PMC

Forward simulation showing the change in population mean female state based on optimal reproductive decisions. Here, females begin the breeding season with an arbitrary distribution of energetic reserves and the overall pattern is decreasing reserves throughout the breeding season. The pattern of decline in condition is similar for a our baseline parameter set that predicts a DA pattern of investment and a ‘good offspring’ set (where offspring exhibit relatively high fitness independent of parental investment relative to the baseline finch model; see text for additional details) which predicts RC. Circles, baseline (DA); squares, good offspring (RC).

Fitness return curves for fixed strategies for a model exhibiting RC. Results are shown here for the good offspring model, where the baseline survivorship of offspring is higher relative to our baseline finch model (see text for additional details). The reduction in fitness for females that do not have the option of foregoing reproduction with males (as opposed to a facultative strategy or fixed investment) is moderate for females mating with males of low or intermediate quality (the height difference between dotted and short dashed lines) relative to a high-quality mate. (a) Poor; (b) medium; (c) good males. Solid line, optimum female investment; dotted line, no reproduction; long-dashed line, minimum; short-dashed line, low female investment.

Fitness return curves are shown here for the finch baseline model (a–c), where females have a random expectation of future mate quality, and the good males late model (d–f), where expected future mate quality is high (see text for additional details). Rows correspond to predictions for different current mate qualities (i.e. low, intermediate or high). Lines on each panel show the average fitness return for a fixed investment with the current mate. Fitness return curves are relatively flat over time and the cost of fixed reproductive investment (the difference in height between fixed strategies and the optimum facultative strategy) is relatively small when the expectation of future mate quality is random (a–c) compared to when future mate quality is predictably good (d–f). (a,d) poor male; (b,e) medium male; (c,f) good male. Solid line, optimum; dotted line, minimum; long-dashed line, low; short-dashed line, high female investment.

Dynamic program results showing the optimal mean level of female investment (D^*) across reproductive opportunities during the breeding season. (a) Results for the finch baseline model; all other panels show results for runs relative to this baseline. (b) Results where reproductive investment is relatively costly. (c) Results where female investment has a relatively high fitness effect on offspring. (d) Results where male quality has a relatively low fitness effect on offspring. (e,f) Results where the distribution of male quality changes during the breeding season so that the average male quality is relatively poor later in the season or relatively good, respectively. (g) Results where offspring baseline survivorship is relatively high. (h) Results where male quality is relatively high late in the breeding season and offspring survivorship is relatively high. In general, (a–f) show a pattern of DA in female reproductive investment, where females invest relatively heavily in offspring of higher quality males. Here, females can have a relatively large impact on offspring fitness independent of the effect of mate quality on offspring fitness. (g,h) A clear pattern of RC, where females invest relatively more in offspring of lower quality males. Here, female reproductive returns are relatively low for higher investment and future mating opportunities are limited. Solid line, good; dashed line, medium; dotted line, poor female state.

Optimal female reproductive investment decisions (D^*) in relation to male quality (poor, intermediate and high). A typical optimal reproductive investment decision matrix from our model (shown here are the optimal decision matrices for our ‘costly reproduction’ model where reproductive investment by females for a given fitness increase in offspring requires a relatively higher energetic expenditure compared to the baseline finch model; see text for additional details). The three matrices each correspond to a different current mate quality, poor (a), intermediate (b) or high (c). Here, females are predicted to forego reproduction with a poor quality male irrespective of energetic state until quite late in the breeding season when terminal reproductive investment is predicted. The overall profile of investment predictions (0 is foregoing reproduction, 1 is minimal investment to produce offspring and 2, 3 and 4 are increasing levels of ‘extra investment’ to enhance offspring fitness) is similar for mates of intermediate and high quality, with low extra investment predicted at higher female energetic state, increasing towards the end of the breeding season. There is a weak interaction between female energetic state and mate quality, with female investment investing slightly more conservatively with intermediate-quality mates.