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1.
Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications 总被引:1,自引:0,他引:1
Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of
individuals representing 54 species of frogs, two species of salamanders, a
caecilian, and a lungfish. Eight of these sites were present in all species
examined, and two were found in all but one species. Alignment of these
conserved restriction sites revealed, among anuran 28S rRNA genes, five
regions of major length variation that correspond to four of 12 previously
identified divergent domains of this gene. One of the divergent domains
(DD8) consists of two regions of length variation separated by a short
segment that is conserved at least throughout tetrapods. Most of the
insertions, deletions, and restriction-site variations identified in the
28S gene will require sequence-level analysis for a detailed reconstruction
of their history. However, an insertion in DD9 that is coextensive with
frogs in the suborder Neobatrachia, a BstEII site that is limited to
representatives of two leptodactylid subfamilies, and a deletion in DD10
that is found only in three ranoid genera are probably synapomorphies.
相似文献
2.
Dihydrotestosterone was implanted directly into the brain of castrated male Cnemidophorus inornatus, a direct sexual ancestor of the parthenogenetic species C. uniparens. Only implants located in the anterior hypothalamus--preoptic area (AH-POA) induced male-typical sexual behavior. Implants in other brain regions, including the ventromedial hypothalamus, failed to elicit courtship or copulatory behavior. Radioimmunoassay revealed no significant difference in the concentrations of circulating androgens between the responding and nonresponding animals. Previous data from this laboratory demonstrated that the AH-POA controls male-like pseudosexual behavior in C. uniparens. The current results support the hypotheses that (i) the AH-POA is the major area of hormone action in the brain controlling male-typical sexual behavior in C. inornatus as in other vertebrates and (ii) the neural circuits controlling male-typical behavior have been conserved in the evolution of the parthenogen C. uniparens. 相似文献
3.
J A Rozendaal 《Memórias do Instituto Oswaldo Cruz》1990,85(2):221-234
A study was made on the distribution of anophelines in Suriname with special emphasis on the principal malaria vector Anopheles darlingi and on the occurrence of other possible vector species. Peridomestic human bait collections of adult mosquitoes and collections of larvae were made in many localities with a recent history of malaria transmission. Stable populations of An. darlingi were only found in the interior, south of the limit of tidal influence, due to year-round availability of breeding habitats in quiet partly sunlit places in flooded forest areas and along river banks. In the area with tidal movement of the rivers, breeding is limited to flooded areas in the wet season. Anopheles darlingi was only incidentally collected in low densities. In the interior, malaria transmission occurred in all places where An. darlingi was found. The absence of malaria transmission along the Upper Suriname River could be explained by the absence of An. darlingi. In the malaria endemic areas, An. darlingi was the most numerous mosquito biting on man. In the tidal region, malaria outbreaks are infrequent and might be explained by the temporary availability of favourable breeding habitats for An. darlingi. However, evidence is insufficient to incriminate An. darlingi as the vector of malaria in this region and the possible vectorial role of other anophelines is discussed. 相似文献
4.
The ITS sequences of Acropora spp. are the shortest so far identified in
any metazoan and are among the shortest seen in eukaryotes; ITS1 was 70-80
bases, and ITS2 was 100-112 bases. The ITS sequences were also highly
variable, but base composition and secondary structure prediction indicate
that divergent sequence variants are unlikely to be pseudogenes. The
pattern of variation was unusual in several other respects: (1) two
distinct ITS2 types were detected in both A. hyacinthus and A. cytherea,
species known to hybridize in vitro with high success rates, and a putative
intermediate ITS2 form was also detected in A. cytherea; (2) A. valida was
found to contain highly (29%) diverged ITS1 variants; and (3) A.
longicyathus contained two distinct 5.8S rDNA types. These data are
consistent with a reticulate evolutionary history for the genus Acropora.
相似文献
5.
Clément Daboné Ralph Buij Adama Oueda Jacques Boko Adjakpa Wendengoudi Guenda Peter DM Weesie 《Ostrich》2019,90(1):53-61
During the last decades, the critically endangered Hooded Vulture Necrosyrtes monachus has strongly declined across its African range. Although direct persecution has been suggested as a major cause of this decline, little is known about the impact of humans on reproductive output in West Africa. We studied the impact of human activities on the reproductive output of Hooded Vultures in the Garango area of Burkina Faso. Twenty and 56 nesting attempts were monitored, respectively, during the breeding season in 2013/14 and 2014/15, to determine reproductive success and identify causes of nest failure. Annual breeding success varied between 0.68 and 0.71 chicks fledged per breeding pair per year and productivity was assessed at 0.57 chicks fledged per territorial pair in 2014/15. The main threats imposed by humans were poaching of eggs, chicks and collection of nest materials, leading to 20% (13 out of 64 breeding attempts) of nest failures over the two years. An additional important reason for nest failure was the pruning and (partial) cutting of nest trees. Despite this high level of human interference, we found that Hooded Vulture nest success increased with proximity to human settlements, probably because breeding vultures benefit from protection by people against persecution and disturbance. 相似文献
6.
