Egg development time in the Zebra Finch Taeniopygia guttata varies with laying order and clutch size

As female birds are able to lay no more than a single egg each day, in those species producing larger clutches the first laid eggs may get a developmental head‐start over later eggs in the clutch. All other things being equal, the differential pattern of development across the clutch may contribute to hatching asynchrony and subsequent inequity in the competition between brood mates, and ultimately increase variance in the quality and fitness of first‐ and last‐laid offspring. It has been suggested that females might allocate resources differently across the laying sequence to moderate the developmental rate and hatching time of different embryos. We tested this theory in the Zebra Finch Taeniopygia guttata, a common model species for investigating maternal effects in birds. We removed 758 eggs from 160 nests shortly after they were laid and used artificial incubators to control for parental effects and monitor hatching times. Eggs from larger clutches consistently hatched sooner than those from average‐sized clutches, demonstrating that the intrinsic properties of an egg can alter the developmental time of embryos. There were also differences in the development time of eggs across the laying sequence, but these patterns were weaker, inconsistent and unrelated to sequential investment across the laying sequence in a straightforward way. This study indicates that maternal resource allocation to eggs across the laying sequence and across clutch sizes can influence development times and play a potentially important role in determining the competitive dynamics of broods.     

Patterns of Metabolism and Growth in Avian Embryos

Metabolic rates of embryos of precocial birds increase rapidlyuntil about 80% through incubation, then increase slowly remainconstant or even decline. In altricial species, embryo metabolicrates increase continuously and at an accelerating rate throughout incubation. Total energy cost of development is higher inprecocial than in altricial species. Growth patterns of altricialand precocial embryos differ in the same way as does metabolicrate. Embryo growth rates decline late in incubation in precocialspecies, but increase continuously in altricial species. Embryometabolic rate in cal/hr (P) is related to embryo mass in grams(M) and growth rate in grams/day (GR) by the equation P = 12.17GR+ 1.66M + 1.81. The energy cost of growth in avian embryos is292 cal/g. The energy cost of maintenance is 1.66 cal/g hr andappeals to be independent of embryo mass. Differences in growthpatterns account for the observed differences in metabolic ratesand total energy costs of development. High energy costs ofmaintenance account for high total developmental costs in piecocialspecies and in species that have unusually long incubation periods.     

The phenology and clutch size of UK Blue Tits does not differ with woodland composition

The deciduous tree-herbivorous caterpillar-insectivorous bird food chain is a well-studied system for investigating the impacts of climate change across trophic levels. To date, across Europe, most attention has focused on the impacts of increasing spring temperature on changes to phenology in Oak-dominated (Quercus spp.) woodlands. Paridae species and Pied Flycatcher Ficedula hypoleuca are the most studied secondary consumers, all of which demonstrate an advancement in reproductive phenology with increases in spring temperature. Shifts in climate and phenology may also impact on reproductive investment in clutch size, and the effects of climate on phenology and clutch size may vary depending on woodland composition. To date, the effects of among-habitat variation in phenology and reproductive investment have received little attention. Insectivorous birds inhabiting woodlands that differ in tree composition may differ in the timing of breeding, due to local tree leafing phenology acting as a cue for egg-laying date and/or clutch size. Moreover, for most insectivorous birds, woodland composition within a territory is likely to be the main determinant of food availability for both adults and chicks. Consequently, if warming springs affect the temporal patterns of food availability differently across different woodland compositions, this may affect the optimal average local phenology for nesting birds. Here, using data from 34 long-term (mean 15 years) nest monitoring sites across the UK, we investigate the effect of woodland tree composition and temperature on Blue Tit Cyanistes caeruleus first egg date (FED) and clutch size. We supplemented the nest monitoring data by quantifying woodland composition, at a site level, through modified point counts. We predict that birds breeding in woodlands with greater proportions of late-leafing species, such as Oak and Ash Fraxinus excelsior, will breed later than those breeding in woodlands with greater proportions of early-leafing species, such as Birch Betula spp. and Beech Fagus sylvatica. We found no evidence for differences in Blue Tit FED or clutch size in relation to the proportion of any of the tree species investigated, after controlling for temperature and latitude (FED: −3.4 and 2.2, clutch size: −0.4 and − 0.2 eggs for one-unit increase in temperature and latitude, respectively). In recent decades and across all sites, clutch size has decreased as spring temperatures have increased, a strategy which could allow birds flexibly to adjust their breeding phenology such that nestling demand coincides with peak food availability. The lack of an effect of woodland composition on Blue Tit phenology suggests Blue Tits do not fine-tune their reproductive phenology to the local tree composition. Whether this lack of evidence for phenological divergence is due to an absence of divergent selection on breeding phenology and clutch size or to gene flow is not clear.     

