A Single Hot Event That Does Not Affect Survival but Decreases Reproduction in the Diamondback Moth,Plutella xylostella

Extremely hot events (usually involving a few hours at extreme high temperatures in summer) are expected to increase in frequency in temperate regions under global warming. The impact of these events is generally overlooked in insect population prediction, since they are unlikely to cause widespread mortality, however reproduction may be affected by them. In this study, we examined such stress effects in the diamondback moth, Plutella xylostella. We simulated a single extreme hot day (maximum of 40°C lasting for 3, 4 or 5 h) increasingly experienced under field conditions. This event had no detrimental effects on immediate mortality, copulation duration, mating success, longevity or lifetime fecundity, but stressed females produced 21% (after 3 or 4 h) fewer hatched eggs because of a decline in the number and hatching success of eggs laid on the first two days. These negative effects on reproduction were no longer evident in the following days. Male heat exposure led to a similar but smaller effect on fertile egg production, and exposure extended pre-mating period in both sexes. Our results indicate that a single hot day can have detrimental effects on reproduction, particularly through maternal effects on egg hatching, and thereby influence the population dynamics of diamondback moth.     

Reproductive and physiological costs of repeated immune challenges in female Wellington tree weta (Orthoptera: Anostostomatidae)

Fitness‐related traits, such as immunity and reproduction, are typically condition dependent, and are predicted to trade off against each other because they share a pool of energy and resources. It is generally assumed that the resources and energy required for immune processes and reproduction is contained in the body fat; however, few studies quantify the effect of an immune insult on fat load. I tested the hypothesis that if mounting an immune response is physiologically costly in terms of consuming limited resources from body fat, and reproduction also relies on these resources, then an immune challenge should cause a reduction in fat load and an associated decline in reproduction. I tested this hypothesis by assaying the fat content of female Wellington tree weta (Hemideina crassidens) after repeated challenges with lipopolysaccharide (LPS), and counting the number of oviposited eggs in addition to assaying the egg protein content, a possible measure of egg quality. In line with my prediction, immune‐challenged females had significantly smaller fat loads and laid significantly fewer eggs than saline‐injected controls. Moreover, the protein content of the eggs laid by immune‐challenged females was significantly lower than that of controls. My experimental results show that an immune challenge with a non‐pathogenic stimulant increases fat consumption, which in turn limits the resources available for reproduction. These findings support the hypothesis that reproduction and immunity are condition dependent, and are traded off against each other. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 38–46.     

CLUTCH-SIZE, INCUBATION AND HATCHING SUCCESS IN THE HOUSE SPARROW AND TREE SPARROW PASSER SPP. AT OXFORD

Clutch-size, incubation and hatching success were studied in P. domesticus and P. montanus in 1961 and 1963–64 at Oxford. The most frequent clutch-size was four eggs in P. domesticus and five eggs in P. montanus . With one exception, colonies of P. domesticus showed no significant annual or local variations in its mean clutch-size; in P. montanus , however, there were significant annual variations in the mean clutch-size. Both species showed a seasonal increase followed by a decrease in their mean clutch-sizes.
Partial incubation occurred during the laying period of the clutch; sufficient incubation for continuous development of the embryo was apparently achieved when the last egg had been laid in clutches of two and three eggs in P. domesticus and in clutches of four eggs in P. montanus , but when the penultimate egg had been laid in larger clutches of both species. On average, hatching in P. domesticus occurred more or less synchronously in all eggs in clutches of two and three eggs, and in all eggs except the last one laid in larger clutches; the last egg in the larger clutches hatched up to a day after the others. It is suggested that this pattern of hatching was brought about by the pattern of incubation during the laying period.
P. domesticus had a lower hatching success than P. montanus , probably because fewer of its eggs were fertile.     

