Induction of embryonic dormancy in the calanoid copepod Acartia hudsonica: heritability and phenotypic plasticity in two geographically separated populations

The planktonic copepod Acartia hudsonica apparently requires summer diapause or dormancy to persist in Narragansett Bay, RI. In estuaries to the north, however, active A. hudsonica populations are present year-round and may not express dormancy. Using a full-sibling rearing design and analysis of variance (ANOVA), I assessed the importance of phenotypic and genetic sources of variation in two geographically separate populations, one from Maine and one from Rhode Island. Both populations showed phenotypic plasticity in the percentage of dormant eggs produced. Moreover, experiments revealed significant sibship-environment interactions in both populations, indicating that the phenotypic plasticity has a genetic component. Both populations also revealed a significant amount of genetic variation in the percentage of dormant eggs produced. For the Maine population, broad sense heritability was high (0.91, 1.10) in two short-day (12L:12D) treatments and near zero (0.08) in the long-day treatment (15L:9D). For a Rhode Island population, broad sense heritability was higher (0.95) in a low-temperature short-day treatment (13.5 °C, 12L:12D) than in a high-temperature short-day treatment (17.5 °C, 12L:12D; h²=0.25).     

Determining the Advantages,Costs, and Trade-Offs of a Novel Sodium Channel Mutation in the Copepod Acartia hudsonica to Paralytic Shellfish Toxins (PST)

The marine copepod Acartia hudsonica was shown to be adapted to dinoflagellate prey, Alexandrium fundyense, which produce paralytic shellfish toxins (PST). Adaptation to PSTs in other organisms is caused by a mutation in the sodium channel. Recently, a mutation in the sodium channel in A. hudsonica was found. In this study, we rigorously tested for advantages, costs, and trade-offs associated with the mutant isoform of A. hudsonica under toxic and non-toxic conditions. We combined fitness with wild-type: mutant isoform ratio measurements on the same individual copepod to test our hypotheses. All A. hudsonica copepods express both the wild-type and mutant sodium channel isoforms, but in different proportions; some individuals express predominantly mutant (PMI) or wild-type isoforms (PWI), while most individuals express relatively equal amounts of each (EI). There was no consistent pattern of improved performance as a function of toxin dose for egg production rate (EPR), ingestion rate (I), and gross growth efficiency (GGE) for individuals in the PMI group relative to individuals in the PWI expression group. Neither was there any evidence to indicate a fitness benefit to the mutant isoform at intermediate toxin doses. No clear advantage under toxic conditions was associated with the mutation. Using a mixed-diet approach, there was also no observed relationship between individual wild-type: mutant isoform ratios and among expression groups, on both toxic and non-toxic diets, for eggs produced over three days. Lastly, expression of the mutant isoform did not mitigate the negative effects of the toxin. That is, the reductions in EPR from a toxic to non-toxic diet for copepods were independent of expression groups. Overall, the results did not support our hypotheses; the mutant sodium channel isoform does not appear to be related to adaptation to PST in A. hudsonica. Other potential mechanisms responsible for the adaptation are discussed.     

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

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

Rate of egg maturation in marine turtles exhibits 'universal temperature dependence'

1. The metabolic theory of ecology (MTE) predicts that, after correcting for body mass variation among organisms, the rates of most biological processes will vary as a universal function of temperature. However, empirical support for 'universal temperature dependence' (UTD) is currently equivocal and based on studies of a limited number of traits. 2. In many ectothermic animals, the rate at which females produce mature eggs is temperature dependent and may be an important factor in determining the costs of reproduction. 3. We tested whether the rate of egg maturation in marine turtles varies with environmental temperature as predicted by MTE, using the time separating successive clutches of individual females to estimate the rate at which eggs are formed. We also assessed the phenotypic contribution to this rate, by using radio telemetry to make repeated measurements of interclutch intervals for individual green turtles (Chelonia mydas). 4. Rates of egg maturation increased with seasonally increasing water temperatures in radio-tracked green turtles, but were not repeatable for individual females, and did not vary according to maternal body size or reproductive investment (number and size of eggs produced). 5. Using a collated data set from several different populations and species of marine turtles, we then show that a single relationship with water temperature explains most of the variation in egg maturation rates, with a slope that is statistically indistinguishable from the UTD predicted by MTE. However, several alternative statistical models also described the relationship between temperature and egg maturation rates equally parsimoniously. 6. Our results offer novel support for the MTE's predicted UTD of biological rates, although the underlying mechanisms require further study. The strong temperature dependence of egg maturation combined with the apparently weak phenotypic contribution to this rate has interesting behavioural implications in ectothermic animals. We suggest that maternal thermoregulatory behaviour in marine turtles, and many other reptiles, is consistent with a strategy of adaptively increasing body temperatures to accelerate egg maturation.     

