THE RELATIVE CONTRIBUTIONS OF TIME AND EGGS TO THE COST OF REPRODUCTION

Whether the trade-off between current and future reproduction in insect parasitoids is mediated by the costs of time or eggs remains an issue of contention. Life-history models predict that parasitoids have some risk of exhausting their lifetime supply of oocytes. I develop a simple conceptual model that assesses the relative contributions of time and eggs to the cost of reproduction by placing them in a common currency: foregone future fitness returns. Although rates of egg limitation observed in nature are modest, eggs still often make the dominant contribution to the overall cost of oviposition. Therefore, models of parasitoid reproduction must recognize the costliness of both time and eggs.     

Age‐specific maternal effects interact with larval food supply to modulate life history in Coleomegilla maculata

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不同生境源的稻飞虱卵寄生蜂对寄主的选择和寄生特眭

稻飞虱重要卵寄生蜂缨小蜂Anagrus flaveolus、A optabilis和寡索赤眼蜂Oligosita aesopi、O.Naias均能在稻田和稻田周围的非稻田生境中生存。而.Ftaveolus为优势种。不同生境来源的卵寄生蜂有着不同的寄生和选择特性。缨小蜂A.Flaveolus能在飞虱科内转换寄主,但需1～2代的适应期。寄主卵对寡索赤眼蜂O.Aesopi的寄生有较大的影响,用褐飞虱和黑尾叶蝉诱集的O.Aesopi呼;不能交叉寄生。稻田内诱集的寄生蜂选择稻飞虱,而杂草地中诱集的缨小蜂则对飞虱T.Pusanus有一定的选择性。非稻田生境对保护稻飞虱卵寄生蜂有很大的作用,但对其寄生特性有较大的影响。     

Reproductive senescence and dynamic oviposition behaviour in insects

We explore the relationship between clutch size behaviour and the likelihood of egg limitation in insects with parasitoid-like life histories. We compare the incidence of egg limitation in insects that produce clutch sizes consistent with maximizing fitness per host (i.e. the single host maximum, or Lack clutch size) with insects exhibiting two types of dynamic behaviour. In the first case, insects produce clutch sizes according to a rule that specifies a negative relationship between egg complement and clutch size; in the second case, clutch size is determined by both egg complement and the host encounter rate using a dynamic state-variable model. The analyses are an extension of models presented by Rosenheim (1996), which predicted a strong positive relationship between the risk of egg limitation and the host encounter rate in the absence of dynamic oviposition behaviour. Our results are consistent with Rosenheim's, but they show that dynamic behaviour can greatly reduce th e risk of egg limitation and weaken the relationship between the host encounter rate and egg limitation.     

CLUTCH SIZE AND EGG SIZE IN FREE-LIVING AND PARASITIC COPEPODS: A COMPARATIVE ANALYSIS

The evolution of reproductive strategies and the trade-off between number and size of eggs were investigated in a comparative analysis of free-living and parasitic copepods. Data from 1038 copepod species were used to obtain family averages for 105 families; the phylogenetic relationships among these families include 94 branching events or 94 independent contrasts on which the analysis was based. Transition from a free-living existence to parasitism on invertebrates resulted in small increases in body size. Transition from parasitism on invertebrates to parasitism on fish was associated with greater increases in body size. After controlling for body size, a switch to fish hosts resulted in an increase in the number of eggs produced and a reduction in egg size. Among all contrasts, there was a negative relationship between changes in relative clutch size and changes in relative egg size, suggesting the existence of a trade-off between egg size and numbers. However, opposite changes in these measures of clutch size and egg size were not quite more frequent than expected by chance, therefore indicating that investments into egg numbers are not necessarily made at the expense of egg size, and vice versa. Latitude affected copepod body size, clutch size, and egg size, whereas the effects of freshwater colonization or size of the fish host were not significant. Comparative analyses at either the genus or species levels within given taxa of copepods parasitic on fish provided limited support for a trade-off between clutch size and egg size, but were hampered by the small number of independent phylogenetic contrasts available. From the family-level comparative analysis, it appears that the evolutionary transition from a free life to parasitism on invertebrates, and the transition from parasitism on invertebrates to parasitism on fish, have led to changes in life-history traits in response to the different selective pressures associated with the different modes of life.     

