Earlier Onset Of Reproduction Research Articles

Population-Based Evidence of Climate Change Adaptation in an Endangered Plant Endemic to a Biodiversity Hotspot.

Climate change is expected to impact both the population structure and geographic distribution of plants. Species distribution models are widely used to assess range shifts and the vulnerability of plants to climate change. Despite the abundance of modeling studies, little is known about how existing populations respond to climate change. We investigated the demographic structure and vulnerability to climate change in Anemone moorei, a sub-shrub with a highly restricted distribution in a biodiversity hotspot. We improved the distribution knowledge through intensive field work. We conducted a census of stem length as a proxy for age for all known populations. We used ensemble forecasting to project distributions considering 10 future climate scenarios and developed a novel climate change vulnerability index for the species' distribution. We found that the mean stem length decreases and the proportion of young plants increases, while the size of fruiting plants decreases as A. moorei faces greater climate change vulnerability. We interpret these results as evidence for the onset of recent adaptation to climate change, consisting of reduced adult longevity and an earlier onset of reproduction. As a result of these changes, the proportion of juveniles in the population increases.

Response to Global Warming of Eichwald's Toad,Bufo eichwaldiLitvinchuk, Borkin, Skorinov and Rosanov, 2008 (Anura; Amphibia) in Iran and Azerbaijan

Global warming is considered to be a major threat to biodiversity and to have an erosive effect on the survival of endangered species. Amphibians are known as a vulnerable group of vertebrates that live and reproduce in both terrestrial and aquatic habitats. The subtropical regions of the world are among the land areas where amphibians will suffer the most from climate change. In the present study, the effect of climate change onBufo eichwaldiinhabiting Hyrcanian forests was investigated. According to our results, the lowest temperature in the coldest season is the most important variable for the presence of this species. Due to the beginning of reproductive activity and mating taking place in late January until the end of February, this variable will have a direct effect on the rate of breeding and thus on the conservation of this species, because the species can find a new suitable area outside of high humanisation and increase its chance of successful breeding. Of course, climate change will cause the average annual temperature to rise by 2070, and this will favour the early onset of reproduction. Therefore, according to the analysis and scenarios considered in this study, global warming cannot have a negative effect on the toad species. However, a careful assessment of the status of other competing species in conjunction with the Talysh toad could provide a better explanation of the impact of climate change.

Global warming leads to larger bats with a faster life history pace in the long-lived Bechstein’s bat (Myotis bechsteinii)

Whether species can cope with environmental change depends considerably on their life history. Bats have long lifespans and low reproductive rates which make them vulnerable to environmental changes. Global warming causes Bechstein’s bats (Myotis bechsteinii) to produce larger females that face a higher mortality risk. Here, we test whether these larger females are able to offset their elevated mortality risk by adopting a faster life history. We analysed an individual-based 25-year dataset from 331 RFID-tagged wild bats and combine genetic pedigrees with data on survival, reproduction and body size. We find that size-dependent fecundity and age at first reproduction drive the observed increase in mortality. Because larger females have an earlier onset of reproduction and shorter generation times, lifetime reproductive success remains remarkably stable across individuals with different body sizes. Our study demonstrates a rapid shift to a faster pace of life in a mammal with a slow life history.

Palaeohistology reveals a slow pace of life for the dwarfed Sicilian elephant

The 1-m-tall dwarf elephant Palaeoloxodon falconeri from the Pleistocene of Sicily (Italy) is an extreme example of insular dwarfism and epitomizes the Island Rule. Based on scaling of life-history (LH) traits with body mass, P. falconeri is widely considered to be ‘r-selected’ by truncation of the growth period, associated with an early onset of reproduction and an abbreviated lifespan. These conjectures are, however, at odds with predictions from LH models for adaptive shifts in body size on islands. To settle the LH strategy of P. falconeri, we used bone, molar, and tusk histology to infer growth rates, age at first reproduction, and longevity. Our results from all approaches are congruent and provide evidence that the insular dwarf elephant grew at very slow rates over an extended period; attained maturity at the age of 15 years; and had a minimum lifespan of 68 years. This surpasses not only the values predicted from body mass but even those of both its giant sister taxon (P. antiquus) and its large mainland cousin (L. africana). The suite of LH traits of P. falconeri is consistent with the LH data hitherto inferred for other dwarfed insular mammals. P. falconeri, thus, not only epitomizes the Island Rule but it can also be viewed as a paradigm of evolutionary change towards a slow LH that accompanies the process of dwarfing in insular mammals.