Seasonal variation in reproductive measures of tropical Roseate Terns Sterna dougallih previously undescribed breeding patterns in a seabird

Seasonal variation in egg-laying, egg size, hatching success, hatchling mass, fledging success and chick growth of Roseate Terms Sterna dougallii breeding on Aride Island (Seychelles), Indian Ocean, were studied in 1997 and 1998. I investigated to what extent two patterns, common in a range of species, were followed by tropical Roseate Terns: (a) seasonal decrease in clutch size, egg size and breeding success and (b) an increase in breeding success with increasing egg weight. In 1997 (a poor year), the earliest nesting birds laid significantly smaller eggs, and chicks were lighter at hatching than those of peak nesting birds. The mean clutch size, of 1.04 eggs, showed no seasonal variation and no 'b'-eggs hatched. In 1998 (a good year) the earliest nesting birds laid eggs of similar size and their chicks were of similar weight to those of peak nesting birds. Mean clutch size, of 1.25 eggs, increased significantly through the season and about 60% of the 'b'-eggs hatched. In 1997, hatching success was 57% whereas in 1998 it was 80%. In both years, breeding success declined significantly through the season. The fact that the earliest breeding birds laid smaller eggs in a poor year and smaller clutches in a good year is in marked contrast to a range of other species, and to temperate-nesting Roseate Terns. Egg volume explained about half of the variance in hatchling mass in both years, but only 15% of the variation in linear growth rate. Hatching date was the only variable with a significant effect on fledging success. Roseate Terns on Aride seemed to sacrifice egg size and clutch size for earliness of laying. Presumably it is a strategy of older birds to lay as early as possible and may be regarded as a response of tropical Roseate Terns to breeding under relatively poor, and seasonally declining, food conditions.     

Patterns of variation in size of Boat-tailed Grackle Quiscalus major eggs

Boat-tailed Grackle Quiscalus major eggs averaged 8^.09 g wet weight. Mean egg weight represented 8 05 % of female body weight. Based on egg weight, Grackle eggs have a shorter incubation period than the general passerine pattern.
Egg weight varied significantly with sequence of laying and between clutches in both two-egg and three-egg clutches. Last laid eggs weighed less than first laid eggs. The mean weight of the first two eggs laid in three-egg clutches did not differ from the mean egg weight of two-egg clutches. The average clutch of two and three eggs weighed 16.33 g and 24.16 g, respectively.
Mean egg weight varied between study colonies and with season. Grackles at East Lake laid eggs that weighed less than grackles at either Alligator Lake or North Lake. Eggs laid during March averaged less than eggs laid later in the season. The locality variation reflects the different timing of nesting between sites rather than food abundance. As nutrient provisioning increases with an increase in egg weight, the seasonal change in egg weight probably reflects improved feeding conditions for the female. This suggests that selection favours beginning laying before reserves of the female are sufficient to lay the largest egg possible.
The size of the young at hatching was correlated with egg size. Newly hate had young averaged 79.6% of fresh egg weight. Egg weight did not determine the probability of hatching or starvation of the young. Females do not appear to adjust egg size facultatively depending on the sex of the young. Eggs producing males and females did not vary significantly in weight, whether comparisons were made within or between clutches.     

Laying characteristics of one- and two-year old pheasants (Phasianus colchicus, L.)

The aim ofthe study was to assess laying traits, the weight of eggs and characters ofthe laying rhythm of pheasants in the first and second years of reproduction. Pheasants (10 cockerels and 50 hens) were kept in aviaries. Daily, individual control of laying was performed beginning with the day of the first laying and ending with the last egg. The following parameters were evaluated: age at first laying, length of the laying period, number of laid eggs and the average weight of the egg in the 8th week of laying. The laying rhythm was also assessed and comprised: the number of egg clutches, the number of eggs in a clutch, the number of eggs in the longest clutch, the number of intervals, the length of intervals and the longest interval between clutches. During the first period of reproduction, in comparison with the second, pheasants laid slightly more eggs of similar average weight. The first laying period was longer than the second and was characterised by a greater number of egg clutches and greater number of intervals between clutches. The greatest number of eggs was laid in 10-egg and longer clutches, although the l-egg clutches were the most numerous. A positive correlation was found between the number of eggs and the number of clutches, the greatest number of eggs in a clutch and the number of intervals between clutches. The similar values of the reproductive characters of one- and two-year old pheasants point to the possibility of longer utilization of these birds than only for one laying period. On the other hand, the considerable variability between the experimental hens with regard to the number and the length of egg clutches, as well as the intervals between them, indicate the possibility to carry out selection taking into account traits characterising the laying rhythm.     

Reproductive Strategies of the Insidious Fish Ectoparasite,Neobenedenia sp. (Capsalidae: Monogenea)

Fish monogeneans are lethal parasites in aquaculture. We provide the first experimental evidence that a notorious fish monogenean, Neobenedenia sp., can produce viable eggs in isolation for three consecutive generations. We infected individual, isolated, farmed barramundi, Lates calcarifer (Bloch) with a single oncomiracidium (larva) of the hermaphroditic monogenean Neobenedenia sp. Isolated parasites reached sexual maturity at day 10 post-hatch (24°C, 35‰) and laid ∼3,300 embryonated eggs over 17 days. Egg production rapidly increased following sexually maturity on day 10 (58±15 eggs) and peaked on day 15 (496±68 eggs) before gradually decreasing. Neobenedenia sp. exhibited egg laying and egg hatching rhythms. Parasites laid eggs continuously, but egg production increased in periods of darkness (64.3%), while the majority of oncomiracidia (81%) emerged from eggs in the first three hours of light. Eggs laid by isolated ‘parent’ parasites hatched and individual emerging oncomiracidia were used to infect more individual, isolated fish, with three consecutive, isolated, parasite generations (F1, F2 and F3) raised in the laboratory. Infection success and egg hatching success did not differ between generations. Our data show that one parasite, in the absence of a mate, presents a severe threat to captive fish populations.     

Lifetime egg production and egg mortality in the damselflyPyrrhosoma nymphula (Sulzer) (Zygoptera: Coenagrionidae)

Artificial oviposition sites were used to estimate egg deposition rates in the field. Females laid an average of 10.76 eggs/minute with a mean duration of 22.81 minutes, giving an average clutch size of 245 eggs. Since one mating corresponded to one clutch of eggs, lifetime mating success was used as a measure of the number of clutches produced. Mean lifetime clutch production was 5.91 clutches per female, equating to 1447 eggs per female per lifetime. Eggs were hatched in the laboratory at temperatures comparable with those in the field. Hatching was highly synchronised and the overall hatching success was 75.1%. Causes of egg mortality in the laboratory were limited to infertility and unhatchability. Since no other sources of egg mortality could be found at the study site, this value was a good reflection of hatching success in the field. Lifetime egg production and hatching success were used to estimate the number of viable offspring produced per female, giving a higher order estimate of reproductive success than has previously been published for a zygopteran.     

BENEFITS OF MULTIPLE MATES IN THE CRICKET GRYLLUS BIMACULATUS

Despite the importance of polyandry for sexual selection, the reasons why females frequently mate with several males remain poorly understood. A number of genetic benefits have been proposed, based on the idea that by taking multiple mates, females increase the likelihood that their offspring will be sired by genetically more compatible or superior males. If certain males have intrinsically “good genes,” any female mating with them will produce superior offspring. Alternatively, if some males have genetic elements that are incompatible with a particular female, then she may benefit from polyandry if the sperm of such males are less likely to fertilize her eggs. We examined these hypotheses in the field cricket Gryllus bimaculatus (Orthoptera: Gryllidae). By allocating females identical numbers of matings but different numbers of mates we investigated the influence of number of mates on female fecundity, and both short- and long-term offspring fitness. This revealed no effect of number of mates on number of eggs laid. However, hatching success of eggs increased with number of mates. This effect could not be attributed to nongenetic effects such as the possibility that polyandry reduces variance in the quantity or fertilizing ability of sperm females receive, because a control group receiving half the number of copulations showed no drop in hatching success. Offspring did not differ in survival, adult mass, size, or development time with treatment. When males were mated to several different females there were no repeatable differences between individual males in the hatching success of their mate's eggs. This suggests that improved hatching success of polyandrous females is not due to certain males having genes that improve egg viability regardless of their mate. Instead, our results support the hypothesis that certain males are genetically more compatible with certain females, and that this drives polyandry through differential fertilization success of sperm from more compatible males.     

