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89 results for “offspring size”
Data from: Distinctive increase in offspring size in sea otters: evolutionary changes in and beyond the trade-off against offspring number
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Multilevel selection on offspring size and the maintenance of variation
<p>Multilevel selection on offspring size occurs when offspring fitness depends on both absolute size (hard selection), and size relative to neighbours (soft selection). We examined multilevel selection on egg size at two biological scales: within clutches and among females, for an external fertilising tubeworm. We exposed clutches of eggs to two sperm environments (limiting and saturating) and measured their fertilisation success. We then modelled environmental (sperm) differences in hard and soft selection on individual eggs, as well as selection on clutch-level traits (means and variances). Hard and soft selection differed in strength and form depending on sperm availability – hard selection was consistently stabilising; soft selection was directional and favoured eggs relatively larger (sperm limitation) or smaller (sperm saturation) than the clutch-mean. At the clutch-level, selection on mean-egg size was largely stabilising; whilst selection on within-clutch variance was weak, but generally negative – although some correlational selection occurred between these two traits. Importantly, we found that the optimal clutch-mean egg size differed for mothers and offspring, suggesting some antagonism between the levels of selection. We thus identify several pathways that may maintain offspring-size variation: environmentally (sperm)-dependent soft selection; antagonistic multilevel selection; and correlational selection on clutch-means and variances. Multilevel approaches are powerful, but seldom used, tools for studies of offspring size and we encourage their future use.</p>
Data from: Sexual selection has minimal impact on effective population sizes in species with high rates of random offspring mortality: an empirical demonstration using fitness distributions
The effective population size (Ne) is a fundamental parameter in population genetics that influences the rate of loss of genetic diversity. Sexual selection has the potential to reduce Ne by causing the sex-specific distributions of individuals that successfully reproduce to diverge. To empirically estimate the effect of sexual selection on Ne, we obtained fitness distributions for males and females from an outbred, laboratory-adapted population of Drosophila melanogaster. We observed strong sexual selection in this population (the variance in male reproductive success was ∼14 times higher than that for females), but found that sexual selection had only a modest effect on Ne, which was 75% of the census size. This occurs because the substantial random offspring mortality in this population diminishes the effects of sexual selection on Ne, a result that necessarily applies to other high fecundity species. The inclusion of this random offspring mortality creates a scaling effect that reduces the variance/mean ratios for male and female reproductive success and causes them to converge. Our results demonstrate that measuring reproductive success without considering offspring mortality can underestimate Ne and overestimate the genetic consequences of sexual selection. Similarly, comparing genetic diversity among different genomic components may fail to detect strong sexual selection.
Data from: A multigenerational effect of parental age on offspring size but not fitness in common duckweed (Lemna minor)
Classic theories on the evolution of senescence make the simplifying assumption that all offspring are of equal quality, so that demographic senescence only manifests through declining rates of survival or fecundity. However, there is now evidence that, in addition to declining rates of survival and fecundity, many organisms are subject to age-related declines in the quality of offspring produced (i.e. parental age effects). Recent modelling approaches allow for the incorporation of parental age effects into classic demographic analyses, assuming that such effects are limited to a single generation. Does this 'single-generation' assumption hold? To find out, we conducted a laboratory study with the aquatic plant Lemna minor, a species for which parental age effects have been demonstrated previously. We compared the size and fitness of 423 lab-cultured plants (asexually-derived ramets) representing various birth orders, and ancestral 'birth-order genealogies'. We found that offspring size and fitness both declined with increasing 'immediate' birth order (i.e. birth order with respect to the immediate parent), but only offspring size was affected by ancestral birth order. Thus, the assumption that parental age effects on offspring fitness are limited to a single generation does in fact hold for L. minor. This result will guide theorists aiming to refine and generalise modelling approaches that incorporate parental age effects into evolutionary theory on senescence.
