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Gabino A. Rodriguez-Almaraz, Ricardo Gomez-Flores and Jaime Rábago-Castro

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Rosaura Ruiz Gutiérrez, Ricardo Noguera Solano and Juan Manuel Rodriguez Caso

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Benito Fraile, Marina C. Rodriguez, Ricardo Paniagua and Francisco J. Saez


In order to investigate the effects of a moderately high temperature on testicular function in urodele amphibians, marbled newts (Triturus marmoratus) wcrc collected from thc field and killed at the end of each period of their spermategenetic cyle; these were: germ cell proliferation up to round spermatids (June), spermiogenesis (September), and the early (December) and late (March) periods of testicular quiescence. The testes of these animals were studied by light microscopy and compared with those of newts which were killed at the same dates and had been exposed previously to moderately high temperatures (30°C) for 1 or 3 months. The results of quantitative studies indicatc that: (1) exposure to high temperatures (for 3 months but not for 1 month) induces germ cell development up to round spermatids during the early phase of testicular quiescence; (2) this temperature has no effect in the period of germ cell proliferation up to round spermatids; and (3) high temperatures inhibit (exposure for 3 months) or decrease (exposure for I month) spermiogenesis during the spermiogenesis period.

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Alfredo Ortega, Ricardo Rodriguez, Lucina Hernandez and Robert Barbault

The activity cycles of Sceloporus grammicus and Sceloporus scalaris were studied from transect census data during several months of the year in two sympatric mountain populations (2480 m) of Mexico. The two species exhibit very similar cycles, resulting from the harshness of the weather. Using at the best their thermic environment these lizards are able to maintain a mean cloacal temperature around 30°C, even in winter. The potential competition between these two species seems to be highly reduced by habitat segregation, S. grammicus being mainly a trunk-dwelling species while S. scalaris is a ground-dwelling one.

Les cycles journaliers d'activité de Sceloporus grammicus et de Sceloporus scalaris ont été étudiés a différentes saisons dans deux populations d'altitude (2480 m) du nord du Mexique. Les deux espèces présentent des cycles très similaires, qui résultent des fortes contraintes climatiques qu'elles subissent. Exploitant au mieux leur environnement thermique, ces lézards parviennent a conserver, pendant leurs phases d'activité, une température interne proche de 30°C, même en hiver. La coexi¬stence de ces deux espèces potentiellement compétitives est facilitée par une ségrégation spatiale, S. grammicus étant principalement inféodé aux troncs d'arbres tandis que S. scalaris est terricole.