Temperature-dependent sex-biased embryo mortality in a bird

Sex ratios have important evolutionary consequences and are often biased by environmental factors. The effect of developmental temperature on offspring sex ratios has been widely documented across a diverse range of taxa but has rarely been investigated in birds and mammals. However, recent field observations and artificial incubation experiments have demonstrated that the hatching sex ratio of a megapode, the Australian brush-turkey (Alectura lathami), varied with incubation temperature; more females hatched at high incubation temperatures and more males hatched at low temperatures. Here, we investigated the causes of this temperature-dependent sex-biasing system. Molecular sexing of chicks and embryos confirmed that male embryo mortality was greater at high temperatures while female embryo mortality is greater at low temperatures, with mortality in both sexes similar at intermediate incubation temperatures. Temperature-dependent sex-biased embryo mortality represents a novel mechanism of altering sex ratios in birds. This novel mechanism, coupled with the unique breeding biology of the brush-turkey, offers a potentially unparalleled opportunity in which to investigate sex allocation theory in birds.     

Unhatched eggs: methods for discriminating between infertility and early embryo mortality

Unhatched eggs are a common phenomenon in birds and are often referred to as being 'infertile', which (confusingly) can mean at least two things: (1) that the ovum has not been fertilized or (2) that the embryo has died during development. These two broad categories of hatching failure can be difficult to distinguish, particularly in the early stages of embryo development. We describe methods to distinguish between infertility (due to insufficient sperm) and early embryo mortality in passerine eggs using the Zebra Finch Taeniopygia guttata as a model. We also describe how we successfully adapted these methods for use on eggs from a wild species, the Tree Sparrow Passer montanus , collected after the incubation period, and show that sperm can be visualized on the perivitelline layer of unhatched eggs even several weeks after laying.     

Intra‐specific variance in sperm morphometry: a comparison between wild and domesticated Zebra Finches Taeniopygia guttata

The Zebra Finch Taeniopygia guttata is a model bird species for the experimental study of behavioural and evolutionary concepts in captivity and especially sexual selection. The validity of sexual selection studies of domesticated birds is of long‐standing concern as little is known about the influence of domestication on sexually selected traits. Most domesticated Zebra Finch populations are maintained under a strict breeding regime to avoid potential inbreeding. However, these breeding regimes may interfere with the processes of sexual selection and influence the evolution of sexually selected traits because they may limit or prohibit active mate choice. Here, we investigated the potential impact of a monogamous breeding scheme in a domesticated population in which active mate choice is largely inhibited, on the evolution of sperm morphometry as a sexually selected trait. We compared sperm morphometric traits (total sperm length and length of sperm head, midpiece and flagellum), and the variance thereof, between a domesticated and two wild Zebra Finch populations. Although we found significant differences between the three populations for certain sperm traits (head length, midpiece length), which may be of importance in postcopulatory sexual selection, overall, variance in sperm morphometry did not differ between the domesticated and the wild Zebra Finch populations. Our results validate the use of domesticated Zebra Finches for further studies of postcopulatory sexual selection and sperm competition.     

