Maternal investment and size-number trade-off in a bee, Megachile apicalis, in seasonal environments

Maternal investment in offspring size and number differed between spring- and summer-emerging individual females of Megachile apicalis, a solitary multivoltine bee. Data from experimentally initiated female populations indicated that spring-emerging females produced a relatively large number of progeny but allocated a small amount of food to each, resulting in small progeny. Adult females of larger body sizes provisioned food at a greater rate than did smaller females, and this body-size effect was significant in spring-emerging females. The large body size of these females allowed them to increase the number of progeny produced under the abundant floral resources that occurred during the spring. Conversely, summer-emerging females produced fewer progeny under the diminishing resources for brood production, but allocated each with more food, producing larger progeny, most of which emerged in the spring of the following year. Field data using trap-nests also indicated the same pattern of seasonal offspring size allocation found in the experimental populations. This maternal investment strategy entails a trade-off between the size and number of progeny, so that the daughters upon emergence can best perform in their brood production under the seasonally variable environments where they reproduce.     

Phenotypic variability in nesting success among Osmia lignaria propinqua females in a glasshouse environment: (Hymenoptera: Megachilidae)

Abstract. 1. The phenotypic variability of several estimates of fitness among seventeen nesting female O.lignaria Cresson was examined in a glasshouse provided with abundant resources.
2. Females exhibited wide variation in: (a) number of nests and cells made and in their rate of construction, (b) the incidence of mortality of offspring, and (c) the percentage of male offspring produced (52–100%).
3. In confirmation of earlier field studies: (a) more offspring of both sexes were produced during the first half of the nesting season, (b) most female offspring were produced early in the nesting season, (c) most parental investment during the last half of the flight season was made in male offspring, (d) there was a decrease in offspring size with season, with females decreasing more than males, and (e) the ratio of female/male body weight was = 1.8. These results appear to be due to ageing rather than to a reduction in resource availability.
4. No relation between female size and fecundity was evident.
5. There was no evidence that small females tended to produce a greater proportion of the smaller sex (males) than did large females.
6. Smaller offspring of both sexes had a much greater probability of dying overwinter than did large offspring. However, where the sexes overlapped in size (large males, small females), almost all females died and almost all males survived. We hypothesize that as size of offspring produced declines with season, a greater proportion of males are produced because they have a much greater probability of surviving at small body sizes.     

Does variation in female body size affect nesting success in Dawson’s burrowing bee,Amegilla dawsoni (Apidae: Anthophorini)?

Abstract.  1. Females of Dawson's burrowing bees vary in body weight over a twofold range. Despite the potential for differences in body weight to affect several aspects of the competition among nesting females, no clear advantages were documented for larger females.
2. Nesting females were not consistently larger than emerging females, nor was there a consistent relationship between body size and the weight of pollen and nectar carried to the nest on provisioning trips. At one nesting location, larger females did not produce larger pre-pupal offspring nor did they produce offspring at a faster rate than their smaller nesting companions.
3. In addition, large body size was not associated with greater success in nest defence despite the fact that nesting females regularly encountered intruders in their burrows. Residency, not body size, determined the outcome of almost all contests for control of a nest burrow. The absence of a large body size effect here appears to stem from an intruder strategy designed to enable nest-searching females to acquire burrows that had been abandoned through death or dispersal of their original owners rather than securing existing nests through an aggressive takeover strategy.
4. Thus, although large body size conveys significant fitness advantages to males, this attribute does not promote female success in either provisioning or defending their nests.     

