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Beringia (1 Viewer)

Jacana

Will Jones
Hungary
Jessica F. McLaughlin, Brant C. Faircloth, Travis C. Glenn & Kevin Winker (2020). Divergence, gene flow, and speciation in eight lineages of trans‐Beringian birds. Molecular Ecology, Accepted article. https://doi.org/10.1111/mec.15574

Determining how genetic diversity is structured between populations that span the divergence continuum from populations to biological species is key to understanding the generation and maintenance of biodiversity. We investigated genetic divergence and gene flow in eight lineages of birds with a trans‐Beringian distribution, where Asian and North American populations have likely been split and reunited through multiple Pleistocene glacial cycles. Our study transects the speciation process, including eight pairwise comparisons in three orders (ducks, shorebirds, and passerines) at population, subspecies, and species levels. Using ultraconserved elements (UCEs), we found that these lineages represent conditions from slightly differentiated populations to full biological species. Although allopatric speciation is considered the predominant mode of divergence in birds, all of our best divergence models included gene flow, supporting speciation with gene flow as the predominant mode in Beringia. In our eight lineages, three were best described by a split‐migration model (divergence with gene flow), three best fit a secondary‐contact scenario (isolation followed by gene flow), and two showed support for both models. The lineages were not evenly distributed across a divergence space defined by gene flow (M ) and differentiation (FST ), instead forming two discontinuous groups: one with relatively shallow divergence, no fixed SNPs, and high rates of gene flow between populations; and the second with relatively deeply divergent lineages, multiple fixed SNPs, and low gene flow. Our results highlight the important role that gene flow plays in avian divergence in Beringia.

Jess McLaughlin made a nice Twitter thread about it here: https://twitter.com/jfmclaughlin92/status/1290681635369869313?s=20

the 8 species/species pairs are:

Long-tailed Duck
Eurasian/American Wigeon
Eurasian/Green-winged Teal
Eurasian/Hudsonian Whimbrel
Pine Grosbeak
Wandering/Grey-tailed Tattler
Bluethroat
Eurasian/Black-billed Magpie
 

jurek

Well-known member
This study has bigger implications. It tests and invalidates the theory that shallow sea barriers are decisive drivers of speciation. 7 bird species separated by the same sea barrier have completely different levels of divergence, from similar populations to different species. I hope it is taken into consideration by those who propose that e.g. bird taxa in Sunda islands must be different simply because sea divides them.
 

pbjosh

missing the neotropics
Switzerland
This study has bigger implications. It tests and invalidates the theory that shallow sea barriers are decisive drivers of speciation. 7 bird species separated by the same sea barrier have completely different levels of divergence, from similar populations to different species. I hope it is taken into consideration by those who propose that e.g. bird taxa in Sunda islands must be different simply because sea divides them.

Jurek, I'm sure you also saw THIS recent paper, discussing how particularly in the Sundas shallow seas can still be drivers of speciation, depending on the species and habitat requirements.

Is it widely held that shallow seas are decisive drivers of speciation? I am just taking an armchair view of this but my impression is that it has up until recently rather been viewed that, in the Greater Sundas most species/species groups are were not likely to have speciated. Only more recently are some species groups getting split again as it is better understood what has speciated despite being occasionally connected.

Of course as I said, this is just an armchair take on it and I welcome being corrected or further commentary!
 

Jacana

Will Jones
Hungary
Yes, I think it is a bit of a straw man argument to suggest that shallow seas are decisive. I think this study just drives home the fact that other factors need to be considered as well, which is what I think everyone knows already.
 

THE_FERN

Well-known member
Any taxonomic implications? I'm not about to fuel the academic "drugs trade" (60 dollars for this pdf) and haven't tried sci hub (this time)
 

pbjosh

missing the neotropics
Switzerland
I scanned through it earlier. High level takeaway was it gives another strong argument for the Whimbrel split (which isn't an issue if you follow a slightly faster moving taxonomy than North America does), and described Pine Grosbeak in a manner that could make you think a split there is entirely reasonable - little genetic flow despite being reunited at intervals due to the connection of the landbridge.
 

Nutcracker

Stop Brexit!
One reason why a shallow sea might still be a barrier (more relevant to the Sunda Islands than Beringia), is if the land exposed during low sea levels is a different habitat - say, dry scrub which doesn't make a connection for species dependent on damp cloud forest habitats at higher altitudes of the [intermittent] islands.
 

jurek

Well-known member
I mean mostly that the 'transferability' of a geographic barrier between species is impossible. Something which separates many species and looks like a good geographic barrier (sea, mountain chain, whatever) may be no barrier to other similar species.

About Sundas, the situation is more complex, for example orangutans in part of Sumatra are closer to Bornean ones, not to the orangutans elsewhere in Sumatra.
 

Snapdragyn

Well-known member
About Sundas, the situation is more complex, for example orangutans in part of Sumatra are closer to Bornean ones, not to the orangutans elsewhere in Sumatra.

I thought it was the reverse - that some orangs on Borneo were closer to ones on Sumatra than to others on Borneo?
 

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