Relative Egg Size Research Articles

Effects of Environmental Conditions and Parental Quality on Inter- and Intraclutch Egg-Size Variation in the Collared Flycatcher (Ficedula Albicollis)

AbstractEgg size is a particularly important life-history trait mediating maternal influences on offspring phenotype. Females can vary their egg-size investment in relation to environmental circumstances, their own breeding condition, and the quality of their mate. Here we analyzed inter- and intraclutch variation in egg size in the Collared Flycatcher (Ficedula albicollis) on the basis of eight years of data. According to our results, mean egg size increased with female condition, but did not differ among young, middle-aged, and old females. The male’s age, body size, and forehead patch size did not influence egg size; thus, we found no evidence for differential investment in egg size in relation to male quality. We found no effect of laying date on egg size when controlling for ambient temperature during the egg formation period, yet temperature had a significant effect on egg size. That result indicates proximate constraints on egg formation. Furthermore, we report on annual differences in intraclutch egg-size variation. Egg size increased within clutches in years with a warm prelaying period; whereas in years when the weather during that period was cold, there was no significant intraclutch trend. Proximate considerations seem to explain the observed patterns of intraclutch egg-size variation; however, we cannot reject the adaptive explanation. Mean egg size and intraclutch egg-size variation were unrelated to clutch size. Therefore, we found no evidence for a trade-off between size and number of eggs within a clutch.

EFFECTS OF ENVIRONMENTAL CONDITIONS AND PARENTAL QUALITY ON INTER- AND INTRACLUTCH EGG-SIZE VARIATION IN THE COLLARED FLYCATCHER (FICEDULA ALBICOLLIS)

Abstract Egg size is a particularly important life-history trait mediating maternal influences on offspring phenotype. Females can vary their egg-size investment in relation to environmental circumstances, their own breeding condition, and the quality of their mate. Here we analyzed inter- and intraclutch variation in egg size in the Collared Flycatcher (Ficedula albicollis) on the basis of eight years of data. According to our results, mean egg size increased with female condition, but did not differ among young, middle-aged, and old females. The male’s age, body size, and forehead patch size did not influence egg size; thus, we found no evidence for differential investment in egg size in relation to male quality. We found no effect of laying date on egg size when controlling for ambient temperature during the egg formation period, yet temperature had a significant effect on egg size. That result indicates proximate constraints on egg formation. Furthermore, we report on annual differences in intraclutch...

Ovarian allometry and the use of the gonosomatic index: a case study in the Mediterranean sardine, Sardina pilchardus

The gonosomatic or gonadosomatic index [GSI=(ovary weight/fish weight)×100] has been widely used in fisheries science and experimental reproductive studies as a simple, low-cost measure of reproductive condition. However, its properties have not been fully evaluated, and several pitfalls, such as size-dependence and changes in ovarian allometry, may invalidate its use. In the present study, we examined ovarian allometry and the appropriateness of GSI for assessing ovarian activity in the Mediterranean sardine Sardina pilchardus. The analysis was based on a large sample of histologically scored females collected over an annual cycle in the eastern Mediterranean (Aegean and Ionian Seas). First, we examined GSI dependence on fish size by comparing ovary weight–on–fish weight relationships in different stages of oocyte development. The effects of recent spawning (incidence of postovulatory follicles) and intensity of follicular atresia were also addressed. In a subsequent step of the analysis, we applied generalized linear models (GLMs) to analyze the relationship between GSI and histological stage, taking into account the parallel effects of additional factors related to geographical region, month of capture, fish length and energetic reserves (fat stage, hepatosomatic index—HSI). Ovarian growth was isometric in all stages of oocyte development and states of atresia, but altered to positive allometric at the stage of oocyte hydration. Oocyte growth and intensity of atresia significantly affected GSI. Fish length, geographical region, month of capture, fat stage and HSI did not substantially affect GSI, further strengthening the appropriateness of the index for the Mediterranean sardine. Finally, we provide first evidence, based mainly on available (but yet limited) published information for other fish species, that: (1) the pattern of ovarian allometry may not be altered by fecundity variations and (2) the pattern of ovarian allometry may reflect the pattern of oocyte growth (i.e. isometric vs. allometric ovarian growth could reflect group-synchronous vs. -asynchronous oocyte development). Alternatively, the pattern of ovarian allometry could reflect the presence or absence of size dependency in the relative fecundity (eggs per gram of body weight) and/or egg size. The isometric ovarian growth in the Mediterranean sardine could be attributed to the lack of such size-dependent effects.

