Did you know that babies take a long time to grow up because their brains use too much energy?

Humans are very slow to develop into adults compared to other animals.

One hypothesis is that slow body growth is due to the high energy demands of the brain.

This study performed MRI and PET scans of 29 people ranging in age from birth to adolescence.

Peak glucose use by the brain was at ~4-5 years of age, accounting for 43% of daily energy requirements. Twice as much as an adult.

This is also the time when the body has the lowest rate of weight gain.

This suggests the brain dominates energy requirements early in life at the expense of body growth, explaining why human children grow so slowly.

It drives the neuronal plasticity (restructuring of the brain) that is critical for learning and memory in children.

Do you want more information?

Background

Humans grow from babies to adults very slowly compared to other animals, even primates.

Humans also have large and highly developed brains.

Hypothesis: high energy demands of the growing brain during childhood/adolescence restricts the growth of the body. The body then has a ‘growth spurt’ in late adolescence, after brain growth slows down.

Materials and Methods

This study analysed MRI (magnetic resonance imaging) and PET (positron emission tomography) scans of the brains and body of 29 people ranging in age from birth to adolescence. MRI measures sizes and dimensions of tissues, while PET measures glucose/energy use.

Results

Brain usage of glucose peaks at ~4-5 years of age, accounting for 43% of daily energy requirements (167g per day in males, 146 in females).

This is also the time when the body has the lowest rate of weight gain.

Glucose use is highest in the cerebrum (e.g. cortex, top part of the brain that does the calculation, planning, higher order functions).

Adult brains use half as much glucose as 4-5 year olds, despite being much bigger.

Discussion

The brain dominates energy requirements early in life at the expense of body growth, explaining why human children grow so slowly.

During development, there is an inverse relationship between brain energy/glucose use and body size.

Not all of the glucose is used by the growing brain for energy. Up to 30% is used for synaptic growth and rearrangement. This neuronal plasticity (restructuring of the brain) is particularly high during childhood and is critical for learning and memory.

Slow growth of human baby’s bodies (to prioritise the brain) first evolved in Homo erectus at least 1.5 million years ago.

In contrast, Neanderthals grew more rapidly but their brains weren’t as developed.

Future Directions

29 people is a rather small cohort from which to draw solid conclusions, so further studies using more people are required.

Ideally, it would be best to measure the same people as they age (longitudinal study), although this is a very long-term project.

Article

Metabolic costs and evolutionary implications of human brain development

Kuzawa et al., 2014 Proc. Natl. Acad. Sci. USA 111:13010-5

Keywords

Brain, neuron, synapse, cerebrum, cortex, learning, memory, plasticity, development, children, baby, adolescent, adolescence, glucose, energy, MRI, PET, scan

Subject

Science, Biology, ST1-10LW, ACSSU030, ST2-10LW, ACSSU072, ST3-10LW, ACSSU043, SC4-14LW, ACSSU150, SC5-14LW, ACSSU175

Did you know the biggest ever dinosaur was recently discovered in Argentina?

It was 26m in length and weighed 60 tons.

One vertebra is 1.13m, its humerous is 1.6m and its femur is 1.91m.

This specimen lived around 77 million years ago and died in a flood, but was still growing when it died (i.e. not yet full size).

It was named Dreadnoughtus after the massive battleships of the early 20^th century that were impervious to attack (like the dinosaur).

Even though it’s massive, it still isn’t as big as a blue whale (~100 tons).

Do you want more information?

Background

The largest dinosaurs are a special group called Titanosauria.

These are the largest land animals ever.

In 2013, bones from a new species called Argentinosaurus were discovered in Northern Argentina and thought to be the biggest dinosaur.

However, a new species have just been discovered.

Materials and Methods

Archaeologists from the USA and Argentina were digging in the Southern Patagonia region of Argentina. The bones are now kept in a museum in Rio Gallegos, Argentina.

Results

The skeleton belongs to a new species of vegetarian Titanosaur named Dreadnoughtus.

It was named after the massive battleships of the early 20^th century that were so large, they were virtually impervious to attack, like this dinosaur.

45% of its bones were recovered (70% excluding the head), which is far more than other specimens of titanosaur (e.g. only 5% of Argentinosaurus).

It lived around 77 million years ago and died in a flood.

One vertebra is 1.13m, its humerous is 1.6m and its femur is 1.91m.

Using these measurements (humeral and femoral circumference), the animal is calculated to be 26m in length and weigh 60 tons. Larger than Giraffatitan (34 tons) and Diplodocus (15 tons).

It is stated on pg.6 of the journal article that Dreadnoughtus had ‘robust pubes’ (not clear what this means).

Discussion

It is possible that the rival species Argentinosaurus could grow to be more than 60 tons, however this is based on only a handful of bones.

The skeleton discovered for Dreadnoughtus is far more complete.

