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Coevolution of relative brain size and life expectancy in parrots (research article)

flyzipper

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I like big brains and I can not lie...

Abstract
Previous studies have demonstrated a correlation between longevity and brain size in a variety of taxa. Little research has been devoted to understanding this link in parrots; yet parrots are well-known for both their exceptionally long lives and cognitive complexity. We employed a large-scale comparative analysis that investigated the influence of brain size and life-history variables on longevity in parrots. Specifically, we addressed two hypotheses for evolutionary drivers of longevity: the cognitivebuffer hypothesis, which proposes that increased cognitive abilities enable longer lifespans, and the expensive brain hypothesis, which holds that increases in lifespan are caused by prolonged developmental time of, and increased parental investment in, large-brained offspring. We estimated life expectancy from detailed zoo records for 133 818 individuals across 244 parrot species. Using a principled Bayesian approach that addresses data uncertainty and imputation of missing values, we found a consistent correlation between relative brain size and life expectancy in parrots. This correlation was best explained by a direct effect of relative brain size. Notably, we found no effects of developmental time, clutch size or age at first reproduction. Our results suggest that selection for enhanced cognitive abilities in parrots has in turn promoted longer lifespans.

 

SumitaSinh

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Thanks for this... I am going to read it thoroughly, when I get time. It can't be read in a hurry.
 

Destiny

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Hmmm I feel like they skipped an important step here. Before comparing brain size to longevity to determine if cognitive complexity extends lifespan, shouldn't you first check if bigger brains actually correlate with higher cognitive complexity? They implied that was what these results are suggesting, but I would disagree.

Maybe I am biased because I keep budgies, but smaller heads don't necessarily mean dumber birds. And bigger heads do not necessarily mean smarter birds. Intelligence is a tricky thing to quantify, especially between different species, so it is hard to say which kind of parrot is the "smartest" but I don't think size has much to do with it.

It also makes me wonder how the results would be altered if the study had included a few other bird species. I assume they looked at a variety of small to large parrot species. But what about comparing brain sizes to longevity between a parakeet and a chicken? Or a chicken and a turkey? Or a hummingbird and an ostrich? Or an ostrich and an emu? What would that have shown? Or maybe go the other direction and look at ONLY one species of parrot and compare body weight at maturity to lifespan of that parrot to see if there is a connection between size and longevity within the same species.

This also raises another question in my mind - how did this study calculate longevity for different parrot species? Was it based on averge lifespan in the wild or in captivity? There can be a significant difference between the two, due to predation, disease, and environmental hazards in the wild. Is this result an artifact of large parrots having unusually long lifespans in captivity? Would it actually hold true for wild bird lifespans?

Perhaps it still would, because smaller birds would be subject to higher predation and tend to die younger and reproduce faster. But that doesn't necessarily mean that their smaller brains are less capable of complex thought. Just that their small bodies fit into a wider range of predator mouths and nature is a scary place for the little ones.

Anyways, just my two cents. Interesting article :)
 

flyzipper

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I echo your questions @Destiny

Some are addressed in the paper ("We estimated life expectancy from detailed zoo records for 133 818 individuals across 244 parrot species"), but I need to find more time to fully digest the article.

The thing that stood out to me is they mentioned this article (Birds have primate-like numbers of neurons in the forebrain), yet didn't dig into the possibility neuron density might be the metric to measure for their comparison, rather than relative size (or maybe not).

From the freshly linked paper...

With their higher neuronal densities (Fig. 3 A–C), songbird and parrot brains accommodate about twice as many neurons as primate brains of the same mass and two to four times more neurons than rodent brains of equivalent mass (Fig. 1B). Songbirds and parrots also show a large brain mass for their body mass compared with nonprimate mammals (Fig. S4 A and B). Consequently, they have many more neurons than a nonprimate mammal of the same body size (Fig. 1E). For instance, the goldcrest’s body mass is ∼9-fold smaller than the mouse, but its brain has ∼2.3-fold more neurons. Large corvids and parrots possess the largest avian brains, harboring the highest absolute numbers of neurons (Fig. 1 D and E and Fig. S4C). Their total numbers of neurons are comparable to those of small monkeys or much larger ungulates (Fig. S5).
It makes me curious what the brain size and neuron density is for this group -- although that list probably does more to disprove the importance of both size and density.

"Knowledge brings more questions than answers“ — Carlos Gershenson
 

SumitaSinh

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Hmmm I feel like they skipped an important step here. Before comparing brain size to longevity to determine if cognitive complexity extends lifespan, shouldn't you first check if bigger brains actually correlate with higher cognitive complexity? They implied that was what these results are suggesting, but I would disagree.

Maybe I am biased because I keep budgies, but smaller heads don't necessarily mean dumber birds. And bigger heads do not necessarily mean smarter birds. Intelligence is a tricky thing to quantify, especially between different species, so it is hard to say which kind of parrot is the "smartest" but I don't think size has much to do with it.

It also makes me wonder how the results would be altered if the study had included a few other bird species. I assume they looked at a variety of small to large parrot species. But what about comparing brain sizes to longevity between a parakeet and a chicken? Or a chicken and a turkey? Or a hummingbird and an ostrich? Or an ostrich and an emu? What would that have shown? Or maybe go the other direction and look at ONLY one species of parrot and compare body weight at maturity to lifespan of that parrot to see if there is a connection between size and longevity within the same species.

This also raises another question in my mind - how did this study calculate longevity for different parrot species? Was it based on averge lifespan in the wild or in captivity? There can be a significant difference between the two, due to predation, disease, and environmental hazards in the wild. Is this result an artifact of large parrots having unusually long lifespans in captivity? Would it actually hold true for wild bird lifespans?

Perhaps it still would, because smaller birds would be subject to higher predation and tend to die younger and reproduce faster. But that doesn't necessarily mean that their smaller brains are less capable of complex thought. Just that their small bodies fit into a wider range of predator mouths and nature is a scary place for the little ones.

Anyways, just my two cents. Interesting article :)
I agree... Brain size is less important, main thing is convolutions of cerebral cortex. Another important point is the ratio of brain and body mass.
 

SumitaSinh

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A very interesting study, I thing it will be reviewed thoroughly in future.
 
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