Seasonal variations in spermatogenesis, testicular weights, vasa deferentia, and androgen levels in neotenic male tiger salamanders, Ambystoma tigrinum

Norris, David O.; Norman, Mark F.; Pancak, Martha K.; Duvall, David

doi:10.1016/0016-6480(85)90291-6

Cited by 43 publications

(15 citation statements)

References 17 publications

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“…In a neotenic population of tiger salamanders in Colorado, androgen levels are moderate during the spring breeding season (4 ng/ml) and decline in June (0.6 ng/ml) before peaking in the fall (38 ng/ml) [42]. Although the highest levels of androgen do not occur during the breeding season, the levels measured during the spring are similar to those that we measured in axolotls and may be sufficient to support reproductive behavior.…”

Section: Androgens Estradiol and Reproduction In Salamanderssupporting

confidence: 73%

“…If so, the pattern in axolotls differs from that of other ambystomids. In neotenic A. tigrinum, the GSI is moderate in March and declines throughout the breeding season, reaching a nadir in June; it then increases rapidly, peaking in August before beginning a gradual decline through the following spring [42]. A similar pattern has been described for A. macrodactylum in Washington State [58], as well as for a salamandrid, Triturus carnifex [65].…”

Section: External Factors Influencing Reproduction In Male Axolotlssupporting

confidence: 61%

“…On the other hand, we have analyzed the data for neotenic A. tigrinum presented by Norris et al [42], and find a slight association between androgen levels and GSI (R 2 = 0.43, p = 0.07). Interestingly, levels of DHT are strongly correlated with GSI in these animals (R 2 = 0.60, p = 0.02).…”

Section: External Factors Influencing Reproduction In Male Axolotlsmentioning

confidence: 88%

“…Specifically, Norris et al [42] quantified androgens (T + DHT) in neotenic tiger salamanders, Ambystoma tigrinum, which range between 0.6 and 39.0 ng/ml. In the spotted salamander, A. maculatum, androgen levels range from 2 to 16.7 ng/ml [13], and values in marbled salamanders, A. opacum, range from 5.2 to 116.7 ng/ml [27].…”

Section: Levels Of Sex Steroids In Axolotls and Other Salamandersmentioning

confidence: 99%

“…tigrinum [13,42]. It seems possible that decorrelating change in day length from time of year confounded the two variables, obscuring differences, although both variables contributed to differences in estradiol levels in females.…”

Section: External Factors Influencing Reproduction In Male Axolotlsmentioning

confidence: 99%

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Ambiguities in the relationship between gonadal steroids and reproduction in axolotls (Ambystoma mexicanum)

Eisthen

Krause

2012

General and Comparative Endocrinology

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Axolotls (Ambystoma mexicanum) are aquatic salamanders that are widely used in research. Axolotls have been bred in laboratories for nearly 150 years, yet little is known about the basic biology of reproduction in these animals. We investigated the effects of changing day length, time of year, and food availability on levels of circulating estradiol and androgens in adult female and male axolotls, respectively. In addition, we examined the effects of these variables on the mass of ovaries, oviducts, and eggs in females and weight, to calculate a form of gonadosomatic index (GSI). In both sexes, GSI was not correlated with levels of circulating steroids. In female axolotls, estradiol levels were influenced by food availability, changes in day length, and season, even when animals were held at a constant temperature and day length was decorrelated with calendar date. In addition, the mass of ovaries, oviducts, and eggs varied seasonally, peaking in the winter months and declining during the summer months, even though our animals were not breeding and shedding eggs. In males, levels of androgens appeared to vary independently of external conditions, but GSI varied dramatically with changes in day length. These results suggest that reproduction in axolotls may vary seasonally, as it does in many other ambystomid species, although both male and female axolotls are capable of reproducing several times each year. The physiological basis of this ability remains enigmatic, given the indications of seasonality contained in our data. IntroductionThe axolotl (Ambystoma mexicanum) is a paedomorphic salamander: it becomes sexually mature while retaining many morphological characteristics of the larval form.Axolotls were first brought to Europe in 1863, where they generated much interest for their ability to reproduce while resembling aquatic larvae, and then in some cases to metamorphose into an animal resembling a common terrestrial salamander, which was equally capable of reproducing [50]. Since their introduction to the research community, axolotls have become a model organism for biological research, used primarily in studies of embryology and regeneration.The natural history of axolotls is poorly understood. Axolotls are native to two lakes, Xochimilco and Chalco, which have been subsumed by present-day Mexico City. Human alteration of this habitat for agricultural purposes dates back hundreds of years [7]; their environment is now so badly degr on IUCN Red List. Recent studies indicate that few individuals exist in the wild [e.g., 12], and it seems likely that the ecology and natural history of axolotls will never be known.Given that axolotls have been bred in laboratories for nearly 150 years, it is perhaps particularly surprising that their reproductive patterns have not been thoroughly documented. Their courtship behaviors [18] and the anatomy of both male and female reproductive systems have been described [38,56], but the physiology of reproduction in axolotls has not been explored. In this study, we measu...

