Abstract:
In insects, lifespan and reproduction are strongly associated with nutrition. The ratio
and amount of nutrients individuals consume affect their life expectancy and reproductive
investment. The geometric framework (GF) enables us to explore how animals
regulate their intake of multiple nutrients simultaneously and determine how these
nutrients interact to affect life-history
traits of interest. Studies using the GF on host-generalist
tephritid flies have highlighted trade-offs
between longevity and reproductive
effort in females, mediated by the protein-to-
carbohydrate
(P:C) ratio that
individuals consume. Here, we tested how P and C intake affect lifespan (LS) in both
sexes, and female lifetime (LEP), and daily (DEP) egg production, in Ceratitis cosyra, a
host-specialist
tephritid fly. We then determined the P:C ratio that C. cosyra defends
when offered a choice of foods. Female LS was optimized at a 0:1 P:C ratio, whereas
to maximize their fecundity, females needed to consume a higher P:C ratio (LEP = 1:6
P:C; DEP = 1:2.5 P:C). In males, LS was also optimized at a low P:C ratio of 1:10.
However, when given the opportunity to regulate their intake, both sexes actively
defended a 1:3 P:C ratio, which is closer to the target for DEP than either LS or LEP.
Our results show that female C. cosyra experienced a moderate trade-off
between LS
and fecundity. Moreover, the diets that maximized expression of LEP and DEP were of
lower P:C ratio than those required for optimal expression of these traits in host-generalist
tephritids or other generalist insects.
