Controlling resource acquisition to reveal a life history trade-off: egg mass and clutch size in an iteroparous seed predator, Prostephanus truncatus

1. A trade-off constraining egg production was investigated and the consequences of egg mass for the offspring life history in Prostephanus truncatus investigated. Fresh egg mass was found to vary between 0.065 and 0.109 mg (about 20% of fresh body mass at emergence) and was correlated both with dry egg mass ( r = 0.8) and with the mass of first-instar larvae ( r = 0.8).
2. There was a negative correlation between egg mass and clutch size: doubling clutch size from eight to sixteen eggs resulted in a reduction in egg mass from 0.09 to 0.07 mg. Resource allocation per clutch was not constant but increased with clutch size. After allowing for the relationship between egg mass and clutch size, heavier females were found to oviposit both heavier eggs and more eggs in a clutch.
3. By placing eggs in prepared seeds that minimized variation in resource acquisition, it was discovered that development period of females, but not of males, was negatively correlated with egg mass. Egg size was not correlated with body size at emergence in either sex.
4. The results are interpreted as revealing a resource-allocation trade-off in egg production.     

Intraclutch egg-size variation and offspring survival in the Kentish Plover Charadrius alexandrinus

We studied the consequences of intraclutch egg-size variation in Kentish Plovers Charadrius alexandrinus in southern Spain to test the hypothesis that females allocate resources preferentially to eggs with the greatest survival potential. Second eggs were larger and had a greater hatching success than the other eggs in a clutch. However, we did not find unequivocal support for the differential allocation hypothesis, because egg failures according to laying order were not due to the causes predicted by the hypothesis, and the change in egg-size with laying order was not consistent between successive clutches of renesting females. This suggests that nutrient availability during egg formation could act as a proximate factor affecting egg-size independently of laying order. Larger eggs produced heavier chicks and, within broods, heavier chicks were most likely to be recruited into the breeding population. By laying clutches with a larger mean egg volume in replacement clutches, females took longer to lay again after failure of the first clutch. Thus, opposing selective forces may act to increase and decrease egg volume. Although a trade-off between egg-size and clutch-size has not been found in precocial birds, our results suggest that there may be a trade-off between egg-size and fecundity, since an increase in the size of eggs within clutches may limit the time remaining within the season to lay second or replacement clutches.     

中国石龙子雌体繁殖特征和卵孵化的地理变异

浙江丽水和广东韶关中国石龙子均年产单窝卵,窝卵数,窝卵重和卵重均与雌体SVL呈正相关,雌体头部形态,繁殖特征,产卵起始时间和孵孵化的热依赖性等有显著的地理变异;韶关石龙子产卵起始时间为5月中旬,比丽水经子约早两周,韶关石龙子窝卵数较大,卵较小,窝卵重与丽水石龙子无显著差异。韶关石龙子特定SVL的窝卵数比丽水石龙子多2．8枚卵,中国经子卵数量和大小之间有种群间权衡,无种数内权衡,同一种群内卵数量与卵大小无关,孵化温度影响石龙子孵出幼体的一些特征,24℃孵出细幼体比32℃孵出幼体大,躯干发育好,剩余卵黄少,韶关24℃孵出幼体的体重,躯干干重小于丽水幼体,韶关32℃孵出幼体的SVL小于丽水幼体,剩余卵黄大于丽水幼体,表明适宜卵孵化温度范围有地理变异。丽水石龙子卵对极端高温和低温的耐受性较强,适宜卵孵化温度范围较宽。     

Covariation between clutch size, egg weight and egg shape: comparative evidence for chelonians

