Sexes of Heloderma

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Sex determination of Heloderma suspectum proves to be difficult. Even experienced field biologists and breeders lead to false sex determinations (Ref. 19).

Obese specimen (a common tendency !) are not to be differentiated by external body shape criteria (Ref. 24).

All sexes of the depicted adult Heloderma are verified by copulation and/or depositing of eggs.

Methods for sex determination in adult Heloderma:

1. Body shape

Head

In comparison to females, the head of a male lizard is much more massive, broader and "higher". A look from the top to a females head shows softer contours and their cheeks are flattened.



Male, adult			Female, adult

Body

The body shape of a male resembles an elongated oval, whereas the body of a female shows a pear shape toward the rear legs.


Male, adult			Female, adult

Tail

The tail of a male tapers evenly to its tip, whereas the female´s tail appears "dented" near the cloaca and does not taper until the last third of the tip.


male, adult			female, adult

Total impression of male and female


male, adult			female, adult

2. Ultrasound

With the help of an experienced physician, inner sexual organs such as gonads and follicles are unequivocally detectable and documented.

The sexual organs are dominated by a yearly cycle. The gonads and follicles enlarge from October to March/April which is the mating season. At the end of May, these have reduced their size and functionality. Taking this into consideration, the best time to determine the sex of the specimens using the ultra-sound method would be shortly before the actual mating season (ref. 46).

Prints of ultrasound examinations of doubtful sexes. You can observe in text on top of the pictures that two sexes had been falsely determinated by only using body shape characteristics of the individuals:



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Ultrasound examinations of sexually mature females in March, representing developing and mature follicles.


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Ultrasound examinations of adult male Heloderma suspectum in the ventral area of the tail spanning 2 cm in distance to the vent.
You can observe large and variable paired soft tissue structures representing the tips of the hemipenisses with their hemipenis pockets (Ref. 35).

Ultrasound examinations of adult female Heloderma suspectum in the ventral area of the tail spanning 2 cm in distance to the vent.
In comparison to the male tail there is no similar structure. The tail in its full length exposes a much more consistent structure using ultrasound imaging (Ref. 35).

Sex-determination in females: no paired structures

Sex determination in young Heloderma:

After several consecutive breedings and observing many hatchlings, I am now of the opinion that it is possible to determine the sex in young Heloderma. Sex determination can be successful in the hatchlings when they are still filled with absorbed yolk. This makes their body shape quite distinct. After hatching, both sexes show characteristic body and head shapes. The length and shape of the tail is less useful for sex determination.

1. Body

The body of a new born male is oval shaped and appears to look bloated. The body of a female hatchling looks bloated only to her rear legs and appears more "pear-shaped". The hatchling female nevertheless has an elongated body shape.

2. Head

In comparison the head of a young male Gila Monster is more triangular in shape. This gives the impression of a larger head than that of a female. The head of a hatchling female is similar in appearance to that of an arrowhead as it softly tapers down into the neck.

Examples of male and female hatchlings from 2005:


male			female

After about one month of growth, these characteristics become difficult and sex determination may not be certain. With the age of about one year young Gila Monsters show more significant body shapes for sex determination.

Examples of the body shape criteria for sex determination of the same individuals after 12 month´s growth.


male			female

Comparison of head shape from the same individuals in pairs at about 12 months after hatching.


left male, right female		left female, right male

There is a much greater need of experience in observation for sex determination in young Heloderma than for adult individuals. Once experienced in the propagation of Heloderma suspectum, a herpetoculturist can have successful accuracy. It is especially true with having additional specimens of the same age for comparison. Photo documentation of specimens immediately after hatching supports this, especially from the side and from the dorsal view.

2. Ultrasound

We tried to determin the sexes of heloderma susp. from 16 months of age by ultrasound examination. The individuals came out of their first hibernation after three months and then tested.

Ultrasound examination of the sexual organs and of the ventral areas of the tail of two 16 month old siblings of Heloderma suspectum.


Mo-2-06 (hatched 10/30/06)


MO-3-06 (hatched 10/30/06)

Both specimens have a snout-vent length (SVL) of more than 230 mm and should therefore have sexual maturity (Ref. 1). In both individuals (siblings) we could detect singular roundish structures (gonade ?) , each. They are located deep in the abdominal caverty. The future will show if there will be a developement of "secondary gonades" .

The two individuals came out as females. Since 2010 eggs were laid and healthy offsprings hatched.

Ultrasound was performed at the Department for radiology (Prof. Dr. G. Alzen) Universitatsklinikum Giessen.
Equipment: Elegra Advanced Ultrasound. Siemens Co. with a 7,5 MHz linear ultrasound head.

Ultrasounds of the tails were performed with a 7,2 - 12,0 MHz linear ultrasound head.