Fecundity and oviposition ofEucelatoria bryani, a gregarious parasitoid ofHelicoverpa zea andHeliothis virescens

We examined longevity, fecundity, and oviposition strategies ofEucelatoria bryani Sabrosky (Diptera: Tachinidae), a gregarious endoparasitoid ofHelicoverpa zea (Boddie) andHeliothis virescens (F.) (Lepidoptera: Noctuidae). Longevity of adult femaleE. bryani was not related to body size. In contrast to longevity, largerE. bryani females had greater potential fecundity than smaller females, as determined by the number of embryonated eggs present in the common oviduct. However, female parasitoid size did not affect primary clutch size (number of eggs deposited in a host). Because embryos in eggs located in the ovisac were larger than those located elsewhere in the common oviduct, maximum primary clutch size may be physiologically limited by the number of fully mature eggs a female has available at one time.E. bryani females adjusted primary clutch size in response to host size, for bothH. zea andH. virescens. This adjustment appears to be adaptive because females did not overexploit hosts by depositing more larvae than a host could support. Adult emergence was not related to host size. Although host weight positively influencedE. bryani progeny weight, increases in progeny size with host size were counterbalanced by increases in primary clutch size with host size.     

Size variation and reproductive success of female Aedes punctor (Diptera: Culicidae)

Abstract. 1. Variation in size (wing length) of females and males within a population of Aedes punctor (Kirby) at emergence was recorded in northern Britain during 1984 and 1985.
2. Wing length correlated well with body dry weight, confirming its usefulness as a measure of body size. In 1984, but not in 1985, mean size decreased significantly as emergence progressed.
3. The size of host-seeking females caught at human bait varied seasonally. This was partly accounted for by size variation during emergence.
4. Of females which fed to repletion, the largest spent least time in contact with the host.
5. In the laboratory, wing length correlated well with potential fecundity (number of ovarioles) and less well with actual fecundity (number of matured follicles) after feeding on human blood.
6. In the field, larger females were more successful at locating hosts, developed more egg clutches in a lifetime and generally lived longer than did smaller ones. Larger females appear to enjoy greater reproductive success than do smaller females.     

Relationships between body size,reproductive traits,and food resource in three species of tropical flesh flies

Intra- and inter-specific comparisons in progeny size and clutch size were used to identify possible selection pressures acting on three sympatric species of ovoviviporous flesh flies. Both progeny and clutch sizes increased with body weight of the female parent in all species. There was no evidence for a simple trade-off between the two traits. In one species, the larger the female adult the smaller the relative biomass of larvae per clutch (total weight of larvae/body weight of female parent). Female flies produced similar progeny and clutch sizes over successive batches. Variation in progeny size did not influence either larval survival or duration of larval and pupal development. However, larger first instar larvae tended to form larger pupae in two of the species. The experiments testing the effect of progeny size on pupal weight under limited food conditions suggest a selective advantage for larger progeny size.     

Intrinsic Factors Affecting Female Choice in House Crickets: Time Cost, Female Age, Nutritional Condition, Body Size, and Size-Relative Reproductive Investment

Few studies have examined potential costs of female choice and factors intrinsic to females that affect choice. To examine these factors, female house crickets, Acheta domesticus, were presented with a simultaneous choice between tapes of a priori attractive and unattractive male chirps. Females varied in age, nutritional condition, body size (potential fecundity), and size-relative reproductive investment. Female age had a significant effect on female choosiness: young females were selective, whereas older females were not selective. Nutritional condition, body size, and size-relative reproductive investment did not affect female choice. Females that chose the call of the attractive male spent approximately twice as long choosing as females that chose the unattractive male call.     

The interplay between natural and sexual selection in the evolution of sexual size dimorphism in Sceloporus lizards (Squamata: Phrynosomatidae)

Sexual size dimorphism (SSD) evolves because body size is usually related to reproductive success through different pathways in females and males. Female body size is strongly correlated with fecundity, while in males, body size is correlated with mating success. In many lizard species, males are larger than females, whereas in others, females are the larger sex, suggesting that selection on fecundity has been stronger than sexual selection on males. As placental development or egg retention requires more space within the abdominal cavity, it has been suggested that females of viviparous lizards have larger abdomens or body size than their oviparous relatives. Thus, it would be expected that females of viviparous species attain larger sizes than their oviparous relatives, generating more biased patterns of SSD. We test these predictions using lizards of the genus Sceloporus. After controlling for phylogenetic effects, our results confirm a strong relationship between female body size and fecundity, suggesting that selection for higher fecundity has had a main role in the evolution of female body size. However, oviparous and viviparous females exhibit similar sizes and allometric relationships. Even though there is a strong effect of body size on female fecundity, once phylogenetic effects are considered, we find that the slope of male on female body size is significantly larger than one, providing evidence of greater evolutionary divergence of male body size. These results suggest that the relative impact of sexual selection acting on males has been stronger than fecundity selection acting on females within Sceloporus lizards.     