Furthermore, this specimen was still growing when it died.

Therefore, Dreadnoughtus is presently the largest dinosaur.

However, it is still not as big as a blue whale (~100 tons).

Future Directions

Only one animal of Dreadnoughtus and Argentinosaurus has so far been discovered. Further skeletons (and more complete) will help resolve the issue of which is biggest.

Article

A gigantic, exceptionally complete titanosaurian sauropod dinosaur from southern Patagonia, Argentina

Lacovara et al., 2014 Scientific Reports 4:6196

Keywords

Dinosaur, sauropod, titanosaur, Dreadnoughtus, Argentinosaurus, archaeology, archaeologist, bone, skeleton, history, whale, animal

Subject

Science, Biology, Archeology, ST1-10LW, ACSSU017, ST2-11LW, ACSSU073, ST3-10LW, ACSSU043, SC4-14LW, ACSSU111, SC5-15LW, ACSSU185

Did you know a brand new type of animal was recently discovered off the coast of Tasmania?

All life forms on Earth are categorised using the taxonomic ranking system.

However, this new animal doesn’t fit into that system.

Dendrogramma look like tiny mushrooms with a stalk (1-2cm) and a disc (0.4-0.8cm).

They can’t swim, so they probably just float about.

They have a single mouth at the end of the stalk that captures food (microorganisms) and expels waste (eats and poos out the same mouth).

It’s possible they are a missing link between cnidarians (corals, jellyfish) and ctenophores (comb jellies), or descendants of Ediacara that were thought to have died out 600 million years ago.

Either way, they are a new type of animal never seen before.

Do you want more information?

Background

All life on Earth is categorised in a taxonomic ranking system.

i.e. Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Humans are categorised as: Eukaryota, Animalia, Chordata, Vertebrata, Mammalia, Primates, Hominidae, Homo, Sapiens

All animals fit into this taxonomic ranking system.

However, a new animal has just been discovered that doesn’t.

Materials and Methods

The Australian National Facility Research Vessel ORV Franklin dragged an epibenthic sled (cage) to collect samples from the ocean near Tasmania at depths of 400m and 1000m. This was performed in 1986, but it wasn’t until much later these unidentified life forms were discovered in these samples following sorting using sieves.

Results

Two closely-related species of animal were discovered that do not fit into current taxonomic categories.

These have been called Dendrogramma.

These animals look like mushrooms with a stalk (1-2cm) and a disc (0.4-0.8cm).

They can’t swim, so they probably just float about.

They have a single mouth at the end of the stalk that captures food (microorganisms) and expels waste (eats and poos out the same mouth).

Their closest relatives are cnidarians (corals, jellyfish), ctenophores (comb jellies) and an extinct group of animals called Ediacara that lived around 600 million years ago.

Discussion

The Ediacara, cnidarians and ctenophores are amongst the earliest and most simple forms of multicellular life.

The Ediacara is suggested to be a ‘failed experiment in multicellularity’, early in the evolution of life on Earth.

Perhaps it didn’t fail. Perhaps the Dendrogramma discovered here are actually descendants of the Ediacara.

Or they could be a missing link between cnidarians and ctenophores.

Future Directions

The genome of Dendrogramma will be sequenced and compared to other animals to determine if they are descendants of Ediacara or an entirely new type of life form.

This could not be performed here, because the specimens were treated with formalin and alcohol, which prevents genomic sequencing.

Article

Dendrogramma, new genus, with two new non-bilaterian species from the marine bathyal of southwestern Australia (animalia, metazoan incertae sedis)–with similarities to some medusoids from the precambrain edicara

Just et al., 2014 PLoS One 9:e102976

Keywords

Animal, taxa, taxonomic, species, phylum, kingdom, class, ocean, Tasmania, Australia, extinct, multicellular, mushroom

Subject

Science, Biology, Zoology, ST1-10LW, ACSSU017, ST2-10LW, ACSSU044, ST3-10LW, ACSSU043, SC4-14LW, ACSSU111, SC5-15LW, ACSSU185

Did you know that species with lots of babies have greater genetic diversity?

Evolution is in large part driven by changes to DNA (genetic diversity).

This helps species adapt to changes in the environment and survive.

Are all species able to adapt at the same rate? Do they all have the same genetic diversity?

This study sequenced the genomes of 76 different animal species and compared their genetic diversity.

Genetic diversity was highest in animals that have lots of offspring that don’t depend on their parents to survive.

In contrast, animals that have low numbers of offspring that depend on their parents to survive have low genetic diversity (e.g. humans).

This means if there are lots of offspring, the species can afford to experiment with diverse genomes, with the fittest surviving. However if there are only a few offspring, it is best to stick close to a genome that is known to be successful (i.e. its parents).

Do you want more information?

Background

Evolution is in large part driven by changes to the DNA/genome.