Life history alterations upon oral and hemocoelic bacterial exposure in the butterfly Melitaea cinxia.

Life history strategies often shape biological interactions by specifying the parameters for possible encounters, such as the timing, frequency, or way of exposure to parasites. Consequentially, alterations in life‐history strategies are closely intertwined with such interaction processes. Understanding the connection between life‐history alterations and host–parasite interactions can therefore be important to unveil potential links between adaptation to environmental change and changes in interaction processes. Here, we studied how two different host–parasite interaction processes, oral and hemocoelic exposure to bacteria, affect various life histories of the Glanville fritillary butterfly Melitaea cinxia. We either fed or injected adult butterflies with the bacterium Micrococcus luteus and observed for differences in immune defenses, reproductive life histories, and longevity, compared to control exposures. Our results indicate differences in how female butterflies adapt to the two exposure types. Orally infected females showed a reduction in clutch size and an earlier onset of reproduction, whereas a reduction in egg weight was observed for hemocoelically exposed females. Both exposure types also led to shorter intervals between clutches and a reduced life span. These results indicate a relationship between host–parasite interactions and changes in life‐history strategies. This relationship could cast restrictions on the ability to adapt to new environments and consequentially influence the population dynamics of a species in changing environmental conditions.

Computed tomography shows high fracture prevalence among physically active forager-horticulturalists with high fertility.

Modern humans have more fragile skeletons than other hominins, which may result from physical inactivity. Here, we test whether reproductive effort also compromises bone strength, by measuring using computed tomography thoracic vertebral bone mineral density (BMD) and fracture prevalence among physically active Tsimane forager-horticulturalists. Earlier onset of reproduction and shorter interbirth intervals are associated with reduced BMD for women. Tsimane BMD is lower versus Americans, but only for women, contrary to simple predictions relying on inactivity to explain skeletal fragility. Minimal BMD differences exist between Tsimane and American men, suggesting that systemic factors other than fertility (e.g. diet) do not easily explain Tsimane women's lower BMD. Tsimane fracture prevalence is also higher versus Americans. Lower BMD increases Tsimane fracture risk, but only for women, suggesting a role of weak bone in women's fracture etiology. Our results highlight the role of sex-specific mechanisms underlying skeletal fragility that operate long before menopause.

Northern ragweed ecotypes flower earlier and longer in response to elevated CO2: what are you sneezing at?

Significant changes in plant phenology and flower production are predicted over the next century, but we know relatively little about geographic patterns of this response in many species, even those that potentially impact human wellbeing. We tested for variation in flowering responses of the allergenic plant, Ambrosia artemisiifolia (common ragweed). We grew plants originating from three latitudes in the Northeastern USA at experimental levels of CO2 (400, 600, and 800 µL L−1). We hypothesized that northern ecotypes adapted to shorter growing seasons would flower earlier than their southern counterparts, and thus disproportionately allocate carbon gains from CO2 to reproduction. As predicted, latitude of origin and carbon dioxide level significantly influenced the timing and magnitude of flowering. Reproductive onset occurred earlier with increasing latitude, with concurrent increases in the number of flowers produced. Elevated carbon dioxide resulted in earlier reproductive onset in all ecotypes, which was significantly more pronounced in the northern populations. We interpret our findings as evidence for ecotypic variation in ragweed flowering time, as well in responses to CO2. Thus, the ecological and human health implications of common ragweed’s response to global change are likely to depend on latitude. We conclude that increased flower production, duration, and possibly pollen output, can be expected in Northeastern United States with rising levels of CO2. The effects are likely, however, to be most significant in northern parts of the region.

Live Fast, Die Young: Experimental Evidence of Population Extinction Risk due to Climate Change.

