Characterization of calcium oxalates generated as biominerals in cacti.
The chemical composition and morphology of solid material isolated from various Cactaceae species have been analyzed. All of the tested specimens deposited high-purity calcium oxalate crystals in their succulent modified stems. These deposits occurred most frequently as round-shaped druses that sometimes coexist with abundant crystal sand in the tissue. The biominerals were identified either as CaC(2)O(4).2H(2)O (weddellite) or as CaC(2)O(4).H(2)O (whewellite). Seven different species from the Opuntioideae subfamily showed the presence of whewellite, and an equal number of species from the Cereoideae subfamily showed the deposition of weddellite. The chemical nature of these deposits was assessed by infrared spectroscopy. The crystal morphology of the crystals was visualized by both conventional light and scanning electron microscopy. Weddellite druses were made up of tetragonal crystallites, whereas those from whewellite were most often recognized by their acute points and general star-like shape. These studies clearly demonstrated that members from the main traditional subfamilies of the Cactaceae family could synthesize different chemical forms of calcium oxalate, suggesting a definite but different genetic control. The direct relationship established between a given Cactaceae species and a definite calcium oxalate biomineral seems to be a useful tool for plant identification and chemotaxonomy. (+info)
Benefits and costs of mutualism: demographic consequences in a pollinating seed-consumer interaction.
Interspecific interactions can affect population dynamics and the evolution of species traits by altering demographic rates such as reproduction and survival. The influence of mutualism on population processes is thought to depend on both the benefits and costs of the interaction. However, few studies have explicitly quantified both benefits and costs in terms of demographic rates; furthermore there has been little consideration as to how benefits and costs depend on the demographic effects of factors extrinsic to the interaction. I studied how benefits (pollination) and costs (larval fruit consumption) of pollinating seed-consumers (senita moths) affect the reproduction of senita cacti and how these effects may rely on extrinsic water limitation for reproduction. Fruit initiation was not limited by moth pollination, but survival of initiated fruit increased when moth eggs were removed from flowers. Watered cacti produced more flowers and initiated more fruit from hand-pollinated flowers than did unwatered cacti, but fruit initiation remained low despite excess pollen. Even though water, pollination and larvae each affected a component of cactus reproduction, when all of these factors were included in a factorial experiment, pollination and water determined rates of reproduction. Counter-intuitively, larval fruit consumption had a negligible effect on cactus reproduction. By quantifying both benefits and costs of mutualism in terms of demographic rates, this study demonstrates that benefits and costs can be differentially influential to population processes and that interpretation of their influences can depend on demographic effects of factors extrinsic to the interaction. (+info)
Allozyme diversity and genetic structure of the leafy cactus (Pereskia guamacho [Cactaceae]).
We examined levels of genetic variation and genetic structure in the leafy cactus (Pereskia guamacho) in arid and semiarid zones in Venezuela. We surveyed genetic diversity within 17 populations using 19 allozyme loci. Genetic diversity was relatively high at both the species (P(s) = 89%, A(s) = 3.26, AP(s) = 3.53, H(es) = 0.24) and population (P(p) = 63%, A(p) = 1.90, AP(p) = 2.42, H(ep) = 0.20) levels. A significant deficit of heterozygote individuals was detected within populations in the Paraguana Peninsula region (F(IS) = 0.301). Relatively low levels of population differentiation were detected at macrogeographic (G(ST) = 0.112) and regional levels (G(ST) = 0.044 for peninsula region and G(ST) = 0.074 for mainland region), suggesting substantial genetic exchange among populations; however, gene flow in this species seems to be regulated by the distance among populations. Overall, estimates of genetic diversity found in P. guamacho are concordant with the pattern observed for other cacti surveyed, namely high levels of polymorphism and genetic diversity with one common allele and several rare alleles per locus. Differences in gene dispersal systems between this species and other cacti studied were not reflected in the patterns of genetic diversity observed. The concentration of the highest estimates of genetic variation in northwestern Venezuela suggests a potential reservoir of plant genetic diversity within xerophilous ecosystems in northern South America. (+info)
Initial net CO2 uptake responses and root growth for a CAM community placed in a closed environment.
To help understand carbon balance between shoots and developing roots, 41 bare-root crassulacean acid metabolism (CAM) plants native to the Sonoran Desert were studied in a glass-panelled sealable room at day/night air temperatures of 25/15 degrees C. Net CO(2) uptake by the community of Agave schottii, Carnegia gigantea, Cylindropuntia versicolor, Ferocactus wislizenii and Opuntia engelmannii occurred 3 weeks after watering. At 4 weeks, the net CO(2) uptake rate measured for south-east-facing younger parts of the shoots averaged 1.94 micro mol m(-2) s(-1) at night, considerably higher than the community-level nocturnal net CO(2) uptake averaged over the total shoot surface, primarily reflecting the influences of surface orientation on radiation interception (predicted net CO(2) uptake is twice as high for south-east-facing surfaces compared with all compass directions). Estimated growth plus maintenance respiration of the roots averaged 0.10 micro mol m(-2) s(-1) over the 13-week period, when the community had a net carbon gain from the atmosphere of 4 mol C while the structural C incorporated into the roots was 23 mol. Thus, these five CAM species diverted all net C uptake over the 13-week period plus some existing shoot C to newly developing roots. Only after sufficient roots develop to support shoot water and nutrient requirements will the plant community have net above-ground biomass gains. (+info)
The genetic structure of a columnar cactus with a disjunct distribution: Stenocereus gummosus in the Sonoran desert.