Avian Egg Odour Encodes Information on Embryo Sex,Fertility and Development

Avian chemical communication is a rapidly emerging field, but has been hampered by a critical lack of information on volatile chemicals that communicate ecologically relevant information (semiochemicals). A possible, but as yet unexplored, function of olfaction and chemical communication in birds is in parent-embryo and embryo-embryo communication. Communication between parents and developing embryos may act to mediate parental behaviour, while communication between embryos can control the synchronicity of hatching. Embryonic vocalisations and vibrations have been implicated as a means of communication during the later stages of development but in the early stages, before embryos are capable of independent movement and vocalisation, this is not possible. Here we show that volatiles emitted from developing eggs of Japanese quail (Coturnix japonica) convey information on egg fertility, along with the sex and developmental status of the embryo. Specifically, egg volatiles changed over the course of incubation, differed between fertile and infertile eggs, and were predictive of embryo sex as early as day 1 of incubation. Egg odours therefore have the potential to facilitate parent-embryo and embryo-embryo interactions by allowing the assessment of key measures of embryonic development long before this is possible through other modalities. It also opens up the intriguing possibility that parents may be able to glean further relevant information from egg volatiles, such as the health, viability and heritage of embryos. By determining information conveyed by egg-derived volatiles, we hope to stimulate further investigation into the ecological role of egg odours.     

Comparative analysis of cell cycle events in zygotic and somatic embryos of Cyclamen persicum indicates strong resemblance of somatic embryos to recalcitrant seeds

Embryo development and germination of Cyclamen persicum have been comparatively characterized for zygotic and somatic embryos with regard to mitotic activity and morphology in order to identify developmental abnormalities in somatic embryogenesis. Zygotic embryo development proved to be highly synchronous with distinct periods of cell division, cell elongation and embryo maturation within a total period of 17 weeks of seed development. Somatic embryo development was accomplished within only 3 weeks, resulting in a mixture of morphologically highly variable embryos. No distinct developmental periods could be identified and no reduction of the mitotic activity was discovered for non-desiccated somatic embryos. Controlled desiccation of somatic embryos severely reduced their germination rate, demonstrating resemblance of somatic embryos to recalcitrant seeds, whereas zygotic Cyclamen seeds could be characterized as typically orthodox.     

大山雀和褐头山雀种间关系研究

在地理分布重叠地区的大山雀Parus major和褐头山雀Parus montanus栖息地海拔高度不同。大山雀栖于海拔2,370米以下,集中于次生杨桦林和老年人工杨树林;褐头山雀栖于海拔2,300米以上,集中于混交林和山杨栎林。它们的栖息地有一定重叠,但重叠值较低。重叠地带觅食生态位的四维中,树种选择一维有所不同,其余三维生态位重叠值均较大。两个种营养生态位有一定重叠,食物大小的重叠值更大。在进化发展过程中,两种山雀间完全的生态分离没有发生。     

Wolbachia infection influences the development of Culex pipiens embryo in incompatible crosses

Wolbachia are maternally inherited endosymbiotic bacteria that infect many arthropod species and have evolved several different ways for manipulating their host, the most frequent being cytoplasmic incompatibility (CI). CI leads to embryo death in crosses between infected males and uninfected females, as well as in crosses between individuals infected by incompatible Wolbachia strains. In the mosquito Culex pipiens, previous studies suggested developmental variation in embryos stemming from different incompatible crosses. We have investigated this variation in different incompatible crosses. Unhatched eggs were separated into three classes based upon the developmental stage reached by the embryos. We found that incompatible crosses involving uninfected females produced only embryos whose development was arrested at a very early stage, irrespective of the Wolbachia variant infecting the male. These results differ from other host species where a developmental gradient that could reach late stages of embryogenesis or even living larvae was observed, and indicate a novel peculiarity of CI mechanism in C. pipiens. By contrast, all incompatible crosses with infected C. pipiens females produced embryos of all three classes. The proportion of embryo classes appeared to be associated with the strains involved, suggesting specific CI properties in different incompatible crosses. In addition, the contribution of parental genome was characterized in embryo classes using molecular markers for each chromosome. Embryo phenotypes appeared linked to the paternal chromosomes' contribution, as described in Drosophila simulans. However, this contribution varied according to maternal infection and independently of male factors.     