Incubation start and egg size in relation to body reserves in the common eider

Avian incubation is often initiated before all eggs are laid. In altricial birds this has been proposed to facilitate brood reduction through asynchronous hatching. However, in precocial birds eggs normally hatch synchronously even if incubation has started before all eggs are laid. Patterns of incubation start may be the adaptive trait selected for both in altricial and precocial species. Several hypotheses have been proposed to explain the timing of incubation start in birds. Decreasing egg-size after incubation start may be adaptively related to an early incubation start, either to ensure synchronous hatching or to decrease fitness cost of late hatched eggs. We have measured individual body condition, egg size and start of incubation in common eider Somateria mollissima, a precocial sea-duck which does not feed during the incubation period. Females in poor body condition start to incubate earlier in the laying sequence than those in good body condition. Furthermore females in poor body condition lay smaller final eggs than females in good body condition. The laying of smaller eggs late in the sequence is therefore probably related to energetic or nutritional state. We propose that females in poor body condition start to incubate early to shorten the nest period in order to reduce their mass loss, but at the cost of reduced size and growth of the ducklings from the eggs laid after incubation start. Females in good body condition on the other hand postpone incubation start at the cost of a longer incubation period and a higher mass loss to the benefit of synchronized hatching and a higher survival of ducklings.

Reproduction in Female Razorback Musk Turtles (Sternotherus carinatus: Kinosternidae)

Reproduction in female razorback musk turtles, Sternotherus carinatus, from southeastern Oklahoma and central Arkansas was examined. At both sites ovulation apparently occurs from late April or early May to at least earlyJuly, with 2 or 3 clutches typically produced per year. Arkansas females grow faster than Oklahoma females, reach maturity at larger sizes (95-100 versus 85-90 mm carapace length) but younger ages (after 5-6 versus 8 winters), reach larger adult sizes (mean carapace length 117 versus 102 mm), produce heavier eggs (5.7 versus 5.2 g), and bigger (3.8 versus 2.3 eggs) and heavier clutches (21.6 versus 11.6 g). For both populations, clutch size increases with body size; egg size also increases with body size, but the relationship is weaker. Unstandardized egg and clutch size exhibit no clear relationship; however, when effects of body size are removed, egg size and clutch size are negatively correlated. Clutch mass relative to body mass does not differ between sites, but relative egg size is greater in Oklahoma.

Male-only care and classical polyandry in birds: phylogeny, ecology and sex differences in remating opportunities.

It has been argued recently that the combination of male-only parental care and classical polyandry in birds is the most interesting and yet the least understood of all avian breeding systems. Despite a huge number of hypotheses, careful comparative analyses have repeatedly failed to identify consistent ecological differences between species showing male-only care and closely related species showing other patterns of care. This has led to the suggestion that such analyses fail because the crucial differences are between ancient lineages rather than between closely related species. Here, therefore, I use comparisons between families to test three well-known hypotheses: that male-only care is associated with: (i) a low rate of fecundity; (ii) large egg size relative to female size; or (iii) female-biased opportunities for remating. Families showing male-only care do not differ from families showing female-only care with respect to rate of fecundity or relative egg size. There is, however, a significant difference between these two groups of families with respect to an index of remating opportunities, nesting density. Families showing female-only care nest at high density, while those showing male-only care nest at very low density. This is one of the first times a consistent ecological correlate has been identified for male-only care in birds. It suggests that female-only care arises (or persists) in families where remating opportunities are abundant for both sexes, whereas male-only care arises (or persists) in families where remating opportunities are rare for both sexes and particularly scarce for males. This in turn suggests that sex differences in remating opportunities are the key ecological factor in determining male-only care and classical polyandry in birds.