Stenocereus gummosus is a columnar cactus endemic to the Sonoran desert that exhibits a disjunct distribution: it is widely distributed in Baja California and restricted to a small coastal area in mainland Sonora. In this paper, we examine the genetic structure and the mating system of this species in order to explore the origin of the disjunction and describe aspects of the pollination biology. Flowers are nocturnal, pollinated mainly by sphingids and self-incompatible. Polymorphism for allozymes (11 loci) was relatively high (P=75%) but moderate levels of heterozygosity were detected (H(o)=0.103 and H(e)=0.261). Sonoran populations exhibited higher levels of genetic variation than peninsular populations. H(e) declined with latitude when just peninsular and two island populations are included. Substantial levels of inbreeding within populations (f=0.60), moderate differentiation among populations (theta=0.10), and no evidence of isolation by distance were detected. The neighbor-joining phenogram showed Sonoran and island populations nested within peninsular populations. Mainland populations showed greater genetic similarity to island populations, supporting a dispersal hypothesis for the origin of the disjunction. Future studies using DNA markers are suggested in order to better understand the forces that have shaped the genetic structure of this species. (+info)
Effects of benomyl and drought on the mycorrhizal development and daily net CO2 uptake of a wild platyopuntia in a rocky semi-arid environment.
The effects of drought and the fungicide benomyl on a wild platyopuntia, Opuntia robusta Wendl., growing in a rocky semi-arid environment were assessed. Cladode phosphorus content, cladode water potential and daily net CO2 uptake were measured monthly in 2000 and 2001 before, during and after the summer rainy period. During 2000, the formation of new roots and new cladodes was severely suppressed in response to a prolonged drought, impairing the development of the symbiotic relationship between the arbuscular mycorrhizal (AM) fungi and the roots. Hence no effect of benomyl application was observed on daily carbon assimilation by this Crassulacean acid metabolism plant. During 2001, drought was interrupted, and new cladodes and roots were formed in response to rainfall. Benomyl was highly effective in suppressing root colonization by AM-fungi; however, daily C assimilation was reduced by benomyl application only in October. Thus, the inhibition of AM-fungal colonization by benomyl did not affect photosynthesis, water uptake and P uptake under prolonged drought. (+info)
Chromosome doubling in vine cacti hybrids.
We performed reciprocal crosses between the tetraploid Selenicereus megalanthus and the diploid Hylocereus species, H. undatus and H. polyrhizus. S. megalanthus x H. undatus gave rise to viable hexaploids and 6x-aneuploid hybrids rather than to the expected triploids. No genuine hybrids were obtained in the reciprocal cross. The pollen diameter of the tetraploid S. megalanthus varied widely, indicating the occurrence of unreduced gametes, while that of H. undatus pollen was very uniform, indicating an extremely low frequency of unreduced gametes. This finding suggests that the hexaploids were formed by chromosome doubling after the formation of the hybrid triploid zygote rather than by fusion of unreduced gametes of the two species. (+info)
Comparative molecular population genetics of the Xdh locus in the cactophilic sibling species Drosophila buzzatii and D. koepferae.
The Xdh (rosy) gene is one of the best studied in the Drosophila genus from an evolutionary viewpoint. Here we analyze nucleotide variation in a 1875-bp fragment of the second exon of Xdh in Argentinian populations of the cactophilic D. buzzatii and its sibling D. koepferae. The major electrophoretic alleles of D. buzzatii not only lack diagnostic amino acids in the region studied but also differ on average from each other by four to 13 amino acid changes. Our data also suggest that D. buzzatii populations belonging to different phytogeographic regions are not genetically differentiated, whereas D. koepferae exhibits a significant pattern of population structure. The Xdh region studied is twice as polymorphic in D. buzzatii as in D. koepferae. Differences in historical population size or in recombinational environment between species could account for the differences in the level of nucleotide variation. In both species, the Xdh region exhibits a great number of singletons, which significantly departs from the frequency spectrum expected under neutrality for nonsynonymous sites and also for synonymous sites in D. buzzatii. These excesses of singletons could be the signature of a recent population expansion in D. buzzatii, whereas they may be simply explained as the result of negative selection in D. koepferae. (+info)