菊属种间杂交胚拯救过程成苗途径的初步研究

对菊属不同种植物进行远缘杂交与胚拯救,研究幼胚发育途径。结果表明：影响胚发育途径的关键因素是基因型、胚龄与激素。杂交父母本基因型差异小,合适的胚龄均有利于子房直接萌发及子房先形成愈伤组织而后萌发成苗;培养基中添加KT 2.0 mg.L-1+IAA 2.0 mg.L-1 有利于子房直接萌发成苗, BA 2.0 mg.L-1+NAA 2.0 mg.L-1 有利于先形成愈伤而后萌发成苗。     

Conspecific-only experience during development reduces the strength of heterospecific song discrimination in Zebra Finches (Taeniopygia guttata): a test of the optimal acceptance threshold hypothesis

Conspecifics during development provide the most reliable sensory cues for species recognition in parental bird species. The Zebra Finch (Taeniopygia guttata) is a sexually dimorphic model species used for investigations of the behavioural cues and neurobiological substrates of species recognition. Regarding acoustic conspecific cues, theory predicts that exposure to both con- and heterospecific vocalisations and other environmental sounds results in more accurate auditory species discrimination, because diverse vocal cues during development shift optimal conspecific acceptance thresholds to be more restrictive to yield fewer acceptance errors. We tested the behavioural preferences of female and male Zebra Finches raised in an outdoor environment (Control) and female and male Zebra Finches reared in an indoor colony with exposure to Zebra Finches only (Restricted), to playbacks of songs of Zebra Finches, Zebra Finches cross-fostered by Bengalese Finches (Lonchura striata var. domestica), and Bengalese Finches. Several behavioural measures revealed minimal sexual dimorphism in discrimination but showed that Control subjects preferred conspecifics’ songs over either the songs of cross-fostered Zebra Finches or Bengalese Finches. Restricted Zebra Finches in contrast did not discriminate behaviourally between the three song types. These results support the concept of a shift in the species acceptance threshold in the restricted treatment resulting in more acceptance errors. We discuss future work to test the role of exposure to diverse vocal cues of both con- and heterospecifics in the ontogeny of song perception in this important laboratory model species for social recognition research.     

Interaction between maternal effects and temperature affects diapause occurrence in the cricket Allonemobius socius

The induction of diapause can be adaptive for egg survival during unfavorable conditions, while direct development can be advantageous under favorable conditions by allowing additional generations to exploit abundant resources. Therefore, the physiological capability of a female to respond to environmental cues indicative of habitat quality by producing eggs of the appropriate developmental phenotype should be under strong selection. Additionally, developing embryos may alter the developmental trajectory initiated by the female in response to changing environmental conditions. In this study, we used a cross-fostering approach to isolate the maternal effects of parental diapause history (not previously studied) and egg-laying temperature from the influence of the incubation environment experienced by the developing embryo on the proportion of diapause eggs produced by the striped ground cricket, Allonemobius socius. We found that an interaction between egg-incubation temperature and parental diapause history strongly affected the proportion of diapause eggs produced and the proportion of eggs that hatched within a 16–18 day incubation period, while egg-laying temperature and all other interactions did not. These novel results indicate that embryos can respond directly to the environmental conditions they experience during development, but that their ability to do so is influenced by maternal effects such as parental diapause history. The results of this study not only provide evidence, for the first time, of parental diapause history affecting diapause proportions, but also raise additional questions about the mechanism by which environmental information is transmitted from parent to offspring and how offspring are able to respond to conditions experienced during their own development.     

Beyond maternal effects in birds: responses of the embryo to the environment

Embryonic growth and development are impacted by environmental conditions. In avian systems, parents tightly control these environments through provisioning of nutrients to the egg and through incubation. Parents can influence embryonic development through egg size, eggshell conductance, hormones, or other substances deposited in eggs and through the onset and temperature of incubation. In addition to these parental influences, evidence suggests that avian embryos are able to perceive and actively respond to their environment during incubation and adjust their own development. Evolution of embryos' responses to developmental environments in birds can be understood in the context of parent-offspring conflicts. When parental investments favor future reproduction over current reproduction, current offspring pay fitness costs, which result in strong selection for offspring that can respond to developmental environments independent of their parents. Here, we review literature indicating that avian embryos actively respond to maternally derived components of the egg, vocalizations, and differences in day length, and we explore these responses in the context of three situations where the consequence of these environments to the fitnesses of offspring and parents differ: the degree of synchrony in hatching, the deposition of hormones in yolks, and seasonal timing of breeding. However, the adaptive significance of responses of embryos to developmental environments arising from parent-offspring conflict has not been adequately explored in birds.     

