High tandem repeat content in the genome of the short-lived annual fish Nothobranchius furzeri: a new vertebrate model for aging research

Background

The annual fish Nothobranchius furzeri is the vertebrate with the shortest known life span in captivity. Fish of the GRZ strain live only three to four months under optimal laboratory conditions, show explosive growth, early sexual maturation and age-dependent physiological and behavioral decline, and express aging related biomarkers. Treatment with resveratrol and low temperature significantly extends the maximum life span. These features make N. furzeri a promising new vertebrate model for age research.

Results

To contribute to establishing N. furzeri as a new model organism, we provide a first insight into its genome and a comparison to medaka, stickleback, tetraodon and zebrafish. The N. furzeri genome contains 19 chromosomes (2n = 38). Its genome of between 1.6 and 1.9 Gb is the largest among the analyzed fish species and has, at 45%, the highest repeat content. Remarkably, tandem repeats comprise 21%, which is 4-12 times more than in the other four fish species. In addition, G+C-rich tandem repeats preferentially localize to centromeric regions. Phylogenetic analysis based on coding sequences identifies medaka as the closest relative. Genotyping of an initial set of 27 markers and multi-locus fingerprinting of one microsatellite provides the first molecular evidence that the GRZ strain is highly inbred.

Conclusions

Our work presents a first basis for systematic genomic and genetic analyses aimed at understanding the mechanisms of life span determination in N. furzeri.     

Large Differences in Aging Phenotype between Strains of the Short-Lived Annual Fish Nothobranchius furzeri

Background

A laboratory inbred strain of the annual fish Nothobranchius furzeri shows exceptionally short life expectancy and accelerated expression of age markers. In this study, we analyze new wild-derived lines of this short-lived species.

Methodology/Principal Findings

We characterized captive survival and age-related traits in F1 and F2 offspring of wild-caught N. furzeri. Wild-derived N. furzeri lines showed expression of lipofuscin and neurodegeneration at age 21 weeks. Median lifespan in the laboratory varied from to 20 to 23 weeks and maximum lifespan from 25 to 32 weeks. These data demonstrate that rapid age-dependent decline and short lifespan are natural characteristics of this species. The N. furzeri distribution range overlaps with gradients in altitude and aridity. Fish from more arid habitats are expected to experience a shorter survival window in the wild. We tested whether captive lines stemming from semi-arid and sub-humid habitats differ in longevity and expression of age-related traits. We detected a clear difference in age-dependent cognitive decline and a slight difference in lifespan (16% for median, 15% for maximum lifespan) between these lines. Finally, we observed shorter lifespan and accelerated expression of age-related markers in the inbred laboratory strain compared to these wild-derived lines.

Conclusions/Significance

Owing to large differences in aging phenotypes in different lines, N. furzeri could represent a model system for studying the genetic control of life-history traits in natural populations.     

Squeezing out the last egg—annual fish increase reproductive efforts in response to a predation threat

Both constitutive and inducible antipredator strategies are ubiquitous in nature and serve to maximize fitness under a predation threat. Inducible strategies may be favored over constitutive defenses depending on their relative cost and benefit and temporal variability in predator presence. In African temporary ponds, annual killifish of the genus Nothobranchius are variably exposed to predators, depending on whether larger fish invade their habitat from nearby rivers during floods. Nonetheless, potential plastic responses to predation risk are poorly known. Here, we studied whether Nothobranchius furzeri individuals adjust their life history in response to a predation threat. For this, we monitored key life history traits in response to cues that signal the presence of predatory pumpkinseed sunfish (Lepomis gibbosus). While growth rate, adult body size, age at maturation, and initial fecundity were not affected, peak and total fecundity were higher in the predation risk treatment. This contrasts with known life history strategies of killifish from permanent waters, which tend to reduce reproduction in the presence of predators. Although our results show that N. furzeri individuals are able to detect predators and respond to their presence by modulating their reproductive output, these responses only become evident after a few clutches have been deposited. Overall our findings suggest that, in the presence of a predation risk, it can be beneficial to increase the production of life stages that can persist until the predation risk has faded.     

