Question to Richard Hoyer regarding Rubber and Rosy boas

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scottriv
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Question to Richard Hoyer regarding Rubber and Rosy boas

Post by scottriv »

As a student of Rosy boas for the last 40 years, I find Richard's information re rubber boas absolutely fascinating and enlightening.

Richard, I am curious as to whether you have any insights or opinions regarding the distributional relationships between Rosy boas and rubber boas?

My loose understanding is that prior to the end of the ice age, the rubber boa was the dominant species in California and that following the end of the ice age, the rosy boas moved in from the south and took over the lower elevations in the south half of the state.

Any opinions would be appreciated.
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Re: Question to Richard Hoyer regarding Rubber and Rosy boas

Post by Richard F. Hoyer »

Scottriv.,
Just now saw your post so sorry for not responding sooner. It is clear to me you are more up to date on the historical aspects of the two species than myself.

What you mention about distribution up to the end of the most recent ice age is similar to the speculation that myself, Richard Toshima, and Dr. Glenn Stewart tossed around about the Rubber Boa’s distribution. That is, at various times, the distribution in the southern parts of its range was more less continuous from the San Jacinto and San Bernardino Mts. north to the southern Sierra Nevada Mts. and west to the Tehachapi Mt., Mt. Pinos, etc.

I can think of two reasons why the Rubber Boa does not occur at lower elevations and competition for prey is not one of them. It is my view that once the species gets a decent toe hold in optimum habitat that contains competitors, the Rubber Boa becomes the dominant species over such species that compete for similar prey such as the Gopher Snake, Mt. Kingsnake, and species of rattlesnakes. I have a small amount of data that supports that scenario which is in turn is supported by applying some basic biological concepts that pertains to that aspect.

So the two factors I see as being those that limit the distribution of the Rubber Boa are snake predation and the species’ moisture requirements. Known snake predators are the Common Kingsnake and Ringneck Snake. But there are a host of suspected snake predators such as the two species of whipsnakes, the Night Snake, and perhaps others species all of which overlap the boa in their distributions.

But since the boa can be found sympatric with all of those species, I tend to consider that the major factor that limits their distribution involves climate conditions / temperature, and moisture. The species seems prone to dehydration when there isn’t sufficient moisture in the form of precipitation / condensation.

Now some of the older literature of the species emphasize a connection between the boa and free water (rivers and streams). But the species can be found in habitats a long distance from any free water. But because they occur at higher elevation in the southern parts of the range, I speculate that humidity and condensation are key factors in the species distribution. But please note the word ‘speculate’ as I have not attempted to investigate or research that aspect.

As for the current distribution of Rosy Boa, likely the species possesses a higher tolerance to arid type conditions than the Rubber Boa. They would be competitors for the same prey base so it is of some interest that the Rosy has not been able to displace the Rubber Boa at higher elevations where we know the two species occur next to each other in S. Calif. There likely are other factors at play that limits the Rosy from existing at higher elevations but I lack experience with the species and thus have no idea what those other factors may be.

Richard F. Hoyer
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Re: Question to Richard Hoyer regarding Rubber and Rosy boas

Post by Scotttriv »

Richard,

Thanks for the detailed answers and speculation.

Since there are no history books on the evolution and distribution of Lichanura and Charina over the last 20,000 years, all we can do is speculate. :)

There is a small group of Rosy boa enthusiasts that have been diligently working to find range extensions throughout their known range.

I agree with you that Rubber boas appear to need a much wetter environment than the Rosy boas.

It is interesting that the Rosys get up above 5000 feet elevation and in parts of the range the Rosys get up very close to where the Rubber boas live.

I am convinced that if you could get a Rubber boa to breed to a Rosy boa, the result would be viable offspring, but so far, nobody has tried.
Richard F. Hoyer
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Re: Question to Richard Hoyer regarding Rubber and Rosy boas

Post by Richard F. Hoyer »

Scottriv,
It seems to me that the Rosy Boa has some rather distinct morphs with respect to coloration. And I recall seeing something that suggests there also may be some size differences between some populations.

