摘要:

A systematic examination was made of isolating mechanisms, as set out by Mayr, that might serve to maintain reproductive isolation between the marine (trachurus) and the freshwater (leiurus) threespine sticklebacks. Field work was conducted in a small British Columbia coastal stream, the Little Campbell River, foryears and complemented with laboratory experiments. Other streams were included late in the investigation.Leiuruspermanently occupies the upper reaches of the stream;trachurusis anadromous and enters the lower reaches to breed in freshwater. Between the breeding grounds of the two, where numbers of both are greatly reduced, hybridization occurs. But it is restricted to a narrow zone.The two species are easily distinguished. Thus, morphological analysis provided firm circumstantial evidence that hybrids are plentiful and that backcrossing occurs, predominately toleiurus. Hybridization was confirmed by rearing offspring under uniform conditions in the laboratory with crosses in all combinations. Such offspring were also used to demonstrate considerable genetic divergence (much of it polygenetic) betweenleiurusandtrachurus.Behavioural experiments demonstrated the absence of ethological isolation and hybrids performed courtship and parental care normally.Nor was genetic incompatibility found in the reared hybrids (F1's or backcrosses); all were vigourous. Seasonal isolation is only partially developed with early spawning migrants oftrachurusmaking a major contribution to hybridization (in the Little Campbell River).Since behavioural and genetic blocks to hybridization are not present, there is no means to prevent hybridization whereleiurusandtrachuruscome together. However, coexistence between the two species is very low. Evidence from observation and experiment in the field and from preference tests showed that ecological isolation is a very powerful barrier to hybridization. The two species show numerous adaptations to the distinctly different habitats they frequent, and each shows a strong affinity for its own habitat. In localities with intermediate or contiguous habitats, coexistence and interbreeding occur. Hybridization is a function of the environment.No selection against hybrids could be detected within the hybrid zone (or with laboratory reared hybrids); yet, one is forced to assume that it is present outside the zone. The very narrow zones as well as the reversed cline that were found indicate there is intense selection against hybrids. What these selective forces are remains to be found. Hybrid zones will probably continue to be poorly understood until a critical analysis of hybrid inferiority is made.Genotypes of either species that remain in the hybrid zone are at a strong selective disadvantage. Hence, reinforcement of ecological isolation probably occurs, and Moore's criticism concerning the spread of such reinforced genotypes would not apply to such cases. Mayr distinguishes between pre- and postmating mechanisms stating that the mode of operation of natural selection will be different for the two. But in threespine sticklebacks one premating mechanism (ecological isolation) and one postmating mechanism (hybrid inferiority) cannot be distinguished. This is so because ecological isolation is the cause of hybrid inferiority.Leiurusandtrachurusare reproductively isolated, have well developed isolating mechanisms, and exhibit considerable genetic divergence. The two, then, fulfill the species definition of Mayr. There is no evidence that introgression occurs. Indeed a reversed cline showing a progressive increase in morphological divergence between the two species as the hybrid zone is approached together with the narrow hybrid zone demonstrates that selection severely restricts gene flow. Collections and observations from other streams corroborate those from the study area. Reproductive isolation betweenleiurusandtrachurusseems to be widespread, throughout their range.

ISSN:0706-652X    

DOI:10.1139/f67-138

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

Kench and pickle salting are being used for the preparation of both light- and heavy-salted cod (Gadus morhua). Because of the potential advantages of brine salting, especially mechanical adaptability, experiments were conducted to determine the practical merits of this process in the preparation of light-salted codfish of the Gaspé-cure type. In a batch operation using an equal weight of fish and brine, good results were obtained using 25% by weight salt solution and 5 hr of salting. With continuous circulation of brine of constant strength at 18 C, optimum conditions were achieved for salting using an 18% brine solution and an 8-hr exposure period. With a brine temperature of 10 C, at a brine concentration of 22%, a curing period of 12 hr was required. In each case the salted product must be "water horsed" for about 24 hr before drying.The water content of the product obtained by brining was higher than that of conventionally prepared fish, but the drying rate was also higher resulting in an overall drying time that was nearly the same. With efficient drying, it was possible to obtain a product which resembled the regular Gaspé-cure in appearance and in chemical characteristics.

ISSN:0706-652X    

DOI:10.1139/f67-139

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

In rainbow trout (Salmo gairdneri) blood plasma concentrations of adrenaline (AD) and noradrenaline (NAD), and liver and heart concentrations of AD increased in response to severe physical disturbance. Skeletal muscle and anterior kidney concentrations of AD and NAD did not change detectably. Maximum plasma concentrations observed during disturbance of the fish were 0.20–0.36 μg AD and 0.05–0.09 μg NAD/ml. These plasma concentrations decreased relatively rapidly during recovery of the fish.Plasma glucose concentrations increased in response to disturbance, the magnitude and duration of the hyperglycemia being greater in those fish with initially high liver glycogen reserves. Liver glycogen concentrations in those fish with initially high (ca. 7%) concentrations apparently decreased in response to disturbance and increased during recovery of the fish, but no change was detected in liver glycogen concentrations in fish in which they were initially low (ca. 2.5%). Heart and skeletal muscle glycogen concentrations decreased in response to disturbance and increased during recovery.In skeletal muscle, the concentration of adenosine 3′,5′-phosphate and the proportion of phosphorylase in theaform increased in response to disturbance of the fish and decreased thereafter.