Asymmetric reproductive isolation between two sympatric annual killifish with extremely short lifespans

Background

Interspecific reproductive isolation is typically achieved by a combination of intrinsic and extrinsic barriers. Behavioural isolating barriers between sympatric, closely related species are often of primary importance and frequently aided by extrinsic factors causing spatial and temporal interspecific separation. Study systems with a severely limited role of extrinsic factors on reproductive isolation may provide valuable insights into how reproductive isolation between sympatric species is maintained. We used no-choice experimental set-up to study reproductive barriers between two closely related sympatric African killifish species, Nothobranchius furzeri and Nothobranchius orthonotus. These fish live in small temporary savannah pools and have complete spatial and temporal overlap in reproductive activities and share a similar ecology.

Principal Findings

We found that the two species display largely incomplete and asymmetric reproductive isolation. Mating between N. furzeri males and N. orthonotus females was absent under standard experimental conditions and eggs were not viable when fish were forced to mate in a modified experimental setup. In contrast, male N. orthonotus indiscriminately mated with N. furzeri females, the eggs were viable, and offspring successfully hatched. Most spawnings, however, were achieved by male coercion and egg production and embryo survival were low. Behavioural asymmetry was likely facilitated by mating coercion from larger males of N. orthonotus and at relatively low cost to females. Interestingly, the direction of asymmetry was positively associated with asymmetry in post-mating reproductive barriers.

Significance

We showed that, in fish species with a promiscuous mating system and multiple matings each day, selection for strong mate preferences was relaxed. This effect was likely due to the small proportion of resources allocated to each single mating and the high potential cost to females from mating refusal. We highlight and discuss the fact that males of rarer species may often coercively mate with females of a related, more abundant species.     

Female fecundity traits in wild populations of African annual fish: the role of the aridity gradient

The evolution of life history is shaped by life expectancy. Life‐history traits coevolve, and optimal states for particular traits are constrained by trade‐offs with other life‐history traits. Life histories contrast among species, but may also diverge intraspecifically, at the level of populations. We studied the evolution of female reproductive allocation strategy, using natural populations of two sympatric species of African annual fishes, Nothobranchius furzeri and Nothobranchius orthonotus. These species inhabit pools in the Mozambican savanna that are formed in the rainy season and persist for only 2–10 months. Using 207 female N. furzeri from 11 populations and 243 female N. orthonotus from 14 populations, we tested the effects of genetic background (intraspecific lineage) and life expectancy (position on the aridity gradient determining maximum duration of their temporary habitat) on female fecundity traits. First, we found that variation in female body mass was small within populations, but varied considerably among populations. Second, we found that fecundity was largely defined by female body mass and that females spawned most of their eggs in the morning. Third, we found that the trade‐off between egg size and egg number varied among lineages of N. furzeri and this outcome has been confirmed by data from two separate years. Overall, we demonstrate that local conditions were important determinants for Nothobranchius growth and fecundity and that eggs size in arid region was less limited by female fecundity than in humid region.     

Size delays female senescence in a medium sized marsupial: The effects of maternal traits on annual fecundity in the northern brown bandicoot (Isoodon macrourus)

