Synchronous Hatching Research Articles

Structure and Functioning of the “Egg Bank” of a Fairy Shrimp in a Temporary Pool: Chirocephalus ruffoi from Pollino National Park (Southern Italy) as a Case Study

AbstractTo investigate their distribution and total numbers, resting eggs of the anostracan Chirocephalus ruffoi were collected from the bed of a temporary pool in southern Italy. Samples were taken at 0.5 m intervals along six transects oriented at 30° from each other, by means of a cylindrical core sampler. The horizontal distribution of intact resting eggs was extremely patchy, with cyst number per core ranging from 191 to 1,400 (CV = 32.7%), corresponding to a mean of between 0.8 and 4.3 cysts cm−3. Differences observed were related to core position and transect orientation, total cyst numbers being markedly higher in the leeward area of the pool compared to the windward area. Marked variation was also evident in vertical distribution, a significant, though weak correlation was recorded between egg density and sediment depth. Cyst‐bank size (± 95% confidence limits) of the pool bed, estimated from the mean cyst number cm−3 obtained for the 6 transects, ranged between 1.0 × 108 and 1.3 × 108 cysts.Hatching in the laboratory was very erratic. Despite significant differences in hatching, the observed variation was unrelated to most of the variables considered (position within sections, cores and transects, pre‐incubation treatment) and was explained only by initial sediment conditions (moist/dry). In none of the experimental conditions tested was synchronous hatching obtained.Possible causal factors (mixing of the bottom sediments by cattle, egg age, storage conditions, differential exposure to environmental cues as well as variability in hatching response even at clutch level) are discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Seasonal adaptation of ex‐ephippio and parthenogenetic offspring of Daphnia magna: differences in life history and physiology

Summary Physiology and life history of ex‐ephippial and parthenogenetic offspring of Daphnia magna Straus were compared to test the hypothesis that females hatching from resting eggs are well adapted to the predictable high‐food conditions of the spring algal bloom. Although ex‐ephippial neonates were smaller than parthenogenetic neonates, they showed higher juvenile growth rates that compensated for the size difference by the time of maturation. At high food concentration, ex‐ephippial females were even larger at maturation than parthenogenetic females, produced more eggs, and reached a higher rate of population increase. The high activity of the ex‐ephippial females was accompanied by higher metabolic rates, which in combination with the low initial mass resulted in reduced survival times under starvation. Thus, the two phenotypic types of offspring produced by Daphnia are adapted to differing conditions. Ex‐ephippial females are superior to parthenogenetic offspring under high food conditions, but inferior when food is limiting. This pattern selects for synchronous hatching of resting eggs in spring when the spring algal bloom is to be expected.

How great tits maintain synchronization of their hatch date with food supply in response to long‐term variability in temperature

Summary Breeding birds increase their fitness by synchronizing their production of chicks with a peak of food abundance. Synchronization is primarily achieved by varying first egg date, but yearly temperature variations may delay or accelerate the food peak after the first egg has been laid. We tested the extent to which great tits (Parus major L.) can strategically change their synchronization of hatch date with the food peak after the first egg has been laid by changing clutch size, laying interval and the amount of incubation. We also tested whether these possible synchronization change mechanisms resulted in changes in breeding success, because if the food peak is late relative to first egg date, we would predict more of the population to have larger clutches and/or a hatch date synchronous with the food peak date. Great tits modified synchronization strategically by varying clutch size and the onset of incubation after clutch completion. When first egg date was early but then followed by cold weather so that the food peak was late, clutch sizes were larger, and when first egg date was late and temperatures were low, mean incubation periods were shorter if the food peak was early. Over the 39‐year period of the study, the period between the first egg date and food peak increased significantly by 1·7 days more than the period between the food peak and hatch date. Great tits have maintained synchronization by significantly increasing their incubation period. Overall, the proportion of nests that had synchronous hatch dates depended on the yearly temperature pattern: the decline in variance between date of clutch completion and hatch was significantly greater in years where prelaying temperatures were higher (i.e. early first egg dates) and has therefore increased in recent years because of climate change. In warm early seasons (and more often in recent years) more of the great tits that laid relatively late had sufficient time to complete their clutches before having to start incubation in order to hatch in time for the food peak. The increased proportion of synchronized nests in recent years probably resulted in increased chick output: a greater proportion of recent nests successfully fledged all of the chicks that hatched and the number of young fledged per successful nest also increased in recent years. These changes may have arisen because the proportion of nests with disadvantageous asynchronous hatching and/or smaller clutches has decreased. As the proportion of great tits that start nesting too late to synchronize has declined so selection for early laying has also declined in recent years.

