Characterization of fecal hormone patterns associated with the reproductive cycle in female veiled chameleons (Chamaeleo calyptratus)

Reproductive Management of Reptiles

Research in reproductive management of reptiles has focused on developing and investigating feasible methods that can be used in clinical practice and laboratory settings, including sexing in monomorphic species and methods of artificial insemination in endangered reptile species. In captive pet reptile species, research is focused on hormonal regulation of reproductive activity. Gonadotropin-releasing hormone (GnRH) agonist implants may temporarily suppress reproductive endocrine system (eg, circulating concentrations of estrogens and progesterone) in female green iguanas but did not influence male iguana behavior and plasma testosterone levels. Additionally, it did not suppress reproductive activity of females of other lizard species (eg, leopard geckos).

Effect of GnRH agonist (deslorelin) on reproductive activity in captive female veiled chameleons (Chamaeleo calyptratus)

Eighteen 5 months old veiled chameleon females (Chamaeleo calyptratus) were used in the study. Seven females received subcutaneous implants with gonadotropin-releasing hormone agonist (GnRH) deslorelin acetate whereas eleven females were used as control animals without any implants. Females were kept in five terraria, in groups of four females (in 3 terraria) and groups of three females (in 2 terraria), respectively. A minimum of one female with GnRH implants was present in each terrarium. They were kept under standard husbandry conditions. Females of both groups (females with GnRH and controls, respectively) were monitored for three years. No differences between females with GnRH implants and females without GnRH implants were observed with respect to the presence of large ovarian follicles, number of eggs/female, or number of clutches/female. GnRH implants did not prevent spontaneous reproductive activity in any of the 7 females with implants. Ovariectomy was performed in 8 females (4 females with GnRH implants and 4 control females). Ten females (3 females with GnRH implants and 7 control females) had to be euthanised. In 17 of 18 female veiled chameleons of this study histologic examination revealed heterophilic granulomatous oophoritis. The use of GnRH agonist implants did not prove to be an appropriate method for the control of reproductive function in captive female veiled chameleons.

ULTRASONOGRAPHIC AND COMPUTED TOMOGRAPHIC CHARACTERISTICS OF THE REPRODUCTIVE CYCLE IN FEMALE VEILED CHAMELEONS (CHAMAELEO CALYPTRATUS)

Female veiled chameleons, Chamaeleo calyptratus, have a high fecundity and fast maturation, which makes them a suitable model species for squamate reproduction. The authors investigated the morphological follicular development of a group of 20 healthy adult animals over a 12-mon period using ultrasonography (US) and CT. Four stages of follicular development could be distinguished by imaging diagnostics and were confirmed by histology: previtellogenesis, vitellogenesis, gravidity, and atresia. Using a linear ultrasound transducer (18 MHz), previtellogenic follicles could be visualized as small, round, hypoechoic structures. Identification of this stage was unreliable on CT. On US, vitellogenic follicles remained round and showed increasing echogenicity from the hypoechoic center outwards, displaying vinyl-like hyperechoic banding in later stages. On CT, early vitellogenic follicles were round, hyperdense structures, which reduced in density as they grew. A hyperdense inner ring with a hypodense central point characterized late vitellogenesis. Following ovulation, eggs became distinctly oval on both CT and US, with formation of a hyperdense or hyperechoic outer ring, respectively. Atresia followed in cases where no ovulation occurred, and was divided into yolky and cystic atresia. Sonographically, early yolky atretic follicles became unevenly shaped, packed against one another, and developed heterogenous content. Late atretic follicles were homogenous and reduced in size. Reduction of density and uneven shape were also observed on CT. Cystic atretic follicles developed an anechoic cavity with a dense peripheral accumulation of content. In many animals 2-3 generations of atretic follicles were observed without indication of impairment to the development of the newest batch of follicles. Thus, follicular atresia need not necessarily lead to a pathological condition in veiled chameleons, at least not within a few consecutive cycles.