The degree to which females allocate resources between current reproduction, future fecundity and survival is a central theme in life history theory. We investigated two hypotheses proposed to explain patterns of reproductive investment, terminal investment and senescence, by examining the effects of maternal traits (age and maternal mass) on annual fecundity in female northern brown bandicoots, Isoodon macrourus (Marsupialia: Peramelidae). We found that annual fecundity in females declined in their final year of reproduction, indicating reproductive senescence. Maternal mass significantly influenced the rate of senescence and, in turn, a female's lifetime reproductive output. Mass had little effect on fecundity in 1st and 2nd year females, but a positive relationship with fecundity in 3rd year females. This meant that heavy, 3rd year females did not suffer the decline in fecundity shown in light 3rd year females. For 1st year females, mass and leg length increased between their first and second reproductive seasons, indicating a temporary shift, from the allocation of resources to reproduction, to increasing condition or structural size post their first breeding event. There were no net changes to body mass in subsequent years. We suggest that this year of post‐reproductive growth has important consequences for senescent effects on reproduction. Overall, results provided support for the effects of senescence on annual fecundity. Our findings were not consistent with the terminal investment hypothesis; reproductive output did not increase in females' final reproductive season despite a rapid decline in survival. However, this notion cannot be entirely dismissed; other measures of reproductive performance not examined here (e.g. offspring mass) may have provided an indication that females did increase their effort at the end of their lifespan. This study highlights the difficulty of measuring reproductive costs and the importance of understanding the combined effects of specific characteristics of an individual when interpreting reproductive strategies in iteroparous organisms.     

The productive and reproductive biology of flowering plants

The life cycles, programme of energy expenditure and allocation to reproduction, and the reproductive efforts of three wildAllium species, i.e.,A. Victorialis ssp.platyphyllum, A. monanthum, andA. Grayi, all native to Japan, were studied and compared. Furthermore, their adaptive strategies were discussed from the point of view of life history strategy. First, the reproductive systems, number of male and female gametes borne, and the number and size of propagules produced were critically investigated. In order to estimate the crude reproductive efficiency (sensu Harper and Ogden, 1970) of these species, sequential harvests were taken and the plants were divided into their component structures, dried and weighed. The quantity of dry weight allocated to sexual or vegetative reproduction was obtained by weighing the seeds, bulbils, or bulblets produced at the end of the season. A. Victorialis ssp.platyphyllum showed a rather low reproductive effort. However, the mean seed output per plant was 34.8±16.8 and the productivity appeared very constant every season. Thus, in the natural populations young plants are borne and recruited every season by means of sexual reproduction. A. monanthum was found to be characterized by annual type dry matter economy. The sexuality and reproductive systems of this species turned out to be extremely complex, and ten different reproductive types were distinguished. The exceedingly low efficiency of sexual reproduction in this species is apparently supplemented by vegetative propagation. The dry matter allocation to daughter bulbs at final harvest was very high; whereas the allocation to sexual reproduction was extremely low. InA. Grayi (a polyploid complex of 4X, 5X, and 6X), a surprisingly high amount of the total annual net assimilate is allocated to the bulbils and bulblets. On the other hand, sexual reproductive effort in this species is exceedingly low, even in obligate amphimictic plants. Thus, the recruitment of individuals in a population of this species appears to be largely dependent on vegetative reproduction. Considering the number of bulbils produced in the scape heads, their dispersibility, germinability, and rapid growth after sprouting, the bulbils evidently possess a function almost comparable to seeds. This species no doubt possesses an adapative strategy to unstable, open habitats exposed to frequent disturbances. It is concluded that the life history strategies of plants, as characterized here in this paper for three wildAllium species, have doubtlessly differentiated by adapting to the respective ecological backgrounds of their habitats.     

Female access and diet affect insemination success,senescence and the cost of reproduction in the male Mexican fruit fly Anastrepha ludens

Hypotheses exploring the influence of dietary conditions on the life‐history trade‐off between survival and reproductive success are extensively tested in female insects but only rarely explored in males. The present study examines the impact of dietary quality and female access on age‐specific reproduction and survival of the male Mexican fruit fly Anastrepha ludens Loew (Diptera: Tephritidae). There is a clear cost of female access for males with access to dietary protein, measurable as a decrease in life expectancy, which is further influenced by the age when females are introduced. A protein deficient diet reduces the lifespan benefit of virginity and masks the detrimental effect of female access on male life expectancy. Dietary protein is not necessary for reproductive success, although access to protein at eclosion improves the lifetime reproductive success of males compared to when it is delayed. Overall, reproductive success diminishes as the male flies age, regardless of the dietary conditions, providing evidence for reproductive senescence in males. Delaying the males' access to a protein source fails to influence the negative effect of age on reproductive ability. Because age‐specific reproductive rates decline with age, regardless of diet, male fitness does not benefit from lifespan extension. Therefore, males can be expected to allocate available resources towards reproductive effort in favour of an extended lifespan, regardless of mate and protein availability.     

