DOI: 10.5061/dryad.cvdncjt11
title: Sex-specific patterns of senescence in artificial insect populations varying in sex-ratio to manipulate reproductive effort

description: Background: The disposable soma theory of ageing assumes that
 organisms optimally trade-off limited resources between reproduction and
 longevity to maximize fitness. Early reproduction should especially
 trade-off against late reproduction and longevity because of reduced
 investment into somatic protection, including immunity. Moreover, as
 optimal reproductive strategies of males and females differ, sexually
 dimorphic patterns of senescence may evolve. In particular, as males gain
 fitness through mating success, sexual competition should be a major
 factor accelerating male senescence. In a single experiment, we examined
 these possibilities by establishing artificial populations of the mealworm
 beetle, Tenebrio molitor, in which we manipulated the sex-ratio
 to generate variable levels of investment into reproductive effort and
 sexual competition in males and females. Results: As predicted,
 variation in sex-ratio affected male and female reproductive efforts, with
 contrasted sex-specific trade-offs between lifetime reproduction, survival
 and immunity. High effort of reproduction accelerated mortality in
 females, without affecting immunity, but high early reproductive success
 was observed only in balanced sex-ratio condition. Male reproduction was
 costly on longevity and immunity, mainly because of their investment into
 copulations rather than in sexual competition. Conclusions: Our
 results suggest that T. molitor males, like females,
 maximize fitness through enhanced longevity, partly explaining their
 comparable longevity. 
description: For the
 three data files provided, data were collected from a single experiment,
 which tested for the cost of reproductive effort at the population level
 on survival (BMC_EVOB-D-19-00289_Survival), reproduction
 (BMC_EVOB-D-19-00289_Fertility) and immunity
 (BMC_EVOB-D-19-00289_Immunity) of females and males of the mealworm
 beetle, <i>Tenebrio molitor</i>, in artificial populations in
 which we manipulated the sex-ratio to generate variable levels of
 investment into reproductive effort and sexual competition. Replicated
 populations (Replicat) of 100 adult beetles of the same age were
 maintained at different sex-ratio condition (75%_male, 50%_male and
 25%male) for their whole lifespan and surveyed for age at death (in
 weeks). During the
 experiment, age specific reproductive capacity of 4 females and 4 males
 haphazardly picked in each population was estimated weekly. To this
 purpose, each female was allowed to lay eggs for 3 days in a Petri dish,
 and was then returned to their initial population box. Two weeks later,
 the number of larvae was counted in each Petri dish to quantify female
 fertility as the number of viable larvae produced per female (Nb larvae).
 At the same time, each male was provided with a standardized virgin female
 for 24 hours and was then returned in its initial population. The female
 was then allowed to lay eggs in the Petri dish for three additional days
 to estimate male fertility, as the number of viable larvae produced by the
 female (Nb larvae). Furthermore, 4
 females and 4 males were also haphazardly picked in each population at the
 age of 2, 4, 6, and 12 weeks to estimate their body condition, as the
 residuals of the regression between their body mass and body size, and
 their immunity. Immunity was estimated from a single sample of hemolymph
 allowing measures of hemocyte concentration (Hemocyte), both the activity
 of naturally activated phenoloxidase enzymes only (PO) and the activity of
 the proenzymes in addition to that of naturally activated phenoloxidase
 enzymes (Total-PO), and antibacterial peptide activity (presence absence :
 ZI (yes/no) and magnitude: ZI size).