Beringia (1 Viewer)

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

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 said:

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.

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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!

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.

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)

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.

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.

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.

jurek said:

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.

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

Kevin Winker, Jack J. Withrow, Daniel D. Gibson, Christin L. Pruett 2023. Beringia as a high-latitude engine of avian speciation. Biological Reviews https://doi.org/10.1111/brv.12945

Beringia is a biogeographically dynamic region that extends from northeastern Asia into northwestern North America. This region has affected avian divergence and speciation in three important ways: (i) by serving as a route for intercontinental colonisation between Asia and the Americas; (ii) by cyclically splitting (and often reuniting) populations, subspecies, and species between these continents; and (iii) by providing isolated refugia through glacial cycles. The effects of these processes can be seen in taxonomic splits of shallow to increasing depths and in the presence of regional endemics. We review the taxa involved in the latter two processes (splitting–reuniting and isolation), with a focus on three research topics: avian diversity, time estimates of the generation of that diversity, and the regions within Beringia that might have been especially important. We find that these processes have generated substantial amounts of avian diversity, including 49 pairs of avian subspecies or species whose breeding distributions largely replace one another across the divide between the Old World and the New World in Beringia, and 103 avian species and subspecies endemic to this region. Among endemics, about one in three is recognised as a full biological species. Endemic taxa in the orders Charadriiformes (shorebirds, alcids, gulls, and terns) and Passeriformes (perching birds) are particularly well represented, although they show very different levels of diversity through evolutionary time. Endemic Beringian Charadriiformes have a 1.31:1 ratio of species to subspecies. In Passeriformes, endemic taxa have a 0.09:1 species-to-subspecies ratio, suggesting that passerine (and thus terrestrial) endemism might be more prone to long-term extinction in this region, although such ‘losses’ could occur through their being reconnected with wider continental populations during favourable climatic cycles (e.g. subspecies reintegration with other populations). Genetic evidence suggests that most Beringian avian taxa originated over the past 3 million years, confirming the importance of Quaternary processes. There seems to be no obvious clustering in their formation through time, although there might be temporal gaps with lower rates of diversity generation. For at least 62 species, taxonomically undifferentiated populations occupy this region, providing ample potential for future evolutionary diversification.