The variation in reproductive variables is documented both within and across species of chelonians. At both the generic and family levels, egg weight and clutch size show positive, significant correlations with adult carapace length. There is a negative correlation across both genera and families between clutch size and egg weight after removing the effects of body size, suggesting an evolutionary trade-off between these two life-history characteristics. However, the trade-off is not complete, since clutch size is positively correlated with clutch weight after removing the effects of body size. Terrestrial species lay fewer and larger eggs for their size than freshwater or marine species, but this association is statistically confounded by the fact that chelonian families form ecological groups. There is no significant association between habitat and clutch weight after removing the effects of body size, nor between latitude and either egg weight or clutch size, but temperate species have a heavier clutch weight after removing the effects of body size. Larger species lay eggs that are more spherical, but after controlling for body size, egg shape is not associated with clutch size. The patterns of covariation between adult weight, egg weight and clutch size contrast with those reported for birds and mammals, and some reasons for these differences are discussed.     

Measuring temporal variation in reproductive output reveals optimal resource allocation to reproduction in the northern grass lizard, Takydromus septentrionalis

We measured the reproductive output of Takydromus septentrionalis collected over 5 years between 1997 and 2005 to test the hypothesis that reproductive females should allocate an optimal fraction of accessible resources in a particular clutch and to individual eggs. Females laid 1–7 clutches per breeding season, with large females producing more, as well as larger clutches, than did small females. Clutch size, clutch mass, annual fecundity, and annual reproductive output were all positively related to female size (snout–vent length). Females switched from producing more, but smaller eggs in the first clutch to fewer, but larger eggs in the subsequent clutches. The mass-specific clutch mass was greater in the first clutch than in the subsequent clutches, but it did not differ among the subsequent clutches. Post-oviposition body mass, clutch size, and egg size showed differing degrees of annual variation, but clutch mass of either the first or the second clutch remained unchanged across the sampling years. The regression line describing the size–number trade-off was higher in the subsequent clutch than in the first clutch, but neither the line for first clutch, nor the line for the second clutch varied among years. Reproduction retarded growth more markedly in small females than in large ones. Our data show that: (1) trade-offs between size and number of eggs and between reproduction and growth (and thus, future reproduction) are evident in T. septentrionalis ; (2) females allocate an optimal fraction of accessible resources in current reproduction and to individual eggs; and (3) seasonal shifts in reproductive output and egg size are determined ultimately by natural selection.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 315–324.     

Female reproductive characteristics of the Balkan wall lizard (<Emphasis Type="Italic">Podarcis taurica</Emphasis>) in the northwestern periphery of its range

We present data on the female reproductive traits of the Balkan wall lizard in the Deliblato Sand, a large continental sandland in the Pannonian area in the northwestern periphery of the species range. The clutch and egg characteristics of the population were investigated on the basis of clutches laid in laboratory conditions by gravid females captured in one locality. Balkan wall lizards produced at least two clutches in a breeding season. Individual females laid clutches of commonly two (range 1–4) eggs. The female body size had no effect on clutch and egg size. There was no trade-off between egg size and clutch size.     

Factors influencing offspring traits in the oviparous multi-clutched lizard,<Emphasis Type="Italic">Calotes versicolor</Emphasis> (Agamidae)

The determinants of offspring size and number in the tropical oviparous multi-clutched lizard,Calotes versicolor, were examined using both univariate and multivariate (path) analyses. InC. versicolor maternal snout-vent length (SVL) and body condition influence clutch mass and clutch size but have no significant influence on offspring size. The positive effect of maternal SVL and body condition on offspring number is counterbalanced by a negative effect of breeding time on egg mass. In fact, breeding time directly influences the offspring body mass and condition through variation in the egg mass. There is a trade-off between offspring mass and condition with offspring number, and breeding time influences both. Offspring hatched from the eggs of early (May–June) or mid (July–August) breeding periods invariably show lower mass and condition than those hatched from the eggs of late breeding season (September–October). Yet, there is no variation in offspring SVL among early, mid and late clutches. Thus, inC. versicolor offspring SVL is optimized while body mass and condition are not optimized.     

