Mean Egg Volume Research Articles

Egg size variability in trematodes: test of the bet-hedging hypothesis.

The hypothesis according to which egg size variability in hermaphroditic parasites results from bet-hedging was investigated in a comparative analysis using trematodes as a model. We hypothesized that the species reproducing mainly by self-fertilization should produce smaller eggs than those species that regularly practice cross-fertilization. Indeed, because self-fertilization is usually associated with inbreeding depression, selection should favor individuals spreading the risk of genetically disturbed development across more but smaller eggs, instead of producing fewer eggs, each possessing a large resource supply, of which many may fail to develop because of genetic deficiencies. On the basis of earlier theoretical and empirical studies, we assumed that the ratio length of testis-length of ovary positively correlates with the mating group size and, hence, with opportunities for cross-fertilization. In accordance with the bet-hedging hypothesis, we found, across trematode species, a positive relationship between this ratio and the mean egg volume produced by adults. This result was, however, observed only for the trematodes infecting birds and not for the species infecting fishes and mammals. In addition, once the influence of trematode phylogeny was taken into account, there was no significant trend, suggesting that phylogenetic legacies played a large role in generating the previous signal. Experimental tests of the bet-hedging hypothesis will be necessary to clarify the matter.

Reproductive biology of the common shrimp Crangon crangon (Decapoda: Crangonidae) in the central Irish Sea

Aspects of the reproductive biology of the common shrimp Crangon crangon (L.) were studied in Port Erin Bay, Isle of Man, Irish Sea. Size at sexual maturity was determined from the proportions of ovigerous females and of females with maturing ovaries. The size at which 50% of females are mature is estimated (±95% confidence intervals) as 12.5±0.48 mm carapace length. Based on the proportions of ovigerous females and of mature females, the main breeding season was from January to June. Mean ovarian dry weights indicated two broods (winter and summer), with females bearing winter broods (WB) having higher gonad indices than those with summer broods (SB). WB females with non-eyed eggs and with eyed eggs differed in the regression of ovarian dry weight on carapace length, indicating preparation for laying a second brood. In both broods the moult stages of berried females were related to egg stage. Moulting will occur following the release of the brood. During embryonic development, mean egg length and egg volume were larger in all stages, and the mean dry weight of individual eggs of all stages heavier, in WB than in SB; there was no difference in egg number, however. Consequently, reproductive investment, the proportion of female weight devoted to egg production, was 67% higher in WB (0.20±0.04) than in SB (0.12±0.03). There is a significant effect of egg volume on brood weight, but not on egg number. In both broods, egg number was a negatively allometric function of female body size in non-eyed eggs and an isometric function of female body size in eyed eggs. Brood mortality during incubation was higher in SB (17%) than WB (10%). Differences in the reproductive variables and investment between the two broods of C. crangon are discussed in the light of reproductive strategies and life history.

The Effect of Trends in Ambient Temperature on Egg Volume in the Tree SparrowPasser montanus

The effect of ambient temperature before and during laying on egg volume in birds has been studied by many authors. The objective of this paper is to show that trends in daily temperatures changes can also influence egg volume. The study was carried out near Warsaw, Poland in 1994 and 1995. We ascertained the laying sequence, size and volume of 1070 eggs in 211 clutches of the Tree Sparrow. The effect of the trend in temperature on the mean egg volume in a clutch explained 0.4% of its variation (0.03% to 4.2%, depending on the brood-period), and the effect of actual temperature explained 0.9% (0.5% to 1.6% depending on the brood-period). The joint effect of temperature and its trend explained 3.1% (1.7% to 8.9% depending on the brood-period) of variation in the mean egg volume in a clutch. The authors discuss possible mechanisms of the effect of temperature and temperature trend on egg volume.