Egg Size, Intrinsic Competition, and Lethal Interference in the Parasitoids Encarsia pergandiella and Encarsia formosa

Recent population dynamic theory predicts that disruption of biological control may occur when one parasitoid species' superiority in intrinsic competition is associated with a lower ability to find and exploit hosts (i.e., ability in extrinsic competition). One might expect such a trade-off, for instance, if parasitoids with larger (and fewer) eggs are more likely to prevail in intrinsic competition than species with smaller (and more numerous) eggs. We tested the idea that relative egg size could be used to predict the outcome of intrinsic competition in two closely related endoparasitoids, Encarsia pergandiella Howard and Encarsia formosa Gahan. Contrary to expectation, the parasitoid species with smaller eggs, E. pergandiella, prevailed in intrinsic competition, regardless of the order that hosts were exposed to the two species. In a literature survey, we found four studies of competing pairs of endoparasitoid species for which: (a) egg size estimates were available and (b) one species was consistently superior in intrinsic competition. In three of the four studies, the small-egged species prevailed in intrinsic competition, as we also found. Although E. formosa lost in intrinsic competition, this species negatively affected E. pergandiella's progeny production by host feeding on and killing hosts containing E. pergandiella eggs. E. formosa females also host fed on conspecific-parasitized hosts. As a mechanism of both intra- and interspecific interference competition, host feeding on parasitized hosts contradicts assumptions about the nature of interference competition in existing population dynamics models.

Reproductive ecology of Japanese anchovy off the Pacific coast of eastern Honshu, Japan

Spawning frequency of offshore migrant populations of Japanese anchovy Engraulis japonicus ranged from 0·34 to 0·90, and was higher than that of inshore Japanese anchovy. In addition, spawning frequency of offshore populations varied in response to the sex ratio. They spawned at water temperatures of 5.0, 8.6 and 12.6° C, indicating that the minimum critical water temperature of offshore Japanese anchovy was considerably lower than that of inshore populations. A significant positive relationship was observed between water temperature and relative batch fecundity of offshore Japanese anchovy. Furthermore, water temperature was negatively related to egg size, suggesting a trade‐o. between relative batch fecundity and egg size for offshore fish. At the same water temperature, relative batch fecundity of offshore populations was higher than that of inshore ones. The comparison of spawning frequency and relative batch fecundity suggests that offshore Japanese anchovy represent a reproductive ecology by which they spawn more eggs than inshore Japanese anchovy within a certain time period.

Reproductive Performance of Inland Fall Chinook Salmon

Abstract Reproductive performance data were collected for inland fall chinook salmon Oncorhynchus tshawytscha from Lake Oahe, South Dakota, in 1988 and 1998. This population exists outside the native geographical range of chinook salmon and completes its entire life cycle in freshwater. Female weights and lengths, total fecundity, relative fecundity (eggs/mm), egg size, and egg survival were all considerably less than reported for anadromous chinook salmon stocks in their native range. Mean weight of spawning females was 2.73 kg in 1988 and 2.01 kg in 1998. Total fecundity was not significantly different at 2,892 eggs in 1988 and 2,496 eggs in 1998. Egg survival to the eyed stage averaged 37.7% in 1988 and 43.8% in 1998 and ranged from 0% to 96%. Relative fecundity (eggs/kg), egg size, and egg survival to the eyed stage were similar for each year. Relative fecundity (eggs/mm of total length) declined from 1988 to 1998. Total fecundity was linearly related to fish length in 1998 and in both years combined....

