Comparative Analyses on the Parasitic Ability and Reproductive Strategy of Cotesia chilonis Based on the Events of Exposure to Hosts

Interspecifically, a reasonable body of evidence supports a trade-off between offspring size and number. However, at the intraspecific level, a whole manner of phenotypic correlations between offspring size and number are observed. These correlations may be predicted when heterogeneity in resource availability, or quality, is considered. Making the assumption that maternal size is a proxy for resource availability, we meta-analytically quantified four phenotypic reproductive correlations within numerous species: (1) maternal size and offspring size, (2) maternal size and offspring number, (3) offspring number and offspring size, and (4) offspring number and offspring size after controlling for maternal size. Within species, maternal size showed a positive correlation with both offspring size and number. Despite this consistency, no correlation between offspring size and number was found. After controlling for maternal size, however, offspring size and number showed a significant negative correlation. A phylogenetic component of our analysis accounted for little heterogeneity in the data, suggesting that our findings show remarkable consistency across taxa. Overall, our results support an observable phenotypic trade-off between offspring size and number. However, this analysis also highlights the importance of considering quality when examining trade-offs, a task that is not always straightforward as quality is context dependant.

Parents have a limited amount of resources to invest in reproduction and commonly trade-off how much they invest in offspring size (or quality) versus brood size. A negative relationship between offspring size and number has been shown in numerous taxa and it underpins evolutionary conflicts of interest between parents and their young. For example, previous work on vertebrates shows that selection favours mothers that produce more offspring, at the expense of individual offspring size, yet favours offspring that have relatively few siblings and therefore attain a greater size at independence. Here we analyse how this trade-off is temporarily affected by stochastic variation in the intensity of interspecific interactions. We examined the effect of the mite Poecilochirus carabi on the relationship between offspring size and number in the burying beetle, Nicrophorus vespilloides. We manipulated the initial number of mites in the reproductive event (by introducing either no mites, 4 mites, 10 mites, or 16 mites), and assessed the effect on the brood. We found a similar trade-off between offspring size and number in all treatments, except in the '16 mite' treatment where the correlation between offspring number and size flattened considerably. This effect arose because larvae in small broods failed to attain a high mass by dispersal. Our results show that variation in the intensity of interspecific interactions can temporarily change the strength of the trade-off between offspring size and number. In this study, high densities of mites prevented individual offspring from attaining their optimal weight, thus potentially temporarily biasing the outcome of parent-offspring conflict in favour of parents.

A large body of knowledge about life-history traits has arisen from research on viviparous fishes of the family Poeciliidae. Still, the wide variation among species in reproductive strategies provides an excellent opportunity to further explore how life-history traits covary and the causes of covariation patterns. In this study, we provide information on brood size, offspring mass at birth, and total reproductive allotment of six poeciliid species (Gambusia sexradiata, Poeciliopsis latidens, Poeciliopsis viriosa, Priapella intermedia, Pseudoxiphophorus jonesii, and Xiphophorus hellerii). Also, we searched for a trade-off between the number of offspring that females produce and the size of each individual offspring. We tested the hypothesis that this trade-off should be stronger in small females because of the space constraints in the reproductive tract that are inherent to a small body size. If this hypothesis were correct, we expected a strong negative relationship between number and size of offspring in small females and a weaker or undetectable relationship between these two life-history traits in larger females. We found evidence of such a size-dependent trade-off in only one species. Small females of Po. latidens that produced relatively large broods experienced the cost of a reduction in the average size of each offspring. In larger females this negative relationship was weaker. Unexpectedly, we found no evidence of this trade-off in the other five poeciliid species and, in contrast, in one species (Priapella intermedia) females that produced numerous embryos were also capable of producing relatively large embryos. We discuss potential explanations for the different patterns of covariation (or lack of covariation) between number and size of offspring that we detected in these viviparous species.

