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Interrelations Among Water and Energy Relations of Reptilian Eggs, Embryos, and Hatchlings 总被引:1,自引:0,他引:1
Reptilian eggs previously categorized with respect to the flexibilityof eggshells appear to fall into two groups: endohydric eggsare those that are invested, by the female parent at the timeof oviposition, with all of the water necessary to completeembryogenesis; and ectohydric eggs which need to absorb waterfrom the nest medium tocomplete embryogenesis. Eggs of the Galapagosland iguana are unusual among most lepidosaurians by havingvery permeable parchment shells, but containing a large albumen(apparently serving as a reservoir of water for the embryo).It appears that the eggs of Galapagos land iguanas can exploitan endohydric habit without the rigid, impermeable shell seenin other endohydric eggs. This ability appears to be mediatedby two factors: eggs of Galapagos land iguanas are laid in drysoils which are essentially impermeable to water, and the verylarge eggs of land iguanas have a relatively small surface areatovolume ratio which results in a relatively small exchangeof water across the eggshell. It appears too that the waterrelations of Galapagos land iguana eggs will affect the energeticsof both the contained embryo and the subsequent hatchling. Withoutadequate water, land iguana eggs will produce hatchlings thatare both smaller and possess less fat to sustain thejuvenileduring the first year of life. 相似文献
3.
R. LAWSON 《Journal of Zoology》1965,145(3):321-325
The bipartite nature of the tooth has been recently used to demonstrate the close relationship between the three existing groups of Amphibia. However, Considerable doubt has remained as to the composition of the two parts of the tooth and the way in which they are linked.
It order to clearify the position the teeth in Hypogeophis were examined. It is clear that the bulk of the crown and the pedicel is composed of dentine which is produced by a continuous layer of odontoblasts. This layer of cells is also responsible for the formation of the fibrous ring which joins the two portions of the tooth. This ring is regarded as an area where the odontoblasts produce fibres and little or no matrix. 相似文献
It order to clearify the position the teeth in Hypogeophis were examined. It is clear that the bulk of the crown and the pedicel is composed of dentine which is produced by a continuous layer of odontoblasts. This layer of cells is also responsible for the formation of the fibrous ring which joins the two portions of the tooth. This ring is regarded as an area where the odontoblasts produce fibres and little or no matrix. 相似文献
4.
Phylogenetic relationships of the garter snakes based on DNA sequence and allozyme variation 总被引:1,自引:0,他引:1
ALAN DE QUEIROZ ROBIN LAWSON 《Biological journal of the Linnean Society. Linnean Society of London》1994,53(3):209-229
We estimated phylogenetic relationships among 26 species of garter snakes (genus Thamnophis ) using allozyme and mitochondrial cytochrome b gene nucleotide sequence variation. Parsimony analyses of the two data sets give substantially different estimates of phylogeny. Several lines of evidence indicate that much of this conflict is due to error associated with the restricted number of characters in each data set. Such sampling error may be reduced by combining all the characters; we therefore present an estimate of phylogeny based on parsimony analysis of all the data combined. All our analyses support several conclusions in conflict with previous views: a very distant relationship between T.errans and T. elegans , non-monophyly of the elegans group (even excluding T: errans ), and nesting of the form validus (previously considered a member of the genus Nerodia ) within Thamnophis.
The combined analysis gives an almost fully resolved tree. However, bootstrapping indicates only weak support for many clades in this tree. Furthermore, paraphyly of the assemblages of cytochrome b gene lineages within T. elegans and T. radix indicate the potential for discordance between the mitochondrial DNA (mtDNA) and species phylogenies through the sorting of ancestral mtDNA polymorphisms. These problems suggest the need for assaying additional characters, especially ones likely to be independent of those used in the present study. 相似文献
The combined analysis gives an almost fully resolved tree. However, bootstrapping indicates only weak support for many clades in this tree. Furthermore, paraphyly of the assemblages of cytochrome b gene lineages within T. elegans and T. radix indicate the potential for discordance between the mitochondrial DNA (mtDNA) and species phylogenies through the sorting of ancestral mtDNA polymorphisms. These problems suggest the need for assaying additional characters, especially ones likely to be independent of those used in the present study. 相似文献
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JAMES D. LAWSON 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1979,12(2):189-191
It is proposed that any future revision of the International Stratigraphic Guide should explicitly approve the use of characteristic faunal and floral assemblages in the definition of lithostratigraphical units, providing that the fossils are readily observable and identifiable in the field and assist in the mapping of the rocks. 相似文献
7.
