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64 results for “clutch size”
Fig. 1 in A Long-Term Comparison Of Laying Date And Clutch Size In The Red-Backed Shrike (Lanius Collurio) In Silesia, Southern Poland
Fig. 1. The number of Red-backed Shrike clutches laid during successive five-day periods (1 = 6–10 May) in the two study periods. For sample size – see text
Incubation temperature as a constraint on clutch size evolution
<p>1. Elucidating factors that limit the number of offspring produced is fundamental to understanding life-history evolution. Here, we examine the hypothesis that parental ability to maintain an optimal physical developmental environment for all offspring constrains clutch size via effects on offspring quality.</p> <p>2. Experimental laboratory studies of birds have shown that a <1°C difference in average incubation temperature has diverse effects on fitness-related post-hatching offspring phenotypes. Thus, the inability of parents to maintain optimal incubation temperatures could constrain clutch sizes.</p> <p>3. A fundamental question that has not been sufficiently addressed is whether larger clutch sizes lead to within nest variation in egg temperature that is large enough to produce offspring with different phenotypes within a brood. This could lead to differential survival among offspring, and could create a tradeoff between offspring number and quality.</p> <p>4. We manipulated clutch size in nests of free-living wood ducks and measured incubation temperature among and within clutches using multiple temperature loggers.</p> <p>5. As clutch size increased, average incubation temperatures were lower and more variable, and eggs took longer to hatch. Notably, the range in average incubation temperature among eggs within nests increased with clutch size and exceeded 1°C in large clutches.</p> <p>6. Clutch size did not affect hatch success. In conjunction with our companion laboratory studies that used artificial incubation to document the effects of temperature variation on fitness-related traits in this species, our work suggests that suboptimal incubation temperatures could be a factor that limits clutch size through diminishing returns on post-hatch offspring quality.</p>
Data from: Nest predation risk explains variation in avian clutch size
Questions about the ecological drivers of, and mechanistic constraints on, productivity have driven research on life history evolution for decades. Resource availability and offspring mortality are considered among the two most important influences on the number of offspring per reproductive attempt. We used a factorial experimental design to manipulate food abundance and perceived offspring predation risk in a wild avian population (red-faced warblers; Cardellina rubrifrons) to identify the mechanistic cause of variation in avian clutch size. Additionally, we tested whether female quality helped explain the extant variation in clutch size. We found no support for the Food Limitation or Female Quality Hypotheses, but we did find support for both predictions of the Nest Predation Risk Hypothesis. Females that experienced an experimentally heightened perception of offspring predation risk responded by laying a smaller clutch than females in the control group. Additionally, predation rates at artificial nests were highest where red-faced warbler clutch size was smallest (at high elevations). Life history theory predicts that an individual should invest less in reproduction when high nest predation risk reduces the likely benefit from that nesting attempt, and indeed we found that birds exhibit phenotypic plasticity in clutch size by laying fewer eggs in response to increasing nest predation risk.
Data from: Female investment in offspring size and number shifts seasonally in a lizard with single-egg clutches
The timing of reproduction strongly influences reproductive success in many organisms. For species with extended reproductive seasons, the quality of the environment may change throughout the season in ways that impact offspring survival, and, accordingly, aspects of reproductive strategies may shift to maximize fitness. Life-history theory predicts that if offspring environments deteriorate through the season, females should shift from producing more, smaller offspring early in the season to fewer, higher quality offspring later in the season. We leverage multiple iterations of anole breeding colonies, which control for temperature, moisture, and food availability, to identify seasonal changes in reproduction. These breeding colonies varied only by the capture date of the adult animals from the field. We show that seasonal cohorts exhibit variation in key reproductive traits such as inter-clutch interval, egg size and hatchling size consistent with seasonal shifts in reproductive effort. Overall, reproductive effort was highest early in the season due to a relatively high rate of egg production. Later season cohorts produced fewer, but larger offspring We infer that these results indicate a strategy for differential allocation of resources through the season. Females maximize offspring quantity when environments are favorable, and maximize offspring quality when environments are poor for those offspring. Our study also highlights that subtle differences in methodology (such as capture date of study animals) may influence the interpretation of results. Researchers interested in reproduction must be conscious of how their organism's reproductive patterns may shift through the season when designing experiments or comparing results across studies.
Experimental evolution of a more restrained clutch size when filial cannibalism is prevented in burying beetles Nicrophorus vespilloides
<p>The over-production of offspring is commonly associated with high hatching failure and a mechanism for dispensing with surplus young. We used experimental evolution of burying beetle populations Nicrophorus vespilloides to determine causality in these correlations. We asked: does eliminating the mechanism for killing 'spare' offspring cause the evolution of a more restrained clutch size, and consequently select for reduced hatching failure? N. vespilloides typically over-produces eggs but kills 1st instar larvae through partial filial cannibalism during brood care. We established replicate evolving populations that either could practice filial cannibalism (Full Care) or could not, by removing parents before their young hatched (No Care). After 20+ generations of experimental evolution, we measured clutch size and hatching success. We found that No Care females produced fewer eggs than Full Care females when allowed to breed on a small corpse, a finding not explained by differences in female quality. On larger corpses, females from both populations laid similar numbers of eggs. Furthermore, hatching success was greater in the No Care populations on small corpses. Our results suggest that the adaptive over-production of offspring depends on a mechanism for eliminating surplus young and that killing offspring, in turn, relaxes selection against hatching failure.</p>
Data and code for: Optimal clutch size revisited: separating individual quality from the costs of reproduction
<p>Life-history theory, central to our understanding of diversity in morphology, behaviour and senescence, describes how traits evolve through the optimisation of trade-offs in investment. Despite considerable study, there is only minimal support for trade-offs within species between the two traits most closely linked to fitness – reproduction and survival – questioning the theory's general validity. We used a meta-analysis to separate quality effects from the costs of reproduction using studies of parental investment and survival in birds. Experimental enlargement of broods caused reduced parental survival. However, the effect of experimental enlargements was small and opposite to the effect of phenotypic quality, where individuals that naturally produced larger clutches also survived better. The opposite effects on survival in experimental and observational studies of parental care provide the first meta-analytic evidence for theory suggesting that quality differences mask trade-offs. Fitness projections using the overall effect size revealed that reproduction presented negligible costs, except when reproductive effort was forced beyond the level observed within species, to that seen between species. We conclude that there is little support for the most fundamental life-history trade-off, between reproduction and longevity, operating within a population. We suggest that within species, the fitness landscape of the reproduction–survival trade-off is flat until it reaches the boundaries of the between-species fast-slow life-history continuum. Our interpretation explains why the costs of reproduction are not apparent and why variation in reproductive output persists within species.</p>
Data from: Female investment in offspring size and number shifts seasonally in a lizard with single-egg clutches
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Data from: Environmental constraints can explain clutch size differences between urban and forest blue tits: Insights from an egg removal experiment
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Incubation temperature as a constraint on clutch size evolution
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Incubation period length varies with temperature, female age, and clutch size in Protonotaria citrea (Prothonotary Warblers)
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Data and code for: Optimal clutch size revisited: separating individual quality from the costs of reproduction
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Data from: Nest predation risk explains variation in avian clutch size
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Experimental evolution of a more restrained clutch size when filial cannibalism is prevented in burying beetles Nicrophorus vespilloides
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Data from: Individual variation and selection for phenotypic plasticity of laying date and clutch size across different environmental conditions in Tree swallow (Tachycineta bicolor)
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Impacts of ambient temperature and clutch size on incubation behaviour onset in a female-only incubator songbird