Great tits provided with ad libitum food lay larger eggs when exposed to colder temperatures

The amount of nutrients deposited into a bird egg varies both between and within clutches of the same female. Larger eggs enhance offspring traits, but as a tradeoff, laying large eggs also infers energetic costs to the female. Income breeders usually lay larger eggs later in the season, when temperatures and food availability are higher. Egg size is thus affected by the daily amount of energy available to produce an egg under cold conditions, but it is less well known in how far temperature exerts direct effects on egg size. We show that great tit females Parus major with access to ad libitum food and breeding in climate‐controlled aviaries varied their egg investments. The size of an individual egg was best predicted by mean temperatures one week pre‐laying, with females laying larger, rather than smaller, eggs under colder conditions. Eggs increased in size over the season, but not significantly over the laying sequence. The degree of daily temperature fluctuation did not influence egg size. In addition to a substantial between‐female variation, sisters were more similar to each other than unrelated females, showing that egg size does also reflect heritable intrinsic female properties. Natural variation in egg size is thus not only determined by energy‐limitation, but also due to females allocating more resources to eggs laid in colder environments, thus increasing early survival of the chicks. That the positive correlation between temperature and egg investments that is found in a natural population is reversed under ad libitum food conditions demonstrates that wild great tits tradeoff own condition with survival prospects of their chicks as a function of available food, not ambient temperature.     

Reproductive responses to photoperiod and temperature by diapausing and nondiapausing populations of Sesamia nonagrioides Lef. (Lepidoptera − Noctuidae)

Abstract.  The influence of long- and short-day cycles on ovipostion and egg hatch of the corn stalk borer, Sesamia nonagrioides were investigated at a range of temperatures. Oviposition was suppressed when insects are exposed to long days through their immature stages and then transferred to short days after mating. Moreover, mean oviposition and egg hatch increased from 15 to 27.5 °C, whereas oviposition declined significantly at 30 °C at both photoperiodic regimes. Females derived from a diapausing population exposed to long days after mating showed a significantly higher egg production compared to females derived from a nondiapausing population. However, when females from a diapausing population were left to oviposit under short days, fewer eggs were produced compared to those exposed to long days after mating. Thus, photoperiod appears to affect reproductive traits of this species in a quantitative manner. Larval diapause duration is positively correlated with fecundity of the adults. There is also a positive correlation between pupal weight of individuals derived from a diapausing population and the postdiapause fecundity of adults.     

Effect of food concentration on the production and viability of resting eggs of the rotifer Brachionus: implications for the timing of sexual reproduction

1. Life‐table experiments with Brachionus calyciflorus test several hypotheses related to the idea that sexual reproduction in monogonont rotifers should occur when food resources are favourable. 2. The food concentration necessary for a fertilised mictic female to produce one phenotypically normal resting egg was higher than that for an amictic female to produce one daughter. At the lowest concentration of Cryptomonas erosa (1.25 × 10³ cells mL^?1), the lifetime fecundity of these two types of females was 0.9 and 1.4, respectively. 3. The lifetime fecundity of both fertilised mictic females and amictic females increased with food concentration to 3.4 resting eggs and 15.2 daughters female^?1, respectively. The approach to maximal fecundity with increasing food concentration was more rapid for fertilised mictic females, such that their lifetime fecundity relative to that of amictic females gradually decreased from 0.64 (at 1.25 × 10³ C. erosa mL^?1) to 0.22 (at 2.5 × 10⁴ C. erosa mL^?1). 4. The probability of a fertilised mictic female producing one or more abnormal resting eggs during her lifetime was high (approximately 75%). The mean proportion of abnormal eggs produced per female varied among the different food‐concentration treatments (26–38%) but was not higher at the low food concentrations. 5. The proportion of normal resting eggs that hatched was high (51–71%); those produced at low food concentrations were no less likely to hatch than those produced at high food concentrations. No abnormal resting eggs hatched. 6. The probability of a fertilised mictic female producing an abnormal resting egg increased rapidly with her age at all food concentrations. The probability of a normal resting egg hatching declined with maternal age at the low food concentration in one of two experiments. 7. The results support the idea that induction of mictic females should occur when food resources are good. Coincidence of sexual reproduction with low food availability risks low production of resting eggs for several reasons. Population size may be small, with a low probability of encounters between young mictic females and males, and fertilised mictic females may be unable to mature and produce resting eggs.     