蜡皮蜥的两性异形和繁殖输出

为研究蜡皮蜥(Leiolepis reevesii)两性异形和繁殖输出,于2002、2003年4月下旬从海南乐东一种群捕获423头蜡皮蜥。经检测得到繁殖雌体的最小体长为89．0mm,据此判定≥89．0mm的个体为性成熟。研究结果表明：①蜡皮蜥具有两性异形,雄性大于雌性且具有较大的头部。成体雄性头长和头宽随体长的增长速率大于雌性,幼体头长和头宽随体长的增长速率无显著的两性差异。以性别和年龄(成、幼体)为因子的双因子ANOVA比较两性头长和头宽与体长的回归剩余值发现,雄性头部大于雌性,幼体头部相对大于成体。②饲养于实验室的母体中有42头于2002、2003年5月22日～7月16日产出正常卵,这些繁殖雌体具有年产多窝卵的潜力。窝卵数和卵重的变异系数分别为0．18和0．13,前者变异度大于后者。窝卵数、窝卵重和卵重均与母体体长无关。卵重与相对生育力之间无显著的负相关性,表明蜡皮蜥缺乏卵数量与卵大小之间的权衡。相对窝卵重与母体体长呈显著的负相关,表明较小的母体具有相对较大的繁殖输出。因雌体繁殖会滞缓其生长,小母体具有相对较大的繁殖输出,至少部分地解释了雌性蜡皮蜥的成体为什么个体较小。     

Experimental manipulation of female reproduction reveals an intraspecific egg size-clutch size trade-off

A negative relationship, or trade-off, between egg size and clutch size is a central and long-standing component of life-history theory, yet there is little empirical evidence for such a trade-off, especially at the intraspecific level. Here, I show that female zebra finches (Taeniopygia guttata) treated chronically during egg formation with the anti-oestrogen tamoxifen lay smaller eggs (by 8%) but produce larger clutches (on average two eggs more) than controls. Decreased egg mass in tamoxifen-treated females was associated with a 50% decrease in plasma levels of the two yolk precursors, vitellogenin and very-low-density lipoprotein. Although tamoxifen-treated females laid more, smaller eggs (and had a higher total expenditure in their clutch), they did not differ from controls in the number of chicks fledged, the mass or size of these chicks at fledging, or the chicks' egg-production performance at three months of age. However, tamoxifen-treated females had lower relative hatching success: they laid more eggs but hatched the same number of chicks. Among individual tamoxifen-treated females, birds that laid the smallest eggs early in their laying sequence laid the largest number of additional eggs, that is, there was a negative correlation, or trade-off, between egg size and clutch size.     

The trade‐off between clutch size and egg mass in tree swallows Tachycineta bicolor is modulated by female body mass

Egg production is a costly component of reproduction for female birds in terms of energy expenditure and maternal investment. Because resources are typically limited, clutch size and egg mass are expected to be constrained, and this putative trade‐off between offspring number and size is at the core of life history theory. Nevertheless, empirical evidence for this trade‐off is equivocal at best, as individual heterogeneity in resource acquisition and allocation may hamper the detection of the negative correlation between egg number and mass within populations. Here, we investigated how female body mass and landscape composition influences clutch size, egg mass, and the relationship between these two traits. To do so, we fitted linear mixed models using data from tree swallows Tachycineta bicolor breeding in a network of 400 nestboxes located along a gradient of agricultural intensity between 2004 and 2011. Our dataset comprised 1463 broods for clutch size analyses and 4371 eggs (from 847 broods laid between 2005–2008) for egg mass analyses. Our results showed that agricultural intensity negatively impacted clutch size, but not egg mass nor the relationship between these two traits. Female mass, on the other hand, modulated the trade‐off between clutch size and egg mass. For heavier females, both traits increased jointly, without evidence of a trade‐off. However, for lighter females, there was a clear negative relationship between clutch size and egg mass. This work shows that accounting for individual heterogeneity in body mass allows the detection of a clutch size/egg mass trade‐off that would have remained undetected otherwise. Identifying habitat and individual effects on resource allocation towards reproductive traits may help bridging the gap between predictions from theory and empirical evidence on life history trade‐offs.     

