摘要:

The effect of captivity on the epidermis ofPseudopleuronectes americanusWalbaum is influenced by the phase of the reproductive cycle. Towards the end of the prespawning period captive male flounder had a higher GSI than flounder from the wild population, and the seasonal epidermal sexual dimorphism in these captive flounder was more pronounced. Flounder maintained in the laboratory during the postspawning period manifested a thick epidermis and increased mucigenesis in late summer, when these characteristics displayed seasonally low values in the inshore population from which the flounder were sampled. Possible regulatory factors and implications for protocols involving captive fish are discussed.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04744.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The hypothesis of evasive mimicry proposes that: (a) the conspicuous coloration of some animals has evolved to warn predators that they are good at avoiding capture; and (b) this conspicuous coloration is mimicked by other, less evasive species which thus gain protection from predation. We have tested these ideas with wild birds as the predators and red and yellow pastry ‘baits’ as the prey. We used a specially constructed bird table to make one of the colours good at ‘escaping’: when a bird was about to eat a bait the observer pulled a cord which activated a mechanism that made the baits of one colour (but not the other) drop out of the bird's reach. We first measured the overall selection by the naive birds by presenting, for one day, a ‘control’ of equal numbers of non‐evasive red and non‐evasive yellow baits. The birds were then trained for 20 days on equal numbers of evasive yellow and non‐evasive red baits, and were then again given a second control (in which the yellows were now non‐evasive ‘mimics’). The training was repeated for 18 days but with red as the evasive colour, and a third control was then presented (with reds now as the mimics). The proportions attacked daily in the two training sessions suggested that the birds were learning to ignore yellows in the first and reds in the second. In comparison with the first control, fewer yellows were eaten after they had been trained to ignore escaping yellows, and more were eaten after they had been trained on escaping reds. We conclude that the results are further evidence for the hypoth

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04745.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Experiments on the newtTriturus cristatus carnifexhave shown that the spleen of specimens, either anaesthetized with chlorobutanol or in a normal condition, stores red blood cells when the animal is well oxygenated and releases these into circulation under conditions of hypoxia. The extreme limits of congestion and decongestion, commonly encountered in nature, can be obtained in the laboratory by exposing the animals to the air or by immersing them in still water. During the shift from a congested to decongested state, the spleen is reduced to less than one‐fifth of its weight, while the erythrocyte concentration and correlated parameters in the blood stream increase by more than 60%. Splenic regulation of the circulating erythrocyte concentration compensates not only for variations in oxygen supply linked to environment, it may also compensate for the cyclical variations in red cell production of this amphibian, whose erythropoietic tissue activity is intermittent and subject to seasonal variation

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04746.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The external morphology of the four postembryonic instars ofRoncus andreinii(di Caporiacco, 1925) is described and compared with one of the relatedR. lubricusL. Koch, 1873 (Gabbutt&Vachon, 1967), with particular emphasis on disposition of the chelal trichobothria in relation to growth.From the evaluation of characters it is concluded that a few morphometric and chaetotaxic characters (i.e. the length, ratio and shape of pedipalpal articles, the ratio of fingers/pedipalpal hand, the chaetotaxy of sternites II and III) represent good specific discriminants, while the relative position of trichobothria along the chelal axis is nearly the same in both species.The localization of the growing and non‐growing regions along the pedipalpal fingers may be of practical use in the search for new taxonomic character

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04747.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

During the early larval life of lampreys, connective tissue strands develop between the notochord and oesophagus, thereby suspending the oesophagus between the two ducts of Cuvier and above the heart, which, unlike adult lampreys, is not enclosed in a rigid pericardial capsule. Examination of histological sections from proammocoetes and young ammocoetes provides strong evidence that the growth of this suspensory tissue is responsible for the dorsal aorta moving to the right and undergoing a concomitant rotation, which shifts the origin of the anterior mesenteric artery on the dorsal aorta from a right ventro‐lateral to a right dorsolateral position. While the heart initially develops the three major layers found in craniates, i.e. epicardium, myocardium and endocardium, the innermost of these breaks down early in larval life. The myocardium thus becomes bathed in blood, a feature which would help compensate for the lack of a coronary artery. After studying the way in which they are formed early in life, it is proposed that the epicardium is best termed the visceral or splanchnic pericardium and that the thin membrane lining the cavity surrounding the heart should be referred to as the parietal or somitic pericardium. The pericardial capsule of the adult, which is made of non‐compliant walls of cartilage and connective tissue. consists of three main components. The anterior component comprises the anteriorly convex post‐branchial wall. The intermediate component is formed by the posterior part of the seventh branchial arch on each side of the body and their posteriorly‐directed processes. The latter processes expand into the cup‐shaped pericardial cartilage, which constitutes the third and most posterior component of the pericardial capsule. A pear‐shaped opening in the connective tissue formed between the two anteriorly‐directed dorsal extensions of the pericardial cartilage allows the cardinal veins to join the single (right) duct of Cuvier, which in turn enters the sinus venosus. The ventral part of the cartilaginous floor of the pericardial capsule contains a large slit of connective tissue through which the ventral hepatic vein passes upwards to enter the sinus venosus. The inner surface of the pericardial capsule contains an elaborate and very well developed network of venous sinuses and sinusoids, which are supplied by blood from the peripharyngeal sinus and are drained by the inferior jugular vein. It is suggested that this network produces fluid which helps lubricate the heart. A description is given of the way in which the adult pericardial capsule is developed during the seven stages of metamorphosis. This sequence demonstrates that much of the development of the capsule takes place during stage 3 and that by the end of stage 6 the form of the capsule has become essentially the same as that of