Determinants of reproductive variables in the brown snake, Storeria dekayi, are examined using path analysis, a method which reveals both direct effects (e.g., of female size on offspring number) and indirect effects (e.g., of female size on offspring size through offspring number). In S. dekayi, there is a clear trade-off between offspring number and offspring size. Part of this trade-off is mediated through the timing of parturition suggesting that placental nourishment contributes to offspring development. However, placental nourishment is not sufficient to result in an uncoupling of offspring number and size. Another clear result is that female size and female condition at ovulation (a size-corrected measure of mass) both influence offspring number. As a result, female size and female condition have indirect effects on offspring size such that overall, larger females and females in better condition produce smaller offspring. Larger females also produce offspring in poorer condition. Additional reproductive mass (mass lost by females at parturition beyond that accounted for by offspring) is determined directly by offspring number suggesting it represents a per-offspring allocation of resources. Captivity has marked effects on repro- duction; females held captive longer produced offspring which were smaller and in poorer condition. Comparisons among species reveals that female size consistently has positive effects on offspring number and offspring size in viviparous snakes but that the effect of offspring number on offspring size varies among species.

The relationship between body size and fitness in parasitoid wasps has several effects on parasitic ability, reproductive behavior in female wasps, and progeny fitness. Female wasps with various body sizes were obtained by mass–rearing a gregarious ectoparasitoid, Sclerodermus pupariae, which is one of the excellent parasites to control the larvae and pupae of Buprestidae and Cerambycidae. We investigated the effects of body size of adult females introduced on Thyestilla gebleri (Coleoptera: Cerambycidae) larvae on their paralysis time, pre–oviposition period, oviposition period and fecundity, and the related fitness of their offspring. Results showed that small female wasps needed more time to paralyze a host and had a higher mortality rate than large female wasps. More offspring were produced by large female wasps than by small female wasps, and the percentage and body size of female offspring was not affected by maternal body size. The duration of the egg stage was not affected by foundress size, nor was that of the pupal stage, but the duration of the larval stage and generation time of small female wasps was longer than that of large females. Our findings suggest that the parasitic fitness and offspring performance are affected by maternal size, and there is need to choose reasonable body size of female wasps, to optimally utilize mass rearing and to control target pests with the lowest mortality cost.

The tradeoff between offspring size and number is ubiquitous and manifestly similar in plants and animals despite fundamental differences between the evolutionary histories of these two major life forms. Fecundity (offspring number) primarily affects parental fitness, while offspring size underpins the fitness of parents and offspring. We provide an overview of theoretical models dealing with offspring size and fitness relationships. We follow that with a detailed examination of life-history constraints and environmental effects on progeny size and number, separately in plants and animals. The emphasis is on seed plants, but we endeavour to also summarize information from distinct animal groups - insects, fishes, reptiles, birds, and mammals. Furthermore, we analyse genetic controls on progeny size and number in two model organisms - Arabidopsis and Drosophila. Despite the deep evolutionary divergence between plants and animals, we find four trends in reproductive strategy that are common to both lineages: (i) offspring size is generally less variable than offspring number, (ii) offspring size increases with increasing parent body size, (iii) maternal genes restrict offspring size and increase offspring numbers, while zygotic genes act to increase offspring size; such parent-offspring conflicts are enhanced when there is sibling rivalry, and (iv) variation in offspring size increases under sub-optimal (harsh) environmental conditions. The most salient difference between plants and animals is that the latter tend to produce larger (fewer) offspring under sub-optimal conditions while seed plants invest in smaller (many) seeds, suggesting that maternal genetic control over offspring size increases in plants but decreases in animals with parental care. The time is ripe for greater experimental exploration of genetic controls on reproductive allocation and parent-offspring conflicts in plants and animals under sub-optimal (harsh) environments.

Reproductive effort and the egg number vs. size trade-off in Physalaemus frogs (Anura: Leiuperidae)

With the exception of a positive relationship between energy expenditure and number of offspring per litter, few links have been made between energy expenditure and life history attributes in mammals. The purpose of this study was to examine relationships between basal metabolic rate (BMR) and life history attributes among 26 species within the Neotomine-Peromyscine rodents. Specifically, I used independent contrasts to determine whether variation in BMR is related to variation in life history attributes that represent reproductive effort and maturation, and I determined if there is an offspring size versus offspring number trade-off. My results demonstrate that within the Neotomine-Peromyscine rodents, 1) there exists an offspring number versus offspring size trade-off whereby taxa that have a large residual number of offspring per litter have a small residual neonate mass, 2) BMR is related to this trade-off whereby taxa that have large residual BMR have small residual neonate mass and a trend towards a large number of offspring per litter, and 3) BMR is not related to total reproductive effort as represented by total litter mass, total weanling mass, or total growth rate of the litter from birth to weaning. My results suggest that high BMR facilitates a large number of small offspring per reproductive event. A large number of small offspring may confer a fitness advantage for taxa with compensatory growth mechanisms for weaned young that minimize fecundity trade-offs with small offspring size.

