Maternal effects,flight versus fecundity trade-offs,and offspring immune defence in the Speckled Wood butterfly, <Emphasis Type="Italic">Pararge aegeria</Emphasis>

Background  

Maternal condition can generate resource-related maternal effects through differential egg provisioning, and can greatly affect offspring performance. In the present study, the speckled wood butterfly Pararge aegeria (L.) was used to investigate whether (after controlling for egg size) maternal age, and increased flight during the oviposition period, resulted in changes in egg provisioning and whether this contributed to variation in offspring performance, i) early in development (egg stage and early post-hatching development), and ii) later in larval development after being exposed to the model viral pathogen system; the baculovirus Autographa californica multinucleocapsid nucleopolyhedrovirus (AcMNPV).     

Butterfly flight activity affects reproductive performance and longevity relative to landscape structure

Due to an overlap in the resources used by the flight muscles with the resources used during egg production, it has been hypothesised that an increased dispersal in fragmented landscapes may result in a physiological trade-off between flight and reproduction. In a common garden experiment, we investigated the effects of increased flight on the reproductive output of female speckled wood butterflies (Pararge aegeria, L.) from closed continuous woodland populations versus open highly fragmented agricultural landscapes in central France. Our flight treatment significantly affected resource allocation to egg size, but had no effect on mean daily fecundity. This treatment effect was similar for females from the two landscapes of origin, and suggests that energetic costs associated with increased flight result in a decrease in resource allocation to egg provisioning. There was a landscape-specific effect of flight on longevity: flight reduced longevity by 21% in woodland females, but had no affect on agricultural females. This result suggests that woodland landscape females further compensate for excessive flight by redirecting resources away from somatic maintenance, resulting in reduced life spans. Our results strongly indicate that increased flight caused by changes in landscape structure may impact on key life history traits such as reproductive success and longevity.     

Ovarian dynamics in Heliconius butterflies: Correlations among daily oviposition rates,egg weights,and quantitative aspects of oögenesis

Both oviposition and ovarian morphology were studied in individual butterflies of the neotropical genus Heliconius, which as adults ingest amino acids from pollen, live up to 6 months, and have continuous oögenesis. Among female Heliconius charitonius, daily oviposition correlates directly with the total number of oöcytes developing in the ovaries. The calculated time required for complete growth of one oöcyte is, however, reasonably constant among individuals of a species with widely varying oviposition rates. Thus, within a species, butterflies laying more eggs per day are not necessarily maturing each at a faster rate, but are processing more oöcytes simultaneously in their ovaries. A further correlation between oviposition rate and adult size suggests that in H. charitonius both ovarian capacity and daily egg production are determined ultimately by extent and/or quality of larval nutrition. Among other Heliconius species, those producing larger eggs generally take longer to make them, but also may develop more oöcytes at the same time in their ovaries. Finally, maximal volume attained by the cap of seven nurse cells associated with each growing oöcyte appears constant within a species and among species is directly proportional to average mature egg weight.     

Some aspects of oögenesis in the stable fly Stomoxys calcitrans (Diptera: Muscidae)

Two distinct patterns of blood ingestion in the female stable fly, Stomoxys calcitrans L. were observed, based on whether or not the female was mated. Mating is not required for oögenesis, but is necessary for oviposition. Virgin females develop eggs but, in the absence of mating, they retain eggs until death. In stable flies, oögenesis appears to be atypical among other dipterans as the penultimate follicles develop and deposit up to 50% yolk before the terminal follicles are matured. Oösorption was seen in the penultimate follicles of virgin females retaining eggs. Accessory-gland implants initiated oviposition in virgin females. However, the total number of eggs laid by such females was 50% less than the number of eggs laid by mated flies.     

Reproductive plasticity, ovarian dynamics and maternal effects in response to temperature and flight in Pararge aegeria

In nature, ovipositing females may be subjected to multiple extrinsic and intrinsic environmental factors simultaneously. To adequately assess a species response to environmental conditions during oviposition it may therefore be necessary to consider the interaction between multiple intrinsic and extrinsic factors simultaneously. Using the butterfly, Pararge aegeria, this study examined the combined effects of extrinsic (temperature and flight) and intrinsic (body mass and age) factors on ovarian dynamics, egg provisioning and reproductive output, and explored how these effects subsequently influenced offspring fitness when egg-stage development occurred in a low humidity environment. Both temperature- and flight-mediated plasticity in female reproductive output was observed, and there were strong temperature by flight interaction effects for the traits oocyte size and egg mass. As females aged, mean daily fecundity differed across temperature treatments, but not across flight treatments. Overall, temperature had more pronounced effects on ovarian dynamics than flight. Flight mainly influenced egg mass via changes in relative water content. A mismatch between the physiological response of females to high temperature and the requirements of their offspring had a negative impact on offspring fitness via effects on egg hatching success.     