A Review and Case Study of 3D Imaging Modalities for Female Amniote Reproductive Anatomy

Recent advances in non-invasive imaging methods have revitalised the field of comparative anatomy, and reproductive anatomy has been no exception. The reproductive systems of female amniotes present specific challenges, namely their often internal "hidden" anatomy. Quantifying female reproductive systems is crucial to recognising reproductive pathologies, monitoring menstrual cycles, and understanding copulatory mechanics. Here we conduct a review of the application of non-invasive imaging techniques to female amniote reproductive anatomy. We introduce the commonly used imaging modalities of computed tomography (CT) and magnetic resonance imaging (MRI), highlighting their advantages and limitations when applied to female reproductive tissues, and make suggestions for future advances. We also include a case study of micro CT and MRI, along with their associated staining protocols, applied to cadavers of female adult stoats (Mustela erminea). In doing so, we will progress the discussion surrounding the imaging of female reproductive anatomy, whilst also impacting the fields of sexual selection research and comparative anatomy more broadly.

Sex steroids are correlated with environmental factors and body condition during the reproductive cycle in females of the lizard Sceloporus torquatus

Reproduction is regulated by multiple factors that influence physiology and behavior to ensure the continuity of species. However, more work is needed to examine the complex relationships between environmental factors and endocrine transducers that modulate reproductive cycles, particularly in lizards. Here, we aimed to characterize the variation in plasma sex steroid levels in different stages of the reproductive cycle in the lizard Sceloporus torquatus and assess whether sex steroid levels were related to environmental factors (temperature, photoperiod, precipitation, and relative humidity) and body condition. Plasma concentrations of estradiol (E₂) and progesterone (P₄) from blood samples were quantified by enzyme-linked immunosorbent assay (ELISA) and radioimmunoanalysis (RIA), respectively. Our results indicate that sex steroid concentrations were positively related to follicular development but negatively related to temperature and precipitation. E₂ increased as the follicles grew, and its concentrations were highest in the preovulatory phase. P₄ showed a similar pattern and persisted during pregnancy. Changes in body condition were non-significant and mainly unrelated to the reproductive stage and plasma sex steroids. Our findings indicate that sex steroids change depending on the season and reproductive stage. We observed high concentrations of E₂ and P₄ in the late vitellogenic and preovulatory stages, probably because of their role in promoting vitellogenesis and ovulation. Additionally, we observed that follicular development is correlated with temperature and photoperiod. To better understand the mechanisms underlying reproduction, future studies of captive populations where environmental factors can be manipulated are needed.

Fecal adrenal hormone patterns during ovulatory and non-ovulatory reproductive cycles in female veiled chameleons (Chamaeleo calyptratus)

The relationship between the reproductive (hypothalamic-pituitary-gonadal; HPG) and adrenal (hypothalamic-pituitary-adrenal; HPA) hormone axes is complex and can vary depending on the species and environmental factors affecting an individual. In an effort to understand this relationship in female veiled chameleons (Chamaeleo calyptratus), the patterns of fecal metabolites of corticosterone (C), estradiol (E), testosterone (T), and progesterone (P) were analyzed by enzyme immunoassay (EIA) during ovulatory (OC; eggs laid) and non-ovulatory cycles (NOC; no eggs laid). Glucocorticoid (GC) metabolites in the fecal extracts were characterized by HPLC and corticosterone EIA performance was assessed by parallelism, accuracy and precision tests. The results indicated that the assay chosen reliably measured the hormone metabolites present in the fecal extracts. Regular, cyclical hormone metabolite patterns consisting of an E peak followed by peaks of T, P and C in close succession were observed during both ovulatory and non-ovulatory cycles; relative levels of P and C, however, were higher during ovulatory cycles. Corticosterone metabolite levels, in particular, increased throughout vitellogenesis and peaked in late vitellogenesis (in non-ovulatory cycles) or around the time of ovulation, and remained elevated throughout the gravid period, falling just prior to oviposition. The results provide evidence of variation in glucocorticoid production throughout different stages of the reproductive cycle, including a role in the ovulatory process; the physiology, however, remains unclear.