CLUTCH SIZE, EGG SIZE, HATCH WEIGHT AND LAYING DATE IN RELATION TO EARLY MORTALITY IN RED GROUSE LAGOPUS LAGOPUS SCOTICUS CHICKS

Clutches of Red Grouse eggs were collected from the wild and subsequent hatching and rearing done in standard conditions in captivity. Variations in chick survival from one clutch to another in the same year were related to differences in hatch weight. Hatch weight was determined only partly by egg size. Weight loss between laying and hatching was related to survival independently of egg size. Variation in this weight loss obscured any simple relationship between egg size and survival, except in eggs laid by captive hens. Intrinsic differences amongst hens caused some variations in laying date, egg size, hatch weight and chick survival. Variations in egg size and hatch weight accounted for less than half the variation in survival; other unmeasured intrinsic factors were also important. Big clutches hatched earlier than small ones. The commonest clutches were of seven and eight eggs, with six and nine frequent. Very big clutches of ten or more eggs were infrequent and chicks from them sometimes survived worse than from smaller clutches. As in other species, the commonest clutch sizes were not the most productive. There was no simple relationship between egg size and clutch size.     

温度对坏鳃指环虫产卵、孵化和发育的影响

实验研究了离体条件下温度对坏鳃指环虫(Dactylogyrus vastator)产卵和孵化的影响,以及在20℃、在体条件下坏鳃指环虫的产卵和发育过程。在离体条件下,坏鳃指环虫的平均产卵量随着温度的升高而增加,在4、10、20、30和35℃时,其平均产卵量分别为0.25、5.9、9.1、9.2和13.4枚/虫;除4℃外,绝大多数虫卵是在离体后的前5h内产出;然而,在体条件下虫体的产卵是连续且稳定的,在20℃条件下平均产卵量为6.5枚/(虫d)。虫卵的孵化时间和孵化持续的时间随着温度的升高而减少,在10、20、30和35℃条件下,孵化时间和孵化持续时间分别为19d、3d、2d、36h和24d、5d、5d、3d,而最高的孵化率(65.5%)却出现在30℃。在20℃条件下,纤毛幼虫在感染7d后90%的虫体都已成熟,因此,在此温度条件下坏鳃指环虫由虫卵发育到成虫大约需要8-10d。为了有效控制指环虫病的暴发,在第一次用药1周后要进行第二次用药。       

Effects of elevated egg corticosterone levels on behavior, growth, and immunity of yellow-legged gull (Larus michahellis) chicks

Eggs of vertebrates contain steroid hormones of maternal origin that may influence offspring performance. Recently, it has been shown that glucocorticoids, which are the main hormones mediating the stress response in vertebrates, are transmitted from the mother to the egg in birds. In addition, mothers with experimentally elevated corticosterone levels lay eggs with larger concentrations of the hormone, which produce slow growing offspring with high activity of the hypothalamo-adrenal axis under acute stress. However, the effects and function of transfer of maternal corticosterone to the eggs are largely unknown. In the present study, we injected corticosterone in freshly laid eggs of yellow-legged gulls (Larus michahellis), thus increasing the concentration of the hormone within its natural range of variation, and analyzed the effect of manipulation on behavioral, morphological, and immune traits of the offspring in the wild. Eggs injected with corticosterone had similar hatching success to controls, but hatched later. Mass loss during incubation was greater for corticosterone-treated eggs, except for the last laid ones. Corticosterone injection reduced rate and loudness of late embryonic vocalizations and the intensity of chick begging display. Tonic immobility response, reflecting innate fearfulness, was unaffected by hormone treatment. Elevated egg corticosterone concentrations depressed T-cell-mediated immunity but had no detectable effects on humoral immune response to a novel antigen, viability at day 10, or growth. Present results suggest that egg corticosterone can affect the behavior and immunity of offspring in birds and disclose a mechanism mediating early maternal effects whereby stress experienced by females may negatively translate to offspring phenotypic quality.     

