Shorebirds prefer a good body to a large brain

Jul 18, 2013
In the African Jacana (Actophilornis africanus), the female mates with several males and it is the males who raise offspring. Credit: Daniel Sol.

In many animal species, males and females differ in terms of their brain size. The most common explanation is that these differences stem from sexual selection. But predictions are not always certain. A team of researchers at the Centre for Ecological Research and Forestry Applications has discovered that a group of coastal birds, shorebirds, do not choose their mates by brain size but "on their physiques".

Some authors have suggested that could promote brain enlargement in males, in other words, that females prefer males with more developed cognitive abilities. Others, however, have suggested that females should have larger brains because they are generally the sex that raises offspring.

"In this study we ask what role sexual selection plays in the evolution of a group of birds, namely . This group's choices are not random, as this family shows great diversity in its mating systems. This makes them an excellent model to study to research the role of sexual selection on brain size evolution," Daniel Sol, a researcher at the Spanish National Research Council (CSIC) in the Centre for Ecological Research and Forestry Applications (CREAF) and co-author of the study published in the Journal of Evolutionary Biology, explains to SINC.

The study, which analysed over 180 , revealed a "surprising" fact to the researchers: polyandrous species - those in which one female mates with various males - have smaller brains relative to their bodies than monogamous and polygynous species, in the latter of which a male mates with several females.

"These results contradict many theories which suggest that sexual selection has played an important role in brain size evolution because if this were the case, polygynous species would also present sexual dimorphism - different sizes between males and females - but according to our analysis, this is not the case," the CREAF researcher continues.

"So we might ask ourselves the question: why do polyandrous species have smaller, more dimorphic brains? The answer is that we don't know. However, in the study we present some results that suggest a possible explanation: that sexual selection might have acted by increasing body size in females instead of reducing their brains."

The conclusion: the scientists have found that in this family of birds, body size evolves much more quickly than brain size. As brain size is measured relative to body size, increased leads to a reduction in relative brain size.

A bigger brain is not needed to take care of children

This study also negates another widespread idea: that parental care requires greater cognitive abilities and thus relatively larger brains.

"If this were the case, females of polygynous species would have larger brains than males because they have to look after their offspring. In reality, however, don't differ in the relative sizes of their brains," Sol clarifies.

Finally, the fact that polygynous species do not have smaller brains than monogamous species negates the "social intelligence" hypothesis, which speculates that brain size has increased in species in which relations between partners or group members are more complex and require greater .

According to the expert, this is due to the fact that in monogamous species, in which the male and female continually interact and have to coordinate with each other to raise offspring, sexual relationships are expected to be more complex than in polygynous species.

"We must tread carefully when deducing that differences in sexual dimorphism in brain size are due to sexual selection. With the evidence we have to date, we cannot conclude that sexual selection has been a significant force in brain size evolution," Sol emphasises.

Explore further: Knowledge of stingrays' sparked-up sex may help deter sharks

Related Stories

In spiders, size matters: Small males are more often meals

Sep 10, 2008

Female spiders are voracious predators and consume a wide range of prey, which sometimes includes their mates. A number of hypotheses have been proposed for why females eat males before or after mating. Researchers ...

Recommended for you

Male monkey filmed caring for dying mate (w/ Video)

Apr 18, 2014

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Orchid named after UC Riverside researcher

Apr 17, 2014

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

Apr 17, 2014

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

Apr 17, 2014

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

gwrede
1 / 5 (1) Jul 18, 2013
Maybe it's the shore that does it?
Baywatch, anyone?
(Couldn't resist.)

More news stories

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.