Cryptic maternal effects in Hippodamia convergens vary with maternal age and body size

Maternal effects can mold progeny phenotypes in various ways and may constitute ecological adaptations. By examining the effect of oviposition sequence on progeny produced by different size classes of female ladybird beetles (produced by controlling larval access to food), we show that maternal signals can change through adult life and alter the developmental programs of progeny, ostensibly to synchronize their life histories with predictable resource dynamics, thus maximizing maternal fitness. We also show that female body size, as determined by larval food supply, interacts with female age to influence progeny fitness. When fed ad libitum as adults, small females reared with limited food access laid fewer, smaller eggs than large females reared with ad libitum food access. Maternal body size interacted with oviposition sequence to influence progeny development, but the latter had greater impact. Eggs laid later by medium and large females hatched faster than those laid earlier, larvae fed longer in the fourth instar, their pupation period was shorter, total developmental time was reduced, and adults emerged with greater mass, most notably daughters. Oviposition sequence effects on progeny from small mothers were non‐significant for total developmental time and progeny mass. Only large mothers increased egg size over time and egg mass was not consistently correlated with developmental parameters, indicating that progeny phenotype was impacted by other, more cryptic, maternal signals. Such signals appear costly, as food limitation during development constrained not only fecundity and egg size but also maternal ability to manipulate progeny phenotype. The production of faster‐developing offspring that mature to larger sizes late in the oviposition cycle may be adaptive for exploitation of ephemeral aphid outbreaks with predictable dynamics of prey abundance and competition.     

Sex ratio regulation in Coccygomimus turionella Linnaeus (Hymenoptera: Ichneumonidae) and its ecological implications

Abstract. 1. Sex regulation and its relevance to the ecology of a k-selected pupal parasitoid was investigated in Coccygomimus turionellae.
2. The ratio varied with host size, females predominating in large hosts.
3. Egg transfer experiments and comparative mortality rates among the progeny of virgin and inseminated females demonstrated that the phenomenon was due to parental behaviour.
4. The study of the mechanism confirmed Aubert's hypothesis of host size estimation with the addition that the host had to be exposed from the poles and had to contain the proper host kairomones.
5. Host size was highly correlated to parasitoid fecundity via influences on size and longevity but not the number of ovarioles per female or daily egg production.
6. Host encounters are more limiting than egg production and host size had no effect on host acceptance.
7. Sex regulation allows a maximal host encounter rate at the same time that it maximizes the reproductive potential of female progeny.
8. Low host density increased the production of female progeny resulting in more offspring searching for the limited resource. Concealed hosts and a high host density resulted in a shift towards a Fisher 1:1 sex ratio.     

Differential Sperm Priming by Male Sailfin Mollies (Poecilia latipinna): Effects of Female and Male Size

Recent interest in sperm competition has led to a re‐evaluation of the ‘cheap sperm’ assumption inherent in many studies of sexual selection. In particular, mounting evidence suggests that male sperm availability can be increased by the presence of females. However, there is little information on how this interacts with male traits presumably affected by female mate choice, such as larger size. This study examines the effects on male sperm availability of female presence, male body size, and female body size in the sailfin molly, Poecilia latipinna. Individual males of variable body sizes were isolated in divided tanks for 3 d, after which time either a female or no female was added to the other side of the tank. Prior to the treatments, larger males had more stripped sperm than smaller males. Female presence significantly increased the amount of sperm males primed, but this effect was strongest in small males. Furthermore, males showed a greater priming response in the presence of larger females than in the presence of smaller females. These results demonstrate that the presence of sexually mature females increases the amount of sperm males have for insemination. Furthermore, traits that indicate female fecundity may be used by males as cues in male mate choice.     