Activity patterns and egg production in Coccophagus bartletti, an aphelinid parasitoid of scale insects

ABSTRACT.

• 1 Daily patterns of oviposition and host-feeding were examined in Coccophagus bartletti Annecke & Insley. Females began to host-feed and oviposit during the second or third day after emergence. Thereafter, both activities occurred regularly.
• 2 During long observation periods (5 h) most oviposition (93%) and host-feeding (90%) occurred within the first 3.5 h of wasps first encountering hosts. Experiments demonstrated that levels of activity were low for the rest of the day, and nocturnal oviposition occurred only if wasps had no alternative.
• 3 Dissection of female wasps that had been exposed to hosts, or withheld from them, for given periods of time, revealed that activity levels are governed by egg availability. Dispersal activity may also be influenced by the physiological state of the ovaries.
• 4 Production of a full complement of eggs (at 24±1°C (12 h L) and 18±1°C (12 h D)) took 48h or longer after host-feeding, and if wasps were withheld from hosts and provided with honey, the effects of egg resorption could be detected after about 10 days. Trends in oögenesis and oösorption in C. bartletti females seem not to conform with interpretations of oögenesis-oösorption cycles in other parasitoids.
• 5 The pattern of activity exhibited by C. bartletti females is not inflexible, but the major aspects mentioned above are species-specific. In general, information is needed about daily and hourly patterns of parasitoid oviposition and host-feeding before experiments are designed to test theories of parasitoid behaviour. Interpretation may otherwise rest on assumptions about their physiological condition.

     

Evidence of divergent growth rates among populations of the lizard Anolis carolinensis based on experimental manipulations of egg size

Geographic variation in body size is of special interest because it affects nearly all aspects of an organism’s life. I examined whether differences in body size among four populations of the green anole lizard, Anolis carolinensis, were attributable to maternal investment in egg size and/or growth rates of embryos and juveniles. Larger body size and larger egg size relative to female size in the northern part of the range have been documented in this species, and suggested to be adaptive responses to more extreme winters. The current study confirmed the trends in adult size and egg size in the north, but rejected the trend of larger egg size relative to body size in the south. To control for differences in maternal investment in egg size among populations, I performed yolk removals on eggs from two northern populations to produce comparably sized eggs relative to one southern population. This manipulation was designed to minimize the confounding effect of maternal investment in yolk, the primary energy reserves for eggs, so that intrinsic differences in embryonic growth due to metabolism could be investigated. I found that differences in juvenile and, potentially, embryonic growth rates existed among populations of A. carolinensis, both due to and independent of differences in egg size. Juveniles from the northernmost population were bigger not only due to larger egg size, but also due to faster juvenile growth and possibly differences in developmental stage of oviposition or conversion of egg mass to hatchling mass. Larger body size may hold a number of advantages in northern populations of this species, including starvation resistance through winters and better competitive access to food resources and warmer microhabitats.     

Egg size and composition in an ageing capital breeder – consequences for offspring performance

1. Egg size is often used as a proxy of egg quality although size and composition may vary, e.g. in insects egg size usually decreases as female ages. Whether this decrease in size reflects reduced concentrations of essential nutrients such as lipids and proteins of eggs laid by ageing females, or does reduced size per se explain often observed lower fitness of later laid eggs is poorly explored. 2. Egg properties were compared with fitness parameters of offspring laid on the first and fourth night during the oviposition period of a capital breeding moth, Cleorodes lichenaria (Hufnagel). The study aim was to explore whether decreased egg size is caused by decreased provisioning into later laid eggs measured as egg protein and lipid concentration, and whether it results in lower fitness of later laid offspring. 3. The fresh and dry weight of eggs decreased over the oviposition period, but the protein and lipid concentration remained constant. Survival of larvae was lower among the fourth night laid offspring on a low quality host Parmelia sulcata Taylor compared to a high quality host Ramalina fraxinea (L.) Ach. No differences were observed in egg fertility or hatchability, neonate survival without food and pupal mass between the offspring produced on different nights. 4. Decreased survival of offspring produced later was rather attributable to absolute provisioning (i.e. lower weight of eggs) than relative provisioning (i.e. decreased concentrations of nutrients in eggs). It is argued that lower survival of later laid smaller eggs on low quality diet is likely attributable to physical and chemical characteristics of host lichens and/or physical properties of tiny neonate larvae.     

