Meeting Abstract
P2.57 Jan. 5 Individual variation and plasticity in egg size in multicolored Asian lady beetles (Harmonia axyridis). PREVOLSEK, Jaime; WILLIAMS, Tony, D*; Simon Fraser University, Burnaby; Simon Fraser University, Burnaby tdwillia@sfu.ca
Evolutionary theory predicts that individual females of iteroparous species should be selected for flexibility in egg (propagule) size such that they can adjust egg size to prevailing conditions or heterogeneous environments; however in at least some oviparous vertebrates (e.g. birds) egg size appears to be relatively inflexible within individuals (Christians 2002). To what extent is this true in other taxa? In insects, as with birds, advances in theory have substantially outpaced empirical data with regard to evolution of progeny size (Fox and Czesak 2000). We investigated inter-individual variation and intra-individual plasticity of egg size in the multicolored Asian lady beetle (Harmonia axyridis). Mean egg mass was 0.246 � 0.019 mg and means clutch size was 21 � 7 eggs. Body mass explained individual variation in total clutch mass (r = 0.46) and clutch size (r = 0.39) but was only weakly related to variation in egg size (r = 0.25). For a given average clutch mass (i.e. total reproductive effort) of 5.4 – 5.7 mg, mean egg size varied from 0.196 � 0.278 mg (by 41%) among individual females. Thus a female�s �decision� on the size of eggs laid had significant effects on her fecundity: �small egg� females laid c.30 eggs whereas �large egg� females laid only c.20 eggs for the same total clutch mass. To investigate intra-individual plasticity in egg size we allowed mated, individual female lady beetles to lay eggs successively on three different experimentally manipulated resource levels (aphid food supply). We will present data on within-individual variability in egg size, clutch size and total clutch mass in relation to resource level. Our prediction is that, contrary to theoretical predictions, individual females have a limited ability to adjust egg size to prevailing conditions.
