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26 results for “terminal investment”
Age, but not an immune challenge, triggers terminal investment in the Pacific field cricket
<p>The terminal investment hypothesis proposes that, when individuals are faced with a threat to survival, they will increase investment in current reproduction. The level of the threat necessary to elicit terminal investment (the dynamic terminal investment threshold) may vary based on other factors that also influence future reproduction. Here, we tested whether there is an interactive effect of age and an immune challenge on the dynamic terminal investment threshold in the Pacific field cricket, <em>Teleogryllus</em> <em>oceanicus</em>. We measured the courtship call, mating attractiveness, ejaculate size and offspring production of <em>T. oceanicus</em> males. We found only limited support for the dynamic terminal investment threshold: there was no consistent evidence of a positive interaction between male age and immune challenge intensity. However, we found evidence for age-related terminal investment: older males produced a larger spermatophore than younger males. Older males also had a slower calling rate compared to younger males, suggesting a potential trade-off between these two pre- and post-copulatory traits. As some, but not, all reproductive traits responded plastically to cues for terminal investment, our research highlights the importance of considering a broad range of pre-and post-copulatory traits when exploring the potential for terminal investment to occur.</p>
Age, but not an immune challenge, triggers terminal investment in the Pacific field cricket
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Evolutionary consequences of pesticide exposure include transgenerational plasticity and potential terminal investment transgenerational effects
<p>Transgenerational plasticity, the influence of the environment experienced by parents on the phenotype and fitness of subsequent generations, is being increasingly recognised. Human-altered environments, such as those resulting from the increasing use of pesticides, may be major drivers of such cross-generational influences, which in turn may have profound evolutionary and ecological repercussions. Most of these consequences are, however, unknown. Whether transgenerational plasticity elicited by pesticide exposure is common, and the consequences of its potential carry-over effects on fitness and population dynamics remains to be determined. Here we investigate whether exposure of parents to a common pesticide elicits intra-, inter- and transgenerational responses (in F0, F1 and F2 generations) in life-history (fecundity, longevity, and lifetime reproductive success-LRS-), in an insect model system, the seed beetle <em>Callosobruchus</em> <em>maculatus</em>. We also assessed sex-specificity of the effects. We found sex-specific and hormetic intergenerational and transgenerational effects on longevity and lifetime reproductive success, manifested both in the form of maternal and paternal effects. In addition, the transgenerational effects via mothers detected in this study are consistent with a new concept: terminal investment transgenerational effects. Such effects could underlie cross-generational responses to environmental perturbation. Our results indicate that pesticide exposure leads to unanticipated effects on population dynamics and have far-reaching ecological and evolutionary implications.</p>
Data from: Testing the terminal investment hypothesis in California oaks
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Evolutionary consequences of pesticide exposure include transgenerational plasticity and potential terminal investment transgenerational effects
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Data from: Modification of reproductive schedule in response to pathogen exposure in a wild insect: support for the terminal investment hypothesis
<p>Trade-offs in the time and energy allocated to different functions, such as reproductive activities, can be driven by alterations in condition which reduce resources, often in response to extrinsic factors such as pathogens or parasites. When individuals are challenged by a pathogen they may either reduce reproduction as a cost of increasing defence mechanisms, or alternatively, modify reproductive activities so as to increase fecundity thereby minimizing the fitness costs of earlier death, a behaviour consistent with the terminal investment hypothesis (TIH). The TIH predicts that individuals with decreased likelihood of future reproduction will maximize current reproductive effort, which may include shifts in reproductive timing. We examined how wild, adult female click beetles <i>(Agriotes obscurus) </i>responded after exposure to the fungal pathogen<i>Metarhizium brunneum</i>. Field-collected beetles exposed to a high concentration of <i>M. brunneum </i>died earlier and in greater numbers than those exposed to a low concentration. Using a multi-variate approach we examined the impact of pathogen challenge on lifespan and a suite of reproductive traits. Stepdown regression analysis showed that only female lifespan differed among the fungal treatments. Fungal-induced reductions in lifespan drove changes in the reproductive schedule, characterized by a decrease in preoviposition period. Moving the start of egg laying forward allowed the females to offset the costs of a shortened lifespan. These changes suggest that there is a threshold for terminal investment which is dependent on strength of the survival threat. From an applied perspective, our findings imply that exposing adult click beetles to <i>M. brunneum </i>to reduce their population densitymight not succeed and is an approach that needs further investigation.</p>
Late-life reproduction in an insect: terminal investment, reproductive restraint or senescence