Laying, egg and hatchability characteristics in ostrich (Struthio camelus) at different age

The experimental material comprised 7 ostrich families (7 males and 14 females) of which five families were at the age of 7 and two at the age of 5 years. In the course of the entire reproductive season, the following parameters were analysed: length of the laying period, mean laying rate, number of eggs laid by one female, proportion ofhatching eggs, egg weight and shape, egg weight lost during incubation, egg fertilisation, percentage of dead embryos and unhatched chicks, hatchability from fertilised and set eggs. Seven year-old ostriches were characterised by shorter laying period (134 days) but, at the same time, by higher proportions of hatching eggs. This group was also characterised by high egg fertilisation (79.7%) as well as high hatchability indices at simultaneous highest embryo mortality during incubation (11.6 %). Five year-old ostriches exhibited a longer laying period (175 days) during which females laid more eggs (49 pcs.). In addition, this group was characterised by a smaller proportion of hatching eggs, better egg fertilisation indices (83.5%) and hatchability results. Moreover, the determined higher egg shape index indicates that the 5 year-old females laid eggs which were more spherical. Recapitulating, the obtained results indicate that, under Polish conditions, better indices of laying performance, egg fertilisation and hatchability were observed in the group of 5 year-old ostriches.     

Consequences of prenatal androgen exposure for the reproductive performance of female pheasants (Phasianus colchicus)

Maternal hormones in vertebrate eggs can mediate important forms of maternal effects. However, the function of hormone transfer to the eggs is still debated, especially because long-term fitness consequences have been little studied. We investigated the effect of prenatal exposure to physiologically elevated yolk testosterone (T) levels on reproduction of female pheasants (Phasianus colchicus) in captivity. We found that females hatching from T-injected eggs (T-females) had a lower egg-laying rate than controls, and their eggs were more frequently infertile than those laid by control females. There were no effects of prenatal maternal treatment on egg size and yolk T concentration, but eggs carrying a female embryo laid by T-females had smaller yolks than eggs with a male embryo, while there was no sex difference in yolk size among the eggs laid by control females. Progeny sex ratio was unaffected by maternal treatment. These findings suggest that the transfer of high androgen levels to the eggs by the mother is constrained by complex trade-offs between direct effects on her daughters' reproduction and by trans-generational differential consequences on male and female descendants.     