Reproductive allocation by the blow fly Lucilia sericata in response to protein limitation

Adult females of the anautogenous blow fly Lucilia sericata (Meigen) (Diptera: Calliphoridae) were fed standardized meals of liquidized liver, in quantities shown to range around the minimum required to initiate yolk deposition. Females from each feeding regime were dissected at daily intervals between 4 and 11 days of age; the number and stage of development of all oöcytes were recorded. Once an initial threshold quantity of protein was ingested, yolk deposition was initiated in all available oöcytes. Subsequently, one of two distinct developmental pathways was followed: arrested development in all oöcytes at an early stage of yolk deposition, or more extensive yolk deposition followed by progressive oösorbtion and the maturation of small batches of eggs. The proportion of females showing oösorbtion relative to arrested follicular development increased with increasing protein meal size, suggesting that the difference in response may be triggered by a second protein threshold, either side of which the arrested development or oösorbtion pathways are followed. The behaviour observed may reflect strategies to maximize reproductive output in this short‐lived, resource‐limited insect species. Flies that display arrested development may have sufficient protein to mature few if any complete eggs, but may subsequently be able to mature a full egg‐batch if they obtain further protein meals; this possibility is offset by the risk of death before finding such a meal. Flies that show oöcyte development and oösorbtion produce smaller egg batches more quickly and hence have a higher probability of achieving at least some reproductive output. By initiating yolk deposition in all oöcytes, female L. sericata retain the potential to adopt either developmental pathway, depending on subsequent protein intake.     

Juvenile hormone control of oögenesis in bumblebee workers, Bombus terrestris

In queenright workers of Bombus terrestris oögenesis is inhibited by the queen, the activity of the corpora allata is suppressed, and the resulting JH titer in the haemolymph remains low. In contrast, in queenless workers the JH production is stimulated on the first day of adult emergence, the JH titer increases, and eggs are rapidly formed. After injection of JH I in newly emerged workers oögenesis can also be induced in the presence of a queen in the same way as in queenless workers. The induced oögenesis is JH dosage dependent, dosages of less than 8 μg stimulate the production of vitellogenins, whereas a complete oögenesis can be induced by high dosages of about 50 μg. From studies on the rate of JH excretion it can be concluded that such high dosages must be injected to obtain the required JH titer during the whole egg maturation of 5 days. It is evident, therefore, that the initiation and the maintenance of oögenesis depends on JH.The injected JH ester is completely degraded to JH acid and JH diol mainly in the hindgut. The excretion starts quickly after the injection, but only traces of unchanged JH are excreted.From these results it can be suggested that a queen inhibits egg maturation in workers by suppressing the JH production in the corpora allata and thus lowering the JH titer. This influence also enables a queen to block oögenesis once stimulated, for instance in queenless workers. Breakdown of JH and excretion are not under the control of the queen and therefore neither of them play any rôle in regulating egg maturation in the worker caste.     

Are brighter eggs better? Egg color and parental investment by House Wrens

ABSTRACT Recent work suggests that avian egg color could be a sexually selected signal to males that provides information about female condition, female genetic quality, or maternal investment in eggs. Theory predicts that egg color should influence male investment if it is an honest signal of the marginal fitness returns on paternal investment; a male should invest more in a colorful clutch if that investment increases offspring success more than an equivalent investment in a less colorful clutch. Some experimental support for this hypothesis has been found for species that lay blue eggs containing the pigment biliverdin, a potentially costly antioxidant. However, the brown eggshell pigment protoporphyrin, a pro‐oxidant associated with poor female condition, has received less attention as a potential predictor of female quality or investment. We performed a cross‐fostering experiment with House Wrens (Troglodytes aedon) in southwest Michigan in 2007 to test whether brown egg color was related to female condition or maternal investment, and whether male provisioning of nestlings was related to egg color. We swapped entire clutches between nests and measured egg characteristics and parental provisioning rates. We found that brighter eggs (i.e., those with less brown pigment) were heavier, and that nestlings that hatched from brighter eggs were fed at higher rates by their foster mothers, but not by their foster fathers. This pattern is consistent with the hypothesis that egg color is a potential signal of egg quality and female investment, but we found no evidence of a male response to this potential signal. This lack of a response could be the result of methodological limitations, a nonadaptive biological constraint, or adaptive indifference because chicks from brighter eggs do not actually yield increasing marginal returns on paternal investment. Clearly, additional study is needed to differentiate among these possibilities.     

