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If the speed of CHC development was only limited by
metabolism and solely related to the role of CHCs in
preventing desiccation, it is still unclear why CHC maturation
would coincide so closely with sexual maturity and take as
long as 11 days in Ch. varipes. Individuals of this species
become highly active and disperse within ~ 48 h of eclosion
(Norris 1959), at which point flies without a mature CHC
profile would be at severe risk of desiccation. It might, therefore,
be expected that to prevent desiccation, ecological selection
would drive CHC profiles to mature as quickly as possible.
Furthermore, it is known that the CHC profiles of
Drosophila species mature in ~ 48 h (Arienti et al. 2010)
and males of the blowfly C. vomitoria in ~ 48 h (Trabalon
et al. 1992). As such, there is no clear physiological reason
for CHC development being so prolonged in Ch. varipes. To
further ascertain the roles of ecological and sexual selection in
maintaining the relationship between CHC development and
sexual maturity, there is a need to assess the biochemical and
genetic underpinnings of CHC development in species such as
Ch. varipes in comparison to other blowflies, such as
C. vomitoria, which show more rapid CHC development.
Lastly, the different rates of CHC development between the
sexes are most likely due to inherent ontogenetic and hormonal
differences; male flies tend to reach sexual maturity earlier
than females (Arienti et al. 2010; Mackerras 1933). However,
it may also be explained by ecological selection; it is possible
that one sex disperses earlier or over greater distances in
search of reproductive resources or mates. Subsequently,
CHCs may have evolved to develop quicker in that sex in
order to accommodate earlier exposure to desiccation stress
during dispersal. A fascinating example of such environmentally
driven sexual dimorphism is seen in Habronattus
jumping spiders, where male-specific body colouration occurs
as an anti-predator adaptation in response to males having
increased activity levels and a higher resulting threat of predation
during mate-searching (Taylor et al. 2019).
To summarise, we report that the development of CHCs in
Ch. varipes is substantially delayed following adult eclosion
and that the major changes in adult CHC expression coincide
with the onset of sexual maturity, which differs between the
sexes. In addition, in line with many other insect species,
there is a negative relationship between increasing adult age
and the chain length of expressed CHCs. However, it is unclear
whether these patterns are the result of ecological or
sexual selection or simply an inherent effect of ontogenetic
hormonal and metabolic changes. Additional behavioural
bioassays could conclude whether these CHC changes signal
sexual maturity. Much would be gained from also explicitly
measuring how CHC expression changes in line with development
of male and female reproductive organs, and how this
corresponds with the onset of reproductive viability. Such
further research in Ch. varipes, and in other insects, will serve
to unravel the role CHCs play in signalling sexual maturity.
Overall, the age-related changes we report in Ch. varipes are
some of the most striking known examples of shifts in adult
CHC profiles among insects, and this species will likely serve
as an ideal model for unravelling the complex ontogeny of
cuticular hydrocarbon expression in insects.