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.

Embryos and eggs for the Cretaceous theropod dinosaur Troodon formosus

ABSTRACT Elongate and asymmetric eggs of the oospecies Prismatoolithus levis occur regularly in the Upper Cretaceous Two Medicine Formation of western Montana. These eggs had previously been assigned to the ornithischian Orodromeus makelai, for both juvenile and adult remains are typically associated with these eggs. Reexamination of the embryos shows them to exhibit at least 24 apomorphies of the clades Dinosauria, Theropoda and Paraves. The embryos also display a pneumatic quadrate, closely placed basal tubera, a high tooth count, a metatarsal II much narrower than IV and a strongly constricted metatarsal III, all possible synapomorphies of the Troodontidae. Presence of large basal tubera and a broadly rounded anterior border of the maxillary fenestra permit assignment to Troodon formosus. Most but not all bones appear ossified, suggesting a developmental level comparable to stages 35–38 of avian embryos and a time approaching hatching. Embryos show a consistent level of development from one egg to another indicating synchronous hatching of the clutch. Embryonic Troodon exhibit long distal segments and radically different hindlimb proportions in comparison to adults. Orodromeus and other small vertebrate remains associated with Troodon egg horizons may represent prey of the adults during egg-laying and brooding. Troodon eggs show several aspects either shared or convergent with some birds, and further demonstrate the close relationship of Troodontidae and Aves. These features include: asymmetric egg form, non-branching angusticanaliculate pores, distinct structural differentiation of the mammillary and overlying prismatic layer, barrel-shaped mammillary cones with a blocky calcite cleavage, and prismatic structure visible throughout the second structural layer.

Effect of food shortage on the physiology and competitive abilities of sand martin (Riparia riparia) nestlings.

We examined developmental and behavioural plasticity of sand martin (Riparia riparia) nestlings hand-reared under laboratory conditions. We created six broods of six 4-day-old nestlings and randomly assigned them to one of the two following feeding regimens, each lasting for 3 days: (1) all nestmates fed a similar, limited amount of food (FR nestlings). This simulated synchronous hatching under conditions of food restriction. (2) Half the brood were food-restricted (FR/AL nestlings), and half were fed ad libitum (AL nestlings), as in asynchronously hatched broods with differential food allocation. Under both regimens, food restriction resulted in a reduction in body mass, intestinal mass, pectoral muscle mass, fat reserves, body temperature and resting metabolic rate (RMR). However, it simultaneously triggered a significant increase in intestinal uptake rates of L-proline and locomotor activity, quantified as frequency of crawling into the artificial nest tunnel by individual nestlings. Locomotor activity and intestinal uptake rates of L-proline by FR nestlings were higher than those of FR/AL young, while body temperature and RMR of FR nestlings were lower. We conclude that food-restricted nestlings responded actively to food shortages by upregulating their gut function, reducing the energy costs of maintenance and increasing locomotor activity. These behavioural and physiological responses were strongest in broods of similar-sized FR nestlings, which can be interpreted as an escalation of sibling competition. Thus, developmental and behavioural plasticity may be an important factor in the evolution of sibling rivalry.