In the Rubber Boa, the one major difference I have detected is where there appears to be two different size morphs. What I have termed as the dwarf phenotype or dwarf morph occurs at several localities all in S. Calif. The large morph occurs throughout the rest of the species distribution with one possible exception. The boa population in the Mt. St. Helena region, where Napa, Sonoma, and Lake Counties meet, may be a semi-dwarf or intermediate form of the species.

As for your proposed crosses between the two species of N.A. boas, would the resultant hybrids be Rubber Rosys or Rosy Rubbers? He he.

I have one first hand anecdotal account in which a Rosy Boas was run over on a sandy road up by Running Spring in the San Bernardino Mts. which is over 6000 ft. The two individuals got out of the car and found the boas to be alive. I was told the specimen survived and was maintained by one of the individuals that lives in Nevada, Reno I believe.

Richard F. Hoyer
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Re: Question to Richard Hoyer regarding Rubber and Rosy boas

Post by Richard F. Hoyer »

Scottri,
Although what I am about to post I covered sometime last year or the year before, I might as well fill in a few more ‘blanks’ for Scott. There are some peculiarities with respect to the distribution of various populations of the Rubber Boa in S. Calif.

The Southern Rubber Boa subspecies population in the San Bernardino Mts. is a diminutive or dwarf form of the species as documented by myself and Dr. Glenn Stewart when we published our SRB study in 2000. Since then, but not yet published, is that dwarf morph populations of the species also occur elsewhere on Mt. Pinos, the Tehachapi Mts., Breckenridge Mt. and likely the Southern Kern Plateau at the very southern extreme of the Sierra Nevada Mts. All of these populations cluster in S. Calif.

The size of my samples from the first mentioned localities are large enough to provide confidence in claiming they are of the dwarf phenotype. My sample size from the S. Kern Plateau is now 25 specimens but even though somewhat scanty, so far, the information on that population strongly suggests it too, is of the dwarf form of the species.

With one possible exception as mention in my previous post, all other populations of the Rubber Boa I have examined in Calif. and all other states and B.C. suggest those populations belong to what I term as the large morph of the the species.

Now finding all dwarf populations occurring close together in S. Calif. seems not all that unusual with respect to the issue of distribution. But
discovering that the boas in the extreme southern Sierras (S. Kern Plateau) are of the dwarf phenotype is surprising as suitable boa habitat is continuous from south to north in the Sierra (at least along the eastern slopes of the Sierras and to the northwest of the S. Kern Plateau), where the large morph of the species has been documented to occur. So one might expect that the boas at the extreme southern end of the Sierras would be of the large morph or perhaps intermediate in range of length between the dwarf and large morph populations.

The same situation may exit at the southern extreme of the Greenhorn Mts. My sample from that region south of Alta Sierra is only about 6 – 8 boas but they too seem to be of the dwarf phenotype. The Greenhorn Mts. are the extreme southwestern part of the Sierras and are immediately west of the S. Kern Plateau across the N. Fork, Kern River gorge that flows from north to south into Lake Isabella. So far, the above situation might be explained by various scenarios.

But now to complicate the picture on distribution is the following: The results from the first mtDNA study of the species (J. Rodriguez-Robles, Stewart, and Pappenfus), indicates that the populations of the boa in the San Bernardino and San Jacinto Mts. nested together in what Javier termed as the ‘Southern Clade’. And it so happens that those two populations comprise the Southern Rubber Boa subspecies. All other boa populations that Javier tested nested together in what he termed as the ‘Northern Clade’. And all of those boa population are of the N. Rubber Boa subspecies.

Not known to Javier is that the Mt. Pinos and Tehachapi Mts. boas were also of the dwarf form but his results showed those two dwarf populations nested in the northern clade whereas mentioned above, the dwarf populations in the San Bernardino Mts. belongs to the southern clade. Although no one has studied the southern clade, SRB population in the San Jacinto Mts., simply by geographical proximity, it can be assumed that those boas are also of the dwarf phenotype. The few voucher specimens from those mts. are all small.

So having dwarf morph populations of the boa belonging to two different subspecies and two different clades produces problems in trying to come up with a reasonable explanation for the distribution of these populations in S. Calif. Other question emerge as well such as did the dwarf form evolve two or more different times. Did the dwarf morph give rise to the large morph or the reverse? Etc..