Macrocentrus cingulum Brischke is a polyembryonic endoparasitoid of Ostrina furnacalis Guenée larvae. The interactions between parasitoid age, host age, and superparasitism could affect reproductive attributes such as parasitism rate and brood size, changing the efficiency of mass-rearing programs producing M. cingulum. The parasitism rate of M. cingulum on O. furnacalis larvae was significantly affected by host age, parasitoid age, and their interactions. Macrocentrus cingulum preferred parasitizing host larvae at late 3rd instars over early or late 4th instars. Older female parasitoids (5, 6, or 7 days after emergence) caused higher parasitism levels on three tested host ages than did younger parasitoids, likely because M. cingulum is synovigenic and the older females had a greater oocyte load in their oviducts. The age of O. furnacalis larvae significantly affected brood size but did not change the developmental time of M. cingulum. Late stage, third instars of O. furnacalis supported the largest parasitoid broods. Both brood size and body size of offspring were influenced significantly by superparasitism. Doubly-stung hosts produced most parasitoid offspring while the body size was smallest. In summary, late 3rd instars of O. furnacalis larvae, combined with adult female parasitoids five or more days old and with two stings were optimal for mass rearing of M. cingumum in the laboratory. © 2025 Society of Chemical Industry.

In laboratory assays, we evaluated the potential impact of host plant substrate types, host-parasitoid group sizes (densities), and parasitoid-to-host ratios on select fitness parameters of the larval endoparasitoid Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae), newly introduced for biological control of emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), in the United States. Results from our study showed that offspring production and critical fitness parameters (body size and sex ratio) of T. planipennisi from parasitized emerald ash borer larvae are significantly influenced by host plant substrate type, host-parasitoid group size, parasitoid-to-host ratio, or a combination in the primary exposure assay. The number of both female and male T. planipennisi progeny was significantly greater when emerald ash borer larvae were inserted into tropical ash [Fraxinus uhdei (Wenz.) Lingelsh.] logs rather than green ash (Fraxinus pensylvanica Marshall). When maintained at a constant 1:1 parasitoid-to-host ratio, assays with larger host-parasitoid group sizes (3:3-12:12) produced significantly greater numbers of both male and female offspring per parental wasp compared with those with the single host-parasitoid (1:1) group treatment. As the parasitoid-to-host ratio increased from 1:1 to 8:1 in the assay, the average brood size (number of offspring per parasitized emerald ash borer larva) increased significantly, whereas the average brood sex ratio (female to male) changed from being female-biased (6:1) to male-biased (1:2); body size of female offspring as measured by the length of ovipositor and left hind tibia also was reduced significantly. Based on these findings, we suggest that the current method of rearing T. planipennisi with artificially infested-emerald ash borer larvae use the tropical ash logs for emerald ash borer insertion, a larger (> or = 3:3) host-parasitoid group size and 1:1 parasitoid-to-host ratio in the primary parasitoid exposure assays.

Relationships involving female size, litter size, offspring size, and offspring survival were examined using records available from a laboratory colony of Peromyscus polionotus. Female size was positively correlated to (1) birth size of offspring, (2) number of offspring per litter, (3) litter mass at birth, (4) size of offspring on day 21, and (5) postnatal gain from day of birth to day 21. In contrast to female size, increased litter size led to (1) reduced birth size, (2) reduced size on day 21, (3) reduced postnatal gain, and (4) reduced survival of offspring. On day 21, mice in litters experimentally reduced to three from four or more individuals were larger, gained more, and were more likely to have survived than offspring in unmanipulated litters, but were similar in the three characteristics to mice in natural litters of three. Results of litter reductions indicate that female P. polionotus do not simply prorate “potential” parental investment into a smaller number of offspring, but rather the interaction between a female and the number of nursing young leads to changes in both investment per progeny and total investment per litter.

