Immature Lizards Research Articles

Dose-dependent effects of flufenoxuron on thyroid system of mature female lizards (Eremias argus) and their offspring

More and more studies are focusing on toxic effect of pesticides on lizards. However, the responses of different life-stage lizards to pesticides have not been reported. In this study, according to RNA-seq library data, thyroxine 5′-deiodinase activity showed significant difference between mature and immature lizard liver. In addition, triiodothyronine (T3) level in immature lizard serum was higher than that in mature lizard serum. Thus, we investigated the thyroid disruption of flufenoxuron with different concentrations (0, 5, 20 mg/kg) to both mature lizards and their offspring. No significant differences were observed in immature lizard body weight compared between control and exposure groups while the body weight of mature lizards was significantly decreased after flufenoxuron exposure. Moreover, the levels of thyroid hormones and the expression of thyroid related genes changed with exposure concentration of flufenoxuron and exhibited different regulation mechanism between mature and immature lizards. In immature lizard liver, trα, trβ, dio1 and ugt genes controlled the thyroid hormone levels interfered by flufenoxuron. In contrast, the thyroxine (T4) pathway in mature lizard liver was significantly disrupted especially by 20 mg/kg flufenoxuron exposure. This study elucidated the different thyroid disruption effects of flufenoxuron to lizards based on different exposure doses and lizard life stages.

Oral and dermal diflubenzuron exposure causes a hypothalamic–pituitary–thyroid (HPT) axis disturbance in the Mongolian racerunner (Eremias argus)

Diflubenzuron (DFB) is a potential endocrine-disrupting chemical. However, its thyroid endocrine effect on reptiles has not been reported. In this study, immature lizards (Eremias argus) were exposed to 20 mg kg−1 DFB once a week for 42 days through oral or dermal routes. Their body weight, plasma thyroid hormone levels, thyroid gland histology and the transcription of hypothalamic–pituitary–thyroid (HPT) axis-related genes in different tissues were assessed to explore the effects of DFB on the HPT axis of lizards. The body weight decreased significantly only after the dermal exposure to DFB. Triiodothyronine (T3) to thyroxine (T4) ratio in the male plasma also significantly increased after the dermal exposure. After oral exposure, the activity of thyroid gland was positively related to the thyroid hormone levels. Furthermore, the alterations in thyroid hormone levels affected the HPT axis-related gene expression, which was tissue dependent and sexually selected. The thyroid hormone receptor genes (trα and trβ) in the brain and thyroid were more sensitive to oral exposure. However, only the dermal treatment affected the trα, trβ and type 2 deiodinase (dio2) genes in the male liver. These results suggest that DFB exposure caused sex-specific changes in the thyroid function of lizards, and the dermal treatment may be an important route for the risk assessment of reptiles.

Colorful tails fade when lizards adopt less risky behaviors

Colorful tails that become cryptic during ontogeny are found in diverse taxa. Nevertheless, the evolutionary bases for this change remain debated. Recent work suggests that colorful tails, deflective displays, and striped patterns may represent antipredator mechanisms used by immature lizards to compensate for being more active and hence more vulnerable to predation (increased movement hypothesis, IMH). I challenged the generality of IMH by comparing foraging behavior and frequency of tail displays across five Acanthodactylus lizards that vary in fundamental life history traits, before and after the tail changed color. As these species underwent changes in tail coloration, they congruently adopted less risky behaviors and reduced the frequencies of tail displays. Contrary to expectation, in two species, the hatchling risky behavior resulted not from increased movements but from longer stay in exposed microhabitats. I suggest that colorful tails and deflective tail displays are synergistic antipredator mechanisms neonates use to minimize the fitness consequences of using various risky behaviors rather than increased movement alone.

Conservation of New Zealand lizards (Lacertilia: Scincidae) by translocation of small populations

