Germinal bed condition in a polyautochronic single-clutched lizard, Bassiana duperreyi (Scincidae)

In lizards, the eggs are produced within small regions of the ovary known as germinal beds (GBs); previous literature suggests that the number of GBs per ovary may be linked to life-history traits such as clutch size and breeding frequency. In the oviparous montane Australian skink Bassiana duperreyi, females produce a single clutch of 3 to 11 eggs each year. Our histological examination of ovaries of this species revealed a single GB per ovary. In combination with previous studies, our results suggest that scincid lizards may offer ideal model systems to explore the functional link between ovarian morphology and life-history traits in lizards. All female reptiles possess a pair of ovaries attached to the dorsal body wall, but the massive interspecific variation in clutch sizes among lizards (Fitch, 1970) is reflected in significant variation in ovarian morphology. The number of eggs that an ovary can produce per clutch is controlled by (1) the number of germinal beds (GBs) per ovary, (2) the total number of follicles per GB, and (3) the proportion of follicles that become vitellogenic (Jones et al., 1982). The germinal bed is a small region on the dorsal ovarian surface consisting of dividing oogonia, naked oocytes and primordial follicles (Jones et al., 1982; Klosterman, 1983; Shanbhag, 2002; Gúmez and Ramìrez-Pinilla, 2004). Oogonia and oocytes are restricted to the GB, and growing follicles emanate from it. The number of GBs per ovary ranges from one to six among the lizard species studied to date (Jones et al., 1982; Jones and Summers, 1984; Shanbhag and Prasad, 1993; Uribe et al., 1995; Shanbhag et al., 1998; Amey and Whittier, 2000; Stewart and Florian, 2000; Sica et al., 2001). Previous studies not only have revealed substantial interspecific variation in GB number within lizards, but also suggest broad patterns. For example, most species with allochronic reproduction (ovulating a single egg from each School of Biological Sciences A08, University of Sydney, NSW 2006, Australia ∗Corresponding author; e-mail: [email protected] ovary alternatively) and monoautochronic reproduction (ovulating a single egg from both ovaries simultaneously) seem to exhibit only one GB per ovary. However, some lizards that ovulate only a single egg from each ovary, nonetheless possess two GBs per ovary (Wilhoft, 1963) or possess one GB but ovulate many eggs per ovary (Jones et al., 1982). The diversity is even greater among polyautochronic lizards (those that ovulate several eggs simultaneously from both ovaries: Jones et al., 1982). Lizards with high fecundity (large clutches and/or multiple clutches within a single breeding season) usually exhibit two GBs, while those producing smaller clutches possess only one GB (Jones et