Hatch or wait? A dilemma in reptilian incubation

Animals often form groups to reduce the risk of predation through the per capita dilution of their individual predation risk. The advantages of grouping also influence the timing of reproduction in many species. In particular, synchrony in the timing of births may have evolved as a predator‐avoidance strategy as it dilutes the risk of predation upon vulnerable newborn and naive young. Eggs of an Australian freshwater turtle, Emydura macquarii, can hatch synchronously despite developmental asynchrony among eggs of a clutch and hatchlings have a reduced predation risk by emerging from the nest as a group. Developmental asynchrony within clutches was induced to reflect natural nests by dividing clutches and incubating them at either 25°C or 30°C. Some eggs were then reunited with their clutch‐mates and hatching occurred synchronously in some of these groups. In groups where synchronous hatching did not occur, less advanced eggs still hatched earlier than the normal incubation period. Synchrony occurred because the less advanced eggs hatched up to five days earlier than the control embryos. We conclude that the less advanced embryos within a clutch either accelerate their development or hatch prematurely to ensure synchrony of hatching and hatchling group formation may facilitate emergence from the nest and dilute predation risk.

The Role of Prolactin in the Regulation of Clutch Size and Onset of Incubation Behavior in the American Kestrel

In most bird species, the timing of incubation onset may influence the degree of hatching asynchrony, which, together with variation in clutch size, affects reproductive success. In some domesticated species that usually show no hatching asynchrony, plasma prolactin concentrations in females rise with the onset of incubation and the end of laying, and this rise enhances incubation behavior and may terminate laying. To investigate whether a rise in prolactin during laying is involved in the regulation of clutch size and incubation onset in a species with hatching asynchrony, we measured plasma concentrations of immunoreactive prolactin (ir-prolactin) in laying American kestrels, Falco sparverius, and quantified clutch size and incubation behavior. In a separate study, we administered one of three concentrations of ovine prolactin (o-prolactin) via osmotic pumps implanted in females when egg 2 of a clutch was laid. ir-Prolactin concentrations during laying were higher in small than in large clutches and increased in parallel with the development of incubation behavior. o-Prolactin treatment enhanced incubation behavior, but did not affect clutch size, possibly because the manipulation was performed after clutch size had already been determined. Consistent with studies on domesticated species that show synchronous hatching, our results indicate that rising prolactin during laying enhances the expression of incubation behavior in a species that shows hatching asynchrony. Further studies are necessary to determine whether the relationship between prolactin and clutch size in the American kestrel is one of causation or of mere association.

Effects of crowding on populations of Aedes albifasciatus larvae under laboratory conditions

Abstract Aedes (Ochlerotatus) albifasciatus (Macquart 1838) (Diptera: Culicidae) is a neotropical flood water mosquito, incriminated as the main vector of the western equine encephalitis virus, and which affects beef and milk production in central Argentina. The short time required to hatch and develop from egg to adult, usually in temporary pools, suggests a strategy which allows for exploitation of transient pools, thus evading predation and interspecific competition. Under these conditions intra specific competition could represent a major density‐dependent source of larval mortality, but the relative importance of density‐dependent regulation of mosquito populations has generated controversy. Therefore we examined the effects of larval density on basic population characteristics of Ae. albifasciatus in the laboratory. Larvae were obtained by synchronous hatching of eggs laid by field‐trapped females. Emerging larvae (L1) were used to build cohorts of different initial densities, kept in plastic trays with 400 ml of distilled water, and food supplied daily during the first 10 days (0.1 g per larvae day−1). Age‐specific development time and specific and relative mortality were estimated, and their relation to initial larval density was assessed through linear and non‐linear regressions and correlation analysis. First hatching was registered 3 h after flooding the eggs. Higher levels of pre‐adult mortality were detected in groups with higher densities. Specific mortality and average time to enter a stage of L1 to L3 could directly be related to initial larval density, but no significant relations were found for L4 and pupae. Results suggest that crowding could be a factor capable of regulating the density of natural populations of Ae. albifasciatus.

