Age, sex, adult and larval diet shape starvation resistance in the Mediterranean fruit fly: an ecological and gerontological perspective.

The ability of an animal to withstand periods of food deprivation is a key driver of invasion success (biodiversity), adaptation to new conditions, and a crucial determinant of senescence in populations. Starvation resistance (SR) is a highly plastic trait and varies in relation to environmental and genetic variables. However, beyond Drosophila, SR has been studied poorly. Exploiting an interesting model species in invasion and ageing studies-the Mediterranean fruit fly (Ceratitis capitata)- we investigated how age, food and gender, shape SR in this species. We measured SR in adults feeding in rich and poor dietary conditions, which had been reared either on natural hosts or artificial larval diet, for every single day across their lifespan. We defined which factor is the most significant determinant of SR and we explored potential links between SR and ageing. We found that SR declines with age, and that age-specific patterns are shaped in relation to adult and larval diet. Females exhibited higher SR than males. Age and adult diet were the most significant determinants of SR, followed by gender and the larval diet. Starvation resistance proved to be a weak predictor of functional ageing. Possible underlying mechanisms, ecological and gerontological significance and potential applied benefits are discussed

The odor of a plant metabolite affects life history traits in dietary restricted adult olive flies.

Food quality shapes life history traits either directly or through response of individuals to additional environmental factors, such as chemical cues. Plant extracts used as food additives modulate key life history traits; however little is known regarding such effects for olfactory chemical cues. Exploiting an interesting experimental system that involves the olive fly (Bactrocera oleae) and the plant metabolite α-pinene we asked whether exposure of adults to this compound modulates adult longevity and female reproduction in similar manner in a stressful - dietary (protein) restricted (DR) and in a relaxed- full diet (FD) feeding environment. Accordingly, we exposed males and females to the aroma of α-pinene and measured lifespan and age-specific fecundity in the above two dietary contexts. Our results demonstrate that exposure to α-pinene increased longevity in males and fecundity in females only under dietary restricted conditions. In relaxed food conditions, females exposed to α-pinene shifted high egg-laying towards younger ages compared to non-exposed ones. This is the first report demonstrating that a plant compound affects key life history traits of adult olive flies through olfaction. These effects are sex-specific and more pronounced in dietary restricted adults. Possible underlying mechanisms and the ecological significance are discussed

Female olive fly.

<p>Female olive fly.</p

Daily pattern on male sexual siganlling.

<p>Daily rhythm of sexual signalling on adult day 6 of sterilized male <i>C</i>. <i>capitata</i> of the Vienna 8 GSS in four different exposure compounds (orange oil, limonene, mixture of 5 pure compounds and control) on yeast hydrolyzate & sugar (YS, left column) and sugar only (S, right column). Values on y axis indicate the mean number (±SE) of males signalling per cage. Ten cages were considered containing 10 males each.</p

Effects of exposure to citrus compounds on male sexual signaling.

<p>Overall levels of sexual signalling activity (mean number of males signalling through the ages of 6 to 10 days old and 16 days old) of Vienna 8 GSS sterilized males medflies that were exposed during day 4 and 5 of adult life to orange essential oil, limonene, and a mixture of 5 pure compounds (limonene, linalool, myrcene, <i>α</i>-pinene and <i>β</i>-myrcene 1:1:1:1:1 ratio) or left unexposed (control) fed on (A) yeast hydrolyzate & sugar (YS) and (B) sugar only (S). On each day of age, observations took place hourly from 07:00 to 20:45 hours in 10 cages (replicates) containing 10 males each. Values on y-axis are mean numbers (±SE) of males signalling per cage per hour observation. Means followed by the same lowercase letter are not significantly different (P>0.05, Tukey’s HSD test).</p

Diet specific effects on male sexual signaling.

<p>Effect of yeast hydrolyzate and sugar (YS) and sugar only (S) on the overall levels of sexual signalling activity (mean daily activity through the ages of 6 to 10 days old and 16 days old) of Vienna 8 GSS sterilized male medflies, that were exposed during day 4 and 5 of adult life to orange essential oil, limonene and a mixture of 5 pure compounds (limonene, linalool, myrcene, <i>α</i>-pinene and <i>β</i>-myrcene, 1:1:1:1:1 ratio) or left unexposed (control). On each day of age, observations took place hourly from 07:00 to 20:45 hours in 10 cages (replicates) containing 10 males each. Values on y-axis are mean numbers (±SE) of males signalling per cage per hour observation (** P<0.001, *P<0.01, <i>t</i>-test YS vs S in each treatment).</p

Longevity parameters of adult medflies that were exposed and non-exposed to the aroma of citrus oil and held in diet restriction (sugar fed only) and in full diet (yeast and sugar fed) food conditions.

<p>Within diet regime, numbers followed by different letters are significantly different (pairwise comparisons log-rank test, P < 0.05).</p

Age specific ratio on male sexual signaling.

<p>Ratio between signalling rates of Vienna 8 GSS sterilized male medflies fed on either yeast hydrolyzate & sugar (YS) or sugar only (S) in relation to age. Males had been exposed during day 4 and 5 of adult life to orange essential oil, limonene, and a mixture of 5 pure compounds (limonene, linalool, myrcene, <i>α</i>-pinene and <i>β</i>-myrcene, 1:1:1:1:1 ratio) or left unexposed (control). On each day of age, observations took place hourly from 07:00 to 20:45 hours in 10 cages (replicates) containing 10 males each. The ratio was estimated considering the average calling for each day of the observation during 07:00 to 20:45 for protein and sugar treatments.</p

Male longevity.

<p>Age-specific survival patterns of sterilized male <i>C</i>.<i>capitata</i> of the Vienna 8 GSS that were either exposed (solid line) or non-exposed (dashed line) to citrus oil: (A) males in full diet (yeast-sugar fed) conditions, (B) male in diet restriction (sugar only fed), (Log-rank pairwise tests reveal significant differences between exposed and non-exposed males fed in sugar, <i>P</i> < 0.05).</p