Third short article written by Maëva Manet; edited by Emiliano Videla.

Embryonic light exposure did not impact laterality or sociality in quails, and why it is of interest.

Nowadays, poultry eggs are incubated in complete darkness to save energy, for both economic and ecological reasons. However, light during incubation can help with normal brain development. Due to the position of the embryo in the egg, where the right eye is turned towards the shell while the left eye is blocked by the body, the two brain hemispheres are unequally exposed to light. This results in an asymmetrical visual system. This phenomenon is called lateralisation. As a consequence, visually-guided behaviours, such as foraging, scanning for predators, or social interactions, also become lateralised. When incubated in the dark, chicks see some of their behaviours less lateralised than normal. Based on this knowledge, Isabelle George and colleagues decided to investigate how embryonic light exposure affects laterality and sociality in quail chicks.

Japanese quail eggs were incubated in the dark in two groups; one of them, the test group, was exposed to light for 41 continuous hours after 15 days of incubation, while the control group remained in the dark. After hatching, the chicks were housed in 10 groups of 6 individuals from the same incubation condition (20 groups total). At three different ages, the 120 chicks were tested in a “turning bias test”: when placed in a T-shaped arena (figure 1), would they prefer to go left, or right, or would they not have any preference? The second test performed was a social motivation test: when alone in their home cages, how much do chicks call to re-establish contact with their peers? In addition, behavioural observations were performed when the chicks were in their home cages: do they perform the same type of behaviour at the same time? Are they grouped together in the cage, or are they apart from each other?

Figure 1: T-shaped arena used for the laterality test. Adapted from George et al. (2021)

Based on previous studies, the chicks exposed to light during incubation were expected to have a more pronounced turning bias (i.e., they would prefer either the right or the left side) than those incubated in complete darkness. Additionally, chicks exposed to light would also be more socially motivated (i.e., they would call more) and be more synchronised (i.e., they would perform the same type of behaviour at the same time and would be grouped rather than apart in their home cages). Unexpectedly, the authors found out that these tests did not show any effect of the embryonic light exposure on laterality or sociality. Another aspect the authors wanted to investigate was the link between laterality and sociality: if a group of chicks was more lateralised, would it also be more social? But here again, no correlation between the laterality index and either of the sociality indexes was found.

The authors addressed the absence of significant results with an in-depth discussion. First, it is possible that the light to which they were exposed was not bright enough. Indeed, quail eggs have brown spots that can reduce the amount of light going through the shell. In addition, in this protocol, the light intensity was ten times lower than that used in another study on chicken’s white eggs. Combined, these two factors form a coherent and strong explanation to the lack of differences between treatments, despite all the previous studies that the authors took into consideration to support their hypotheses. Consequently, the authors make clear that these results only show the effect of this specific protocol of embryonic light exposure on these specific observations in these specific chicks. These results are therefore not necessarily applicable to all light exposures, or all chicks.

As a whole, this paper highlights the possibility to create interesting discussions about non-significant results, often overlooked in the scientific community. Indeed, pressures on publishing significant results are common in almost every field, and non-significant results often are rejected due to two possible reasons. On the one hand, one can argue that it sometimes is difficult to interpret non-significant results. Statistics can only prove when there is a difference; hence, does the non-significancy mean that more means are required to highlight a difference, or is there genuinely no difference? On the other hand, journals tend to look for exciting results, rather than null results.

Either way, this article accentuates the importance of publishing this kind of results to spread knowledge. In the first scenario, the existence of published results coming to the same null conclusion could ease its interpretation. One may even gather the data from the different studies to form a meta-analysis of all the data combined, decreasing the likelihood that more means are needed to highlight a difference. In the scenario where articles are rejected because they are not exciting enough, one should keep in mind that two differently treated animals behaving the same is knowledge in itself, and discarding it may result in more studies to answer the same question. This will not only translate into a waste of time and money, but it will also especially cost more animals, purposelessly taking place in a study of an already-discredited hypothesis.

REFERENCES

George, I., Lerch, N., Jozet-Alves, C., & Lumineau, S. (2021). Effect of embryonic light exposure on laterality and sociality in quail chicks (Coturnix coturnix japonica). Applied Animal Behaviour Science, 236(February). https://doi.org/10.1016/j.applanim.2021.105270

Last modified: Tue, 04 Jan 2022 13:43:16 GMT