Hormonal control of seasonal color change in female spiny-footed lizards: an observational and experimental approach

Breeding coloration of females often signals aspects of their reproductive status, suggesting a link between color and sex steroid hormones. In this study, we examined the relationships between 2 sex steroid hormones (progesterone and β-estradiol) and reproductive coloration in female spiny-footed lizards Acanthodactylus erythrurus. We first explored natural variation in female plasma hormone levels and coloration during their reproductive cycle. β-estradiol was negatively related to brightness and positively related to red saturation, whereas progesterone was not significantly related to coloration. After identifying key relationships, plasma hormone concentrations were manipulated by creating 3 experimental female groups (β-estradiol-treated, progesterone-treated, and control), and the effects on coloration were monitored. β-estradiol-treated females, in which there was a rise in both β-estradiol and progesterone levels, lost their red coloration earlier than females in the other 2 experimental groups, whereas progesterone treatment had no significant effect on female coloration. Our results suggest that high levels of either β-estradiol alone or β-estradiol together with progesterone trigger the loss of red coloration in female spiny-footed lizards, and that progesterone alone does not affect coloration. We hypothesize that changes in female breeding color might be regulated by β-estradiol in species in which conspicuous coloration is displayed before ovulation, and by progesterone in species in which this color is displayed during gravidity.

Diagnostic Imaging of Reproductive Tract Disorders in Reptiles

Diagnostic imaging of the reproductive tract in reptiles is used for gender determination, evaluation of breeding status, detection of pathologic changes, and supervising treatment. Whole-body radiographs provide an overview and support detection of mineralized egg shells. Sonography is used to evaluate follicles, nonmineralized eggs, and the salpinx in all reptiles. Computed tomography is able to overcome imaging limitations in chelonian species. This article provides detailed information about the performance of different imaging techniques. Multiple images demonstrate the physiologic appearance of the male and female reproductive tract in various reptile species and pathologic changes. Advantages and disadvantages of radiography, sonography, and computed tomography are described.

Reproductive Medicine in Lizards

Common reproductive problems in captive male lizards are hemipenile plugs in hemipenial sac, unilateral prolapse of hemipenis, or bilateral prolapse of hemipene. Although the orchiectomy is performed as a treatment for testicular disease, the effectiveness in reducing aggressive behavior is unclear. Female captive lizards suffer from cloacal prolapse, preovulatory follicular stasis, or dystocia. The veterinarian must differentiate between the disorders because the treatment differs. Mating, physical, or visual contact with the male stimulates ovulation and prevents preovulatory follicular stasis. Surgical intervention is usually required for dystocia. This article discusses selected procedures and use of ultrasonography and diagnostic endoscopy.

The Veiled Chameleon (Chamaeleo calyptratus Duméril and Duméril 1851): A Model for Studying Reptile Body Plan Development and Evolution

Vertebrate model organisms have facilitated the discovery and exploration of morphogenetic events and developmental pathways that underpin normal and pathological embryological events. In contrast to amniotes such as Mus musculus (Mammalia) and Gallus gallus (Aves), our understanding of early patterning and developmental events in reptiles (particularly nonavians) remains weak. Squamate reptiles (lizards, snakes, and amphisbaenians) comprise approximately one-third of all living amniotes. But studies of early squamate development have been limited because, in most members of this lineage, embryo development at the time of oviposition is very advanced (limb bud stages and older). In many cases, squamates give birth to fully developed offspring. However, in the veiled chameleon (Chamaeleo calyptratus), embryos have progressed only to a primitive pregastrula stage at the time of oviposition. Furthermore, the body plan of the veiled chameleon is highly specialized for climbing in an arboreal environment. It possesses an entire suite of skeletal and soft anatomical modifications, including cranioskeletal ornamentation, lingual anatomy and biomechanics for projection, autopodial clefting for grasping, adaptations for rapid integumental color changes, a prehensile tail with a lack of caudal autotomy, the loss of the tympanum in the middle ear, and the acquisition of turreted eyes. Thus, C. calyptratus is an important model organism for studying the role of ecological niche specialization, as well as genetic and morphological evolution within an adaptive framework. More importantly, this species is easily bred in captivity, with only a small colony (<10 individuals) needed to obtain hundreds of embryos every year.

