Tail differences between female and male Galapagos (Chelonoidis nigra) hatchlings
There has been discussion on another thread regarding sexing hatchlings by tail characteristics.
I would like to offer another perspective and suggest that in some cases, it can be done with a relatively high percentage of certainty, at least in some subspecies of Galaps. I do not have enough experience with other species of tortoises to suggest if this applies.
Consider that when hatching a group of Galapagos tortoises, there may be some with long tails (6-7 dorsal scale row(s) on tail). There will also be those with short tails with 2-3 row(s) of dorsal tail scales. Those with a line of 6 -7 dorsal scales are very likely male. Those with a line of 2-3 dorsal tail scales are likely female. Most of a hatch will have 4-5 dorsal scales and, in my opinion, sex cannot be suggested.
On the islands there has been considerable studies done on Chelonoidis nigra hoodensisand the ongoing repatriation program. I have no experience with this subspecies. Temperature dependent sex determination (Sancho, Ana, et al) has been reported with a pivotal incubation temperature of 28.3 C and a range of transition temperatures of 25.2-31.4 degrees C. A limited number of incubation temperatures was utilized to generate the data. The authors caution that not all of the C. nigra complex have similar pivitol or transitional temperature ranges.
Sex determination was identified by gross observation of the gonads at autopsy, histoloical gonad examination or laproscopic examination. The number of large dorsal scales were counted as well. The numbers in the study are relatively small.
Their results include:
“The number of large dorsal scales in the tails of hatchlings identified as males ranged from 4‒7 (n = 10, x̅ =4.9), females ranged from 2‒5 (n = 10, x̅ = 3.7). Male hatchlings had significantly more large dorsal scales on their tails than did females (t = 2.48, d.f. = 18, two tailed P = 0.023).”
The above is not offered to generate argument but rather to suggest there are some individual hatchings with tail morphology to suggest sexual dimorphism.
These photos are from 2004 and are suboptimal put perhaps illustrate some of the differences in tail morphology of hatchlings. I apparently do not have good photos showing the dorsum of hatchling tails.
Reference: https://pdfs.semanticscholar.org/2e...57.2009400275.1530046409-734113714.1530046409
There has been discussion on another thread regarding sexing hatchlings by tail characteristics.
I would like to offer another perspective and suggest that in some cases, it can be done with a relatively high percentage of certainty, at least in some subspecies of Galaps. I do not have enough experience with other species of tortoises to suggest if this applies.
Consider that when hatching a group of Galapagos tortoises, there may be some with long tails (6-7 dorsal scale row(s) on tail). There will also be those with short tails with 2-3 row(s) of dorsal tail scales. Those with a line of 6 -7 dorsal scales are very likely male. Those with a line of 2-3 dorsal tail scales are likely female. Most of a hatch will have 4-5 dorsal scales and, in my opinion, sex cannot be suggested.
On the islands there has been considerable studies done on Chelonoidis nigra hoodensisand the ongoing repatriation program. I have no experience with this subspecies. Temperature dependent sex determination (Sancho, Ana, et al) has been reported with a pivotal incubation temperature of 28.3 C and a range of transition temperatures of 25.2-31.4 degrees C. A limited number of incubation temperatures was utilized to generate the data. The authors caution that not all of the C. nigra complex have similar pivitol or transitional temperature ranges.
Sex determination was identified by gross observation of the gonads at autopsy, histoloical gonad examination or laproscopic examination. The number of large dorsal scales were counted as well. The numbers in the study are relatively small.
Their results include:
“The number of large dorsal scales in the tails of hatchlings identified as males ranged from 4‒7 (n = 10, x̅ =4.9), females ranged from 2‒5 (n = 10, x̅ = 3.7). Male hatchlings had significantly more large dorsal scales on their tails than did females (t = 2.48, d.f. = 18, two tailed P = 0.023).”
The above is not offered to generate argument but rather to suggest there are some individual hatchings with tail morphology to suggest sexual dimorphism.
These photos are from 2004 and are suboptimal put perhaps illustrate some of the differences in tail morphology of hatchlings. I apparently do not have good photos showing the dorsum of hatchling tails.
Reference: https://pdfs.semanticscholar.org/2e...57.2009400275.1530046409-734113714.1530046409