Sporophila (4 Viewers)

[Jacana]

Nguyen, T.N., M. Repenning, C.S. Fontana, and L. Campagna (2024)
Genomic islands of speciation harbor genes underlying coloration differences in a pair of Neotropical seedeaters
Evolution (advance online publication)
doi: 10.1093/evolut/qpae051

Incomplete speciation can be leveraged to associate phenotypes with genotypes, thus providing insights into the traits relevant to the reproductive isolation of diverging taxa. We investigate the genetic underpinnings of the phenotypic differences between Sporophila plumbea and S. beltoni. S. beltoni has only recently been described based, most notably, on differences in bill coloration (yellow vs. black in S. plumbea). Both species are indistinguishable through mtDNA or reduced-representation genomic data, and even whole-genome sequencing revealed low genetic differentiation. Demographic reconstructions attribute this genetic homogeneity to gene flow, despite divergence in the order of millions of generations. We found a narrow hybrid zone in southern Brazil where genetically, yet not phenotypically, admixed individuals appear to be prevalent. Despite the overall low genetic differentiation, we identified three narrow peaks along the genome with highly differentiated SNPs. These regions harbor six genes, one of which is involved in pigmentation (EDN3) and is a candidate for controlling bill color. Within the outlier peaks we found signatures of resistance to gene flow, as expected for islands of speciation. Our study shows how genes related to coloration traits are likely involved in generating prezygotic isolation and establishing species boundaries early in speciation.

I wonder if we will see an SACC proposal to re-lump these taxa in the future? Looking back at the old proposal to split, I was surprised how readily it was accepted without any genetic evidence.

 

[l_raty]

Nguyen, T.N., M. Repenning, C.S. Fontana, and L. Campagna (2024)
Genomic islands of speciation harbor genes underlying coloration differences in a pair of Neotropical seedeaters
Evolution (advance online publication)
doi: 10.1093/evolut/qpae051

There is a preprint at Genomic islands of speciation harbor genes underlying coloration differences in a pair of Neotropical seedeaters

I wonder if we will see an SACC proposal to re-lump these taxa in the future? Looking back at the old proposal to split, I was surprised how readily it was accepted without any genetic evidence.

Does this really sound worse than Corvus corone vs. C. cornix ?

 

[Jacana]

There is a preprint at Genomic islands of speciation harbor genes underlying coloration differences in a pair of Neotropical seedeaters


Does this really sound worse than Corvus corone vs. C. cornix ?

Or Vermivora cyanoptera vs chrysoptera or the Redpolls, or indeed several other Sporophila taxa.

The SACC are a pretty conservative body as a rule and given that this study contradicts several of the findings in the description paper which they made the decision on, I just wonder whether a lumping proposal will appear and if so, whether it would pass.

 

[cajanuma]

Or Vermivora cyanoptera vs chrysoptera or the Redpolls, or indeed several other Sporophila taxa.

The SACC are a pretty conservative body as a rule and given that this study contradicts several of the findings in the description paper which they made the decision on, I just wonder whether a lumping proposal will appear and if so, whether it would pass.

I get the sense though that they (or at least quite a few members) have seen genetics as one of many data points and not the end-all and be-all. So in the presence of other evidence of reproductive isolation (narrow hybrid zone) the lack of genetic differentiation is not necessarily a problem.

 

[pbjosh]

It's a really cool paper to read if you're a Sporophila fan / nerd An interesting case of very little measurable difference but the birds already behaving pretty well as two species or at least maintaining the morphological traits that presumably are the foundation of an incipient prezygotic reproductive barrier, despite ongoing gene flow. As Cajanuma points out, I am not sure SACC would use pure genomics to adjudicate if there were a proposal, given that Sporophila is currently understood to tip from variation to speciation seemingly quite easily.

I've never seen beltoni but I find Sporophila speciation in general fascinating. This case really makes me think, again, about S ardesiaca vs S nigricollis in the context of this case and also the variation within S corvina (also mentioned in the paper). The variation in corvina is pretty well known to be quite clinal and phenotypically mixed individuals are abundant over a large region of overlap. It seems, at least to me, that it's not too controversial to not separate the white and dark bellied forms. On first sniff, it also doesn't seem outlandish to maintain beltoni as separate based on a limited hybrid zone and the birds maintaining morphological distinction and to some degree behaving as species despite the gene flow. And as far as I know the genetics and in general intergradation and pretty much everything about S ardesiaca is unstudied?

When I've seen what I presumed were ardesiaca they were in the exact same wet fields with what looked to be bog standard nigricollis and the two different species / morphs / forms / whatever were perching next to each other and singing. I couldn't tell a difference in song or anything else about them other than belly color. But I don't think anything is known about this form really? Perhaps they maintain the difference despite gene flow and it is a good case of incipient speciation, or perhaps, given the sympatric distribution, it's just a case of two color morphs. Inferring how a genetic analysis would go from the above study of beltoni you'd need to probably collect or get blood samples from vouchered breeding pairs and use whole genome sequencing to try to figure out if the females are mating associatively with males or what is going on, assuming any genetic signal can even be found, as the females are presumably completely unidentifiable otherwise. Pretty interesting stuff.

 

[Jacana]

I get the sense though that they (or at least quite a few members) have seen genetics as one of many data points and not the end-all and be-all. So in the presence of other evidence of reproductive isolation (narrow hybrid zone) the lack of genetic differentiation is not necessarily a problem.

It's interesting how perceptions can vary. I agree that they don't only go on genetics and I wasn't suggesting that, quite the reverse . It's just that genetics often seems to be a critical point that they often want in conjunction with other parameters. Usually when these proposals come up they are because of a genetic and/or phenotypic study with little investigation into behaviour etc and often a proposal will be rejected until the last piece can be put in place. In this instance, it was the genetics which was missing. Just look at their latest proposal to split the Cattle Egrets. It's quite clear from the proposal that if this wasn't an extralimital split, they would want to reject it on the lack of genetics.