Reptile & Amphibian Forums

4.2" snout vent, stripes very vague and faded, very little orange coloration
found 50 miles east of San Diego
If any one could make a positive I.D. I would appreciate it.

Subspecies: E. g. rubricaudatus, Western Red-tailed Skink

Thanks for the I.D. Chris, but just for the record this is not the first skink that I have ever caught. I have only been in the area for 2 years now and have caught a few westerns, but they had all retained enough of the stripe pattern for scale counting I.D. This is my first Gilbert though and I'm glad to hear it. This will make species #30 on my socal herp checklist. And where I'm from it's mostly fasciatus, obsoletus, septentrionalis, and S. lateralis so the I.D.s are a little easier. I'm glad I took so many photos now before feeding it to that kingsnake. Thanks again, Nathan

William:
I have only observed Glibert Skinks from the Tehachapi Mts. northward and Western Skinks from the San Bernardino Mts. Northward so am not aware of the variation that exists in both species.

But unless the variety of Gilbert's Skink east of San Diego is grossly different from all others I have observed, I confess that the picture has me confused. The basic body coloration as observed from the photo is Gilbert's Skink for sure unless there is a hint of a black stripe on the upper body behind the head. Total SV length is also what one would expect of a Gilbert's Skink. But the head size, shape, and what can be discerned of coloration is that of a Western Skink. I have never seen a Gilbert's Skink with a head that is anything like that in the photo.

I wonder if these species will possibly hybridize where their distributions are sympatric.

At any rate, I will ask Robert Hansen to log on to this web site so he can perhaps provide some insight.

Richard F. Hoyer

Hi Richard,
The photo threw me too. I have heard that the two hybridize around Temecula, but can't recall where I heard it. I have seen some good sized westerns down here and the large adults can have quite a bit of orange on the head. Caught two large ones this week at 64 mm SVL.

From my perspective, it looks distinctly looks like E. gilberti. Perhaps it is the subtle clues: gapes between scales, pale sides, lack of dark stripes, or simply from handling dozens of gilberts and Western Skinks. I will try to post some images of Gilbert and Western Skinks. One of the Gilbert’s skinks I found, retained stripes and looked a lot more like a Western Skink than the one Nathan pictured.

Gilbert’s Skink from Kern Co. This individual looks near identical to the specimen Nathan posted. There are more skink images on other posts

Western Skink from Contra Costa Co.

Remarkably large, male Gilbert’s with distinctly broad head. From Inyo Co.

Believed to be a female Gilbert’s, from same location as the Large male. Size and location helped separated this individual from the Western Skink. From desert mtns. of Inyo Co.

Western Skink from San Bernardino Co.

On one of these message boards somebody reported a while back on ongoing genetic studies which indicated the situation with these skinks was messy. Basically that some populations of Gilbert's and Westerns appear more closely related to each other than they are they do to other populations which are nominally of the same species. I'd like to know more...

Hello Carl:

Jon Richmond and Tod Reeder published an important paper in Evolution in 2002 suggesting that the gilberti/skiltonianus complex is an example of "ecological speciation", and that current taxonomy does not accurately reflect phylogeny within this group (i.e., some populations of skiltonianus appear to be more closely related to populations of gilberti than to other skiltonianus, based on mtDNA). However, they did not recommend taxonomic changes pending acquisition of other data & further analyses. I'd be happy to email you a PDF reprint if you care to wade through the paper (it's great stuff!). Jon is continuing this research for his Ph.D. at U Conn, and is including mate choice experiments with lizards housed in the lab.

Cheers,

Bob

Thanks, Bob, I now have the paper you referred to in front of me. A particularly interesting aspect of this story (to me) is the isolated pops out in the desert. --- Carl B.

This is an interesting paper. If the data is correct, then "gilberti" is not a valid species but a morph. It could be considered the same species as E. skiltonianus and the whole complex considered a single polymorphic species. Or one can recognize the different independently derived populations as different species if these skinks are reproductively isolated from E. skiltonianus and from each other. The authors took the prudent course and refrained from recognizing these lineages as different species before there is data to tell us more about the relationships among these populations. In this day and age in which people name new species indiscriminantly, often on the basis of minor or even non-existent differences, the restraint these authors showed is both laudable and rare.

CK:
I have not read the 2002 paper so am not certain if my commments are off base. But from the input Bob Hansen gave me in late 2000 and early 2001, there was consideration that these heretofore considered two species of skinks were really only one as mtDNA data could not separate them well or at all. And if I recall correctly, the authors thought that populations of the two skink species were allopatric or possibly parapatric.

But Bob knew of one locality where he had observed both species sympatrically and on April 28, 2001, I took him to my boas sites in the Tehachapi Mts. were I had mentioned I had observed both species together. At the very first outcrop we examined, we found an adult male of each species. From my observations, the two species also exist side by side on Breckenridge Mt. and in the southern part of the Greenhorn Mts. just north of Breckenridge.

I may be reading too much into the situation but at this point, it seems to me that we now have an example of where mtDNA results show a weakness perhaps not heretofore considered.

I too applaud the authors for showing restraint and waiting to gather more information.

Richard F. Hoyer

I have yet to come across records of Eumeces skiltonianus from the Tehachapi Mtns. Even Stebbins 2003 Field guide does not acknowledge their existence in that range. The most south he mentions the species is the Piute and Greenhorn Mtns. I would be interested in learning more of your E. skiltonianus observation in the Tehachapi Mtns and on Breckenridge, so I can include that information with my writings regarding the Distribution of E. in California.

Will
Fieldnotes@msn.com

William:
I just assumed that it was known that the W. Skink had been documented from those ranges as it is reasonably common. Same applies to the San Bernardino Mts. which is even further south.

During the 1993 - 1997 SRB study, from 1994 on I collected gravid females of various species of lizards in order to collect eggs to test in feeding trials with the SRB. I know I obtained eggs from W. Skinks that originated in the San Benardino Mts. and may have done the same from specimens in the Tehachapi Mts. to test the eggs against the boas I found in that range as well. Those feeding trial would have taken place between 1997 - 2000.

Since I really know little about such matters, you might contact Bob Hansen to obtain his input on W. Skink distribution in S. Calif. Just from casual observations, it is my recollection that adult male W. Skinks during the reproductive season have heads that are somewhat enlarged compared to females, often have considerable red head pigment, and the older males lack all hint of blue on the tail and have faded dorsal-lateral stripes. In that regard, again if my memory serves me correctly, they are not all that different from older, large males I have observed in S.W. Oregon.

Richard F. Hoyer

I probably should have been more precise with the initial post about the Tehachapi Skinks. They are not recorded in the Tehachapi Mtns. But as for the Coast Range, Transverse Mtns south into Baja California the species is recorded and is very common.

Bob:
Could you forward a copy of that paper as it may come in handy as a reference.

Thanks, Richard F. Hoyer

Some current Taxon data regarding possible new “Gilberti” species

Eumeces “gilberti” Van Denburgh, 1896—Gilbert’s Skink Richmond and Reeder (2002, Evolution 56: 1498–1513) presented evidence that populations previously referred to Eumeces gilberti represent three lineages that separately evolved large body size and the loss of stripes in late ontogenetic stages. Although they considered those three lineages to merit species recognition, they did not propose specific taxonomic changes in that paper. We have placed the name “gilberti” in quotation marks to indicate that it refers to a group composed of several species.

Information from:
CROTHER, B.I., 2000. Scientific and Standard English Names of Amphibians and Reptiles of North America North of Mexico, with Comments Regarding Confidence in Our Understanding. SSAR Herpetological Circular 29 [Updated: Herpetological Review, 2003, 34(3), 196-203. Study of Amphibians and Reptiles]

Fieldnotes wrote:
"Eumeces “gilberti” Van Denburgh, 1896—Gilbert’s Skink Richmond and Reeder (2002, Evolution 56: 1498–1513) presented evidence that populations previously referred to Eumeces represent three lineages that separately evolved large body size and the loss of stripes in late ontogenetic stages. Although they considered those three lineages to merit species recognition, they did not propose specific taxonomic changes in that paper. We have placed the name “gilberti” in quotation marks to indicate that it refers to a group composed of several species.

Information from: CROTHER, B.I., 2000. Scientific and Standard English Names of Amphibians and Reptiles of North America North of Mexico, with Comments Regarding Confidence in Our Understanding. SSAR Herpetological Circular 29 [Updated: Herpetological Review, 2003, 34(3), 196-203. Study of Amphibians and Reptiles]"

Me:
The situation described in Richmond and Reeder's paper is far more complicated than Crother's brief summary. All of the "species" in the E. skiltonianus complex (skiltonianus, gilberti and lagunensis) share a common ancestor, which presumably most closely resembles skiltonianus morphologically because other members of Eumeces from other parts of the world resemble skiltonianus more closely than they do gilberti. However, the first lineage to diverge from the ancestral stock is E. gilberti, specifically the Sierran population (known as "clade I" in Richmond and Reeder). Therefore there is a possibility that the gene(s) that regulates ontogeny and which codes for gilberti morphotype may have arisen quite early in the evolution of this group. It is even possible that this gene(s) may be widespread within the skiltonianus group, so that almost any population within the range of skiltonianus has the genetypic potential to produce an individual or a group of individuals that resemble gilberti morphologically. Indeed Richard F. Hoyer claims (in a message within this thread) that some populations of E. skiltonianus in S. Oregon sometimes contain individuals that superficially resemble E. gilberti from Inyo County.

In most populations of E. skiltonianus, this genetic potential is not expressed phenotypically, ostensibly because the habitats inhabited by E. skiltonianus are maladaptive to the gilberti morphotype. Given an opportunity to exploit a more arid, warmer habitat, the gene(s) that codes for gilberti morphotype can then be expressed because this morphotype is favored by natural selection in such habitats. The gilberti morphotype may have arisen more than once, but if the gene(s) that codes for this morphotype is the same gene(s) and if this gene(s) has arisen only once, the independently evolved populations of gilberti can indeed form a monophyletic group. Mayr and Ashlock (1991) explains:

“When taxa are more distantly related it is often uncertain whether homoplasy is due to parallelism or to convergence. There is actually no good criterion for the demarcation of parallelism against convergence. The usual definition of parallelism-possession of similar features in two or more lineages which share a common ancestry-is vulnerable, because how far back should one go? Birds and bats share common ancestry, but their wings surely represent a convergence, as may all the songbird "parallelisms" listed above. A far more serious problem is raised by the propensity of genotypes to produce a certain phenotype, such as stalked eyes in certain acalypterate dipterans, which is manifested in only some of the possessors of a genotype. Parallelism in this case can be defined as homologous similarity, since the common ancestor evidently had the genetic propensity even if it was not expressed phenotypically. Gosliner and Ghiselin provided a good analysis of the various species of parallelism. They concluded (1984:258) that ‘parallelism means that taxa began with the same initial conditions and independently underwent the same changes’ (see the discussion of parallelophylly in Chapter 10).”

Perhaps the genetic potential of skiltonianus to develop the gilberti morphotype is similar to the genetic potential to develop “stalked eyes in certain acalypterate dipterans.” Until this possibility has been ruled out (and it definitely has not been), it would be premature to claim that the 3 lineages of gilberti evolved convergently even if they had evolved independently. According to Mayr and Ashlock, taxa which have evolved through parallelophyly can be considered monophyletic. Thus it may be justifiable to consider the 3 lineages of gilberti to be the same species, even if they had acquired their gilberti morphotype independently, if it can be shown that the gene(s) that controls the development of this morphotype is the same in all 3 lineages. Another fact that lends support to the recognition of E. gilberti as a single species is the fact that two of these lineages may be interbreeding freely when they are in contact with each other. Richmond and Reeder wrote:

“The boundaries of mtDNA clades A and I correspond with an intergradation zone between distinct subspecies (the Sierran E. g. gilberti and E. g. rubricaudatus). The most conspicuous intermediate character is juvenile tail color, which is a purplish blend of the pink-tailed E. g. rubricaudatus and the bright blue tails of E. g. gilberti. Other intermediate characters include the size at the onset of shifts in color pattern and other aspects of subadult coloration (Rodgers and Fitch 1947). If the morphology serves as a reliable proxy for gene flow, the implication is that members of the independently derived E. gilberti clades are interbreeding in the contact zone.”

Finally, there is some evidence that there are perhaps only 2, not three, lineages of gilberti, since gilberti clades A and C are derived from the same population of skiltonianus (namely the coastal subspecies currently known as E. s. skiltonianus), albeit from different sublineages within this subspecies.

In conclusion, there is definitely good arguments that can be made to consider E. gilberti a valid biological species, even if the morphotype that is characteristic of this species may have evolved more than once, because the gene(s) that codes for this morphotype may be the same in all these instances and it may have evolved early, in the common ancestor of skiltonianus, lagunensis and gilberti. The 3 lineages that comprise E. gilberti may have evolved in parallel and can therefore considered monophyletic using the Mayr-Simpson definition of monophyly. Adding weight to this argument is the fact that two apparently independently evolved lineages (A and I)of gilberti are interbreeding freely in their contact zone and the fact that gilberti clades A and C may have evolved from the same ancestral population of E. skiltonianus, again perhaps by expressing the same gene phenotypically, albeit independently. The alternative, suggested by Richmond and Reeder, of recognizing 3 to 5 “evolutionary species” is less tenable because at least two of the 3 gilberti “evolutionary species” interbreed freely with one another. 2 or more “evolutionary species” that interbreed freely with each other cannot be "evolutionary species" since these species, because they share the same gene pool, cannot be on different evolutionary trajectories, which is how "evolutionary species" are defined. In fact, the 3 (or 2) lineages of gilberti appear to be on the same evolutionary trajectory! They all evolved from a skiltonianus-like ancestor and they all look and behave the same. They even inhabit similar habitats and they interbreed freely when they come into secondary contact.

Very interesting info guys. I had no idea there was so much controversy between the two (or one or more) species. I am going back out Wed. and Thur. to see if I can locate some more of the same population. FYI - it was in the mid sixties with a cool breeze when I found this one. It was at the base of a tunnel 6" deep in somewhat loose moist soil 20 feet from the the edge of a hill where I had just found 2 Anniella pulchra.

Richard:

Thanks for your email alerting me to this discussion.

The skink is definitely a gilberti, and probably a female. Size alone (ca. 107 mm SVL) rules out skiltonianus. Additionally, you will note that the lateral striping disappears rather abruptly just posterior to the hind limbs; in skiltonianus the lateral striping extends well onto the sides of the tail (as can be seen clearly in William's Contra Costa Co. skiltonianus). Additionally, this San Diego Co. animal is a female, as evidenced by retention of vestiges of the juvenile pattern. This is a characteristic of the pink-tailed forms of gilberti (rubricaudatus and cancellosus), with females retaining traces of juvenile striping well into adulthood. William's Kern Co. gilberti is also a female and shows this pattern nicely. Males of similar size are unicolored. This distinction does not hold for the blue-tailed ssp. of gilberti.

Cheers,

Bob Hansen

Robert:
I find all of this of considerable interest as it seems to parallel situations with some Slender Salamander populations, Ensatina, some of the garter snake complexes, even C. bottae to some degree.

And William, thanks for posting those photos. If you look at the fourth photo you mention as being a "Gliberts" from Inyo county, I swear I have observed adult Westerns in S. Oregon (particularly males) with very similar coloration -- all brown tails with not a hint of blue on the tail, brown dorsally with hint of stripes barely discernable on the dorsal surface, yet well beyond the distribution of Gilberts.

Then Brad A. showed me an adult Gilberts I believe came from the White Mts. and it was as small or smaller than some adult male Westerns I have observed.

And Bob, I have only found one juvenile Gilberts in the Tehachapi Mts. and it had a vivid pink tail. Yet none of the adult females I have observed have any vestige of stripes on the head or body as shown on the head of the specimens in Nathan's photo or Williams 4th photo of the Inyo county specimen. It will be of considerable interest to see how the crossing experiments turn out.

In similar type tests, either this year or next, I hope to cross dwarf female C. bottae with large morph males. Already have results from the reciprocal cross (N=2) which resulted in neonates of large morph weights and lengths. If dwarf C. bottae females only produce neonates of dwarf weights and lengths, this may be an explanation as to why the two size morphs are able to retain some degree of dististiveness even where they are sympatric.

Richard F. Hoyer

The skink is definitely a gilberti, and probably a female. Size alone (ca. 107 mm SVL) rules out skiltonianus. Additionally, you will note that the lateral striping disappears rather abruptly just posterior to the hind limbs; in skiltonianus the lateral striping extends well onto the sides of the tail (as can be seen clearly in William's Contra Costa Co. skiltonianus). Additionally, this San Diego Co. animal is a female, as evidenced by retention of vestiges of the juvenile pattern. This is a characteristic of the pink-tailed forms of gilberti (rubricaudatus and cancellosus), with females retaining traces of juvenile striping well into adulthood. William's Kern Co. gilberti is also a female and shows this pattern nicely. Males of similar size are unicolored. This distinction does not hold for the blue-tailed ssp. of gilberti.

Cheers,

Richard F. Hoyer wrote:

'And William, thanks for posting those photos. If you look at the fourth photo you mention as being a "Gliberts" from Inyo county, I swear I have observed adult Westerns in S. Oregon (particularly males) with very similar coloration -- all brown tails with not a hint of blue on the tail, brown dorsally with hint of stripes barely discernable on the dorsal surface, yet well beyond the distribution of Gilberts.

Then Brad A. showed me an adult Gilberts I believe came from the White Mts. and it was as small or smaller than some adult male Westerns I have observed.'

Me:
There are several reasons why some individuals of gilberti from Inyo County resemble skiltonianus from S. Oregon. These reasons are found in Richmond and Reeder's (2002) paper.

1. "The morphology of E. skiltonianus occurring throughout the Pacific Northwest is similar to that of contiguous populations along the coast of California, all of which are placed in a single subspecies, E. s. skiltonianus." (p. 1505)

2. "A central-eastern E. gilberti clade (C; hereafter called the Inyo clade due to its regional affinity with Inyo County) includes populations that are restricted to the low and middle elevations of the White, Inyo, Argus, and Panamint Ranges (46¡V49), as well as a population in the eastern Sierra Nevada (50; Figs. 3, 4). This group represents a third independently derived gilbertilike clade that is most closely related to coastal lineages of E. skiltonianus (31, 32)..." (p.1505)

3. "Individuals of two populations within the southwestern E. gilberti clade A (represented by 20 and 21; Fig. 3) show a reversal toward smaller body size and a tendency to retain faded striping in adults.... These reversals appear to occur in isolated populations that persist in the southwestern deserts, where permanent or semipermanent water sources create suitable riparian habitat within warm, arid environments. Similar situations are observed in some Inyo E. gilberti populations (C). Although body morphology has reversed to a more skiltonianus-like condition, SVL of individuals at these localities is still substantially larger than in E. skiltonianus, and the striped pattern is either lost or significantly faded." (p. 1506)

To summarize, the populations of gilberti of Inyo County are most closely related (according to mtDNA) to the coastal California populations of skiltonianus, which are in turn morphologically most similar to skiltonianus of the Pacific Northwest. Add to that the propensity for some populations of Inyo County gilberti to retain the juvenile pattern, these facts thus account for your observation that some individuals of skiltonianus of S. Oregon are morphologically very similar to the gilberti of Inyo County.

At that size, retaining stripes, I would actually go with western skink.

Are you serious, you’re thinking that the skink is retaining its stripes? Besides the SVL, length alone indicates that it is E. gilberti. E. skiltonianus max SVL length is only 3.2 inches. Either, this guy’s first skink that he’s has ever caught turns out to be a recorded breaker, or it is a monderate size, commonly found, 4.2 inch Gilbert’s Skink.

Yep, you're right, I blew that. I looked very quickly and got the wrong dimensions. Nice work fieldnotes.