<p>1. The Terminal Investment, Reproductive Restraint or Senescence theories may explain individual late-life patterns of reproduction. The terminal investment hypothesis predicts that individuals increase reproductive allocation late in life as prospects for future survival decrease. The other two hypotheses predict reduced reproduction late in life, but for different reasons. Under the Reproductive Restraint hypothesis, individuals restrain their reproductive effort to sustain future survival and gain more time for reproducing, whereas under the Senescence process, reproduction is constrained because of somatic deterioration. While these hypotheses imply that reproduction is costly, they should have contrasted implications in terms of survival after late reproduction and somatic maintenance.</p> <p>2. Testing these hypotheses requires proper consideration of the effects of age-dependent reproductive effort on post-reproduction survival and age-related somatic functions. We experimentally tested these three hypotheses in females of the mealworm beetle, Tenebrio molitor, an iteroparous and income breeder insect. We manipulated their age-specific allocation into reproduction and observed the effects of this manipulation on their late life- fecundity, post-reproduction survival and immunocompetence as a measurement of somatic protection.</p> <p>3. We found that females exhibit age-related declines in fecundity and that this reproductive senescence is accelerated by a cost of early reproduction. The cost of reproduction had no significant effect on female longevity and their ability to survive a bacterial infection, despite that some immune cells were depleted by reproduction. We found that female post-infection survival deteriorated with age, which could be partly explained by a decline in some immune parameters. Importantly, females did not increase their reproductive effort late in life at the expense of their late-life post-reproduction survival.</p> <p>4. Late-life reproduction in T. molitor females is senescing and not consistent with a terminal investment strategy. Rather, our results suggest that females allocate resources according to a priority scheme favouring longevity at the expense of reproduction, which is in line with the reproductive restraint hypothesis.</p> <p>5. Such a priority scheme also shows that a relatively short-lived insect can evolve life history strategies hitherto known only in long-lived animals. This puts in perspective the role of longevity in the evolution of life history strategies. </p>
Data from: Male mealworm beetles increase resting metabolic rate under terminal investment
Harmful parasite infestation can cause energetically costly behavioural and immunological responses, with the potential to reduce host fitness and survival. It has been hypothesized that the energetic costs of infection cause resting metabolic rate (RMR) to increase. Furthermore, under terminal investment theory, individuals exposed to pathogens should allocate resources to current reproduction when life expectancy is reduced, instead of concentrating resources on an immune defence. In this study, we activated the immune system of Tenebrio molitor males via insertion of nylon monofilament, conducted female preference tests to estimate attractiveness of male odours and assessed RMR and mortality. We found that attractiveness of males coincided with significant down-regulation of their encapsulation response against a parasite-like intruder. Activation of the immune system increased RMR only in males with heightened odour attractiveness and that later suffered higher mortality rates. The results suggest a link between high RMR and mortality and support terminal investment theory in T. molitor.
Males following a terminal investment strategy can fake their body odors to females, yet they cannot fake the odor of their microbiome
<p><span>Terminal investment and dishonesty are likely the only strategies by which sick males in our study could attract females to reproduce. We show that immunocompromised male yellow mealworm beetles (<em>Tenebrio molitor</em>) employing a terminal investment strategy can fake their bodily sex pheromones to females, yet they cannot fake the fecal odor of their microbiome. The results of this study have important methodological recommendations for future studies in the field of terminal investment strategy, showing the need to consider the role of sex odors and signals produced by the microbiome.</span></p>
Reproductive effort and terminal investment in a multi-species assemblage of Amazon electric fish
<p>The terminal investment hypothesis (TIH) predicts that individuals with favorable prospects for future reproduction (i.e., high residual reproductive value, RRV) should moderate current reproductive investment in favor of growth, survival, and future reproduction, whereas those with low RRV should 'terminally invest' by diverting somatic resources towards current reproduction at the expense of future reproduction. However, support for the TIH in wild animal populations is fragmentary, and the ecological contexts of terminal investment remain poorly known. We report a remarkable case of simultaneous terminal investment involving five sympatric species of the electric knifefish genus <i>Brachyhypopomus</i>, from Amazonian floodplain and terra firme stream habitats. We found that terminal investment is synchronized by seasonal breeding, in response to circannual environmental variation in mortality risk. Four species exhibit a uniseasonal iteroparous (annual) life history with complete post-reproductive mortality after a single breeding season. One species (<i>B. beebei</i>) exhibits a two-year multiseasonal iteroparous life history with breeding in two seasons and post-reproductive mortality after the second. In mature females and (most) males of the annual species, as well as in both mature female and male <i>second-year</i> (but not first-year) <i>B. beebei</i>, we documented an increase in two metrics of reproductive effort (size-adjusted gonad mass and electric signal amplitude) and a concomitant reduction in somatic condition (size-adjusted somatic mass) – all in response to proximity to the end of the common breeding season, when RRV approximates zero. In mature <i>first-year</i> <i>B. beebei</i>, we documented neither an increase in reproductive effort nor a decline in somatic condition, implying an alternative strategy of reproductive restraint. Our findings support Kirkwood's disposable soma theory, which posits that death by reproductive exhaustion can be delayed if terminal investment is replaced by reproductive restraint, allowing individuals to survive and breed in a subsequent season. Deferral of the terminal investment response in annual species, and the origin of a gonadal regression-regeneration sequence, may open pathways for rapid evolutionary transitions to multiseasonal iteroparity. Excepting the age (year-group) dependency of terminal investment in <i>B. beebei</i>, we were unable to identify intrinsic cues or extrinsic environmental cues for the terminal investment response in <i>Brachyhypopomus</i>.</p>
Age-specific fecundity under pathogenic threat in an insect: terminal investment versus reproductive restraint