Hatching asynchrony in the Eurasian kestrel Falco tinnunculus: an experimental test of the brood reduction hypothesis

Summary 1. We tested the brood reduction hypothesis by manipulating hatching spans of Eurasian kestrel Falco tinnunculus (Linnaeus) broods during two low vole years (1996–97) in western Finland. In addition, half the broods in 1997 were food supplemented during the entire nestling period. 2. Nestling mortality was high, occurring in 55% of nests, and the effect of manipulated hatching span on fledging success was more pronounced than either the effects of year or supplementary food. In contrast to the predictions tested, fledging success was higher in synchronous than asynchronous nests, both when food was limiting and when food conditions were substantially improved by food supplements. 3. We found no evidence that brood reduction resulted in higher quality (body mass) of surviving young in low vole years. On average, fledglings were heavier at synchronous than asynchronous nests. This was only the case, however, when food was limiting. 4. Most nestling mortality occurred when the chicks were 2 weeks old, and age of death did not differ between the brood types. Parents at synchronous nests fed their broods at a higher rate than at asynchronous broods, this divergence arising only in the latter part of nestling period. 5. This is the first hatching span experiment where synchronous hatching seemed more profitable than asynchronous during conditions of both food scarcity and food abundance. The higher parental workload at synchronous nests could, however, counterbalance the benefits of synchronous hatching. 6. Hatching in natural broods of Eurasian kestrel is more synchronous in low vole years compared to high vole years. The fact that synchronous broods out‐performed asynchronous broods in both ‘low’ years of the study is consistent with the facultative manipulations. The benefit of asynchrony in high vole years is still unclear.

The Effects of Temperature on Egg Development African Mayfly Povilla adusta (Ephemeroptera: Polymitarcidae)

Egg masses were prepared from a packet of eggs of Povilla adusta Navas and incubated in the laboratory at constant temperatures and hatching success expressed by the logarithmic equation log Y = 0.14T + 1.42 (r2 = 0.028, P > 0.1). Hatching success was highest (84.85%) in eggs kept outside the incubator at laboratory temperature (33.2oC) followed by those incubated at 35oC (76.52%) and 30oC (65.46%) in that order. No hatching occurred in eggs incubated at 15oC, 20oC and 25oC. Minimum and mean incubated periods were the same at temperature at which eggs hatched. Hatching duration was short (1 - 2 days), which indicates synchronous hatching. A comparison of these results with previous findings suggests that Povilla adusta is warm adapted and as such, is confined to the tropical region in Africa where water temperatures are higher. Journal of Aquatic Sciences Volume 14, April 1999, pp. 47-50 KEY WORDS: Mayflies, temperature, egg development, distribution, Africa.

HATCHING ASYNCHRONY IN GREAT TITS: A BET-HEDGING STRATEGY?

Previous studies have shown that asynchronous hatching in birds tends to result in fewer, but higher quality, offspring than does synchronous hatching. However, very few studies have considered the consequences of such a pattern for the recruitment of offspring as subsequent breeders. We recorded nestling survival and fledgling body mass in experimentally synchronous and asynchronous broods of the Great Tit, Parus major. Using six different juvenile survival models, taken from published studies of the species, we calculated the expected number of offspring recruited with each hatching pattern and survival function. The sex of fledglings was included in the analysis. When comparing the estimates of surviving juveniles between synchronous and asynchronous broods, we found no significant difference in the means with any of the six models. However, the distributions of recruitment were different: the expected number of recruits was more variable with synchrony than with asynchrony. This suggests that hatching asynchrony in the Great Tit may serve as a bet-hedging strategy. A larger proportion of asynchronous broods than of the synchronous broods experienced brood reduction, but fledgling body masses for the reduced synchronous broods were lower than those for the reduced asynchronous broods. This suggests that synchronous hatching inhibits adaptive brood reduction in the Great Tit. There was considerable individual variation in the level of brood reduction within the same area and season. We argue that conditions also may be unpredictable at a small scale (parental abilities, territory quality, or parasite load). In consequence, high-quality parents may benefit from synchrony, but low-quality parents benefit from asynchrony, within the same year.