FACTORS AFFECTING THE EGG SIZE OF RED-BILLED GULLS LARUS NOVAEHOLLANDIAE SCOPULINUS

The factors influencing the egg size of the Red-billed Gull Larus novaehollandiae scopulinus were studied at Kaikoura, New Zealand, between 1964 and 1972. In two- and three-egg clutches there was a trend for the eggs to become smaller in the sequence of laying. Length, breadth and volume of eggs of one-, two- and three-egg clutches declined significantly as the season progressed. The size of eggs from single-egg clutches tended to be smaller than eggs from two-egg clutches laid at the same time. There were correlations between the proportions of one-egg and of three-egg clutches being laid at a given period and the mean egg volume of two-egg clutches. When the mean egg volume of two-egg clutches increased there was a corresponding increase in the proportion of two- and three-egg clutches laid. When the mean egg volume of two-egg clutches decreased there was an increase in the proportion of single-egg clutches laid. The egg size of the Red-billed Gull showed no direct correlation with the abundance or availability of food; the largest eggs were produced early in the season when food was in short supply. In spite of an increase in the food supply in the middle of the breeding season, birds laying at this time produced smaller eggs than birds which laid earlier in the season. However, early breeders which relayed at the peak in food abundance on average produced a larger replacement clutch than originals laid early in the season. It is suggested that the birds nesting early in the season are able to produce the largest eggs because they are the most efficient foragers for food, and those which nest later in the season produce smaller eggs, even at peak food abundance, because of their inefficiency or inexperience. Early breeders laying replacement clutches tended to lay larger eggs and larger clutches than birds which are producing their first clutches at the same time. Two-year-old females laid eggs which were significantly shorter than older aged birds while the breadth and volume of the egg increased with the age of the female up to the fifth year. There was a trend for females to lay larger eggs when mated with older rather than younger males. No statistical differences in egg size were detected between females changing or retaining the partner of the previous season. Female body weight and egg volume were positively correlated in females weighing less than 275 g but not for heavier females. It is suggested that the seasonal decline in egg size and clutch size results from a decrease in the availability of food and the ability of the individual to exploit the resource.     

Egg quality and parental ornamentation in the blue tit Parus caeruleus

Components of avian egg quality often show remarkable variation between females and yet the causes of variation in this fitness-related trait remain poorly understood. We investigated the egg size and yolk carotenoid investment of blue tit Parus caeruleus females in relation to multiple parental traits. We show that females produce eggs with more colourful yolks when mated to ultraviolet (UV) attractive males. Since yolk carotenoids may enhance offspring fitness, but may be available to females in limiting amounts, the correlation we found suggests adaptive egg quality adjustment in response to mate attractiveness, but an experimental approach is required to rule out alternative explanations. Yolk colour was also correlated with laying date and yolk mass. Though the effect of laying date could not be explained by ambient temperature during egg formation, it suggests a proximate constraint of general carotenoid availability on yolk composition. Egg size was not affected by male attractiveness; however, females with a brighter crown produced larger eggs, suggesting that crown coloration might indicate individual quality in females too.     