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04748.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

We measured purring in unrestrained intact pumas, cheetahs and domestic cats. Domestic cats,Felis silvestrisf.catus, purr at a frequency of 26·3 ±; 1·95 (S.D.) Hz. The frequency at mid‐expiration exceeds that at mid‐inspiration by 2·4 ± 1·3 Hz. Purring frequency for individuals does not change with age. Purring can occur simultaneously with other vocalization. Two‐channel acoustic measurements confirm that the primary mechanism for sound and vibration production is a centrally driven laryngeal modulation of respiratory flow. The diaphragm and other muscles appear to be unnecessary for purring other than to drive

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04749.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Factor analysis of the linear dimensions of 92 species of kingfisher indicated that morphological differences were associated with four diet categories (aquatic, littoral, terrestrial and fossorial animals). Analysis of covariance confirmed the significance of these differences for culmen, tarsus and tail length but not for wing length. Habitat factors resulted in some significant differences but these were less easy to interpret. One case of intraspecific variation showed similar trends for culmen length.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04750.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The behaviour of captive nilgai(Boselaphus tragocamelus)was studied at Whipsnade Wild Animal Park, Bedfordshire, UK, by the method of focal animal sampling. There were four principal feeding periods: at dawn, in the morning, in the afternoon and during the evening. The activity pattern of the male differed significantly from that of the females but otherwise the various age/sex classes behaved similarly. There were significant associations between the classes and significant differences in the mean distances to the nearest neighbour. Play fighting, in the form of neck wrestling, occurred in the calves, mainly the males. The adult male revealed signs of territoriality and the females showed evidence of the existence of social hierarchy. Blackbuck(Antelope cervicapra)sharing the enclosure reacted with the nilgai as if they were conspecifics but other ungulates present ignored them. The area of the enclosure appeared to be adequate and it is concluded that the animals are being managed correctly.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04751.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

A phylogenetic analysis was performed on the genera and subgenera within the freshwater triclad family Dugesiidae, based on 19 terminal taxa and 17 morphological characters. The phylogenetic tree proposed has length of 27 steps and consistency index of 0.66. This phylogenetic hypothesis implies that the current genusDugesiais paraphyletic and that its subgeneraGirardia, SchmidieaandDugesia S.S.should be elevated to the rank of genus. The generaCura, SpathulaandNeppiaare presumed monophyletic by default because the database was unable to provide autapomorphies for any of these genera. The generaDugesia S.S.andNeppiashare sistergroup relationship. Several characters are discussed which were previously considered to be of phylogenetic importance but were not included in the present analysis. It is emphasized that sensory organs form potentially useful set of phylogenetic characters for the Dugesiidae.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04752.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Twelve South African hedgehogs(Atelerix frontalis)were subjected to nine‐week experimental protocol comprising four weeks of simulated summer conditions (14L: 10D and 25 °C), and transition week followed by four weeks of simulated winter conditions (10L: 14D and 15 °C).Six control hedgehogs, with access to foodad libitumthroughout the experiment, did not increase their energy intake during winter yet retained stable body mass. Six experimental hedgehogs, of similar body size, experienced restricted diet during the last three weeks of each season. These hedgehogs displayed significantly lower energy intake than controls during food restriction and lost approximately 7% of their body weight in both seasons, although this weight loss was not significant.Both groups displayed lower digestive efficiencies in winter, together with decline in activity. However, there remained no significant effect of food restriction on these parameters.Neither control nor experimental hedgehogs displayed torpor during summer and, whilst both groups became torpid in winter, the duration of torpor was significantly longer in experimental hedgehogs following food restriction.Analysis of fluctuations in body mass suggest that experimental hedgehogs supplemented their restricted diet with energy derived from body reserves during both seasons. However, the ability of this species to modify the duration of torpor in response to additional energetic stress indicates thatA. frontaliscan control its energetic expenditure in order to limit the depletion of body reser

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1991.tb04753.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY