摘要:

The embryonic and early larval development ofAscaphuswas studied by culturing embryos at 11 °C. Twenty stages of normal development are morphologically defined by using a standard staging system for anuran amphibians.Cleavage stages are distinctive. The first cell division is unique because two separate furrows develop and then fuse to form a single cleavage plane. The large, yolky cytoplasm continues to influence cell divisions, and a blastula develops with very large vegetal cells and small, irregular shaped animal cells. There is a conspicuous, translucent blastocoel in the late blastula, and during gastrulation this structure is displayed forward by the internal migration of cells. Except for slight differences in proportions, the gastrula and neurula stages resemble the typical anuran pattern. Circulation (stage 20) begins when large vitelline veins develop on the yolk sac and direct the return of blood flow to the heart.At hatching, the tadpole has a large yolk sac, little skin pigmentation, and no gills. Mouthparts and opercular coverings of the branchial arches develop slowly. Hind limb buds develop at the base of the tail, but they are soon concealed as a skin membrane develops and covers these structures.The reproductive strategy for this primitive and highly aquatic frog is unusual: there is a small number of large eggs that develop slowly and produce tadpoles that continue this slow developmental process

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02509.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Breeding, population dynamics and seasonal changes in physical and physiological parameters were examined in the northern quoll (Dasyurus hallucatus) at Mitchell Plateau, Western Australia, between September 1981 and November 1982. Females gave birth to a single litter of young in July or August. Births were earlier on near‐coastal sites than on inland sites. Litter size was greater on inland sites and litter size differed between years. By September all females were either carrying pouch young or were lactating. Lactation ceased by April. Testosterone levels in males peaked in July. There were significantly more male than female pouch young. However, in only one grid was the adult sex ratio different from parity, with an excess of females in September 1981 and 1982. Embryonic mortality was>53% but loss of pouch young was small. Although males and females moved similar distances between successive recaptures, the extent of movement varied seasonally, being greatest in September. Males were generally larger and heavier than females. Seasonal variations were recorded for most physical and physiological parameters. The most pronounced changes occurred towards the end of the dry season (July to September) for both males and females. Over this period there was a significant decline in weight (males), haematocrit (males), plasma albumin (males) and leucocytes (both males and females) and significant elevations in values of haemoglobin and both free and protein‐bound Cortisol in both males and females. Few males survived the post‐mating period from July to September. They appeared to decline in condition over this period more markedly than females: they lost more weight, their haematocrit and plasma albumin values declined to a greater extent, and they were more heavily infected with lice (Boopia uncinata). Males with lower testosterone and higher free and protein‐bound Cortisol had increased prospects of surviving the breeding season, which suggests that it is the dominant males that are less likely to survive the breeding season. Individuals in the three major populations at Mitchell Plateau differed greatly in their physiological values. The high‐density population in a sandstone area had intermediate levels of free Cortisol and higher haematocrit values than both the other populations, and higher levels of haemoglobin than the population on laterite s

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02510.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Leiolepis belliani, a cursorial, beach‐dwelling lizard, moves by running and jumping. The lizards' ability to flatten dorsoventrally, thereby increasing surface area and decreasing wing loading, may also confer parachuting ability. We measured locomotor performance of three ecologically relevant tasks: running, jumping and parachuting. In addition, we investigated whether, with the effect of size removed, locomotor performance capabilities are correlated, and whether they correlate with morphological features. Larger lizards fell and ran faster and jumped further. Lizards that were experimentally prevented from flattening fell faster than control lizards. When the effects of size were removed, limb length was uncorrelated with jumping and running performance; performance measures also were not correlated amongst themselves. The scant natural historical data available for this species suggests that lizards do not use their parachuting capability, and that dorsoventral flattening may have evolved for some other purpose.Leiolepismight serve as a useful model in understanding the evolution of gliding lizards (e.g.Draco

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02511.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The bolyeriid snakesCasarea dussumieriandBolyeria multocarinataare unique among vertebrates in possessing an intramaxillary joint that separates the maxilla into anterior and posterior segments. In contrast to previous studies, which suggest that this joint permits enhanced elevation of the anterior maxillary teeth, our films of liveCasareashow that the snout and anterior maxillary teeth are actively depressed 15° 20° below rest position through bilateral retraction of the palatomaxillary arches. Patterns of bone movement in livingCasareasupport the hypothesis that a caudally directed force is transmitted to the snout via the medial bones of the palatomaxillary arch, suggesting functional affinities betweenCasareaand higher henophidians.The intramaxillary joint, in conjunction with the curvature of the mandibles, allows the jaws ofCasareato encircle hard, cylindrical prey held transversely in the mouth. Because the Mauritian terrestrial vertebrate fauna lacks mammals and is dominated by skinks and geckos, whichCasareais known to consume, we suggest that the intramaxillary joint functions in a manner analogous to that achieved by quite different maxillary modifications in colubrid scincivores. Although the origin of the bolyeriid intramaxillary joint remains unclear, its structural refinement and evolutionary stability may be due to selection pressures arising from limited prey diversit

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02512.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The functional morphology of the digestive system of terrestrial isopods (woodlice) has been investigated. Observations have been made on live juveniles ofOniscus asellusandPorcellio scaberin which some digestive processes can be observed directly through the cuticle. The fine structure of the foregut of juveniles and adults of these two species has been studied by light microscopy and scanning and transmission electron microscopy. The passage of coloured dyes and colloidal gold through the digestive system has also been followed.The digestive system ofOniscus asellusandPorcellio scaberis divided into five regions. The foregut (1), and the anterior chamber (2), papillate region (3) and rectum (4) of the hindgut, are ectodermal in origin and lined with cuticle. The hepatopancreas (5), which opens into the foregut, consists of four blind‐ending tubules which are endodermal in origin and not lined with cuticle. A powerful muscular sphincter is present between the papillate region and the rectum. There is no peritrophic membrane in the lumen of either the hepatopancreas or the hindgut.Fragments of food passviathe oesophagus to the proventriculus of the foregut where they are briefly masticated before passing rapidly into the anterior chamber of the hindgut. During this process, the food is mixed with secretions derived from the hepatopancreas. The anterior chamber possesses a pair of dorsal channels formed from a typhlosole and lateral infoldings of the gut wall. When the hindgut is full of food, contraction of muscles surrounding the gut forces liquids and fine food particles back into the foregutviathe typhlosole channels which open at the junction of the anterior chamber and papillate region. This material, which contains fluids derived from the hepatopancreas, and products of digestion, is filtered in the foregut and passed into the lumen of the hepatopancreas where further digestion, and absorption of nutrients, takes place. The hepatopancreas may secrete these fluids back on to the food in the anterior chamber and receive products of digestionviathe typhlosole channels several times during a digestive cycle.The lumen of the foregut, hindgut and hepatopancreas often contains a dense population of microorganisms which may be involved in digestion. Residual material in the hindgut passes eventually into the rectum where faecal pellets are compacted before they are voided.The ability of terrestrial isopods to recycle and retain fluids within the digestive system, by the development of the typhlosole channels (which are not present in marine isopods), may have been a major contributory factor in their successful transition from water to lan

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02513.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The daytime resting sites of 13 radio‐tracked polecats (Mustela putorius) were recorded in a mountainous and a lowland study area in Switzerland. Information on breeding sites was collected from questionnaires distributed throughout the country. At all resting sites, the polecats were completely invisible from more than a metre distant. During summer, when polecats mainly live in forests, individuals used many different hiding‐places (e.g. small self‐dug burrows, woodpiles, heaps of branches and dry leaves, dense vegetation). Such places were used for short periods, and then abandoned. Above ground, the polecats sometimes built nests of dry grass or moss. In winter, the polecats slept mainly inside barns, stables and other buildings. These resting sites were changed less frequently. In rainy weather throughout the year, subterranean places were preferred. Breeding polecats were often found inside houses, and obviously did not avoid human presence.The importance of different types of resting sites for polecats is discussed. In summer, the quality of a resting place is of less importance than its distance from the foraging area, but in winter, warm resting places are essential and buildings are therefore considered an important resource for polecats in Switzerland. The seasonal habitat change can more readily be explained as a consequence of thermoregulatory problems than of food availability, and the distribution of polecats in Switzerland may be affected by the availability of suitable winter resting places. The northern limit of polecat distribution and its historical changes can be explained by the changing availability of human buildings which provide winter resting

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02514.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The mechanism of mouth expansion in fish, consisting of jaws, suspensoria (j) and hyoids (h) has been modelled by a four‐bar isosceles linkage. This model provides insight into limitations and demands of the expansion system used in feeding, as it can be optimized with regard to maximum mouth volume increase. The optimum length ratio of hyoids and jaws was found to be h/j = 0–7. This optimum is modified by mouth bottom depression, jaw protrusion and swimming.To expand the mouth, at least two forces are required; one exerted by the sternohyoid and ventral body muscles, the other by the epaxial muscles through transmission in the quadrato‐articular joints. (Data from EMG experiments confirm the synchronous activity of these muscle groups.) Force transmission and mouth volume increase are constraining quantities, which can be compromised. This leads to a model of the initial mouth shape which is actually found in many ‘generalized’ fishes, and to demands concerning volume and physiological cross‐sectional area of the muscles involved.Options for specific relative lengths of jaws and hyoids (h/j‐ratios) are, for various fish species, compared with model predictions. The applicability of the model approach is shown by the obt

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02515.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Three species of rhizocephalan barnacle were found to be infesting 293 specimens ofMunida sarsiHuus from the Porcupine Sea‐bight (49–52°N, 11–14°W):Tortugaster boschmai, Lernaeodiscus ingolfiand, by far the most common,Triangulus munidae. Each species was found to have its own preferred abdominal segment site of emergence and particular effect on both male and female host pleopod structure.Triangulus munidae, however, caused a series of pleopod structure forms which led to the definition of a range of pleopod ‘Types’ for male and female hosts, including a peculiar masculinization of the female hosts' pleopods. The hormonal mechanisms behind these modifications are discussed.Depth was found to have an influence upon the host‐parasite relationship, there being both an increase in the percentage infestation ofM. sarsi anda decrease in the effects ofT. munidaeon the host's pleopod structure with an increase in depth. At extremes of their bathymetric ranges, the host becomes more susceptible to infestation, while the effect of the parasite on its hos

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02516.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The reproductive biological parameters of laboratory bred and maintained individuals from three species of Australian conilurine rodents,Notomys alexis, Pseudomys australisandP. nanuswere determined. Considerable' divergence was found in interbirth intervals (indicative of gestation length) in nonsuckling and suckling mothers, litter size, growth rate of pups, age at weaning, and time of sexual maturity in both males and females. It is concluded that selection has been for rapid production and development of young inP. nanus, whereas inP. australisand, especiallyN. alexis, litter size has been maximized within the constraints of the mammary formula. These data further emphasize the high degree of plasticity of the reproductive system in this assemblage of old endemic murid rodents of Australasia.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02517.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1989.tb02518.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY