Annual Variation in Reproductive Cycles of Scincid Lizards (Ctenotus) in Central Australia

Abstract

Reproductive cycles of seven species of syntopic Ctenotus (Reptilia: Scincidae) were examined through mark-recapture studies of 2,727 lizards over three years (1985-88) on an arid spinifex-grassland site near Alice Springs in central Australia, supplemented with data from dissection of 1,465 museum specimens. Timing of reproduction based on dissection of museum samples varied only slightly between species. Ctenotus brooksi and C. pantherinus laid eggs three to four weeks earlier in spring (September) and summer (January) than did other species. A double-pulse of egg production (one clutch in November and one in January) suggested that some females may produce two clutches per activity season, but there was no direct evidence of multiple clutching by individual females from either the museum dissections or the mark-recapture field studies. Oviposition was spread over two months in spring and two months in summer so that at any one time the proportion of mature females that were reproductive was low. Adult females grew larger than males in most species, and the sex ratio was male-biased in all but one species (C. pantherinus). Reproductive output varied greatly between years in the field studies and correlated with hydric conditions of the environment. Generally, reproductive activity was low in the first and third years of the study (dry years) and high in the second year of the study after winter and spring rainfall. Ctenotus pantherinus did not follow this pattern and had a similar level of reproductive output in the first two years. Clutch and egg size increased with maternal size across most species. Clutch sizes of C. pantherinus were significantly larger than the clutch sizes of the other species, and egg sizes of C. leonhardii were larger than the egg sizes of other species, after correction for the relative body sizes. Age and size at maturity differed between species (and between years within a species). The largest species, C. pantherinus, grew fastest and matured within 11 months after hatching, as did the small-bodied species C. piankai. Other species matured at 12 to 18 months of age. Life-history variables and timing of reproduction were similar for both the field population and the broad patterns identified in the museum collections. Interspecific comparisons revealed one species (C. pantherinus) to be different from the other species in its life-history variables and responses to environmental conditions. Reproductive activity was greatly influenced by rainfall, and the low recruitment in average and dry years suggested that successful reproduction may be rare in central Australian Ctenotus.