Fecundity and size at maturity of Palaemon longirostris (Decapoda, Palaemonidae) in the Mira River estuary (SW Portugal)

Summary The reproductive traits of female Palaemon longirostris were examined in this study. The mean fecundity was 957±282 SD. The mean egg volume increased 17% from the early to the late development stage. By using the allometric model, no simple volumetric relationship was found between brood size and carapace length at any egg stage. For both early and late egg stages, a negative allometric level was obtained. During embryogenesis, egg loss was estimated at 5%, with no apparent effect on female size. Size at maturity was studied using morphometric analyses, assuming that the attainment of sexual maturity involves morphological changes of the pleura in order to form a brood chamber. A Mature 1 analysis evidenced overlapping “growth-phase” lines, suggesting that adult females may moult to a resting condition after breeding. The obtained regression lines indicate the presence of different morphotypes, but do not correspond to young and adult prawns. To determine size at maturity, a Mature 2 analysis was run for the young-like morphotype in an attempt to locate an intersection point delimiting the young and the adult growth phases. The estimated size closely matched the size of the smallest ovigerous prawn.

Seasonal change in egg-volume variation within a clutch in the Bull-headed Shrike, Lanius bucephalus

I studied the seasonal change in egg volume in Bull-headed Shrikes, Lanius bucephalus, to explore the importance of egg-volume variation within a clutch. The mean egg volume did not change over a season; however, the coefficient of variation in egg volume in six-egg clutches significantly increased in 1994 and 1995 but did not change in 1996. Peaks in arthropod biomass occurred early in the breeding seasons in 1994 and 1995, but late in the season in 1996. Higher food availability was related to a reduction in variation in egg volume within a clutch. A significant difference in egg volume was found within six-egg clutches, and the first egg was the smallest. Nestlings that hatched from small eggs early in the hatching order suffered lower mortality rates than nestlings that hatched from large eggs laid late in the hatching order. The duration of time between settlement of a female in a male territory and clutch initiation decreased with date. Intraclutch variation in egg volume may be caused by a trade-off between the time to develop an egg and the volume of the first egg within a clutch. Because eggs that hatch first do not need to be large for the hatchling to survive, the Bull-headed Shrikes may advance the clutch-initiation date at the cost of reducing the volume of the first egg.

Embriologia do siri Arenaeus cribrarius (Lamarck) (Crustacea, Brachyura, Portunidae)

Ovigerous females of Arenaeus cribrarius were collected at Ubatuba, Sao Paulo, and maintaining in aquaria under controlled temperature (25±1oC), salinity (35±1‰) and photoperiod (12:12). A small sample of eggs was collected for each 24h, for morphological description, chromatic changes and biometric analysis throughout the embryonic development. Eight egg stages were photographed and had their small and large diameters measured under a microscope provided with camera lucida. The egg's shape was low elliptical during all the embryogenesis and showed size increase (24.4%) and volume (91.1 %), when the last stage were compared with the first one. According to mean egg diameter and volume, the eggs should be pooled in three different groups (1-3; 4-6; 7-8) corresponding to initial, intermediate and final stages. The attained results were compared with the literature which emphasizing the species of Portunidae's family.

LIFE HISTORY AND REPRODUCTION OF SYNCHELIDIUM LENOROSTRALUM (AMPHIPODA, OEDICEROTIDAE) IN A TEMPERATE SANDY SHORE, SOUTHERN KOREA

Abstract The life history and population structure of the amphipod Synchelidium lenorostralum were studied monthly for one year in the sandy shore at Dolsando, southern Korea. The life-history pattern was annual and iteroparous, with two dominant recruitments in fall (October to December) and spring (March to May). The sex ratio was female-biased, especially during breeding periods. The maximum size of females was 10.8 mm and 1.4 times larger than that of males. The mean body length of adults and brood size were greater in the spring breeding period than in the fall. There was a positive relationship between the brood size and body length of ovigerous females. The mean egg volume of stage I was more than 0.04 mm3 in December and March, but in other months it was less than 0.03 mm3. Egg volume was positively related to body length of ovigerous females and increased significantly at the phase between stage I and II. However, no significant relationship between egg volume and brood size was found. At any giv...

