Cytochemistry of Oogenesis and Early Embryonic Development

Cytochemical investigations on oocyte development, fertilizationand early embryonic development have been reviewed. Inter andintra-group variability in the succession of metabolic phaseswas considered with respect to selection pressures which inturn appeared to modulate phases. Quantitative investigationswere particularly considered. In early development, attention was focused on changes in thechromosomal organization which might reflect on control of development.Some of the unusual forms of chromosomal organizations in earlydevelopment were discussed. Cytochemical studies have not offered any insights into precociousdifferentiation, but they have added substantially to the understandingof chemical and organizational changes during oogenesis andearly development.     

Reserve Size,Conspecific Density,and Translocation Success for Black Rhinoceros

Abstract: Fighting and accidental injury commonly cause black rhinoceros (rhino; Diceros bicornis) death after release. Smaller reserves and higher conspecific density after release (release density) might increase a rhino's encounter rate with hazards like fenced boundaries and conspecifics. We conducted a science-by-management experiment on the influence of reserve size and release density on rates of movement, association, and injury and death amongst 39 black rhinos during the first 100 days after their release into 4 Namibian and 8 South African reserves ranging in size from 670 ha to 45,000 ha. Association rates were negatively related to reserve size and positively correlated with release density. There was also a negative relationship between the proportion of the reserve traversed by individual rhinos and reserve size. In reserves ≥18,000 ha association rates were consistently zero but became elevated in reserves ≤11,500 ha and at release densities ≤9 km²/rhino. Daily displacement did not increase with increasing reserve size >8,500 ha but in smaller reserves daily displacements indicated higher encounter rates by released rhinos with fenced boundaries. Three rhinos received fight-related injuries requiring intervention and 2 of 4 deaths were fight-related. All injuries and 3 deaths occurred in reserves ≤11,500 ha. Model selection based on Akaike's second-order Information Criterion indicated that the parameter release density alone best explained mortality risk. Traditionally considered risk factors, rhino sex, age, and presence of resident conspecifics, were superseded by the risk posed by releases into smaller reserves. Reserves ≤11,500 ha and release densities ≤9 km²/rhino pose an increasing risk to rhino survivorship and so larger reserves and lower densities than these should be favored as release sites.     

Genetic Control of Acoustic Behavior in Crickets

Evidence is presented that acoustic behavior in field cricketsis under firm genetic control. The calling song of adult malesis highly stereotyped and species specific. Hybrids can be madeby crossing two species of Teleogryllus with dissimilar callingsongs. The calling songs of the hybrids are uniquely differentfrom that of either parental species, and in addition the songsof the two reciprocal hybrids are different from each other.Genetic control of song production is polygenic and multichromosomal;sex-linkage of some song determinants is also indicated. Femalephonoresponse to calling song was measured on a Y-maze. Speciesspecificity of phonoresponse was confirmed and in addition,hybrid females prefer hybrid song to either parental song. Thepossibility that calling song production in the male and itsreception in the female are genetically coupled is discussed.     

Protective mechanisms and acclimation to solar ultraviolet-B radiation in Oenothera stricta

Abstract Mechanisms of plant protection and acclimation to potentially damaging solar ultraviolet-B (UV-B, 280–320 nm) radiation incident on the Earth's surface were examined in Oenothera stricta. Attenuation of this radiation in the upper leaf epidermis reduces the penetration of UV-B radiation to the mesophyll where damage to physiologically sensitive targets can occur. The epidermis is a highly selective radiation filter that can attenuate up to 95% of the incident UV-B radiation and yet transmit between 70% and 80% of the visible radiation. Exposure to UV-B radiation significantly reduced the degree of epidermal UV-B transmittance by as much as 33%. No significant reduction in epidermal transmittance of visible radiation was observed as a result of UV-B exposure. The plasticity in epidermal UV-B transmittance results from production of flavonoid and related phenolic compounds in the tissue. Absorbance of UV-B radiation in llavonoid extract solutions from epidermal and mesophyll tissues significantly increased by as much as 100% and 35%, respectively, after exposure to UV-B radiation. Photosynthetic rates of leaves exposed to UV-B radiation were not significantly reduced at dose rates representative of the radiation flux found in the habitat of this species, but significant photosynthetic depression was observed at dose rates that exceed the field UV-B flux. The phenotypic plasticity in epidermal UV-B transmittance resulting in decreased penetration of damaging UV-B radiation to the mesophyll may reduce the rate of damage to a level where repair mechanisms can keep pace with reduced injury.     

