Haematology and Plasma Chemistry of Male Lizards, Psammodromus algirus. Effects of Testosterone Treatment (original) (raw)
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Canadian Journal of Zoology, 2004
Testosterone can benefit individual fitness by increasing ornament colour, aggressiveness, and sperm quality, but it can also impose both metabolic and immunological costs. However, evidence that testosterone causes immuno suppression in freely living populations is scant. We studied the effects of testosterone on one component of the immune system (i.e., the cell-mediated response to phytohaemagglutinin), parasite load, and metabolic rate in the common wall lizard, Podarcis muralis (Laurenti, 1768). For analyses of immunocompetence and parasitism, male lizards were implanted at the end of the breeding season with either empty or testosterone implants and were returned to their site of capture for 5–6 weeks before recapture. For analyses of the effects of testosterone on metabolic rate, male lizards were captured and implanted before hibernation and were held in the laboratory for 1 week prior to calorimetry. Experimental treatment with testosterone decreased the cell-mediated respo...
Blood Testosterone Level: A Season-Dependent Factor Regulating Immune Reactivity in Lizards
Immunobiology, 1990
An attempt to study the interaction between testosterone (Ts) and the immune system of the lizard Chalcides ocellatus led to three major findings: 1) Endogenous serum Ts levels in both males and females peak in spring and are minimal during summer; 2) Injection of Ts in either male or female lizards induces significant depletion of lymphoid elements, reduction in serum antibody titers to rat erythrocytes and increase in skin allograft survival; 3) A distinct inverse correlation between endogenous serum Ts levels and lizard immunocompetence is observed from March to September. The data obtained strongly suggested that concentration of circulating Ts is a season-related factor that is critical in defining the immune profile of lizards.
Behavioral Ecology, 1997
According to the immunocompetence hypothesis, testosterone stimulates the expression of male sexually selected traits while decreasing immunocompetence. This proposed trade-off was studied by experimental supplementation of testosterone to small, subordinate, dull-colored male lizards, Piammodromus algirus. Experimental males showed a tendency to overlap their home range with fewer small males than did control males and tended to be more aggressive. However, control males were observed more frequently attending females than experimental males. The area of patches of breeding coloration, the number of ticks, and the frequency of recoveries of testosterone-supplemented and control males did not differ significantly. The results suggest that small adult males with high levels of testosterone behave more aggressively, which may be advantageous to securing a breeding territory in the next season. However, the hormone did not apparently affect ornamentation or parasite load. We argue that, whatever the mechanisms involved, blocking effects of testosterone may be adaptive because being cryptic facilitates a sneaking strategy, and low ectoparasite load may improve survival. I n some species of vertebrates, the expression of ornamental traits in males may depend on an individual's condition and age (Andersson, 1994; Johnstone, 1995). The development of such traits is also mediated by testosterone; males with high levels of circulating testosterone have the most elaborately developed secondary sexual traits (Iigon et aL, 1990; Rand, 1990, 1992). Testosterone, however, exerts a simultaneous and detrimental effect on the immune system (Folstad and Karter, 1992) and on growth (Crews et aL, 1985; Thomson et aL, 1993) and increases aggressiveness, which in turn increases energy expenditure and lowers life expectancy (Marler and Moore, 1988, 1989, 1991). Thus, there is a trade-off between production of elaborate ornaments that are useful during courtship and other body condition, including the ability to resist pathogen infection. Only those individuals able to cope with the negative consequences of elevated testosterone would be able to exhibit the most elaborate ornaments.
Acta ethologica, 2002
In some species, more aggressive individuals are more successful in resource competition. High testosterone level is associated with increased activity and aggressive behavior, and this may have a direct effect on metabolic rate and cause an increase in energy expenditure. Here, I examined the influence of exogenously administered testosterone on aggressiveness and body growth in juvenile Psammodromus algirus male lizards. Juvenile males were given testosterone-filled (experimental) or empty (control) implants. Testosterone produced an increase in aggressiveness and activity in the experimental males. However, despite being more aggressive, experimental males did not acquire larger home ranges than control males. Experimental males also experienced a significant reduction in growth rate over the 2-month period following implantation. Experimental males also were in poorer condition at the completion of the experiment, compared to control males. These results suggest that although an elevated testosterone level may have positive effects on aggressiveness and activity, it also may have negative effects manifested as reduced growth rate and body condition.
General and Comparative Endocrinology, 2008
The Texas horned lizard (Phrynosoma cornutum) is protected in several states due to its apparently declining numbers; information on its physiology is therefore of interest from both comparative endocrine and applied perspectives. We collected blood samples from free-ranging P. cornutum in Oklahoma from April to September 2005, spanning their complete active period. We determined plasma concentrations of the steroids, progesterone (P), testosterone (T), and corticosterone (CORT) by radioimmunoassay following chromatographic separation and 17β-estradiol (E2) by direct radioimmunoassay. T concentrations in breeding males were significantly higher than in non-breeding males. P showed no significant seasonal variation within either sex. CORT was significantly higher during the egglaying season compared to breeding and non-breeding seasons for adult females and it was marginally higher in breeding than in non-breeding males (P=0.055). CORT concentrations also significantly increased with handling in non-breeding males and egg-laying females. Perhaps most surprisingly, there were no significant sex differences in plasma concentrations of P and E2. Furthermore, with respect to seasonal differences, plasma E2 concentrations were significantly higher in breeding females than in egg-laying or non-breeding females, and they were significantly higher in breeding than in non-breeding males. During the non-breeding season, yearling males exhibited higher E2 concentrations than adult males; no other differences between the steroid concentrations of yearlings and adults were detected. In comparison to other vertebrates, the seasonal steroid profile of P. cornutum exhibited both expected and unexpected patterns, and our results illustrate the value of collecting such baseline data as a springboard for appropriate questions for future research.