Data from: Heterochrony in the evolution of Trinidadian guppy offspring size: maturation along a uniform ontogenetic trajectory
The size and maturity of Trinidadian guppy (Poecilia reticulata) offspring vary among populations adapted to environments of differential predation. Guppy offspring born to low-predation, high-competition environments are larger and more mature than their high-predation ancestors. Here we ask: what specific changes in developmental or birth timing occur to produce the larger, more mature neonates? We collected specimens across the perinatal window of development from five populations and quantified musculoskeletal maturation. We found that all populations undergo similar ontogenetic trajectories in skeletal and muscle acquisition; the only difference among populations is when neonates emerge along the trajectory. The smallest neonates are born with 20% of their skeleton ossified, whereas the largest neonates are born with over 70% of their skeleton ossified. The area of the major jaw-closing muscle is relatively larger in larger offspring, scaling with length as L2.5. The size range over which offspring are birthed among populations sits along the steepest part of the size–maturity relationship, which provides a large marginal increase in fitness for the high-competition female. Because of the functional effects of producing more mature offspring at birth, offspring size may be the first and most critical life-history trait selected upon in highly competitive environments.
Data from: Disentangling genetic and prenatal maternal effects on offspring size and survival
Organizational processes during prenatal development can have long-term effects on an individual's phenotype. Because these early developmental stages are sensitive to environmental influences, mothers are in a unique position to alter their offspring's phenotype by differentially allocating resources to their developing young. However, such prenatal maternal effects are difficult to disentangle from other forms of parental care, additive genetic effects, and/or other forms of maternal inheritance, hampering our understanding of their evolutionary consequences. Here we used divergent selection lines for high and low prenatal maternal investment and their reciprocal line crosses in a precocial bird—the Japanese quail (Coturnix japonica)—to quantify the relative importance of genes and prenatal maternal effects in shaping offspring phenotype. Maternal but not paternal origin strongly affected offspring body size and survival throughout development. Although the effects of maternal egg investment faded over time, they were large at key life stages. Additionally, there was evidence for other forms of maternal inheritance affecting offspring phenotype at later stages of development. Our study is among the first to successfully disentangle prenatal maternal effects from all other sources of confounding variation and highlights the important role of prenatal maternal provisioning in shaping offspring traits closely linked to fitness.
Data from: Resident species with larger size metrics do not recruit more offspring from the seed bank in old-field meadow vegetation
1. According to the traditional 'Size Advantage' (SA) hypothesis, plant species with larger body size are expected to be more successful when competition is intense, i.e. within severely crowded vegetation. Recent studies in old-field habitats, however, have shown that those species with greater numerical abundance as resident plants generally have a relatively small minimum reproductive threshold size (MIN), not a relatively large maximum potential body size (MAX). 2. In this study, we test for a size advantage in terms of species abundance representation in the soil seed bank, and we extend the SA hypothesis to include two additional size metrics: leaf size and seed size. Specifically, we ask, for resident species within a crowded old-field meadow: is larger seed size, leaf size, and/or body size associated with greater reproductive / recruitment success (i.e. number of germinable seeds within — and establishing plants emerging from — the soil seed bank)? We collected soil cores for a greenhouse experiment to record relative species abundances of germinable seeds in the seed bank, and we used a field experiment to record local abundances of species emerging from the resident seed bank within denuded plant neighbourhoods over three subsequent field seasons. 3. We found no general support for the SA hypothesis involving any of the size metrics, and none of the latter was a strong predictor of the number of germinable seeds emerging from soil cores in the greenhouse experiment. However, for species establishing in the field experiment from the seed bank over the three-year survey period, more abundant species in years 2 and 3 tended to be those with smaller MIN, and thus smaller MAX. In addition, within more crowded neighbourhoods, representation of reproductive plants was generally greater for species with relatively small MIN (and hence small MAX). 4. Synthesis. Our results extend support for the 'Reproductive Economy Advantage' hypothesis in old field habitats, to include not just established, largely undisturbed vegetation, but also very early stages of recruitment from seed within locally crowded plant neighbourhoods. Specifically, more successful species here are not those with relatively large potential body size (MAX); they are species capable of producing at least some offspring despite severe body size suppression, because they have a relatively small MIN.