Evidence has accumulated in recent decades on the drastic impact of climate change on biodiversity. Warming temperatures have induced changes in species physiology, phenology, and have decreased body size. Such modifications can impact population dynamics and could lead to changes in life cycle and demography. More specifically, conceptual frameworks predict that global warming will severely threaten tropical ectotherms while temperate ectotherms should resist or even benefit from higher temperatures. However, experimental studies measuring the impacts of future warming trends on temperate ectotherms' life cycle and population persistence are lacking. Here we investigate the impacts of future climates on a model vertebrate ectotherm species using a large-scale warming experiment. We manipulated climatic conditions in 18 seminatural populations over two years to obtain a present climate treatment and a warm climate treatment matching IPCC predictions for future climate. Warmer temperatures caused a faster body growth, an earlier reproductive onset, and an increased voltinism, leading to a highly accelerated life cycle but also to a decrease in adult survival. A matrix population model predicts that warm climate populations in our experiment should go extinct in around 20 y. Comparing our experimental climatic conditions to conditions encountered by populations across Europe, we suggest that warming climates should threaten a significant number of populations at the southern range of the distribution. Our findings stress the importance of experimental approaches on the entire life cycle to more accurately predict population and species persistence in future climates.

Early-life reproduction is associated with increased mortality risk but enhanced lifetime fitness in pre-industrial humans.

The physiology of reproductive senescence in women is well understood, but the drivers of variation in senescence rates are less so. Evolutionary theory predicts that early-life investment in reproduction should be favoured by selection at the cost of reduced survival and faster reproductive senescence. We tested this hypothesis using data collected from preindustrial Finnish church records. Reproductive success increased up to age 25 and was relatively stable until a decline from age 41. Women with higher early-life fecundity (ELF; producing more children before age 25) subsequently had higher mortality risk, but high ELF was not associated with accelerated senescence in annual breeding success. However, women with higher ELF experienced faster senescence in offspring survival. Despite these apparent costs, ELF was under positive selection: individuals with higher ELF had higher lifetime reproductive success. These results are consistent with previous observations in both humans and wild vertebrates that more births and earlier onset of reproduction are associated with reduced survival, and with evolutionary theory predicting trade-offs between early reproduction and later-life survival. The results are particularly significant given recent increases in maternal ages in many societies and the potential consequences for offspring health and fitness.

Family relationships in childhood, pubertal timing, and subsequent reproductive strategies among adolescents

The evolutionary theory of socialization of Belsky, Steinberg, and Draper was investigated on the empirical basis of a longitudinal sample of 26 adolescent girls and boys who were born in Berlin during German reunification, as well as their mothers. Consistent with the theory, pubertal timing of the girls (but not of the boys) was predicted by the quality of parental relations in childhood, and pubertal timing of the girls (but not of the boys) was a significant predictor of the age at first intercourse. The results suggest that there are different developmental pathways for girls and boys with respect to the predictions of the evolutionary theory of socialization of Belsky et al. The findings also support the hypothesis that early onset of reproduction and frequent reproduction may be two different aspects of a quantitative reproductive strategy.

Early onset of reproduction in the agile antechinus, Antechinus agilis

Ovulation in the agile antechinus, Antechinus agilis, usually occurs when the rate of change of photoperiod in spring is increasing at 127–137 s day–1. We report responses to a much slower rate of change of photoperiod in a population in far east Gippsland, Victoria, and discuss the ecological consequences and management significance of early breeding.

Selection on flowering time in Mediterranean high-mountain plants under global warming

Under climate warming, plants will undergo novel selective pressures to adjust reproductive timing. Adjustment between reproductive phenology and environment is expected to be higher in arctic and alpine habitats because the growing season is considerably short. As early- and late-flowering species reproduce under very different environmental conditions, selective pressures on flowering phenology and potential effects of climate change are likely to differ between them. However, there is no agreement on the magnitude of the benefits and costs of early- vs. late-flowering species under a global warming scenario. In spite of its relevance, phenotypic selection on flowering phenology has rarely been explored in alpine plants and never in Mediterranean high mountain species, where selective pressures are very different due to the summer drought imposed over the short growth season. We hypothesized that late-flowering plants in Mediterranean mountains should present stronger selective pressures towards early onset of reproduction than early-flowering species, because less water is available in the soil as growing season progresses. We performed selection analyses on flowering onset and duration in two high mountain species of contrasting phenology. Since phenotypic selection can be highly context-dependent, we studied several populations of each species for 2 years, covering their local altitudinal ranges and their different microhabitats. Surrogates of biotic selective agents, like fruitset for pollinators and flower and fruit loss for flower and seed predators, were included in the analysis. Differences between the early- and the late-flowering species were less than expected. A consistent negative correlational selection of flowering onset and duration was found affecting plant fitness, i.e., plants that bloomed earlier flowered for longer periods improving plant fitness. Nevertheless, the late-flowering species may experience higher risks under climate warming because in extremely warm and dry years the earlier season does not bring about a longer flowering duration due to summer drought.

