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Lee, R. D. (2003). Rethinking the evolutionary theory of aging: transfers, not births, shape senescence in social species. Proc Natl Acad Sci U S A, 100(16), 9637–9642.
Abstract: The classic evolutionary theory of aging explains why mortality rises with age: as individuals grow older, less lifetime fertility remains, so continued survival contributes less to reproductive fitness. However, successful reproduction often involves intergenerational transfers as well as fertility. In the formal theory offered here, age-specific selective pressure on mortality depends on a weighted average of remaining fertility (the classic effect) and remaining intergenerational transfers to be made to others. For species at the optimal quantity-investment tradeoff for offspring, only the transfer effect shapes mortality, explaining postreproductive survival and why juvenile mortality declines with age. It also explains the evolution of lower fertility, longer life, and increased investments in offspring.
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Turner, A., & Kirkpatrick, J. F. (2002). Effects of immunocontraception on population, longevity and body condition in wild mares (Equus caballus). Reprod Suppl, 60, 187–195.
Abstract: Contraception is becoming a common approach for the management of captive and wild ungulates yet there are few data for contraceptive effects on entire populations. Management-level treatment of mares with porcine zona pellucida (PZP) vaccine resulted in zero population growth of the Assateague Island wild horse population within 1 year of initiation of treatment. Contraceptive efficacy was 90% for mares treated twice in the first year and annually thereafter. For mares given a single initial inoculation, contraceptive efficacy was 78%. The effort required to achieve zero population growth decreased, as 95, 83 and 84% of all adult mares were treated in each of the first 3 years, compared with 59 and 52% during the last 2 years. Mortality rates for mares and foals after the initiation of management-level treatments decreased below historic and pretreatment mortality rates of approximately 5%. Two new age classes have appeared among treated animals (21-25 years and > 25 years), indicating an increase in longevity among treated animals. Body condition scores for all horses, all adult mares and non-lactating mares increased significantly between summer 1989 and autumn 1999 but did not change significantly in lactating mares. These results provide reliable data for the construction of realistic models for contraceptive management of free-roaming or captive ungulate populations.
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Wallin, L., Strandberg, E., & Philipsson, J. (2001). Phenotypic relationship between test results of Swedish Warmblood horses as 4-year-olds and longevity. Livestock Production Science, 68(2-3), 97–105.
Abstract: The relationship between longevity and different traits scored in the Swedish Riding Horse Quality Test (RHQT) was studied to evaluate their use as predictors of survival. Data comprised 1815 Warmblood horses born between 1969 and 1982 that had participated in the RHQT as 4-year-olds. Survival information was obtained via a questionnaire sent to owners of horses that had participated in the RHQT between 1973 and 1986. All phenotypic values of traits scored at 4 years of age were adjusted for the effect of place/year (event). Survival analysis was performed taking into account censoring. Traits having significant effects on longevity were: conformation, legs (included in conformation), orthopaedic status, jumping ability, and the horses' combined classification score for dressage and jumping talents, respectively. Orthopaedic health had the greatest influence on longevity, and demonstrated the importance of judging health traits in young sports horses. The results of this study confirmed that there is a significant phenotypic relationship between many of the RHQT traits and longevity, and thus the possibility of using them as predictors of survival.
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