Now about 8 or so years ago, Dr. Stewart’s last grad student, Richard Toshima, produced another mtDNA study of the species which incorporated a much greater geographical representation of the species and large sample size. I supplied Glenn and Rick with a large number of tissue samples. The last four samples I sent them were from four boas that had been collected on the S. Kern Plateau.

Rick’s result agreed with the results that Javier had obtained but with one very striking difference. The last four samples that Rick tested that came from the boa population on the S. Kern Plateau turned out to nest with the southern clade along with the two SRB populations in the San Bernardino and San Jacinto Mts. Now the gap between those two SRB, southern clade populations and the southern clade population in the extreme southern Sierras
is close to 100 miles.

It took me a bit of time to convince Rick and Glenn that the boas on the S. Kern Plateau were not SRBs despite the fact the mtDNA results placed them in the southern clade with the two SRB populations. As a population, the southern Sierra boa population does not key out to belong to the SRB subspecies.

There simply is too much overlap of key characteristics between the SRB and the other boa populations in southern Calif. That is, about 38 % of the boas on Mt. Pinos will key out to be SRBs whereas the other 62% key out to be NRBs. There is somewhat less overlap in key traits between the SRB and boas from the Tehachapi Mts. but I believe far more than taxonomists would accept as being expected for subspecies designations. Although my sample from the S. Kern Plateau is only 25, about 40% of those boas would key out to be SRBs and the other 60% key out to be NRBs.

I suspect that the above situation and the constituent distributions of the various boa populations, is as clear as mud, even for taxonomists.

Richard F. Hoyer
Scotttriv
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Re: Question to Richard Hoyer regarding Rubber and Rosy boas

Post by Scotttriv »

Yes, a Rubber Rosy would be lots of fun.

I wish I could pay one of my breeder friends to do it, because I would love to see what the offspring looked like.

That is pretty cool finding a Rosy boa up at 6000 feet near Running Springs......do you remember any more details on the location?

I looked on Google Earth and that area looks more like Rubber boa territory than Rosy territory.

I'm sure this has probably been discussed plenty of times before, but aren't the "dwarf" Southern Rubber Boas just a classic example of what happens to a race when their habitat and rainfall levels continue to shrink over thousands of years?

They shrink because their preferred habitat is shrinking in the southern part of the range?
Richard F. Hoyer
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Re: Question to Richard Hoyer regarding Rubber and Rosy boas

Post by Richard F. Hoyer »

Scottriv,
I could take you to the precise road as it is a forest service road into what was called the Allison Ranch. When I took the gentleman there and opened the gate at the entrance is when he related the occurrence of what had transpired. He showed me the spot just inside the gate where the left front tire had gone over the Rosy Boa in loose sand.

I had found several S. Rubber Boas on the Allison Ranch property which is just west across a small ravine from a church camp that use to be called Camp Ono Go or some such name. This is on the north side of Hwy. 18. On the south side of the highway, it droops off precipitously in elevation and the vegetation on that south facing slope is more in line with rattlesnake and Rosy Boa type habitat. All of the Striped Racers I observed in the San Bernardino Mts. were on that south slope below the highway and not on the north side.

I am not aware of what you mention in your last three sentences about habitat and rainfall in connection to size.

Richard F. Hoyer
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scottriv
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Re: Question to Richard Hoyer regarding Rubber and Rosy boas

Post by scottriv »

Richard,

It would be a blast to take you out on a herping trip, anytime you are down in the LA area :)

I don't get up to Oregon very often :)

What I was saying regarding dwarfism in Southern Rubber Boas was just my speculation,,,,allow me to elaborate:

It is my opinion that Rubber boas were the dominant boa throughout California during the last Ice Age.

California was much colder and wetter and Rubber Boas would have thrived from sea level to the lower mountains from south of the mexican border easily into Oregon and Washington.

As the Ice Age receded and the weather became hotter and drier, it is my contention that the Rubber Boas distribution receded to areas that remained wet and to the higher elevations in the mountains where it was cooler. This shrinking of the Rubber Boa distribution range would have been greatly impacted by the dry weather loving Rosy Boas migrating in from the south.