Female body size, fecundity parameters and foundation of new colonies in Anelosimus jabaquara (Araneae, Theridiidae)

Summary. As in other social spider species, subadult Anelosimus jabaquara females found new colonies after solitary dispersal. Some individuals, however, usually remain and reproduce in their natal nests. To test the hypothesis that large females disperse more often than smaller ones, we compared the body size of A. jabaquara females that remained in their natal colonies with those that left to build solitary webs. We also compared clutch size, egg diameter, total egg volume and spiderling size in both conditions. Emigrating females were significantly larger and laid larger clutches. The smaller females that had not dispersed laid significantly larger eggs, although their total egg volume was lower. Spiderlings of solitary females were smaller and had a smaller range of size variation than those from colonies. We discuss the implications of these results in terms of costs and benefits of dispersion for spiders in different nutritional conditions.     

宁波滑蜥两性异形和雌性繁殖

蜥蜴的雌性繁殖特征对理解两性异形的进化原因起着重要作用。于2011年4月在安徽滁州采集宁波滑蜥(Scincella modesta),定量研究该种形态特征的两性异形和雌性繁殖特征,检验成体形态特征两性异形与雌性繁殖的相关性。研究共采集43条(17♀♀,26♂♂)宁波滑蜥,雄性和雌性个体的最大体长分别为47.4 mm和46.6 mm。雌雄两性在体长和头宽上没有差异,而在腹长和头长上差异显著,雄性有较大的头长,雌性有较大的腹长。宁波滑蜥年产单窝卵。窝卵数和窝卵重与雌体体长及腹长呈正相关,卵重与雌体体长无相关性。窝卵数及卵重的变异系数分别为0.20和0.12。卵长径与窝卵数呈负相关,而卵短径与窝卵数无关。雌体主要通过增加窝卵数来增加繁殖输出。这些结果表明,宁波滑蜥是雌雄个体大小同形的两性异形模式,性选择使得雄性有着较大的头长,以具有较高的交配成功率,生育力选择使得雌性有着较大的腹长,以具有较大的生育力和繁殖输出。     

Clutch size variation in the Nazca booby: a test of the egg quality hypothesis

In obligately siblicidal bird species, aggressive behavior bya dominant chick results in a fixed brood size of one, yetthese species usually show clutch size variation between individuals.Simmons proposed that variation in clutch size in obligatelysiblicidal species is related to a trade-off between egg qualityand egg quantity: some individuals produce a single highly hatchable egg, while others produce two small, lower qualityeggs. We tested the egg quality hypothesis as an explanationfor observed clutch size variation in the Nazca booby (Sulagranti), an obligately siblicidal seabird. We tested the assumptionthat egg volume is positively correlated with hatchabilityand the prediction that eggs from one-egg clutches are largerthan eggs from two-egg clutches. We did not find a positive relationship between egg volume and hatchability in this species.Eggs from two-egg clutches were either equivalent in volumeor larger than eggs from one-egg clutches. Thus, the egg qualityhypothesis was rejected as an explanation for clutch size variationin the Nazca booby. Instead, two-egg clutches appear to befavored because of the insurance value of the second-laid egg,while one-egg clutches result from food limitation.     