Data from: Selection and constraints on offspring size-number trade-offs in sand lizards (Lacerta agilis)
The trade-off between offspring size and number is a central component of life-history theory, postulating that larger investment into offspring size inevitably decreases offspring number. This trade-off is generally discussed in terms of genetic, physiological or morphological constraints; however, as among-individual differences can mask individual trade-offs, the underlying mechanisms may be difficult to reveal. In this study, we use multivariate analyses to investigate whether there is a trade-off between offspring size and number in a population of sand lizards by separating among- and within-individual patterns using a 15-year data set collected in the wild. We also explore the ecological and evolutionary causes and consequences of this trade-off by investigating how a female's resource (condition)- vs. age-related size (snout-vent length) influences her investment into offspring size vs. number (OSN), whether these traits are heritable and under selection and whether the OSN trade-off has a genetic component. We found a negative correlation between offspring size and number within individual females and physical constraints (size of body cavity) appear to limit the number of eggs that a female can produce. This suggests that the OSN trade-off occurs due to resource constraints as a female continues to grow throughout life and, thus, produces larger clutches. In contrast to the assumptions of classic OSN theory, we did not detect selection on offspring size; however, there was directional selection for larger clutch sizes. The repeatabilities of both offspring size and number were low and we did not detect any additive genetic variance in either trait. This could be due to strong selection (past or current) on these life-history traits, or to insufficient statistical power to detect significant additive genetic effects. Overall, the findings of this study are an important illustration of how analyses of within-individual patterns can reveal trade-offs and their underlying causes, with potential evolutionary and ecological consequences that are otherwise hidden by among-individual variation.
Data from: Does the cost of development scale allometrically with offspring size?
1.Within many species, larger offspring have higher fitness. While the presence of an offspring size-fitness relationship is canonical in life-history theory, the mechanisms that determine why this relationship exists are unclear. 2.Linking metabolic theory to life-history theory could provide a general explanation for why larger offspring often perform better than smaller offspring. In many species, energy reserves at the completion of development drive differences in offspring fitness. Development is costly so any factor that decreases energy expenditure during development should result in higher energy reserves and thus subsequently offspring fitness. 3.Metabolic theory predicts that larger offspring should have relatively lower metabolic rates and thus emerge with a higher level of energy reserves (assuming developmental times are constant). The increased efficiency of development in larger offspring may therefore be an underlying driver of the relationship between offspring size and offspring fitness, but this has not been tested within species. 4.To determine how the costs of development scale with offspring size, we measured energy expenditure throughout development in the model organism Danio rerio across a range of natural offspring sizes. We also measured how offspring size affects the length of the developmental period. We then examined how hatchling size and condition scale with offspring size. 5.We find that larger offspring have lower mass-specific metabolic rates during development, but develop at the same rate as smaller offspring. Larger offspring also hatch relatively heavier and in better condition than smaller offspring. That the relative costs of development decrease with offspring size may provide a widely applicable explanation for why larger offspring often perform better than smaller offspring.
No evidence for increased fitness of offspring from multigenerational effects of parental size or natal carcass size in the burying beetle Nicrophorus marginatus
<p>Multigenerational effects (often called maternal effects) are components of the offspring phenotype that result from the parental phenotype and the parental environment as opposed to heritable genetic effects. Multigenerational effects are widespread in nature and are often studied because of their potentially important effects on offspring traits. Although multigenerational effects are commonly observed, few studies have addressed whether they affect offspring fitness. In this study we assess the effect of potential multigenerational effects of parental body size and natal carcass size on lifetime fitness in the burying beetle, <i>Nicrophorus marginatus</i> (Coleoptera; Silphidae). Lifespan, total number of offspring, and number of offspring in the first reproductive bout were not significantly related to parental body size or natal carcass size. However, current carcass size used for reproduction was a significant predictor for lifetime number of offspring and number of offspring in the first brood. We find no evidence that multigenerational effects from larger parents or larger natal carcasses contribute to increased fitness of offspring.</p>
Temperature-mediated variation in selection on offspring size: a multi-cohort field study
