Seasonal and continuous spermatogenesis in the viviparous lizard Sceloporus grammicus, a study of two populations in contrasting environments from the Central Mexican Plateau

The annual histological changes of the seminiferous tubules and anterior testicular ducts were described for the viviparous lizard, Sceloporus grammicus, in two populations inhabiting contrasting environments; relating the reproductive activity of males with temperature, rainfall and photoperiod for each population. Adult males were collected monthly in Zacualtipán and Tizayuca, Hidalgo state, Mexico. Testes and anterior testicular ducts were removed and fixed in formalin, dehydrated in alcohol, embedded in paraffin, sectioned at 5 μm and stained using hematoxylin-eosin. In the Zacualtipán population, the results revealed strong annual variations in stages of the germ cells, and diameter and height of the epithelia of seminiferous tubules, ductuli efferentes and ductus epididymis. In the Tizayuca population, the histological observations of the testis and anterior testicular ducts demonstrated spermiogenesis and spermiation throughout the year, an unusual pattern of reproductive activity, which had not been described previously in any populations of this species. The observed spermatogenesis patterns are not explained by a single environmental factor; but by the local set of environmental cues. In both populations, during spermatogenesis a single population of germ cells developed synchronously, followed by one massive spermiation event, which is characteristic of reptilian species. Our observations show differences between the two populations studied, which might be indicative of plasticity in response to local environmental conditions.