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1.
We studied several determinants of laying date variation and the relationship between laying date and reproductive success in the Snow Petrel Pagodroma nivea . The effects of female body size and condition, year, individual laying period, colony size, mate fidelity, previous reproductive success, and duration of the pre-laying exodus on laying date, were investigated during a 3-year study. The average laying date was 4 December. The laying period was compressed into 10–16 days and was very constant from year to year, both for the population as a whole and for individual females. The laying period of individual females varied from year to year on average by less than one day. Body size explained 24% of the variation in laying dates, with large females laying their egg later than small ones. Laying in large colonies occurred c. 2 days later than in small colonies, mainly because a higher proportion of large females bred in large colonies. There was no effect of mate fidelity, age, body condition and previous reproductive success on laying date, but the duration of the pre-laying exodus was strongly correlated with laying date. Smaller females had shorter pre-laying exodus (c. 17.7 days) than larger ones (c. 20.4 days). During the three years of the study reproductive success either increased, decreased or did not vary with laying date. Although body size is not maintained by selection on laying date alone, the genetic body size component of this species suggests that balancing selection on body size may act through laying date.  相似文献   

2.
Demographic parameters were estimated for snow petrels Pagodroma nivea nesting at Pointe Géologie Archipelago, Adélie Land, Antarctica between 1963 and 1990; 21 years of data on adult survival and 27 years of data on breeding success are available. The average age of first return and first breeding were 8.1 and 9.9 years respectively and there was no signifcant difference between the sexes. The overall breeding success averaged 51.3% and was very variable between years (21–80%). Breeding failure was mostly due to incubation failure and annual breeding success was negatively correlated with average snow falls in October–November and October–March. Breeding frequency was very low, averaging 52% of seasons during a reproductive lifetime. Good quality sites, with high occupancy rate and high breeding success were few in the study plots. Poor years in 1966–1967, 1976–1977 and 1983–1984, with low breeding success, very low proportions of nets with breeding attempts and high numbers of non-breeders, occurred 1 year after large-scale El Niño Southern Oscillation (ENSO) events. Snow petrels exhibited very low philopatry. Only 45 birds have been recovered in the study plots from a total of 1115 banded fledglings giving an estimated rate of return of 12.9% between fledging and 3 years old. Annual survival between 3 and 10 years was 91.4%. Annual adult survival (93.4%), though variable, was low during poor years of 1977–1978 and 1983–1984. Adult survival of males (94.7%) was not significantly different from that of females (93.9%). Over the study period, the population of Pointe Géologie was stable. Using the estimated parameters, a Leslie model gave a growth rate of 0.948%, which was probably compensated by immigration (5.7% per year). Restricted numbers of good-quality sites at the place of birth could have led young birds to prospect other colonies and could have selected low philopatry. High adult survival, strong site tenacity and capacity to spread breeding over a long lifetime are probably part of the adaptive strategy of this small fulmarine petrel facing highly variable environmental conditions.  相似文献   

3.
We examined how variations in parental quality affect the reproductive success of a long-lived seabird, the snow petrel (Pagodroma nivea). In particular, we focused on how prebreeding body condition (prebreeding body mass adjusted for structural size) influences the hatching success of male and female snow petrel. Condition in females, but not in males, had a significant effect on hatching success. Among breeding pairs, early body condition of pairs was not significantly related to their hatching success. Laying date had a significant effect on hatching success, but this was due to heavy snowfalls during the beginning of the laying period. We suggest that females in poor early condition would not be able to build up sufficient body reserves necessary for successful incubation during the energy-demanding egg formation period. Moreover males, being structurally larger, would have a higher fasting capacity. These results show that the hatching success of the snow petrel is clearly influenced by female condition and suggest that effects of variations in environmental conditions may depend on body condition of individuals. However, the year of the study appeared to be an unusually poor year for reproduction, which may be why female body condition appears to be important. Accepted: 24 June 1998  相似文献   

4.
Recent studies have shown that the Antarctic Circumpolar Wave and the related sea-ice cover around the Antarctic continent may have a profound effect on the lower trophic levels of the marine environment. In particular, extensive sea-ice cover enhances the survival of krill. However, the effects of sea-ice cover on top predators remain poorly understood. Using time series from 1973 to 1999, we examine the influence of regional sea-ice extent on a number of indices of breeding performance of an avian predator, the Snow Petrel, in Antarctica. The percentage of breeding pairs was highly variable and there were fewer birds breeding when sea-ice cover was extensive during July. By contrast, overall breeding success and fledgling body condition were improved during years with extensive sea-ice cover during the preceding November and July–September. These results indicate that the same sea-ice conditions may have different effects on the breeding performance of a species. The overall increase in winter sea-ice extent during the last decade appears to have resulted in an overall improvement of the quality of fledglings produced, and thus probably of future recruitment.  相似文献   

