Gull help needed (1 Viewer)

[Butty]

Sure. But a) population-level effects comprise individual events, and b) I felt that Mr/Ms Fern was talking about the principle, and - in principle - there seems no reason to think that gene-flow is impossible.

 

[THE_FERN]

Puzzled. If a bird from one population/species breeds successfully - even only once - with, and within the range of, birds of another population/species then that is gene-flow between those populations, even if only in one direction and minute.

Agree. So for us humans we might think that one "hybrid" event every year or every few years will make no difference and the populations will remain "distinct". But because of the speed at which many [not all] genes evolve [slowly] then even this low level of genetic interchange can be enough to prevent the populations diverging genetically.

 

[THE_FERN]

and not because they have smith genes but because of intraspecific variation

We can't possibly know that. It's likely that the genes are the same in this case. Not all genes have to be different between 2 species for the species to be unable to interbreed, for example.

The phylogeny for the individual in some sense is the sum of the phylogenies of its individual genes. A phylogeny for any one gene might suggest that the taxa are from the same population—why modern studies try to sample several to get an "overall" view.

 

[Waxwings]

Yes we can see different more or less well marked phenotypes but then we can for redpolls too...

The recent research on redpolls proposed lumping them because it found that they "lack population genetic structure by either geography or ecotype [phenotype] boundaries" and that genetics failed to group the individuals according to their current species classification. The researchers suggest that phenotypic differences are probably driven by environmental factors.

I don't think there has been any suggestion of similar issues with gulls. EHG and AHG do have consistent genetic differences (albeit small ones) between populations.

 

[THE_FERN]

The recent research on redpolls proposed lumping them because it found that they "lack population genetic structure by either geography or ecotype [phenotype] boundaries" and that genetics failed to group the individuals according to their current species classification. The researchers suggest that phenotypic differences are probably driven by environmental factors.

I don't think there has been any suggestion of similar issues with gulls. EHG and AHG do have consistent genetic differences (albeit small ones) between populations.

Well I've asked about this before. I'm unaware of any good recent molecular studies. I'd be keen to know what and how extensive any differences are. For example, I'd be willing to bet many [herring, caspian etc] are less divergent than mainland and Gran Canaria robins. There are small but consistent differences between populations of humans... [that's how we can reconstruct past migration patterns of H. sapiens out of Africa etc] ...but sensible people still treat us as one species.

I like molecular because a) it gives indication of how birds have behaved over time [broadly whether they've thought they're different over a period] and b) a range of markers gives a range of time estimates. Of course, recently diverged or incipient species may be kept apart by other things like behaviour which haven't had time to show up in the genes yet ["incomplete lineage sorting"]. Gulls may fall into this category. I'd like the evidence so I can make up my own mind.

[People try to identify / ascribe individuals of other things to races where they are generally accepted not to be specifically distinct—wagtails comes to mind—so recording and assigning gulls is still valid even if you don't think they're different species. Just don't ask me to do it.]

Edit: this wasn't the first molecular study to advocate lumping redpolls. The important point is that phenotypic distinctiveness may not indicate population differentiation.

 

[lou salomon]

If you're into genetics, The Fern, the dissertation work of Viviane Sternkopf might be of interest to you, attached. But I doubt you would be able to read it as it is in german. Maybe some of the figures give you some insight, though.

 

[THE_FERN]

If you're into genetics, The Fern, the dissertation work of Viviane Sternkopf might be of interest to you, attached. But I doubt you would be able to read it as it is in german. Maybe some of the figures give you some insight, though.

Thanks I was [vaguely] aware of this. See Fig 1.2 f), the bit highlighted in the rectangle for an example of what I was talking about. This clade is unresolved—genetically indistinguishable. Without being able to read the details, I can see from Fig 3.9 that at best divergences are very recent for larger gulls: of the order of <=500,000 yrs. I understand Fig 3.14 to indicate [very] incomplete lineage sorting.

 

[dantheman]

I was thinking of it as an example where in the recent past (last couple of centuries?) it wasn't an American breeder - presumably the earliest ones in N America would still also have hybridised with AHG. (As an aside - how recent is the Greenland population of LBBG?) as an example of a vagrant hybridising.

Just to clarify this aside to this interesting thread - re Lesser Black-back Gulls - turns out they colonised Greenland in the 1980s. Whence wintering birds and then more latterly start of breeding birds to N America came from (earlier vagrants from Iceland or elsewhere).

(Imagine there has always been some toing and froing of vagrant gulls between the WP and Nearctic irrespective of more recent breeding increases of some of the larger gulls linked to eg tips.)

 

[HH75]

I don't think there has been any suggestion of similar issues with gulls. EHG and AHG do have consistent genetic differences (albeit small ones) between populations.

One difference between large gulls and redpolls is that, with a few notable exceptions (the whole Thayer's/Kumlien's/Iceland conundrum, for example), a lot of large gulls breed in areas where lots of ornithologists and field birders live. Thus, even leaving aside instances of hybridisation/gene flow, we can almost intuitively grasp that, say, (European) Herring and Lesser Black-backed Gulls behave as good species, regardless of the genetic differences. We can see what goes on, and they clearly act as separate entities most of the time. Therefore, while grasping that a species is actually a human concept to help us make sense of the natural world around us, these two birds would qualify as 'species' under any species concept, and many other large white-headed gulls are similar. Redpolls, on the other hand, largely breed in remote northern areas, at least most of the taxa do, so we have far less of an idea of what is going on where taxa meet. Though, being selfish, as I've only seen Lesser Redpoll myself, I'd not be averse to a lump of them all...

 

[THE_FERN]

Thus, even leaving aside instances of hybridisation/gene flow, we can almost intuitively grasp that, say, (European) Herring and Lesser Black-backed Gulls behave as good species, regardless of the genetic differences. We can see what goes on, and they clearly act as separate entities most of the time. Therefore, while grasping that a species is actually a human concept to help us make sense of the natural world around us, these two birds would qualify as 'species' under any species concept

Here's the nub of it. Imposing a discontinuous taxonomy ("species", "genera" etc) on a continuously varying thing (populations of individuals) will never be anything other than subjective. So "... Intuitively grasp...would qualify as 'species'..." can only really be understood as your personal view (which you're welcome to of course). I try to come to my own position on these things---and it may differ from yours. We'll both be equally right (or wrong).

(We should also be clear what we're trying to achieve with our taxonomy. Is it to label things which are morphologically distinct, more generally distinct (e.g. Different behaviour, genetics) and/or reflect evolutionary history?)

I feel that people rely too much on "expert" committees like SACC etc to make decisions for them. Some well qualified people on this forum sometimes publicly disagree (mentioning no names). I like the debate and do not feel duty bound to tow the "expert" line. But that's because I understand and have thought through the philosophical issues. I know this isn't true for everyone. I dread the day when there's a single global taxonomy, even if it makes my life easier when preparing for trips etc

 

[Butty]

Trouble is... people love to be told what to do/think - what line to toe - and you see that almost daily (ish) on here... 'Suchnsuch is a species now', etc, etc. Depressing.

 

[smiths]

There is actually no proof that ANY American gull has ever successfully bred (i.e. reproduced) in Europe...