Is There a Sexual Conflict over Hatching Asynchrony in American Robins?

-Many hypotheses have been proposed to explain the occurrence of hatching asynchrony in altricial birds. According to one hypothesis, parents would benefit from hatching asynchrony because the offspring would spend less energy on sibling rivalry. Another hypothesis states that there is a sexual conflict over hatching spread, with one parent trying to minimize investment at the expense of its mate. The latter hypothesis was suggested from a study where males survived better following asynchronous than following synchronous hatching of the brood, with opposite results for females. I tested this hypothesis by manipulating hatching spread in another altricial bird with biparental care, the American Robin (Turdus migratorius), and by observing food provisioning late in the nestling period. The hypothesis was supported because males seemed to contribute less, and females more, to asynchronous broods. Males did not take less care than females of the smaller nestlings within the brood, but when the brood had partially fledged it was mostly the female that fed the young that remained in the nest. Provisioning of the parents combined did not seem to be less with asynchronous than with synchronous hatching, lending no support to the siblingrivalry reduction hypothesis. Received 14 October 1996, accepted 31 March 1997. THE YOUNG OF MOST ALTRICIAL BIRDS do not hatch simultaneously but over a period of one or more days. Many hypotheses have been proposed to explain hatching asynchrony (Magrath 1990, Stoleson and Beissinger 1996). For instance, the cost to the parents may be reduced because less energy is spent on sibling rivalry (the Sibling Rivalry Reduction Hypothesis; Hahn 1981), and any offspring mortality that occurs may take place at an early stage of breeding so that little energy is wasted (Lack 1954). Hatching asynchrony also may help to spread out the peak demand for food of individual offspring (Hussell 1972, Mock and Schwagmeyer 1990). Evidence suggests that parents need to work less with asynchronous than with synchronous hatching in some species (Fujioka 1985, Mock and Ploger 1987) but not in others (Bryant and Tatner 1990). The best way of assessing the costs of breeding would be to follow the subsequent survival and fecundity of the parents. When this was done in a study of Blue Tits (Parus caeruleus), there was no evidence that parents benefitted from hatching asynchrony (Slagsvold et al. 1994, 1995). In the study of Blue Tits, data for the two parents were combined. However, males and females seemed to differ in their re' E-mail: tore.slagsvold@bio.uio.no sponses, males having improved survival with asynchronous hatching, females with synchronous hatching. We therefore suggested that a sexual conflict exists between the sexes over the degree of hatching spread, with one parent trying to minimize investment at the expense of its mate (the Exploitation of Mate Hypothesis; Slagsvold et al. 1995). In Blue Tits, the conflict apparently is won by the female because hatching is rather synchronous despite a large clutch size. The female alone incubates, and by delaying incubation until most eggs have been laid, she can reduce the hatching span. Why would a female benefit from synchronous hatching of her brood? One possibility is that with synchronous hatching, the male may contribute more because otherwise the whole brood would starve to death. Breeding success may be more variable with synchronous than with asynchronous hatching (Amundsen and Slagsvold 1997) such that synchronous broods may be more sensitive to the amount of male parental care. The male may invest less if the brood contains some small, undernourished young with low survival prospects. Relative to the female, then, he may give greater priority to molting and territory defense than to parental care (e.g. Svensson and Nilsson 1997). In addition, males may be less certain of paternity of later-hatched young and hence reduce investment in these offspring. In support of these

Composition of Wood Duck Eggs in Relation to Egg Size, Laying Sequence, and Skipped Days of Laying