蓝尾石龙子杭州和宁德种群繁殖生活史特征的差异

测定处于不同纬度的浙江杭州和福建宁德的蓝尾石龙子(Eumeceselegans)种群的个体大小和繁殖特征。宁德种群的产卵时间为5月27日—6月22日,早于高纬度杭州种群(6月4日—7月12日)。宁德种群最小繁殖雌体及性成熟个体大小均显著小于杭州种群。宁德和杭州两种群的相对窝卵重无显著差异;当统计去除母体体长的影响之后,两地种群的窝卵数和窝卵重也无显著差异,但杭州种群的卵重量显著大于宁德种群。蓝尾石龙子窝卵数和卵重量呈负相关,窝卵数和卵大小的权衡存在种群间差异。特定窝卵数条件下,杭州种群的卵重量显著大于宁德种群。由此可见,蓝尾石龙子种群间的繁殖生活史特征存在显著差异,而且与母体大小的差异密切相关。推测不同纬度地区的蓝尾石龙子种群的繁殖策略存在差异。     

Individual Variation in Trophic Egg Production: Evidence for Maternal Manipulation in Response to Resource and Competition Levels

Females of the subsocial shield bug Parastrachia japonensis (Heteroptera: Parastrachiidae) incorporate trophic eggs (nutritive eggs) into their egg mass. Considerable variation occurs among females in trophic egg number and the proportion of an egg mass that is composed of trophic eggs. Because trophic eggs are essential to the development and survival of young, this variation could significantly impact female fitness. We tested the hypothesis that trophic egg abundance is induced by maternal phenotype (weight, body size) and resource exposure. We predicted that resource limitations would cause females to produce fewer fertile eggs and more trophic eggs and that larger and heavier females would produce more of each egg type. Females ovipositing early in the season are exposed to different resource conditions than those that oviposit late. Thus, we compared egg production patterns between these two groups and several other factors related to nesting. No correlation was seen between body size and trophic egg abundance, or, indeed, egg production, overall; however, heavier females produced heavier egg masses. Counter to our prediction, late females, which had greater access to food, produced significantly more total eggs, fewer fertile eggs, and more trophic eggs than early females. A binomial generalized linear model analysis indicated that the factors most correlated with the percentage of an egg mass destined to become trophic eggs were resource abundance, resulting from early or late oviposition, and distance of the nest from the host tree, with closer females producing more trophic eggs. The findings support our hypothesis that resource availability and, to a lesser extent, maternal phenotype affect trophic egg abundance.     

Juvenile exposure to predator cues induces a larger egg size in fish

When females anticipate a hazardous environment for their offspring, they can increase offspring survival by producing larger young. Early environmental experience determines egg size in different animal taxa. We predicted that a higher perceived predation risk by juveniles would cause an increase in the sizes of eggs that they produce as adults. To test this, we exposed juveniles of the mouthbrooding cichlid Eretmodus cyanostictus in a split-brood experiment either to cues of a natural predator or to a control situation. After maturation, females that had been confronted with predators produced heavier eggs, whereas clutch size itself was not affected by the treatment. This effect cannot be explained by a differential female body size because the predator treatment did not influence growth trajectories. The observed increase of egg mass is likely to be adaptive, as heavier eggs gave rise to larger young and in fish, juvenile predation risk drops sharply with increasing body size. This study provides the first evidence that predator cues perceived by females early in life positively affect egg mass, suggesting that these cues allow her to predict the predation risk for her offspring.     

Manipulation of laying effort reveals habitat-specific variation in egg production constraints in Great Tits (Parus major)

It has been suggested that a bird's clutch size is not limited by the amount of resources available at the time of laying but that differences in the availability of food for nestlings is the ultimate underlying factor determining spatio-temporal variations in clutch size. However, habitat-related variations in egg production ability has yet to be investigated explicitly. We studied the breeding of Great Tits Parus major in deciduous and coniferous forests in the same area. The sizes of both the clutches and the eggs were, on average, larger in the former habitat than in the latter. A number of females were induced to lay more eggs than usual by removing four eggs from designated experimental clutches early in the laying period. These manipulated females laid approximately one egg more than control females, with the number of additional eggs laid not differing between the habitats. However, in both study years the relative size of the extra eggs – relative to the mean size of earlier laid eggs of the same clutch – was smaller in the coniferous habitat than in the deciduous habitat, while there was no habitat-related difference in the relative size of the last-laid eggs of control clutches. This result indicates that some form of proximate limitation during egg-laying period can contribute to the relatively small clutches and eggs in the coniferous habitat. Our results emphasize the need to take egg production costs into account when attempting to account for spatial variation in the reproductive behaviour of birds.     