<p><span><span><span><span><span><span><span><span><span><span><span>Ambient temperature is assumed to be the major cue used by passerines to synchronize their laying and hatching dates to the expected peak of prey availability. While laying eggs, females are still able to fine-tune their hatching date following increasing or decreasing patterns of ambient temperature, mostly via changes in incubation onset. The onset of incubation behaviour in relation to the laying sequence could have later consequences for the duration of the incubation period and the extent of hatching asynchrony. Clutch size is also known to affect incubation patterns and might therefore condition potential responses to changing temperatures. In this study we assessed the effect of ambient temperature and clutch size on the onset of four different incubation behaviours: partial and full nocturnal incubation, and partial and full diurnal incubation. We also evaluated the effect of the onset and duration of each incubation behaviour on the total duration of diurnal full incubation and the extent of hatching asynchrony. To achieve our aims, we monitored incubation behaviour using temperature data loggers during the egg laying period in three Mediterranean Great Tit <i>Parus major</i> populations in three consecutive years. Our results showed that increasing temperatures were related to an advance of diurnal partial incubation, but not to its duration, nor to the onset of full incubation behaviour. We did not find any effect of ambient temperatures on nocturnal incubation. However, females lengthened nocturnal partial incubation and delayed the onset of nocturnal full and diurnal partial incubation, when laying larger clutches. Longer diurnal incubation before clutch completion was associated with greater hatching asynchrony. Moreover, longer diurnal partial incubation shortened the duration of the full incubation period. In conclusion, increasing ambient temperatures during the egg-laying period advanced diurnal partial incubation, indirectly shortening the full incubation period and increasing hatching asynchrony.</span></span></span></span></span></span></span></span></span></span></span></p>
Data from: Genomic dissection of variation in clutch size and egg mass in a wild great tit (Parus major) population
Clutch size and egg mass are life history traits that have been extensively studied in wild bird populations, as life history theory predicts a negative trade-off between them, either at the phenotypic or genetic level. Here, we analyse the genomic architecture of these heritable traits in a wild great tit (Parus major) population, using three marker-based approaches - chromosome partitioning, quantitative trait locus (QTL) mapping and a genome-wide association study (GWAS). The variance explained by each great tit chromosome scales with predicted chromosome size, no location in the genome contains genome-wide significant QTL, and no individual SNPs are associated with a large proportion of phenotypic variation, all of which may suggest that variation in both traits is due to many loci of small effect, located across the genome. There is no evidence that any regions of the genome contribute significantly to both traits, which combined with a small, non-significant, negative genetic covariance between the traits, suggests the absence of genetic constraints on the independent evolution of these traits. Our findings support the hypothesis that variation in life history traits in natural populations is likely to be determined by many loci of small effect spread throughout the genome, which are subject to continued input of variation by mutation and migration, although we cannot exclude the possibility of an additional input of major effect genes influencing either trait.
Data from: Two eggs, two different constraints: a potential explanation for the puzzling intra-clutch egg size dimorphism in Eudyptes penguins
Phenotypic plasticity and phenotypic stability are major components of the adaptive evolution of organisms to environmental variation. The invariant two-egg clutch size of Eudyptes penguins has recently been proposed to be a unique example of a maladaptive phenotypic stability, while their egg mass is a plastic trait. We tested whether this phenotypic plasticity during reproduction might result from constraints imposed by migration (migratory carry-over effect) and breeding (due to the depletion of female body reserves). For the first time, we examined whether these constraints differ between eggs within clutches and between egg components (yolk and albumen). The interval between colony return and clutch initiation positively influenced the yolk mass, the albumen mass, and the subsequent total egg mass of first-laid eggs. This time interval had only a slight negative influence on the yolk mass of second-laid eggs and no influence on their albumen and subsequent total masses. For both eggs, female body mass at laying positively influenced albumen and total egg masses. Female investment into the entire clutch was not related to the time in the colony before laying but increased with female body mass. These novel results suggest that the unique intraclutch egg size dimorphism exhibited in Eudyptes penguins, with first-laid eggs being consistently smaller than second-laid eggs, might be due to a combination of constraints: a migratory carry-over effect on the first-laid egg and a body reserve depletion effect on the second-laid egg. Both these constraints might explain why the timing of reproduction, especially egg formation, is narrow in migratory capital breeders.
