Sexual dimorphism and sexual selection in a montane scincid lizard (Eulamprus leuraensis)

Abstract

Sex-based divergences in body sizes and/or shapes within a species imply that selective forces act differently on morphological features in males versus females. That prediction can be tested with data on the relationship between morphology and reproductive output in females, and between morphology and realized paternity (based on genetic assignment tests) in males. In a sample of 81 field-collected adult Blue Mountains water skinks (Eulamprus leuraensis), males and females averaged similar overall body sizes (snout-vent lengths (SVLs)). Reproductive success (based on 105 progeny produced by the females) increased with SVL at similar rates in both sexes (as expected from the lack of sexual size dimorphism). Multiple paternity was common. Males had larger heads than females of the same body size, and (as predicted) reproductive success increased with relative head size in males but not in females. Males also had relatively longer limbs and shorter trunks than females, but we did not detect significant sex differences in selection on those traits. Reproductive success in both sexes was increased by relatively longer hind limbs. Our data clarify mating systems in this endangered species, and suggest that mating systems are diverse within the genus Eulamprus.

Population demography of an endangered lizard, the Blue Mountains Water Skink

“…Our skeletochronological estimates of age (= n LAGs – 1) agree well with those predicted (based on body size) by the Von Bertalanffy function fitted to our mark-recapture data (Figure 1). Born at approximately 30 mm snout-vent length and weighing 0.7 g [14], these lizards attained maturation at SVLs of about 70 mm SVL and 7 g (this study; [13]) within two to three years (Figure 1). Growth slowed thereafter, eliminating any correlation between age and body size in lizards that were more than three years of age (Figure 1).…”

“…Most of the lizards in our study population may live to reproduce only once or twice before dying. The mean age of males that sired offspring (based on paternity analyses from Dubey et al [13]) was 2.88 years (N = 18; varying from one to five) and the mean age of adult males (i.e., > 52 mm SVL) for which juveniles were not assigned was 2.25 years (N = 16; from two to six). The mean age of females that produced litters was 3.00 years (N = 38; from two to six years old) whereas three adult (SVL > 66 mm) but nonreproductive females averaged 1.33 years of age (from one to two).…”

“…Offspring mass and litter size are similar in the two species. However, the proportion of females reproducing is higher in E. leuraensis than in E. tympanum (91% versus 30 to 60%, respectively; [13,19]).…”

“…Gene flow between populations is very limited, and animals within each of the two major parts of the species’ distribution (Blue Mountains versus Newnes Plateau) have been isolated from each other for at least a million years [11,12]. In addition, this species has low annual fecundity (one to five neonates per annual litter; [13,14]), further reducing the ability of populations to recover from the effects of episodes of higher-than-usual mortality [15,16]. …”

“…As well as clarifying basic issues such as growth rates and age at maturity, we took advantage of data from our earlier studies to explore the effects of maternal age on reproductive output and progeny quality (based on data from Dubey et al , [13] and Dubey & Shine, [14]) and to compare population age structure to various site-specific parameters (including indices of genetic diversity from Dubey & Shine, [11,12]).…”