Influence de l’accessibilité des ressources anthropiques sur les paramètres reproducteurs de deux colonies de Goélands leucophées Larus michahellis

This study aims at determining breeding chronology and reproductive parameters (clutch-size, egg volume, hatching success and chick survival rates) in two Yellow-legged Gull Larus michahellis colonies showing a marked difference in anthropogenic food resources accessibility. For instance, one of the colonies studied, established on Ratonneau island, is very close to the large refuse dumps of Marseille city while the other, established on Bagaud island, is 30 km distant from the nearest refuse dump. The mean laying date of the first egg showed a significant difference between the two colonies. Although mean clutch-size does not significantly differ between the two colonies, complete 3-egg clutches were more frequent at Ratonneau. Mean egg volume was significantly different between the two colonies with a markedly smaller volume forthe C-egg in the colony that was farther from human food sources. Moreover, hatching success and chick survival rates were significantly lower on Bagaud than on Ratonneau. All these differences may be linked to marked differences in resource accessibility, and in this way, anthropogenic food resources accessibility may be partly responsible for the clear difference in the demographic patterns of the two colonies for the last twenty years. These results could be used to calibrate more accurately certain demographic modelling in order to improve the population management of this superabundant bird species.

LIFE HISTORY OF MAGPIE POPULATIONS SYMPATRIC OR ALLOPATRIC WITH THE BROOD PARASITIC GREAT SPOTTED CUCKOO

Parasites can have dramatic effects on life-history decisions of hosts such as timing of reproduction, clutch size, and investment in individual offspring, depending on the timing of parasite effects on host fitness. Moreover, parasites may influence the optimum values of important life-history traits such as clutch size and brood size by having different fitness effects for large and for small values. Here, by analyzing data from a Magpie (Pica pica) population sympatric with the Great Spotted Cuckoo (Clamator glandarius), we demonstrated that Magpies laying a large clutch suffer less from parasitism than do those laying a small clutch, because the first have a higher probability of successfully raising some of their own offspring. Therefore, we predicted that (1) Magpie hosts in sympatry with Great Spotted Cuckoos should produce more eggs, and (2) eggs should be smaller than those in areas of allopatry. We also predicted that (3) this change in life history should be directly related to selection pressures by cuckoos, as evidenced from current levels of parasitism and Magpie rejection of cuckoo model eggs. We tested these predictions by comparing the life-history parameters of 15 European host populations that are either sympatric or allopatric with the parasite. In accordance with predictions, we found an increase in clutch size and a decrease in egg volume of Magpies in populations sympatric with the Great Spotted Cuckoo, as compared to allopatric populations, even when statistically controlling for laying date and latitude. By using parasitism rate and experimentally testing the ability of Magpies to recognize and reject mimetic and nonmimetic model eggs, we were able to test prediction 3 in the 15 Magpie populations. Clutch size was positively related to the rejection rate of nonmimetic model eggs, whereas mean egg volume was significantly negatively related to the rejection rate of mimetic model eggs. These findings provide evidence of a strong influence of the parasitic Great Spotted Cuckoo on the life history of its Magpie host.

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.

Male calling, mating and oviposition in Isoperla curtata (Plecoptera: Perlodidae)

The reproductive biology (drumming call, mating behaviour, fecundity and egg structure) of Isoperla curtata, an endemic species from the Southern Iberian Peninsula, is described. The male's mating call has a diphasic pattern, with a mean of 17.3 beats per call (range = 8-27; SD = 4.7) and a duration of 792.9 ms per call (range = 228-1312; SD = 307.9). This call differs from that of other species of Isoperla in having two distinct phases with different millisecond intervals, and is species-specific. Mating lasts between 131 and 3864 seconds (mean = 2180.9 s and SD = 1027.8). Since males and females mate more than once (mean number of matings per female was 1.85 and per male 2.25), the species is polyandric and polygynic. The position adopted by the male during mating is different from that described for other stonefly species. Other mating behaviours are interpreted as displacement manoeuvers, tactile stimulation and possibly sexual selection by cryptic female choice. There was a statistically significant correlation between size and the number of matings in females (r = 0.849; p = 0.016), but not in males. Each female laid between one to four egg masses composed of an average of 88.7 eggs. Maximum fecundity was 319 eggs. The mean egg volume was 80.5 × 105 µm3 which is very similar to that of other Isoperla species. An outstanding morphological characteristic of the egg is the lobed outline of the chorion cells.

