Parallel geographic variation in body shape and reproductive life history within the Australian scincid lizard Lampropholis delicata

1. Interspecific comparisons suggest that lizard life history and morphology coevolve and that reproductive output may be constrained by morphology. However, the interplay between morphology and life-history characteristics remains poorly investigated in intraspecific comparisons. We studied variation in body shape (relative interlimb length) and reproductive life-history characteristics along a latitudinal gradient of populations of Lampropholis delicata, a small oviparous Australian scincid lizard, to examine whether reproductive expenditure is correlated with body shape. 2. Our analyses revealed considerable geographic variation in mean body size, body shape and reproductive life history. The variation in reproductive traits (i.e. clutch size, egg size, clutch volume and relative clutch volume) was not a simple consequence of variation in body size among populations. Mean clutch size and mean egg size were equally variable among populations. 3. Latitude accounted for approximately 30% of the variance in life-history phenotypes among populations, presumably mediated by differences in climate. Overall, lizards in southern populations tended to mature at a smaller size, have larger interlimb lengths as adults and produce clutches with more and larger eggs, as compared to lizards in northern populations. 4. Our results suggest a trade-off between the number and the size of offspring within but not among populations. Lizards in southern populations were able to produce larger eggs, without a concomitant reduction in clutch size, because adults were larger in absolute terms, and they had larger abdominal volumes relative to body size. 5. Relative interlimb length accounted for 71% of the variance in relative clutch volume among populations. This positive correlation between body shape and relative clutch volume may have arisen because: (1) body shape constrains reproductive expenditure below optimal levels or (2) body shape has itself evolved to allow optimal levels of reproductive expenditure, as determined by life-history trade-offs.