Changes in the behavior of the female short-tailed cricket,Anurogryllus muticus (De Geer) (Orthoptera: Gryllidae) following mating

InAnurogryllus muticus females, mating stimulates burrow construction, burrow provisioning, feeding, egg production, and egg-laying. Since mating often occurs before the ovaries are fully developed, the time span between mating and oviposition is used for increased food intake and the accumulation of nutrient reserves in the fatbody. Oviposition triggers maternal care of eggs and emerging hatchlings, and blocks egg consumption. Hatchling behavior is investigated. When hatchlings eat eggs, they prefer newly laid over older, embryonic eggs.     

Brood ball size but not egg size correlates with maternal size in a dung beetle,Onthophagus atripennis

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Access to multiple mates increases fecundity but does not affect per‐offspring maternal investment in a marine gastropod

Females of many organisms mate more than once and with more than one male, suggesting that polyandry confers some advantage to the female or her offspring. However, variation in maternal investment in response to mate choice and mate number can confound efforts to determine if there are benefits of polyandry. Access to multiple mates could increase maternal investment in offspring via a number of different mechanisms. Few studies have determined if investment is influenced by mate choice and number, and data are particularly lacking for marine invertebrates. This study was designed to determine if maternal investment and offspring size increase with access to increasing numbers of mates in the protandrous intertidal slipper snail Crepidula cf. marginalis. Virgin female slipper limpets were exposed to one, three, or five potential mates and their fecundity, egg size, and hatchling size were measured for multiple clutches. Treatment had a significant effect on fecundity, with fecundity increasing with the number of potential mates. Treatment did not have an effect on the size of eggs or hatchlings, on the variation in egg size or hatchling size within broods, or on the frequency of oviposition. Treatment did alter the variation in average offspring size among females, but not in the way predicted by theory. The main result, that access to multiple mates does not have an effect on per offspring maternal investment, makes C. cf. marginalis an ideal candidate to study the effects of polyandry on offspring fitness without having to take into account confounding effects of variation in maternal investment.     

Hormonal aspects of oögenesis in the flies Phormia regina and Sarcophaga bullata

The corpora allata (CA) and median neurosecretory cells (MNC) of Phormia regina and Sarcophaga bullata become active with increasing age of the fly, on a diet of sugar alone. To prevent or retard oögenesis the CA or MNCs must be removed shortly after emergence, with subsequent protein meals. Topical JH application partially compensates for CA or MNC removal. This shows that the MNC activate the CA, and not vice versa. The trauma of either operation slightly depresses egg development.Injection of ecdysone into both species in the stage of initial yolk deposition causes the primary oöcytes to degenerate. This leads to development of the penultimate oöcytes. Older and younger egg stages are not sensitive to ecdysone. In P. regina the application of JH to females with developing primary oöcytes stimulates yolk deposition in the penultimate oöcytes.     

Factors promoting maternal trophic egg provisioning in non-eusocial animals

The adaptive function of trophic egg-laying is generally regarded as extended parental investment to the offspring. However, the evolutionary factors promoting trophic egg-laying are still unclear, because the amount of maternal investment per offspring should be ideally equal between smaller offspring with trophic eggs and larger offspring without any additional investment. Several authors have suggested that trophic egg-laying should evolve only when egg size is constrained, but this hypothesis has not been evaluated. We investigated the evolutionary mechanisms of trophic egg-laying by two different approaches. First, we evaluated morphological constraints on egg size in two sibling ladybird species, Harmonia axyridis, which is known to produce trophic eggs, and H. yedoensis. Second, we theoretically predicted the optimal proportion of trophic eggs to total eggs and egg size in relation to environmental heterogeneity, predictability of environmental quality, and investment efficiency of trophic egg consumption. The intra- and interspecific morphological comparisons suggest that morphological constraints on the evolutionary determination of egg size are weak at best in the two ladybird species. Moreover, we theoretically showed that small egg size and trophic egg-laying are favoured in heterogeneous environments when mothers cannot adjust egg size plastically. We also showed that even a small reduction in investment efficiency makes a trophic egg strategy unlikely, despite relatively high environmental predictability. We conclude that trophic egg provisioning may be a flexible maternal adaptation to a highly heterogeneous environment rather than a response to a morphological constraint on egg size.     