Comparative Biochemistry and Physiology Part A: Physiology, 1995
Young and adult male house sparrows were captured once reproduction had finished (early summer) and before molting had taken place. They remained in outdoor aviaries until molting was completed (late summer). Half of them received a chronic treatment of testosterone. A blood sample was collected both at the beginning and at the end of the captivity period. Both young and adult birds showed a hemoconcentration from the beginning to the end of the summer, which is suggested to be related to the natural cycle of water shortage. White blood cell number was higher in young than in adults but no change was observed during the study period. Plasma proteins and their nitrogenous wastes decreased over the summer months which raised the hypothesis of plasma proteins as a store for amino acid needs during molting. Testosterone increased erythrocyte number and blood hemoglobin content. It also altered leucocyte number, but in an age dependent manner. It also increased plasma proteins, but only in adult birds. Plasma triglycerides were unaltered by age, month of sampling or testosterone treatment.
Reproduction, 1990
Progesterone, 17-hydroxyprogesterone, androstenedione, 5\g=a\-dihydrotestosterone, dehydroepiandrosterone, testosterone and oestradiol concentrations in the plasma were measured by simultaneous radioimmunoassay in males of the lizard Podarcis s. sicula. Hormonal determinations were performed at monthly intervals from January to December (except for August). Testosterone and androstenedione reached peak values of 174\m=.\8 ng/ml and 21\m=.\4 ng/ml in the mating season (spring) and then testosterone fell abruptly to 5\m=.\9 ng/ml in June remaining at this level during hibernation when dehydroepiandrosterone (DHA) reached a maximal level of 28\m=.\5\m=+-\9\m=.\3 ng/ml. Castration resulted in a marked decrease of testosterone, androstenedione, dihydrotestosterone and DHA values, with DHA being significantly lowered only during the winter season. In castrated animals, however, testosterone and androstenedione persisted conspicuously in the plasma during the breeding period, suggesting that adrenal sex steroid output may change during the annual reproductive cycle. In intact animals, progesterone and oestradiol exhibited peak values during the refractory period after the mating season. We suggest a probable role of oestradiol in the induction of the refractory period in this lizard.
Journal of Herpetology, 2002
Assessment of reproductive status in animals generally depends on monitoring hormone concentrations in plasma, but blood sampling often involves significant stress to the subject. Monitoring steroid profiles by assaying excreted steroids in urine and/or fecal samples is non-invasive, but does pose some problems. Unlike plasma assays, urinary and fecal steroid analyses are of relatively little value in monitoring rapid, short-term changes in hormone concentrations because there is a significant delay between production and excretion of steroids. However, such assays do enable measurement of "pooled" hormone concentrations over time .
General and Comparative Endocrinology, 2017
Sexual steroids influence reproductive behaviours and promote secondary sexual traits. In male lizards, increasing levels of testosterone (T) bolster conspicuous colouration, stimulate territoriality, and trigger antagonistic interactions among rivals. Moreover, in colour polymorphic species, reproductive strategy, aggressiveness and T levels can differ between morphs. Therefore, T level is considered as an important mechanism that regulates the expression of colour polymorphism and sexual behaviours of males. But in the polymorphic territorial wall lizard (Podarcis muralis), a lack of relationship between morphs and aggressiveness challenges the notion that T plays such a role. To examine this issue, we compared adult T levels among three colour morphs (white, yellow and red) through repeated sampling during the mating season. High T levels were observed at the onset of the mating season followed by a significant decrease, a pattern documented in other lizard species. Mean T levels did not differ among morphs. However, yellow males maintained significantly higher T levels over time and displayed a stronger subsequent decline. Overall, in this species, seasonal T patterns differ among morphs, not mean values. Previous studies revealed that T suppresses the immune response; suggesting that a strong initial investment promoted by high T levels may trade-off against immunity (maintenance). Further experimental investigations are required to clarify the relationship between T and reproductive effort in polymorphic species that exhibit complex temporal pattern of T levels.
General and Comparative Endocrinology, 1992
Progesterone (P), 17-OH-progesterone (17-OH-P), androstenedione (A), dehydroepiandrosterone (DHEA), testosterone (T), So-dihydrotestosterone (So-DHT), and 17pestradiol (E2) were measured by RIA in plasma and testes of 114 males of the oviparous lizard Podarcis s. sicula raJ a species that displays annual hibernating cycles. Hormones were determined each month from January until December, except for August. Testosterone peaked at 174.8 rig/ml of plasma after emergence (March), while SWDHT and A peaked in April. Plasma DHEA increased during hibernation. During the refractory period there were progressive increases in P and E, plasma levels. The testicular peak of T, in March, coincided with that observed in plasma. The striking increases in testicular T and A in early July occurred at a time when plasma androgen concentrations were low. Sa-DHT increased in April when spermatogenesis with spermiation occurred and then decreased alongside a second peak of T. There is an apparent separation of plasma and testicular androgen concentrations during the reproductive cycle. 6 1992 Academic press, IIIC.