Sexual reproduction and diapause of Hexarthra sp. (Rotifera) in short-lived ponds in the Chihuahuan Desert

1. In the life cycle of monogonont rotifers it is generally assumed that diapausing eggs invariably hatch into amictic stem females which produce female offspring parthenogenetically. Diapausing eggs are only produced by later generations after sexual reproduction has been induced by environmental cues. 2. We show that populations of an undescribed Hexarthra species inhabiting small temporary ponds in the Chihuahuan Desert deviate from this life cycle pattern. These ponds may dry within days and up to 85% of females were mictic. Females producing male offspring and diapausing eggs were observed 1 or 2 days, respectively, after ponds had filled with water. 3. Under laboratory conditions, 7–46% of females hatching from re‐hydrated sediments were sexual. Male offspring of these females can fertilise other mictic stem females leading to diapausing egg formation. In laboratory experiments, females produced fully developed diapausing eggs within 1.9 days at 20 °C and 1.2 days at 30 °C. 4. In addition, embryonic development time (1.1–0.3 days at temperatures between 12 and 30 °C) and juvenile period (2.1–0.5 days for the same temperature range) are shorter than those of other rotifer species. In short‐lived habitats, the potential for rapid population development and production of new diapausing eggs may be crucial in the long‐term survival of populations.     

Artificial miniaturization causes eggs laid by crowd-reared (gregarious) desert locusts to produce green (solitarious) offspring in the desert locust, Schistocerca gregaria

The mechanism underlying the phase-dependent polyphenism in hatchling body coloration was studied by testing for a possible causal relationship with egg size in the desert locust, Schistocerca gregaria. Crowd-reared (gregarious) females typically produce large, black offspring, whereas females reared in isolation (solitarious) deposit small, green offspring. We first tested for possible genetic differences in the role of egg foam by washing or separating eggs from two strains of locust. No solitarizing effect was found in either of the strains tested, supporting a previous finding, using another laboratory strain, to show that the hatchling body coloration and size are pre-determined in the ovary of the mother and no egg foam factor is involved in the control of the hatchling body coloration. Topical application of fenoxycarb, a juvenile hormone analog (JHA), and implantation of extra corpora allata (CA), taken from Locusta migratoria, caused gregarious female adults of S. gregaria to produce small eggs. Some eggs laid by CA-implanted females produced green hatchlings. All large eggs chosen among those deposited by gregarious females produced black hatchlings. When eggs were either kept on dry filter paper at nearly saturated relative humidity during embryogenesis or pricked with a needle so that some egg yolk was squeezed out, some produced small, green hatchlings. These results suggested that the amount of egg yolk or the availability of yolk material may determine the body coloration of hatchlings.     

Effects of experimentally increased egg production on female body condition and laying dates in the great skua Stercorarius skua

We investigated the effects of increased egg production on body condition as well as on measures of reproductive performance in great skuas, Stercorarius skua, over two subsequent years. We experimentally increased egg production from the normal two to six eggs. Six eggs might also be produced under natural circumstances after repeated clutch loss. After the production of the last egg we measured: (i) body mass, (ii) pectoral muscle, and (iii) haematocrit, total red blood cell count and mean corpuscular volume, as indicators of body condition. We took the same measurements of control females who had produced the normal clutch of two eggs. The measurements were repeated one year after the manipulation, and survival, laying dates, clutch sizes and hatching success were recorded for up to three consecutive years. After producing six eggs, females were lighter, had smaller pectoral muscles and lower haematological values than control females. Hatching success of eggs was significantly reduced. Even one year after the experiment there were still differences in body condition. Annual survival was not affected by the manipulations, although there was an indication that survival costs depended on whether chicks were raised after the increased egg production. While pair bonds and egg sizes were not affected in the post‐experimental year, females started breeding significantly later than in the previous year. Two years after the experiment laying dates had advanced again and were not different from those of control females. This pattern of maintaining survival and egg sizes, but delaying breeding in the post‐experimental year was found for two independent groups of females which had both been subjected to increased egg production. These results present evidence that increased egg production can have long‐term effects on female body condition and aspects of reproduction. However, although present, the costs of extra eggs appear to have been relatively small in the great skua in comparison to the two other bird species for which inter‐annual effects have been reported.     

中国石龙子雌体繁殖特征和卵孵化的地理变异

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

A photoperiod gene regulates vitellogenesis in Lymnaea peregra (Mollusca: Gastropoda: Pulmonata)

Summary

Populations of the fresh-water snail Lymnaea peregra from different localities vary in their capacity to lay eggs, responding either to long day or to short day photoperiods. These responses are genetically determined by a single gene locus with the long day allele dominant over the short day allele. Although previtellogenic stages of oogenesis are not affected by an inhibitory photoperiod, vitellogenesis is essentially shut down. The volumes of the dorsal bodies, which are endocrine organs that mediate vitellogenesis, are significantly smaller in snails maintained in an inhibitory photoperiod. Implantation of cerebral ganglia with attached dorsal bodies, both from egg laying animals and from dormant animals that have the potential to lay eggs in the postoperative photoperiod, into snails that were inhibited by insufficient photoperiod resulted in a significant increase in vitellogenesis in the ovotestes of the hosts. An increase in host dorsal body volume was also observed. The photoperiod gene appears to control some aspect of the cerebral ganglion that activates the dorsal body to produce a hormone that stimulates vitellogenesis in the ovotestes. Photoperiodic control of reproduction may be a factor contributing to the diverse life history strategies observed in this species.     