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7.
W. K. Steele 《Polar Biology》2005,28(9):672-679
This study investigated the trophic hierarchy status of the Antarctic petrel (Thalassoica antarctica) and snow petrel (Pagodroma nivea) within the Southern Ocean food-web off Dronning Maud Land, Antarctica. During 1991/92 ten Antarctic petrel and ten snow petrel carcasses were collected from Jekselen (71°59S, 02°35W) and Robertskollen (71°28S, 03°15W) respectively, in the northern Ahlmannryggen, Dronning Maud Land. Collagen from the dense bone of the humeri of these carcasses was extracted and the stable carbon and nitrogen isotope ratios of these samples determined. The snow petrel bone collagen samples displayed a mean 13C value of –23.9±0.7 (range: –24.7 to –22.9; n=9) and a mean 15N value of 15.2±1.6 (range: 12.9 to 18.4; n=10). The corresponding values for Antarctic petrel bone collagen were –24.8±1.0 (range: –26.2 to –22.8; n=9) and 13.2±0.6 (range: 12.5 to 13.9; n=8) respectively. The difference between the species 13C values may indicate differences in their foraging habitat. It has previously been suggested that the snow petrel has a higher wing loading than other Procellariiforme species, making the snow petrel less adapted to pelagic foraging than related species and more likely to forage close to the sea ice edge. Algae growing under sea ice apparently can have comparatively high 13C values, possibly due to growing under carbon dioxide limited conditions. If so, animals foraging close to the sea ice edge might be expected to show higher 13C values in their body tissues than animals foraging farther out over the open ocean. However, the high 13C of snow petrel collagen is possibly more likely to be related to the correspondingly high 15N values found in this tissue, and hence caused by snow petrels including offal from high trophic level Antarctic mammals and birds in their diet.  相似文献   

8.
9.
I consider the possibility of selection favouring large body size in a population of snow petrels (Pagodroma nivea), a long‐lived seabird species. I measured natural selection on body size traits in a population from 1987 to 1998. There was evidence of selection on body size associated with fecundity and survival. Directional selection on bill length and stabilizing selection on tarsus length associated with reproductive success were detected among males. Selection associated with survival favoured males with longer bills. However, selection was weak in all cases. No evidence of selection acting on female body size traits was detected. Offspring–parents regression suggested that bill length and tarsus length were heritable. Although I was able to identify the targets of selection in this population, I could not demonstrate the ecological implications of both tarsus length and bill length variation. The selection on male, but not on female, body size traits suggests factors such as intrasexual competition for nests and/or mates rather than factors such as feeding efficiency as mechanisms of selection on bill size.  相似文献   

10.
Bird observations were made as part of a preliminary biological survey of the southern half of the Mawson Escarpment in the southern Prince Charles Mountains, Mac.Robertson Land between 26 January and 4 February 1998. A new breeding colony of snow petrels (Pagodroma nivea) is described, together with details of individual snow petrel sightings. At 440 km from the coast, the snow petrel colony is the furthest inland of any confirmed breeding site for this species. Accepted: 1 May 2000  相似文献   

11.
Larvae of Rhinoestrus purpureus (Brauer) and Rhinoestrus usbekistanicus Gan (Diptera: Oestridae) cause nasal myiases of equids. During a recent epidemiological survey in southern Italy some morphological and taxonomical doubts arose concerning the identification of Rhinoestrus third stage larvae on the basis of the features of the posterior spiracles and the distribution of dorsal spines on the third segment. Four different morphotypes were retrieved: R. usbekistanicus-like, R. purpureus-like and two morphotypes with shared features. The genes encoding for the mitochondrial cytochrome oxidase I (COI) and for the ribosomal subunits 16S and 28S of the four morphotypes of Rhinoestrus were investigated to determine whether they belonged to a single taxon or they displayed genetic differences indicative of more than one species. The three genes showed a very low level of sequence variation (COI 0-0.43%, 16S 0-1.45%, 28S 0-0.23%) falling within the intraspecific ranges previously described for Oestridae species. Finally, the peritreme features and the spinulation of the third segment of the four morphotypes examined could not be used to differentiate the two species.  相似文献   

12.
P M Borodin 《Genetika》1987,23(6):1003-1010
It was shown by D.K. Belyaev and the coworkers that stress can lead to changes in the degree of manifestation of genetic variation in a number of quantitative traits, such as fertility, growth rate and endocrine functions. The effects of emotional stress on the meiotic process in male mice were established. Stress inhibits both replication and repair of DNA at corresponding stages of meiosis. These are the reasons for an increase in X-Y and autosomal univalent frequency and recombination frequency in the 1-st and 2-nd chromosomes. Thus, stress leads to redistribution of recombination frequencies in the genome and produces the new spectrum of combination variation. The data presented support the concept of D.K. Belyaev that stress has substantial influence on the rate of evolution.  相似文献   

