Bone growth and age in Rana saharica, a water frog living in a desert environment

The structure and the histological. expression of annual bone growth marks of Moroccan water frogs (Rana saharica) from an arid climate region (northe rn edge of the Sahara desert) differ from the pattern observed in water fro gs from temperate climate regions. At early ages, when growing rates are hi gh, the osteogenic activity of the froglets never stops completely, and dur ing the resting period the histological marks formed in the bone are mostly annuli. However, growth marks formed in older individuals are mostly well defined thin LAGs, which correspond to a complete stop in of osteogenesis. Males and females mature when they are two years old. The oldest males and females were six years old. One-year-old froglets showed a wide range in bo dy size (22.4 to 40.9 mm) associated with an extended period of metamorphos is. Considering LAG diameter as the diameter of the phalange at a given age , we obtained successive phalange diameters for each individual correspondi ng to each year of its life. The diameter of the LAG1 of adults of Rana sah arica is significantly larger than the diameter of the LAG1 of one year old juveniles. We found similar results studying the tibiofibulae of the siste r taxon of R. saharica, Ii. perezi. Larger froglets were thus more successf ul than smaller ones in generating the adult samples suggesting the existen ce of size mediated selection. Extended breeding periods, which allow vario us metamorphosis peaks along the year, would be apparently disadvantageous for the species, since only froglets of a few subcohorts would be able to s urvive. However, this strategy could be of importance in Mediterranean and desert areas where local conditions change dramatically from year to year.