The successful removal of rodents from islands around New Zealand has enabled translocation of rare species of lizards to new sites within their former range. Four species of skinks were translocated to Korapuki Island, Mercury Islands, New Zealand: Cyclodina alani, C. oliveri, C. whitakeri and Oligosoma suteri. Responses of three of the lizard species to release were predicted using a deterministic population model then compared with the actual performance of wild populations. The population models predicted that if populations of about 30 C. whitakeri and O. suteri were released, C. whitakeri would be increasing by 7% p.a. and O. suteri would be increasing by over 35% p.a. during year five. If 20 C. alani were released, the population could be increasing by 70% p.a. during year five. Population expansions are being recorded for all three species, but observed population increases were lower than those predicted for two species, partly because of low catchability of immature lizards. The lowest rate of increase (up to 7% p.a.) was for C. whitakeri. Low rates of population expansion found in species such as C. whitakeri raise a conundrum: the rarer a species is, and the lower its annual reproductive output, the larger the number of individuals that may be required for translocations to succeed. Translocations may be regarded as successful when new populations are self-sustaining and comprised only of locally born animals. Despite the populations increasing, it may not be possible to claim success for the three intensively studied species on Korapuki Island until at least 20 years after release. This is because of longevity of the founders, which are still being caught up to 12 years after release. Extreme longevity, and hence prolonged post-release monitoring, is likely to be a recurrent problem for translocations of rare lizards.

Ontogenetic plasticity of food habits in the Mexican spiny-tailed iguana, Ctenosaura pectinata.

Ontogenetic shifts from insect consumption by juveniles to plant consumption by adults are rare in the herbivorous lizard family Iguanidae. My investigations on diet and digestive tract anatomy of the iguanid lizard Ctenosaura pectinata show that this species has an ontogenetic diet shift. Insects were rare in adult diets but constituted 86.5% (by volume) of the food eaten by the smallest juveniles. All age classes ate some plant parts from a range of plant types, but flowers and leaves of legumes were a primarily food source. Non-adult lizards had the widest food niche breadths. Arthropods in the diet of juveniles and immatures covaried seasonally with the decline of arthropod abundance. Several hypotheses could explain this ontogenetic plasticity in diet. I rejected hypotheses that gut structure constrained juveniles to an arthropod diet and that insect consumption was purely an artifact of plant consumption because (1) size-adjusted gut morphology and capacity was similar among age classes, and (2) no food plants sampled had an excessive density of arthropods. I supported an alternative hypothesis that juveniles can eat plants but do not because insects provide a more nutritious diet. This conclusion was based on the observation that the juvenile hindgut is similar to that of herbivorous adults, and the propensity for juveniles to consume primarily, but not exclusively, insects when they were most abundant. The hindgut represents the site of fermentative plant fiber breakdown in many herbivorous lizards. Insect foods can compensate for size-related nutritional needs (energy and protein) and digestive limitations in juveniles. Opportunistic feeding to maintain a broad diet might help juvenile and immature lizards through high-predation-risk growth periods by reducing searching costs, increasing nutritional and energetic gains due to associative effects, and increasing new food exposure.

Vitellogenesis in Anolis pulchellus: Induction of VTG‐like protein in liver explants from male and immature lizards

Vitellogenin (VTG) synthesis has been described as an ideal system to study the hormonal regulation of gene expression. In Xenopus the molecular aspects of this control have been analyzed; however, in other non-mammalian species such as reptiles, very few studies approaching this level have been undertaken. We report on the induction by estradiol-17 beta of VTG-like proteins in liver explants from adult males and immature male and female lizards (A. pulchellus). A concentration of 10(-7) M was optimum for adult males while a higher concentration (10(-6) M) is required for the immature animals. No differences were observed in the hormonal induction in male and female immature animals, suggesting that there are no sexual distinctions in the liver at this stage. The effect of the hormone in male liver appears to be primarily on mRNA synthesis, since increases in 3H-uridine incorporation in total RNA were prevented by addition of 1 microgram/ml of the RNA polymerase II inhibitor alpha-Amanitin; however, rRNA synthesis was also increased as observed by agarose gel analysis. A 48 hr lag period was required for the detection of the intracellular as well as the secreted VTG-like protein. Electrophoretical analysis of the secretory products revealed the induction of a group of phosphoproteins immunologically related to yolk lipovitellin whose molecular weights range from 116,000 to 200,000.

