Plant and Animal Reproductive Strategies: Lessons from Offspring Size and Number Tradeoffs

Abstract

The tradeoff between offspring size and number is ubiquitous and manifestly similar in plants and animals despite fundamental differences between the evolutionary histories of these two major life forms. Fecundity (offspring number) primarily affects parental fitness, while offspring size underpins the fitness of parents and offspring. We provide an overview of theoretical models dealing with offspring size and fitness relationships. We follow that with a detailed examination of life-history constraints and environmental effects on offspring size and number, separately in plants and animals. The emphasis is on seed plants, but we endeavor to also summarize information from distinct animal groups-insects, fishes, reptiles, birds, and mammals. Furthermore, we analyse genetic controls on offspring size and number in two model organisms-Arabidopsis and Drosophila. Despite the deep evolutionary divergence between plants and animals, we find four trends in reproductive strategy that are common to both lineages: (i) offspring size is generally less variable than offspring number, (ii) offspring size increases with increasing parent body size, (iii) maternal genes restrict offspring size and increase offspring numbers, while zygotic genes act to increase offspring size; such parent-offspring conflicts are enhanced when there is sibling rivalry, and (iv) variation in offspring size increases under sub-optimal (harsh) environmental conditions. The most salient difference between plants and animals is that the latter tend to produce larger (fewer) offspring under sub-optimal conditions while seed plants invest in smaller (many) seeds, suggesting that maternal genetic control over offspring size increases in plants but decreases in animals with parental care. The time is ripe for greater experimental exploration of genetic controls on reproductive allocation and parent-offspring conflicts in plants and animals under sub-optimal (harsh) environments.

Competing Physiological Demands During Incipient Colony Foundation in a Social Insect: Consequences of Pathogenic Stress

“…Arrows represent the direction in which metabolic energy is diverted to: I, immunity; R, reproduction. Hypothesized investment strategies fall within three theoretical allocation "decisions" in response to infection (Schwenke et al, 2016;Dani and Kondandaramaiah, 2017;Duffield et al, 2017). The second row describes predicted fitness outcomes resulting from each investment strategy.…”

Evolution of larval competitiveness and associated life‐history traits in response to host shifts in a seed beetle

“…Because body size and egg size simultaneously influence many aspects of growth and reproduction (e.g. there is a well‐established trade‐off between egg size and fecundity; Fox & Czesak, ; Dani & Kodandaramaiah, ), the evolution of larval competition strategy should affect a suite of developmental and life‐history traits (Guedes & Smith, ).…”

Defining features of age‐specific fertility and seed quality in senescing indeterminate annuals

“…The reduction in fertility during late‐senescence phase in both Arabidopsis and Brassica (Figs. A, A) can be attributed to weakened maternal control over: (1) resource allocation to seeds (Wuest et al., ), and (2) seed size optimization (Dani and Kodandaramaiah, ). The notion that selection weakens during successive rounds of reproduction in iteroparous adults (Hamilton, ) may also explain why low fertility and senescence go together in indeterminate annuals.…”

“…B); or (2) produce fewer, bigger, and stress‐hardy seeds with greater offspring viability probability (Fig. C; Dani and Kodandaramaiah, ). Such scenarios may alter the maternal optimum for seed size (m* in Fig.…”

“…(B) The senescing parent may maintain fertility by incrementally restricting seed size, as probability of offspring viability declines with parent's age. (C) The senescing parent with depleting internal resources will have weaker control over seed size, may produce bigger and more viable seeds at a cost to fertility (m** in 1C is closer to o* in 1A; also see Dani and Kodandaramaiah, ). Solid lines = young parent; dashed lines = resource‐limited senescing parent; red curve = fertility.…”