Seasonal constraints and reproductive performance in female Common hamsters ( Cricetus cricetus)

Common hamsters ( Cricetus cricetus) are hibernators and therefore show a pronounced seasonal breeding behaviour. Previous studies suggest that an early onset of reproduction after vernal emergence can be crucial for reproductive success in the current year. In Vienna, the winter 2005/06 was exceptionally cold and snow cover lasted until late March. This enabled us to investigate the effects of harsh winter conditions on seasonal timing and reproductive success in female Common hamsters. We investigated differences in the timing of the active season, reproductive performance and physical condition before hibernation between 2006 and previous years (2003–05) to determine potential environmental effects. Hamsters were live-trapped throughout the active period, weighed, individually marked and reproductive status was determined. The number of litters per season and litter size were determined in individual females. Vernal emergence in 2006 was considerably delayed and females mated significantly later than in 2003–05. Reproductive output in 2006 was about half that of the preceding years. This was particularly pronounced in the size of the females’ first litters per season. The number of litters per female was similar in all periods. Almost 90% of the females in 2006 mated shortly after parturition and overlapped lactation of the first and gestation of the second litter. In 2003–05, only about one-third of the focal females successfully produced a litter after a postpartum oestrus. The time delay in spring 2006 led to a shorter active season compared to previous years reflecting the time constraints in this species. In conclusion, the results demonstrate that environmental factors can affect seasonal timing, reproductive output and preparation for hibernation in female Common hamsters.

Ontogenetic changes in tolerance to herbivory in Arabidopsis

Tolerance to herbivory-the ability of plants to maintain fitness despite herbivore damage-is expected to change during the life cycle of plants because the physiological mechanisms underlying tolerance to herbivory are linked to growth, and resource allocation to growth changes throughout ontogeny. We used the model plant Arabidopsis thaliana to test two hypotheses: that tolerance increases as plants grow, and that tolerance decreases at the onset of reproduction. We chose three accessions previously reported to vary for resistance to herbivory in order to explore whether tolerance and resistance are inversely related. Cabbage looper (Trichoplusia ni) larvae were allowed to feed on plants at either the four-leaf, six-leaf, or 1st-flower developmental stage until 50% of the leaf area was removed. Overall, we found a trend for increased tolerance with ontogenetic stage, but there were important differences among accessions in their response to herbivory at different stages. Tolerance did not decrease with the onset of flowering, nor did we find any correlation between resistance and tolerance levels. Three main plant traits correlated strongly with tolerance: stem mass, an earlier onset of reproduction and a longer fruiting period. This study suggests there may be considerable variation in ontogenetic patterns of tolerance in natural populations of A. thaliana, and warrants further investigations with more accessions or natural populations, and detailed measurements of traits purported to contribute to tolerance in our quest to understand the mechanisms of tolerance to herbivory.

Endocrine mechanisms of primate life history trade‐offs: Growth and reproductive maturation in vervet monkeys

Life history theory predicts that the timing of maturation will result from a trade-off between growth and the age of first reproduction. This trade-off and its mechanisms of action are still poorly understood in many species and have not been well studied at the individual level. This study examined hypothesized trade-offs between growth and reproductive maturation in wild populations of vervet monkeys (Cercopithecus aethiops) from Kenya, East Africa. Individuals were sampled from four populations in widely separated sites differing in temperature, altitude, and rainfall. Biological samples and morphometric measures were collected from 50 adult males, 83 adult females, and 225 juveniles. Gonadal steroids and leptin levels were analyzed by radioimmunoassay of sera from 136 juvenile males and 90 juvenile females. Cross-sectional profiles of morphometric and endocrine data were used to assess the onset and cessation of growth in relation to sexual maturation. Gonadal steroids were used to assess sexual maturation and breeding onset. Leptin was used as an index of nutritional state. Estimates of mortality were derived from population age-structure. Across populations, higher resource productivity and nutrient status were associated with more rapid growth. Shorter growth duration was associated with earlier reproductive onset. These findings provide support for models of trade-offs between the timing of growth completion and reproductive onset, but they are contradicted by the evidence that reproduction precedes the cessation of growth in these populations. The biphasic actions of estradiol provide an alternative model and mechanism for the growth-reproduction trade-off.

