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89 results for “offspring size”
Data from: Morphological and functional maturity of the oral jaws covary with offspring size in Trinidadian guppies
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Data from: indirect costs of reproduction and the tradeoff between offspring size and number: a framework illustrated by fitness costs and benefits of ovarian fluid
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Recent evolution of large offspring size and post-fertilization nutrient provisioning in swordtails
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Ecological and behavioural drivers of offspring size in marine teleost fishes
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Data from: Adaptive maternal investment in the wild? Links between maternal growth trajectory and offspring size, growth, and survival in contrasting environments
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Data from: Parental genetic similarity and offspring performance in blue tits in relation to brood size manipulation
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Changing food availability and its effect on the heritability of offspring size in woodland passerine birds
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Data from: Density-dependent offspring interactions do not explain macroevolutionary scaling of adult size and offspring size
Most lifeforms exhibit a correlated evolution of adult size (AS) and size at independence (SI), giving rise to AS-SI scaling relationships. Theory suggests that scaling arises because relatively large adults have relatively high reproductive output, resulting in strong density-dependent competition in early life, where large size at independence provides a competitive advantage to juveniles. The primary goal of our study is to test this Density Hypothesis, using large datasets that span the vertebrate tree of life (fishes, amphibians, reptiles, birds, and mammals). Our secondary goal is to motivate new hypotheses for AS-SI scaling, by exploring how subtle variation in life-histories among closely-related species is associated with variation in scaling. Our phylogenetically-informed comparisons do not support the Density Hypothesis. Instead, exploration of AS-SI scaling among life-history variants suggests that steeper AS-SI scaling slopes are associated with evolutionary increases in size at independence. We suggest that a positive association between size at independence and juvenile growth rate may represent an important mechanism underlying AS-SI scaling, a mechanism that has been underappreciated by theorists. If faster juvenile growth is a consequence of evolutionary increases in size at independence, this may help offset the cost of delayed maturation, leading to steeper AS-SI scaling slopes.
Data from: Viviparity does not affect the numbers and sizes of reptile offspring
<ol> <li>Viviparity (live-bearing) has independently evolved from oviparity (egg-laying) in more than 100 lineages of squamates (lizards and snakes).</li> <li>We might expect consequent shifts in selective forces to affect per-brood reproductive investment (RI = total mass of offspring relative to maternal mass) and in the way in which that output is partitioned (number <i>versus</i> size of offspring per brood). Based on the assumption that newly-born offspring are heavier than eggs, we predicted that live-bearing must entail either increased reproductive investment or a reduction in offspring size and/or fecundity.</li> <li>However, our phylogenetically-controlled analysis of data on 1,259 squamate species revealed no significant differences in mean offspring size, clutch size or RI between oviparous and viviparous squamates.</li> <li>We attribute this paradoxical result to (1) strong selection on optimal offspring sizes, unaffected by parity mode, (2) the lack of a larval stage in amniotes, favouring large eggs even in the ancestral oviparous mode, and (3) the ability of viviparous females to decrease the mass of uterine embryos by reducing extra-embryonic water stores.</li> <li>Our analysis shows that squamate eggs (when laid) weigh about the same as the hatchlings that emerge from them (despite a many-fold increase in embryo mass during incubation). Most of the egg mass is due to components (such as water stores and the eggshell) not required for oviductal incubation. That repackaging enables live-born offspring to be accommodated within the mother's body without increasing total litter mass.</li> <li>The consequent stasis in reproductive burden during the evolutionary transition from oviparity to viviparity may have facilitated frequent shifts in parity modes.</li> </ol>
Data from: Offspring size and reproductive allocation in harvester ants
A fundamental decision that an organism must make is how to allocate resources to offspring, both with respect to size and to number. The two major theoretical approaches to this problem, optimal offspring size and optimistic brood size models, make different predictions that may be reconciled by including how offspring fitness is related to size. We extended the reasoning of Trivers and Willard (1973) to derive a general model of how parents should allocate additional resources with respect to the number of males and females produced, and among individuals of each sex, based on the fitness payoffs of each. We then predicted how harvester ant colonies should invest additional resources, and tested three hypotheses derived from our model, using data from three years of food supplementation bracketed by six years without food addition. All major results were predicted by our model: Food supplementation increased the number of reproductives produced. Male, but not female, size increased with food addition; the greatest increases in male size occurred in colonies that made small females. We discuss how use of a fitness landscape improves quantitative predictions about allocation decisions. When parents can invest differentially in offspring of different types, the best strategy will depend on parental state as well as the effect of investment on offspring fitness.
Data from: Interspecific competition alters nonlinear selection on offspring size in the field
Offspring size is one of the most important life-history traits with consequences for both the ecology and evolution of most organisms. Surprisingly, formal estimates of selection on offspring size are rare, and the degree to which selection (particularly nonlinear selection) varies among environments remains poorly explored. We estimate linear and nonlinear selection on offspring size, module size, and senescence rate for a sessile marine invertebrate in the field under three different intensities of interspecific competition. The intensity of competition strongly modified the strength and form of selection acting on offspring size. We found evidence for differences in nonlinear selection across the three environments. Our results suggest that the fitness returns of a given offspring size depend simultaneously on their environmental context, and on the context of other offspring traits. Offspring size effects can be more pervasive with regards to their influence on the fitness returns of other traits than previously recognized, and we suggest that the evolution of offspring size cannot be understood in isolation from other traits. Overall, variability in the form and strength of selection on offspring size in nature may reduce the efficacy of selection on offspring size and maintain variation in this trait.
