Possible Role of Nitric Oxide Emission from Bird Embryos

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.

Attainment of thermoregulation as affected by environmental factors

The review addresses the development of thermoregulation in poultry embryos as well as the effect of acute and chronic changes of environmental factors on this process and the incubation temperature being the foremost. In poultry, the early development of adaptive body functions, like the thermoregulatory system, is characterized by the following peculiarities. First, the development of peripheral as well as central nervous thermoregulatory mechanisms start during the prenatal ontogeny. However, their maturity is attained during early postnatal development. In the perinatal period, environmental factors have a high effect on development of temperature regulation. Second, acute changes in the environmental conditions induce as a rule first uncoordinated and immediately nonadaptive reactions. Later, the uncoordinated nonadaptive reactions change into coordinated (adaptive) reactions. Prenatal environmental influences may have a training effect on the postnatal efficiency of the thermo-regulatory system. Third, functional systems of the organism develop from an open loop system without feedback control into a closed system controlled by a feedback mechanism. During this critical period, the actual environment modulates the development of the respective physiological control systems for the entire life period, especially by changes in neuroorganization and expression of related effector genes. Knowledge on these mechanisms might be specifically used to generate long-term adaptation of the organism to the postnatal climatic conditions (perinatal epigenetic temperature adaptation). In poultry, perinatal epigenetic temperature adaptation was developed by changes in the incubation temperature. When a comparison is made in birds, which were incubated at 37.5 degrees C, a low incubation temperature induced postnatal cold adaptation, and warm incubation temperature induced postnatal heat adaptation. Perinatal epigenetic temperature adaptation exhibited changes in the neuronal thermosensitivity in the hypothalamus as well as in the peripheral thermoregulatory mechanisms. These alterations could be already found at the end of incubation. Further, temperature-experienced embryos have a lower c-fos expression than in the control after acute heat stress.