Interrelations Among Water and Energy Relations of Reptilian Eggs, Embryos, and Hatchlings

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.     

Interspecific conflict in lizards: Social dominance depends upon an individual's species not its body size

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.     

THE TEETH OF HYPOGEOPHIS ROSTRATUS (AMPHIBIA, APODA) AND TOOTH STRUCTURE IN THE AMPHIBIA

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.     

Epidermal club cells and the innate immune system of minnows

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.     

Complex Cell Response depends on Interslit Spacing

PSYCHOPHYSICAL studies have established that the human central visual system contains a large number of independent channels each of which responds maximally to a selectively oriented sine wave grating of a given spatial frequency and hardly at all to gratings of spatial frequencies differing by a factor of two^1–4. Electrophysiological studies with moving sinusoidally modulated grating patterns have demonstrated that there exists a class of neurones in the striate cortex of cats⁵ and monkeys⁶ each member of which is maximally selective to a given spatial frequency and orientation.     

Fossils and lithostratigraphy

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.