<p>The terminal investment hypothesis predicts that as an organism's prospects for survival decrease, through age or when exposed to a pathogenic infection, it will invest more in reproduction, which should trade-off against somatic maintenance (including immunity) and therefore future survival. Attempts to test this hypothesis have produced mixed results, which, in addition, mainly rely on the assessment of changes in reproductive effort and often overlooking its impact on somatic defences and survival. Alternatively, animals may restrain current reproduction to sustain somatic protection, increasing the chance of surviving for additional reproductive opportunities. We tested both of these hypotheses in females of the yellow mealworm beetle, Tenebrio molitor, an iteroparous insect with reproductive tactics similar to that of long-lived organisms. To achieve this, we mimicked pathogenic bacterial infections early or late in the life of breeding females by injecting them with a suspension of inactivated Bacillus cereus, a known natural pathogen of T. molitor, and measured female age-specific fecundity, survival, body mass and immunity. Inconsistent with a terminal investment, females given either an early or late-life immune challenge did not exhibit reduced survival or enhance their reproductive output. Female fecundity declined with age and was reduced by the early but not the late immune challenge. Both early and late-life fecundity correlated positively with life expectancy. Finally, young and old females exhibited similar antibacterial immune responses, suggesting that they both restrained reproduction to sustain immunity. Our results clearly demonstrate that age-specific reproduction of T. molitor females under pathogenic threat is inconsistent with a terminal investment. In contrast, our results instead suggest that females used a reproductive restraint strategy to sustain immunity and therefore subsequent reproductive opportunities. However, as infections were mimicked only, the fitness benefit of this reproductive restraint could not be shown.</p>
Female investment in terminal reproduction or somatic maintenance depends on infection dose - data
<p>This is the data used in an experiment investigating the effects of infection dose on fecundity compensation in the red flour beetle.</p>
Data from: Age-dependent variation in the terminal investment threshold in male crickets
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Age-specific fecundity under pathogenic threat in an insect: terminal investment versus reproductive restraint
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Data from: Male mealworm beetles increase resting metabolic rate under terminal investment
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Late-life reproduction in an insect: terminal investment, reproductive restraint or senescence
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Reproductive effort and terminal investment in a multi-species assemblage of Amazon electric fish
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Data from: Modification of reproductive schedule in response to pathogen exposure in a wild insect: support for the terminal investment hypothesis
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Data from: Sexual cannibalism increases male material investment in offspring: quantifying terminal reproductive effort in a praying mantis
Models of the evolution of sexual cannibalism argue that males may offset the cost of cannibalism if components of the male body are directly allocated to the eggs that they fertilize. We tested this idea in the praying mantid Tenodera sinensis. Males and females were fed differently radiolabelled crickets and allowed to mate. Half of the pairs progressed to sexual cannibalism and we prevented cannibalism in the other half. We assess the relative allocation of both male-derived somatic materials and ejaculate materials into the eggs and soma of the female. Our results show that male somatic investment contributes to production of offspring. The eggs and reproductive tissues of cannibalistic females contained significantly more male-derived amino acids than those of non-cannibalistic females, and there was an increase in the number of eggs produced subsequent to sexual cannibalism. Sexual cannibalism thus increases male material investment in offspring. We also show that males provide substantial investment via the ejaculate, with males passing about 25% of their radiolabelled amino acids to females via the ejaculate even in the absence of cannibalism.
Data from: Effect of juvenile hormone on senescence in males with terminal investment
Senescence, a decline in survival and reproductive prospects with age, is controlled by hormones. In insects, juvenile hormone (JH) is involved in senescence with captive individuals, but its effect under natural conditions is unknown. We have addressed this gap by increasing JH levels in young and old wild males of the damselfly Hetaerina americana. We assessed survival in males that were treated with a JH analogue (methoprene), which is known to promote sexual activity, and an immune challenge, which is known to promote terminal investment in reproduction in the studied species. We replicated the same procedure in captivity (to control for environmental variation), where males were deprived of any activity or food. We expected old males to show the lowest survival after being treated with JH and immune-challenged, because the effect of terminal investment on senescence would be exacerbated by JH. However, this should be the case for wild animals, but not for captive animals, as the effects of JH and immune challenge should lead to an increase in high energetic-demanding activities only occurring in the wild. Old animals died sooner compared with young animals in both the wild and captivity, confirming that males are subject to senescence. In wild but not captive animals, JH decreased survival in young males and increased it in old males, confirming that JH is sensitive to the environment when shaping animal senescence. Immune challenge had no effect on survival, suggesting no effect of terminal investment on senescence. Additionally, contrary to the expected effects of terminal investment, with an immune challenge, recapture rates increased in young males and decreased in old males. Our results show that male senescence in the wild is mediated by JH and that terminal investment does not cause senescence. One explanation is that animals undergoing senescence and terminal investment modify their feeding behaviour to compensate for their physiological state.
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