Effect of human chorionic gonadotropin in chameleons

Effect of human chorionic gonadotropin in chameleons

by Alex Laube Tiermedizin Science

After a study on sperm collection in chameleons was already published this year, further results from the largely same team of authors now follow. The aim is to further research the basics of assisted reproduction, i.e. medical assistance in reproduction, in chameleons.

At Louisiana State University, 24 Veiled Chameleons were kept under standardised conditions for over a year. All animals came from a dealer who had taken them from the population of wild Veiled Chameleons in Florida. All were kept individually in ReptiBreeze, equipped with automatic sprinklers and artificial plants. Temperatures were around 28-29°C during the day with spots to seek higher values. 12 h UV-B irradiation per day was offered. Crickets and zophobas were fed. Before the start of the study, all 24 chameleons were clinically examined and several parasite treatments were carried out. Only after a month of acclimatisation did the actual study begin.

The first experiment tested what dose of human choriogonadotropin (hCG) is needed to increase the hormone levels of testosterone in the blood by 50%. Eleven Veiled Chameleons were randomly assigned to one of three groups. The three groups received injections of 100, 200 or 300 IU hCG under the skin at two-week intervals. Blood samples were taken before the first hormone injection and at 30 minutes, one hour, two hours, four hours, eight hours, 12 hours and 24 hours afterwards.

The second experiment tested the effect of hCG treatment on sperm production. 13 Veiled Chameleons were randomly assigned to a treatment or a control group. Once a week for one month, the animals in the first group were treated with 100 IU of hCG, while the second group was only injected with the same volume of isotonic saline. After a four-week break, the groups were switched and the experiment repeated. Blood samples to measure testosterone levels were taken before treatment and on day 15 and 30 afterwards. Semen was collected by electroejaculation under anaesthesia on the day before treatment and 30 days after.

The results showed that the testosterone level in male Veiled Chameleons increased significantly directly after the administration of hCG and remained elevated for about 24 hours. However, it did not matter which dose of hCG had been given beforehand. It could also be shown that the testosterone level increased significantly after the administration of hCG compared to the control group, which only received saline solution. The number of successful electroejaculations could be increased under hCG.

Effects of exogenous human chorionic gonadotropin administration on plasma testosterone and semen production in the Veiled Chameleon (Chamaeleo calyptratus)
Sean M. Perry, Sarah R. Camlic, Michael Lierz, Mark A. Mitchell
Journal of Herpetological Medicine and Surgery 33 (3), 2023, pp. 180-191
DOI: 10.5818/JHMS-D-22-00038

Long-term study on sperm collection in chameleons

Long-term study on sperm collection in chameleons

by Alex Laube Tiermedizin Science

Assisted reproduction has become increasingly common in the conservation of extremely rare animals such as the Spix’s macaw or northern white rhinoceros in recent years. In reptiles, on the other hand, there have only been a few studies on assisted reproduction, and only a few on chameleons in particular. Scientists from the USA have now conducted a study on male Veiled and Panther Chameleons (Chamaeleo calyptratus and Furcifer pardalis).

At Louisiana State University, 16 males of each species were kept under standardised conditions for over a year. The panther chameleons were purchased from a US breeder, the Yemen chameleons from a dealer who had taken them from the introduced wild chameleon population in Florida. All males were kept individually in ZooMed screen cages, equipped with automatic sprinklers and artificial plants. Temperatures were around 28-29°C during the day with spots to seek higher values. 12 h UV-B irradiation per day was offered. They were fed with crickets and zophobas.

Before the start of the study, all 32 chameleons were clinically examined and parasites were treated. Only after a month of acclimatisation did the actual study begin. During the study year, all chameleons were put under anaesthesia twice a month. Each time, blood was taken from the ventral tail vein or the jugular vein to determine the testosterone concentration. Ultrasound was used to measure the size of the testicles. In addition, each time an attempt was made to obtain sperm by electroejaculation. Electroejaculation involved inserting a small metal probe into the cleaned cloaca. Each chameleon was then treated up to three times in succession with up to 15 electric shocks of 0.1/0.2/0.3 mAs. The semen collection experiments were stopped as soon as the animal ejaculated. The sperm collected was preserved and examined for ejaculate volume, presence of sperm, sperm motility, concentration, and morphology.