Captive Care, Raising, and Breeding of the Veiled Chameleon (Chamaeleo calyptratus)

Squamate reptiles comprise approximately one-third of all living amniotes. In most of these species, it is difficult to study gastrulation and neurulation because the embryos are at a late stage of development at the time of oviposition. This is not the case, however, in veiled chameleons (Chamaeleo calyptratus), which are increasingly being used as a model organism to study these and other developmental and evolutionary phenomena. Originating from the Arabian Peninsula, veiled chameleons are arboreal specialists that possess extensive morphological specializations for climbing. They naturally inhabit semitropical habitats, but they also have an almost 30-yr history of being bred in captivity. Veiled chameleons breed readily and do not require a period of cooling to induce the reproductive cycle, and females can produce ∼45-90 eggs multiple times per year. Thus, compared with other reptiles, relatively few animals are needed to maintain a productive breeding colony. Herein, we present the conditions, equipment, and techniques required for proper husbandry and breeding of veiled chameleons within a laboratory environment.

Overlap of female reproductive cycles explains shortened interclutch interval in a lizard with invariant clutch size (Squamata: Gekkonidae: Paroedura picta)

Variable clutch size is unambiguously an ancestral state in reptiles. Only several lizard lineages have evolved so-called invariant clutch size, where all females lay just one or two eggs per clutch. This mode of reproduction is characteristic for geckos. In some gecko lineages, decreased fecundity in a single clutch is compensated by conspicuous shortening of interclutch intervals. The proximate mechanism of high clutch frequency in these geckos is not known. Here, we document that three subsequently laid clutches develop simultaneously in females of the Madagascar ground gecko (Paroedura picta). The extremely short interclutch intervals in this species-even as short as a week-thus could be attributed to the overlap of female reproductive cycles. Such overlap should be associated with altered female hormonal cycles. Based on measurements of hormonal levels, we suggest that cycles of estradiol and progesterone during reproductive cycles of females in P. picta are largely independent. Thus, in contrast to the presumable ancestral reptile state, higher levels of progesterone do not seem to interfere with vitellogenesis in this species. We discuss potential consequences of this derived mode of reproduction, such as possible simultaneous maternal transfer of nutrients and other yolk components to several subsequent clutches.

Fecal hormone patterns during non-ovulatory reproductive cycles in female veiled chameleons (Chamaeleo calyptratus)

Reproductive failure, in particular preovulatory stasis, is a common problem in captive female reptiles. For a better understanding of its pathogenesis, the patterns of fecal estradiol (E2), testosterone (T), progesterone (P) and their metabolites of 21 anovulatory female veiled chameleons, Chamaeleo calyptratus, were compared with those of 25 animals which ovulated during at least one cycle over the study period. Regular, cyclical hormone patterns, consisting of E2 peaks followed by simultaneous T and P peaks, were observed in all animals, regardless of whether oviposition occurred, indicating continuous ovarian activity. P concentrations were; however, significantly lower in animals undergoing anovulatory cycles. The average time period between the E2 and the T peak was 24.8 days, between the E2 and the P peak 26.5 days, and between the T and P peak 2.6 days. The mean length of reproductive cycles between two sequential ovulatory complexes (oviposition to oviposition) was 132.5 days (range 112-156 days). The results provide evidence that reproductive "failure" occurs more frequently than suspected with some females alternating between ovulatory and anovulatory cycles without any outward evidence of the variation in ovarian cycles. It is proposed that this may be related to physiological adaptation to adverse environmental conditions for breeding and that husbandry factors in captivity are primarily responsible for the progression from a physiological to pathological process.