Life-history consequences of resource allocation of two bdelloid rotifer species

Two bdelloid species,Macrotrachela quadricornifera (aquatic species) andPhilodina vorax (terrestrial moss species), with similar survival but different age-specific fecundity schedules, were analyzed daily to determine growth rates and the volume invested in reproduction. The two species had similar growth patterns and started reproduction while still growing. In both, the size at maturity was independent of age.M. quadricornifera resumed growth after reaching a size plateau when reproduction was over, whileP. vorax continued to reproduce until death. Although the net reproductive rate ofP. vorax was consistently lower than that ofM. quadricornifera, the same percent of adult volume was invested in reproduction over its life time because its eggs were relatively bigger. The difference in reproductive rates is probably related to different partitioning of equal amounts of relative biomass: more small eggs for the aquatic rotifer vs. fewer big eggs for the terrestrial rotifer. Egg size might be related to the selective pressures of the environments.     

Clutch and egg size in ladybird beetles

There was a significant positive correlation between the number of ovarioles and clutch size in the 8 species of cocinellid studied. There was no intraspecific correlation between egg size and clutch size under standard conditions. These tactics are discussed in terms of the allocation of resources to reproduction.      

Variation in ovariole number and egg size of species of Dacus (Diptera; Tephritidae) and their relation to host specialization

Abstract. 1. An analysis of the number of ovarioles/ovary is presented for fourteen species of Dacus ranging from broad generalists (D.tryoni (Frogg.)) to strict host specialists (D.aglaia Hardy). For eight species data on egg size and the incubation time of eggs is also presented. Interrelationships among these life history variables and their relationships to host specialization were examined. 2. There was a broad positive relationship between the breadth of the natural host range (i.e. excluding cultivated fruits) and ovariole number (and hence potential fecundity). Highly polyphagous species had thirty-five to forty ovarioles/ovary while the specialists ranged from eight to twenty. 3. D.musae (Tryon), a specialist on banana, was an exception having an ovariole number similar to that of the most polyphagous species. 4. There was no clear relationship between egg size and ovariole number across eight species, though monophages were not fully represented in this analysis. Among these eight species there was no significant relationship between wing length and egg length, nor was there any such relationship among individuals within species. 5. There was considerable variation among species in the incubation time (at 25°C) for eggs, ranging from 24 h for D.cucumis French to 53 h for D.cacuminatus (Hering). This variation was only weakly related to egg size, though D.cucumis produced the largest eggs of any species examined. 6. Possible explanations for a relationship between potential fecundity and host range are discussed in terms of the balance between the abundance of host resources for generalists and their predictability for specialists. However, the observed relationship between ovariole number and host range must remain tentative, given that only fourteen species from one genus have been examined. Considerably more data is required for other dacines, for species in other tephritid subfamilies, and for other phytophagous insect groups to determine whether the relationship is generally applicable.     

Swimming speed and Reynolds numbers of eleven freshwater rotifer species

We obtained data on the swimming speed of 11 freshwater rotifer species. These data were analyzed in terms of Reynolds numbers given the fact that rotifers are in the evolutionary boundary between the use of cilia and swimming appendages. Swimming speed ranged from 0.174 to 0.542 mm ^–1. Philodina acuticornis odiosa was the fastest rotifer in terms of absolute speed. However, Gastropus hyptopus, the smallest of the rotifers analyzed, was the fastest (2.849) in terms of body-lengths s^–1. Reynolds numbers (Re) among the 11 species analyzed varied from 0.023 to 0.301. Lecane furcata had the smallest Re, while Epiphanes senta had the highest Re. The two bdelloid rotifers analyzed in this work swam five times faster than they crept. The importance of Reynolds numbers and drag coefficients are discussed in view of the present results and data found in the literature.     

First description of the serotonergic nervous system in a bdelloid rotifer: Macrotrachela quadricornifera Milne 1886 (Philodinidae)

Class Bdelloidea of phylum Rotifera comprises aquatic microinvertebrates that are known for both obligate parthenogenesis and for resisting desiccation through a dormant reversible state. In the frame of an investigation about the role of the nervous system in controlling life cycle, reproduction and dormancy, we describe the serotonergic system of a bdelloid, Macrotrachela quadricornifera, using serotonin immunohistochemistry and confocal laser scanning microscopy. Serotonin immunoreactivity is present in the cerebral ganglion, lateral nerve cords and peripheral neurites. The cerebral ganglion consists of perikarya that send neurites cephalically to the rostrum and corona. A pair of neurites exits the cerebral ganglion as lateral nerve cords, and proceeds caudally to the pedal ganglion where additional neurites enter the foot. Based on the location of serotonergic immunoreactivity, we hypothesize that the neurotransmitter is involved in both motor activity (e.g., ciliary beating, inchworm-like locomotion) and sensory activity. A comparison between the serotonergic nervous systems of M. quadricornifera and species of Monogononta reveals differences in the numbers and patterns of cerebral perikarya, peripheral perikarya, and periperhal neurites. These differences may have functional significance for understanding adaptations to specific environments and/or systematic significance for reconstructing the rotiferan ground pattern.     

Bdelloid rotifers in aerophytic mosses: influence of habitat structure and habitat age on species composition

The rotifer species composition from two different moss species growing on roofs of different ages was investigated.     

Avian egg size: variation within species and inflexibility within individuals

Egg size is a widely-studied trait and yet the causes and consequences of variation in this trait remain poorly understood. Egg size varies greatly within many avian species, with the largest egg in a population generally being at least 50% bigger, and sometimes twice as large, as the smallest. Generally, approximately 70% of the variation in egg mass is due to variation between rather than within clutches, although there are some cases of extreme intra-clutch egg-size variation. Despite the large amount of variation in egg size between females, this trait is highly consistent within individuals between breeding attempts; the repeatability of egg size is generally above 0.6 and tends to be higher than that of clutch size or laying date. Heritability estimates also tend to be much higher for egg size (> 0.5) than for clutch size or laying date (< 0.5). As expected, given the high repeatability and heritability of egg size, supplemental food had no statistically significant effect on this trait in 18 out of 28 (64%) studies. Where dietary supplements do increase egg size, the effect is never more than 13% of the control values and is generally much less. Similarly, ambient temperature during egg formation generally explains less than 15% of the variation in egg size. In short, egg size appears to be a characteristic of individual females, and yet the traits of a female that determine egg size are not clear. Although egg size often increases with female age (17 out of 37 studies), the change in egg size is generally less than 10%. Female mass and size rarely explain more than 20% of the variation in egg size within species. A female's egg size is not consistently related to other aspects of reproductive performance such as clutch size, laying date, or the pair's ability to rear young. Physiological characteristics of the female (e.g. endogenous protein stores, oviduct mass, rate of protein uptake by ovarian follicles) show more promise as potential determinants of egg size. With regards to the consequences of egg-size variation for offspring fitness, egg size is often correlated with offspring mass and size within the first week after hatching, but the evidence for more long-lasting effects on chick growth and survival is equivocal. In other oviparous vertebrates, the magnitude of egg-size variation within populations is often as great or greater than that observed within avian populations. Although there are much fewer estimates of the repeatability of egg size in other taxa, the available evidence suggests that egg size may be more flexible within individuals. Furthermore, in non-avian species (particularly fish and turtles), it is more common for female mass or size to explain a substantial proportion of the variation in egg size. Further research into the physiological basis of egg-size variation is needed to shed light on both the proximate and ultimate causes of intraspecific variation in this trait in birds.     

Prefeeding larval development time is not correlated with egg size in regular echinoids (Strongylocentrotus species)

Summary

We compared prefeeding development times, from fertilized egg to prism larva, for Strongylocentrotus embryos from four clutches of eggs (each from a different species) differing in size. Development times did not vary consistently with egg diameter, and trends among eggs of different sizes varied with stage of development. In some cases, development times for eggs of intermediate diameter (S. franciscanus) were longer than those for larger or smaller eggs. Although mean egg diameters in clutches ranged from 84 μm (S. purpuratus) to 162 μm (S. pallidus), differences in development time to the last embryonic stage (prism) were very small. We conclude that the inverse relationship between parental investment in offspring and premetamorphic development time in echinoids depends only on the functional consequences of reduced size of feeding larval stages: effects of egg size on prefeeding development time are not evident.     

食物浓度对角突臂尾轮虫种群增长、个体大小和卵大小的影响

以蛋白核小球藻为食物 ,应用群体累积培养法研究了食物浓度对角突臂尾轮虫种群增长、个体大小和卵大小等的影响 .结果表明 ,食物浓度对角突臂尾轮虫种群增长率、个体大小和卵大小均有极显著影响 .其中 ,轮虫种群增长率与食物浓度间呈曲线相关 ;当食物浓度为 8.2 4 5 3× 10 6cells·ml-1时 ,种群增长率达最大值 0 .6 0 85d-1;在所研究的食物浓度范围内 ,轮虫个体具有随食物浓度的增大而增大的趋势 ,轮虫卵体积在中等食物浓度范围 (6 .0× 10 6～ 9.0× 10 6cells·ml-1)时较大     

Impacts of egg and larval size on survival and growth of Atlantic cod under different feeding conditions

Large eggs (1·38 mm) of Atlantic cod reared in the laboratory produced large larvae. However, large larvae had low survival rates. Results also indicated that the first few days' of growth of cod larvae mainly resulted in an increase in mass. Exogenous feeding tended to result in faster growth than endogenous feeding. In the delayed feeding groups (larvae not fed until 67 degree-days), larvae from large eggs grew faster than those from small eggs (1·28 mm) after feeding commenced, while there was no significant difference in growth rate within feeding groups. Compensatory growth was detected in the delayed feeding groups.     

Effect of female size on fecundity and egg size in white-spotted charr: comparison between sea-run and resident forms

The relationships between fecundity, egg size and female size of sea-run form were compared with resident form, using white-spotted charr, Salvelinus leucomaenis. Both fecundity and egg size increase with female size. However, the relationship between egg size and female size differed significantly between the resident and sea-run forms. Egg sizes of sea-run and resident were similar even though sea-run fish were much larger. ? 1998 The Fisheries Society of the British Isles     

Parent–offspring conflict and selection on egg size in turtles

The trade‐off between offspring size and number can present a conflict between parents and their offspring. Because egg size is constrained by clutch size, the optimal egg size for offspring fitness may not always be equivalent to that which maximizes parental fitness. We evaluated selection on egg size in three turtle species (Apalone mutica, Chelydra serpentina and Chrysemys picta) to determine if optimal egg sizes differ between offspring and their mothers. Although hatching success was generally greater for larger eggs, the strength and form of selection varied. In most cases, the egg size that maximized offspring fitness was greater than that which maximized maternal fitness. Consistent with optimality theory, mean egg sizes in the populations were more similar to the egg sizes that maximized maternal fitness, rather than offspring fitness. These results provide evidence that selection has maximized maternal fitness to achieve an optimal balance between egg size and number.     

Influence of egg size differences within egg clutches on larval parameters in nine libellulid species (Odonata)

Abstract.  1. In libellulids, egg size differs between species and populations. There are also size differences within egg clutches of individual females.
2. Past experiments suggest that there are two different types of egg clutches in libellulids. Egg size decreases significantly during oviposition in species that perform non-contact guarding during oviposition. In contrast, in species ovipositing in tandem, egg size is randomly distributed.
3. This study deals with the possible consequences of egg size variation within the different egg clutch types. The study examined whether there is a correlation between egg development time, offspring sex or larval size and egg size.
4. The current experiments were conducted in Namibia and Germany. Five non-contact guarding and four tandem guarding libellulid species were used.
5. In some species larger eggs needed more time to develop, in some species no correlation between egg size and egg development time could be found, whereas in other species larger eggs developed faster.
6. The sex ratio was biased towards females in Leucorrhinia dubia and in Sympetrum striolatum and egg size was not associated with gender.
7. In both egg clutch types larger eggs resulted in larger larvae. In this study, evidence was found that the effects of egg size diminished with progressing larval development under good conditions. However, it is possible that the effects may have a greater influence under harsh circumstances.     

Seasonal variation of egg size and number in a Daphnia pulex population

Seasonal variation of egg size and number was examined in a Daphnia pulex population inhabiting a vernal pond. In this population, size at maturity declines at midseason, probably as an adaptive response to size-selective predation by larvae of the salamander Ambystoma. The larger early season individuals produce more and larger eggs than the smaller late season individuals. Age at maturity does not vary between seasons. Laboratory experiments indicate that temperature may affect egg size, egg number and size at maturity. However, field data suggest that temperature accounts for only a small fraction of the total variation in egg size and number. Indirect measures of nutrition indicate that food limitation does not cause the seasonal decline in egg size and number. The seasonal change in reproductive traits is well correlated with changes in invertebrate and vertebrate predation. Examination of predator feeding preferences and their impact on Daphnia mortality indicate that variation of reproductive traits is most likely a complex adaptation to changing predation regimes.     

Correlations between egg size and egg energetic content within and among biotypes of the genus Poeciliopsis

That a positive correlation exists between egg size and egg energetic content is an assumption of empirical and theoretical studies of life-history evolution. Although assumed, this relationship lacks substantiative support, particularly at the intraspecific level. To this end, we evaluated the validity of this assumption within and among clonal and bisexual females of the desert fish Poeciliopsis . As anticipated, we found generally high correlations between the two variables at all levels studied. Thus, egg volume remains a reliable and often precise indicator of maternal investment in this species.     

Reproductive variation and adult size in two co-occurring grasshopper species

ABSTRACT. 1. Egg sizes and clutch sizes of the grasshoppers Chorthippus brunneus (Thunb.) and Myrmeleotettix maculatus (Thunb.) were compared among three years and among three sites less than 1.3 km apart. Relationships between these reproductive traits and date of egg laying, body size and body condition were sought.
2. M.maculatus , the smaller species, laid fewer but larger eggs; and only the eggs of this species showed significant differences between sites and years.
3. A negative correlation between egg size and number per clutch was evident between species and years, but generally not among sites and among individuals of a population.
4. However, a hidden negative correlation between egg size and number was uncovered within populations when the relationship was examined for females of a given mature weight.
5. Variation in the number of eggs per clutch was explained statistically by a positive relationship between female body weight and egg number. Also, both interpopulation and intrapopulation comparisons revealed that for M.maculatus , but not for C.brunneus , females with long hind femurs laid large eggs.     

Effect of host diet and adult parasitoid diet on egg load dynamics and egg size of braconid parasitoids attacking Anastrepha ludens

The quantity and quality of host nutrients can affect fitness‐related traits in hymenopteran parasitoids, including oogenesis. The present study tested the prediction that a high host quality will influence oogenesis‐related traits positively in synovigenic parasitoids, and that a high‐quality adult parasitoid diet can positively affect the same parameters, potentially compensating for development on low‐quality hosts. Four braconid parasitoid species with contrasting life histories are reared on a low‐quality diet [Anastrepha ludens Loew (Diptera: Tephritidae) larvae reared on mango] or a high‐quality (artificial) diet. Adult parasitoids are provided with a high‐quality (honey ad libitum), moderate‐quality (honey every other day) or low‐quality (guava pulp) diet. Generalist species that encounter high variation in host quality naturally are predicted to be more flexible in dealing with nutrient shortfalls than specialist species. By contrast to the predictions, low‐quality hosts yield parasitoids with higher egg loads in two species: Opius hirtus Fisher and Diachasmimorpha longicaudata Ashmead. However, as predicted, a high‐quality adult diet exerts a positive effect on egg load (Utetes anastrephae Viereck), egg size (Doryctobracon crawfordi Viereck) and egg maturation rate (D. longicaudata, O. hirtus and U. anastrephae). The generalist D. longicaudata varies in egg load and maturation rate depending on host quality and adult diet, respectively. Evidence of the combined effect of both factors on parasitoid fertility is presented for the specialist O. hirtus. The theoretical and practical implications of these findings are discussed.