The effect of male mating history on paternal investment, fecundity and female remating in the seed beetle Callosobruchus maculatus

1. In many organisms, males provide nutrients to females via ejaculates that can influence female fecundity, longevity and mating behaviour. The effect of male mating history on male ejaculate size, female fecundity, female longevity and female remating behaviour in the seed beetle Callosobruchus maculatus was determined.
2. The quantity of ejaculate passed to females declined dramatically with successive matings. Despite the decline, a male's ability to fertilize a female fully did not appear to decline substantially until his fourth mating.
3. When females multiply mated with males of a particular mated status, the pattern of egg production was cyclic, with egg production increasing after mating. Females multiply mated to virgins had higher fecundity than females mated to non-virgins, and females mated to twice-mated males had disproportionately increased egg production late in their life.
4. Females that mated to multiple virgins, and consequently laid more eggs, experienced greater mortality than females mated only once or mated to non-virgins, suggesting that egg production is costly, and rather than ameliorating these costs, male ejaculates may increase them by allowing or stimulating females to lay more eggs.
5. Females mating with non-virgin males remated more readily than did females mated to virgins. Females given food supplements were less likely to remate than females that were nutritionally stressed, suggesting that females remate in part to obtain additional nutrients.     

Body size and fecundity in the waterstrider Aquarius remigis: a test of Darwin's fecundity advantage hypothesis

The general female bias in body size of animals is usually attributed to fecundity selection. While many studies have demonstrated a positive relationship between body size and fecundity, the most common interpretation of fecundity selection is that larger females have larger abdomens and can hold more eggs, yet the relationship between abdomen size and fecundity has rarely been examined. For the waterstrider, Aquarius remigis, we find a significant relationship between body size and fecundity and demonstrate that the target of fecundity selection is abdomen size. Thus, larger females have higher fecundities because they have larger abdomens and not because of their total size per se. The rate at which fecundity increases with increasing abdomen size exceeds that which would be expected due to a simple volume constraint and suggests that other factors, such as increased ability to obtain resources, may contribute to the increase in fecundity with body size. Selection intensities estimated from our data indicate that fecundity selection could be a significant selective force on both total and abdomen lengths. Previous studies have found that abdomen size increased faster than body size and thus, larger females had relatively larger abdomens. The relationship of abdomen length and thorax length in A. remigis is hypoallometric and indicates that larger females have relatively smaller abdomens. We hypothesize that this may reflect conservation of abdomen size in females developing under poor conditions. Finally, while egg size is not directly related to body size, we find a trade-off between egg size and number when female abdomen length is held constant, suggesting that selection on egg size may influence abdomen length only indirectly through its effects on fecundity.     

Female fecundity and early offspring growth in the guppy, <Emphasis Type="Italic">Poecilia reticulata</Emphasis>

We examined the relationships between family (female parentage), body size of females, brood retention time between mating and parturition, female fecundity, and early growth of offspring in the guppy Poecilia reticulata. Mature, virgin females from a single brood were mated with a single male. Results of generalized linear models indicate that the effect of the family on female fecundity and offspring growth was significant, which suggested that these traits are genetically determined to a certain extent. Larger females at the time of mating produced larger broods, although female body size at the time of parturition did not affect brood size, in contrast to the results of some previous studies in guppies. Brood size was negatively associated with the body size of neonates. Results highlighted significant associations between brood retention time and female fecundity as well as offspring growth. In addition, the interaction between the family and brood retention time was significantly associated with female fecundity and offspring growth. Females of some families had longer retention times of larger broods, whereas those of other families had shorter retention times of smaller broods. On the other hand, females with longer brood retention times produced smaller neonates with slower growth. Since the family also affected the brood retention time, selection may work against the duration of brood retention of females via the size, growth and number of offspring, depending on environmental factors such as the intensity of predation or competition in neonates.     

