Abstract:
INTRODUCTION : A changing environment can select on life-history traits and tradeoffs
in a myriad of ways. For example, global warming may shift phenology and
thus the availability of host-plants. This may alter selection on survival and fertility
schedules in herbivorous insects. If selection on life-histories changes, this may
in turn select for altered nutrient intake, because the blend of nutrients
organisms consume helps determine the expression of life-history traits.
However, we lack empirical work testing whether shifts in the timing of
oviposition alter nutrient intake and life-history strategies.
METHODS : We tested in the marula fruit fly, Ceratitis cosyra, how upward-selection
on the age of female oviposition, in comparison with laboratory adapted control
flies, affects the sex-specific relationship between protein and carbohydrate intake
and life-history traits including lifespan, female lifetime egg production and daily
egg production. We then determined the macronutrient ratio consumed when
flies from each selection line and sex were allowed to self-regulate their intake.
RESULTS : Lifespan, lifetime egg production and daily egg production were
optimised at similar protein to carbohydrate (P:C) ratios in flies from both
selection lines. Likewise, females and males of both lines actively defended
similar nutrient intake ratios (control =1:3.6 P:C; upward-selected = 1:3.2 P:C).
DISCUSSION : Our results are comparable to those in non-selected C. cosyra,
where the optima for each trait and the self-selected protein to carbohydrate
ratio observed were nearly identical. The nutrient blend that needs to be ingested for optimal expression of a given trait appeared to be well conserved across
laboratory adapted and experimentally selected populations. These results
suggest that in C. cosyra, nutritional requirements do not respond to a
temporal change in oviposition substrate availability.