Data from: Differences in offspring size predict the direction of isolation asymmetry between populations of a placental fish
Crosses between populations or species often display an asymmetry in the fitness of reciprocal F1 hybrids. This pattern, referred to as isolation asymmetry or Darwin's Corollary to Haldane's rule, has been observed in taxa from plants to vertebrates, yet we still know little about which factors determine its magnitude and direction. Here we show that differences in offspring size predict the direction of isolation asymmetry observed in crosses between populations of a placental fish, Heterandria formosa. In crosses between populations with differences in offspring size, high rates of hybrid inviability occur only when the mother is from a population characterized by small offspring. Crosses between populations that display similarly sized offspring, whether large or small, do not result in high levels of hybrid inviability in either direction. We suggest this asymmetric pattern of reproductive isolation is due to a disruption of parent-offspring coadaptation that emerges from selection for differently sized offspring in different populations.
Data from: Constraints on the adult-offspring size relationship in protists
The relationship between adult and offspring size is an important aspect of reproductive strategy. Although this filial relationship has been extensively examined in plants and animals, we currently lack comparable data for protists, whose strategies may differ due to the distinct ecological and physiological constraints on single-celled organisms. Here, we report measurements of adult and offspring sizes in 3,888 species and subspecies of foraminifera, a class of large marine protists. Foraminifera exhibit a wide range of reproductive strategies; species of similar adult size may have offspring whose sizes vary 100-fold. Yet, a robust pattern emerges. The minimum (5th percentile), median, and maximum (95th percentile) offspring sizes exhibit a consistent pattern of increase with adult size independent of environmental change and taxonomic variation over the past 400 million years. The consistency of this pattern may arise from evolutionary optimization of the offspring size-fecundity trade-off and/or from cell-biological constraints that limit the range of reproductive strategies available to single-celled organisms. When compared with plants and animals, foraminifera extend the evidence that offspring size covaries with adult size across an additional five orders of magnitude in organism size.
Data from: Collective dispersal leads to variance in fitness and maintains offspring size variation within marine populations
Variance in fitness is well known to influence the outcome of evolution but is rarely considered in the theory of marine reproductive strategies. In coastal environments, turbulent mesoscale eddies can collect larvae into 'packets' resulting in collective dispersal. Larvae in packets return to the coast or are lost offshore in groups, producing variance in fitness. Using a Markov process to calculate fixation probabilities for competing phenotypes, we examine the evolution of offspring size and spawning duration in species with benthic adults and pelagic offspring. The offspring size that provides mothers with the highest mean fitness also generates the greatest variance in fitness, but pairwise invasion plots show that bet-hedging strategies are not evolutionarily stable: maximizing expected fitness correctly predicts the unique evolutionarily stable strategy. Nonetheless, fixation can take a long time. We find that selection to increase spawning duration as a risk-avoidance strategy to reduce the negative impacts of stochastic recruitment success can allow multiple offspring sizes to coexist in a population for extended periods. This has two important consequences for offspring size: 1) coexistence occurs over a broader range of sizes and is longer when spawning duration is longer, because longer spawning durations reduce variation in fitness and increase the time to fixation, and 2) longer spawning durations can compensate for having a non-optimal size and even allow less optimal sizes to reach fixation. Collective dispersal and longer spawning durations could effectively maintain offspring size variation even in the absence of good and bad years or locations. Empirical comparisons of offspring size would, therefore, not always reflect environment-specific differences in the optimal size.
Data from: Offspring fitness and the optimal propagule size in a fluctuating environment
Propagule size is an important maternal effect on offspring fitness and phenotype in birds and other oviparous animals. The performance of propagules often increases with size, but a fluctuating environment may introduce temporal variation in the optimal phenotype. Understanding these mechanisms will provide novel insights into the eco-evolutionary dynamics of life history strategies in parental reproductive investment. We investigated the interaction between propagule size (measured as egg volume) and environmental conditions on offspring mortality and phenotype in a Norwegian house sparrow population. Increased propagule size reduced offspring mortality in early life, with more pronounced effects under heavy precipitation. However, the optimal propagule size for low offspring mortality until recruitment shifted from large to small as temperature increased. Propagule size had no significant effect on fledgling body mass and tarsus length. These results reveal a potential for eco-evolutionary dynamics in propagule size, as populations adapt to fluctuating environmental conditions. The ultimate outcome of this dynamic process will also depend on variation in parental fitness and trade-offs with other life-history traits, particularly clutch size.
