Abstract
Environmental stressors can severely limit the ability of an organism to reproduce as lifespan is decreased and resources are shifted away from reproduction to survival. Although this is often detrimental to the organism’s reproductive fitness, certain other reproductive stress responses may mitigate this effect by increasing the likelihood of progeny survival in the F1 and subsequent generations. Here we review three means by which these progeny may be conferred a competitive edge as a result of stress encountered in the parental generation: heritable epigenetic modifications to nucleotides and histones, simple maternal investments of cytosolic components, and the partially overlapping phenomenon of terminal investment, which can entail extreme parental investment strategies in either cytosolic components or gamete production. We examine instances of these categories and their ability to subsequently impact offspring fitness and reproduction. Ultimately, without impacting nucleotide sequence, these more labile alterations may shape development, evolution, ecology and even human health, necessitating further understanding and research into the specific mechanisms by which environmental stressors are sensed and elicit a corresponding response in the parental germline.
Highlights
Under a traditional Darwinian view of evolution, variation in organismal fitness from generation to generation was thought to be almost exclusively due to germline nucleotide mutations, and non-genetic heritability was discounted
What we term “simple maternal effects” present more holistic changes to the cytosolic composition of gametes and offspring as a result of macromolecular loading from the parental germline. This is distinguished from the similar and partially overlapping phenomenon of terminal investment, which we will define as meeting the following criteria: (i) the current internal and external environment must elicit a high likelihood of mortality for the organism and (ii) the investment must represent a substantial reallocation of resources such that a subset of offspring benefit, but there is a significant cost to the organism’s survival and chance of future reproduction
From the epididymis to sperm is thought to contribute to germ cell reprogramming (Chan et al, 2018). Though these examples highlight the importance of non-coding RNAs, they underscore the enormous variation in epigenetic mechanisms and the difficulty of determining whether conservation exists across organisms
Summary
Under a traditional Darwinian view of evolution, variation in organismal fitness from generation to generation was thought to be almost exclusively due to germline nucleotide mutations, and non-genetic heritability was discounted. What we term “simple maternal effects” present more holistic changes to the cytosolic composition of gametes and offspring as a result of macromolecular loading from the parental germline This is distinguished from the similar and partially overlapping phenomenon of terminal investment, which we will define as meeting the following criteria: (i) the current internal and external environment must elicit a high likelihood of mortality for the organism and (ii) the investment must represent a substantial reallocation of resources such that a subset of offspring benefit, but there is a significant cost to the organism’s survival and chance of future reproduction. We examine these three categories of cellular parental investment in a broad range of taxa, including a brief look at their evolutionary basis and significance
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