-We collected 138 freshly laid Wood Duck (Aix sponsa) eggs from 13 nests to determine the effects of egg size, laying sequence, and skipped laying days on egg composition. All components except yolk ash and eggshell, both wet and dry, increased in direct proportion to fresh-egg mass. Egg size increased during the first half of laying and decreased thereafter. The effects of laying sequence were component-specific. Absolute levels of neutral lipids (comprising 65.6% of dry yolk) were near average until about 75% of the clutch was completed and then declined. Mass of albumen components tended to increase sharply with the first few eggs and then decrease as laying progressed. Fat indices (egg lipid/lean dryegg content) tended to be highest in the first 40% of the clutch. We interpret laying-sequence effects on egg composition as adaptations that enable female Wood Ducks to initiate incubation before clutch completion and still allow for synchronous hatching without compromising the hatching success of first-laid eggs. Hens frequently skipped a laying day between the penultimate and ultimate egg, which tended to increase the mass of the yolk component in last-laid eggs compared with those that were laid the day following the penultimate egg. Received 16 August 1996, accepted 19 February 1997. VARIATION IN AVIAN EGG SIZE is largely attributable to differences among species, and contrasting developmental modes dictate primary differences in constituent proportions (Ricklefs 1977, Carey et al. 1980, Sotherland and Rahn 1987). Egg size also varies considerably within species, typically varying more among than within clutches (Ricklefs 1984, Rohwer 1986, Hepp et al. 1987). Intraspecific variation in egg size is related to proximate factors such as laying date (Runde and Barrett 1981, Bancroft 1984), food supply (Horsfall 1984, Pierotti and Bellrose 1986), and age (Ryder 1975, Crawford 1980, Gratto et al. 1983). Such factors however, exercise their influence within the confines of a large heritable component of egg size (Ojanen et al. 1979, Van Noordwijk et al. 1980). Recent attention has been focused on intraspecific variation in the composition of eggs. As with egg size, egg composition typically varies more among than within clutches (Ricklefs 1984, Bancroft 1985, Alisauskas 1986, Hepp et al. 1987) and has been shown to vary with re' E-mail: kennamer@srel.edu 2 Present address: W1396 Stokdyk Ingelse Road, Oostburg, Wisconsin 53070, USA. 3Present address: National Park Service, Southeast Support Office, 100 Alabama Street Southwest, Atlanta, Georgia 30303, USA. spect to female quality in Wood Ducks (Aix sponsa) as indexed by post-laying body mass (Hepp et al. 1987). Egg composition, however, is not known to vary greatly due to other factors (e.g. clutch size; Rohwer 1986, Arnold et al. 1991; but see Owen and West 1988). Intraclutch variation in egg composition has received less attention (but see Nisbet 1978, Alisauskas and Ankney 1985, Rohwer 1986, Meathrel and Ryder 1987). Nest attentiveness in precocial waterfowl commonly increases through the laying period with persistent incubation beginning after the clutch has been completed (Caldwell and Cornwell 1975, Cooper 1978, Afton 1980, Kennamer et al. 1990). Despite up to four days of total asynchrony among eggs in experimentally manipulated Lesser Snow Goose (Chen caerulescens) clutches, hatching synchrony can still be achieved (Davies and Cooke 1983). Kennamer et al. (1990) documented 100% hatching success in a Wood Duck clutch with up to four days of natural cumulative asynchrony. Apparently, embryos communicate with one another to synchronize their hatching by adjusting developmental rates (Vince 1964, Ockleford and Vince 1985). Reasons for such a complicated incubation strategy in species that hatch synchronously may relate to a combination of egg-viability and nest-predation effects (Arnold et al. 1987, Flint et al. 1994). In any case, egg com-

Surface disinfection of Atlantic halibut and turbot eggs with glutaraldehyde: evaluation of concentrations and contact times