Rosy Boas can handle extremely dry areas and would have been happy to displace the Rubber Boas in areas that were getting warmer and drier.

I believe that the Southern Rubber Boa probably lived all the way down into the Mountains of Baja during the Ice Age and has seen it's range shrink dramatically as a result of Rosy Boas out competing it and hotter dryer weather making it tougher to thrive.

IMO, The current (mountain top) Island populations of SRB are struggling to survive and are experiencing dwarfism as a result of their struggle to compete in a hotter dryer environment. As you go further north into the state where it is cooler and wetter, you don't see any more dwarfism.

Lichanura trivirgata trivirgata, the mexican rosy boa is a dwarf subspecies compared to the other races of rosy and this may be because Mexican rosy boas live in a very, very hot and dry environment where it may be tougher to get lots of easy food......just my speculation :)
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scottriv
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Re: Question to Richard Hoyer regarding Rubber and Rosy boas

Post by scottriv »

I sent you a private message
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scottriv
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Re: Question to Richard Hoyer regarding Rubber and Rosy boas

Post by scottriv »

With regards to the dwarfism in the Southern Rubber Boas, the scientific term is "Insular Dwarfism"

Wiki has a good explanation:

Possible causes of insular dwarfism

There are several proposed explanations for the mechanism which produces such dwarfism.[3][4]

One is a selective process where only smaller animals trapped on the island survive, as food periodically declines to a borderline level. The smaller animals need fewer resources and smaller territories, and so are more likely to get past the break-point where population decline allows food sources to replenish enough for the survivors to flourish. Smaller size is also advantageous from a reproductive standpoint, as it entails shorter gestation periods and generation times.[3]

In the tropics, small size should make thermoregulation easier.[3]

Among herbivores, large size confers advantages in coping with both competitors and predators, so a reduction or absence of either would facilitate dwarfing; competition appears to be the more important factor.[4]

Among carnivores, the main factor is thought to be the size and availability of prey resources, and competition is believed to be less important.[4] In tiger snakes, insular dwarfism occurs on islands where available prey is restricted to smaller sizes than are normally taken by mainland snakes. Since prey size preference in snakes is generally proportional to body size, small snakes may be better adapted to take small prey.[5]

https://en.wikipedia.org/wiki/Insular_dwarfism



The Southern Rubber Boas have been reduced to island populations and appear to be suffering from "insular dwarfism".
Richard F. Hoyer
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Re: Question to Richard Hoyer regarding Rubber and Rosy boas

Post by Richard F. Hoyer »

Scott,
Thank for the education (and link). The explanations could explain the dwarf morphs that occur as isolated populations in the 'sky island' habitat that exist in S. Calif. But it does not fit the dwarf morph population on the S. Kern Plateau and what may be a dwarf population in the southern part of the Greenhorn Mts.

When I am long gone, perhaps someone will eventually be able to put the pieces of he puzzle together.

As a side note, in an attempt to possibly try to determine the mode of inheritance of the size factor, I have made reciprocal crosses between dwarf and large morph boas. That is, I first crossed large morph females X dwarf morph males then later crossed dwarf morph female X large morph males.

I have been able to consummate some backcrosses between the F-1 from the above first cross and so far, the result have not really shed light on the mode of inheritance.

Richard FH
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Kelly Mc
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Re: Question to Richard Hoyer regarding Rubber and Rosy boas

Post by Kelly Mc »

scottriv wrote:
The Southern Rubber Boas have been reduced to island populations and appear to be suffering from "insular dwarfism".


Insular dwarfism and gigantism (gallotia sp example) isnt a malady that organisms "suffer from" like chromosome anomalies or pituitary disorders. They are only dwarfed in comparison to mainland counterparts. Its not a disorder or syndrome any more than human populations of one part of the world being of statistically smaller or larger stature than another.

Interestingly the many varieties and grouped disorders of congenital dwarfism that are often random in expression in human births also occur in version across most animal families, with usually fatal results.

I only add because the use of the word suffering implies an abnormality at odds with selection - which insular dwafism is not.
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