Parental effects in orb-web spiders of the genus Argiope (Araneae: Araneidae)

Non-genetic factors act in parallel to genetic factors to shape offspring phenotype.The magnitude of inherited genetic and non-genetic factors and the interaction between them determines the susceptibility and direction of selection on different life-history traits. In this thesis, I explored the adaptive parental effects mediating reproductive output and offspring quality in the orb-web spider genus, Argiope spp.First, I assessed the effect of predation as an environmental factor on the physiology and foraging behaviour of Argiope spiders. Then I tested the effects of parental physiological traits, i.e. resting metabolic rate (RMR), age and condition on reproductive output and offspring performance. Finally, I addressed the importance of additive genetic effects and heritability of different life-history traits in offspring. The results revealed that exposure to predation risk altered the foraging behaviour and significantly elevated RMR in the spider. RMR was not correlated with reproductive output or offspring quality, however, female spiders reduced their RMR after mating. This can be an adaptive response for female spiders at the onset of the egg producing process to mediate self-maintenance costs and to allow the allocation of more resources to reproduction. Temporal variation of maternal effects showed that egg sacs laid early in life were larger and offspring emerged with larger body size, however these spiderlings were less tolerant to starvation than spiderlings produced later in the season. This is possibly due to increase in egg size with maternal age. Testing the effect of condition revealed that maternal and paternal condition had asymmetrical effects on egg sac mass. There was also a trade-off between offspring body size and their tolerance to starvation. Analysing half-sib spiderlings showed that egg size and web hub size were heritable traits, suggesting these traits are less plastic and subjected more to selection than other traits. These findings provide insight into the adaptive parental effects, which may have long lasting impact on internal state and behaviour of offspring and hence population dynamics.