Great info, I was thinking about this while reading and thought similarly, it would make sense that the SN xanthoptica would colonize the coast and not vice versa since the xanthoptica lineage is unique on the coast but definitely not a closed question.
Lots of great info here, I’ll have to read through another time, I just wanted to check and see if Lake Corcoran was a better match as a barrier/bridge to/from the Sierra Nevada xanthoptica. It seems that it overlaps in epoch (Pleistocene), but maybe had drained before the time xanthoptica crossed over.
Something fascinating about all the large lakes (and their role in species dispersal) that used to exist across California in the distant and not-so-distant past!
Ring species are definitely fascinating. My favorite one is the Song Sparrow. For some reason, the sparrows do not breed in eastern California and southern Nevada. Starting from the southwestern-most subspecies and going clockwise, you have heermanni in western Cal and Central Valley being olive-brown with blackish streaking and gray fringes to the mantle. gouldii surrounding the San Francisco area who tend to be more reddish-olive. cleonensis in the northwestern corner of the state who is red overall with well defined streaking. montana from northeastern California to Utah with brownish-gray with clean white underparts with brownish-red streaking. Lastly, fallax in Arizona with redder streaking but pale brown-gray body.
heermanni and fallax overlap ranges in Coachella Valley, completing the ring. The research confirmed that out of 400 sampled birds, only 8 putative hybrids were found. The plumage characteristics are clear and consistent and they’re ecologically divergent with heermanni preferring coastal-type riparian while fallax liked desert scrub riparian.
I think the biggest problem with splitting the species is where do you draw the line of one species from the other. This isn’t the only evolutionary divergence in the Song Sparrow either. mtDNA results showed that Aleutian Island Song might be elevated to species status as they are reproductively isolated from the rest of the population and the two island subspecies are genetically more different than the other 22 subspecies combined!
Hi @yerbasanta. In that paper, Kuchta, Parks and Wake do mention (p. 240) the prehistory of the Central Valley as an inland sea connecting to the Pacific via the Monterey Bay plain. They note that the sea converted to a lake (i.e. Lake Corcoran) around 2 mya (million years ago) and then the drainage shifted to exit through the Golden Gate around 600,000 years ago. They also mention (pp. 241–242) that their earlier work had dated the coastal arm of the Ensatina complex to more than 2 mya, which raises the question of how Ensatinas could have spread down the coast before there was a continuous Coast Range in place.
In 1997, Wake proposed that around 5 mya Ensatinas colonized an island mass of Salinian terrane (i.e. the granite rocks that form land west of the San Andreas fault, such as the Santa Cruz Mountains, Point Reyes and Bodega Head) and that this was where ssps. xanthoptica and eschscholtzii originated. Under this theory, the island territory was reconnected to mainland California around 2 mya, allowing ssp. xanthoptica to spread north to meet ssp. oregonensis and ssp. eschscholtzii to spread south to meet ssp. klauberi. But this theory didn’t seem to be a good explanation for the high genetic distance (i.e. low relatedness) detected between nearby populations in coastal central California. Kuchta, Parks and Wake set out to examine the genetic makeup of these populations in more detail so as to better explain how they might have evolved.
My main takeaway from the paper is that the relationships are a lot more complex than was previously expected. Ssp. oregonensis is actually two distinct clades that are not very closely related, with oregonensis [1] having a fragmented coastal distribution that hints to it being stranded in several remnants of coastal plain following post-glacial sea level rise. Ssp. xanthoptica [1] probably orignated in the Sierra and colonized the coast quite recently (during the Pleistocene), but the reverse hypothesis cannot be totally ruled out. Ssp. xanthoptica [2] and the northern and southern lineages of ssp. eschscholtzii are all related to xanthoptica [1], but the paper doesn’t say much about how they arrived where they are now.
The same authors, along with a colleague, wrote another 2009 paper that seems more likely to provide answers to those questions. Maybe this is the one I need to read next!
Fascinating, thank you for the explanation. I honestly feel as though I need an animation to put it all together in my head since there’s so many moving pieces, and I’m not used to thinking on geological time scale and thinking about multiple landmasses with species moving across them with highly dynamic barriers (like fresh and saltwater).
I’ll have to sit down and read the paper several times I think, since it’s just such a great example of how evolution can be so complex in space and time, along with being able to trace this through molecular phylogenetics!
In regard to how Ensatina may have spread down the coast without a contiguous mountain range, do you think it plausible that one or more were able to hitch a ride on a downed log? Given the fire and flood history in CA, I could imagine some living in/on a downed or live tree, being washed down a river by flooding, out to sea, and then washed inward on a current (possibly storm-driven). Maybe that’s too far-fetched, but I think more implausible things have been documented before!
I agree that animation has a great potential to convey hypothesized evolutionary histories for groups of organisms, especially when changes in sea-level, climate, habitat and even tectonic plates are involved. I wish I knew some good tools to use for that that didn’t require real animation skills.
Rafting is definitely how species have spread from time to time, such as the ancestors of the New World monkeys reaching South America from Africa. And while it’s very occasional over long distances, it’s much more plausible over short ones. I don’t know whether the UC Berkeley researchers have analyzed the likelihood of that explaining any Ensatina distribution patterns though.
It’s been many, many years since I’ve done such, but PowerPoint had quite simple animation tools that could demonstrate a sequence of events overtime. FWIW… Microsoft tutorial for animation
I ran across this short nature documentary (from KQED) on Ensatina radiation in CA, it really helped me think about this in a different way. Though there are probably some omissions or slight mischaracterizations, I’d be really interested to hear what you think about it: Ensatina Salamanders Are Heading For a Family Split
Yes @yerbasanta that’s a really nice video! Thanks for sharing it. And the close-up photography is wonderful. Also, the explanation on the aposematic coloring of xanthoptica and the camouflage coloring of platensis is nicely done.
In terms of genetic relationships it focuses on the classic “ring species” hypothesis, which still seems to have a lot of truth in it. The more recent messy details raised by phylogenetic analysis would make for a pretty complex story to convey in a four-minute video. At least two of the seven recognized Ensatina subspecies (oregonensis and platensis) have been shown to be polyphyletic, meaning they’re made up of different lineages, some of which are more closely related to other subspecies.
It’s broadly true that “coastal clade” of xanthoptica and eschscholtzii spread down the coast from north to south, while the “inland clade” of southern platensis, croceater and klauberi spread along the Sierra Nevada into southern California, but I’m pretty sure the animation in the video where the subspecies appear in their current locations progressively from north to south is a wild oversimplification. In reality, the species has been slowly dispersing, evolving, interbreeding and occasionally replacing other populations over a fairly long period. For much of that time, the forbears of today’s populations may not have been recognizable using today’s subspecies categories, and even if they were recognizable they would likely have had different distributions.
So we don’t (and possibly can’t) know enough to show where the subspecies originated except to say that the inland and coastal clades radiated separately from north to south where they met (and discovered that they can’t interbreed or don’t want to). Nevertheless the visualization is a good way to get the basic picture of a ring species.
BTW, the second Kuchta et al paper from 2009 gives a lot more detail on the interrelationships between the subspecies and clades.