Red foot, Yellow foot, Cherry head Shared Genetics?

[Dinosaur_Owner]

Hello I was wandering if anyone else has considered the possibility that the common red foot tortoise is actually a naturally occurring hybrid between yellow foots and cherry heads. I looked up the naturally ranges of all three tortoises. It looks as though yellow foots are located in northern countries of south america. Cherry heads are mostly isolated in Brazil but the red foot tortoises range over laps both the cherry head and the yellow foot. Also you can look at the sizes of all three tortoises generally speaking yellow foots are the largest followed by red foots and then followed by the smaller cherry heads. Another thing to mention is the coloration. As red foots age they get yellow heads like the Yellow foots, but retain red feet like the cherry heads who are red all over. So I hypothesize that the red foot tortoise is really a naturally occurring composite creature that sprang from the shared genetics of yellow foots and cherry heads. I'm not saying the modern red foot genome is a 50/50 split between the two species but I do believe the regular red foots are the byproduct of these two species that then went on to genetically stabilize and form the composite species we know today. Does anyone have any thoughts on the topic?

 

[Redstrike]

I think the idea is reasonable but I have reservations.

1) Hybridization does not always lead to phenotypic intermediates (i.e. the coloration). Further, there are yellow, red, and orange coloration found in many different C. carbonaria locales complicating the issue.

2) Range overlap does not translate to species hybridizing, though it is an important component for it to occur. There are behavioral, mechanical, phenological, and habitat differences that can really put a wrench into hybridization between distinct species.

3) Chelonidis carbonaria's range stretches North to South from Veneuzula to Bolivia and East-West from Ecuador to Brazil (via Vinke & Vetter). This constitutes a large area with an array of climates and habitats. Given this it's likely on species will exhibit various phenotypes along the N-S/E-W gradients. This happens a lot and leads to distinct populations exhibiting different colorations, sizes, etc.

4) Hybridization often leads to sterile offspring which arrests the cycle.

I lean more toward a common ancestor for C. denticulata & C. carbonaria with divergence occurring to produce two similar but different species.

You may be 100% correct but until I see a comprehensive genetic study for the two species, I can't say one locality of redfoot is a hybrid between the southern locality of redfoot and a yellowfoot.

 

[Dinosaur_Owner]

I think the idea is reasonable but I have reservations.

1) Hybridization does not always lead to phenotypic intermediates (i.e. the coloration). Further, there are yellow, red, and orange coloration found in many different C. carbonaria locales complicating the issue.

2) Range overlap does not translate to species hybridizing, though it is an important component for it to occur. There are behavioral, mechanical, phenological, and habitat differences that can really put a wrench into hybridization between distinct species.

3) Chelonidis carbonaria's range stretches North to South from Veneuzula to Bolivia and East-West from Ecuador to Brazil (via Vinke & Vetter). This constitutes a large area with an array of climates and habitats. Given this it's likely on species will exhibit various phenotypes along the N-S/E-W gradients. This happens a lot and leads to distinct populations exhibiting different colorations, sizes, etc.

4) Hybridization often leads to sterile offspring which arrests the cycle.

I lean more toward a common ancestor for C. denticulata & C. carbonaria with divergence occurring to produce two similar but different species.

You may be 100% correct but until I see a comprehensive genetic study for the two species, I can't say one locality of redfoot is a hybrid between the southern locality of redfoot and a yellowfoot.

Yes, absolutely genetic testing would have to be completed to see if my hypothesis is correct. I would love to see how their genomes compared to one another even if it disproved my hybrid hypothesis.

 

[domalle]

Yes, absolutely genetic testing would have to be completed to see if my hypothesis is correct. I would love to see how their genomes compared to one another even if it disproved my hybrid hypothesis.

Mostly agree with Redstrike's authoritative response above but Chelonoidis carbonarius in South America ranges from the northernmost states of Colombia and Venezuela to Paraguay and Argentina in the south. May be present in the west of Peru but not known to occur in Ecuador.

 

[cdmay]

Hello I was wandering if anyone else has considered the possibility that the common red foot tortoise is actually a naturally occurring hybrid between yellow foots and cherry heads. I looked up the naturally ranges of all three tortoises. It looks as though yellow foots are located in northern countries of south america. Cherry heads are mostly isolated in Brazil but the red foot tortoises range over laps both the cherry head and the yellow foot. Also you can look at the sizes of all three tortoises generally speaking yellow foots are the largest followed by red foots and then followed by the smaller cherry heads. Another thing to mention is the coloration. As red foots age they get yellow heads like the Yellow foots, but retain red feet like the cherry heads who are red all over. So I hypothesize that the red foot tortoise is really a naturally occurring composite creature that sprang from the shared genetics of yellow foots and cherry heads. I'm not saying the modern red foot genome is a 50/50 split between the two species but I do believe the regular red foots are the byproduct of these two species that then went on to genetically stabilize and form the composite species we know today. Does anyone have any thoughts on the topic?

Good question and topic.
ALL of the South American tortoise species of the genus Chelonoidis likely have a common ancestor---this includes the giant Galapagos animals as well.
Denticulata and carbonaria, the yellow-foot tortoise and the red-foot tortoise respectively, are considered sister taxon. Clearly they have a common origin as do all of the Testudo species of tortoise in Europe. What caused them to split off and become distinct species over time is beyond me. Mostly likely (I'm guessing here) populations became isolated and through this isolation eventually emerged and distinct populations. How denticulata and carbonaria became their own species while living in close proximity in northern South America likely has to do with habitat preferences. Although again, this is a guess.
Like our native box turtles here in the United States, red-foot tortoises in South America have expressed their innate genetic potential to come in a fairly wide range of colors and sizes as populations spread out and inhabited wildly different parts of the continent.
As for red-footed tortoises being the result of a naturally occurring (although obviously very distant) hybridization between the S.E. Brazil tortoises (the so-called cherryheads) and denticulata, I kind of doubt it. But who knows?

 

[Michael231]

Recent genetic work by Farias et al. (2007) as well as Vargas-Ramirez et al. (2010) have sampled from a specific locale (in the former) and across the range (in the latter). Through PCR sampling of the cytochrome b gene (a mitochondrial gene) and molecular clock analysis to divergence, as well as the calculation of within/between-group divergence and the formation of haplotypes, the authors (at least in the latter) proposed that gene flow is occurring between denticulata, and that in carbonaria it is somewhat restricted due to their habitat preferences. Given that only the former authors proposed any haplotype sharing (indicative of potential hybridization or incomplete lineage sorting), and the latter did not, it seems likely that the common red-footed tortoise is its own species, given that it doesn't fall within the haplotypes of any denticulata. The studies' MCA also supports a divergence from yellowfoots of aprox. 12-13 mya.

Beyond these findings, it is very likely that if common red-footed tortoises were in fact hybrids that there would be no F2 offspring, due to the abnormal mutation rates in hybrid animals. Haldane's rule states the more likely sterile sex to be the heterogametic sex (i.e. the male), so a cross between two hybrids is very unlikely.