Temperature effects on egg size and their fitness consequences in the yellow dung fly Scathophaga stercoraria

Organisms and parts of an organism like eggs or individual cells developing in colder environments tend to grow bigger. A unifying explanation for this Bergmann's rule extended to ectotherms has not been found, and whether this is an adaptive response or a physiological constraint is debated. The dependence of egg and clutch size on the mother's temperature environment were investigated in the yellow dung fly Scathophaga stercoraria. Smaller eggs were laid at warmer temperatures in the field and the laboratory, where possible confounding variables were controlled for. As clutch size at the same time was unaffected by temperature, this effect was not due to a trade-off between egg size and number. Temperature-dependent egg sizes even persisted within individuals: when females were transferred to a cooler (warmer) environment, they laid third-clutch eggs that were larger (smaller) than their first-clutch eggs. The fitness consequences of these temperature-mediated egg sizes were further investigated in two laboratory experiments. Neither egg and pre-adult survivorship nor larval growth rate were maximized, nor was development time minimized, at the ambient temperature corresponding to the mother's temperature environment. This does not support the beneficial acclimation hypothesis. Instead, this study yielded some, but by no means conclusive indications of best performance by offspring from eggs laid at intermediate temperatures, weakly supporting the optimal temperature hypothesis. In one experiment the smaller eggs laid at 24 °C had reduced survivorship at all ambient temperatures tested. Smaller eggs thus generally performed poorly. The most parsimonious interpretation of these results is that temperature-mediated variation in egg size is a maternal physiological response (perhaps even a constraint) of unclear adaptive value. This revised version was published online in November 2006 with corrections to the Cover Date.     

Repeatability of Foreign Egg Rejection: Testing the Assumptions of Co‐Evolutionary Theory

Most theoretical models of coevolution between brood parasites, whether interspecific or conspecific, and their hosts explicitly assume consistent individual behaviour in host egg‐rejection responses. Accordingly, hosts cast as acceptors always accept, whereas ejectors always reject parasitic eggs when exposed to stable ecological conditions. To date, only few studies have attempted to test this critical assumption of individual repeatability in egg‐rejection responses of hosts. Here, we studied the repeatability of egg rejection in blackbirds (Turdus merula) and song thrush (T. philomelos), species in which females are reported to reject simulated, non‐mimetic foreign eggs at intermediate frequencies at the population level. However, intermediate rates of acceptance and rejection can be consistent with either or both intra‐ and interindividual variability in rejection behaviours. Our experiments revealed generally high individual consistency in these hosts’ responses to experimentally introduced non‐mimetic and mimetic model foreign eggs. Individuals also responded faster on average to second than to first trials within the same breeding attempts, but the difference was statistically significant only in blackbirds. These results are consistent with the critical assumption of co‐evolutionary models, that statistically egg rejection is mostly individually repeatable, but also reveal that some individuals in both species change their responses even within the short time‐window of one breeding attempt. The data suggest that individuals reject foreign eggs faster when perceived parasitism risk is greater because of repeated introductions of experimental parasitic eggs. We provide methodological recommendations to facilitate experimental and meta‐analytical studies of individual egg rejection repeatability and discuss how to reduce technical constraints arising from disparate treatments and variable sample sizes for future studies.     

Study on the concentration of circulating primordial germ cells (cPGCs) in early chick embryos

Experiments were conducted to elucidate the factor that influences the concentration of circulating primordial germ cells (cPGCs) in two-day old chick embryos. The concentration of cPGCs was observed to be highest at stage 14 (66.9 +/- 23.2 microliters) and decreased thereafter. However, considerable egg to egg variations in cPGC concentration, especially at stages 13, 14, 15, and 16 were observed. After conducting experiments to elucidate the source of egg to egg variation in cPGC concentration among embryos, it was revealed that there are hens that lay eggs which contain either constantly high (more than 80 PGCs/microliter) or constantly low (less than 30 PGCs/microliter) concentration of cPGCs. The results obtained from the present experiments showed that one of the major source of egg to egg variation in the concentration of cPGCs was due to the individual differences among females that produced the eggs.     

