Tall young females get ahead: size-specific fecundity in wild kangaroos suggests a steep trade-off with growth

Abstract

When resources are limited, organisms face allocation conflicts. Indeterminate growth creates a persistent conflict with reproduction, as growth may enhance future reproduction, but diverts resources from current reproduction. Little is known about allocation trade-offs in mammals with indeterminate growth. We studied growth and reproduction in adult female eastern grey kangaroos (Macropus giganteus), an iteroparous mammal with indeterminate growth. Allocation trajectories varied with age and size: for 4-year-old females, fecundity increased from 30 to 82% from shortest to average-sized individuals. Older females had high fecundity regardless of size. The smallest females grew 30% more annually than average-sized females, but females that reached average size at an older age had lower growth rates. Environmental conditions affected allocation to size and reproduction. Rainy springs increased fecundity from 61 to 84% for females that had previously reproduced, but rainy winters reduced leg growth. Females in better relative condition grew 40% more than average, whereas most young of females below average relative condition failed to survive to 10 months of age. These results highlight an age-specific trade-off between growth and reproduction. Tall young females benefit from a smaller trade-off between somatic growth and early fecundity than shorter females of the same age, but older females appear to favor reproduction over growth regardless of size. Our study highlights how individual heterogeneity determines trade-offs between life-history components. We speculate that cohort effects affect age-specific reproductive success in this long-lived mammal.

Influence of maternal body size, condition, and age on recruitment of four brown bear populations

“…Brown bears in our study areas, like other long-lived species, invest early in rapid growth in structural size, which is completed by 8−14 years of age; subsequent growth in lean mass occurs when available resources allow (Hilderbrand et al 2018). However, there is individual heterogeneity that likely affects lifehistory tradeoffs between early body growth and reproduction, as seen in other species (see Quesnel et al 2018). Our data suggest that larger females more successfully reproduce and recruit offspring into the population.…”

Universality of indeterminate growth in lizards rejected: the micro-CT reveals contrasting timing of growth cartilage persistence in iguanas, agamas, and chameleons

“…Sebens 3 brought more accurate definitions with a detailed description of growth curves which are variations on attenuating or asymptotic growth. Ectothermic vertebrates (fish, amphibians and reptiles) are considered as groups with indeterminate body growth 4–9 (but see 10–16 ), while endotherms (birds and mammals) are determinate growers 4,17 (but see 18–21 ). Nevertheless, current literature is pointing to the problematic classification of animal taxa to specific groups according to the available definitions of body growth 22–25 .…”

Are You What You Eat? How Protein and Carbohydrate Availability during Development Influence Cricket Cognition and other Fitness Conferring Traits in Adulthood

“…This shift in nutrient intake, even over a short time as adults, could have reversed the adverse consequences of being on either extreme juvenile diet, as was found by a grasshopper study (Ageneotettix deorum; Joern and Behmer, 1997). Similar to what I observed in my study, other studies also provide evidence that growth and early fecundity can be beneficial to fitness (e.g., in the female eastern grey kangaroo Macropus gigantus; Quesnel et al, 2018).…”

“…Another study on birds, using the Siberian jay (Perisoreus infaustus), showed that females trade off reproduction and longevity so as not to risk mortality (Griesser et al, 2017). A complex trade-off between age, size, and fecundity exists in female eastern grey kangaroos (Macropus giganteus), in that older females will trade-off small size in favour of reproduction (Quesnel et al, 2018). More recently, a study of Siberian dwarf hamsters (Phodopus sungorus) and water voles (Arvicola amphibious),…”