Data from: A conceptual framework for clutch size evolution in songbirds
Causes of evolved differences in clutch size among songbird species remain debated. I propose a new conceptual framework that integrates aspects of traditional life history theory, while including novel elements, to explain evolution of clutch size among songbirds. I review evidence that selection by nest predation on length of time that offspring develop in the nest creates a gradient in offspring characteristics at nest-leaving (fledging), including flight mobility, spatial dispersion, and self-feeding rate. I postulate that this gradient has consequences for offspring mortality rates and parental energy expenditure per offspring. These consequences then determine how reproductive effort is partitioned among offspring, while reproductive effort evolves from age-specific mortality effects. Using data from a long-term site in Arizona, as well as from the literature, I provide support for hypothesized relationships. Nestling development period consistently explains fledgling mortality, energy expenditure per offspring, and clutch size while accounting for reproductive effort (i.e., total energy expenditure) to thereby support the framework. Tests in this paper are not definitive, but they document previously unrecognized relationships and address diverse traits (developmental strategies, parental care strategies, energy requirements per offspring, evolution of reproductive effort, clutch size) that justify further investigations of hypotheses proposed here.
Data from: It takes two: heritable male effects on reproductive timing but not clutch size in a wild bird population
<p>Within-population variation in the traits underpinning reproductive output has long been of central interest to biologists. Since they are strongly linked to lifetime reproductive success, these traits are expected to be subject to strong selection and, if heritable, to evolve. Despite the formation of durable pair bonds in many animal taxa, reproductive traits are often regarded as female-specific, and estimates of quantitative genetic variation seldom consider a potential role for heritable male effects. Yet reliable estimates of such social genetic effects are important since they influence the amount of heritable variation available to selection. Based on a 52-year study of a nestbox-breeding great tit (Parus major) population, we apply 'extended' bivariate animal models in which the heritable effects of both sexes are modelled to assess the extent to which males contribute to heritable variation in seasonal reproductive timing (egg laying date) and clutch size, while accommodating the covariance between the two traits. Our analyses show that reproductive timing is a jointly expressed trait in this species, with (positively covarying) heritable variation for laydate being expressed in both members of a breeding pair, such that the total heritable variance is 50% larger than estimated by traditional models. This result was robust to explicit consideration of a potential male-biased environmental confound arising through sexually dimorphic dispersal. In contrast to laydate, males' contribution to heritable variation in clutch size was limited. Our study thus highlights the contrasting extent of social determination for two major components of annual reproductive success, and emphasises the need to consider the social context of what are often considered individual-level traits.</p>
Data from: Higher rates of pre‐breeding condition gain positively impacts clutch size: a mechanistic test of the condition‐dependent individual optimization model
1. A combination of timing of and body condition (i.e., mass) at arrival on the breeding grounds interact to influence the optimal combination of the timing of reproduction and clutch size in migratory species. This relationship has been formalized by Rowe et al. in a condition-dependent individual optimization model (American Naturalist, 1994, 143, 689-722), which has been empirically tested and validated in avian species with a capital-based breeding strategy. 2. This model makes a key, but currently untested prediction; that variation in the rate of body condition gain will shift the optimal combination of laying date and clutch size. This prediction is essential because it implies that individuals can compensate for the challenges associated with late timing of arrival or poor body condition at arrival on the breeding grounds through adjustment of their life history investment decisions, in an attempt to maximize fitness. 3. Using an 11-year data set in arctic-nesting common eiders (Somateria mollissima), quantification of fattening rates using plasma triglycerides (an energetic metabolite), and a path analysis approach, we test this prediction of this optimization model; controlling for arrival date and body condition, females that fatten more quickly will adjust the optimal combination of lay date and clutch size, in favour of a larger clutch size. 4. As predicted, females fattening at higher rates initiated clutches earlier and produced larger clutch sizes, indicating that fattening rate is an important factor in addition to arrival date and body condition in predicting individual variation in reproductive investment. However, there was no direct effect of fattening rate on clutch size (i.e., birds laying on the same date had similar clutch sizes, independent of their fattening rate). Instead, fattening rate indirectly affected clutch size via earlier lay dates, thus not supporting the original predictions of the optimization model. 5. Our results demonstrate that variation in the rate of condition gain allows individuals to shift flexibly along the seasonal decline in clutch size to presumably optimize the combination of laying date and clutch size.
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