Jump to content


New study shows Elassoma are closely related to Centrarchidae


9 replies to this topic

#1 Guest_TomNear_*

Guest_TomNear_*
  • Guests

Posted 18 February 2012 - 01:16 PM

Hello All-Attached is a recently published study that uses nuclear gene DNA sequence data to investigate the phylogenetic relationships of Elassoma. In this paper we find that Elassoma is strongly resolved as the sister lineage of Centrarchidae. Based on this result, we propose a classification of Centrarchidae that includes Elassoma. Our opinion is this move reduces taxonomic name redundancy. For instance, if Elassoma was classified in it's own taxonomic family the names Elassoma and Elassomatidae would refer to the same clade, the names are redundant. By treating Elassoma as Centrarchidae, the family name reflects this resolved phylogeny and is not redundant.

Enjoy!

Best wishes,
Tom Near

Attached Files



#2 Guest_blakemarkwell_*

Guest_blakemarkwell_*
  • Guests

Posted 18 February 2012 - 11:22 PM

Is there a reason that your stance to sink Elassoma/Elassomatidae within Centrarchidae is favored over just constructing a name for the Elassomatidae + Centrarchidae clade? I definitely see utility in both; I guess it comes down to how genetically and morphologically distinct/unique the Elassoma are in respect to the other centrarchids. Congrats to all the NANFA members involved in this research (I recognize a lot of em!). Elassoma has always been a favorite!

#3 Guest_TomNear_*

Guest_TomNear_*
  • Guests

Posted 19 February 2012 - 12:13 AM

Blake, one motivation was to reduce redundant names, Elassoma and Elassomatidae describe the same lineage of species. There is no information differences between the two names. Also, giving the current scheme of taxonomic ranks (genus, subfamily, family, suborder, order, etc) it is easiest to have the classification reflect the phylogeny by classifying Elassoma as Centrarchidae.

The ranking of family is arbitrary and it is tempting to treat taxonomic ranks as equivalent evolutionary lineages that we can evolutionarily compare in meaningful ways, but clearly they cannot be thought of that way. What we are saying is that among all living species of teleost fishes, Elassoma and Centrarchidae are sister lineages and putting them in Centrarchidae reduces redundancy of ranked taxonomic names and most easily communicates the evolutionary relationships.

Stability of classifications are desired; however, we approach the science of phylogeny and taxonomic classification knowing that our phylogenetic inferences are as good as the data and analyses, and will likely change to some extent as new datasets are brought to bear on specific questions.

#4 Guest_blakemarkwell_*

Guest_blakemarkwell_*
  • Guests

Posted 19 February 2012 - 12:59 AM

Yes, but so do all monogeneric families. However, I realize this is different because Elassoma is so closely related to Centrarchidae, and the move just makes sense. The incongruencies sure are rampant across taxa -- genera as closely related as Ambystoma and Dicamptodon are often times treated in different families, yet stuff as divergent as Gobio and Notemigonus are often united under Cyprinidae. I feel answers from ecology, behavior, and morphology are really vital for these broader groupings, especially if they're concordant or roughly so with the molecular data.

If evolutionary relationships trump stability and previous classifications, then why do we have ichthyologists with a working knowledge of phylogenetics that merit Ammocrypta and Crystallaria as distinct genera, yet not Etheostoma and Nothonotus (I'm being funny :biggrin: )? I know -- it was hard to see my snubs not united under the same clade (Ulocentra), but I follow the data, and the fact that Neoetheostoma is wedged in between Adonia and Ulocentra is good enough for me.

Edited by blakemarkwell, 19 February 2012 - 01:22 AM.


#5 Guest_gerald_*

Guest_gerald_*
  • Guests

Posted 20 February 2012 - 03:22 PM

Tom are you saying that at least two genera are needed to properly define a family, and that existing one-genus families should be merged into their closest related family? Or am I over-generalizing your intent in sinking Elassoma into Centrarchidae? (I have not yet read your paper and apologize if I'm way off base or missing something clearly stated in your paper). Seems to me that allowing one-genus families to stand is useful if they are truly divergent from other genera in their sister family. Especially with tiny fish like Elassoma whose extinct relatives (potentially other genera) we may never find. I suppose sub-family designations could be a workable solution.

Blake, one motivation was to reduce redundant names, Elassoma and Elassomatidae describe the same lineage of species. There is no information differences between the two names. Also, giving the current scheme of taxonomic ranks (genus, subfamily, family, suborder, order, etc) it is easiest to have the classification reflect the phylogeny by classifying Elassoma as Centrarchidae.


Edited by gerald, 20 February 2012 - 03:26 PM.


#6 Guest_TomNear_*

Guest_TomNear_*
  • Guests

Posted 20 February 2012 - 07:44 PM

Gerald, I am not saying that all monogeneric families should be subsumed into the families of which they are sister lineages. However, it seems a way to reduce name redundancy and communicate the phylogeny is to recognize Elassoma as a centrarchid.

There is a problem when we start applying measures of divergence in assessing our ranks. There is no criteria and one should not attempt to frame a set of criteria. So as we resolve the percomorph teleost tree of life, I think we are going to see a number of changes to higher taxonomy like what we propose in this paper.

Some monogeneric families like Aphredoderidae and Percopsidae will likely continue as ranked families, but each of these lineages have a number of extinct genera that are classified in these families. Such "stem" lineages argue for their continued recognition. Other monogeneric families like Inermiidae are changed because they are found to be nested well within other families, such as Haemulidae.

The data is pretty convincing, Elassoma is a centrarchid. Other than Percopsiformes, and maybe some dorky atherinomorphs, I cannot think of any other families of North American freshwater fish that are sister lineages and endemic to North America.

#7 Guest_blakemarkwell_*

Guest_blakemarkwell_*
  • Guests

Posted 20 February 2012 - 08:08 PM

I think the case with Elassoma is that it has such a close relationship to Centrarchidae that it would be silly to have it stand alone. There are obviously solid, monogeneric famiies that are truly not closely related to other clades at that level of resolution. One example of that in salamanders is Rhyacotritontidae, but there are not too many examples with native fish, save some percopsiforms that have fossils of closely related forms that justify their position.

I'm also not sure that the miniaturization of Elassoma is so novel that warrants family rank per se. The dusky salamanders (Desmognathus) have a few species out of the 20 or so that are miniature, and it all seems to arise from heterochrony.

I've always felt the stickleback stance (Smegmamorpha) for Elassoma was dubious at best. I think if you have something that looks like a minature sunfish swimming around with bigger versions of itself like mud sunfish and Enneacanthus, and is only found in the North American coastal plain, then it is probably a sunfish.

#8 Guest_blakemarkwell_*

Guest_blakemarkwell_*
  • Guests

Posted 20 February 2012 - 08:14 PM

Ooops, sorry. I posted before I saw Tom's reply.

#9 Guest_TomNear_*

Guest_TomNear_*
  • Guests

Posted 21 February 2012 - 08:04 AM

Blake, you point out what is probably the most important result from our study: Smegmamorpha is not a clade. The evidence for this grouping was shaky at best and require "special pleading" (Johnson and Patterson 1993).

#10 Guest_rjmtx_*

Guest_rjmtx_*
  • Guests

Posted 23 February 2012 - 05:46 PM

This is great news... now my old smeared and smelly Hubbs et al. key to the FW fishes of Texas is right, again. Now to contact all my past ichthyology lab students and let them know what's what...

I appreciate you and your lab's hard work, Tom.



Reply to this topic



  


0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users