Age-determination in the tropical agamid garden lizard, Calotes versicolor (Daudin), based on bone histology

Male garden lizards showed excellent positive correlations between body weight and S-V length; body weight and tail girth; and body weight and gonad weight, suggesting the utility of these parameters as indirect markers of chronological age. However, the reliability of such morphometric data needed rapport from a more accurate method of bone histology based on the techniques of ‘skeletochronology’. Cross-sections of diaphyses of the humerus and femur of bones lizards of a complete age series revealed that while in young, immature and sexually mature lizards who have not yet completed a year in the wild there are no distinct annulations, the representative of fully mature and old lizards exhibited an alternation of thinner and thicker annulations arranged concentrically. Cross-sections of phalanges of old lizards also showed agreement with the annulations in diaphysis. The thinner annulations (LAC), corresponding with the period of slow growth, as in temperate species of lizards, were haemotoxylinophilic (chromophilic) and showed yearly growth patterns, their number representing the age of the lizards in years. Transverse sections of humeral epiphysis of old lizards exhibited, in contrast to the cartilaginous nature of young immature lizards, an almost complete calcification and bony union, suggesting a limitation of further growth. Thus, based on the recurrence of growth lines (LAC) in the diaphysis of long bones and in the phalanges, it is possible as in temperate species of lizards and turtles, to determine accurately the age of individuals belonging to a wild population of tropical lizards.

Age-related changes in testicular histology and androgen levels of the immature spiny-tailed lizard, Uromastix hardwicki

Age-related changes in testicular histology and androgen levels have been studied during the first 16 weeks of life of the immature spiny-tailed lizard ( Uromastix hardwicki). In the young lizards which emerge from eggs in late June to early July, until approximately 3 months of age, the seminiferous tubules contain only two types of cells: gonocytes and pre-Sertoli cells. Subsequently, in the month of October (age: 12–16 weeks) there is a marked proliferation of germ cells accompanied by an increase in the diameter of the seminiferous tubules and weight of the testis. The interstitial cells which are markedly differentiated even in the earliest phase of posthatching development are considerably hypertrophied in early August (age: 4–5 weeks). Plasma titers of testoslerone, as measured by radioimmunoassay, showed an initial rise in August followed by a second major peak at the end of October. Testicular testosterone concentrations expressed per milligram of tissue were lowest in July and maximal in August. A significant increase in testosterone concentration in both the plasma and the testicular tissue was also observed following administration of FSH and LH to immature lizards. It is suggested that, in the immature spiny-tailed lizard, androgenesis resulting in detectable levels of testosterone in peripheral plasma and testicular tissue precedes gamatogenic activity. Furthermore, the steroidogenic tissue in this species has been shown to be responsive to exogenous gonadotropins even in the earliest phase of posthatching development.

Fat and Breeding Cycles in a Montane Population of Sceloporus graciosus

Sceloporus graciosus, at 1600m on the western slope of the California Sierra Nevada, is active from mid-April (males) or early May (females) until late August (females) or late September (males). Young and immature lizards are active from mid-April to early October. Fat accumulates at the end of the breeding season to maximal levels prior to hibernation. During dormancy, males use about half the autumnal fat, at a rate of 0.04 KCal/gm body weight/month. During dormancy, females use 0.01 KCal/gm body weight/ month. In the spring in females fat is used for egg production, and fat bodies shrink as eggs develop. Liver lipids of females are maximal during ovogenesis. Breeding females comprise two size groups: about 2/3 females are estimated 2-3 years old (49-58 mm SLV) and 1/3 are estimated 4 or more years old 59-4 mm SVL). The smaller group has a mean clutch size of 4.80 ane d the larger has a mean clutch size of 5.41 ? .23. Most of the larger females breed at the ae ea beginning of the breeding season (in late May) and younger females may breed from the same time until July. A few large females may lay a second clutch, but a single clutch is the rule. Incubation takes at least 6 or 7 weeks but a late summer decline in soil temperatures seems to prolong development. It is suggested that, under certain conditions, a few young may not emerge until spring.

Aspects of the Ecology of a Sonoran Desert Population of the Western Banded Gecko, Coleonyx variegatus (Sauria, Eublepharinae)