The evolution of senescence and post-reproductive lifespan in guppies (Poecilia reticulata)

The study of post-reproductive lifespan has been of interest primarily with regard to the extended post-menopausal lifespan seen in humans. This unusual feature of human demography has been hypothesized to have evolved because of the “grandmother” effect, or the contributions that post-reproductive females make to the fitness of their children and grandchildren. While some correlative analyses of human populations support this hypothesis, few formal, experimental studies have addressed the evolution of post-reproductive lifespan. As part of an ongoing study of life history evolution in guppies, we compared lifespans of individual guppies derived from populations that differ in their extrinsic mortality rates. Some of these populations co-occur with predators that increase mortality rate, whereas other nearby populations above barrier waterfalls are relatively free from predation. Theory predicts that such differences in extrinsic mortality will select for differences in the age at maturity, allocation of resources to reproduction, and patterns of senescence, including reproductive declines. As part of our evaluation of these predictions, we quantified differences among populations in post-reproductive lifespan. We present here the first formal, comparative study of the evolution of post-reproductive lifespan as a component of the evolution of the entire life history.

Guppies that evolved with predators and that experienced high extrinsic mortality mature at an earlier age but also have longer lifespans. We divided the lifespan into three non-overlapping components: birth to age at first reproduction, age at first reproduction to age at last reproduction (reproductive lifespan), and age at last reproduction to age at death (post-reproductive lifespan). Guppies from high-predation environments live longer because they have a longer reproductive lifespan, which is the component of the life history that can make a direct contribution to individual fitness. We found no differences among populations in post-reproductive lifespan, which is as predicted since there can be no contribution of this segment of the life history to an individual's fitness.

Prior work on the evolution of post-reproductive lifespan has been dominated by speculation and correlative analyses. We show here that this component of the life history is accessible to formal study as part of experiments that quantify the different segments of an individual's life history. Populations of guppies subject to different mortality pressures from predation evolved differences in total lifespan, but not in post-reproductive lifespan. Rather than showing the direct effects of selection characterizing other life-history traits, post-reproductive lifespan in these fish appears to be a random add-on at the end of the life history. These findings support the hypothesis that differences in lifespan evolving in response to selection are confined to the reproductive lifespan, or those segments of the life history that make a direct contribution to fitness. We also show, for the first time, that fish can have reproductive senescence and extended post-reproductive lifespans despite the general observation that they are capable of producing new primary oocytes throughout their lives.

     

Stress-Induced Tradeoffs in a Free-Living Lizard across a Variable Landscape: Consequences for Individuals and Populations

Current life history theory suggests that the allocation of energetic resources between competing physiological needs should be dictated by an individual’s longevity and pace of life. One key physiological pathway likely to contribute to the partitioning of resources is the vertebrate stress response. By increasing circulating glucocorticoids the stress response can exert a suite of physiological effects, such as altering immune function. We investigated the effects of stress physiology on individual immunity, reproduction and oxidative stress, across an urban landscape. We sampled populations in and around St. George, Utah, examining corticosterone in response to restraint stress, two innate immune measures, reproductive output, and the presence of both reactive oxygen metabolites and antioxidant binding capacity, in populations of common side-blotched lizards (Uta stansburiana) experiencing variable levels of environmental stress. Additionally, using capture-mark-recapture techniques, we examined the relationships between these physiological parameters and population-level differences. Our results reveal elevated physiological stress corresponds with suppressed immunity and increased oxidative stress. Interestingly, urban populations experiencing the most physiological stress also exhibited greater reproductive output and decreased survival relative to rural populations experiencing less physiological stress, demonstrating a tradeoff between reproduction and life maintenance processes. Our results suggest that environmental stress may augment life history strategy in this fast-paced species, and that shifts in life history strategy can in turn affect the population at large. Finally, the urban environment poses definite challenges for organisms, and while it appears that side-blotched lizards are adjusting physiologically, it is unknown what fitness costs these physiological adjustments accrue.     

