In general, chelonians are widely distributed, occupying areas with significant environmental variation, which may lead to great variations in their ecology such as morphological characteristics, sexual dimorphism, population structure, and reproductive aspects. In this context, our main objective was to characterize populations of Phrynops geoffroanus and Mesoclemmys tuberculata in areas of Caatinga and Atlantic Forest in Northeast Brazil to evaluate the relative importance of intraspecific factors and environmental differences in determining ecological parameters. Samples were collected in semiannual surveys (dry and rainy season) over a year. We measured morphometric variables and the mass of captured animals and correlated the reproductive pattern with the season and adults' reproductive condition. We did not find significant differences in size, maximum straight-line carapace length (SCL), or body mass of both species, regardless of sex, between the studied environments. We recorded reproductive males of both species throughout the year (dry and rainy seasons), and testicular volume was positively correlated with SCL. In contrast, eggs and oocytes were recorded exclusively in females collected during the rainy season. However, we found eggs and vitellogenic follicles simultaneously, indicative of multiple clutches in a reproductive season. In P. geoffroanus, we did not find a significant relationship between clutch size and female SCL, although egg volume was positively correlated with SCL. In M. tuberculata, we did not find a meaningful relationship between any of these parameters. Finally, the ecological parameters evaluated differed considerably between species and environments, presenting similar patterns in Caatinga and Atlantic Forest.

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