YEAR-LONG ULTRASONOGRAPHIC OBSERVATION OF FOLLICULAR FEATURES IN CAPTIVE YELLOW-MARGINED BOX TURTLES (CUORA FLAVOMARGINATA) FROM TAIWAN

Ultrasonography is widely used to examine reproductive systems in chelonians. Previous studies have described how follicular size is associated with the reproductive stages of yellow-margined box turtles (YMBTs), but our understanding of follicular morphology remains limited. This study describes the different ultrasonographic appearances of preovulatory follicles of these turtles in Taiwan. Randomly selected 28 adult captive female turtles were examined under ultrasonography, weekly from November 2012 to November 2013. The females were divided into ovulatory and non-ovulatory groups with equal number coincidentally based on the whole-year ovulation records. The ovulatory group had significantly larger follicles than the non-ovulatory group (average size of largest follicle, [Formula: see text][Formula: see text]mm versus [Formula: see text][Formula: see text]mm; [Formula: see text]). Across both groups, preovulatory follicles exhibited five different morphologies: previtellogenic, homogeneous, heterogeneous, atretic, and multilayered. The multilayered follicles were only observed in the ovulatory group during the late preovulatory (February) and early ovulatory periods (March), resulting in a significant correlation with ovulatory stage ([Formula: see text]). During the preovulatory period (from December to February), homogeneous follicles were the predominant follicles in both groups. During the ovulation period, heterogeneous follicles were the main follicles, but only in the ovulatory group. Finally, atretic follicles were predominant in the non-ovulatory group during the early latent period (August). This study provides detailed ultrasonographic data clarifying the correlation between turtle follicular morphology and reproductive cycle. A better understanding of how such morphology is associated with reproductive stages should improve breeding programs in zoos and thus facilitate conservation efforts.