Maternal effects can form an important source of variation in offspring fitness and have important evolutionary and ecological consequences. To explore genetic control for body size of newborn offspring, the present study examined maternal brood size and offspring body size in 14 strains and performed cross experiments in an ovoviviparous fish, guppy. Correlation analyses among the strains indicated that the strains with larger brood size have smaller offspring body size. Diallel and reciprocal crosses among four strains revealed a large maternal, but no paternal, contribution to offspring body size. To examine whether offspring body size is determined by maternal genotypes and whether offspring body size correlates with albinism, backcrosses were performed between a wild-type strain with large offspring body size and an albino strain. Offspring body size differed from both the parental strains in one generation of backcrossing but was not significantly different from the paternal strains after three generations. In the backcross generations, the offspring yielded by albino individuals showed significantly smaller body size than those yielded by normal individuals. These results indicated that offspring body size is determined by maternal genotypes, suggesting that offspring body size is influenced by the maternal albinism gene or the maternal locus linked with the albinism locus. The significant negative correlation between maternal brood size and offspring body size detected through our experiments showed that the maternal genetic character of brood size strongly correlated with offspring body size, indicating genetic trade-off between maternal brood size and offspring body size in the guppy.

Female fitness is often influenced by trade-offs in energy allocated to reproduction or self-maintenance that is dependent upon the life history of the organism. Maternal body size and condition are factors that are often positively correlated with clutch size and offspring size. We investigated whether maternal body size (snout–vent length, SVL) and condition (residual of mass on SVL) could predict measures of reproductive success including clutch size, offspring body size (SVL), and offspring survival in the territorial Eastern Red-backed Salamander (Plethodon cinereus). Brooding females and their eggs were collected and then housed in a controlled laboratory setting. We recorded the number of eggs found with each female and separated offspring from females once hatched. At 40 d after hatching, we measured the SVL and mass of females and juveniles. Maternal SVL, but not condition, was positively related to clutch size and offspring SVL; however, there was no significant relationship between clutch size and offspring SVL, indicating no trade-off between number and body size of offspring. In the laboratory, survival of the offspring to 185 d post-hatching was positively related to maternal SVL and negatively related to maternal condition. Also, the mean SVL, measured on day 40, of the offspring that survived to 185 d was significantly greater than the SVL of the offspring that did not survive, indicating a benefit of larger offspring body size. Finally, subsequent egg production (number of new oocytes produced by females following the current reproductive bout) was positively related to maternal SVL and condition (measured 185 d after hatching their previous clutches). These results suggest that larger maternal body size and condition of Eastern Red-backed Salamanders provide increased reproductive success through the number and body size of offspring produced in current or subsequent reproductive bouts and in offspring survival. Large body size in territorial animals like P. cinereus provides benefits for holding high quality territories as well as for increased reproductive success.

ABSTRACTThe trade‐off between offspring size and number is a crucial concept in life‐history theory, offering key insights into animal reproductive strategies. Our study examines the relationship between reproductive characteristics, morphological traits, and metabolism in a total of 290 female Phrynocephalus lizards across 10 species. Reproductive, morphological, and metabolic traits were compared by analyzing Phrynocephalus lizard species with viviparous and oviparous reproductive modes. The results show no significant differences in reproductive traits between oviparous (6) and viviparous (4) species. Snout‐vent length and standard metabolic rate positively correlated with offspring mass, while no correlation was found with offspring number. The lack of a trade‐off between offspring size and number indicates that larger females invest more in offspring mass rather than offspring number. These results, at least in this genus, were inconsistent with the classic prediction that females give priority to adjusting the number rather than the size of their offspring, enabling us to understand the evolution of the reproductive strategy in reptiles.

The nutritional regimens of wasp parasitoids can influence the body size of their progeny and their parasitization capacity. This study aimed to evaluate the impact of food resources (glucose, honey, and no food control) on the body size of offspring and the parasitization capacity of Paracentrobia subflava (Girault) (Hymenoptera: Trichogrammatidae), an egg parasitoid of the corn leafhopper pest Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae). Female P. subflava were exposed to D. maidis eggs for 72 h under three feeding treatments: glucose, honey, and no food control. The body size of the emerged offspring was measured, and parasitization capacity was evaluated by assessing the abundance, rate of parasitism, and emergence rate of P. subflava. The results showed that female offspring from mothers fed with glucose or honey had significantly larger head sizes than offspring from unfed mothers. Male offspring from fed mothers exhibited longer forewings than those from unfed mothers. However, no significant differences were observed in the total abundance of egg parasitoids, parasitism rates, or emergence rates across the feeding treatments. These findings suggest that sugar‐based diets affect the size and shape of offspring body structures in P. subflava but do not impact their parasitization capacity, highlighting the proovigenic nature of this species.