<p><span><span><span><span><span><span><span><span><span><span><span><span><span>Offspring size is a key life history trait that often covaries negatively with temperature. Most studies focus on how temperature alters selection on offspring size during early life history stages such as embryos or larvae. The degree to which temperature alters the relationship between offspring size and post-metamorphic performance remains unclear as field studies across multiple temperature regimes are rare.</span></span></span></span></span></span></span></span></span></span></span></span></span></p> <p><span><span><span><span><span><span><span><span><span><span><span><span><span>I deployed over 6000 individuals of known offspring size, into the field across 28 cohorts spanning 4 years for the model marine invertebrate, <i>Bugula neritina</i> and monitored their survival, growth and reproduction.</span></span></span></span></span></span></span></span></span></span></span></span></span></p> <p><span><span><span><span><span><span><span><span><span><span><span><span><span>Offspring size closely tracked the local environmental temperature across cohorts. This offspring size-temperature covariance appeared to be adaptive, at least from the perspective of mothers. When temperatures were warmer, the relationship between offspring size and performance was weak; when temperatures were cooler, the relationship was strongly positive.</span></span></span></span></span></span></span></span></span></span></span></span></span></p> <p><span><span><span><span><span><span><span><span><span><span><span><span><span>Estimates of selection based on maternal fitness differed from those based on offspring fitness, suggesting temperature-mediated parent-offspring conflict over offspring provisioning exists. I also found evidence for temporal autocorrelation in temperature and selection on offspring size.</span></span></span></span></span></span></span></span></span></span></span></span></span></p> <p><span><span><span><span><span><span><span><span><span><span><span><span><span>That temperature affects the relationship between offspring size and post-metamorphic performance further complicates the challenge in understanding the ubiquitous covariance between offspring size and temperature.</span></span></span></span></span></span></span></span></span></span></span></span></span></p>
Figure 1 from: Antoł A, Czarnoleski M (2018) Size dependence of offspring production in isopods: a synthesis. In: Hornung E, Taiti S, Szlavecz K (Eds) Isopods in a Changing World. ZooKeys 801: 337-357. https://doi.org/10.3897/zookeys.801.23677
Figure 1 In Porcellioscaber, the dry mass of clutches (A) and clutch size (B) increased linearly with female body mass, but the mean dry mass of offspring did not depend on female mass in a consistent way (C). Lines represent fitted regressions A y = -0.13+0.08x (r = 0.83, p<0.001) B y = -0.32+0.74x (r = 0.83, p<0.001) C y = 0.1+0.00006x (r = 0.14, p = 0.15).
Figure 3 from: Antoł A, Czarnoleski M (2018) Size dependence of offspring production in isopods: a synthesis. In: Hornung E, Taiti S, Szlavecz K (Eds) Isopods in a Changing World. ZooKeys 801: 337-357. https://doi.org/10.3897/zookeys.801.23677
Figure 3 The literature search identified 79 species of isopods that were studied with respect to at least one of the following relationships: clutch size with female size (A), offspring size with female size (B), and clutch size with offspring size (C). Each graph shows how frequently a given nature of each relationship was found among the studied isopod species. The exact number of species for which the relationships A, B, C were evaluated is given by N. For each type of the relationships A, B, C each species was classified according to the nature of this relationship. If a relationship for a given species was consistently reported to be significantly positive, negative, or non-significant, the species was marked by a positive (+) or negative (-) symbol or by NS. Species for which mixed results were reported in the literature, showing either non-significant/significantly positive relationships or non-significant/significantly negative relationships, were marked by NS/+ or NS/-, respectively. Colour intensity indicates values along a 1–4 scale of confidence to the support provided by each relationship pattern (+, -, NS, NS/+ and NS/-) to hypotheses (i–iii). Relationship A: a positive relationship predicted between female body size and clutch mass/clutch size (hypothesis i). Relationship B: a positive correlation predicted between the average offspring mass in a brood and female body mass (hypothesis ii). Relationship C: a negative correlation predicted between the mean mass of offspring and the number of offspring per brood (hypothesis iii).
Figure 2 from: Antoł A, Czarnoleski M (2018) Size dependence of offspring production in isopods: a synthesis. In: Hornung E, Taiti S, Szlavecz K (Eds) Isopods in a Changing World. ZooKeys 801: 337-357. https://doi.org/10.3897/zookeys.801.23677
Figure 2 In Porcellioscaber, the heaviest offspring were released by large females that produced small clutches. The plane represents a multiple regression model fitted to the data; the partial slopes depicted on the edges were calculated by setting the other predictor value to its minimum and maximum values.
Data from: Resident species with larger size metrics do not recruit more offspring from the seed bank in old-field meadow vegetation
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Individual variation in parental tradeoffs between the number and size of offspring at the pre- and post-natal stages
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No evidence for increased fitness of offspring from multigenerational effects of parental size or natal carcass size in the burying beetle Nicrophorus marginatus
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Data from: Differential allocation of parental investment and the trade-off between size and number of offspring
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Data from: Disentangling genetic and prenatal maternal effects on offspring size and survival
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Data from: Sexual selection has minimal impact on effective population sizes in species with high rates of random offspring mortality: an empirical demonstration using fitness distributions
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