Frog erythrocytes

[JimC]

I was helping my son Nick make sense of a biology prac they had done at school, using the microscope. One of the standard comparisons they made was between a slide of frog blood, where the erythrocytes (red blood cells) are clearly nucleated, and human cells, where (when mature) they are anucleate. Nick asked me why...

I knew, of course, that mammals are the only vertebrates with consistently anucleate erythrocytes. I made a tentative suggestion that mammals needed to transport a greater volume of oxygen, so erythrocytes "slimmed down" to a basic model may be more efficient at oxygen transport. However, I am unsure whether an adaptive answer such as this is reasonable, or whether it is one of those historical accidents of the evolutionary process which are good cautionary tales for adaptationists such as myself.

PS - I love having a son who asks "why" questions that make me think twice...

[Xamonas Chegwé]

I understand it as being a making room thing as well, Jim. Mammalian RBCs are very small compared to other cells and contain almost no organelles, maximising their ability to carry oxygen and pass through the tiniest of capillaries.

I wonder what dinosaur erythrocytes looked like...

[JimC]

I understand it as being a making room thing as well, Jim. Mammalian RBCs are very small compared to other cells and contain almost no organelles, maximising their ability to carry oxygen and pass through the tiniest of capillaries.

I wonder what dinosaur erythrocytes looked like...

I bet they would be nucleated, just like their avian descendents...

The reasons for the lack of nuclei in mammalian erythrocytes that we were both speculating about ultimately come down to efficiency of oxygen transport. One would have thought the same selective pressures applied to birds, given their active, homeothermic metabolism...

(I should really post this conundrum on RDF, I suppose...)

[Xamonas Chegwé]

I understand it as being a making room thing as well, Jim. Mammalian RBCs are very small compared to other cells and contain almost no organelles, maximising their ability to carry oxygen and pass through the tiniest of capillaries.

I wonder what dinosaur erythrocytes looked like...

I bet they would be nucleated, just like their avian descendents...

The reasons for the lack of nuclei in mammalian erythrocytes that we were both speculating about ultimately come down to efficiency of oxygen transport. One would have thought the same selective pressures applied to birds, given their active, homeothermic metabolism...

(I should really post this conundrum on RDF, I suppose...)

I was thinking that the lack of nuclei and the resulting improvement in oxygen transport contributed to mammals reaching the sizes that they are capable of and doing so while maintaining a very active lifestyle. It would be interesting to see if this feature were shared by some of the larger dinos. According to Wiki, there are a few non-mammalian species (a genus of salamander and a few fish) that also lack nuclei in their erythrocytes, which would imply that the phenotype has evolved independently on more than one occasion.

[JimC]

I understand it as being a making room thing as well, Jim. Mammalian RBCs are very small compared to other cells and contain almost no organelles, maximising their ability to carry oxygen and pass through the tiniest of capillaries.

I wonder what dinosaur erythrocytes looked like...

I bet they would be nucleated, just like their avian descendents...

The reasons for the lack of nuclei in mammalian erythrocytes that we were both speculating about ultimately come down to efficiency of oxygen transport. One would have thought the same selective pressures applied to birds, given their active, homeothermic metabolism...

(I should really post this conundrum on RDF, I suppose...)

I was thinking that the lack of nuclei and the resulting improvement in oxygen transport contributed to mammals reaching the sizes that they are capable of and doing so while maintaining a very active lifestyle. It would be interesting to see if this feature were shared by some of the larger dinos. According to Wiki, there are a few non-mammalian species (a genus of salamander and a few fish) that also lack nuclei in their erythrocytes, which would imply that the phenotype has evolved independently on more than one occasion.

But why wouldn't the same apply to large active birds like the current ratites?

I am leaning towards an accident of historical contingency, which is unusual for an arch-adaptationist such as myself...

(bumped to show the influxers that it's not all gin and cunnilingus here at Ratz... )

[Boadacia!]

I often wonder if in the future when we screw around more destroying Antarctica, if some long locked frozen swamp might give us some dino' blood? Or have I got my tectonics timing all wrong?