MATERNAL EFFECTS AND THE PERVASIVE IMPACT OF NESTLING HISTORY ON EGG SIZE IN A PASSERINE BIRD

Environmental conditions experienced during ontogeny may have important and permanent consequences for life-history traits of individuals. The aim of this work was to determine whether conditions experienced during early life, as expressed by prefledgling condition, have any bearing on the volume of eggs subsequently laid by females in a small passerine bird species, the pied flycatcher (Ficedula hypoleuca). I first show a genetic influence on egg volume by dam-offspring regression. The existence of maternal effects is shown by comparing resemblances between average egg volumes of offspring to those of their paternal and maternal grandmothers. Path analysis shows that when controlling for the influence of maternal egg volume, the average volume of eggs produced in a lifetime is positively related to the body condition of a female measured while she is still at the nest. Thus, body condition at fledgling affects egg volume beyond the ability of maternal egg volume to predict offspring egg volume. Although there may be a persistent maternal effect of egg volume on itself or linked to a property correlated with egg volume, the maternal performance trait involved remains unknown, except for maternal egg volume itself. Given the effects that egg volume may have on reproductive success, which are partly determined prior to leaving the nest, maternal effects may have important consequences for lifetime fitness of offspring.     

PHYLOGENETIC ANALYSIS OF REPRODUCTIVE TRAITS OF MANIRAPTORAN THEROPODS AND ITS IMPLICATIONS FOR EGG PARATAXONOMY

Abstract:  A phylogenetic analysis of reproductive and oological (egg) traits of theropod taxa allows determination of the sequence in which these traits evolved in Theropoda. Our results indicate that several avian reproductive traits, such as adults sitting on eggs, asymmetrical eggs, unornamented eggshell surface, and complex eggshell ultrastructure, were already present in non-avian maniraptorans, and could have evolved in more basal theropods. In addition, non-avian maniraptorans laid two eggs at a time and orientated their eggs subvertically or subhorizontally in their nests, features not retained by neornithine birds. Based on our cladistic analysis it is also possible to infer the phylogenetic affinity of ootaxa of unknown parentage: Protoceratopsidovum was laid by a maniraptoran more derived than oviraptorids, and Parvoolithus probably belonged to a Cretaceous bird. Finally, our analysis reveals that many of the high-level categories of egg parataxonomy (morphotypes and basic types) are unnatural groupings (i.e. non-monophyletic). We recommend that these high-level categories be abandoned because oofamilies are sufficient to categorize egg taxa.     

The effect of egg load on readiness to accept a low-quality host plant is weak and age dependent in a geometrid moth

Abstract.  1. Most empirical and theoretical studies treat egg load as a major determinant of insect oviposition behaviour, and predict a positive link between egg load and readiness to oviposit.
2. In the present study, the correlation between egg load and readiness to lay eggs on a low-ranked host was examined in wild-caught moths, Scotopteryx chenopodiata L. (Lepidoptera: Geometridae).
3. No overall effect of egg load on oviposition could be detected. However, there was a significant interaction between egg load and wing wear: in only one wing-wear class, out of four, high egg load tended to promote oviposition, while in the three other classes the effect was insignificant.
4. The results suggest that the effect of egg load on oviposition may depend on the age of the ovipositing insect.     

THE RESPONSE TO SELECTION FOR FAST LARVAL DEVELOPMENT IN DROSOPHILA MELANOGASTER AND ITS EFFECT ON ADULT WEIGHT: AN EXAMPLE OF A FITNESS TRADE-OFF

A selection experiment using Drosophila melanogaster revealed a strong trade-off between adult weight and larval development time (LDT), supporting the view that antagonistic pleiotropy for these two fitness traits determines mean adult size. Two experimental lines of flies were selected for a shorter LDT (measured from egg laying to pupation). After 15 generations LDT was reduced by an average of 7.9%. The response appeared to be controlled primarily by autosomal loci. A correlated response to the selection was a reduction in adult dry weight: individuals from the selected populations were on average 15.1% lighter than the controls. The lighter females of the selected lines showed a 35% drop in fecundity, but no change in longevity. Thus, there is no direct relationship between LDT and adult longevity. The genetic correlation between weight and LDT, as measured from their joint response to selection, was 0.86. Although there was weak evidence for dominance in LDT, there was none for weight, making it unlikely that selection acting on this antagonistic pleiotropy could lead to a stable polymorphism. In all lines, sex differences in weight violated expectations based on intrasex genetic correlations: Females, being larger than males, ought to require a longer LDT, whereas there was a slight trend in the opposite direction. Because the sexual dimorphism in size was not significantly altered by selection, it appears that the controlling loci are either invariant or have very limited pleiotropic effect on developmental time. It is suggested that they probably control some intrinsic, energy-intensive developmental process in males.     

Global warming and positive fitness response in mountain populations of common lizards Lacerta vivipara

Recent global warming threatens many species and has already caused population‐ and species‐level extinctions. In particular, high risks of extinction are expected for isolated populations of species with low dispersal abilities. These predictions rely on widely used ‘climatic envelope’ models, while individual responses, the ultimate driver of a species response to climate change, have been most often neglected. Here, we report on some changes in life‐history traits of a dispersal‐limited reptile species (a poorly studied taxa) living in isolated populations. Using long‐term data on common lizards collected in southern France, we show that individual body size dramatically increased in all the four populations studied over the past 18 years. This increase in body size in all age classes appeared related to a concomitant increase in temperature experienced during the first month of life (August). Daily maximum temperature in August increased by 2.2°C and yearling snout‐vent‐length increased by about 28%. As a result, adult female body size increased markedly, and, as fecundity is strongly dependent on female body size, clutch size and total reproductive output also increased. For one population where capture–recapture data were available, adult survival was positively related to May temperature. All fitness components investigated therefore responded positively to the increase in temperature, such that it might be concluded that the common lizard has been advantaged by the shift in temperature. We contrast these short‐term results with the long‐term habitat‐based prediction that these populations located close to mountain tops on the southern margin of the species range should be unable to cope with the alteration of their habitat. To achieve a better prediction of a species persistence, one will probably need to combine both habitat and individual‐based approaches.     

Phenotypic divergence in reproductive traits of a moth population experiencing a phenological shift

Allochrony that is reproductive isolation by time may further lead to divergence of reproductive adaptive traits in response to different environmental pressures over time. A unique “summer” population of the pine processionary moth Thaumetopoea pityocampa, reproductively isolated from the typical winter populations by allochronic differentiation, is here analyzed. This allochronically shifted population reproduces in the spring and develops in the summer, whereas “winter” populations reproduce in the late summer and have winter larval development. Both summer and winter populations coexist in the same pine stands, yet they face different climatic pressures as their active stages are present in different seasons. The occurrence of significant differences between the reproductive traits of the summer population and the typical winter populations (either sympatric or allopatric) is thus hypothesized. Female fecundity, egg size, egg covering, and egg parasitism were analyzed showing that the egg load was lower and that egg size was higher in the summer population than in all the studied winter populations. The scales that cover the egg batches of T. pityocampa differed significantly between populations in shape and color, resulting in a looser and darker covering in the summer population. The single specialist egg parasitoid species of this moth was almost missing in the summer population, and the overall parasitism rates were lower than in the winter population. Results suggest the occurrence of phenotypic differentiation between the summer population and the typical T. pityocampa winter populations for the life‐history traits studied. This work provides an insight into how ecological divergence may follow the process of allochronic reproductive isolation.     

Short- and long-term effects of litter size manipulation in a small wild-derived rodent

Iteroparous organisms maximize their overall fitness by optimizing their reproductive effort over multiple reproductive events. Hence, changes in reproductive effort are expected to have both short- and long-term consequences on parents and their offspring. In laboratory rodents, manipulation of reproductive efforts during lactation has however revealed few short-term reproductive adjustments, suggesting that female laboratory rodents express maximal rather than optimal levels of reproductive investment as observed in semelparous organisms. Using a litter size manipulation (LSM) experiment in a small wild-derived rodent (the common vole; Microtus arvalis), we show that females altered their reproductive efforts in response to LSM, with females having higher metabolic rates and showing alternative body mass dynamics when rearing an enlarged rather than reduced litter. Those differences in female reproductive effort were nonetheless insufficient to fully match their pups’ energy demand, pups being lighter at weaning in enlarged litters. Interestingly, female reproductive effort changes had long-term consequences, with females that had previously reared an enlarged litter being lighter at the birth of their subsequent litter and producing lower quality pups. We discuss the significance of using wild-derived animals in studies of reproductive effort optimization.     

Tolerance of a perennial herb, <Emphasis Type="Italic">Pimpinella saxifraga</Emphasis>, to simulated flower herbivory and grazing: immediate repair of injury or postponed reproduction?

