-normally distributed variables should be applied. One hundred Wistar rats (50 male and 50 female rats) from weaning (day = 25, weight = 35-40 g) to 70 days of age were fed with a commercial diet. Water and diet were offered "ad libitum". Body weight and height were recorded every two or four days, respectively. Percentiles of weight vs age, height vs age and weight vs height were plotted for male and female rats. The statistical criterion for classifying the anthropometric measurements into nutritional categories was based on percentiles cutoff and Z-score. The Z-score was calculated according to: Z = (standard mean value-subject value/standard deviation of standard). The statistical anthropometric categories of growing rats were similar to those obtained in children. This evidence suggest that the rat can be used as an experimental model to infer and predict the nutritional response in children.
Assuntos
Antropometria/métodos , Crescimento/fisiologia , Ratos Wistar/crescimento & desenvolvimento , Animais , Peso Corporal , Feminino , Masculino , Estado Nutricional , RatosRESUMO
UNLABELLED: Nutritional dwarfing (ND) is the result of nonorganic causes reflective of a voluntary or unintentional reduction in food intake, inappropriate eating behavior, dissatisfaction with body weight or unhealthy approaches toward weight control. Patients with ND have reached an equilibrium between their genetic growth potential and their nutritional intake. This study was undertaken to compare on a growing rat model the metabolic alterations in terms of substrate utilization (SU), oxygen consumption (VO2) and growth rate velocity. Twenty male weanling Wistar rats were randomized to 3 groups: control (C), experimental 4 (E4) and 8 (E8). C was fed "ad libitum" with a stock diet, E4 and E8 were underfed by 80% of the requirements during four or eight weeks, respectively. During the depletion phase the following measurements were performed: 1a) body weight (Wt), 1b) length, 1c) Weight for Length ratio z-score, 2) Body composition (BC) by EM-SCAN Tobec Model 3 000, Springfield. USA, 3) VO2 by indirect calorimetry, ECO-OXYMAX. RESULTS: 1) wt for length was -0.70 +/- 0.43 for E4 (t = 4 weeks) and 1.44 +/- 0.32 for E8 (t = 8 weeks), 2% of fat mass was within the normal range, 3) VO2 was not significantly different between groups. Chronic suboptimal nutrition (80%) decreased growth velocity which was the sole manifestation of nutritional inadequacy.
Assuntos
Nanismo/etiologia , Metabolismo Energético , Distúrbios Nutricionais/complicações , Animais , Composição Corporal , Crescimento , Masculino , Estado Nutricional , Ratos , Ratos WistarRESUMO
OBJECTIVE: The purpose of our study was to assess the influence of different levels of calcium (Ca) in a diet containing 30% protein on the rehabilitated of the body size from protein-energy malnutrition (PEM) and to establish the optimal Ca/protein ratio for attaining a normal body composition. METHODS: Weanling female Wistar rats were fed with protein-free diet up to a weight deficit of 20 +/- 1%. Then they were arranged in groups (TO) and fed diets with 30% protein and 0.0, 0.2, 0.4, 0.6, 0.9 or 1.2% Ca for 28 days (T28). Food and deionized water were given ad libitum. Body weight and length were recorded every 3 days. At T28, the animals were sacrificed to determine femur composition. RESULTS: At T13, weight-for-age (W/A) was within the normal range for rats consuming > or = 0.6% Ca. At T28 all groups showed adequate W/A. Although length-for-age was adequate during rehabilitated period, rate of weight gain improved when Ca was > or = 0.6%. Femur length did not show significant difference between groups. Total femur Ca content and mg Ca/g of dry-weight tissue increased with increments in dietary Ca concentration and tended to plateau with 0.4% Ca. Ca/P ratio reached the highest value with 0.9% Ca. CONCLUSIONS: Our findings indicate that at a dietary protein level of 30% the Ca/protein ratio is a limiting factor in attaining of normal body size; this is achievable when Ca concentration is 1.2% and the Ca/protein ratio is 0.04.
