Is Protista defunct?

[Skye]

I've heard people say this before. Modern systematics would make it seem so, as the Kingdom is not monophyletic and green algae would be better off grouped with plants than protists in any case. The botanists probably claim them anyway. So should people stop using it, and should it no longer be taught in classes or textbooks?

[Dak]

untill the protists have actually been put into other kingdoms (afaik, there's no consensus on where most of them should go), i guess k.protista is still usefull, as a kinda 'kingdom errata'.

 

like the imperfecta order(?) in fungi.

[SkepticLance]

I think Skye is correct. It is a bit like calling Pluto a planet. Might have a little utility on the populist basis, but little meaning scientifically.

 

Amoeba and Chlamydomonas are not really related. So why call them both protists?

[Dak]

if not, you'd have to call them 'misc' or 'unclassified', which is pretty much what protista means

[Skye]

untill the protists have actually been put into other kingdoms (afaik, there's no consensus on where most of them should go), i guess k.protista is still usefull, as a kinda 'kingdom errata'.

 

like the imperfecta order(?) in fungi.

Fungi is one of the five kingdoms. Animals, plants, fungi, protists and monera. Let's say I said to you Dak, I want you, on behalf of humanity, to reorganise protista. So let's say we have three domains; bacteria, archaea and eukarya. Then within eukarya you have something like this,

http://www.ucmp.berkeley.edu/alllife/eukaryotasy.html

 

That's a little speculative I think, maybe choanoflagellates are closely related to animals, I'm not sure. But anyways let's assume it's something like that. How would you organise the protists?

[Dak]

Fungi is one of the five kingdoms.

 

as in, iirc fungi imperfecta are 'fungi that we dont know which order they belong to', hence 'protists' are 'thingies that we dont know which kingdom they belong to'.

 

Animals, plants, fungi, protists and monera. Let's say I said to you Dak, I want you, on behalf of humanity, to reorganise protista. So let's say we have three domains; bacteria, archaea and eukarya. Then within eukarya you have something like this,

http://www.ucmp.berkeley.edu/alllife/eukaryotasy.html

 

That's a little speculative I think, maybe choanoflagellates are closely related to animals, I'm not sure. But anyways let's assume it's something like that. How would you organise the protists?

 

they seem pretty-much already organised within that system? eg, chlorophyta go in the 'green algi' bit

 

problem is, you get different groupings dependant on wether you divvy them up cladistically, genetically, or by ribosomal-subunit ananlysis (to take the three examples from my text book). so... for a text book, i guess there's little choice but to use k.protista untill there's actually a consensus as to where these clades go. it would suck, for example, if a text book taught the classification that you linked to, only to have most scientists choose a different one a few years later.

 

having said that, i kinda like the way my text book deals with it -- making it clear it's a 'misc' kingdom, and then going on to deal with them cladistically for ease of study (eg, flagelates, algi, etc -- tho, looking at the green algi, rhodophytai, chromista groups in your link, i guess that 'algi' doens't make that much sence apart from as a learning aide)

 

maybe choanoflagellates are closely related to animals, I'm not sure.

 

iirc, choanoflagellates contain dinoflagellates, which bear a remarcable resembelance to the cells that sponges use to trap their food, hence the suspicion that evolution may have vaiguley gone dinoflagellates --> sponges --> other animals.

 

[edit] actually, it's not dinoflagellates, but i can't remember which group it is[/edit]

[Skye]

I think the problem with protists is that if you start diviving them up, you end up with at least a half dozen different groups. And I'm not sure anybody really wants to give slime molds the same status systematically as animals. But that's also the problem with the three domains organisation, and people seem to be accepting that. I think it's interesting how the family tree is still being sketched out, even the major branches.

 

The choanoflagellates are similar to choanocytes of sponges, I think it is all the choanoflagellates. They both have a collar dealy (choano=collar) and flagella inside. But I'm not sure if they are similar aside from that. I found the link below, but it's only one gene.

 

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VRT-43F87N0-R&_coverDate=06/26/2001&_alid=289081454&_rdoc=1&_fmt=&_orig=search&_qd=1&_cdi=6243&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=71f3acee230259f425177763a6078803#toc2

 

A problem is that the choanocyte is a differentiated somatic cell of sponges, it's not the germ cell. It would make alot more sense if choanoflagellates resembled the germ cells, then the differentiated cells could have come after.

[Mokele]

IMHO, some paraphyletic groups, or even polyphyletic groups, are taxonomically useful. For instance, reptiles are polyphyletic, but it's a useful grouping for communication. That's the main thing: taxonomy was created for the purposes of communication. Some accuracy and reflection of biological reality is advantageous, but total accuracy would prevent any utility for communication.

 

Mokele

[bombus]

When I was in school protista were a separate group, along with protozoa and (I think) protophyta. When many years later I went to Uni, Protozoa were classed as a form of Protista.

 

So Protista includes all the 'primative' single celled plants, animals and in-betweenies and is still used - I think...