Reproductive Capability Is Associated with Lifespan and Cause of Death in Companion Dogs

Reproduction is a risky affair; a lifespan cost of maintaining reproductive capability, and of reproduction itself, has been demonstrated in a wide range of animal species. However, little is understood about the mechanisms underlying this relationship. Most cost-of-reproduction studies simply ask how reproduction influences age at death, but are blind to the subjects'' actual causes of death. Lifespan is a composite variable of myriad causes of death and it has not been clear whether the consequences of reproduction or of reproductive capability influence all causes of death equally. To address this gap in understanding, we compared causes of death among over 40,000 sterilized and reproductively intact domestic dogs, Canis lupus familiaris. We found that sterilization was strongly associated with an increase in lifespan, and while it decreased risk of death from some causes, such as infectious disease, it actually increased risk of death from others, such as cancer. These findings suggest that to understand how reproduction affects lifespan, a shift in research focus is needed. Beyond the impact of reproduction on when individuals die, we must investigate its impact on why individuals die, and subsequently must identify the mechanisms by which these causes of death are influenced by the physiology associated with reproductive capability. Such an approach may also clarify the effects of reproduction on lifespan in people.     

Evidence of reproductive cost in the triphasic life history of the red alga Gracilaria chilensis (Gracilariales,Rhodophyta)

The extent of changes in basic physiological and demographic traits associated with reproduction was investigated in the highly cultivated haploid–diploid red alga, Gracilaria chilensis. Sixty individuals bearing vegetative and reproductive fronds collected in the natural population of Niebla (39°52′?S, 73°23′?W), in Chile, were cultivated under controlled culture conditions. Our results demonstrated that vegetative fronds have a higher survival rate and a better growth rate than reproductive ones irrespective of the type of individual analyzed (male gametophyte, female gametophyte, and tetrasporophyte). Moreover, the reproductive fronds clearly showed a decrease in photosynthetic activity compared to non-reproductive ones. In males and tetrasporophytes, the photosynthetic reduction in reproductive individuals could be explained by a physical effect of reproductive structure development as well as spores release, disrupting the continuity of the photosynthetic cortical tissues. Translocation of photoassimilates from nearby vegetative tissue or the previous accumulation of photosynthetic products seems to be a prerequisite for reproductive structure development in this species. Altogether, these results document for the first time in G. chilensis that reproduction has a strong physiological effect on male, female, and tetrasporophyte fronds. This trade-off between reproduction, growth, and survival suggest the existence of reproductive costs in the life history of G. chilensis.     

Inbreeding alters context‐dependent reproductive effort and immunity in male crickets

Infection can cause hosts to drastically alter their investment in key life‐history traits of reproduction and defence. Infected individuals are expected to increase investment in defence (e.g., by increasing immune function) and, due to trade‐offs, investment in other traits (e.g., current reproduction) should decrease. However, the terminal investment hypothesis postulates that decreased lifespan due to infection and the associated reduction in the expectation for future offspring will favour increased investment towards current reproduction. Variation in intrinsic condition will likely influence shifts in reproductive investment post‐infection, but this is often not considered in such assessments. For example, the extent of inbreeding can significantly impact an individual's lifetime fitness and may influence its reproductive behaviour following a threat of infection. Here, we investigated the effects of inbreeding status on an individual's reproductive investment upon infection, including the propensity to terminally invest. Male crickets (Gryllodes sigillatus) from four genetically distinct inbred lines and one outbred line were subjected to a treatment from an increasing spectrum of simulated infection cue intensities, using heat‐killed bacteria. We then measured reproductive effort (calling effort), survival and immune function (antibacterial activity, circulating haemocytes and haemocyte microaggregations). Inbred and outbred males diverged in how they responded to a low‐dose infection cue: relative to unmanipulated males, outbred males decreased calling effort, whereas inbred males increased calling effort. Moreover, we found that inbred males exhibited higher antibacterial activity and numbers of circulating haemocytes compared with outbred males. These results suggest that an individual's inbreeding status may have consequences for context‐dependent shifts in reproductive strategies, such as those triggered by infection.     

