Phenotypic Effects of Leptin in an Ectotherm: A New Tool to Study the Evolution of Life Histories

Leptin is the 16 kDa hormone product of the mouse obesity (ob) gene (Halaas et al., 1997). Mice that are homozygous for a mutation of the ob gene (ob/ob) do not produce leptin and, consequently, suffer from obesity and diabetes, with similar effects to those observed in victims of morbid human obesity syndrome (Boston et al., 1997). One of the primary functions of leptin appears to be as a lipostat in the homeostasis of fat stores (adiposity); however, extensive research into obesity has revealed that leptin has many other phenotypic effects. Most are correlated with adiposity, including the regulation of metabolic rate, feeding and activity rates, body temperature and the onset of puberty (Flier, 1997). Interestingly, a correlation between adiposity and the onset of reproduction (puberty) in mammals has long been recognized and a hormonal signal sought (Kennedy and Mitra, 1963; Frisch