To evaluate the effects of glutaraldehyde treatment at different disinfection temperatures, Atlantic halibut, Hippoglossus hippoglossus (L.), and turbot, Scophthalmus maximus (L.), eggs, incubated at 5 and 12°C, respectively, were disinfected with 400–1200 mg glutaraldehyde l-1 at three different contact times (2.5, 5 and 10 min). Egg batches of both poor and good quality were tested for halibut. Positive effects were more pronounced in poor than in good-quality batches at hatching. Egg disinfection had a highly positive effect on the viability of yolk-sac larvae in both types of batches. A level between 400 and 800 mg l-1 at a contact time of 5–10 min was optimal for halibut: at lower levels, the bactericidal effect was reduced, and at higher levels, there were indications of toxic effects. Halibut eggs disinfected with optimal doses of glutaraldehyde had furthermore a reduced hatching time and more synchronous hatching as compared with untreated eggs. Turbot was more sensitive to higher doses than halibut, and the best larval performance was obtained for 400–800 mg glutaraldehyde l-1 at a contact time of 2.5 min. A further evaluation should, however, be performed before recommendations are given for species incubated at temperatures higher than 5°C.

Behavioral Interactions among Brood Parasites with Precocial Young: Canvasbacks and Redheads on the Delta Marsh

I studied brood parasitism among 110 Aythya nests and filmed 125 interactions at 14 Canvasback (A. valisineria) and 5 Redhead (A. americana) nests to describe hostparasite behavior. Redheads outnumbered breeding Canvasbacks by about 5.4 to 1 on the Delta Marsh, Manitoba, and heavily parasitized Canvasback nests (x ± SE = 7.6 ± 2.8 eggs/nest). High rates of parasitism resulted in delayed host embryo development, up to 23% longer incubation periods, and extended brooding behavior at nests containing unhatched or late-hatching eggs. Females followed potential hosts to locate nests, made prelaying nest visits, and selected active rather than deserted nests to parasitize. Parasitic laying was not markedly deterred by host resistance and occurred at all stages of host laying and incubation, resulting in only 34% of parasitic Redhead eggs hatching in successful Canvasback nests. Laying females aggressively displaced incubating hosts, causing eggs to be accidentally displaced from nests. Host Canvasback eggs were five times as likely to be cracked and twice as likely to be dislodged from nests than were parasitic Redhead eggs. Hosts limited defensive actions to pushing against intruders or pecking at the heads of parasitic females, resulting in some parasitic eggs being deposited outside nest bowls. Incubating females may be constrained from using highly aggressive behavior to deter brood parasites partly because of fitness costs of fighting and breaking or displacing their own eggs. The existence of host defensive behavior suggests that brood parasitism may present significant fitness costs, even among species with nidifugous precocial young, by affecting the critical processes of synchronous hatching and nest exodus.

Seasonal Decline in Clutch Size of the Barnacle Goose in Svalbard

We examined seasonal decline in clutch size in the high arctic Barnacle Goose Branta leucopsis in Svalbard. Females that arrived first at the breeding ground nested first, had the longest prelaying period, produced the largest clutches and also had the longest incubation period. Nevertheless, their brood size at hatching was larger than late nesters. These results do not support the nutrient reallocation hypothesis which suggests that seasonal decline in clutch size in arctic nesting geese results from the mobilization of nutrient reserves during the period before egg laying. Instead, we propose that geese which arrive late at the breeding area spend relatively less of their reserves on eggs. They do this presumably to achieve synchronous hatching with early nesting birds and/or to prevent a late breeding season which may reduce gosling survival, adult survival and/or future fecundity.

Development, hatching, and infectivity of Echinostoma caproni (Trematoda) eggs, and histologic and histochemical observations on the miracidia.

Light microscopy studies were done on the eggs and miracidia of the intestinal trematode Echinostoma caproni. Eggs were obtained by homogenizing adult worms derived from ICR mice in artificial spring water (ASW). To study egg development and to obtain miracidia, eggs were incubated in ASW in either a light or a dark environment for 10 days at 28 degrees C. Egg development was characterized and staged at 2-day intervals from day 0 to day 10 postembryonation. No significant difference in development was seen in eggs maintained under conditions of light or darkness. Eggs maintained in darkness for 10 days and exposed to incandescent light produced a large synchronous hatch of miracidia within 3 h of exposure to light. As expected, miracidia used to expose Biomphalaria glabrata snails produced patent infections at 5-7 weeks postinfection (p.i.). Embryonated eggs aged from 0 to 10 days that had been fed to B. glabrata snails also produced infections within 4 weeks of infection. Miracidial longevity studies showed that 50 newly hatched miracidia maintained at either 4 degrees, 12 degrees, 22 degrees, or 38 degrees C lived for 6, 28, 14, and 5 h, respectively. Histology studies were done on whole miracidia stained in 0.01% neutral red and in Schneider's acetocarmine. Histochemistry studies of miracidia stained with alcian blue (pH 2.5) showed the presence of acid mucopolysaccharides in the epidermal plates; miracidia treated with periodic acid-Schiff plus 0.5% malt diastase showed the presence of glycogen in the body and in the epidermal/subepidermal region. Miracidia stained with Lillie's Oil Red O showed the presence of sparse neutral fat droplets in the body.

