Offspring emergence
Pupae assigned for emergence studies were placed singly into 50 ml
falcon tubes with a 3 mm hole drilled in the centre of the screw cap to
allow air flow. Tubes were given individual identification numbers and
also labelled with the identification number of the mother. Pupae were
observed daily for date of emergence on working days and again video
recordings were used to determine the date of emergence on weekends.
Pupae were observed for a maximum of 50 days. Any pupae that had not
emerged by 50 days, were recorded as a failed emergence (Hargrove 2004).
Each emerging fly remained in the tube until it died of starvation. Sex
of emerging flies and date of death were recorded. By measuring how long
a fly survived starvation, we indirectly quantified the impact of
maternal investment without any effect of offspring feeding. This is an
ecologically relevant measure as in natural conditions the newly emerged
fly is likely to be most vulnerable to mortality from failure to find a
blood meal. Therefore, the energy reserves it has available to find a
host before starvation is a key fitness trait.