Aging in the colonial chordate,Botryllus schlosseri

What mechanisms underlie aging? One theory, the wear-and-tear model, attributes aging to progressive deterioration in the molecular and cellular machinery which eventually lead to death through the disruption of physiological homeostasis. The second suggests that life span is genetically programmed, and aging may be derived from intrinsic processes which enforce a non-random, terminal time interval for the survivability of the organism. We are studying an organism that demonstrates both properties: the colonial ascidian, Botryllus schlosseri. Botryllus is a member of the Tunicata, the sister group to the vertebrates, and has a number of life history traits which make it an excellent model for studies on aging. First, Botryllus has a colonial life history, and grows by a process of asexual reproduction during which entire bodies, including all somatic and germline lineages, regenerate every week, resulting in a colony of genetically identical individuals. Second, previous studies of lifespan in genetically distinct Botryllus lineages suggest that a direct, heritable basis underlying mortality exists that is unlinked to reproductive effort and other life history traits. Here we will review recent efforts to take advantage of the unique life history traits of B. schlosseri and develop it into a robust model for aging research.     

SEXUAL SELECTION AFFECTS THE EVOLUTION OF LIFESPAN AND AGEING IN THE DECORATED CRICKET GRYLLODES SIGILLATUS

Recent work suggests that sexual selection can influence the evolution of ageing and lifespan by shaping the optimal timing and relative costliness of reproductive effort in the sexes. We used inbred lines of the decorated cricket, Gryllodes sigillatus, to estimate the genetic (co)variance between age‐dependent reproductive effort, lifespan, and ageing within and between the sexes. Sexual selection theory predicts that males should die sooner and age more rapidly than females. However, a reversal of this pattern may be favored if reproductive effort increases with age in males but not in females. We found that male calling effort increased with age, whereas female fecundity decreased, and that males lived longer and aged more slowly than females. These divergent life‐history strategies were underpinned by a positive genetic correlation between early‐life reproductive effort and ageing rate in both sexes, although this relationship was stronger in females. Despite these sex differences in life‐history schedules, age‐dependent reproductive effort, lifespan, and ageing exhibited strong positive intersexual genetic correlations. This should, in theory, constrain the independent evolution of these traits in the sexes and may promote intralocus sexual conflict. Our study highlights the importance of sexual selection to the evolution of sex differences in ageing and lifespan in G. sigillatus.     

Crickets increase sexual signalling and sperm protection but live shorter in the presence of rivals

The sociosexual environment animals experience through their life can shape the evolution of key life history traits, including longevity. Male–male competition, for instance, may influence the resources allocated to traits involved in male reproductive success. Here, I test whether lifelong exposure to a competitor male influences male investment in pre‐ and post‐copulatory sexual traits (calling effort and sperm quality) and how this affected the oxidative status and longevity of male field crickets (Gryllus bimaculatus). As expected, the visual exposure to a mating competitor promoted a higher calling effort in the male crickets but resulted in a decline in the haemolymph antioxidant content. The haemolymph antioxidant content negatively covaried with the antioxidant content of the sperm but interestingly, only when the males were exposed to a competitor. This suggests that when mating competition is high, males may prioritize sperm antioxidant protection against somatic maintenance. Finally, I provide evidence that male–male competition imposes additional costs to reproduction, as males exposed to a mating competitor lost a significant proportion of body antioxidant defences and body mass over time and in long term, had a reduced lifespan. Overall, this study strongly suggests that intrasexual competition may impose additional oxidative costs during reproduction for males, with negative consequences on lifespan. Moreover, the results highlight the role of oxidative stress as a physiological mechanism underlying the trade‐off between reproduction‐longevity and through which sexual selection may contribute to the evolution of senescence patterns.     