Cellular Aspects of the Control of Physiological Color Changes in Amphibians

SYNOPSIS. The present paper is concerned mainly with the melanin-dispersingeffect of melanocyte-stimulating hormones (MSH's) on the skinmelanophores of amphibians. In addition, some of the more recentevidence for the unihumoral theory of the control of color changeis reviewed. The mechanism of dispersion of melanin is stillunknown, but evidence is accumulating that the action of MSHmay be mediated by an increase in the melanophoric content ofadenosine 3', 5'-monophosphate (cyclic AMP). For example, cyclicAMP has a specific, reversible melanin-dispersing effect onthe melanophores of the isolated skin of R. pipiens and Xenopuslaevis. It also has a reversible "melanophore—expanding"effect on the tissue—cultured embryonic melanophores ofthe spotted salamander, Ambystoma maculatum. The effect of cyclicAMP on melanophores of R. pipiens does not require sodium butis inhibited by hypertonicity. Finally, new evidence is presented that confirms that the melanin-dispersingeffect of catecholamines on melanophores of X. laevis is mediatedby beta adrenergic receptors,because it is blocked by the highlyspecific ß—blocking agent, propranolol. On theother hand, the melanin-aggregating effect of catecholamineson amphibian melanophores appears to be mediated by alpha adrenergicreceptors. There is even a possibility that the effects of catecholaminesare also mediated through a control of cyclic AMP levels inmelanophores, with beta adrenergic stimulation producing anincrease in cyclic AMP levels, followed by dispersion of melanin,and alpha adrenergic stimulation producing a decrease in cyclicAMP levels, followed by aggregation of melanin.     

Control of Drag-Line Spinning in Certain Spiders

Araneomorph spiders from many different families show some regionaldifferentiation of the duct which carries the drag-line silk,but only in the orb-web spiders is there a well-defined controlvalve. This valve, and its associated muscles, is described for Araneusdiadematus (Argiopidae), an ecribellate spider, and is comparedwith that found in Uloborus octonarius (Uloboridae), a cribellatespider. It is suggested that the remarkable similarity betweenthe valves in these two groups implies evolutionary convergence. Some evidence is presented which suggests that variations inbody pressure are used to control the drag-line spinning, atleast in the more primitive Araneomorphs.     

Specificity of Cellular Immune Reactivity to Virus-induced Tumours

SPECIFICITY is one of the chief hallmarks of immune reactions. In many cases, specificity has been defined by reactivity against some antigens and not against others, but the results of direct tests may be misleading. In many cases, in transplantation and tumour immunology, direct reactivity may be absent in spite of the presence of the antigen. With HL-A antigens, the CYNAP phenomenon (cytotoxicity negative, absorption positive) has been described¹. Virus-induced tumours may have relatively small amounts of tumour specific cell surface antigens which are detectable only by absorption tests^2,3. In addition, immune reactions may occur against a particular antigen on one material and against different antigens on another material. With antibody reactions, specificity can be confirmed by the appropriate absorption experiments^4,5. With cellular immune reactions, comparable demonstration of specificity has been very difficult.     

Development of First-Generation Schizonts of Eimeria bovis in Cultured Bovine Cells

SYNOPSIS. Monolayer primary and secondary cultures of embryonic bovine kidney, spleen, intestinal and testicle cells, and secondary cultures of embryonic bovine thymus, maintained in lactalbumin hydrolysate, Earle's balanced salt solution and ovine serum were observed for a maximum of 21 days after inoculation of E. bovis sporozoites. The sporozoites entered the cells in all of these cultures but underwent development only in primary cultures of kidney and intestinal cells and in secondary cultures of kidney, spleen, thymus, intestinal, and testicle cells. In acellular media, the sporozoites retained motility no longer than 21 hr. In the cell cultures, free motile sporozoites were seen for as long as 18 days after inoculation. Sporozoites entered cells anterior end first; the process of penetration required a few seconds to about a minute. Sporozoites were also observed leaving host cells. Intracellular sporozoites were first seen 3 min after inoculation; they were observed at various intervals up to 18 days after inoculation. In transformation of sporozoites into trophozoites a marked change in size and appearance of the nucleus took place before the change in shape of the body occurred. Trophozoites were first found 7 days after inoculation, multinucleate schizonts after 8 days, and schizonts with merozoites after 14 days. Schizonts containing merozoites were seen only in kidney, spleen, and thymus cells. The mature schizonts were smaller and represented a much lower proportion of the total number than in comparable stages of infections in calves. Schizonts with many nuclei occurred in intestinal cells; the most advanced stage seen in testicle cells was the binucleate schizont. Nuclear and cytoplasmic changes were observed in the infected cells.