A population of Coleonyx variegatus was studied during 1965-66 at a low-altitude Sonoran Desert mountain range. Seasonal activity extended from April through October, with intermittent activity during winter months. Mean distances between capture points ranged from 10.9 m for immature males to 43.7 m for immature females. Frequency of broken or regenerated tails was positively correlated with body length; in the largest size group 74.1 % were broken. Growth rates varied from 9.7 mm/month in immature lizards to no discernible growth for large adults. Gravid females were found from April through September, occurring most frequently in May and June. Two or more clutches of two eggs each are produced annually. Males had enlarged testes from April through August. Hatchlings appeared from July through November. Many individuals of both sexes reached sexual maturity when less than 1 year old, but some did not mature until their 2nd year. Males were captured more frequently than females from January through May, perhaps indicating more extensive wanderings. An estimated 66% of the population was reproductive in May, the height of the breeding season. Among five study areas, abundance was highest on a S-facing slope. Population density in one area was estimated to be 12-25 geckos/ha. INTRODUCTION The lizard subfamily Eublepharinae (family Gekkonidae) contains five genera: Aeluroscalabates Gunther, an arboreal forest gecko found in Indonesia; Eublepharis Gray, a terrestrial desert genus occurring in southwestern Asia, Hainan and Loo-Choo islands; Hemitheconyx Stejneger and Holodactylus Boettger, ground-dwelling desert genera found in West Africa and Somaliland; and Coleonyx Gray, a terrestrial genus distributed from southwestern United States to Central America (Kluge, 1967). Kluge (1962) divided Coleonyx into northern (brevis and variegatus) and southern (elegans and mitratus) species groups. Little is known of the life history of any eublepharine gecko. Inger and Greenberg (1966) described aspects of reproduction of Aeluroscalabates felinus in Borneo, but knowledge of the other Old World genera is restricted to a few scattered observations. Coleonyx has been the most intensively studied genus in the subfamily, but most published life history data are based on captive individuals of C. variegatus or miscellaneous field observations. Dixon (1970a, b, c) listed pertinent literature for Coteonyx, C. brevis and C. variegatus. In spite of the long reference list for eublepharine geckos, there has been no population study of any species; life histories of all members of the subfamily remain relatively unknown. A field study of the western banded gecko (Coleonyx variegatus Baird) was conducted at Phoenix South Mountain Park, Maricopa Co., Ariz., during 1965-66. Turner (1962), Williams (1968, 1970) and Hadley (1970) studied arthropods in the same general vicinity.

Hormonal control of pigmentary sexual dimorphism in Sceloporus occidentalis

Studies were performed to investigate the hormonal basis for sexual dimorphism in ventral pigmentation of Sceloporus occidentalis. Immature lizards of both sexes were similar in appearance, but males developed dark pigmentation as they approached maturity. The distinctive male pigment pattern resulted from increases in the number of scale rows containing melanophores, scale melanophore density, and degree of melanophore expansion. Treatment of immature male and female lizards with androgen pellets resulted in precocious development of the typical male pattern although young males showed a greater level of pigment dispersion than did young females. Castrated adult males showed a decline in level of melanophore expansion but not in number of scale rows occupied by melanophores. Androgen replacement therapy maintained precastration levels of pigment dispersion. Castrated adult females showed no decline in pigment dispersion from precastration condition but responded to androgen treatment by increased melanophore expansion.

RESPONSE OF THE MALE REPRODUCTIVE SYSTEM OF LIZARDS (ANOLIS CAROLINENSIS) TO UNNATURAL DAY-LENGTHS IN DIFFERENT SEASONS

1. The reproductive system of adult male anoles was stimulated by artificially lengthened days at all seasons of the year. At least a few males were brought into full breeding condition in experiments initiated from November through August. Sperm were produced at all seasons. 2. A refractory period, such as occurs in passerine birds, did not appear to be present in Anolis. 3. A previous exposure to short days was not essential for obtaining a response to a long photoperiod. 4. Both the testes and accessory sex organs exhibited progressively greater responses in successive experiments through the fall, winter, and spring. 5. The seasonal gradient of response which produced increasingly larger testes could be accounted for by the increasingly larger number of spermatogonia at the beginning of each experiment. The gradient in response of the accessory sex organs was dependent on the normal cyclic fluctuations of their histology and the abundance of hypertrophied interstitial cells. 6. The inherent rhythms of both the gonad and accessory sex organs were not disturbed by 60 days' exposure to 9- or 6-hour photoperiods during the fall and winter. However, such exposures near or after the peak of spermatogenesis resulted in premature atrophy of all reproductive organs. 7. Comparison of the effects of 14-, 16-, and 18-hour day-lengths suggested that the longer the day-length the more rapid the response. Extremely long days, however, appeared to have detrimental effects upon some individuals. 8. Most immature lizards of less than 55 mm. snout-vent length responded poorly to the experimental conditions. All that responded well were growing rapidly. Those that grew to 60 mm. or more had reproductive organs as large or larger than older adults. 9. Captive lizards exposed to natural day-length for 60 days at any time between February and July tended to have larger testes than wild lizards sacrificed on the same date.