Oxidative shielding and the cost of reproduction

Life‐history theory assumes that reproduction and lifespan are constrained by trade‐offs which prevent their simultaneous increase. Recently, there has been considerable interest in the possibility that this cost of reproduction is mediated by oxidative stress. However, empirical tests of this theory have yielded equivocal support. We carried out a meta‐analysis to examine associations between reproduction and oxidative damage across markers and tissues. We show that oxidative damage is positively associated with reproductive effort across females of various species. Yet paradoxically, categorical comparisons of breeders versus non‐breeders reveal that transition to the reproductive state is associated with a step‐change reduction in oxidative damage in certain tissues and markers. Developing offspring may be particularly sensitive to harm caused by oxidative damage in mothers. Therefore, such reductions could potentially function to shield reproducing mothers, gametes and developing offspring from oxidative insults that inevitably increase as a consequence of reproductive effort. According to this perspective, we hypothesise that the cost of reproduction is mediated by dual impacts of maternally‐derived oxidative damage on mothers and offspring, and that mothers may be selected to diminish such damage. Such oxidative shielding may explain why many existing studies have concluded that reproduction has little or no oxidative cost. Future advance in life‐history theory therefore needs to take account of potential transgenerational impacts of the mechanisms underlying life‐history trade‐offs.     

The Evolution of Senescence and Post-Reproductive Lifespan in Guppies (Poecilia reticulata)

The study of post-reproductive lifespan has been of interest primarily with regard to the extended post-menopausal lifespan seen in humans. This unusual feature of human demography has been hypothesized to have evolved because of the “grandmother” effect, or the contributions that post-reproductive females make to the fitness of their children and grandchildren. While some correlative analyses of human populations support this hypothesis, few formal, experimental studies have addressed the evolution of post-reproductive lifespan. As part of an ongoing study of life history evolution in guppies, we compared lifespans of individual guppies derived from populations that differ in their extrinsic mortality rates. Some of these populations co-occur with predators that increase mortality rate, whereas other nearby populations above barrier waterfalls are relatively free from predation. Theory predicts that such differences in extrinsic mortality will select for differences in the age at maturity, allocation of resources to reproduction, and patterns of senescence, including reproductive declines. As part of our evaluation of these predictions, we quantified differences among populations in post-reproductive lifespan. We present here the first formal, comparative study of the evolution of post-reproductive lifespan as a component of the evolution of the entire life history. Guppies that evolved with predators and that experienced high extrinsic mortality mature at an earlier age but also have longer lifespans. We divided the lifespan into three non-overlapping components: birth to age at first reproduction, age at first reproduction to age at last reproduction (reproductive lifespan), and age at last reproduction to age at death (post-reproductive lifespan). Guppies from high-predation environments live longer because they have a longer reproductive lifespan, which is the component of the life history that can make a direct contribution to individual fitness. We found no differences among populations in post-reproductive lifespan, which is as predicted since there can be no contribution of this segment of the life history to an individual's fitness. Prior work on the evolution of post-reproductive lifespan has been dominated by speculation and correlative analyses. We show here that this component of the life history is accessible to formal study as part of experiments that quantify the different segments of an individual's life history. Populations of guppies subject to different mortality pressures from predation evolved differences in total lifespan, but not in post-reproductive lifespan. Rather than showing the direct effects of selection characterizing other life-history traits, post-reproductive lifespan in these fish appears to be a random add-on at the end of the life history. These findings support the hypothesis that differences in lifespan evolving in response to selection are confined to the reproductive lifespan, or those segments of the life history that make a direct contribution to fitness. We also show, for the first time, that fish can have reproductive senescence and extended post-reproductive lifespans despite the general observation that they are capable of producing new primary oocytes throughout their lives.