Perennial, polycarpic herbs can respond to herbivory either by (1) regrowth in the same season in order to compensate for lost reproductive structures or by (2) postponing reproduction until the following growing season. We tested these response patterns with the perennial umbellifer Pimpinella saxifraga by simulating flower herbivory and shoot grazing both in the field and in a common garden experiment. In the field, both simulated flower herbivory and grazing effectively suppressed current reproduction, whereas no statistically significant effects of previous-year treatments on growth or reproduction were found in the following year. In the common garden, in the first year the species fully compensated for simulated flower herbivory in vegetative parameters but seed set was reduced by 26%. After 2 years of flower removal, the plants overcompensated in shoot and root biomass by 47 and 46%, respectively, and compensated fully in reproductive performance. Simulated grazing resulted in 21% lower shoot biomass in the first season, but the root biomass was not affected. In the second season the root biomass increased by 43% as compared to the control plants. However, regrowth following simulated grazing resulted in a significant delay in flowering with the consequence that the seed yield of fertile plants was reduced by 55% as compared to the control plants. These results suggest that in resource-rich garden conditions P. saxifraga may immediately repair injuries caused by flower herbivory, but repairs more extensive shoot injury less successfully. Delayed phenology decreases the benefits of immediate repair. In resource-poor conditions, the benefits of regrowth can be negligible. Accordingly, in our field population, the plants postponed their reproduction until the following year in response to simulated grazing and frequently in response to flower removal. When the plants gain very little from regrowth, the costs of reproduction would select for postponed reproduction in response to injury.     

The oxidative costs of reproduction are group-size dependent in a wild cooperative breeder

Life-history theory assumes that reproduction entails a cost, and research on cooperatively breeding societies suggests that the cooperative sharing of workloads can reduce this cost. However, the physiological mechanisms that underpin both the costs of reproduction and the benefits of cooperation remain poorly understood. It has been hypothesized that reproductive costs may arise in part from oxidative stress, as reproductive investment may elevate exposure to reactive oxygen species, compromising survival and future reproduction and accelerating senescence. However, experimental evidence of oxidative costs of reproduction in the wild remains scarce. Here, we use a clutch-removal experiment to investigate the oxidative costs of reproduction in a wild cooperatively breeding bird, the white-browed sparrow weaver, Plocepasser mahali. Our results reveal costs of reproduction that are dependent on group size: relative to individuals in groups whose eggs were experimentally removed, individuals in groups that raised offspring experienced an associated cost (elevated oxidative damage and reduced body mass), but only if they were in small groups containing fewer or no helpers. Furthermore, during nestling provisioning, individuals that provisioned at higher rates showed greater within-individual declines in body mass and antioxidant protection. Our results provide rare experimental evidence that reproduction can negatively impact both oxidative status and body mass in the wild, and suggest that these costs can be mitigated in cooperative societies by the presence of additional helpers. These findings have implications for our understanding of the energetic and oxidative costs of reproduction, and the benefits of cooperation in animal societies.     

DOES BATEMAN'S PRINCIPLE APPLY TO BROADCAST-SPAWNING ORGANISMS? EGG TRAITS INFLUENCE IN SITU FERTILIZATION RATES AMONG CONGENERIC SEA URCHINS

Evolutionary biologists generally invoke male competition and female choice as mechanisms driving sexual selection. However, in broadcast-spawning organisms sperm may be limiting and females may compete, in the Darwinian sense, for increased mating success. In this study, I investigate how species differences in egg and sperm traits result in different patterns of fertilization among three closely related sea urchins (Strongylocentrotus purpuratus, S. franciscanus, and S. droebachiensis). Field studies demonstrate that all three species achieve similar percentages of eggs fertilized when eggs and sperm are released simultaneously. However, when sperm must disperse before encountering eggs, differences arise among species such that those with the smaller eggs and faster but shorter-lived sperm achieve relatively fewer fertilizations than do species with larger eggs and slower but longer-lived sperm. A field hybridization experiment, field estimates of sperm dispersal, correlations of egg size to field rates of fertilization, laboratory studies of fertilization kinetics, and a simulation model all suggest that it is attributes of the egg (probably egg size) that are responsible for the differences. These patterns of fertilization match the species' patterns of dispersion; species that do well only when sperm and eggs are released in close proximity are more aggregated, species that do relatively well when sperm and eggs are released farther apart are more dispersed. These results are consistent with the notion that eggs of different species are adapted to maximize reproductive success under different degrees of sperm limitation and suggest that male competition and female choice may not be an appropriate dichotomy in broadcast-spawning organisms.     

Latitudinal patterns of egg size and maternal investment trade-offs in reef corals

Aim

The aims were to test the role of temperature in latitudinal patterns of egg size and investigate maternal investment trade-offs among coral taxa.

Location

Global, from 34° S to 34° N.

Time period

1981–2020.

Major taxa studied

Reef coral species from the order Scleractinia.

