Abstract
The patterned way in which individuals allocate finite resources to various components of reproduction (e.g. mating effort, reproductive timing and parental investment) is described as a reproductive strategy. As energy is limited, trade-offs between and within aspects of reproductive strategies are expected. The first aim of this study was to derive aspects of reproductive strategies using complete reproductive histories from 718 parous Western Australian women. Factor analysis using a subset of these participants resulted in six factors that represented ‘short-term mating strategy’, ‘early onset of sexual activity’, ‘reproductive output’, ‘timing of childbearing’, ‘breastfeeding’, and ‘child spacing’. This factor structure was internally validated by replication using a second independent subset of the data. The second aim of this study examined trade-offs between aspects of reproductive strategies derived from aim one. Factor scores calculated for each woman were incorporated in generalised linear models and interaction terms were employed to examine the effect of mating behaviour on the relationships between reproductive timing, parental investment and overall reproductive success. Early sexual activity correlates with early reproductive onset for women displaying more long-term mating strategies. Women with more short-term mating strategies exhibit a trade-off between child quantity and child quality not observed in women with a long-term mating strategy. However, women with a short-term mating strategy who delay reproductive timing exhibit levels of parental investment (measured as breastfeeding duration per child) similar to that of women with long-term mating strategies. Reproductive delay has fitness costs (fewer births) for women displaying more short-term mating strategies. We provide empirical evidence that reproductive histories of contemporary women reflect aspects of reproductive strategies, and associations between these strategic elements, as predicted from life history theory.
Highlights
Individuals may exhibit particular strategies to optimize their reproductive output for maximum fitness
Factor structures with one to eleven factors were tested and the six-factor model was the most parsimonious factor structure to exhibit good fit (x2(4) = 4.426, p = 0.351, Root Mean-Square Error of Approximation (RMSEA) = 0.017, PCLOSE = 0.717, Comparative Fit Index (CFI) = 1.000, Tucker-Lewis Index (TLI) = 0.998)
Testing Internal Validity with Second Data Subset Subjecting the second data subset to an exploratory factor analysis with a six-factor set with the eleven variables included above resulted in good fit statistics (x2(4) = 6.692, p = 0.153, RMSEA = 0.043, PCLOSE = 0.499, CFI = 0.999, TLI = 0.989)
Summary
Individuals may exhibit particular strategies to optimize their reproductive output for maximum fitness. Trade-offs are inevitable, and occur within and between elements of reproductive strategies [2]. Aspects of reproductive strategies include mating effort, timing of reproduction and parental effort [5]. Real life measures of these aspects of reproductive strategies and their outcomes include variables such as age at menarche [6], number of sexual partners (desired [7] or actual [8]), age at first birth [9,10] and number of children born [8]. These, and other similar variables, to indicate ‘strategies’ and fitness outcomes. To our knowledge, the empirical organisation of reproductive variables into larger strategies has not been demonstrated for humans
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