Male mate choice, male availability and egg production as limitations on polyandry in the red-necked phalarope

In sequentially polyandrous birds, a female's second mate faces a substantial risk of cuckoldry due to rapid mate switching and stored sperm. Secondary males are potentially available to females because males arrive asynchronously and/or are recycled into the breeding pool following nest predation. In a study of red-necked phalaropes, Phalaropus lobatus, a sex-role reversed shorebird, we tested the hypotheses that the proportion of females that become polyandrous is proximately limited by: (1) the ability of females to produce eggs, (2) the availability of males as mates and (3) male mate choice. In a colour-banded population in which rates of nest loss were manipulated by researchers, females that produced second clutches required similar lengths of time to complete clutches as those contemporaneously producing first clutches, and increased their egg size relative to their first clutch, making egg limitation unlikely. There was no correlation between an annual measure of males' availability as potential mates following nest losses and the proportion of females that were polyandrous. The majority of males that lost clutches (66%) re-paired with their original female significantly more often than expected by random mate choice (P<0.0001). Although 76% of polyandrous nestings involved renesting males, only 6% (N=46) of renesting males changed mates if their original female was still available. Renesting males that changed mates did not select for or against females that had already produced clutches (NS). Our results suggest that the level of polyandry in this species is not constrained by the females' abilities to produce more eggs or by the number of males recycling back into the breeding pool. Instead, the proportion of females that become polyandrous is limited by males choosing to renest with their original females, thereby decreasing their probability of caring for eggs potentially fertilized by a female's previous mate.     

Geographic variation in embryonic diapause,cold‐hardiness and life cycles in the migratory locust Locusta migratoria (Orthoptera: Acrididae) in China

To investigate geographic adaptation of the migratory locust Locusta migratoria in China, locusts were collected from six localities, ranging from 47.4°N to 19.2°N. Using offspring from the various populations, we compared embryonic diapause, reproductive traits, cold‐hardiness and adult body size. The incidence of embryonic diapause was influenced by the genetic makeup, parental photoperiod, and incubation temperature of the eggs. The northern strain (47.4°N) produced diapause eggs under all photoperiodic conditions, whereas the other strains produced a higher proportion of diapause eggs when exposed to a short photoperiod. The incubation temperature greatly influenced diapause induction. At a low temperature, all eggs entered diapause, even some of those from a tropical strain (19.2°N) in which no diapause was induced at high temperatures. Photoperiodic changes during the parental generation affected the incidence of embryonic diapause. Diapause intensity decreased with decreasing original latitude. Cold hardiness was compared by exposing eggs in diapause to either ?10 or ?20°C for various periods; the northern strain was more cold‐hardy than the southern strain, although some eggs in the tropical strain were probably not in a state of diapause. Adult body size and head width showed a complicated pattern of variation along the latitudinal gradient, whereas egg pod size (egg pod width and egg number) and hatchling weight tended to decrease with decreasing latitude. These results reveal that L. migratoria has adapted to local environments and that the latitudinal gradient appears to play an important role in shaping L. migratoria life cycle and development.     

Estimated, in situ, rates of egg production for the copepod centropages typicus (Krøyer) in the new york bight

Centropages typicus (Krøyer) and Pseudocalanus sp. are the two predominant copepods in the Continental Shelf waters immediately south of Long Island, New York. The estimated, in situ, rate of egg production for Centropages typicus ranged from 5 to 230 eggs female^?1 day^?1 during this study. Variability was partly attributed to seasonal variation in water temperature and partly to variations in the physiological condition of individual females. It could not be shown that the ability to produce eggs varied seasonally due to factors related to food. Egg production by Pseudocalamus sp. is probably from 1–10 eggs female^?1 day^?1. The two reproductive behaviours result in average abundances of adults that are approximately the same, although the peaks are at different times of the year, indicating that Centropages typicus has a higher mortality between the egg and adult stages than Pseudocalanus sp.