Into a box interiors: clutch size variation and resource allocation in the European pond turtle

Abstract

In order to highlight the temporal dynamics of different stages of follicula distribution on reproductive output, we analysed the female size and the reproductive frequency of the European pond turtle, Emys orbicularis, using 191 ultrasonographic and 67 x-ray images (collected from 2000 to 2011 in two different localities of a coastal plain area of NorthWestern Italy). To compare digital image results we also used anatomical topography of autopsied females. Although reproductive females were significantly longer in one locality and larger in the second one, clutch size did not differ between localities. Two main clutches were produced during a year, with occasionally a third one. Shelled eggs were frequent in May, June and July, while follicula were present till August, with a decrease in follicular size especially in July and August. Despite the presence of a number of follicles in late summer and in autumn, a third expected clutch was only an exceptional event, differently from what happens in other sites of the species’ distribution range. The permanence of follicles after the last deposition is interpreted as a possible extra energy source during the very hot and dry summers of coastal central Italy and for the hibernating phase.