Effect of body size and temperature on generation time in zooplankton

Effect of body size and temperature on generation time in zooplankton

Larger eggs in resident brown trout living in sympatry with anadromous brown trout

Abstract– Freshwater resident brown trout (Salmo trutta L.) in the stream Jorlandaan (southwestern Sweden) had larger eggs (range of actual mean egg wet weights, 65.9–108.5 mg) than both sympatric migratory trout (76.8–84.2 mg) and trout from five other Swedish streams with allopatric resident (23.7–80.1 mg) or migratory populations (44.5–121.9 mg), after accounting for differences in body size. In Jörlandaån, some resident females even had a larger absolute mean egg weight than any of the migratory females found in the stream. Resident trout had low absolute fecundity, and our data suggest that resident females in Jörlandån produce large eggs at the expense of their fecundity. The extremely large relative egg size in resident Jörlandaån females suggests that the production of large offspring enhances fitness, possibly through increased fry survival.

The Maturity Index,the evolution of nematode life history traits, adaptive radiation and cp-scaling

Nematodes are increasingly being used in environmental studies. One of the potential parameters to measure the impact of disturbances and to monitor changes in structure and functioning of the below-ground ecosystem is the nematode Maturity Index; an index based on the proportion of colonizers (r-strategists s.l.) and persisters (K-strategists s.l.) in samples. In this paper the original allocation of nematode taxa on the colonizer-persister scale, and the tolerance and sensitivity of colonizers and persisters are discussed from an evolutionary viewpoint. The phenomenon that neither relative egg size nor body length is an unequivocal character to scale nematodes suggests that the main selection for life history traits occurred independently in the major evolutionary branches.

The paradox of bdelloid egg size

Egg volumes or relative egg size (RES) of seven bdelloid species were plotted against life-history traits, and recovery rates from 7-day desiccation periods to find evidence for the costs and benefits of producing a few big, or many small eggs. Increased RES of bdelloids is correlated with decreased fecundity and longevity, increased age at maturity, increased egg developmental time and increased recovery from desiccation for both embryos and adults. The production of large eggs represents a cost for the bdelloid rotifer, which, at first sight, does not receive compensating advantages. This paradox, however, is only superficial, as it is suggested that an increase of recovery and, in particular, increased viability of late embryos compensates for the loss of fitness related to the production of large eggs.

Host body size as a factor determining the egg complement of Strepsiptera, an insect parasite

The egg complement (total number of eggs produced by a single female) differs greatly among the species of Strepsiptera. The maximum is found in Stichotrema dallatorreanum (750,000 eggs), and the minimum in Triozocera minor (984 eggs). Based on the egg complement of 31 species in 11 genera, the following conclusions were drawn: (1) The egg complement is generally smaller in those species whose hosts gregariously cohabit in a very limited area, or are distinct flower-visitors, compared with those whose hosts display the above two traits weakly; (2) The egg complement is determined by the size of the maternal body. The size of female strepsipterans is reduced when they parasitize smaller host such as males and workers, as compared with those that parasitize larger host such as females and queens; likewise, the size of the strepsipterans becomes larger on increase in size of hosts, showing that their egg complements are principally determined by the size of host species; (3) The increase in the egg complement is compensated for by the reduction in egg size. The relative egg size (length of the firstinstar larva/length of maternal body) is conspicuously reduced according to an increase in the size of the female strepsipterans.

Do Female Zebra Finches Vary Primary Reproductive Effort in Relation to Mate Attractiveness?

AbstractFemale choice and mate preference have been shown to affect female reproductive effort both prior to copulation (e.g. females seeking extra-pair copulation) and during parental care ('secondary' reproductive effort) in relation to mate quality. Here we show that female zebra finches, Taeniopygia guttata, vary their 'primary' reproductive effort in egg production in relation to the attractiveness of their male partner, for some components of reproduction but not others. Females were allowed to choose 'preferred' and 'non-preferred' males in standard mate choice trials, and were then paired sequentially with each male. Preferred males had significantly higher song duration and song frequency than non-preferred males confirming that females preferred attractive, higher quality males. Male attractiveness had a positive, but weak, effect on clutch size: in breeding experiments individual females laid on average 0.5 eggs more when paired with their preferred male compared to the non-preferred male. However, there was no significant difference in breeding propensity (whether females laid eggs or not), number of days between pairing and laying, mean egg size or egg quality (protein and lipid composition) in relation to male type. These results suggest that components of primary reproductive effort in individual female zebra finches are relatively non-plastic traits.

