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Early Reproduction (early + reproduction)
Selected AbstractsLifespan is unrelated to investment in reproduction in populations of mammals and birds in captivityECOLOGY LETTERS, Issue 10 2007Robert E. Ricklefs Abstract We examined the relationship between number of offspring produced to a certain age and subsequent longevity in captive zoo populations of 18 species of mammal and 12 species of bird. The age cut-offs in each analysis were set to include 50%, 75% and 90% of the offspring produced in each of the population samples. Only one of 68 regressions was significant, and its slope was positive. In addition, we examined the relationship between age at first reproduction up to a certain age and longevity after that age, generally 5 years (3,8), among 17 species of mammal and 12 species of bird. Only one of these regressions had a significantly positive slope, indicating that early reproduction rarely reduces lifespan. Overall, we found no evidence that producing offspring in a zoo environment influences the age at death. Thus, although trade-offs might apply in natural populations under resource limitation, neither pregnancy, growth of the foetus and lactation in mammals, nor egg production in birds, reduces lifespan in the absence of such stress. If genetically based or other intrinsic antagonistic pleiotropy underlies the evolution of senescence, it was not evident in our analyses. [source] Pulsed resources affect the timing of first breeding and lifetime reproductive success of tawny owlsJOURNAL OF ANIMAL ECOLOGY, Issue 2 2010A. Millon Summary 1.,According to life-history theory, environmental variability and costs of reproduction account for the prevalence of delayed reproduction in many taxa. Empirical estimates of the fitness consequences of different ages at first breeding in a variable environment are few however such that the contributions of environmental and individual variability remains poorly known. 2.,Our objectives were to elucidate processes that underpin variation in delayed reproduction and to assess lifetime consequences of the age of first breeding in a site-faithful predator, the tawny owl Strix aluco L. subjected to fluctuating selection linked to cyclical variation in vole density (typically 3-year cycles with low, increasing and decreasing vole densities in successive years). 3.,A multistate capture,recapture model revealed that owl cohorts had strikingly different juvenile survival prospects, with estimates ranging from 0·08 to 0·33 respectively for birds born in Decrease and Increase phases of the vole cycle. This resulted in a highly skewed population structure with >75% of local recruits being reared during Increase years. In contrast, adult survival remained constant throughout a vole cycle. The probability of commencing reproduction was lower at age 1 than at older ages, and especially so for females. From age 2 onwards, pre-breeders had high probabilities of entering the breeding population. 4.,Variation in lifetime reproductive success was driven by the phase of the vole cycle in which female owls started their breeding career (26,47% of variance explained, whether based on the number of local recruits or fledglings), more than by age at first breeding or by conditions experienced at birth. Females who postponed reproduction to breed for the first time at age 3 during an Increase phase, produced more recruits, even when accounting for birds that may have died before reproduction. No such effects were detected for males. 5.,Sex-specific costs of early reproduction may have accounted for females being more prone to delay reproduction. Contrary to expectations from a best-of-a-bad job strategy, early-hatched, hence potentially higher-quality females were more likely to breed at age 1, but then experienced rapidly declining food resources and so seemed caught in a life-history trap set by the multiannual vole cycle. [source] Birthweight and paternal involvement predict early reproduction in British women: Evidence from the National Child Development StudyAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 2 2010Daniel Nettle There is considerable interest in the mechanisms maintaining early reproduction in the most socioeconomically disadvantaged groups in developed countries. Previous research has suggested that differential exposure to early-life factors such as low birthweight and lack of paternal involvement during childhood may be relevant. Here, we used longitudinal data on the female cohort members from the UK National Child Development Study (n = 3,014,4,482 depending upon variables analyzed) to investigate predictors of early reproduction. Our main outcome measures were having a child by age 20, and stating at age 16 an intended age of reproduction of 20 years or lower. Low paternal involvement during childhood was associated with increased likelihood of early reproduction (O.R. 1.79,2.25) and increased likelihood of early intended reproduction (O.R. 1.38,2.50). Low birthweight for gestational age also increased the odds of early reproduction (O.R. for each additional s.d. 0.88) and early intended reproduction (O.R. for each additional s.d. 0.81). Intended early reproduction strongly predicted actual early reproduction (O.R. 5.39, 95% CI 3.71,7.83). The results suggest that early-life factors such as low birthweight for gestational age, and low paternal involvement during childhood, may affect women's reproductive development, leading to earlier target and achieved ages for reproduction. Differential exposure to these factors may be part of the reason that early fertility persists in socioeconomically disadvantaged groups. We discuss our results with respect to the kinds of interventions likely to affect the rate of teen pregnancy. Am. J. Hum. Biol., 2010. © 2009 Wiley-Liss, Inc. [source] Early reproductive maturity among Pumé foragers: Implications of a pooled energy model to fast life historiesAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2009Karen L. Kramer Life history theory places central importance on relationships between ontogeny, reproduction, and mortality. Fast human life histories have been theoretically and empirically associated with high mortality regimes. This relationship, however, poses an unanswered question about energy allocation. In epidemiologically stressful environments, a greater proportion of energy is allocated to immune function. If growth and maintenance are competing energetic expenditures, less energy should be available for growth, and the mechanism to sustain rapid maturation remains unclear. The human pattern of extended juvenile provisioning and resource sharing may provide an important source of variation in energy availability not predicted by tradeoff models that assume independence at weaning. We consider a group of South American foragers to evaluate the effects that pooled energy budgets may have on early reproduction. Despite growing up in an environment with distinct seasonal under-nutrition, harsh epidemiological conditions, and no health care, Pumé girls mature quickly and initiate childbearing in their midteens. Pooled energy budgets compensate for the low productivity of girls not only through direct food transfers but importantly by reducing energy they would otherwise expend in foraging activities to meet metabolic requirements. We suggest that pooled energy budgets affect energy availability at both extrinsic and intrinsic levels. Because energy budgets are pooled, Pumé girls and young women are buffered from environmental downturns and can maximize energy allocated to growth completion and initiate reproduction earlier than a traditional bound-energy model would predict. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source] Fetal programming: Adaptive life-history tactics or making the best of a bad start?AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 1 2005James Holland Jones Fetal programming is an ontogenetic phenomenon of increasing interest to human biologists. Because the downstream consequences of fetal programming have clear impacts on specific life-history traits (e.g., age at first reproduction and the general age-pattern of reproductive investments), a number of authors have raised the question of the adaptive significance of fetal programming. In this paper, I review in some detail several classical models in life-history theory and discuss their relative merits and weaknesses for human biology. I suggest that an adequate model of human life-history evolution must account for the highly structured nature of the human life cycle, with its late age at first reproduction, large degree of iteroparity, highly overlapping generations, and extensive, post-weaning parental investment. I further suggest that an understanding of stochastic demography is essential for answering the question of the adaptive significance of fetal programming, and specifically the finding of low birth weight on smaller adult body size and earlier age at first reproduction. Using a stage-structured stochastic population model, I show that the downstream consequences of early deprivation may be "making the best of a bad start" rather than an adaptation per se. When a high-investment strategy entails survival costs, the alternate strategy of early reproduction with relatively low investment may have higher fitness than trying to play the high-investment strategy and failing. Am. J. Hum. Biol. 17:22,33, 2005. © 2004 Wiley-Liss, Inc. [source] Variations in size structure, growth and reproduction in Japanese plantain (Plantago asiatica L.) between exposed and shaded populationsPLANT SPECIES BIOLOGY, Issue 1 2001Tsuyoshi Kobayashi Abstract Plantago asiatica is a perennial herb that is distributed over a wide range of east Eurasia. The population structure, growth and reproduction in exposed (E-) and shaded (S-) populations of P. asiatica were examined in the Kanto District of eastern Japan. In both populations, the plant size structure showed a bimodal distribution during spring to early summer, in which the two modes corresponded to smaller seedlings and larger overwintered plants, respectively. In autumn, this distribution became unimodal due