Short‐term effects of culling on the ecology and population dynamics of the yellow‐legged gull

Summary1. Culls are being performed in many yellow‐legged gullLarus cachinnanscolonies in the Mediterranean region, but little is known of their effects on this species. Between 1992 and 1996, 25 000 breeding yellow‐legged gulls were culled in the colony of the Medes Islands, north‐western Mediterranean, because of the possible role of gulls in the transmission of pathogens and as predators on other bird species. In the present study the effect of the culls on several ecological parameters and on the population dynamics of the colony were analysed.2. Some breeding parameters (nest density, clutch and egg sizes, chick growth and breeding success, intraspecific predation, size and body condition of adults), diet (importance of the different prey categories and width of the trophic niche) and population dynamics of the colony were analysed during the years of cull. The annual culls did not include the entire colony, so culled and unculled areas were distinguished.3. Nests density decreased significantly both in the culled and the unculled areas. No significant difference in clutch size was detected between culled and unculled areas in any year, but clutch size decreased significantly through time within the culled areas. In three‐egg clutches the mean egg volume was significantly larger in unculled than in culled plots, whereas no significant year effect was found. No differences were detected in the mass or in the body condition of chicks throughout the study, whereas both fledging success and breeding success increased significantly over the period of the study. Intraspecific predation had decreased significantly by 40% two years after the beginning of the study. Size and body condition of adults varied between years but no trend was observed.4. Despite the large decrease in breeding gull numbers and an expected reduction in intraspecific food competition, no changes in diet were detected during the study. The dietary niche width was very similar between years, and gulls continued to exploit the same foraging resources.5. Annual censuses showed that from 1960 to 1992, colony size increased at a rate of 5% per year. During the culling period, between 21% and 29% of the breeding adults were killed, and colony size decreased progressively at an estimated rate of 19% per year. The estimated annual adult survival according to ring recoveries during the culling period was 74%. A demographic model was developed to assess the observed changes in numbers of yellow‐legged gulls. This suggested that gulls born in the Medes Islands were emigrating during the years of culling, with a particularly high estimated emigration rate of 25% per year since 1994.6. The planning of culling programmes by wildlife agencies has not always taken into account the multiple factors responsible for the population dynamics of colonies and the effects of culls. Culling at the Medes Islands probably failed to reduce the breeding numbers of yellow‐legged gulls at the metapopulation level, due to the emigration of birds to neighbouring colonies that had recently increased in numbers. Thus, the potential problems linked to large numbers of gulls in a colony may simply have been transferred to other sites.

Reproduction of Cochlearius cochlearius (boat-billed heron) and Butorides virescens (green-backed heron) in La Manzanilla, Jalisco, Mexico

Reproduction of the herons Cochlearius cochlearius (boat-billed heron) and Butorides virescens (green-backed heron) was recorded for La Manzanilla estuary, Jalisco, Mexico, from April to August 1997. Two breeding sites were studied: site A presented 11 nests of C. cochlearius (54.5% were reused) and 16 nests of B. virescens (6.2% were reused); site B exhibited 8 nests of C. cochlearius and 22 nests of B. virescens (13.6% were reused). Mean height of nests of C. cochlearius was higher (308.42 ± 23.81 cm) than that of B. virescens (115.13 ± 4.73 cm). Clutch size of B. virescens (2.71 ± 0.08) was significantly larger than that of C. cochlearius (1.88 ± 0.12). Mean egg volume of B. virescens at site A (18.02 ± 0.19 cm3) was larger than the volume at site B (16.95 ± 0.30 cm3). The eggs of C. cochlearius (35.01 ± 1.04 cm3) were almost twice the size of those of B. virescens. The first nesting species was C. cochlearius, which exhibited a breeding period from April to August and an incubation period of 20 days. The breeding period of B. virescens was shorter and more homogeneous, from May to July, with a mean incubation period of 19.4 days. The breeding success estimated for both species fluctuated between 50 and 87%; the highest values were associated with viability and the lowest with flying success.