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Section: Androgens Estradiol and Reproduction In Salamanderssupporting

confidence: 73%

Section: External Factors Influencing Reproduction In Male Axolotlssupporting

confidence: 61%

Section: External Factors Influencing Reproduction In Male Axolotlsmentioning

confidence: 88%

Section: Levels Of Sex Steroids In Axolotls and Other Salamandersmentioning

confidence: 99%

Section: External Factors Influencing Reproduction In Male Axolotlsmentioning

confidence: 99%

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Ambiguities in the relationship between gonadal steroids and reproduction in axolotls (Ambystoma mexicanum)

Eisthen

Krause

2012

General and Comparative Endocrinology

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Ultrastructure and lectin cytochemistry of the cloacal ventral glands in the male newtTriturus marmoratus marmoratus

Romo

Paniagua

Fraile

et al. 1999

Microsc. Res. Tech.

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Sexual and seasonal differences in the vomeronasal epithelium of the red‐backed salamander (Plethodon cinereus)

Dawley

Crowder

1995

J of Comparative Neurology

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Sexually dimorphic behaviors often are associated with sexually dimorphic neural structures. Perinatal hormonal levels influence structural sexual dimorphism, and seasonal structural changes also can be the result of seasonal hormonal fluctuations. We compared the volume of vomeronasal organs of male and female red-backed salamanders (Plethodon cinereus) throughout the year. Odorants are delivered to vomeronasal receptors through nasolabial grooves when salamanders touch the bases of these grooves to objects (nose tapping). Males may locate and identify potential mates through nose tapping during the prolonged breeding season that lasts from October through May. We compared vomeronasal organ data through multiple regression by using total body size, sex, and season as variables that may influence vomeronasal organ volume. Gonads also were examined as an indicator of reproductive status. Total body size and sex significantly affect vomeronasal organ volume; as body size increases, so does vomeronasal organ volume, and males have significantly larger vomeronasal organs than females at all times of the year. During the summer, both males and females have larger vomeronasal organs than at any other time of the year. Summer also is a period of intense foraging and the initiation of a new cycle of gametogenesis. Previous studies of circulating hormone levels in amphibians have shown that the initial stages of gametogenesis correspond to a period of low estradiol and testosterone levels but high gonadotropin-releasing hormone levels. The functional significance of sexual and seasonal differences in the vomeronasal organs of P. cinereus may relate to the neurogenesis of specialized receptors for courtship and mating. o 1995 WiIey-Liss, Inc.

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Seasonal variations in spermatogenesis, testicular weights, vasa deferentia, and androgen levels in neotenic male tiger salamanders, Ambystoma tigrinum

Cited by 43 publications

References 17 publications

Ambiguities in the relationship between gonadal steroids and reproduction in axolotls (Ambystoma mexicanum)

Ambiguities in the relationship between gonadal steroids and reproduction in axolotls (Ambystoma mexicanum)

Ultrastructure and lectin cytochemistry of the cloacal ventral glands in the male newtTriturus marmoratus marmoratus

Sexual and seasonal differences in the vomeronasal epithelium of the red‐backed salamander (Plethodon cinereus)

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