Facultative sex allocation in snow skink lizards (Niveoscincus microlepidotus)

Abstract

Mathematical models suggest that reproducing females may benefit by facultatively adjusting their relative investment into sons vs. daughters, in response to population‐wide shifts in operational sex ratio (OSR). Our field studies on viviparous alpine skinks (Niveoscincus microlepidotus) document such a case, whereby among‐ and within‐year shifts in OSR were followed by shifts in sex allocation. When adult males were relatively scarce, females produced male‐biased litters and larger sons than daughters. The reverse was true when adult males were relatively more common. That is, females that were courted and mated by few males produced mainly sons (and these were larger than daughters), whereas females that were courted and mated by many males produced mainly daughters (and these were larger than sons). Maternal body size and condition also covaried with sex allocation, and the shifting pattern of sexual size dimorphism at birth may reflect these correlated effects rather than a discrete component of an evolved sex‐allocation strategy.

Maternal basking behaviour determines offspring sex in a viviparous reptile

“…Mathematical models predict that natural selection will stabilize population sex ratios to 1 : 1 (Fisher 1930), as was the case for overall offspring sex ratios in our natural population. However, adaptive shifts in individual female allocation patterns are now well established (Trivers & Willard 1973), including in a congeneric species of snow skink (Olsson & Shine 2001). The benefit of facultative sex-ratio adjustment may relate to sex differences in the importance of adult body size for reproductive success.…”

Sex ratios

“…However, recent studies of taxa with CSD (mammals, birds, frogs, lizards, snakes, spiders) have reported shifts in offspring sex ratios consistent with adaptation (Madsen and Shine, 1992;Komdeur et al, 1997;Creel et al, 1998;Sheldon, 1998;Kruuk et al, 1999;Nager et al, 1999;Sheldon et al, 1999;Aviles et al, 2000;Sakisaka et al, 2000;Olsson and Shine, 2001). Furthermore, in some of these cases individuals appear to show extremely precise control of their offspring sex ratio.…”

Temperature-Dependent Sex Determination in Vertebrates

“…Facultative sex allocation of offspring appears to occur in several species of skink, and TSD is one of several possible mechanisms that may allow a female to "choose" the sex of her offspring in these species. Olsson and Shine (2001) found that the Australian snow skink Niveoscincus microlepidotus can produce male-biased litters in years when adult males are scarce, while the reverse was true in years when adult males were relatively more common than adult females.…”