摘要:

Two types of pectoral girdles occur among frogs. Arciferal girdles have overlapping epicoracoid cartilages; in firmisternal girdles the epicoracoid cartilages are fused along the ventral midline. Cineradiographic experiments of jumping frogs show that the epicoracoid cartilages of arciferal girdles move relative to each other at the time of landing. Recordings of landings on a force platform reveal that the pectoral girdle of frogs is loaded compressively through the glenoid. This loading regime coupled with differential mobility between firmisternal and arciferal girdles results in differences in stress distribution in the two girdles during landing. The patterns of stress distribution suggest that variation seen among frogs in other aspects of pectoral morphology in addition to the condition of the epicoracoid cartilages may be best understood when analysed from a biomechanical perspective.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb04278.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Quantitative biochemical comparisons of albumin differences within the snake family Colubridae were performed, using micro‐complement fixation analysis. These tests support the recognition of the subfamilies Colubrinae and Natricinae, and corroborate their distinctness from snakes usually placed in the subfamilies Xenodontinae and Lycodontinae. Genetic differentiation within each of the two latter subfamilies is much greater than that measured within either the Colubrinae or the Natricinae. Reallocation of some genera and recognition of some additional taxa are proposed and a summary classification of the revised family Colubndae is presente

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb04279.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

A study of the reproduction of Krefft's river tortoise,Emydura krefftii, was conducted in the perched dune lakes of Fraser Island, Queensland. Mature male specimens exhibit a postnuptial pattern of spermatogenesis typical of temperate‐zone turtles elsewhere, with a peak in spermatogenic activity in autumn and a cessation of activity during the breeding season in spring and early summer. The spermatogenic cycle is paralleled by seasonal variation in testicular weight (standardized for body size) and in the diameter of the seminiferous tubules. Sperm are abundant in the epididymal canals throughout the year. Mating was observed in autumn, late winter and spring.Females have a cyclic reproductive pattern, with distinct phases of follicular enlargement, ovulation and oviducal period, and quiescence. Yolk begins to accumulate in the ovaries in late summer, and the accumulation continues unabated through the winter, presumably by the transfer of material from fat stores to the ovaries. Ovulations occur from late winter to mid‐summer. Atresia of follicles that fail to ovulate was demonstrated histologically.Emydura krefftiilay up to three clutches of hard‐shelled ellipsoid eggs per season. Each clutch contains between four and 10 eggs; the number is strongly correlated with maternal body size. Reproductive potential ranges from 12 eggs per annum for a female that has recently matured (carapace lengthc.150 mm), to 30 eggs per annum for a full‐sized female (lengthc.250 mm). Selected life‐history traits ofEmydura krefftiiare discussed in the context of findings for other populations of the species and for other species of freshwat

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb04280.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Several hundred starlings(Sturnus vulgaris)were introduced to New Zealand from Great Britain during1860–1880. Allozymic variation at 24 loci was analysed in winter populations sampled at six localities in each country. New Zealand samples had fewer alleles per locus but the same mean heterozygosity (3% per locus) and proportion of polymorphic loci as did British samples. Winter populations in Britain contain European migrants and were genetically homogeneous. Paradoxically, genetic distances among derived New Zealand populations, and between New Zealand and Great Britain were much greater, similar in magnitude to those observed among allopatric populations in other avian species. The geographical pattern of genetic variation in New Zealand suggests that reproductive isolation of populations and random drift have contributed to the development of population differentiatio

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb04281.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Pachyornis, which is extinct, was a huge bird with massively thick leg bones. These have been measured, to assess their strength. A mathematical model is used to calculate the forces that must have acted on them, whenPachyornisran. Hence it is shown that the stresses likely to have acted on them are similar in magnitude to the stresses experienced (in stenuous activities) by bones of modem birds and mammals. The femur and tarsometatanus, however, seem disproportionately strong in comparison with the tibiotanus.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb04282.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Theromyzon tessulatumwere reared individually from hatching until they attained sexual maturity. They were fed at different seasons and cultured at one of two temperature regimes. A series of weight measurements enabled growth curves to be constructed. Observations were also made on the digestive processes. In keeping with at least one other sanguinuous glossiphoniid, a restricted and constant number of blood meals precede reproduction and the hungry and sated stages show contrasting and distinctive behaviour. A notable feature is the great increase in weight after feeding resulting from the absorption of water and its incorporation into the body tissues. It probably enters through the body surface. The role of microorganisms within epithelial cells of certain crop caecae, was also considered.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb04283.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Simultaneous hermaphroditism is an infrequent mode of reproduction among bivalves of the family Unionidae: only five of the 220 North American species are simultaneous hermaphrodites. However, hermaphroditic individuals of otherwise predominantly dioecious species have been encountered in 30 of I01 species examined. These hermaphroditic individuals as well as simultaneous hermaphrodites can exhibit considerable variability in the ratio of spermatogenic: oogenic tissue within the gonad, and the purposes of this paper are to determine the underlying causes of both this variability and the occurrence of occasional hermaphroditic individuals among dioecious species. Results indicate that the ratio of male: female gonodal tissue of a simultaneous hermaphrodite is bimodally distributed, and several hypotheses to account for this observation are presented. It is proposed that populations occurring in different habitats and under conditions of different individual density are subject to fundamentally different sexual selection pressures acting on ratios of allocation to male and female gametes. Occasional hermaphroditism among otherwise predominantly dioecious species was in this study associated with infection of the gonads by digenean trematodes. A model of sexual determination among unionids presented in this paper proposes that sex is determined by genetically controlled hormone levels: occasional hermaphrodites result from alterations in these hormone levels caused by developmental errors and trematodal infections which mimic the results of such errors. Predictions of this model are consistent with observed levels of variability in male: females gonadal tissue among occasional hermaphrodites.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb04284.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Pelagic first crab stages of the deep‐sea spider crab,Dorhynchus thomsoni, are reported from mid‐water samples taken at a variety of localities in the Porcupine Seabight and the Rockall Trough. Some of these samples were from hauls made near the surface over depths of 3000 m or more.An analysis of these pelagic samples, and of benthic catches ofD. thomsoniheld by the Institute of Oceanographic Sciences and the British Museum (Natural History), indicate that most females and at least some males undergo the puberty prior to the third crab instar, these individuals therefore probably pass through a total of only three larval and three post‐laval instars. There is at least a possibility that some individuals moult after the moult of puberty, unlike any other spider

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb04285.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY