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RE: C. bottae taxonomy - A new wrinkle

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Posted by: CKing at Fri May 23 13:07:46 2008  [ Report Abuse ] [ Email Message ] [ Show All Posts by CKing ]  
   

>>CK,
>>Don't know what happened to my prior post.
>>
>>The reason that Javier's data shows the majority of the Sierra Nevada subclade specimens occurring on the western slopes of the Sierra Nevada Mts. is more likely due to the nature of how specimens are collected than being representative of the true distribution of that subclade. A number of variables are involved with how specimens end up as vouchers and invariably such collecting does not represent an accurate picture either of relative abundance or geographical representation. Thus, there is considerable risk at trying to arrive at meaningful conclusions simply based on the origin of vouchers.>>

Certainly. Let's not forget also that animal ranges are not static. It is changing all the time as new habitats are created and old habitats are lost, even in the absence of human intervention. The rubber boa migrated north millions of years before modern human beings even evolved and before there were human beings in the Western Hemisphere. Something interesting happened in the past, and rubber boas are now absent from the San Gabriel Mountains.

>>As for both subclades not occurring in each other's region, I suspect that this situation is similar to what occurs with many recognized subspecies where they retain their individual identities beyond where intergradation occurs, sometimes in very narrow zones.>>

One good thing about mtDNA data is that it can often reveal evidence of lineage mixing. For example, R. G. Zweifel claims that there is a large zone of intergradation in L. zonata in the northern part of its range between L. z. zonata and L. z. multicincta. Most of the snakes in the intergrade zone have the mtDNA haplotype of the relatively young lineage of multicincta, including those within the range of Zweifel's L. z. zonata. However, there is one interesting specimen from Oregon (loc. #31 AF136216; MVZ 225920; US: Oregon, Jackson Co., northeast of Ashland) which has a mtDNA haplotype that is much older than any of the multicincta specimens, and which is closer to the older multifasciata mtDNA haplotype. In fact, #31 is closely related to multifasciata from Kern, Santa Barbara, Monterey and Santa Cruz Counties. So, the supposed zone of intergradation between zonata and multicincta appears to be a zone of intergradation between an ancient lineage of L. z. multifasciata and a newer lineage of L. z. multicincta instead. L. z. zonata may actually be either L. z. multifasciata or L. z. multifasciata x L. z. multicincta! I think in that case, L. z. multifasciata would be an invalid name, and it would be synonymized with L. zonata. L. z. multicincta appears to be much more successful and swamped the L. z. multifasciata mtDNA haplotype in northwestern California. It was perhaps fortuitous that the loc. #31 was sampled or this fact would not have come to light. So, if there is intergradation between the Northwestern subclade and the Sierra Nevada subclade, mtDNA data has the potential of revealing it.

>>I am not familiar with Robert Inger. Long ago I recognized the exact same thing not only for the boa but for other secretive species. That is why I cited the paper by W. Gibbons in that his results match my own experience and my analysis vouchers in institutional collections, that is, the history of specimens being vouchered over time. As you may have noted in many publications, they will mention this or than species has a spotty distribution. Well, where suitable habitat is spotty, such characterization are probably correct. But in some instances, the spotty distribution is really a reflection of the spotty nature of finding and vouchering specimens.>>

Certainly. But mtDNA evidence again may provide valuable insights into whether distributional gaps are real or not. MtDNA is often used for determining lineage divergence date, so it is often possible to figure out how recently a species may have occupied a particular part of its range. The relatively young lineage age of the various populations of the southern rubber boa shows that they have only occupied their present range recently. This is probably the result of these boas having undergone a severe population decline in the recent past and then recovering subsequently to rapidly expand their range. Additionally, using mtDNA data, we can figure out how a species has expanded its range. In the case of the rubber boa, mtDNA tells us that the Northwestern subclade originated somewhere in Kern County, then it migrated west towards the coast and then expanded its range northward to Monterey, Santa Cruz, and Marin Counties, and then continuing north to northwestern California, Oregon and Washington. From there it went east, but there is no evidence of it going into the western slopes of the Sierra Nevada Mountains, at least not yet. This subclade may well have invaded the eastern slopes of Sierra Nevada but we just don't know because of a lack of data. The Sierra Nevada lineage is a bit younger than the Northwestern subclade, so it has had less time to expand its range. So, it is quite possible that Sierra Nevada subclade may not have had the time to stray too far from the Sierra Nevada mountains. It certainly had less time than the Northwestern subclade to colonize new areas. It may not have had enough time to expand northward to Mt. Lassen or to western Nevada. We just don't know until the mtDNA data of snakes from these areas have been determined.

>>If you review the older field guides by Stebbins, you will note he refers to the boa as having a spotty distribution. Before his latest revision of 2003, he contacted me asking me to comment on his treatment of the Rubber Boa and Sharp-tailed Snake. I mentioned the same thing about spotty collecting giving an erroneous perception and mentioned that suitable boa habitat is continuous from northern Kern County all the way to B. C. sop how could the species have a spotty distribution? Since he too understands and accepts habitat association as valid, you will note in the latest edition he dropped the 'spotty distribution' for he species as a whole but retained it for the southern part of the species range where it is indeed spotty.
>>
>>Richard F. Hoyer

The southern rubber boa has a spotty distribution probably because of some relatively recent catastrophic event. The lineage itself is old, but the various branches of this lineage diverged relatively recently from each other, probably from a small, restricted population that had an even more restricted distribution than it is "enjoying" today. Many of the older branches of this lineage may have died out during the catastrophe, leaving but a single lineage to later expand into its present range. Since most of the current range of the rubber boa probably is uninhabitable during the last ice ages because of glaciation at high elevations, these boas were probably forced into lower elevations during the ice ages. While they are there, they may have to compete against the closely related rosy boa, albeit quite unsuccessfully. The rosy boa, being larger and better adapted to arid conditions, may have had the upper hand in the interspecific competition between the small morph southern rubber boa. Without competition from the Rosy boa, it is certainly possible, even probable, that the rubber boa's range in the north is much more continuous than thought.


   

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