Locomotor impairment of gravid lizards: is the burden physical or physiological?
Article first published online: 25 DEC 2001
Journal of Evolutionary Biology
Volume 13, Issue 2, pages 263–268, March 2000
How to Cite
Olsson, Shine and Bak-Olsson (2000), Locomotor impairment of gravid lizards: is the burden physical or physiological?. Journal of Evolutionary Biology, 13: 263–268. doi: 10.1046/j.1420-9101.2000.00162.x
- Issue published online: 25 DEC 2001
- Article first published online: 25 DEC 2001
- costs of reproduction;
- locomotor impairment;
- Niveoscincus microlepidotus;
- physiological exhaustion
Pregnancy is associated with reduced locomotor performance in several reptile species, but the reasons for this reduction remain unclear. Previous authors generally have assumed that the decreased maternal mobility is due to the physical burden of the clutch, but our data on a viviparous Tasmanian scincid lizard (Niveoscincus microlepidotum) suggest a different interpretation. Running speeds of gravid female skinks decrease during gestation (as litter mass increases), but this locomotor impairment is due to physiological changes associated with pregnancy, rather than simple physical burdening. Maternal running speeds are unrelated to litter masses, and do not increase in the week after parturition. Females with very large abdominal fat-bodies (due to ad libitum feeding in the laboratory), equivalent in mass to the litter, nonetheless run rapidly. If the locomotor ‘costs’ of reproduction reflect all-or-none physiological changes associated with pregnancy, then the magnitude of such costs may correlate only weakly with the actual level of reproductive investment. Because life-history models predict that the relationship between fecundity and ‘cost’ has important evolutionary consequences, our results highlight the need to clarify the causal basis for locomotor impairment in gravid reptiles.