Life-History Traits Related to Host Selection in Mycophagous Drosophilids

1. Mycophagous drosophilids in Hokkaido, northern Japan, differ in fungal host selection from each other. Differences in life-history traits among them are explained by 'habitat' characteristics influential to the demography of adults and larvae. 2. Pleurotus fungi, to which three Hirtodrosophila species are specialized, produce fruiting bodies, usually in large clumps, intermittently throughout the fly breeding season on the large, dead logs or stumps of elms. On the other hand, the appearance of fruiting bodies is temporally unpredictable in fungi other than Pleurotus, being restricted, respectively, to particular seasons and influenced greatly by weather conditions. Newly emerging adults of polyphagous species have higher abilities to withstand starvation than those of the stenophagous Hirtodrosophila species, in order to cope with their temporally unpredictable habitats. However, habitat unpredictability for mature adults that have already found a fungal patch and fed and/or bred on it is reversed between the stenophagous and polyphagous species. The three Hirtodrosophila species specialized to Pleurotus fungi show significantly higher ratios of reproductive allocation than the other polyphagous species. There will be no chance for mature adult flies of the Hirtodrosophila species to find another breeding site. They are, therefore, regarded as living in spatially unpredictable habitats and to allocate more energy to current reproduction. On the other hand, mature adults of polyphagous species are expected to find another site more easily owing to their polyphagous nature, and invest some energy for residual reproductive value. 3. Five species preferring decayed fungi allocate nearly equal proportions of energy to reproduction, but partition is differently allocated to either large clutches or to large eggs. This differentiation of strategies is related to the difference in larval habitats. Larval habitats are regarded as more unstable for species utilizing fungi of shorter duration. In short-lasting habitats, larvae growing up within a short period would be favoured by natural selection. Larval developmental time is negatively correlated with relative egg size. Drosophila brachynephros and D. curvispina, which are somewhat specialized to soft, deliquescent Coprinus fungi, take the large-egg strategy to cope with their short-lasting larval habitats. On the other hand, H. histrioides, frequently using Polyporellus fungi with large, long-lasting fruiting bodies, take the opposite strategy, producing many small eggs. The same positive correlation between the developmental time and the duration of fungi preferred is also seen among species breeding on fresh fungi. However, the developmental time is always shorter in species preferring decayed fungi than in species preferring fresh ones if the relative egg size is the same. 4. The positive correlation between larval developmental time and adult survival, which is the basis for Sevenster & van Alphen's hypothesis that the difference in life histories promotes the co-existence of competing species in temporally variable environments, is tested for mycophagous drosophilids. It is demonstrated that there is a negative rather than positive correlation between larval developmental time and adult survival time under starvation. Adult starvation resistance is directly correlated with adult body size, and larval developmental time with relative egg size. This study suggests that the relations between larval developmental time and adult survival can be reversed according to the combinations of adult and larval habitats.

Effect of dietary protein level on spawning performance and amino acid composition of eggs of Nile tilapia, Oreochromis niloticus

Oreochromis niloticus were maintained on three purified, isocalorific diets of different dietary protein levels (10, 20 and 35%), with casein and gelatin as protein sources. The dietary protein influence on spawning interval, fecundity, relative fecundity (number of eggs per unit weight) and egg size at four successive spawnings was investigated. The protein, moisture, free and bound amino acid composition of the spawned eggs were determined. O. niloticus females fed 20 and 35% protein levels maintained their spawning cycle, whereas at 10% spawning intervals were prolonged after about 4 months of feeding. Females fed 20 and 35% protein diets produced a higher number of eggs per spawn than those fed 10%, especially at later spawnings. But relative fecundity and egg size did not differ significantly between the treatments. The amount of protein in eggs of females maintained on 35% protein diet was significantly higher than in others. However, the moisture content of the eggs did not vary among the diets. Of the free amino acids, methionine, valine, tyrosine, serine, glycine and proline were influenced by the dietary regime. The total (free + protein bound) individual amino acids in the eggs were not affected by dietary protein level. However, the total overall amino acid pool of eggs in the 35% protein level was higher than in the others.