诱导水稻抗褐飞虱的化学激发子筛选

【目的】化学激发子具有毒性低、不易产生抗药性等特点,因此开发基于化学激发子的害虫防控技术,能够降低农药的使用量,促进农业生产的可持续发展。本研究旨在筛选能够诱导水稻产生对褐飞虱Nilaparvata lugens抗性的化学激发子。【方法】将茉莉酸(JA)、茉莉酸甲酯(MeJA)、水杨酸(SA)、水杨酸甲酯(MeSA)、油菜素内酯(BR)、苯甲酸苄酯(BB)、独脚金内酯(SLs)、萘乙酸(NAA)、吲哚丁酸(IBA)、草酸钠(SO)、硅酸钾(PS)和叶枯唑(Bis)12种化合物以根吸或叶鞘涂抹处理水稻,测定这些化合物处理水稻后褐飞虱的卵孵化率和24 h总产卵量。【结果】12种候选化合物中,仅茉莉酸甲酯、油菜素内酯和苯甲酸苄酯对褐飞虱卵孵化率和24 h总产卵量有显著影响。5 mg/L MeJA根吸处理水稻使褐飞虱的卵孵化率显著降低(达58.8%,降低了20.1%),而0.5 mg MeJA叶鞘涂抹处理水稻同时降低了褐飞虱的卵孵化率(达53.3%,降低了35.4%)和24 h总产卵量(达203.5粒/株,降低了15.6%),且其涂抹的浓度越高,褐飞虱的卵孵化率和24 h总产卵量越低。5 mg/L BR根吸处理水稻可以显著降低褐飞虱的卵孵化率(达59.5%,降低了22.1%),但是不影响褐飞虱的24 h总产卵量;褐飞虱的卵孵化率随BR处理浓度增高而降低,其浓度为20 mg/L时,褐飞虱的卵孵化率下降了41.8%。5 mg/L BB根吸处理水稻可以显著降低褐飞虱的24 h总产卵量(达100.3粒/株,降低了26.2%)。体外试验结果表明,MeJA和BR处理对褐飞虱卵孵化率无明显影响,说明两者对褐飞虱卵无直接毒害作用。【结论】化合物茉莉酸甲酯、油菜素内酯和苯甲酸苄酯可以提高水稻对褐飞虱的抗性,其中茉莉酸甲酯和油菜素内酯具有化学激发子的作用。     

Ovarian activity and reproduction in the frog, Rana esculenta

Rana esculenta specimens were collected, during the last 13 years, in well-defined areas around Naples. The annual ovarian cycle shows distinct phases of recrudescence (starting September; vitellogenesis), breeding (late March-early July; egg deposition and active oogenesis) and quiescence (July-August; no follicular growth). Previtellogenic follicles are recruited for vitellogenesis in early September and in between two successive ovulatory waves. Breeding congregations are generally formed after a heavy rain fall and eggs are laid in standing waters, temporary or permanent. A maximum of three clutches of eggs is produced during the breeding season, at roughly monthly intervals. All mature females reproduce to some extent. Ovarian weight and clutch size are positively correlated to body weight. Depending upon the body size, the potential clutch size ranges from 1000 to 3500 eggs during the first wave of ovulation and it is notably smaller in the successive wave(s) of ovulation. Egg masses and tadpoles are left unprotected and mortality is high. The life cycle from the fertilized egg to completion of metamorphosis is 2 months and oogenesis in the ovary starts in the larva before the onset of metamorphic climax. Young females hatching from the first clutch of eggs may reach sexual maturity and breed in May the following year; those hatching from the last clutch require nearly 20 months to reach sexual maturity. The importance of some endocrine and exocrine factors for the regulation of ovarian activity and reproduction is discussed.     

Length rather than year‐round spawning,affects reproductive performance of RAS‐reared F‐generation pikeperch,Sander lucioperca (Linnaeus, 1758) – Insights from practice

The continuous production of large numbers of high quality gametes is essential for aquaculture, particularly in candidate species, such as pikeperch, Sander lucioperca (L.). The common practice of year‐round reproduction is under suspicion of inflicting adverse effects on the quality of the gametes through the disturbance of endogenous rhythms. We hypothesized that such perturbation does not affect RAS‐reared F‐generation broodstock. Reproductive performance (number of eggs) and gamete quality (fertilization and hatching rate) were assessed over the course of 3 years covering six independent, photothermal shifted spawning seasons in a commercial pikeperch hatchery (n = 31 egg batches of F‐generation fish in total). No substantial differences in fertilization or hatching rates could be detected between the individual spawning seasons. Fecundity varied, but there are indications for a size effect on female fecundity with intermediate sized females producing higher number of eggs (~65–70 cm). Low egg quality could be detected in batches of very large fish. In conclusion, size‐specific broodstock composition, but not year‐round reproduction of F‐generation pikeperch spawners affects the reproductive performance.     