The DNA doesn’t change in the adult, but when it is passed onto its offspring.

These random changes (genetic diversity) are beneficial, because they help a species adapt to changes in the environment (i.e. survive).

In contrast, low genetic diversity makes species vulnerable to extinction. For example, endangered species with only a few breeding pairs have very low genetic diversity. If they are challenged (i.e. infectious disease), they can all die.

Do all animals have the same amount of genetic diversity? Do their genomes change/evolve at the same rate?

Materials and Methods

The transcriptomes (RNA transcripts) of 76 different animal species (2-10 individuals per species, total = 374) were sequenced using RNA-seq (sequences RNA instead of DNA). mRNA is the intermediate between gene and protein. Other RNAs were also sequenced.

Results

Genetic diversity (changes in DNA/genome) was highest in the slipper shell (medium-sized sea snail) (8.3%).

Lowest in the subterranean termite (0.1%).

Genetic diversity is not related to geography (where the species lives).

However, it is related to species size (big), lifespan (long), offspring quantity (fecundity, high) and quality (propagule size, low).

It is most highly associated with propagule size, which is the size/stage of offspring when they leave their parents (egg or juvenile).

There is an inverse correlation between genetic diversity and parental investment in their offspring.

Ants, bees, termites, turtles, seahorses, mammals and birds have high parental investment and low genetic diversity.

Mussels, sea urchins and starfish have low parental investment and high genetic diversity.

Discussion

Genetic diversity is high in animals that have lots of offspring that are able to survive on their own without parental help. Here, the species can experiment with many different genomes, with only the fittest surviving.

For species that have high parental investment into a small number of offspring (e.g. humans), it is too risky to experiment with dramatic changes to the genome. Instead, it is safer to stick close to a genome that is proven to be successful. That is, if the parent survived to adulthood, then it is likely that the offspring will as well.

This was the first study to compare the genome and genetic diversity between many different animal species.

Article

Comparative population genomics in animals uncovers the determinants of genetic diversity

Romiguier et al., 2014 Nature 515:261-3

Keywords

Gene, genome, genetic, DNA, polymorphism, mutation, animal, species, diversity, offspring, evolve, evolution, sequence, sequencing

Subject

Science, Biology, Genetics, Evolution, Zoology, ST3-10LW, ACSSU043, SC4-14LW, ACSSU150, SC5-15LW, ACSSU185

Did you know that genes control the age that girls have their first period?

A huge study was conducted by 166 institutions from around the world that analysed the genome/DNA sequences of over 180,000 women.

They identified 106 regions of the genome (loci) that affect the timing of puberty/first period in girls.

This includes several genes that regulate the production of hormones (e.g. oestrogen) and body weight.

This makes sense, because it is well known that hormones and body size strongly influence the timing of puberty. It emphasises the complex interplay between genes and environment (nature v’s nurture).

It might be possible in the future to sequence these 106 regions to predict when girls will have their first period. Would this be useful?

Do you want more information?

Background

Virtually all of aspects of our bodies are controlled by a mixture of genes and environment (i.e. nature v’s nurture).

Girls begin puberty and get their first period (menarche) between 10-15 years of age (average 12-13).

Do genes influence the timing of the first period in girls?

Materials and Methods

A large collaboration involving scientists at 166 institutions from around the world analysed the genomes of 182,416 women of European descent (i.e. Caucasian) and correlated specific genes and regions of the genome with the onset of puberty.

Results

This huge study identified 106 genomic loci that are associated with the onset of menarche/puberty in girls.

That is, specific sequences/differences in the DNA at 106 regions of the genome that affect the timing of the first period.

These regions can be inside genes, near genes or in between genes.

Usually, they affect the expression of a gene or the activity/function of the protein it produces.

Each of these DNA sequences/loci has only a weak affect on period timing, however when several are combined, they have a stronger affect.

29 of the loci/genes affect the production of hormones (e.g. oestrogen), 9 affect body weight and 3 affect height. This makes sense, because it is well known that body size strongly influences the timing of puberty.

Discussion

It might be possible in the future to sequence these 106 regions to predict when girls will have their first period (approximate timing).

While this study focuses on the genetic influence on puberty/period timing, there are clearly also environmental factors that contribute.

Interestingly, several genes associated with body size were identified in this study. Size/weight is also strongly affected by diet and lifestyle, thus emphasising the complex interplay between genes and environment.

Article

Parent-of-origin-specific allelic associations among 106 genomic loci for age at menarche

Perry et al., 2014 Nature 514:92-7

Keywords

Gene, genetic, genome, DNA, sequencing, loci, locus, GWAS, puberty, period, menarche, adolescence, development, hormone, oestrogen, weight, body, nature, nurture

Subject

Science, Biology, Genetics, SC4-14LW, ACSSU150, SC5-15LW, ACSSU184