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1Interspecific gene flow is pervasive throughout the tree of life. Although detecting 2 gene flow between populations has been facilitated by new analytical approaches, 3 determining the timing and geography of hybridization has remained difficult, 4 particularly for historical gene flow. A geographically explicit phylogenetic 5 approach is needed to determine the ancestral population overlap. In this study, 6 we performed population genetic analyses, species delimitation, simulations, and a 7 recently developed approach of species tree diffusion to infer the phylogeographic 8 history, timing and geographic extent of gene flow in lizards of the Sceloporus 9 spinosus group. The two species in this group, S. spinosus and S. horridus, are 10 distributed in eastern and western portions of Mexico, respectively, but 11 populations of these species are sympatric in the southern Mexican highlands. We 12 generated data consisting of three mitochondrial genes and eight nuclear loci for 13 148 and 68 individuals, respectively. We delimited six lineages in this group, but 14 found strong evidence of mito-nuclear discordance in sympatric populations of S. 15 spinosus and S. horridus owing to mitochondrial introgression. We used 16 coalescent simulations to differentiate ancestral gene flow from secondary contact, 17 but found mixed support for these two models. Bayesian phylogeography 18 indicated more than 60% range overlap between ancestral S. spinosus and S. 19 horridus populations since the time of their divergence. Isolation-migration 20 analyses, however, revealed near-zero levels of gene flow between these ancestral 21 populations. Interpreting results from both simulations and empirical data 22 indicate that despite a long history of sympatry among these two species, gene 23 flow in this group has only recently occurred.24

We describe the gonadal and abdominal fat storage cycles for a population of Caiman crocodilus fuscus kept in captivity at a breeding farm. The reproductive cycles of males and females are clearly seasonal. Vitellogenic follicles were observed in females year-round; however, the follicular growth that produces the preovulatory follicles for the breeding season occurs in November-May (most of the dry season to the beginning of the rainy season). These months correspond with the presence of physiologically reproductive males. Oviposition takes place during the wet season (April-August) and the births occur at the end of this season (September-November). Fat storage was not related to reproductive activity, and did not vary by month or between sexes. Although environmental and hormonal conditions have been improved for these captive animals, they maintain a strongly seasonal reproductive cycle, historically fixed to oviposit in the most favorable period for nest construction and hatching during the rainy season.