COLIN F. HALBGEWACHS TRACY A. MARCHANT ROBIN C. KUSCH DOUGLAS P. CHIVERS 《Biological journal of the Linnean Society. Linnean Society of London》2009,98(4):891-897
Thousands of fish species belonging to the Superorder Ostariophysi possess specialized club cells in their epidermis. Damage to the cells, as would occur during a predator attack, releases chemical substances that evoke antipredator responses in nearby shoalmates. These chemical substances have often been referred to as alarm substances and the cells that release them as alarm cells. Understanding the evolution of the cells in an alarm context has been difficult. The fish needs to be captured prior to the chemicals being released, hence the benefit to the receiver is unclear. Recent studies have suggested that the club cells are part of the immune system and are maintained by natural selection owing to the benefits that they confer against pathogens, parasites, and general injury to the epidermis. In the present study, we gave fathead minnows intraperitoneal injections of cortisol, a known immunosuppressant, or injections of a control substance (corn oil). We found that fish exposed to cortisol had suppressed immune systems (as measured by a respiratory burst assay) and that they also reduced their investment in club cells. This is the best evidence to date indicating that the club cells of Ostariophysan fishes are part of the innate immune system and that the alarm function of the cells evolved secondarily. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 891–897. 相似文献
8.
Perennial grasses are being considered as candidates for biofuel feedstocks to provide an alternative energy source to fossil fuels. Miscanthus×giganteus (miscanthus), in particular, is a grass that is predicted to provide more energy per sown area than corn ethanol and reduce net carbon dioxide emissions by increasing the storage of carbon belowground. Miscanthus uses more water than Zea mays (maize), mainly as a result of a longer growing season and higher productivity. Conversion of current land use for miscanthus production will likely disrupt regional hydrologic cycles, yet the magnitude, timing, and spatial distribution of effects are unknown. Here, we show the effects of five different scenarios of miscanthus production on the simulated Midwest US hydrologic cycle. Given the same historic precipitation observations, our ecosystem model simulation results show that on an annual basis miscanthus uses more water than the ecosystems it will likely replace. The actual timing and magnitude of increased water loss to the atmosphere depends on location; however, substantial increases only occur when miscanthus fraction cover exceeds 25% in dry regions and 50% in nearly all of the Midwest. Our results delineate where large‐scale land use conversion to perennial biofuel grasses might deplete soil water resources. Given the fact that some watersheds within the Midwest already have depleted water resources, we expect our results to inform decisions on where to grow perennial grasses for biofuel use to ensure sustainability of energy and water resources, and to minimize the potential for deleterious effects to water quantity and quality. 相似文献
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10.
Abstract Animals frequently compete for resources (food, shelter, etc.) against conspecifics as well as against individuals of other species; larger animals typically are dominant over smaller ones. Although body size thus correlates with social dominance in interspecific as well as intraspecific encounters, the causal connection remains unclear. That is, one species might dominate another not simply because of larger size, but some other species‐specific attribute. In such a case, we expect an animal of the subordinate taxon to be subservient to all members of the ‘dominant’ species, even those too small to pose a physical threat. This scenario can be tested by staging encounters over resource use in the laboratory. We conducted such trials using a guild of sympatric montane lizards (Reptilia: Scincidae), that compete for shelter sites (rock crevices), with larger species routinely displacing smaller taxa. Remarkably, neonates of larger species effectively deterred adults of smaller species from entering occupied retreat sites – even when the neonates were much smaller than the adults they displaced. Thus, the outcomes of interspecific interactions in this system depend upon the species of the participants, not their relative body sizes. Measurements of bite force confirm that the neonates of the most dominant species posed little physical threat to heterospecific adults, so that species‐specific variation in fighting ability cannot explain this puzzling result. However, juveniles often share shelter sites with conspecific adults, so that avoidance of neonates may reduce the risk of attack by an unseen adult resident. 相似文献