Evaluation of offspring size-number invariants in 12 species of lizard.

The optimal division of resources into offspring size vs. number is one of the classic problems in life-history evolution. Importantly, models that take into account the discrete nature of resource division at low clutch sizes suggest that the variance in offspring size should decline with increasing clutch size according to an invariant relationship. We tested this prediction in 12 species of lizard with small clutch sizes. Contrary to expectations, not all species showed a negative relationship between variance in offspring size and clutch size, and the pattern significantly deviated from quantitative predictions in five of the 12 species. We suggest that the main limitation of current size-number models for small clutch sizes is that they rely on assumptions of hierarchical allocation strategies with independence between allocation decisions. Indeed, selection may favour alternative mechanisms of reproductive allocation that avoid suboptimal allocation imposed by the indivisible fraction at low clutch sizes.

11-Ketotestosterone induces silvering-related changes in immature female short-finned eels, Anguilla australis.

The developmental transition from a residential, immature 'yellow' eel to a migratory, maturing adult 'silver' eel is accompanied by many morphological changes that appear to be under endocrine control. High circulating levels of the teleost, and usually male-specific, androgen 11-ketotestosterone (11-KT) are found in migrating female short-finned eels, Anguilla australis. We examined the role of this steroid in silvering by implanting immature, female short-finned eels either with blank vehicles or with vehicles containing 11-KT. Six weeks after they had received the implants, eels treated with 11-KT had developed 'chisel-shaped' snouts and black pectoral fins with tapered ends, and the size of their eyes had increased significantly. 11-KT treated eels had a thicker dermis than control eels and an epidermis with fewer or no mucous cells. Ventricular mass at the end of the experiment was two-fold larger than in control eels. 11-KT treated eels also had larger livers and gonads. Ovaries contained predominantly cortical alveolus stage III oocytes, as opposed to the smaller gonads of control eels containing previtellogenic stage II oocytes. All of these changes correspond to changes during the developmental transition from yellow to silver eels in the wild. This demonstrates that silvering in eels is under endocrine control and that the presumed male-specific steroid 11-KT is capable of inducing silvering-related changes in a female teleost. We discuss how species-specific responses to 11-KT may differ depending on tissue-specific androgen receptor abundance and how a dual demand on liver function can explain the apparently positive effects of 11-KT on liver growth.