Data from: Dispersal duration mediates selection on offspring size
Offspring size varies at all levels of organisation, among species, mothers and clutches. This variation is thought to be the result of a tradeoff between offspring quality and quantity, where larger offspring perform better but are more costly to produce. Local environmental conditions alter the benefits of increased offspring size and thereby mediate selection on this trait. For sessile organisms, dispersal is a crucial part of the offspring phase, and in animals, bigger offspring tend to better endure longer dispersal distances than smaller offspring because they have more energy. Theory predicts that increasing distances between suitable habitats strengthens selection for larger offspring. We manipulated the dispersal duration of offspring of different sizes in the bryozoan Watersipora subtorquata and then examined the relationship between offspring size and post-metamorphic performance in the field. We found that selection on offspring size is altered by larval experience. Larger offspring had higher post-settlement performance if the larval period was short but, contrary to current theory, performed worse when the larval period was extended. The reversal of the relationship between offspring size and performance by extending the larval phase in Watersipora may be due to the way in which offspring size affects growth in this species. Regardless of the mechanism, it appears that experiences in one life-history stage alter selection on offspring size in another stage, even when they occupy identical habitats as adults.
Data from: Post-hatching parental care masks the effects of egg size on offspring fitness: a removal experiment on burying beetles
Parents can increase the fitness of their offspring by allocating nutrients to eggs and/or providing care for eggs and offspring. Although we have a good understanding of the adaptive significance of both egg size and parental care, remarkably little is known about the co-evolution of these two mechanisms for increasing offspring fitness. Here, we report a parental removal experiment on the burying beetle Nicrophorus vespilloides in which we test whether post-hatching parental care masks the effect of egg size on offspring fitness. As predicted, we found that the parent's presence or absence had a strong main effect on larval body mass, while there was no detectable effect of egg size. Furthermore, egg size had a strong and positive effect on offspring body mass in the parent's absence, while it had no effect on offspring body mass in the parent's presence. These results support the suggestion that the stronger effect of post-hatching parental care on offspring growth masks the weaker effect of egg size. We found no correlation between the number and size of eggs. However, there was a negative correlation between larval body mass and brood size in the parent's presence, but not in its absence. These findings suggest that the trade-off between number and size of offspring is shifted from the egg stage towards the end of the parental care period, and that post-hatching parental care somehow moderates this trade-off.
Data from: Squamate hatchling size and the evolutionary causes of negative offspring size allometry
Although fecundity selection is ubiquitous, in an overwhelming majority of animal lineages, small species produce smaller number of offspring per clutch. In this context, egg, hatchling and neonate sizes are absolutely larger, but smaller relative to adult body size in larger species. The evolutionary causes of this widespread phenomenon are not fully explored. The negative offspring size allometry can result from processes limiting maximal egg/offspring size forcing larger species to produce relatively smaller offspring ('upper limit'), or from a limit on minimal egg/offspring size forcing smaller species to produce relatively larger offspring ('lower limit'). Several reptile lineages have invariant clutch sizes, where females always lay either one or two eggs per clutch. These lineages offer an interesting perspective on the general evolutionary forces driving negative offspring size allometry, because an important selective factor, fecundity selection in a single clutch, is eliminated here. Under the upper limit hypotheses, large offspring should be selected against in lineages with invariant clutch sizes as well, and these lineages should therefore exhibit the same, or shallower, offspring size allometry as lineages with variable clutch size. On the other hand, the lower limit hypotheses would allow lineages with invariant clutch sizes to have steeper offspring size allometries. Using an extensive data set on the hatchling and female sizes of > 1800 species of squamates, we document that negative offspring size allometry is widespread in lizards and snakes with variable clutch sizes and that some lineages with invariant clutch sizes have unusually steep offspring size allometries. These findings suggest that the negative offspring size allometry is driven by a constraint on minimal offspring size, which scales with a negative allometry.
Density dependence of clutch size and offspring sex ratio in starling colonies
<p><span>Optimal life-history theory predicts that individuals should adjust both the number and the sex of their offspring to maximize fitness in response to environmental and social factors such as breeding density. While reductions in optimal clutch size are well-studied in birds, the evidence for sex ratio adjustments is still equivocal and, so far, we lack a thorough understanding of how these strategies interact to maximize fitness. Here, we investigate how breeding density simultaneously affects brood sex ratio and clutch size in a sexually dimorphic and polygynous bird. We tested the prediction that mothers breeding at a higher density lay smaller clutches and overproduce daughters, the sex with less variable fitness returns and that disperses further away from their natal territory. We distributed nest boxes at either a high (HD) or a low density (LD) and monitored clutch sizes and sex ratios during five years in a wild breeding colony of spotless starlings. While mothers breeding in HD nests produced more daughters than those breeding in LD nests, the density dependence of clutch size varied among years, with a tendency to lay smaller clutches in HD nests. Our results suggest that mothers consistently adjust offspring sex ratio in response to breeding density, whereas adjustments in clutch size varied in a more complex way. These results support the role of sex allocation strategies in response to density and show that further theoretical and empirical research is required to understand the interaction between clutch size and sex ratio adjustments in animals.</span></p>
Supplementary material 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
Table S1 : Explanation note: Results of the literature search for reports of at least one of the following relationships in isopods: clutch size vs female size, offspring size vs female size, offspring size vs clutch size.
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