Reduction in egg hatch after a sublethal dose of chlorfluazuron to larvae of the common cutworm, Spodoptera litura

Abstract.  The effects of a sublethal dose of chlorfluazuron on egg hatching in Spodoptera litura are examined under laboratory conditions. When LD₁₀ of chlorfluazuron is topically applied to newly moulted fifth-instar larvae of either sex, a significant reduction in both the number of eggs laid and subsequent hatching is observed after mating but no significant differences in daily of oviposition are observed when compared with the controls. In addition, examination of the unhatched eggs reveals that the number of unfertilized eggs is greater than those that were fertilized but there are significantly more unfertilized eggs laid by treated insects. Interference by chlorfluazuron, transferred by copulation through sperm fluids or ova, appears improbable. All the fertilized unhatched eggs in the treated crosses die at an earlier stage than those of the controls. In the female-treated crosses, the egg size is significantly reduced compared with the control or male-treated crosses. During mating, the treated-males transferred significantly lower-weight spermatophores into the females. The weight of spermatophores transferred by untreated males is the same to both treated and untreated females. The duration of mating is not affected by chlorfluazuron treatment.     

Egg hatching of two locusts,Schistocerca gregaria and Locusta migratoria,in response to light and temperature cycles

The present study showed that the eggs of the desert locust, Schistocerca gregaria, and the migratory locust, Locusta migratoria, responded to photoperiod by hatching when placed on sand in the laboratory. S. gregaria mainly hatched during the dark phase and L. migratoria during the light phase. The importance of light as a hatching cue depended on the magnitude of the temperature change during the thermoperiod; photoperiod played a more important role in the control of hatching time in both species when the magnitude of the temperature change was small. In addition, the eggs of the two species that were covered with sand did not respond to photoperiod and hatched during both the light and dark phases, indicating that light did not penetrate through the sand. Because locust eggs are normally laid as egg pods and a foam plug is deposited between the egg mass and the ground surface, we tested a possibility that naturally deposited eggs perceived light through the foam plug. The eggs that were deposited and left undisturbed in the sand hatched during the light and dark phases at similar frequencies. These results suggest that the eggs of both locust species responded to light and controlled their hatching timing accordingly but would not use light as a hatching cue in the field. The evolutionary significance of the ability of eggs to respond to light in these locusts was discussed.     

FREQUENCY-DEPENDENT FITNESS CONSEQUENCES OF INTRASPECIFIC NEST PARASITISM IN SNOW GEESE

The reproductive efficiency, defined as the number of breeding recruits produced per egg laid; of intraspecific nest parasites; of hosts in parasitized nests; and of unparasitized nesting females, was measured for 14 years for lesser snow geese Anser caerulescens caerulescens nesting near Churchill, Manitoba, Canada. Relative efficiencies were 0.71–0.88, 0.91, and 1.0 for eggs of parasites, hosts, and unparasitized birds, respectively. Differences in the hatching probabilities of the three classes of eggs produced the efficiency differences. Parasitic success was limited by the parasites' failure to place more eggs than expected by chance into nests at the appropriate time relative to host incubation. Host nesting success was lower when more than one parasitic egg was added to the clutch. No differences in gosling survival and breeding recruitment probabilities were detected among any categories of goslings. Thus, hatching parasitic young are at no disadvantage relative to parental young, and there is no support for the hypothesis that increased success of host young at later stages of reproduction might offset negative effects at the egg stage. The hatching efficiency of parasitic eggs declined more rapidly than that of parental eggs as the parasitism rate increased. Efficiencies were similar when 3–4% of the eggs laid per year were parasitic, but relative parasitic efficiency was significantly lower when the parasitism rate was 8–9% or more. Using ancillary information and assumptions about the fecundity, viability, and behavioral flexibility of parasitic and parental females, we conclude that intraspecific nest parasitism could compete with nesting as a reproductive strategy in this population. The conditional use of parasitism by a large component of the population in certain years, however, combined with negative-frequency dependent success, limits the potential spread of a purely parasitic strategy in this population.