Mate Choice and Spawning Success in the Fighting Fish Betta splendens: the Importance of Body Size, Display Behavior and Nest Size

Courtship displays should be exaggerated enough to attract mates and yet tempered so as not to deter them. We tested this hypothesis in the fighting fish Betta splendens by studying courtship displays and body size and their relationships with male parental quality and female fecundity, as well as the effects of display behavior and body size on mate choice decisions and spawning success. Because of their high degree of parental investment, males are expected to be discriminating in their choice of mates. Males who displayed more frequently built larger nests, a measure of parental quality, but larger males did not. When females were paired with males with high display rates, however, the pair had fewer eggs in their nest, even when accounting for female body mass. In a mate choice test using computer‐generated male stimuli that differed only in display behavior, females showed no preferences for displaying males vs. non‐displaying males, or for males with higher display rates vs. lower display rates. In similar tests in which the computer‐generated males differed only in size, females preferred larger males, but also preferred males that differed with respect to body size (negative assortative mating). Males preferred computer‐generated females that performed courtship displays over non‐displaying females, but showed no preferences for female body size. Neither a female's body size nor her display behavior was a significant predictor of her fecundity as estimated by the number of eggs released during spawning. Thus, our results suggest that female B. splendens must balance male parental quality (nest size) with the risk of potentially disruptive or dangerous behavior during spawning, and that females may minimize these risks through negative size‐assortative mating. Female display behavior, while unrelated to fecundity in our study, may attract males because it indicates reproductive readiness or serves a species‐recognition function.     

Fitness Consequences of Maternal Effects in Streblospio benedicti (Annelida: Polychaeta)

SYNOPSIS. The degree to which a female partitions resourcesbetween fecundity and per offspring investment is a centralquestion in life-history theory. Maternal effects may influencethe nature of this tradeoff through their effect on per offspringinvestment and subsequent offspring fitness. The purpose ofthis study was to determine the effect of female age and sizeon brood size (number of offspring), per offspring investment,and fitness in the polychaete Streblospio benedicti. Early stageembryos were collected from brooding females of known age andsize over a period of 100 days; these embryos were counted andanalyzed for their C and N content. Female size had a positiveeffect on brood size; larger females produced larger broods.However, brood size decreased with female age (females did notincrease in size after reaching sexual maturity). Brood sizedeclined 20–46% between 60 and 160 days of age. Duringthis same age period per offspring investment, measured in termsof C and N, increased by 25%. Offspring survivorship and sizeat two weeks post-release from the female were used as measuresof offspring fitness. Offspring survivorship increased 28% between60 and 160 days of age. Increased growth in offspring from olderfemales resulted in a 23% increase in offspring size at twoweeks. Including the maternal age effect in two population modelsfor S. benedicti increased population growth rate (). Populationgrowth was increased to a greater degree when the maternal effectwas modeled by enhancing offspring survival compared to whenfecundity was increased by the same proportional amount. Thissuggests that the maternal effect may be adaptive, particularlywhen conditions for offspring survival and growth are poor.     

Components of male fitness in relation to body size in Epirrita autumnata (Lepidoptera, Geometridae)

Abstract. 1. The effect of body size on different components of male fitness was studied for Epirrita autumnata , a geometrid known for its eruptive population dynamics. Body size is the main determinant of female fecundity in this species.
2. Longevity of males was found to have a weak negative correlation with body size at low temperatures. No significant correlation was found at higher temperatures.
3. We found no correlation between male size and female fecundity or egg size which is consistent with the small size of spermatophores in this species.
4. Small and large males were equally successful when allowed to compete for females in laboratory conditions.
5. In one or two field collections, males found mating were larger than males found singly. Large males also had an advantage in finding of virgin females, offered experimentally. No size-assortative mating was recorded.
6. We conclude that size-dependent mate location ability is the factor accounting for most of the variance in male fitness in E.autumnata. The dependence of fitness on body size may well be equally strong in males and females.     