Density Dependence, Hatching Synchrony, and within‐Cohort Cannibalism in Young Dragonfly Larvae

We present two laboratory experiments designed to show how cannibalism and its effects on population numbers and size structure vary in response to density, size, and food manipulations in larvae of the dragonfly Epitheca cynosura. Because young larvae of this species interact at very high densities after hatching asynchronously from clumps of egg masses, our efforts focused on these early stages. In one experiment, we varied the combination of sizes (instars) and the presence of food for 233 pairs of early—instar larvae. Cannibalism was uncommon if larvae were of the same instar (only 2.4% of such pairs exhibited cannibalism), frequent (53%) if larvae differed by one instar, and certain (100%) if a two—instar size difference was present. The rate at which cannibalism increased with size differences between larvae was greater when food was absent than it was when food was provided. In a second experiment, we subjected replicate cohorts of newly hatched dragonflies to manipulations of hatching synchrony, initial density, and food availability. Asynchronous hatching over 25 d produced a broad size distribution apparently conducive to cannibalism, whereas synchronous hatching over 3 d initially precluded cannibalism. As a result, strong density—dependent mortality only appeared following the asynchronous hatch. For high—density, asynchronous treatments, cannibalism significantly reduced size variation and tightened size distributions over the course of development. Survivors from high—density treatments were significantly larger than were low—density survivors. More abundant food allowed larvae to reach larger sizes, but did not improve survival. Survival was affected mainly by the density and size distribution of larvae. These results suggest that cannibalism was more important than exploitative competition for food in determining the size and survival of dragonflies in the laboratory. We conclude that when juveniles hatch asynchronously in close proximity, cannibalism can: (1) contribute to population regulation by imposing greater per capita mortality at high densities, and (2) increase population synchrony by exerting size—specific mortality on smaller individuals throughout development.

The function of hatching asynchrony in the blue-footed booby

The blue-footed booby (Sula nebouxii) commonly hatches two eggs 4 days apart; then the senior (first-hatched) chick aggressively dominates the other and sometimes kills it. Two hypotheses explaining the function of the hatching interval were tested by creating broods with synchronous hatching: the facultative brood reduction hypothesis of Lack (1954) and the sibling rivalry reduction hypothesis of Hahn (1981). The results contradicted most predictions of both hypotheses: synchronous broods formed an aggressive hierarchy similarly to asynchronous broods (controls), and subordinate chicks grew poorly (Fig. 1) and died frequently, similarly to junior chicks in control broods. However, compared with synchronous broods, asynchronous broods showed less aggression (Fig. 2), diminished food allocation to subordinate chicks (Fig. 3) and less total food consumption (30% fewer feeds at age 0–10 days). These behavioral comparisons took into account the different ages of chicks in different treatments. The results suggest that natural asynchrony makes brood reduction more efficient and decreases the costs of sibling aggression to parents, in terms of their future survival or fecundity, as proposed by Mock and Ploger (1987). Further, in exaggeratedly asynchronous broods (8-day hatch interval) junior chicks suffered more aggression (Fig. 4) and grew more slowly than junior chicks in control broods. This result supports the hypothesis of optimal hatch asynchrony of Mock and Ploger (1987).