Life history trade-offs explain the evolution of human pygmies

Explanations for the evolution of human pygmies continue to be a matter of controversy, recently fuelled by the disagreements surrounding the interpretation of the fossil hominin Homo floresiensis. Traditional hypotheses assume that the small body size of human pygmies is an adaptation to special challenges, such as thermoregulation, locomotion in dense forests, or endurance against starvation. Here, we present an analysis of stature, growth, and individual fitness for a large population of Aeta and a smaller one of Batak from the Philippines and compare it with data on other pygmy groups accumulated by anthropologists for a century. The results challenge traditional explanations of human pygmy body size. We argue that human pygmy populations and adaptations evolved independently as the result of a life history tradeoff between the fertility benefits of larger body size against the costs of late growth cessation, under circumstances of significant young and adult mortality. Human pygmies do not appear to have evolved through positive selection for small stature-this was a by-product of selection for early onset of reproduction.

Aspects of the life history of Siderastrea stellata in the tropical Western Atlantic, Brazil

Summary This paper presents the first study of the life history of a Brazilian reef coral, with reference to Siderastrea stellata. Fecundity and growth rate were determined for four colony size classes collected from the Itacolomis Reefs, Brazil (16°53.816′S; 039° 04.965′W). Colony size-frequency distribution was analyzed to evaluate the potential for maintenance, growth and recovery of the population. The fecundity of size class 1 (up to 2.5 cm in diameter or 5 cm2) was significantly lower than that of the other three classes, which did not differ among themselves (averaging 8 oocytes/polyp). Colonies with less than 1.8 cm in diameter (or 2.5 cm2) did not have gametes. The number of mature polyps tended to increase with colony size: some polyps of class 2 (2.5 < x ≤7.9 cm diameter) colonies did not have oocytes, while polyps from classes 3 (7.9 < x ≤ 12.6 cm diameter) and 4 (× >12.6 cm diameter) were always fertile. The linear extension was similar among the four size classes, being around 2.5 mm per year, corresponding to an annual increase of 5 mm in colony diameter. The first gametes occurred in the third year, with planulation occurring during the fourth year of life. Colony size-frequency distribution showed the presence of many size classes, as would be expected on undisturbed reefs. Class 2 colonies were the most abundant; the largest colony was 486 cm2 (or 25cm diameter), i.e. possibly 50 years old. Ten percent of colonies were within size class 1 (recruits) and 90% were sexually mature. The early onset of reproduction, brooding of larvae, intermediate size (average colony size at the studied site was 62 cm2, or 9 cm diameter), and massive corallum may be advantageous in the habitat preferentially occupied by S. stellata, namely, the reef top and horizontal substrates in shallow waters <10 m deep. The presence of large colonies, characterized by lower mortality rate, larger reproductive output and greater longevity, also indicates a low probability of population extinction. Disturbances that decrease colony sizes to less than 20 cm2 (or 5 cm in diameter), corresponding to a 10 years old colony, may sharply reduce the population's prospects of survival, since below this size, maximum fecundity has yet to be attained.

Competitive interactions between native and exotic earthworm species as influenced by habitat quality in a California grassland

Worldwide, anthropogenic disturbance has contributed to reductions in native earthworm abundance and diversity and subsequent establishment of exotic populations. Exotic earthworm species dominate the earthworm community primarily in nutrient-enriched soils characteristic of urbanized and rural areas, while native species persist in less disturbed habitat. We hypothesized that exotic species may displace native species through competitive interactions, but only under conditions of high resource availability. To test this we manipulated both grassland productivity and the presence and density of intra- and interspecific competitors in field and laboratory experiments with two common species, the native megascolecid Argilophilus marmoratus Eisen 1893 and the exotic lumbricid Aporrectodea trapezoides Dugés 1828. Overall, Ap. trapezoides maintained greater relative growth than Ar. marmoratus. The difference in growth between the two species declined with decreasing habitat quality, primarily due to lower relative growth of Ap. trapezoides in less productive grasslands. As the competitor species, Ap. trapezoides had a negative effect on both itself and Ar. marmoratus in all habitat types, while Ar. marmoratus as competitor had a more neutral effect. Reproductive development followed the same general pattern, but to become reproductive Ap. trapezoides required almost double the amount of relative growth as Ar. marmoratus. Both species had a negative effect on potential food resources, including microbial biomass and belowground plant biomass, but Ap. trapezoides reduced resources more than Ar. marmoratus in all habitat types. Ap. trapezoides achieved a greater relative growth than Ar. marmoratus in soils with high resource availability, but it lost proportionally more mass as resources declined. Thus, Ap. trapezoides attempting to colonize less productive grasslands may simply deplete available resources and fail to achieve sufficient growth for reproductive development. Our results suggest that interspecific competition has the potential to prevent Ar. marmoratus from recolonizing pastures dominated by Ap. trapezoides. Both species respond to enhanced resources in these pastures, but in resource-rich habitats Ap. trapezoides may exclude Ar. marmoratus through greater and faster growth per unit resource consumption coupled with earlier onset of reproduction. Ar. marmoratus is the weaker competitor of the two, but its negative effect on Ap. trapezoides in less productive grassland may exacerbate the role of resource limitation in preventing Ap. trapezoides from expanding its range.

