AGE, EGG-SIZE AND BREEDING SUCCESS IN THE HERRING GULL LARUS ARGENTATUS

The breeding biology of the Herring Gull Larus argentatus was studied in 1969, 1970 and 1972 on Skokholm, Pembrokeshire. The distribution of laying dates in three years is given; median laying date was always about 10 May. Laying dates of individual pairs were fairly constant between two years, but females up to nine years of age apparently advanced their laying date in successive years. In 1969 there was a decline in clutch-volume index during the season but this was not found in 1970 or 1972. Females laid clutches of similar volume in successive years, although the volume did vary with age, increasing up to 7 or 8 years of age and then declining. Hatching success was highest in the earliest of four periods in 1970 (69%) and lowest in the last (51%); in 1972 the corresponding figures were 71% and 63% and the seasonal trend was not significant. Chick mortality was higher in 1970 (69%) than in 1972 (59%); in 1970 there was significant seasonal variation in chick survival but in 1972 there was not. In 1970 chick survival was positively correlated with hatching weight (and hence egg-size) and chick survival was also related to growth which was itself correlated with hatching weight. There were no such correlations in 1972. Mean chick production in 1970 was 0.60 per pair and in 1972 0.70. In both years later breeders were less successful, but the seasonal range of mean success was less in 1972. In the discussion it is shown that some of these differences between years could be due to changes in the age structure of the population and it is suggested that the correlation between egg-size and chick survival in 1970 may be an artefact of the age structure.     

SEXUAL SIZE DIMORPHISM AND EGG-SIZE ALLOMETRY IN BIRDS

We tested the hypothesis that egg size should evolve in sexually dimorphic birds to reduce costs associated with more rapid growth by nestlings of the larger sex. Consistent with this hypothesis, we found that in species in which males were larger, females laid proportionately larger eggs as sexual size dimorphism increased. However, this result was also consistent with the hypothesis that egg size varied allometrically with both male and female body size. Furthermore we found that in species in which females were larger, relative egg size decreased as size dimorphism increased, which is consistent with the “allometry hypothesis” but not the “cost-reduction hypothesis. That male body size contributes to the allometric relationship between egg size and body size suggests that the basis for the allometric relationship is not wholly a mechanical one stemming from the physical requirements of developing, transporting, and laying an egg of a particular size. Rather, the relationship seems likely to be tied more directly to body size itself the tact that male body size influences a female trait suggests that egg size–body size relationships otter some scope for investigating the basis for allometric relationships in general.     

捻转血矛线虫卵发育至三期幼虫需热量的线性回归数理统计模型分析

对捻转血矛线虫卵在不同温度条件下进行培养,观测了发育至第三期幼虫所需的不同历期．由此分析两种线性回归模型、结果表明第二种回归模型y'＝1977.3940＋8.3315x较为适合．此模型能较好地表达温度与发育历期的数理统计关系,所推算的发育起点温度为8.3℃,有效积温为82.4（日.度）．     

POLYMORPHISM IN THE DESMID XANTHIDIUM REGULARE AND ITS TAXONOMIC IMPLICATIONS

This paper refers to a case of polymorphism in the desmid genus Xanthidium Ehr. It is based on material from Lake Dais Irmaios, the main body of water in the Zoological and Botanical Garden in Recife, Pernambuco, northeastern Brazil, collected at 4 different times of the year during 1967 and 1968. A detailed examination of almost 1300 specimens showed an enormous variety in form of Xanthidium regulare Nordst., X. fragile Borge, and X. pseudoregulare Borge, thus allowing the authors to draw the following conclusions: (1) the name X. regulare Nordst. should be retained until further and more detailed studies on form variation within the species are available; (2) the names X. regulare Nordst. var. asteptum Nordst. in Borge, X. regulare Nordst. var. sexangulare Grönbl., X. regulare Nordst. var. sexangulare Grönbl. f. robustior Grönbl., X. fragile Borge, X. fragile Borge forma, and X. fragile Borge var. depauperatum Borge should be considered synonymous, all referring to a single variety of X. regulare Nordst., var. asteptum Nordst. in Borge emend. C. Bic. & L. M. Carv.; (3) X. pseudoregulare Borge must be treated as a variety of X. regulare Nordst. and must be called X. regulare Nordst. var. pseudoregulare (Barge) C. Bic. & L. M. Carv. Finally, a key is given to the 3 varieties of X. regulare Nordst. proposed in the present paper.     

PHOSPHOGLUCONATE DEHYDROGENASE POLYMORPHISM AND SALINITY IN THE WHITE SANDS PUPFISH

The phosphogluconate dehydrogenase (Pgdh) locus is the only polymorphic allozyme locus observed among 37 loci examined in all four populations of a New Mexico state Endangered species, the White Sands pupfish (Cyprinodon tularosa). We report evidence suggesting that this polymorphism may be associated with salinity. Salinity levels vary widely within and between habitats occupied by White Sands pupfish. The frequency of the Pgdh¹⁰⁰ allozyme was correlated with salinity but not with temperature. Frequency of Pgdh¹⁰⁰ differed between low (3.76 parts per thousand (ppt)) and high (9.23 ppt) salinity sites at Malpais Spring despite no obvious barriers to fish movement. Frequencies of Pgdh¹⁰⁰ in two introduced populations differed from that of the presumptive founding stock and correlated with salinity in the current habitats.     

同种介形类壳体的多态性兼及化石介形类的物种鉴定

介形类个体发育过程中壳体形状及各种构造的多态性,以及各种外界环境因素对分形类壳体各种分类特征形态变化的影响是十分明显的。该文较系统地阐述了在介形类个体发育中壳体形状、大小、肌痕、边缘毛细管带、边庭、铰合构造及纹饰的变化,并介绍了成年期雌、雄性壳体及左、右壳瓣在形态上的差异;列举了环境因素(主要是水体温度、含盐度、深度)对介形类壳体各分类特征形态变化的影响。基于以上事实,提出了古生物工作者在介形类化石鉴定中应注意的一些问题并讨论了某些描述术语的具体标准。     

THE DISTRIBUTION OF GROUP D STREPTOCOCCI IN CATTLE AND SHEEP

Numbers and types of Lancefield group D streptococci have been determined in samples from the colons of 17 cattle and 9 sheep. Mean total streptococcal counts of 8 × 10⁴/g in cattle and 2 × 10⁶/g in sheep were obtained. Streptococcus bovis was found in every sample and was the predominant species in 15 of the cattle and 6 of the sheep. Other group D streptococci ( Strep. faecalis, Strep. faecium and Strep. durans ) were rare in cattle, but in sheep they formed a significant proportion of the population. Of 60 Strep. faecium, Strep. durans and related strains, 51 fermented raffinose. Many of the strains of Strep. faecium were also atypical in that they fermented sorbitol and appreciably reduced tetrazolium in broth at pH 6.0.
Strep. bovis remained the predominant streptococcus in faeces samples from 4 dairy cows when they were tested again after an interval of 17 and 18 months.     

THE EXCHANGE OF PHOSPHATIDYLCHOLINE AND OF PHOSPHATIDYLINOSITOL IN SHEEP BRAIN

—The exchange of phospholipids between liposomes and brain mitochondria has been studied in the presence of pH 5·1 supernatant fluids derived from rat, guinea pig, sheep and ox brains. The exchange phenomenon was similar to that observed in liver and heart, but phosphatidylinositol and not phosphatidylcholine was the most rapidly exchanging phospholipid. The phosphatidylcholine exchange activity was purified 186-fold from sheep brain and the protein fraction contained two major and several minor protein species. The phosphatidylcholine and phosphatidylinositol exchange activities have been shown to have very similar molecular weights and isoelectric points. However, their behaviour in response to changes in liposomal surface charge suggested that separate proteins might be involved in stimulating the exchange of the two phospholipid classes.     

PHYSIOLOGICAL STRESS AND COLOR POLYMORPHISM IN THE INTERTIDAL SNAIL NUCELLA LAPILLUS

The intertidal snail Nucella lapillus exhibits considerable variation in shell color both within and between populations differentially exposed to wave action. Populations from high-wave-energy shores tended to be highly polymorphic and were dominated by pigmented morphs (especially brown), while those at more sheltered locations exhibited less polymorphism and were predominantly white. Field and laboratory experiments were conducted to determine the role of physiological stress and selective predation in maintaining the observed distribution of color morphs. The results demonstrated that 1) physiological stress from high temperature and desiccation during periods of tidal emersion was greater on protected shores, 2) under similar natural conditions, brown morphs heated up faster, attained higher temperatures, desiccated more rapidly, and suffered greater mortality than did white morphs, and 3) when pairs of brown and white morphs were tethered intertidally there was virtually no mortality of either morph on the exposed shore or in shaded microhabitats on the protected shore, but brown morphs suffered much greater mortality in sunny microhabitats on the protected shore. These findings demonstrate that the interpopulation variation in shell color of N. lapillus is in part a response to a selective gradient in physiological stress. Selection for crypsis by visually hunting predators did not appear to play a prominent role; however, only adults were considered, and the predation experiments were conducted in the fall before shorebirds that prey on whelks had arrived from their summer feeding grounds. Further experimentation to quantify the effects of visual predators such as birds and fish, particularly on juvenile snails, is necessary to assess adequately the importance of predation.