The relationship between pre‐oviposition flight behaviour and reproductive timing in whitefly parasitoids

Although the timing of oögenesis appears to be a major life‐history organizer in the parasitoid Hymenoptera, relatively little is known about how this trait correlates with population dispersal by flight in these wasps. Pre‐oviposition flight behaviours of 1‐day‐old female wasps in a vertical flight chamber are measured to test correlations between these traits and with reproductive timing. The focus of the present study is on two genera of whitefly parasitoids (Encarsia and Eretmocerus) that differ in reproductive timing when feeding on a shared host (Bemisia tabaci). The two Eretmocerus species engage in vertical flight within 3 min of release far more frequently than the three Encarsia species. Because the former typically possess a more time‐limited reproductive strategy than the latter, this lends support for a positive interspecific association between early‐life reproduction and early‐life flight incidence. Within species, however, egg load does not correlate with flight propensity for any of the tested species. Furthermore, in Eretmocerus eremicus, the relationship between effective flight distance (i.e. the product of vertical climb rate and flight duration) and egg load appears to be labile rather than fixed because different trials show evidence for either negative or positive correlations between these variables. The source of this context dependence may be variation in either biotic (e.g. longevity) or abiotic (e.g. temperature and relative humidity) factors.     

Evidence that the ovaries of Musca domestica do not maintain cyclicity by regulating the corpus allatum.

When the female housefly retains eggs, vitellogenesis in the penultimate oöcytes is suppressed during continued protein feeding. Allatectomy of gravid females or of females with developing oöcytes did not prevent maturation of a second batch of eggs. This result does not support the claim of Adams (1970) that an oöstatic hormone, produced by ovaries with retained eggs, inactivates the corpus allatum (CA) and thereby prevents development of the next batch of eggs.The report of Adams and Hintz (1969) that the CA regulates egg maturation depends on their removal of ring gland, which they incorrectly refer to as ‘allatectomy’. In the present report, removal of the ring gland from 1 day old females suppressed egg development, whereas removal of the CA alone did not. Therefore, sufficient CA hormone for reproduction was secreted within 24 hr of emergence, and it was the removal of the corpus cardiacum, and not the CA, that had prevented egg development in the experiments of Adams and Hintz.     

Ecdysone,juvenile hormone and oögenesis in Rhodnius prolixus

Oviposition and oögenesis can be inhibited in female Rhodnius prolixus by ecdysone given by the digestive tract. The inhibition is dose-dependent, and doses higher than 4.0 ng ecdysone/mg body weight drastically reduce the size and shape of the whole ovaries. In ecdysone-treated insects, normal oviposition and oögenesis can be re-established by a subsequent blood meal without ecdysone, or by the application of a juvenile hormone analogue.These results suggest that ecdysone inhibits juvenile hormone production.     

Influence de modifications des conditions lumineuses sur les rythmes circadiens de vitellogenese et d'ovulation chez Drosophila melanogaster

Under photoperiodic conditions (LD 12:12), a rhythm was observed in the frequencies of ovarian egg chambers and of mature oöcytes. Females reared and kept in permanent darkness (DD) did not show any rhythm. After a transition from LD 12:12 to DD, the rhythm of vitellogenesis remained almost unchanged for at least 5 days while the rhythm of oöcytes retention disappeared.Suppression of a suitable oviposition substrate resulted in an accumulation of mature oöcytes in the ovaries. When a conveneint medium was given again, the egg-laying proved to be highly dependent on the light conditions. Most of the oöcytes remained in retention during the light phase. Significant egg-laying only occurred after the beginning of darkness. In such conditions females can lay one egg every 3 min.The egg-laying rhythm observed under cyclic light conditions thus arises from two separate physiological processes: oöcyte production (vitellogenesis) which has a circadian, endogenous rhythm and oviposition which is directly dependent on the light conditions.