I just noticed that INaturalist uses Argynnis cybele as the name of the Great Spangled Fritillary, which I have always known as Speyeria cybele. Curious, I went to BugGuide to look for additional information and found this statement on the Speyeria genus page - " Historically, and often still, Speyeria and Fabriciana (and most other “Greater Fritillaries”) have been included within an expansive concept of the closely related Eurasian genus Argynnis.
Since I have know both BugGuide and INat to stay on top of taxonomic changes, I am really curious if anyone can shed some light on the current concepts of these genera. Thanks!
Genus is not really well defined thing, it is subjective. It is required to be monophyletic which means there is a common ancestor and everything descended from that ancestor is in the genus.
Since it is not well defined one way to think about it would be all species that diverged from each other in less than x millions of years ago which of course is impossible to know exactly. Another might be all species with dna above x% the same. We might also want to vary the number depending on the type of organism.
This paper is a good starting point for this approach.
Zhang, Jing, Qian Cong, Jinhui Shen, Paul A. Opler and Nick V. Grishin
2020 Genomic evidence suggests further changes of butterfly names. Taxonomic Report of the International Lepidoptera Survey 8(7): 1-40, 33 figs. {6 Nov 2020}
Basically it uses dna to try to clump species together and somewhat objectively say what a genus should be.
Basically it argues that Speyeria is more closely related to other Argynnis than other butterflies we put in the same genus so we should make Speyeria a subgenus of Argynnis. It seems most experts agree with Argynnis, but it is still a subjective decision on how to split butterflies into genera
Even if all experts agree there is a lot of inertia to overcome to implement it in various lists/books/websites. For example Oeneis is not monophyletic, Neominois ridingsii is more closely related to other american Oeneis than Oeneis uhleri is, so taxonomy should be changed to either Oeneis ridingsi or Davidina uhleri but that hasnt been implemented in either bugguide or inaturalist.