Oogenesis and Ovarian Histology in Two Populations of the Viviparous Lizard Sceloporus grammicus (Squamata: Phrynosomatidae) From the Central Mexican Plateau Abraham Lozano, 1,2 * Aurelio Ram  ırez-Bautista, 1 and Mari Carmen Uribe 3 1 Laboratorio de Ecolog  ıa de Poblaciones, Centro de Investigaciones Biol ogicas, Universidad Aut onoma del Estado de Hidalgo, A.P. 1-69 Plaza Ju arez, C.P. 42001, Pachuca, Hidalgo, M exico 2 CIIDIR Unidad Durango, Instituto Polit ecnico Nacional, Sigma 119, Fraccionamiento 20 de Noviembre II, Durango, Durango 34220, M exico 3 Laboratorio de Biolog  ıa de la Reproducci on Animal, Departamento de Biolog  ıa Comparada, Facultad de Ciencias, Universidad Nacional Aut onoma de M exico, 04510 M exico D.F., M exico ABSTRACT The annual histological changes in ovar- ian morphology (oogenesis, follicular atresia, and cor- pus luteum) are described for the Mexican lizard Sceloporus grammicus, in two populations that inhabit contrasting environments (vegetation categories, cli- mate, precipitation, and temperature) from Hidalgo State, Mexico. Two germinal beds were situated on the dorsal surface of each ovary of this species. In both the populations, oogenesis involves two major processes: previtellogenesis and vitellogenesis. The histological changes during previtellogenesis are similar to those for other reptilian sauropsids, whereas vitellogenesis differs and the features of this last process are described for the first time. In early previtellogenesis, primary oocytes have fibrillar chromosomes and the ooplasm stains slightly. The primordial follicles are sur- rounded by a granulosa composed of cuboidal follicular cells. During late previtellogenesis, the oocyte had an eccentric nucleus with lamp-brush chromosomes and multiple nucleoli. The granulosa becomes multilayered and polymorphic, containing three cell types: small, intermediate, and pyriform. The zona pellucida was homogeneous and clearly observed. In early vitellogen- esis, the oocyte showed several small acidophilic gran- ules distributed in the center and the periphery of the oocyte. As vitellogenesis progresses, the yolk platelets move toward the central area of the oocyte and they fuse to form acidophilic and homogeneous yolk. Lipid droplets were distributed irregularly in the ooplasm of the oocyte. In Zacualtip an, the results revealed a strong seasonal reproductive activity. Females had vitellogenic follicles from July to September, and preg- nant females were founded from September to March. In Tizayuca, the results showed an unusual pattern of reproductive activity. Females with vitellogenic follicles and pregnant females were found throughout the year, indicating continuous reproduction. We suggest that the observed differences in reproductive activity from these populations indicate adaptative fine tuning in response to local environmental conditions. These results contribute to the knowledge of variation in vitellogenesis and reproductive strategies of this spe- cies and among spiny lizards overall. J. Morphol. 000:000–000, 2014. V C 2014 Wiley Periodicals, Inc. KEY WORDS: Reptilia; folliculogenesis; reproductive cycle; vitellogenesis; geographic variation INTRODUCTION Ovarian follicular growth in reptilian sauropsids, as in all vertebrates is an essential reproductive process of females. Therefore, the identification and definition of morphological changes in the reptilian oocyte (nucleus, ooplasmic components, and storage of yolk), and its peripheral structures (zona pellu- cida, granulosa, and theca) during the female repro- ductive cycle are important for understanding the evolution of oogenesis (Tokarz, 1978; Wallace, 1978; Guraya, 1989). The ovary of reptilian sauropsids changes dra- matically in shape and size according to the stage of the reproductive cycle, and the number and sequence of developmental stages of follicles (Tokarz, 1978; Guraya, 1989). Ovarian germ ele- ments are: 1) oogonia, which are located in germi- nal beds, 2) oocytes, germ cells that initiate meiosis advancing to the diplotene stage of Additional Supporting Information may be found in the online ver- sion of this article. Contract grant sponsors: FOMIX 2012/191908, SEP-PROMEP- 1103.5/03/1130, and CONACYT 313438. *Correspondence to: Abraham Lozano, CIIDIR Unidad Durango, Instituto Polit ecnico Nacional, Sigma 119, Fraccionamiento 20 de Noviembre II, Durango, Durango 34220, M exico. E-mail: abraham.lozano.m@gmail.com Received 18 October 2013; Revised 5 February 2014; Accepted 27 February 2014. Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jmor.20275 V C 2014 WILEY PERIODICALS, INC. JOURNAL OF MORPHOLOGY 00:00–00 (2014)