Spawning periodicity, fecundity and egg size in laboratory-held stocks of a substrate-spawning tilapiine, Tilapia zillii (Gervais)

Inter-spawning-interval (ISI) in serially-spawning Tilapia zillii averaged 26 days in environmentally-controlled aquaria, and exhibited a complex and variable relationship to fish size. Mean number of days elapsed spawn −1 (based upon both spawning and non-spawning fish amongst the 101 females studied) was considered the best estimate of spawning periodicity and averaged 61 days. The shortest spawning cycle was just 7 days. Fecundity increased with increasing maternal size and ranged from 461 to 11,640 eggs clutch −1 (mean=3606±280). Egg size varied only within a relatively narrow window. Variations in egg size did not, generally, relate to maternal size; mean egg diameter was 1.5 mm. Regression analysis revealed strong and significant relationships between fish size (total length and body weight) and fecundity, relative fecundity and total egg volume. Relationships between fish size and various indices of egg size (mean egg diameter, mean egg dry weight and mean egg volume) were far weaker.

Endosulfan-enhanced crest induction in Daphnia longicephala: evidence for cholinergic innervation of kairomone receptors

Daphnia longicephala were reared from early embryogenesis in the presence or absence of crest-inducing kairomones released by Anisops grants (Notonectidae) and from birth in one of five concentrations of the organochlorine pesticide, endosulfan (0,0.1,1.0,10 or 100 ug I*1). The morph- ology of the daphnids was measured 3 days after birth and on production of the first brood of eggs. The reproductive parameters, first brood size, age at first reproduction, mean egg volume and total egg volume, were also measured. Endosulfan significantly induced crest development in 3-day-old daphnids at 0.1,1.0 and 10 ug I1 in the presence and absence of Anisops kairomone, although crest size in the absence of kairomone was only marginally greater than controls. A concentration of 10 ug 1~' endosulfan significantly enhanced crest growth of kairomone-exp osed daphnids at maturity. The Anisops kairomone alone induced a large crest in D.longicephala, reduced first brood size, mean egg volume and total egg volume, and increased age at maturity. The coefficient of variation of mean egg volume was significantly reduced by Anisops kairomone. It is hypothesized that endosulfan enhances crest development by inhibition of y-aminobutyric acid (GABA), an inhibitory neurotransmitter at cholinergic nerve junctions.

The egg size variation of the Treecreeper Certhia familiaris in south-western Sweden

Egg measurements were in 1994—1996 collected on a Treecreeper population nesting in artificial nest sites erected in deciduous forests in south-western Sweden. The mean egg volume was 1.21±0.091(SD)cm3 (n=533) and the mean weight was 1.26±0.100g (n=133). The mean volume decreased as the clutch size increased from 1.26±0.091cm3 (4-egg clutch) to 1.16±0.079cm3 (7-egg clutch). Within clutches, the volume showed on average an 8% increase from first to last laid egg, and the size and laying order coincided for about 50% of the eggs on each separate day in the laying sequence. The egg sizes of neighbouring clutches with laying start on the same day tended to vary in parallel from first to last egg, indicating a constraining influence of environmental origin on egg formation. The size of an egg was positively correlated with the ambient temperature of the first two or three days before laying. This relation was less clear during periods of falling temperature, probably because the temperature influence was counteracted by the tendency of the female to successively increase egg investments in the laying sequence. The consequences and adaptive value of this trait are discussed.

Ovarian weight as an index of fecundity, maturity, and spawning periodicity

Ovarian weight and related indices such as gonadosomatic index were used to index fecundity, egg maturity, and spawning season in gizzard shad Dorosoma cepedianum. Individually, in simple regression, fecundity and mean egg volume each accounted for only about 50% of the variability in ovarian weight. Together, in multiple regression, fecundity and mean egg volume accounted for 86% of the variation in ovarian weight. The percentage of the variability in ovarian weight explained by each independent variable, while holding constant the value of the other independent variable (partial coefficient of determination), was 72% for fecundity and 78% for mean egg volume. Thus, ovarian weight of gizzard shad confounded information about fecundity and egg maturity and separately could not index them adequately. Attempts to remove the effect of fecundity, so that ovarian weight could serve as an index of maturity, and to remove the effect of egg size so that ovarian weight could serve as an index of fecundity, were unsuccessful. Nevertheless, seasonal oscillations of ovarian weight served as a crude indicator of population Spawning Season.