菊属种间杂交胚拯救过程成苗途径的初步研究

对菊属不同种植物进行远缘杂交与胚拯救,研究幼胚发育途径.结果表明:影响胚发育途径的关键因素是基因型、胚龄与激素.杂交父母本基因型差异小,合适的胚龄均有利于子房直接萌发及子房先形成愈伤组织而后萌发成苗;培养基中添加KT 2.0 mg·L-1 IAA 2.0 mg·L-1有利于子房直接萌发成苗,BA 2.0 mg·L-1 NAA 2.0 mg·L-1有利于先形成愈伤而后萌发成苗.     

EMBRYO GROWTH AND SEED SIZE IN RAPHANUS SATIVUS: MATERNAL AND PATERNAL EFFECTS IN VIVO AND IN VITRO

Theories on the evolution of the angiosperm seed disagree as to the effects of different plant tissues on embryo growth. To examine the relative contributions of maternal and paternal genes on embryo growth, we conducted controlled crosses in the greenhouse with wild radish plants (Raphanus sativus), looked for maternal, paternal, and interaction effects on embryo development, and compared the performance of embryos within fruits and in embryo culture. Maternal plant identity affected fruit set, seeds per fruit, embryo developmental stage, and mean seed weight. In embryo culture, maternal effects were found for cotyledon size and embryo weight. Paternal effects were fewer or smaller in magnitude than maternal effects. The identity of the pollen donor affected embryo developmental stage and mean seed weight. In culture, paternal effects were detected for cotyledon size and embryo weight. Our results demonstrate that both maternal and paternal elements affect embryo growth. The fact that maternal effects are greater than paternal effects on embryo development in culture may result from cytoplasmic elements or maternal nuclear genes. Embryo performance in vivo compared to that in vitro varied among maternal plants. The interaction between an embryo and its endosperm and maternal tissues may be either positive or negative, depending upon the maternal plant and the embryo's developmental stage.     

Response to begging calls by Zebra Finch parents: "first come, first served" rule may overcome a parental preference between chicks

In birds, parents may provide differential food provisioning among offspring according to their sex. Here, we test the hypothesis that events linked to the fine dynamics of begging behaviour could modulate parental preferences. After evaluating the preference related to chick sex for each parent of six Zebra Finch Taeniopygia guttata pairs, we studied the possible modifications of this preference when offspring begging was asynchronous. Our observations show that male parents follow a "first come, first served" rule, whereas females keep their initial choice. Although this study remains preliminary due to the sample size, it underlines the potential importance of investigating fine temporal features of begging behaviour to fully understand parents' provisioning strategies.     

The behavioural and physiological strategies of bird and reptile embryos in response to unpredictable variation in nest temperature

Temperature profoundly affects the rate and trajectory of embryonic development, and thermal extremes can be fatal. In viviparous species, maternal behaviour and physiology can buffer the embryo from thermal fluctuations; but in oviparous animals (like most reptiles and all birds), an embryo is likely to encounter unpredictable periods when incubation temperatures are unfavourable. Thus, we might expect natural selection to have favoured traits that enable embryos to maintain development despite those fluctuations. Our review of recent research identifies three main routes that embryos use in this way. Extreme temperatures (i) can be avoided (e.g. by accelerating hatching, by moving within the egg, by cooling the egg by enhanced rates of evaporation, or by hysteresis in rates of heating versus cooling); (ii) can be tolerated (e.g. by entering diapause, by producing heat‐shock proteins, or by changing oxygen use); or (iii) the embryo can adjust its physiology and/or developmental trajectory in ways that reduce the fitness penalties of unfavourable thermal conditions (e.g. by acclimating, by exploiting brief windows of favourable conditions, or by producing the hatchling phenotype best suited to those incubation conditions). Embryos are not simply passive victims of ambient conditions. Like free‐living stages of the life cycle, embryos exhibit behavioural and physiological plasticity that enables them to deal with unpredictable abiotic challenges.