13.
Linkage disequilibrium and genetic variability   总被引:1,自引:0,他引:1  
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14.
Social identity and genetic variability   总被引:1,自引:0,他引:1  
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15.
It is well understood that genetic tumors develop in certain interspecific Nicotiana hybrids. Nicotiana species are divided into “plus” and “minus” groups and crosses between “plus” and “minus” species give rise to tumorous hybrids. However, it has been proposed that parents and hybrids derived from crosses among members within the same group do not produce tumors. In this study, genetic tumors were only obtained in Nicotiana glauca, which exhibited tumor features similar to those of N. glauca × N. langsdorffii. Our results suggest that genetic factors may control tumor formation independent of tumor induction dependent on the specific interspecific cross. Genetic tumor formation exhibited high B-type and D-type cyclin expression levels, indicating tumor cells are characterized by an uncontrolled cell cycle.  相似文献   

16.
CHRISTOPHER R. BROWN 《Ibis》1988,130(6):527-534
Energy expenditures of Salvin's Prions Pachyptila vittata salvini , Blue Petrels Halobaena caerulea and Great-winged Petrels Pterodroma macroptera during growth were estimated from measurements of oxygen consumption. Total energy expended during growth was calculated to be 6877 kJ and 10206 kJ for the smaller Salvin's Prions and Blue Petrels, respectively, and 22697 kJ for the larger Great-winged Petrels. A further 2390 kJ, 3067 kJ and 11801 kJ, respectively, was calculated to be accumulated as body tissue. Food requirements for growth, estimated from energy requirements, diets and assimilation efficiencies were estimated to amount to 1519 g and 932 g for Salvin's Prions and Blue Petrels, respectively, and 4577 g for Great-winged Petrels.  相似文献   

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18.
The findings are presented of a macro and microscopic investigation of 89 hydatid hepatic cysts removed intact from 59 patients by total pericystectomy. Detailed analysis revealed significant morphostructural variability and cysts grouped into 10 types were characterized, providing useful clinical indications. Only 30 cysts resulted fertile (33.7%), probably due to mean age of sample; 7 of these were "classic" cysts, 1 "septated" and 22 "multivesicular" packed with daughter cysts (DC), of varying turgidity or collapsed. Among the remaining 59 sterile cysts, 52 were degenerated and classified as "hyperlaminated" cysts due to the presence of large convoluted sheets of laminar tissue (SLT) surrounded by varying amounts of caseous (40 specimens), granular (6) or gelatinous (6) matrix. Moreover, "multivesicular", "acephalocyst", "caseous" and "serous" cysts were also recovered among the sterile specimens. Some "multivesicular" cysts (14) appeared as "transitional forms" towards the various types of "hyperlaminated" cysts containing all different forms of DC and large SLT intermingled with a variously degenerated matrix. The comprehensive study allows to hypothesize the train of events leading, over the years, to the gradual transformation and degeneration of the larval form Echinococcus granulosus in the human liver.  相似文献   

19.
Knowledge of the genetic population structure lies at the heart of mapping studies aiming genes responsible for Mendelian and complex traits. The Quebec population, which is of mostly French descent, is considered an excellent model for such genetic epidemiological endeavours because it is a young founder population. Yet, the assessment of the founder effect has relied mostly on the observed distribution of monogenic diseases and on the analysis of the underlying mutations with investigations focusing on the Saguenay region. To eliminate this clinical bias and to obtain a more complete image of the genetic diversity, different regional populations of Quebec were investigated by analysing neutral markers that represent maternal, paternal and X chromosome lineages. Results indicate that Quebec does not appear more homogeneous nor significantly different from European populations. However, a series of regional founder effects, particularly visible at the level of rare variants, are observed. These effects can be explained by the successive migrations of descendants of the first immigrants from the initial sites of settlement towards the outer regions. Depending on the number of founders and their diversity, as well as on the degree of isolation and the magnitude of the interbreeding with the neighbouring or local populations, such as Amerindians or later migrants, the consequences of these regional founder effects are more or less detectable in the contemporary population.  相似文献   

20.
Karlin S  Feldman MW 《Genetics》1981,97(2):475-493
The equilibrium behavior of one-locus viability selection models is studied numerically. The selection schemes include randomly chosen viabilities, viabilities chosen to measure a hypothetical distance between the alleles making up the genotype and viabilities that obey various allelic dominance relations. From 3 to 8 alleles are considered. Among the key conclusions are (1) equilibria that are most polymorphic do not usually have the highest mean fitness, (2) the more structure there is in the choice of the viability model, the greater is the level of polymorphism at equilibrium, and (3) for the numbers of alleles chosen here, the equilibrium reached by iteration from the centroid of the allele frequency simplex is the best predictor of the equilibrium attainable from randomly chosen starting vectors. Preliminary evidence shows that this is not the case for 16 alleles.  相似文献   

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