Life-history variation within a three-spined stickleback population in the Camargue

Among individuals of female three-spined sticklebacks Gasterosteus aculeatus from a population in the Camargue, southern France, studied in 12 successive years, adult L _T ranged from 31–64 mm, clutch size ranged from 33–660 eggs, and mean egg diameter per clutch ranged from 1.15–1.67 mm. Because the population was strictly annual, inter-annual variation corresponded to variation among generations having experienced different environmental conditions. Body mass varied significantly among years, suggesting an effect of varying environmental conditions. Gonad mass and clutch size increased with body mass, but mean egg diameter was not correlated to body mass. Body mass-adjusted gonad mass, interpreted as reproductive effort per clutch, did not vary significantly among years, suggesting that this trait was not influenced by environmental conditions. Body mass-adjusted clutch size and egg size varied significantly among years. Inter-annual variation in body length at breeding, clutch size and egg size was of the same order of magnitude as inter-population variation reported by other authors for this species. During the breeding season, reproductive effort and clutch size tended to increase. Egg size tended to decrease during the breeding season but this seasonal pattern varied among years. Observed life-history variation is discussed both in terms of its evolutionary significance and methodological implications in the study of life-history variation among populations.     

Fecundity compromises attractiveness when pigments are scarce

Theory predicts that the trade-off between ornamentation andfecundity limits female attractiveness. However, there is littleevidence on this theoretical trade-off and its proximate background.Our aim was to study whether pigment availability modulatesthis potential relationship in blue-footed booby females. Wesupplemented females with dietary carotenoids after laying thefirst egg and assessed the change in foot color, a carotenoid-basedsexually selected trait in both sexes. We measured the changein body mass and in the levels of plasma antioxidants and carotenoids.Also, we registered the mass and volume of eggs. Surprisingly,experimental females reduced zeaxanthin concentration in plasma,but not other carotenoids or total antioxidant levels. Conversely,they increased foot color intensity and laid heavier secondeggs and larger second and third eggs than controls. Furthermore,under natural conditions (controls), ornamentation was negativelyassociated with the mass and volume of second eggs, but theassociation was reversed under conditions of high carotenoidavailability (experimental females). Results suggest that carotenoidavailability may mediate the theoretical trade-off between ornamentationand fecundity. We highlight that pigment limitation for femalescould represent an evolutionary pathway to male choosiness inthe blue-footed booby.     

Experimental dissociation of the effects of diet, age and breeding experience on primary reproductive effort in zebra finches Taeniopygia guttata

Reproductive performance varies with age in a wide range of organisms, and increasingly such patterns are interpreted in terms of state-dependent models. We sought to characterise 'state' with regards to age-related variation in clutch size, egg mass and timing of breeding in captive zebra finches Taeniopygia guttata , focusing on the roles of diet quality, age and breeding experience. Females on a high-quality diet laid larger clutches of larger eggs than did females on a low-quality diet. The effect of age on reproductive performance was examined by comparing females breeding (i.e. paired) for the first time at either 3- and/or 6-months of age. Clutch size increased with age but on the low-quality diet only, not on the high-quality diet. Furthermore, clutch size decreased between 3- and 6-months of age in birds bred first on the high-quality diet and then on the low-quality diet. Age did not affect egg mass but older birds had shorter laying intervals. Reproductive performance did not differ between females breeding at 6-months of age for the first or second time: the effects of age were not due to 'training' effects or experience specific to breeding (e.g. undergoing the physiological process of egg formation). In conclusion, nutritional condition (diet) emerged as a central component of state that could strongly influence, and even reverse, any age-dependent increase in primary reproductive performance.