Trade‐offs in nest site selection in coastal populations of Lapwings Vanellus vanellus

In coastal populations of Lapwings Vanellus vanellus in southwestern Sweden, arable fields predominated as foraging habitat before laying. Females caught more large prey items on arable fields and shores than on pastures. Close to egg laying, females foraged mainly near their future nest sites. Arable land and pastures were used to a similar extent for nesting. We found no difference in nest predation between habitats. Egg volume varied among females and was correlated with wing‐length, body mass and condition. Mean egg volume also was positively correlated with feeding time on arable land before laying. Pairs nesting on arable fields therefore generally produced larger eggs than those on pastures. The distances between nests and chick foraging areas, however, were significantly longer for birds nesting on arable land than for those on pastures. Moreover, in 2 of 3 years, the proportion of hatched chicks that survived until fledging was negatively correlated with this distance. There was no difference in chick survival between broods hatched on arable fields and pastures. We suggest that nest site selection and offspring production involve a trade‐off between the benefits of nesting close to rich feeding grounds for adults and the costs of moving long distances between nest sites and chick‐rearing areas.

Egg size and clutch size in the reproductive investment of American Kestrels

We studied causes and consequences of egg‐size variation among clutches of American kestrels (Falco sparverius). Egg. from 275 clutches were measured 1990 to 1992. To test the hypothesis that the size of eggs was contrained by food availability in the pre‐laying period, we censused small mammal populations in the three years and performed a food supplementation experiment in 1990 and 1991. Kestrels did not advance the date they laid their first egg but did lay significantly larger eggs in response to extra food. The size of eggs was correlated with small mammal abundance on the territoty, and females in good body condition tended to lay large eggs. Body size did not affect egg size, and there were no relationship between agg size and laying date except in 1900, the poorest food year. Clutches with a large mean egg volume had better hatching success than clutches containing small eggs. We argue that there is a phonetypic component to egg size in kestrels, and that kestrels use egg size to fine‐tune reproductive investiment to available resources.

The Costs of Being Late: Consequences of Delaying Great Tit Parus major First Clutches

The hypothesis that late breeding entails reproductive costs to birds was tested by comparing breeding traits of control and delayed great tit Parus major clutches. In our study area, great tits and house sparrows Passer domesticus compete for nesting boxes. Since early March, nesting boxes were checked twice a week and initiated sparrow nests removed, to allow great tits to breed. 'Delayed' great tit pairs were those which, having a territory, had the nesting where they eventually bred occupied by sparrows, and therefore did not start laying until these abandoned the nesting box. Delayed pairs were assumed to be a random sample of the population. Age composition (1-year vs. older birds) and tarsus length did not differ between control and delayed birds. In 1990-92, a total of 40 pairs had their breeding delayed, while 56 acted as controls. The mean laying date of delayed pairs was at least 10 days later than controls. Delayed first clutches were smaller and took longer to hatch than controls, but mean egg volume did not differ between them. Fledging success was lower in delayed nests. Young from delayed broods were lighter at day 15 and reached a lower asymptotic weight. The mean growth rate of the nestlings was negatively related to clutch size, and differed between years, but did not differ between control and delayed broods. Control pairs were more likely to produce a second clutch, if the first one succeeded, or a replacement clutch, if the first one failed, than delayed pairs. The total production of fledglings per pair per season was higher in control pairs. Control pairs were more likely to recruit at least one young into the local breeding population than delayed pairs. However, it is not known whether late fledglings dispersed further. Our results show that delayed pairs produced fewer fledglings, of lower quality, and were less likely to recruit them into the local breeding population than controls. Therefore, the causal relationship between poor breeding performance and late breeding is supported.