The evolution of sexual size dimorphism in cottontail rabbits (Sylvilagus,Leporidae)

In mammals, ‘female‐biased’ sexual size dimorphism (SSD), in which females are larger than males, is uncommon. In the present study, we examined Sylvilagus, a purported case of female‐biased SSD, for evolutionary correlations among species between SSD, body‐size, and life‐history variables. We find that: (1) although most species are female‐biased, the degree and direction of SSD vary more than was previously recognized and (2) the degree of SSD decreases with increasing body size. Hence, Sylvilagus provides a new example, unusual for a female‐biased taxon, in which allometry for SSD is consistent with ‘Rensch's Rule’. As a corollary to Rensch's Rule, we observe that changes in SSD in Sylvilagus are typically associated with larger, more significant changes in males than females. Female‐biased SSD could be produced by selection for larger females, smaller males, or both. Although larger female size may be related to high fecundity and the extremely rapid fetal and neonatal growth in Sylvilagus, we find little evidence for a correlation between SSD and various fecundity‐related traits in among‐species comparisons. Smaller male size may confer greater reproductive success through greater mobility and reduced energetic requirements. We propose that a suite of traits (female dispersion, large male home ranges, reduced aggression, and a promiscuous mating system) has favoured smaller males and thus influenced the evolution of SSD in cottontails. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 141–156.     

Modelling age‐ and density‐structured reproductive biology and seasonal survival of Apanteles galleriae Wilkinson (Hym., Braconidae)

Abstract: The biology of Apanteles galleriae Wilkinson, an important biological control agent of wax moths, is well described in the literature. We developed models simulating the functional response of fecundity and female progeny proportion of adult females as a function of age, host and/or parasitoid density to integrate current knowledge. Daily pattern of age‐related fecundity and female progeny proportion of different parasitoids was also examined. We investigated the effect of sex, mating status and seasonal time on adult longevity. We derived survival data of females in two different seasonal periods. We found that 50% of adult life span is important for an efficient fecundity. The patterns of host and/or parasitoid density‐dependent fecundity and sex ratio varied considerably. The highest fecundity and female progeny proportion occurred with one parasitoid and one female equivalent host. Longevity of adults was affected by sex and month periods, but mating status did not affect their longevity. Female survival was greater between December and May relative to June and November. Our results indicated that age, host and parasitoid density, and the timing of rearing influenced the life processes of parasitoids.     

Ejaculate size, second male size, and moderate polyandry increase female fecundity in a seed beetle

Several hypotheses have been proposed to explain the evolutionof polyandry in species that provide nuptial gifts. When nuptialgifts are in the form of nutritional elements in the ejaculateand ejaculate size is correlated with male body size, femalescan accrue both direct (nutritional) and indirect (genetic)benefits from multiple mating. We examined remating decisionsin females of the seed beetle Stator limbatus and, using pathanalysis, examined the effects of male body size on the sizeof his ejaculate, the amount of ejaculate that was successfullytransferred to females, and the overall effect of these variableson female fecundity. Larger males produced larger ejaculatesand consequently transferred a larger ejaculate to females,but the effects on female fecundity differed between the females'first and second mates. Both larger first and second males wereable to transfer more of their ejaculate to females than weresmaller males. Both the total amount of ejaculate transferredby these males and polyandry (number of matings) were positivelycorrelated to female fecundity independently of each other.However, larger second males were more successful at stimulatingfemale fecundity independently of how much ejaculate they transferred.We also provide evidence that females are choosy during theirsecond mating opportunity. Both female choosiness and higherfemale investment after mating with larger second males suggestthat females may benefit from both direct and indirect effectsfrom multiple mating. We also conclude that male body size isunder both directional fecundity selection and directional sexualselection.