Assuntos
Composição Corporal , Constituição Corporal , Cálcio da Dieta/administração & dosagem , Desnutrição Proteico-Calórica/reabilitação , Envelhecimento , Animais , Peso Corporal , Cálcio/análise , Proteínas Alimentares/administração & dosagem , Feminino , Fêmur/anatomia & histologia , Fêmur/química , Ratos , Ratos WistarRESUMO
OBJECTIVE: We sought to determine the prematurity rate in infants of HIV-positive mothers and to characterize the incidence and severity of neonatal respiratory disease in this population. STUDY DESIGN: From 1990 to 1994, 600 live-born infants of HIV-infected mothers were enrolled prenatally (73%) or postnatally (27%) from five U.S. centers. Logistic regression was used to determine the association of HIV status in the infant with prematurity (< or = 37 weeks), low birth weight (< or = 2.5 kg), and very low birth weight (< or = 1.5 kg) rates. The incidence of respiratory distress syndrome (RDS), bronchopulmonary dysplasia, meconium aspiration syndrome, and neonatal pneumonia was compared with anticipated rates for gestational age and birth weight. RESULTS: Very high rates of prematurity (19%), low birth weight (18.3%), and very low birth weight (3.3%) were found in the infants of HIV-positive mothers; and HIV infection in the infant was associated with younger gestational age. The overall incidence of RDS was 3% (17/600), which coincided with the anticipated rate, after adjusting for prematurity and birth weight. Only five infants (all < or = 1.5 kg) had bronchopulmonary dysplasia, and none required assisted ventilation beyond 14 days. Three term infants had mild meconium aspiration syndrome, and there were no cases of documented neonatal pneumonia. CONCLUSION: Infants born to HIV-positive mothers exhibited high prematurity and low birth weight rates, and the odds of prematurity were higher in infants who were infected with HIV. Despite the high incidence of prematurity and perinatal risk of this population, incidence and severity of neonatal respiratory disease were not higher than would be expected from available neonatal data in populations not exposed to HIV.
Assuntos
Displasia Broncopulmonar/epidemiologia , Soropositividade para HIV/epidemiologia , Recém-Nascido Prematuro , Síndrome de Aspiração de Mecônio/epidemiologia , Pneumonia/epidemiologia , Complicações Infecciosas na Gravidez/epidemiologia , Efeitos Tardios da Exposição Pré-Natal , Síndrome do Desconforto Respiratório do Recém-Nascido/epidemiologia , Adulto , Estudos de Coortes , Feminino , Humanos , Incidência , Recém-Nascido de Baixo Peso , Recém-Nascido , Recém-Nascido de muito Baixo Peso , GravidezRESUMO
The present study was performed to determine the stage of the erythropoietic pathway which is affected by starvation or protein deprivation and whose manifestation is a depressed response to exogenous erythropoietin (EPO). The response to recombinant human EPO was measured in post-hypoxic polycythemic mice by determination of 59Fe uptake into red cells, spleen and femur and/or erythroid colony forming units (CFU-E) and erythroid precursor cell concentrations in femoral marrow. Experimental mice were either starved or fed one of seven different diets whose protein (casein) content ranged from 0 to 20%. All diets were isocaloric. The response of mice maintained on the standard diet (Purina Lab chow) was taken as the normal one. Starvation during the 48-hour period immediately before EPO injection had no effect on the response to the hormone. Starvation, and protein deprivation to a lesser extent, during the 48-hour period following EPO, on the other hand, significantly reduced the response. There was a progressive increase in the response as the casein content of the diet was increased. A normal response was observed when dietary casein concentration was 10%. These findings indicate that nutritional deprivation or dietary protein alterations during the period immediately following EPO injection in polycythemic mice can have detrimental effects on the erythroid response in a model in which nutritional deprivation was relatively short and acute. They also indicate that the subnormal response is not due to a decreased size of the erythroid progenitor pool available for differentiation but to deficient rates of differentiation of erythropoietic units.