Potential ‘costs of reproduction’ in a skink: Inter- andintrapopulational variation

Reproductive costs are important determinants of reproductive effort in squamate reptiles.Consequently, differences in costs of reproduction between populations of geographically or climatically widespreadspecies are likely to result in different patterns of reproductive effort. In the present study, the effect ofpregnancy on sprint speed was examined in a small viviparous skink, Niveoscincus ocellatus (Gray 1845), from twopopulations at the climatic extremes of its distribution. Decreased sprint speed has the potential to be an importantcost of reproduction in this species, through a reduced ability to avoid predation and/or decreased foragingefficiency. Lizards inhabiting the colder site were larger than those from the warmer site and, contrary to predictionsfrom life history theory, had a higher reproductive effort. In both populations, sprint speed was lowerin pregnant lizards than in either the same individuals after birth or non-pregnant control lizards. Within eachpopulation, sprint speed was unrelated to the level of reproductive effort of the female in terms of either absolutemass of the reproductive burden or the burden relative to her post-partum body mass. However, within eachpopulation, the mass of the clutch that an individual female was carrying relative to snout–vent length wasan important determinant of her sprint speed while pregnant. Thus, within each population, a relatively high reproductiveburden may potentially increase costs of reproduction in this species. Despite this relationship and predictionsfrom life history theory suggesting that annual reproductive effort will be lower in populations with a largebody size and delayed maturity, it is suggested that a higher reproductive effort at the cold site is possible becausethey have a higher absolute sprint speed because of their larger size and a relatively higher abundance of cover atthe cold site, and differences in predation pressure may alter selective pressures on reproductive investment.