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The Importance of Size in the Evolution of Complexity in Ants

Tue, 16 Sep 2014 10:14:37 +0000

Ants are amongst the most abundant and successful species on Earth. They live in complex, cooperative societies, construct elaborate homes and exhibit many of the hallmarks of our own society. Some ants farm crops, others tend livestock. Many species have a major impact on the ecosystems they live in, dispersing seeds, consuming huge quantities of […]

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Understanding Catfish Colonisation and Diversification in The Great African Lakes

Fri, 05 Sep 2014 10:29:42 +0000

Why some regions or habitats contain vast, diverse communities of species, whilst others contain only relatively few species, continues to be the subject of scientific research attempting to understand the processes and conditions that allow and adaptive radiation. The Great African Lakes exist as freshwater ‘islands’, with spectacularly high levels of biodiversity and endemism. They […]

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Sex Differentiation Begins During Early Development

Wed, 27 Aug 2014 14:04:57 +0000

Males and females look different from each other, and these sexual dimorphisms are the result, largely, of sex differences in the expression of certain genes. Typically, scientists have studied sexual dimorphism in sexually mature adult animals, as this is the lifestage where differences are most apparent. However, many sex-specific phenotypes arise from sex-biased development, so […]

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Extinction and Species Declines:Defaunation in the Anthropocene

Mon, 18 Aug 2014 10:35:52 +0000

We are in the grips of a mass extinction. There have been mass extinctions throughout evolutionary history, what makes this one different is that we’re the ones causing it. A recent review paper from GEE’s Dr Ben Collen discusses the current loss of biodiversity and suggests that our main concerns are species and population declines, […]

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Defaunation in the Anthropocene
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Evolving Endemism in East Africa’s Sky Islands

Fri, 08 Aug 2014 14:16:32 +0000

The World’s biodiversity is not evenly distributed. Some regions are hot spots for species richness, and biologists have been trying better to understand why these regions are special and what drives evolution and diversification. A recent paper by GEE’s Dr Julia Day and recent PhD graduate Dr Siobhan Cox, investigated the diversification of White-Eye Birds […]

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Mother’s care is key to a big brain

7 September 2010

Coverage in the New Scientist

The evolution of big-brained mammals may be due to maternal investment, rather than metabolism, according to a new study by scientists at UCL (University College London) and the University of Cambridge.
Published today in Proceedings of the National Academy of Sciences (PNAS) the study analysed data sets of the brain sizes of 197 marsupial and 457 placental mammals to test the influences of metabolism versus maternal investment on brain size evolution.

MRI brain scan

Contrary to popular hypotheses, researchers found that marsupial mammals, for example kangaroos and possums, had relative brain sizes that are just as big as placental mammals (dogs, horses etc), and even tend to be bigger-brained in some cases.

Big brains in both groups were correlated to length of maternal care, for example a longer period of lactation.  However, basal metabolic rate, or the energy an animal expends at rest, did not correlate with marsupial brain size, whereas they did correlate in placental mammals.  High metabolism was previously thought to be a requirement for big brains as brain tissue is costly to run.

Marsupial brains grow slowly and mainly after birth in the mother’s pouch, whereas placental mammal brains grow rapidly during gestation, where they benefit from the high metabolic rate of the mother.  This study suggests that large brain size can evolve in mammals with low metabolisms as long as they have a period of extended maternal care after birth. 

The researchers also suggest that the evolution of the hugely enlarged brains of some primates can be accounted for by their extended brain growth both during gestation and after birth during a lengthy maternal caring period.

Dr Vera Weisbecker, a joint postdoctoral fellow at the University of Cambridge, Jena University (Germany) and UCL’s Department of Genetics, Evolution & Environment, and lead author of the paper said: “Maternal investment is a much more  universal factor in the evolution of big brains than metabolic rate”.

Dr Anjali Goswami, UCL Department of Genetics, Evolution & Environment and Earth Sciences, and co-author of the paper added, “For a long time, our interest in our own large brains has focused the field on placental characteristics, such as high basal metabolic rate, and made us overlook the role of maternal care after birth on the evolution of big brains. 

“However, if we take primates out of the equation, we discover that marsupials, despite having much lower metabolic rates, have similarly sized brains, or sometimes even bigger brains, than their placental mammal counterparts.  So clearly, evolving big brains isn’t just about having a high metabolism.  Instead, it seems that maternal care is the most consistent factor driving the development of big brains across all mammals.”

Brain development in the two groups is a case of ‘the hare and the tortoise’.  Placental mammals are the ‘hares’ – their brains develop very fast during gestation, with relatively little growth after birth.  Marsupials are the ‘tortoises’ – they are born with very little of their brain developed but then grow slowly and steadily for an extended period after birth whilst they are  being cared for by their mothers.

“It appears that primate brains benefit from the best of both methods of increasing brain size – their brains grow rapidly during gestation in line with their fellow placental mammals, but also develop significantly after birth during a maternal care period which is only comparable to marsupials in terms of length,” added Dr Goswami.

The research was funded by a Volkswagen Foundation Evolution Initiative Postdoctoral Fellowship Grant to V Weisbecker.

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