ISSN:0706-652X    

DOI:10.1139/f67-140

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

Adenosine 5′-monophosphate aminohydrolase (EC 3.5.4.6) activity of prerigor cod muscle could be extracted with water or 0.02 Msuccinate buffer in about 90% yield, but 0.02 MKCl gave a low yield. With postrigor muscle, the enzyme tended to be associated with the fibrillar protein fractions. The activity of the unpurified enzyme, measured by apH-stat, showed a maximum atpH 7.0 in 0.02 Msuccinate, and aboutpH 6.6 in 0.1 MKCl. AtpH 7.0, activities were maximal and approximately equal in 0.1 MKCl, 0.1 MNaCl, and 0.04 Mpotassium succinate. Phosphate buffer inhibited the reaction under certain conditions. The enzyme was sensitive to glass and other surfaces, and this seemed to be responsible for loss of activity during dialysis. The activation energy was 10 kcal per mole and the Michaelis–Menten constant was 1.4 × 10−3moles per litre.

ISSN:0706-652X    

DOI:10.1139/f67-141

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

Further studies on the swimming performance of fingerling sockeye salmon at fixed velocities have been conducted in relation to fatigue time. The method of probit analysis, commonly used in dealing with bioassay data, was found to be suitable for determining times to 50% fatigue and in providing a measure of variance despite the presence of some erratic behaviour. For sockeye acclimated to 15 C (mean length = 13.6 cm) the velocity at which 50% fatigued was 54.4 cm/sec or 4.0 lengths/sec (L/sec). The 5% and 95% fatigue velocities were 3.1 and 4.8 L/sec, respectively. Larger fish required longer exposure times for determining maximum sustained speeds, extending from approximately 120 min for fingerlings to 500 min for adults.Using the method of increasing velocity steps the effect of temperatures from 5 to 27.5 C was examined. When acclimated to 15 C fingerling sockeye exhibited only a 4% reduction in swimming speed at 10 and 20 C. Temperatures above the lethal level caused a rapid decline in swimming ability approaching the extinction point at 27.5 C.Recommendations for standard procedures in the study of swimming speeds are made.

ISSN:0706-652X    

DOI:10.1139/f67-142

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

A 20-year study showed that forming a pond near the mouth of Ellerslie Brook, Prince Edward Island, did not change the seasonal pattern of brook trout movements between fresh- and salt water. Delay in movements of trout through the pond and a tidal pool below the dam resulted in heavy natural and angling mortalities in those areas. Movements between fresh- and salt water were almost eliminated. Natural seeding of stream above pond was not demonstrably affected.

ISSN:0706-652X    

DOI:10.1139/f67-143

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

Aporocotyle margolisin.sp., from the bulbus arteriosus ofMerluccius productus(Ayres) caught off Vancouver Island, is described and figured. Records ofAporocotylefrom other hosts are discussed.

ISSN:0706-652X    

DOI:10.1139/f67-144

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

Dorsal aortic blood pressure, heart rate, and oral water pressure were recorded in adult sockeye salmon (Oncorhynchus nerka) while they were resting in darkened aquaria or swimming in an illuminated tunnel-respirometer. Pressures were recorded on an oscillograph attached to pressure transducers connected with cannulae in the dorsal aorta and oral cavity. The velocity of the water in the swimming chamber was increased in stepwise fashion every 30 min until the fish stopped swimming and were swept against an electrified grid. At the cessation of swimming, which was considered as the onset of fatigue, water velocity was decreased to a minimum which permitted the fish to rest and dorsal aortic blood pressure, heart rate, and oral water pressure were recorded for about 1 hr as they returned toward resting levels. Resting values were 44/38 mm Hg (systolic/diastolic) and 49 heartbeats/min. At maximal swimming speed dorsal aortic blood pressure was 55/49 mm Hg and heart rate was 83 beats/min. No abrupt changes in cardiovascular function occurred at the onset of fatigue.A number of morphological (length and weights of the body and ventricle) and cardiovascular (pressures, rates) variables were measured in six adult sockeye salmon. A significant correlation was found between hematocrit, ventricle weight, and heart rate; a change in one apparently caused adjustments in the other two in order to maintain a constant supply of oxygen to the tissues during subfatigue levels of activity.The effects of removal and replacement of blood or isotanic saline in the dorsal aorta were observed in three adult sockeye salmon. Removal of blood produced a proportionate decrease in blood pressure and an increase in heart rate. Neither dilution of the blood by replacement with saline nor increase in blood volume from addition of saline had any significant effect on heart rate and blood pressure.

ISSN:0706-652X    

DOI:10.1139/f67-145

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

This communication presents the results of a study of the pituitaries of 150 sockeye salmon in various stages of sexual maturation from the time they entered freshwater till after completion of spawning. In the homologue of the adenohypophysis, nine different cell types were distinguished. On the basis of changes in tinctorial and histochemical properties and relative proportions of each of these cells, it was concluded that the sockeye pituitary contains six different hormone-producing cell types. One of these probably possesses a gonadotrophic function. Degenerative phenomena in the pituitary were found in the sexually ripe and the spent salmon, but only to a limited extent. The implications of the changes in the occurrence of the six different cell types and the degenerative alterations are discussed in relation to gonad development and the death after spawning.

ISSN:0706-652X    

DOI:10.1139/f67-146

出版商:NRC Research Press    

年代:1967

数据来源: NRC

摘要:

not available

ISSN:0706-652X    

DOI:10.1139/f67-147

出版商:NRC Research Press    

年代:1967

数据来源: NRC