DM Woolley 《The Journal of cell biology》1977,75(3):851-865
Motile spermatozoa from the golden hamster have been arrested by rapid freezing and then fixed with glutaraldehyde at low temperature after substitution with ethylene glycol. As far as can be judged, the flagellar waveforms thus stabilized are similar to those seen in living sperm; in contrast, fixation in glutaraldehyde, without prior freezing, induces agonal changes in flagellar conformation. The characteristics waveform after freeze substitution contains three bends. Approx. half of these flagella are entirely planar. The rest are three dimensional, with the third bend displaced in a regular way from the plane containing the proximal two bends. From the geometry of these flagella, it is concluded that the plane of action of a given bending cycle undergoes a clockwise twist (from a forward viewpoint) as the cycle is succeeded by new bending cycles. This "twisted plane" undulation is quite different from helical movement. The twisting seems to occur abruptly, between cycles, as if each bending cycle has a preferred plane of action. The mechanism underlying the twisting is uncertain. However, on the basis of the angular displacements between the preferred planes, and the findings from electron microscopy, the following idea is presented as a working hypothesis: that, if the most proximal plane of bending is topographically determined by peripheral doublet 1, then successive distal planes of action are influenced predominantly by doublets 2, 3, etc., in clockwise sequence. The merits and weaknesses of this hypothesis are discussed. 相似文献
7.
Claudia C. Soliz-Gamboa Dana? M. A. Rozendaal Greg��rio Ceccantini Veronica Angyalossy Klaas van der Borg Pieter A. Zuidema 《Trees - Structure and Function》2011,25(1):17-27
Knowledge on juvenile tree growth is crucial to understand how trees reach the canopy in tropical forests. However, long-term
data on juvenile tree growth are usually unavailable. Annual tree rings provide growth information for the entire life of
trees and their analysis has become more popular in tropical forest regions over the past decades. Nonetheless, tree ring
studies mainly deal with adult rings as the annual character of juvenile rings has been questioned. We evaluated whether juvenile
tree rings can be used for three Bolivian rainforest species. First, we characterized the rings of juvenile and adult trees
anatomically. We then evaluated the annual nature of tree rings by a combination of three indirect methods: evaluation of
synchronous growth patterns in the tree- ring series, 14C bomb peak dating and correlations with rainfall. Our results indicate that rings of juvenile and adult trees are defined
by similar ring-boundary elements. We built juvenile tree-ring chronologies and verified the ring age of several samples using
14C bomb peak dating. We found that ring width was correlated with rainfall in all species, but in different ways. In all, the
chronology, rainfall correlations and 14C dating suggest that rings in our study species are formed annually. 相似文献
8.
Rozendaal FP 《Tijdschrift voor gerontologie en geriatrie》2005,36(2):77-80
The clinical manifestations of thyroid diseases in the elderly are often atypical and can easily be attributed to other medical conditions or 'normal aging'. Two nursing home patients with hyperthyroidism are described. Due to the atypical presentation of the thyroid disease their complaints were attributed to other conditions. In both patients there was a significant delay in diagnosis and treatment of hyperthyroidism. In elder patients signs and symptoms of thyreotoxicosis are frequently related to cardiovascular, gastrointestinal and neuropsychiatric disorders. Most often occur atrial fibrillation, worsening of cardiac failure and angina pectoris, weight loss, anorexia, constipation, cognitive impairment and delirium. Delay of diagnosis and treatment of hyperthyroidism may be potentially harmful to the patient. Untreated thyreotoxicosis may lead to serious cardiovasculair complications (particularly cardiac failure and cerebrovascular accidents), mental deterioration and osteoporosis. In elder people with unexplained and vague signs and symptoms thyroid function should always be checked. The TSH assay is a very accurate diagnostic test for screening thyroid function. A normal TSH indicates euthyroidism with an accuracy of almost 100%. The medical treatment for hyperthyreoidism in the elderly are antithyroid drugs. When an euthyroid state is rendered, suppletion with L-thyroxine may be nessecary. Radioactive iodine treatment is preferred in some cases though there may be practical difficulties with the application of this treatment in nursing home patients because temporary isolation is necessary. 相似文献
9.
Leaf size and leaf display of thirty-eight tropical tree species 总被引:1,自引:0,他引:1
Trees forage for light through optimal leaf display. Effective leaf display is determined by metamer traits (i.e., the internode,
petiole, and corresponding leaf), and thus these traits strongly co-determine carbon gain and as a result competitive advantage
in a light-limited environment. We examined 11 metamer traits of sun and shade trees of 38 coexisting moist forest tree species
and determined the relative strengths of intra- and interspecific variation. Species-specific metamer traits were related
to two variables that represent important life history variation; the regeneration light requirements and average leaf size
of the species. Metamer traits varied strongly across species and, in contrast to our expectation, showed only modest changes
in response to light. Intra- and interspecific responses to light were only congruent for a third of the traits evaluated.
Four traits, amongst which leaf size, specific leaf area (SLA), and leaf area ratio at the metamer level (LAR) showed even
opposite intra- and interspecific responses to light. Strikingly, these are classic traits that are thought to be of paramount
importance for plant performance but that have completely different consequences within and across species. Sun trees of a
given species had small leaves to reduce the heat load, but light-demanding species had large leaves compared to shade-tolerants,
probably to outcompete their neighbors. Shade trees of a given species had a high SLA and LAR to capture more light in a light-limited
environment, whereas shade-tolerant species have well-protected leaves with a low SLA compared to light-demanding species,
probably to deter herbivores and enhance leaf lifespan. There was a leaf-size-mediated trade-off between biomechanical and
hydraulic safety, and the efficiency with which species can space their leaves and forage for light. Unexpectedly, metamer
traits were more closely linked to leaf size than to regeneration light requirements, probably because leaf-size-related biomechanical
and vascular constraints limit the trait combinations that are physically possible. This suggests that the leaf size spectrum
overrules more subtle variation caused by the leaf economics spectrum, and that leaf size represents a more important strategy
axis than previously thought.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.