Is the Adipostatic Signalling Function of Leptin Conserved in Seasonal Vertebrates? A Systematic Narrative Review

Using a systematic approach, this review investigates whether the adipostatic signalling function of leptin is conserved across the vertebrate taxa (mammals, birds, reptiles and fish), with a focus on seasonally reproducing species. Of the 49 studies analysed, only nine investigated sub-eutherian mammals (monotreme, n = 1; marsupials, n = 0 birds, n = 4; reptiles n = 2 and fish, n = 2); therefore, it was not possible to draw solid conclusions for these taxa. Nevertheless, the evidence collated in this review appears to suggest that an adipostatic function of leptin is absent in avian fish species. Further investigation is required for sub-eutherian and reptilian species as the presented results were inconclusive. Twenty-five species of eutherian mammals were investigated across 40 studies. The adipostatic signalling function of leptin was not observed in all eutherian species, leading to the suggestion of species-specific functionality which may extend to sub-eutherian mammals and reptiles. Further research is necessary across a variety of species of all taxa to confirm whether or not the adipostatic function of leptin is confined to therian mammals.