Egg size in relation to fertilization dynamics in free-spawning tropical reef fishes

In marine invertebrates that spawn by simply releasing their gametes into the water (free-spawning), fertilization success likely is often limited by low sperm concentrations, due to dispersion of mates and dispersal of gametes by water movements. Production of large, low density eggs might be advantageous when sperm concentrations consistently are low, because large target size might increase egg/sperm encounters, and more low than high density eggs could be produced per clutch. Although average fertilization success in the labrid Thalassoma bifasciatum is ∼95% in both group spawns (in which multiple males compete for fertilizations by producing large quantities of sperm) and pair (mono-male) spawns, it is slightly lower in pair spawns, due to low level sperm limitation that arises because pair-spawning males release near the minimum number of sperm necessary for maximum fertilization. I examined whether variation in egg size and content in T. bifasciatum and other free-spawning fishes is related to variation in spawning mode, to assess whether compensatory production of large, low-density eggs might be contributing to high fertilization success in pair spawns. I found no difference between the volume or density of eggs of (1) pair- and group-spawning females of T. bifasciatum, or (2) pair-and group-spawning congeneric species of labrids, scarids, and serranids, or (3) labrids and scarids with vigorous, rapid spawning movements (which could turbulently diffuse gamete clouds) and those with slow movements. Further, egg density does not decline with increasing egg volume among those fishes. Assuming that egg size can affect fertilization success, then sperm limitation seems unlikely to represent a significant problem for pair-spawning T. bifasciatum, probably because mates place their vents close together during gamete release. The situation regarding sperm limitation in other fishes, and effects of environmentally generated water turbulence on it, are less clear. Interspecific variation in the size and content of these fishes' eggs may relate to provisioning of offspring for different larval life-histories.

Egg size in relation to body size in rotifers: an indication of reproductive strategy?

Egg size in relation to body size in rotifers: an indication of reproductive strategy?

CLUTCH SIZE AND EGG SIZE IN FREE-LIVING AND PARASITIC COPEPODS: A COMPARATIVE ANALYSIS.

The evolution of reproductive strategies and the trade-off between number and size of eggs were investigated in a comparative analysis of free-living and parasitic copepods. Data from 1038 copepod species were used to obtain family averages for 105 families; the phylogenetic relationships among these families include 94 branching events or 94 independent contrasts on which the analysis was based. Transition from a free-living existence to parasitism on invertebrates resulted in small increases in body size. Transition from parasitism on invertebrates to parasitism on fish was associated with greater increases in body size. After controlling for body size, a switch to fish hosts resulted in an increase in the number of eggs produced and a reduction in egg size. Among all contrasts, there was a negative relationship between changes in relative clutch size and changes in relative egg size, suggesting the existence of a trade-off between egg size and numbers. However, opposite changes in these measures of clutch size and egg size were not quite more frequent than expected by chance, therefore indicating that investments into egg numbers are not necessarily made at the expense of egg size, and vice versa. Latitude affected copepod body size, clutch size, and egg size, whereas the effects of freshwater colonization or size of the fish host were not significant. Comparative analyses at either the genus or species levels within given taxa of copepods parasitic on fish provided limited support for a trade-off between clutch size and egg size, but were hampered by the small number of independent phylogenetic contrasts available. From the family-level comparative analysis, it appears that the evolutionary transition from a free life to parasitism on invertebrates, and the transition from parasitism on invertebrates to parasitism on fish, have led to changes in life-history traits in response to the different selective pressures associated with the different modes of life.