Anti‐ageing strategies: prevention or therapy?

Biogerontology—the study of the biological basis of ageing—is now a mature research field that could eventually offer effective applications to ease the burden of old age. Unlike other research fields that focus predominantly on producing information, a central characteristic of biogerontology is that it searches for means of preventing the onset of age‐related diseases and improving quality of life in old age. Biogerontologists have already produced a large body of descriptive and mechanistic data that allows them to define some general principles of ageing. Although their accumulated research has not yet uncovered any universal markers of ageing, the principles that have been derived could lead to the development of practical and effective anti‐ageing strategies based on rational approaches. ![][1] First, the ‘life‐history principle’ describes ageing as an emergent phenomenon that takes place primarily in protected environments, and which allows survival beyond the natural lifespan that would occur in the wild. By contrast, the natural lifespan of a species, also termed the ‘essential lifespan’ (ELS; Rattan, 2000) or ‘warranty period’ (Carnes et al , 2003), is the time required to fulfil the Darwinian purpose of life; that is, successful reproduction. Species that undergo fast maturation and have an early onset of reproduction with high reproductive potential generally have a short ELS, whereas slow maturation with late onset and low potential is concurrent with a long ELS. For example, the ELS for Drosophila is less than a week but that for Homo sapiens is about 50 years, even though both species can and do live for much longer periods in protected laboratory environments and modern societies, respectively. Consequently, the period of extended survival beyond the ELS is defined as the period of ageing. Second, the ‘non‐genetic principle’ asserts that there is neither a genetic cause for, nor a programme that controls, the ageing process. … [1]: /embed/graphic-1.gif

Living slow and dying young? Life‐history strategy and age‐specific survival rates in a precocial small mammal

1. Mammalian life histories can be ordered along a slow-fast continuum from slow-developing, long-lived species with low reproductive rates at one end to rapidly developing, short-lived species with high reproductive rates at the other. Body size and mortality rate are strong correlates of the slow-fast axis, whereby juvenile and adult mortality rates correlate positively but are linked to certain life-history traits with differing strengths. The strong covariation of life-history traits renders it difficult to evaluate the adaptive value of single life-history elements. Species that deviate from the common pattern might help to identify specific selected strategies. 2. Caviomorph rodents show an unusual combination of life-history traits. Like slow-living mammals, they produce few precocial young after long gestation periods, but they have the early maturation potential of their fast-living counterparts. This combination of life-history traits suggests low levels of juvenile mortality but high adult mortality rates, and thus an unusually low ratio of juvenile to adult mortality compared to other small mammals. To test these predictions, we modelled age-specific survival probabilities using capture-recapture data from a wild population of Cavia magna. 3. Patterns of age-specific survival rates were in accordance with the predictions, but atypical for small mammals. Levels of adult survival were low, and comparable to those of much smaller rodent species. Juvenile survival probabilities were high relative to those reported for other small mammals and reached adult levels after only 1 month. The ratio of adult to early juvenile survival depended strongly on the date of birth. Whereas survival of young from the first birth cohort in spring did not differ from that of adults, early survivorship of later cohorts was lower. 4. Our results fit expectations from life-history theory and suggest that high levels of adult mortality selected for the early onset of reproduction in wild cavies. The comparatively low juvenile mortalities are probably a consequence of the precocial state of the cavy offspring. We suggest that the reproductive strategy of cavies represents a different solution to the trade-off between fecundity and juvenile survival compared to altricial small mammals.