Populations of Prosopis glandulosa var. torreyana in the Chihuahuan desert have a fixed dimorphic system of nectar production in which half the individuals produce nectar (are nectarful) and the ...other half are nectarless. We analyzed the impact of nectar production on different estimates of fitness, comparing nectarful against nectarless individuals in size, mating system, seed traits, and fruit set in a 1-ha scrubland. Of the reproductive individuals (358), 46% were nectarful and 54% were nectarless. Neither tree size nor flowering phenology differed between nectar morphs. Fixation indices (F) for both progeny (F = -0.2) and adults (F = -0.45) were negative, and high heterozygosities were found in adults and progeny (H = 0.45). No differences were found between nectar morphs for F, H, and single (t(s) = 1.1) and multilocus (t(m) = 1.03) outcrossing rates. Controlled pollinations showed differences between selfing and control treatments with no differences between nectar morphs. Nectarless individuals produced significantly more pollen grains than did nectar producers, but all other measured floral traits showed no differences. Nectarful trees were visited by pollinators 21 times more often and had a significantly higher overall fruit set than did nectarless trees. No differences between nectar morphs in seed mass or in percentage seed germination were found, but heavier seeds tended to have higher heterozygosities. Both morphs had similar success as females, but nectarless trees had approximately approximately 7% higher male function. We discuss three possible scenarios for the evolution of the fixed dimorphism in nectar production, two involving unstable phases (substitution of one morph by the other, and evolution towards dioecy) and one stable scenario (maintenance of the dimorphic system).
We report the frequency of 3 globose cacti (Mammillaria carnea, M. haageana, and Coryphantha pallida) associated with nurse plants or bare areas and assess the size of plants in each site. We found 3 ...times more cacti established beneath nurse plants than in bare areas, and all cacti species were the same size when associated with shrub cover or bare areas. Under a plant canopy, the size structure was pyramidal, whereas in bare areas, individuals were found isolated with an even size structure, and few small plants were recorded. There was a positive relationship between the type of shrub cover and the associated globose cacti. We found more individuals of all 3 species of cacti associated with Prosopis laevigata than with Mimosa luisana, but size structure was similar between them. We discuss 2 possible scenarios that may result from the nurse-protégé interaction. /// Registramos la frecuencia de establecimiento do tres cactáceas globossas (Mammillaria carnea, M. haageana y Coryphantha pallida) asociadas con plantas nodriza y en áreas rasas y evaluamos el tamaño de las plantas en cada sitio. Encontramos 3 veces más cactáceas establecidas debajo de plantas nodriza que en áreas rasas, y todas las especies de cactáceas fueron del mismo tamaño cuando se asociaron con áreas cubiertas de arbustos o con áreas rasas. Bajo la cubierta de las plantas, el tamaño estructural fue piramidal, mientras que en áreas rasas, se encontraron individuos aislados con un tamaño estructural parejo y se registration pocas y pequeñas plantas. Hobo una relación positivia entre el tip de cubierta de arbusto y la cactácea globosa asociada. Encontramos más individuos de las tres especies de cactaáceas asociadas con Prosopis laevigata que con Mimosa luisana, pero el tamaño estructural fue similar entre ellas. Discutimos 2 posibles escenarios que pueden resultar de la interacción entre nodriza y protegido.
Since gastric acid is an important luminal factor in the absorption of non-heme iron, the effect of omeprazole on the absorption of iron in a rat model was studied. Iron absorption studies were ...performed on rats on a normal diet (N = 42) and rats fed an iron-deficient diet (N = 43) for three weeks. Rats were orally dosed with 40 mumol/kg of omeprazole or placebo daily for two days prior to iron absorption studies. Rats were orally dosed with 1 mmol of ferrous chloride, ferric chloride or food iron (dietary suspension) containing 11 micrograms of iron and labeled with 1 microCi of 59Fe. Omeprazole-treated rats on the normal diet had no significant reduction in the absorption of ferric, ferrous, or food iron. In the rats on the iron-deficient diet, the absorption of ferrous iron decreased from 76 +/- 7.5% (mean +/- SE) in control rats to 38 +/- 8.5% in the omeprazole-treated rats (P less than 0.003) and the absorption of food iron decreased from 65 +/- 7.5% in control rats to 37 +/- 6.5% in the omeprazole-treated rats (P less than 0.016). There was no significant reduction in the absorption of ferric iron. Omeprazole therapy is unlikely to be associated with significant iron malabsorption in normal patients but may reduce iron absorption in pathological states associated with increased iron absorption such as iron deficiency.
Seed dormancy and endozoochorous dispersal have important effects on population dynamics, i.e. seed bank formation, spatial and temporal bet-hedging, avoidance of crowding and decreased ...sib-competition. Seeds having primary dormancy do not germinate, even if adequate environmental and dispersal conditions are met, until an after-ripening period is completed. This study examined the effects on germination rates of seed dispersal by vertebrates and primary dormancy (i.e. how germination rates changed in time) in the prickly pearOpuntia rastrerafrom the southern Chihuahuan Desert. Ripe fruits, scats of coyote, mule deer, woodrat, common pig and pellets of the northern raven were collected in 1992 during the ripe fruit peak (August). A factorial design was used to assess the effect of disperser and seed age on germination rates using these seeds collected in 1992. In 1992, 1993 and 1994 (fresh, 1- and 2-year-old seeds, respectively) germination success after 3 months was determined for 100 seeds of each disperser, plus a control of uneaten seeds. We found differences in germination rates both between dispersers and years. All but one disperser (deer) decreased germination rates with respect to the control. Germination steadily increased with ageing of seeds, implying the presence of primary dormancy (embryo immaturity). Our results show that despite the large disperser coterie associated withOpuntia rastrera, seeds have an obligate primary dormancy which seems to result in seed bank formation. Seed germination and seedling establishment will depend on selection pressures caused mainly by environmental variability in deserts (unpredictable rainfall, extreme temperatures, safe-site availability). Nevertheless, endozoochorous dispersal provides some additional advantages (e.g. habitat colonization, genetic variability, avoidance of long-term local extinction) that needs further research.
Reproductive Biology of Cactaceae Mandujano, María del Carmen; Carrillo-Angeles, Israel; Martínez-Peralta, Concepción ...
Desert Plants
Book Chapter
Floral biology in the Cactaceae represents a new field of research, with only 2% of approximately 2,000 species having been studied. Studies on breeding systems cover functional and morphological ...floral traits of sexual expression, while research on mating (hybridization) systems includes experiments on pollination, morphological and functional floral traits vis-à-vis estimation of out-crossing rates, and inbreeding depression. Most cacti are hermaphroditic with some exceptions of dioecy. Herkogamy and dichogamy seem to be common, and are coupled with self-incompatibility and inbreeding depression as mechanisms to avoid selfing; these traits are important in guiding the evolution of mating (fertilization) systems from mixed to mainly either out-crossing or selfing in all three subfamilies. We found no clear pattern between mating systems and genetic diversity. The impressive variety of fertilization and breeding systems, as well as the genetic diversity within Cactaceae highlights the complex evolution of this family and the plasticity of their reproductive response to the spatially and temporally unpredictable habitats in which they occur. This chapter reviews information on the floral biology, pollinators and genetics of Cactaceae, covering about 70 references: 36% on genetics, 43% on different aspects of pollination ecology, and 21% on diverse subjects with limited descriptions.
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