摘要:

The tribe Diamesini is a characteristic element of the chironomid fauna of the Holarctic alpine and montane areas. It is represented in the E African mountains by three species:Diamesa kenyaeFreeman,Diamesa ruwenzoriensisFreeman andDiamesa freemanisp. nov.The adults of the three species, the pupa and larva ofD. freemani, and the larva ofD. kenyae, are all described in detail. Several morphological features indicate that the AfrotropicalDiamesaare derived from a relatively plesiomorphic lineage of the genus. Other characters indicate possible sister‐species occurring in the Alps, the Caucasus mountains and the Himalaya. Three lines of evidence suggest a northern origin of the AfrotropicalDiamesa:the relatively young age of the E African mountain peaks, the proposed phylogeny of the genus, and the present distribution of the tribe Diamesin

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1986.tb01332.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Collared lemmings,Dicrostonyx groenlandicus, maintained in the laboratory under short‐day photoperiods (2 h light: 22 h dark) grew faster than their cohorts kept under long‐day photoperiods (22 h light: 2 h dark). Significant differences in cranial, visceral and body components were found in both sexes. Linear regressions of skull‐body parameters were compared to those of wild lemmings trapped at Eskimo Point, Northwest Territories, Canada, during three consecutive summers from 1973 to 1975. The data support the conclusion that variation in body size and skull development associated with changes in population density are, in part, due to photoperiod influences. The importance of this facultative response is discussed in relation to current theories on thermal regulation and variations in subnivial breeding success observed in this sp

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1986.tb01333.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

A video system, consisting of a high‐resolution, infrared‐sensitive, surveillance television camera, time‐date generator, video recorder and high‐resolution monitor, was developed for naturalistic observation of the subaquatic activities of larval mayflies. Exemplars were isolated from light, sound and mechanical disturbance, and their burrowing behaviour was recorded for subsequent slow‐motion analysis. Larvae of silt‐inhabitingHexagenia limbatawere observed to be ploughers that displaced and compacted soft substrate in the excavation of an open tunnel. The head and prothoracic legs had the principal roles in substrate displacement, while the mesothoracic and metathoracic legs drove the body forward. Five stereotyped burrowing cycles were distinguished, although one, termed the Alternate Undercut because of the motions of the prothoracic legs, predominated. Larvae of clay‐inhabitingPentagenia vittigerawere observed to chisel and gouge out compacted substrates, also creating an open burrow. Their mandibular tusks were used to dislodge substrate, while the prothoracic legs displaced loosened substrate and widened the opening. The body was driven forward either by strong abdominal flexions or by activity of the mesothoracic and metathoracic legs. Four burrowing cycles were distinguished, two of which, the Tusk Gouge and the Chisel and Sweep, predominated. Differences in proportion and armature of the head and appendages correlated with the different substrate ty

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1986.tb01334.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Multiple‐group principal component analysis and discriminant analysis were used to investigate the morphological differences between adult skulls of male and female minks, badgers and otters from Norway. The first principal component axis, calculated from the variance‐covariance matrix of log‐transformed data, was interpreted as a growth‐free size axis in all three species, while the other components were interpreted as representing shape. Having largely separated size and shape variation, these two aspects of sexual dimorphism could be studied. The standardized component scores were subjected to an analysis of variance and discriminant analyses were performed on size‐in and size‐out data. Sexual dimorphism was disclosed on eight of the 12 components in minks and on seven of the 12 components in badgers and otters. In mink the multivariate differences were more due to size than to shape, whereas in badgers and otters most of the multivariate differences were due to shape, but the differences in size were also significant. The shape dimorphism was shown to be functionally related to jaw and neck muscles. The results were discussed in relation to recent theories to explain the evolutionary significance of sexual dimorphism in body size of mustelids. It was concluded that these theories do not fully explain the dimorphism found in the skulls of the moderately dimorphic badge

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1986.tb01335.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Vertical enamel prism decussation in the inner‐layer enamel of rhinoceroses occurs as the result of vertical translation, in opposite senses, of zones of ameloblasts, which begins very shortly after amelogenesis commences at the enamel‐dentine junction. Prisms in the centre of the decussating zones are stacked in the Pattern 3 arrangement. Zone boundary prisms adopt intermediate orientations, are locally nearly perpendicular to the enamel surface, and have a cylindrical, Pattern 1 cross‐section. Decussation also continues in the outer‐layer enamel, but the prisms all have occlusal‐going courses: the occlusal‐going zones of the inner enamel continue as the more occlusally oriented zones of the outer layer. Abrasion resistance to diamond polishing and soft abrasive projectile erosion (air‐polishing with NaHCOs) and resistance to ion beam erosion is greater with distance from the nearest prism boundary discontinuity. Polished surface areas containing longitudinally sectioned prisms are more prone to ‘air‐polishing’ and ‘airbrading’ erosion than areas with transversely sectioned prisms. These observed relationships fully explain the relief developed a

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1986.tb01336.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY