摘要:

Population densities of foxes of the genusVulpesover most of Canada have shown a fairly regular 9 to 10 year cycle upon which has been superimposed a trend toward increase in numbers. These changes in density are investigated with reference to changes in frequency of the two genes that determine the presence of black rather than red pigment of the pelage. Of the 14 27-year series of gene frequency data, only two show any apparent correlation with the 9 to 10 year cycle in population density. These two, each with a negative correlation whose probability is less than.001, are for the "Alaskan black" gene in the North West Territories and for the "Canadian black" gene in Quebec. On the basis of these latter data the hypothesis is forwarded that there is some selective factor that may operate against these two "black" genes in an expanding population and may favor their increase in frequency when the population is decreasing in size. It is believed that this hypothesis is sufficient to explain the gradual decrease in gene frequency associated with the gradual increase in the size of the population. This hypothesis is utilized to explain the east–west gradient in gene frequency on the basis of negative selection from presumed eastern and western glacial refugia.

ISSN:1923-4287    

DOI:10.1139/cjr50d-005

出版商:NRC Research Press    

年代:1950

数据来源: NRC

摘要:

The species of mosquitoes now known to occur at Churchill, Man., are listed and include 12 species of Culicinae and four of Chaoborinae. Evidence is advanced that one of these,Aedes communisDeG., may really be two species; and a method is suggested of separating some of the black-legged species ofAedeswithout using larval characters or scaling. Some observations on larval habits and habitats, seasonal development, species associations, temperature relationships, and natural enemies are given. Rearing methods used in the field and in the insectary are described. Seasonal changes in numbers, species composition, and activity of the adult population are studied, and quantitative estimates of the influence of meteorological factors on activity are made. Mating habits are described, and adult feeding habits, both on nectar and on blood, are discussed and illustrated. Observations on the development and number of eggs of some species are recorded.

ISSN:1923-4287    

DOI:10.1139/cjr50d-006

出版商:NRC Research Press    

年代:1950

数据来源: NRC

摘要:

The first-instar larvae of 19 sarcophagid and one anthomyiid, and the second-instar larvae of four tachinid species parasitic in nymphal and adult grasshoppers in Canada are described in detail and keys presented for their identification.

ISSN:1923-4287    

DOI:10.1139/cjr50d-007

出版商:NRC Research Press    

年代:1950

数据来源: NRC