摘要:

The structure of the reproductive systems of hatchling and 1 ‐year‐old alligators was investigated macroscopically and histologically. Sex is fully determined at the time of hatching and irreversible thereafter. Constant temperature laboratory experiments revealed that the sex of Alligator miuissippiensis is determined by the temperature of egg incubation, 30°C or below producing females, and 34°C or above, males. Experiments in which eggs were shifted from female‐producing temperatures to male‐producing temperatures and vice versa at weekly intervals during incubation demonstrated that the temperature‐sensitive period for sex determination is around 20 and 35 days after egg laying. In the wild, temperature probes were placed in alligator nests constructed in three different habitats: wet marsh, dry marsh and levee (elevated firm ground). The position of the eggs in the nests were mapped at 60 days incubation and the sex of the enclosed hatchlings correlated with the nest temperatures at that site. Levee nests were hot (34°C) and hatched approximately 100% males. Wet marsh nests were cool (30°C) and hatched approximately 100% females. Dry marsh nests had an intermediate temperature profile, the hottest location (34°C) being the top centre of the nest. Males developed from eggs in this location and females from eggs around the periphery and base of the nest. The sex ratio in dry marsh nests was five females to one male. The natural sex ratio at hatching was determined for a large area of representative habitat for four consecutive years and averaged five (±0.7) females to one male. Females hatched from eggs incubated at 30°C weighed more than males hatched from eggs incubated at 34°C because the former contained more absorbed abdominal yolk. These extra energy reserves enable females to grow faster and become larger than males in the early years of life. This means that heavy females become sexually mature ahead of either light females or light males, and because of the reproductive lifestyle of alligators, this early maturity constitutes a selective biological advantage for the evolution of temperature‐dependent sex determination in Alligator mississippiensis. The occurrence of temperature‐dependent sex determination in alligators has wide‐ranging implications for embryological, teratological, molecular, phylogenetic, conservat

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb05781.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The skinksMabuya sechellensisandM. wrightiiscavenged among the seabird colonies of Cousin Island. particularly under the colony of Lesser noddiesAnous tenuirostriswhich, in 1979, contained about 60.000 pairs. The density of skinks in different areas of the island did not vary greatly through the year. The mean density ofM. sechellensiswas 1393 individuals/ha equivalent to a biomass of 21.7 kg/ha and ofM. wrightii320 individuals/ha equivalent to 17.7 kg/ha. These biomass figures are the highest recorded for any terrestrial lizard population. Skink and Lesser noddy density were closely correlated. The skinks deposited fat equivalent to up to about 50% of their lean dry weight during the noddy nesting season but were leaner and lighter at other times. Our calculations of the amount of skink food emanating from the noddy colonies, in the form of faeces, dropped fish and eggs suggest that there is sufficient to maintain a skink population of the density observed.The skinks bred throughout the year, the largerM. wrightiimore frequently than the smallerM. sechellensis, and the young/adult ratio was higher inM. wrigh:htii.The possible relevance of these differences to the two species' coexistence is discussed. The young/adult ratio varied according to skink density; in both species few young were found at high density.Mean home range sizes ofM. sechellensisandM. wrightiiwere 26·6 and 78· m2, respectivel

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb05782.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

This paper discusses the relationship between aggressive behaviour and sexual maturity, prepubertal castration and wounding in male Bank voles,Clethrionomys glareolus.In neutral arena tests in the laboratory, sexually mature males exhibited more aggressive components of behaviour than immature males or than adult males that had been castrated prepubertally. Mature males also exhibited fewer amicable components than the immature or castrated males. During several months residence in large outdoor enclosures, mature males consistently had more fresh skin wounds (inflicted by other voles) than did either immature or castrated males. The relevance of these results to the population ecology of Bank voles is discussed.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb05783.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Crows walk at low speeds but hop to go faster, setting their feet down out of phase with each other. In contrast, various other bipeds that hop set their feet down in phase with each other. Films of four species of crows have been analysed to obtain quantitative descriptions of their gaits. Comparisons are made with kangaroos, hopping rodents and a small passerine bird.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb05784.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The body masses of various moas have been estimated, measurements have been made of their leg bones and allometric equations have been calculated. Corresponding equations have been calculated for various groups of living birds, using new data and data from the literature. The two families of moas are compared with each other, with modern ratites and with flying birds. Shortening of the tarsometatarsus in moas and narrowing of the pelvis in other ratites are interpreted as adaptations concerned with balancing the bird on its feet. following reduction of the wings.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb05785.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Rana esculenta specimens were collected, during the last 13 years, in well‐defined areas around Naples. The annual ovarian cycle shows distinct phases of recrudescence (starting September; vitellogenesis), breeding (late March‐early July; egg deposition and active oogenesis) and quiescence (July‐August; no follicular growth). Previtellogenic follicles are recruited for vitellogenesis in early September and in between two successive ovulatory waves. Breeding congregations are generally formed after a heavy rain fall and eggs are laid in standing waters, temporary or permanent. A maximum of three clutches of eggs is produced during the breeding season, at roughly monthly intervals. All mature females reproduce to some extent. Ovarian weight and clutch size are positively correlated to body weight. Depending upon the body size, the potential clutch size ranges from 1000 to 3500 eggs during the first wave of ovulation and it is notably smaller in the successive wave(s) of ovulation. Egg masses and tadpoles are left unprotected and mortality is high. The life cycle from the fertilized egg to completion of metamorphosis is 2 months and oogenesis in the ovary starts in the larva before the onset of metamorphic climax. Young females hatching from the first clutch of eggs may reach sexual maturity and breed in May the following year; those hatching from the last clutch require nearly 20 months to reach sexual maturity. The importance of some endocrine and exocrine factors for the regulation of ovarian activity and reproduction is disc

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb05786.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Colonies ofPlecotus auritus(L.) andMyotis daubentoni(Kuhl) occupying the same roost showed no interspecific interaction. They utilized separate areas of the roost, departed from and returned to it at different times and foraged in different habitats on different groups of insects. P.auritusemerged from the roost before dusk, foraged singly in woodland areas with slow, hovering flight and fed on insects commonly found flying in woodland, on insects and spiders gleaned from foliage and on insects caught inside the roost.M. daubentoniemerged from the roost after dusk, flew fast and low over water and around riparian vegetation and foraged on long, straight beats. They frequently foraged in groups, and fed opportunistically on insects which fly in swarms in riparian habitats. The diets of the two species occupying the same roost did not differ from those established in areas where each species was found alone.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb05787.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Vibrissae are highly refined vibrotactile receptors that are present on most mammals. The Golden hamster exhibits three different behaviours of its mystacial, supraorbital, and genal vibrissae. During rest, all the vibrissae are reclined and motionless. When hamsters are alert, the vibrissae are partly or fully erect and essentially motionless. During active investigation, the mystacial vibrissae “whisk” or “sweep” through antero–posterior excursions. The genal vibrissa moves only slightly in periodic erection. The supraorbital vibrissae carry through a wide erection arc and have limited excursions with movements of the upper eyelid. The mystacial vibrissae whisk quickly (about 16 sweepsls). Whisking is divisible into contact (relatively high amplitude, low frequency), non–contact (relatively low amplitude, high frequency), and double–pump (combination contact and non–contact) types, and can be either bilaterally symmetric or asymmetric. The dimensions of the mystacial territory around the snout change throughout whisking due to coordinated changes in the shape of the mystacial pad and the tilting of the vibrissae relative to the pad. Such differential movements have implications for sensory physiology as they point to an ability for fine sensory monitoring of

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb05788.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb05789.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1983.tb05790.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY