Egg color as an adaptation for thermoregulation

ABSTRACT.   Avian embryos are incubated at temperatures only 2–6 °C below that at which hyperthermia begins to influence survival. In habitats where sunlight directly strikes the eggs, even for short periods, heat gain may be a substantial threat to survival, and reflective pigmentation may reduce the rate of heat gain. The results of previous studies suggest that light-colored eggs acquire heat slower than dark eggs, but artificial pigments were used to create differences in egg coloration. This approach is problematic because natural eggshell pigments have low absorbance in the near-infrared waveband that encompasses about half of incident solar radiation. We used naturally-pigmented eggs to measure the influence of egg coloration on heat gain. Triads ( N = 18) of eggs from Brewer's ( Euphagous cyanocephalus ), Red-winged ( Agelaius phoeniceus ), and Yellow-headed ( Xanthocephalus xanthocephalus ) blackbirds were crossed with six nests of each species and either exposed to full sunlight or placed under a diffusing umbrella. Thermisters recorded internal egg temperature every minute until an asymptotic temperature was reached. Eggs in full sunlight acquired heat more rapidly than eggs in the shaded environment, but heat gain did not vary with egg color in either environment. Eggs placed in Yellow-headed Blackbird nests took longer to reach asymptotic temperature, but there was no significant egg-by-nest interaction. Thus, it appears that differences in reflectivity of eggshell pigments in the visible range (400–700 nm) do not result in different rates of heat acquisition. The thermoregulation hypothesis was not supported.     

GENETIC AND SOCIAL INHERITANCE OF BODY AND EGG SIZE IN THE BARNACLE GOOSE (BRANTA LEUCOPSIS)

We present heritability estimates for final size of body traits and egg size as well as phenotypic and genetic correlations between body and egg traits in a recently established population of the barnacle goose (Branta leucopsis) in the Baltic area. Body traits as well as egg size were heritable and, hence, could respond evolutionarily to phenotypic selection. Genetic correlations between body size traits were significantly positive and of similar magnitude or higher than the corresponding phenotypic correlations. Heritability estimates for tarsus length obtained from full-sib analyses were higher than those obtained from midoffspring-midparent regressions, and this indicates common environment effects on siblings. Heritabilities for tarsus length obtained from midoffspring-mother regressions were significantly higher than estimates from midoffspring-father regressions. The results suggest that this discrepancy is not caused by maternal effects through egg size, nor by extra-pair fertilizations, but by a socially inherited foraging site fidelity in females.     

一种采集稻纵卷叶螟卵的高效简便新方法

研究了稻纵卷叶螟Cnaphalocrocis medinalis Guenee的"烧杯+湿纱布"卵收集方法,并与"塑料袋收集法"和"塑料杯收集法"进行了比较。结果表明,"烧杯+湿纱布"卵收集法能显著地延长了稻纵卷叶螟成蛾的寿命、提高单雌产卵量和卵孵化率。采用此法收集稻纵卷叶螟的卵更高效和简便。     

The formation of improved tetraploid population of red crucian carp × common carp hybrids by androgenesis

Bisexual fertile diploid androgenetic individuals (A0) (2n=100) were formed by androgenesis. In this way, the diploid spermatozoa from male allotetraploid hybrids (AT) (4n=200) of red crucian carp (Carassius auratus red var.) (♀) × common carp (Cyprinus carpio L.) (♂) were used to fertilize the UV-treated hap- loid eggs of goldfish (Carassius auratus), and living androgenetic diploid fish were developed. The A0 became sexually mature at the age of 2 years, and they fertilized with each other to form their offspring (A1). In this study, we observed the chromosomal number, gonadal structure and appearance of A1 fish. The results are as follows: (1) In A1, there were 85% tetraploids (A1-4n), 10% triploids (A1-3n) and 5% diploids (A1-2n), suggesting that diploid A0 could produce diploid gametes. It was concluded that the formation of diploid gametes generated from diploid A0 was probably related to the mechanism of pre-meiotic endoreduplication. (2) Among A1, only A1-4n possessed normal ovaries and testes. The mature males of A1-4n produced white semen. Under the electron microscope, the head of diploid sperm generated by A1-4n was bigger than that of haploid sperm generated by red crucian carp. In the testes of the A1-4n, there were many mature normal spermatozoa with a head bearing plasma mem- brane and a tail having the typical structure of "9 2" microtubules. Between the head and the tail, there were some mitochondria. The ovaries of A1-4n developed well and mainly contained II, III and IV-stage oocytes. The IV-stage oocytes were surrounded by inner and outer follicular cells. The micropyle was observed on the oolemma of follicular cells. There were abundant yolks and plenty of endoplasmic reticulum in the cytoplasm of IV-stage oocytes. Because A1-2n and A1-3n were distant crossing diploid hybrids and triploid hybrids respectively, they possessed abnormal gonads, and no mature semen and eggs were observed. (3) Compared with allotetraploids, the A1-4n fish not only had advantages such as fast growth rate and strong resistibility but also showed some new good performances such as high ratio of body width to body length, smaller heads and shorter tails. These results indicated that an- drogenesis could produce bisexual fertile tetraploids and improve the shape of allotetraploid hybrids as well, which will be of great significance in both the cell genetics research and fish breeding.     

稻田飞虱卵寄生蜂群落结构和动态的初步研究

报道了广东省四会市大沙镇稻田中褐飞虱Nilaparvata lugens卵期寄生蜂的结构和动态。该群落由缨小蜂科和赤眼蜂科的6个属、共19种卵寄生蜂组成。其中,稻虱缨小蜂Anagrus nilaparvatae、长管稻虱缨小蜂A. longitubulosus和拟稻虱缨小蜂A. paranilaparvatae是群落中的优势种群,它们对控制褐飞虱种群卵期的存活率起主要作用。6个属在群落中的优势地位相对稳定,但不同物种包括优势种类在群落中的地位并不稳定。早、晚稻前期,群落的寄生蜂数量与稻田褐飞虱数量正相关;中期,寄生蜂数量在一定的范围内波动;后期,其数量先上升,然后急剧下降。水稻生长前、中和后期,寄生蜂对褐飞虱卵的平均寄生率分别约为76%,70%和50%。     

Seasonal patterns of egg parasitism and natural biological control of rice brown planthopper in Indonesia

1 Egg mortality is known to be an important factor in brown planthopper (BPH) (Nilaparvata lugens) population dynamics in tropical Asia, but few quantitative data are available on the role of egg parasitoids. 2 Field studies are reported at two sites in Java, Indonesia, over a period of 4 years in both wet and dry seasons, where no chemical pesticides were used. Rice plants previously infested in the laboratory with BPH eggs were exposed to natural parasitism and predation in experimental fields for periods of 5 days. 3 Egg batches were dissected from both experimental and control plants after field exposure at seven fortnightly intervals through the rice growing season and BPH nymphs and adult parasitoids were allowed to emerge. 4 Parasitism by species of Oligosita (Hymenopera, Trichogrammatidae) and Anagrus (Hym., Mymaridae) varied between 18% and 61% in dry, and from 1% to 65% in wet, seasons. There was generally a trend from low to higher rates through wet seasons, contrasting with more uniform higher levels through dry seasons. 5 Reduction in BPH survival as a result of egg parasitism varied between 29% and 91%. Generally parasitism was density independent. 6 It is suggested that lower initial levels of parasitism in dry seasons may be due to the longer fallow period between dry and wet, than between wet and dry, resulting in lower local populations of appropriate natural enemies. 7 Unlike previous studies in Asia, little evidence was found for egg predation as an important mortality factor. 8 The conservation of egg parasitoids should form part of any rice pest management programmes in tropical Asia.     

颍上八里河自然保护区鹭卵3种重金属残留分析

2005年5月,采集了淮河地区颍上八里河集群繁殖的夜鹭(Nycticorax nycticorax)和小白鹭(Egrettagarzetta)鸟卵共18枚,用原子吸收法测定了卵壳、内容物中重金属Cd、Pb、Cr的残留量。结果表明,所有卵壳样品中均检出一定水平的Cd、Pb和Cr残留量,夜鹭卵壳中重金属残留量为Pb>Cr>Cd,小白鹭卵壳中重金属残留量为Cr>Pb>Cd,卵壳中Pb和Cr残留量的种间差异都不显著,但Cd的种间差异显著;在2种鹭卵内容物中,Cr都被检出,在夜鹭卵内容物样品中,Pb只被部分检出,Cd在2种鹭卵内容物样品中都没有被检出,3种重金属在内容物中残留量的种间差异都不显著。2种鹭卵壳中Pb和Cd残留量极其显著地高于卵内容物,但Cr的这种残留分布上的差异不显著。本研究进一步证明卵壳可用作重金属污染物的指示物,监测和评价湿地生态系统中重金属的污染状况。     

Life-History Characteristics and Fitness in Descendents of Parthenogenetic and Ex-Ephippio Females of Daphnia Magna

Daphnids of ex-ephippial and parthenogenetic origin differ substantially in life-history. Possible maternally transmitted ex-diapause effects of differing female origin on the fitness of their offspring were studied across multiple clones in Daphnia magna. Ex-ephippial daphnids responded in egg size to different constant food concentrations with the same pattern as parthenogenetic females. Significant differences in egg characteristics between females of different origin were only found for the first clutch produced under high food. The smaller size of eggs in ex-ephippial females, however, did not translate into size differences of first-clutch neonates. A trend for lower mass density per body volume was detected in offspring from ex-ephippial females in comparison with parthenogenetic daphnids. Hence, an ex-diapause effect transmitted by ex-ephippial mothers to their parthenogenetic offspring is likely. However, there was no difference in life-histories and fitness between offspring produced by females of ex-ephippial and parthenogenetic origin at both, high and low food concentrations across multiple clones. Thus, a significant ex-diapause effect on fitness in successive parthenogenetic generations may not be expected in D. magna at the population level.     

A quantitative trait locus for recognition of foreign eggs in the host of a brood parasite

Avian brood parasites reduce the reproductive output of their hosts and thereby select for defence mechanisms such as ejection of parasitic eggs. Such defence mechanisms simultaneously select for counter-defences in brood parasites, causing a coevolutionary arms race. Although coevolutionary models assume that defences and counter-defences are genetically influenced, this has never been demonstrated for brood parasites. Here, we give strong evidence for genetic differences between ejector and nonejectors, which could allow the study of such host defence at the genetic level, as well as studies of maintenance of genetic variation in defences. Briefly, we found that magpies, that are the main host of the great spotted cuckoo in Europe, have alleles of one microsatellite locus (Ase64) that segregate between accepters and rejecters of experimental parasitic eggs. Furthermore, differences in ejection rate among host populations exploited by the brood parasite covaried significantly with the genetic distance for this locus.     

Interactions among host diet, nutritional status and gastrointestinal parasite infection in wild bovids

In this study, I explored the interactions among host diet, nutritional status and gastrointestinal parasitism in wild bovids by examining temporal patterns of nematode faecal egg shedding in species with different diet types during a drought and non-drought year. Study species included three grass and roughage feeders (buffalo, hartebeest, waterbuck), four mixed or intermediate feeders (eland, Grant's gazelle, impala, Thomson's gazelle) and two concentrate selectors (dik-dik, klipspringer). Six out of the nine focal species had higher mean faecal egg counts in the drought year compared to the normal year, and over the course of the dry year, monthly faecal egg counts were correlated with drought intensity in four species with low-quality diets, but no such relationship was found for species with high-quality diets. Comparisons of dietary crude protein and faecal egg count in impala showed that during the dry season, individuals with high faecal egg counts (> or =1550 eggs/g of faeces) had significantly lower crude protein levels than individuals with low (0-500 eggs/g) or moderate (550-1500 eggs/g) egg counts. These results suggest that under drought conditions, species unable to maintain adequate nutrition, mainly low-quality feeders, are less able to cope with gastrointestinal parasite infections. In particular, during dry periods, reduced protein intake seems to be associated with declining resilience and resistance to infection.