The adaptive significance of maternal effects : a study of two geographically distinct populations of the spotted snow skink, Niveoscincus ocellatus
thesisposted on 2023-05-28, 00:09 authored by Hall, AJ
I manipulated basking opportunity and circulating blood plasma corticosterone levels in gravid female Niveoscincus ocellatus and their offspring to investigate the relative importance of genetic, environmental and postnatal effects on offspring fitness. In this way, the potential of maternal effects to produce fitness enhancing traits in offspring from two geographically distinct populations were explored. In the first experiment, females were collected from their natural population (Orford on the East Coast and Miena on the Central Plateau) shortly after ovulation and were maintained in twelve and four hour basking treatments throughout gestation. Both populations responded to increased basking opportunity in the same way, by giving birth earlier and producing significantly larger offspring with significantly slower sprint speeds compared to offspring from mothers maintained in four hour basking treatments. The absence of genetic x environment interactions indicate populations are genetically similar and maternal basking opportunity alone is sufficient to generate many of the phenotypic differences observed in natural populations of N. ocellatus. Further, populations differed significantly in thermal sensitivity of offspring growth rate. Growth rate of Orford offspring was not affected by maternal or postnatal basking opportunity, however, Miena offspring were significantly affected by both maternal and offspring basking opportunity. Male biased sex ratios were also observed in Orford females with limited basking opportunity, but there was no effect of maternal thermal treatment on offspring sex in the Miena population. In a second experiment, corticosterone treatment of gravid females differentially affected Orford and Lake Mackenzie offspring. No effects (or sex-specific effects) on offspring phenotypes were detected, however, male biased sex ratios were observed in Orford females treated with corticosterone and Lake Mackenzie females in both corticosterone and control treatments produced a larger proportion of unviable offspring compared to Orford females. Maternal and offspring corticosterone treatment had no effect on growth rates of offspring from Orford, however corticosterone treated offspring from Lake Mackenzie showed a significant decrease in growth rate. These results indicate that maternal effects are responsible for generating many of the observed phenotypic differences and subsequent life history traits between populations in N. ocellatus, and potentially other taxa, and further, populations show a difference in degree of control over maternally affected traits. This research highlights the ecological end evolutionary significance of maternal effects in generating phenotypic traits in offspring that are adapted to local environmental conditions.
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