Methods

We compiled a comprehensive geo-referenced global dataset of egg sizes (diameter or volume) and fecundity (number of eggs per area) for colonial corals (Scleractinia; 123 species, 5359 observations and 39 localities), substantially enhanced by new field collections (>88% of observations). We used Bayesian phylogenetic multilevel models to test for Rass' rule (a hypothesized negative relationship between egg size and temperature); we also included other environmental variables and life history traits. We also tested whether a trade-off exists between egg size and fecundity in broadcast spawning hermaphroditic corals with horizontal symbiont transmission (HHT).

Results

We found a significant relationship between coral egg size and symbiont transmission. Eggs from coral species with vertical symbiont transmission were c. 18.8% smaller than those from species with horizontal symbiont transmission. We also found non-significant relationships between egg size and sea surface temperature (SST) for broadcast spawning corals and between egg size and fecundity specifically for HHT species.

Main conclusions

Contrary to recognized latitudinal patterns of egg size across taxa, our study does not provide support for Rass' rule in corals. Additionally, our findings do not support a maternal investment trade-off between egg size and fecundity for HHT species. Our study used a phylogenetic framework that should be a standard practice when studying interspecific variation, including investigation of maternal investment and identification of the influence of multiple predictors on larval fitness (egg size), in addition to trade-offs affecting propagule influx (fecundity). Both these functional traits are vital and have direct consequences for population maintenance and connectivity in sessile organisms, such as corals.     

Comparative biology and life tables of Trichogramma cacoeciae,T. brassicae and T. evanescens (Hymenoptera: Trichogrammatidae) with Ephestia kuehniella and Cadra cautella (Lepidoptera: Pyralidae) as hosts at three constant temperatures

Egg parasitoids of the genus Trichogramma (Hym. Trichogrammatidae) have been successfully utilized for biocontrol of several Lepidopteran pests worldwide. Because of their low host specificity Trichogramma can be mass reared more easily in large numbers and on different natural and factitious hosts. Life table parameters were assessed for Trichogramma cacoeciae Marchall, T. evanescens Westwood and T. brassicae Bezdenko on Ephestia kuehniella Zeller and Cadra cautella Walker at three temperatures (20, 25 and 30°C) as the potential factitious hosts for mass rearing. Female longevity ranged between 9.77 and 2.56 days in our experiments. Fecundity ranged from 73 to 91 parasitized eggs in C. cautella and 76–109 parasitized eggs in E. kuehniella. T. brassicae exhibit similar values of the intrinsic rate of increase ratio (r _m) 0.5407 and 0.5478; the finite rates of increase (λ) were 1.717 and 1.7295 and the doubling times 1.28 and 1.26 at 25 and 30°C, respectively, in C. cautella. The mean duration of one generation (T) varied between 8.25 and 13.37 days for T. cacoeciae, 8.14 and 13.47 days for T. brassicae and 8.23 and 13.18 days for T. evanescens in C. cautella. Generation times for T. cacoeciae varied between 8.23 and 14.68 days, 8.28 and 14.37 days for T. brassicae, and 7.74 and 14.58 days for T. evanescens in E. kuehniella eggs. Both species (T. cacoeciae, T. brassicae) had the same intrinsic rate of increase (r _m; 0.5700 and 0.5704), finite rate of increase (λ; 1.7682, 1.7691) and doubling time (Dt, 1.21) at 30°C in E. kuehniella, respectively.     

Influence of female age, body size and environmental conditions on annual egg production of the bullhead

A population of bullhead Cottus gobio inhabiting a mountainous river network, was examined for the influence of maternal condition (total length, L _T, and age class in years) and environmental factors (water temperature and fish density) on fecundity, egg size and net annual reproductive effort ( E _R, defined as the ratio of total egg production mass to body mass) within several stocks. Regardless of location within the drainage network, bullhead reproduction was synchronous, with only a single batch and fecundity ranging from 69 to 896 eggs per female. As with L _T fecundity increased with age, although the difference between age classes 5 and 6 years was smaller than between other age classes. Egg diameter also increased with age from age classes 2 to 4 years, but then tended to decrease for age classes 5–6 years. Multiple stepwise regression was used to examine the effect of female L _T, water temperature and fish densities on bullhead egg production for each of the four age classes (2, 3, 4 and 5–6 years) separately. When statistically significant, water temperature always had a positive effect and fish densities a negative effect, on fecundity and egg size. The L _T always had a positive effect on fecundity for all the age classes. In contrast, L _T had a positive effect on egg size and E _R only for female reaching maturity (2 years), whereas intermediate aged females (3–4 years) were insensitive and the oldest fish showed a negative response.