The results suggest that Veiled Chameleons follow a so-called prenuptial reproductive strategy under constant husbandry conditions. The testosterone concentration in the blood already increased before the sperm volume of the males had reached its maximum. The months of May, April, and June brought the best sperm volumes, the most sperm was produced by electroejaculations in the third attempt. Testicle sizes also varied throughout the year, with the largest measurements from August to December.

Panther chameleons, on the other hand, seem to follow a postnuptial reproductive strategy. In them, most sperm could only be obtained well after the highest point of testosterone concentration. The electroejaculations worked best in March, April, May and June. Much more often than in Yemen chameleons, electroejaculation in panther chameleons worked already in the first attempt. The size of the testicles also varied throughout the year, but most were largest in the months mentioned above. Together with the factors mentioned above, the volume of ejaculate, sperm concentration, sperm motility and sperm morphology also changed during the year.

The authors recommend that electroejaculation in chameleons should generally only be performed under anaesthesia. The success rate for spermatozoa in the two highest cases was 82 and 88%, which is similar to the success in other reptiles during their reproductive season. The mortality rate among the 32 animals was only 0.12% over the whole year. One panther chameleon died after 10 months during the 20th anaesthesia, after death kidney damage was detected. From the low mortality rate, the authors conclude that electroejaculation rather does not play a role in the development of kidney disease, as was suspected in other studies. However, an examination of the blood for kidney values was not carried out on any of the surviving chameleons after the study. It also remains unclear what role the lack of imitation of rainy and dry seasons during the year plays for both species and their reproductive cycle.

Characterizing the annual reproductive cycles of captive male veiled chameleons (Chamaeleo calyptratus) and panther chameleons (Furcifer pardalis)
Sean M. Perry, Sarah R. Camlic, Ian Konsker, Michael Lierz, Mark A. Mitchell
Journal of Herpetological Medicine and Surgery 33 (1), 2023, pp. 45-60
DOI: 10.5818/JHMS-D-22-00037

New research on the Labord’s chameleon in Kirindy, Madagascar

New research on the Labord’s chameleon in Kirindy, Madagascar

by Alex Laube Science

Furcifer labordi is known as the world’s shortest-lived chameleon. Within three months, these animals grow from hatchling to adult chameleons, mate, lay eggs and mostly die immediately afterwards. Scientists at the University of Göttingen researched whether the short lifespan has an influence on the mating strategy of Furcifer labordi.

The study site was the dry forest of Kirindy in western Madagascar. Kirindy is located about 60 km north of the coastal town of Morondava and about 20 km from the sea in the Menabe region. During the rainy season in early 2020, 39 Furcifer labordi of both sexes were fitted with radio transmitters there. Weight and body length at the time of discovery as well as some other values were measured, and the sleeping height of the animals found at night was noted. The animals were released at the site where they were found. The researchers then tracked the chameleons twice during the day and once at night for several weeks using telemetry to record GPS data and establish movement and behaviour patterns.

The results of the study show that female Furcifer labordi in Kirindy are very site-faithful. They only cover short distances. In contrast, male Furcifer labordi move much more and over longer distances, so that seven to fourteen times more males than females could be observed in a forest section. The observed females mated with up to six different males – however, the researchers repeatedly found unmarked males among the observed females. This suggests that Furcifer labordi could actually have a significantly higher number of different reproductive partners. The individually very different body sizes of the males as well as differently pronounced nasal processes had no connection to movement patterns. Furthermore, it could be shown that Furcifer labordi does not occupy and defend territories. This means that presumably the short lifespan actually leads to competition for the few available females being more intense – and as observations show also more aggressive – than in other chameleon species. This study is the first investigation of the mating system of a Malagasy chameleon.

Sex-specific movement ecology of the shortest-lived tetrapod during the mating season
Lennart Hudel & Peter M. Kappeler

Published in Scientific Reports 12
Open Access (free download possible)
DOI https://doi.org/10.1038/s41598-022-14156-3