In a new study on Tanganyika cichlids, three scientists[1] [2] [3] from Uppsala University in Sweden have shown that intricate rearing behaviour varies with brain size in females. The only previously published study showing similar patterns concerned predatory animals.

Tropheus moori – one of the species used in the study. – Picture www.jjphoto.dk

How the vertebrate brain has developed throughout the course of evolution is still not clear, and we are still not certain if brain functions in a specific species develop to match a demanding environment. One way of learning more about this is to compare brain size and structure in closely related species living under dissimilar circumstances.

“It is important to look at differences between males and females since females often distinguish themselves from males, both in behaviour and appearance”, says Niclas Kolm, lead-author of the study.

The study looked for correlations between brain size and ecological factors in a large number of specimens from 39 different species of Tanganyika cichlid. Lake Tanganyika is especially suitable for this type of study since it is inhabited by cichlid groups exhibiting significant dissimilarities in both brain structure and ecology, and whose ancestry is well known. Tanganyika cichlids varies dramatically from species to species when it comes to factors such as body size, diet, habitat, parental care, partner selection, dissimilarities between the sexes, mating behaviour, and brain structure.

The result of the study showed a correlation between brain size and the two factors diet and parental care behaviour. Species where only the female fish cares for egg and fry turned out to have bigger brains than species where both parents engage in parental care. The brain was however only larger in females; there was no difference in brain size between males of the two groups.

The largest brains of all were found in algae-eating cichlids. These fishes live in environments characterized by a high level of social interaction. “This indicates that social environment have played a role in brain development”, says Kolm.

The study was published in the web version of “Proceedings of the Royal Society of London Series B” on September 17. You can find it here (http://journals.royalsociety.org/content/j114062824820l76/).

A 380 million-year-old pregnant fossil has been discovered by researchers from University of Western Australia. The fossil was unearthed in the Kimberleys and contains a 6 cm embryo with its umbilical cord intact. Mother and baby belong to an extinct species of shark-like fish that could be found in lakes and seas for almost 70 million years before it disappeared. This is the oldest example of a mother of any species giving birth to live young.

“This is also the first evidence of sex in vertebrates with jaws resulting in the oldest known example of a fish giving birth to live young rather than expelling a clutch of eggs,” says Dr Kate Trinajstic, Research Associate at the University of Western Australia, to News.com.au.

The fossilized species has been given the name Materpiscis attenboroughi. Mater is the Latin word for “mother” and piscis is the word for “fish”, so the genus name literary means mother-fish in Latin. The second part of the name, attenboroughi, is of course an homage to celebrated broadcaster and naturalist Sir David Attenborough. The fossilized fish belongs to the placoderm fishes, a group of fish commonly referred to as ’the dinosaurs of the seas’ since they dominated lakes and seas during the Middle Palaeozoic Era (c. 420 to 350 million years ago).

The fossil has now been given a new home at the Western Australian Museum.

Read the full story in Narelle Towie’s article at News.com.au. At this page, you can also see pictures of the fossil and drawings of what the fish might have looked like when it was still alive.

http://www.news.com.au/perthnow/story/0,21498,23772231-948,00.html?from=public_rss

The fossil find was published in the science journal Nature on May 29 this year.