to seedling growth. However, this change occurred later in the S-population because of suppressed growth in the seedlings. In the S-population, flowering also began later in the growing season and the threshold plant size for flowering was larger than that of the E-population. Biomass allocation to the rhizomes was greater in autumn in the reproductive plants of the S-population. Growth and biomass allocation in plants grown from seeds collected from each population were compared under phytotron conditions. Near a saturated photon flux density, E-population plants had a higher relative growth rate than S-population plants. Therefore, E-population plants should allocate resources to reproductive organs sooner. Shaded population plants were not vigorous in their growth and reproduction. Seed size (dry weight per grain) was significantly greater in the S-population than in the E-population, both in the field and under phytotron conditions. These results suggest that ecotypic differentiation in life-history strategies, which is mainly due to light availability, occurs among local P. asiatica populations. The effects of severe trampling on early reproduction in the E-population are also discussed. [source] Synchrony between growth and reproductive patterns in human females: Early investment in growth among Pumé foragersAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2010Karen L. Kramer Abstract Life history is an important framework for understanding many aspects of ontogeny and reproduction relative to fitness outcomes. Because growth is a key influence on the timing of reproductive maturity and age at first birth is a critical demographic variable predicting lifetime fertility, it raises questions about the synchrony of growth and reproductive strategies. Among the Pumé, a group of South American foragers, young women give birth to their first child on average at age 15.5. Previous research showed that this early age at first birth maximizes surviving fertility under conditions of high infant mortality. In this study we evaluate Pumé growth data to test the expectation that if early reproduction is advantageous, then girls should have a developmental trajectory that best prepares them for young childbearing. Analyses show that comparatively Pumé girls invest in skeletal growth early, enter puberty having achieved a greater proportion of adult body size and grow at low velocities during adolescence. For early reproducers growing up in a food-limited environment, a precocious investment in growth is advantageous because juveniles have no chance of pregnancy and it occurs before the onset of the competing metabolic demands of final reproductive maturation and childbearing. Documenting growth patterns under preindustrial energetic and demographic conditions expands the range of developmental variation not otherwise captured by normative growth standards and contributes to research on human phenotypic plasticity in diverse environments. Am J Phys Anthropol, 2010. © 2009 Wiley-Liss, Inc. [source] Estimates of heritability for reproductive traits in captive rhesus macaque femalesAMERICAN JOURNAL OF PRIMATOLOGY, Issue 9 2010Christine Gagliardi Abstract Records from a colony of captive Indian rhesus macaques (Macaca mulatta) were used to estimate heritability for a number of reproductive traits. Records were based on a total of 7,816 births by 1,901 females from 1979 to 2007. Heritability was estimated with a linear animal model using a multiple trait derivative free REML set of programs. Because no male parents were identified, the numerator relationship matrix contained female kinships established over six generations. Reproductive traits included female age at the birth of the first, second and last infant, age at death, inter-birth intervals, number of infants born per female and infant survival. Heritability for each trait was estimated as the ratio of the additive genetic variance to phenotypic variance adjusted for significant fixed effects. Estimates of heritability for early reproduction ranged from 0.000±0.072 for birth interval after the first reproduction to 0.171±0.062 for age of female at the first infant. Higher estimates of heritability were found for female longevity [0.325±0.143] and for productivity of deceased females born before 1991 [0.221±0.138]. Heritability for infant survival ranged from 0.061±0.018 for survival from 30 days to 1 year to 0.290±0.050 for survival from birth to 30 days when adjusted to an underlying normal distribution. Eight of the 13 estimates of heritability for reproductive traits in this study were different from zero [P<0.05]. Generally, heritability estimates reported in this study for reproductive traits of captive rhesus macaque females are similar to those reported in the literature for free-ranging rhesus macaque females and for similar reproductive traits of other species. These estimates of heritability for reproductive traits appear to be among the first for a relatively large colony of captive rhesus macaque females. Am. J. Primatol. 72:811,819, 2010. © 2010 Wiley-Liss, Inc. [source] | ||||||||||