Saturday , September 25 2021

House sparrow status signal theory no longer flies

For decades, evolutionary biologists have pointed to the house block as a textbook example of the status signal hypothesis at work.

But a multinational study with UNSW is about suggesting such a theory is for the birds.

Status signaling in the animal world refers to how physical properties convey information about the strength and ranking of an individual in the group. Like stripes and marks on a military uniform, physical markings in the animal world can tell other members to be careful to challenge an individual who carries them.

In the world of birds, the size of the bible on the household pair – a black patch on the feather's feather – has been associated with the bird's influence in the flock. The bigger the bib, the better the ability of the game, with cuckoldry and reproductive success, some of the potential associated privileges.

Study writer, Professor Shinichi Nakagawa of UNSW's School of Biological, Earth and Environmental Sciences says that the status signaling hypothesis describes a survival system designed to prevent unnecessary spending on energy.

"To avoid unnecessary fights is important as many animal species have developed signals to indicate their fighting ability," said A / Professor Nakagawa.

"The banner size of familiar house mice has been an iconic example of such status signaling, often called" badge of status. "

So accepted is this perception of house work as Sir David Attenborough, in the acclaimed television series The birds (1998) spent a few minutes of movies to make an analogy between the size of the bib markings in spades and their corresponding military rank.

But how much evidence is there for the relationship between the size of the bible and the status of the ticks of house tracks?

Not much, suggests the research document.

In a meta-analysis of both published and unpublished studies since the idea first floated in the 1980s, A / Professor Nakagawa and his international colleagues found a number of trends that made them question the question of the strength of the original hypothesis.


UNSW Professor Shinichi Nakagawa has been involved in papers that first confirmed, then rejected the idea of ​​bib size in sparrows associated with the status.

The first was that the published data from each subsequent study as tested the hypothesis has shown a gradual decrease in the correlation between the evidence and the original theory. In other words, as more and more data has rolled in over time, less and less correlation has been found.

"This is a very well-known phenomenon known as" time delay "bias, says A / Professor Nakagawa.

"The initial results usually come from a study with a small sample size with great effect, but later studies with larger sample sizes can reveal that the actual effect is much smaller than the original result."

The effect size (ie correlation) is a measure of between -1 and 1 where a point of 1 indicates a perfectly positive correlation between male bit size and social lines, 0 represents none at all, while – 1 describes a perfect negative correlation. The authors observed that in the published studies, the effect size decreased over time, and recently published effects could no longer be distinguished from zero ".

But perhaps most telling was the data analysis of the unpublished studies. Not only did the sparrow's house size decrease in relation to observed dominant behavior, but the authors suspected that this would be an example of "publication bias".

A / Professor Nakagawa explains:

"Public bias is where non-significant results, such as being unable to find a relationship or negative results, are less likely to be published," he says.

"There are many reasons for this, but two main reasons are: First, journals are less likely to take negative results because the authors may have had" wrong "study designs or sample size too small to detect an effect, and secondly, the authors do not publish for the same reasons. "

Interestingly, A / Professor Nakagawa was involved in previously published studies that supported the idea of ​​bib size that correlates with status signaling.

"The original meta-analysis was conducted during my PhD student more than a decade ago," said A / Professor Nakagawa.

"Yes, I really found a strong relationship between bib size and male social ranking. However, I used to use the published work until then. Given the set of published studies, I did not find any evidence of disclosure bias.

"What this shows is the importance of updating a meta-analysis."

So if there is doubt about the relationship between the household size and size of the household, does the mark mean anything at all? A / Professor Nakagawa thinks they do, saying that this will be subject to further studies.

"One thing we know is sure that the size of the bible is an age indicator," he says.

"Even women seem to prefer older men as their partner, especially when it comes to extra saving. But we do not really know if women use the size of the bible to assess male age or not. So it's good to find this."

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