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    Interesting study into the sex role reversal of shorebirds

    NewsBird NewsWednesday 13 March 2013
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    A study has been carried out lately to look into shorebirds and their behaviours and it has shed some light on the reason why some species reverse the roles of the sexes. 

    The roles tend to be reversed with the male bird being left to carry out the parental duties.
     
    The team of researchers, from Europe, discovered that the change was often triggered when there was an imbalance between the number of males and females. 
     
    It was reported in the study that the switch occurred when the number of males outweighed the number of females, making it beneficial for males to stay with their mate. 
     
    The findings from the research were published in the journal Nature Communications. 
     
    There was an argument put forward that suggested conventional sex roles were widespread due to the fact that females invested considerable energy in producing eggs. This argument suggests that this energy made the survival of the offspring a priority to the mother. 
     
    The co-author Andras Liker, from the University of Sheffield, told the BBC that though plenty of research has suggested reasons for animals contrasting types of breeding behaviour, we are still “from the full understanding of this question”.
     
    He said: "A simple possibility is that, among other things, the opportunity to find a new partner can influence mating and parenting decisions, hence the number of males and females in a population - the adult sex ratio (ASR) - may be important."
     
    He went on to suggest that this theory had also been suggested by a number of mathmatical models, however, it had not been systematically studied. 
     
    The team compared the ASR between shorebirds that had non-conventional sex roles and collected the data from the published literature on the sex ratio, mating and parental behaviour of these species.
     
    Prof Liker went on to explain that many of the known examples of role reversal were seen in shorebirds, which is why they were selected for the study. 
     
    "Sex role reversal also occurs in some other groups of birds, such as kiwis and tinamous, but - in general - it is rare (in birds). It also occurs in frogs and fish, like seahorses and pipefish," he told BBC News.
     
    "[It] has been a formidable puzzle for evolutionary biologists ever since Darwin," he explained.
     
    "Our study is the first supporting the idea that sex ratio plays an important part in the evolution of role reversal."
     
    Tamas Szekely, another co-author from the University of Bath said that the research group had been investigating sex role reversal for over 20 years, which made it “extremely pleasing to see such a clear-cut result”.
     
    "When there are lots of males in a population, it's harder to find females so it benefits males to stay with their mate and look after the young," Prof Szekely observed.
     
    "However, the females often take advantage of this and leave the male holding the baby while they go and find another mate."
     
    Prof Liker said that he hoped the team's findings would lead to further research on the significance of population sex ratios.
     
    "For example, it would be very interesting to know what factors generate sex ratio differences between different species or populations," he said.
     
    "This may originate either from the differential production of male and female offspring, or may be the result of the different mortality of adult males and females.
     
    He added: "Sex differences in body size, migration, or other behaviour can expose the males and females to different causes of mortality, and if one sex survives better than the other the ASR becomes biased."
     
    Source: BBC
     
     
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