Reproduction,dominance, and caste: endocrine profiles of queens and workers of the ant <Emphasis Type="Italic">Harpegnathos saltator</Emphasis>

The regulation of reproduction within insect societies is a key component of the evolution of eusociality. Differential patterns of hormone levels often underlie the reproductive division of labor observed among colony members, and further task partitioning among workers is also often correlated with differences in juvenile hormone (JH) and ecdysteroid content. We measured JH and ecdysteroid content of workers and queens of the ant Harpegnathos saltator. In this species, new colonies are founded by a single queen, but after she dies workers compete in an elaborate dominance tournament to decide a new group of reproductives termed “gamergates.” Our comparisons revealed that queens, gamergates, and inside workers (non-reproductive) did not differ in levels of JH or ecdysteroids. However, increased JH and decreased ecdysteroid content was observed in outside workers exhibiting foraging behavior. Application of a JH analog to virgin queens of H. saltator, although effective at inducing dealation, failed to promote egg production. Together, these results support the hypothesis that JH has lost its reproductive function in H. saltator to regulate foraging among the worker caste.     

Mechanism,induction factors,and adaptive significance of dealation in the subterranean termite <Emphasis Type="Italic">Reticulitermes speratus</Emphasis> (Isoptera,Rhinotermitidae)

Summary. We studied the dealation of a subterranean termite Reticulitermes speratus Kolbe from three different angles; mechanism, induction factors, and adaptive significance. During nuptial flight alates prevent the wings from breaking off by holding the wings in a 3-dimensional configuration. In the process of dealation, the alates hold the wings in a 2-dimensional configuration, half spread the wings in a lowered position, and bend the abdomen back toward the wings, thereby exerting high pressure at the basal sutures. This separates the wings from the body. The primary factor determining the timing of dealation appears to be isolation from other alates: It induces alates to shed their wings, whereas pairing has no effect on dealation in this species. Alates of termites are especially vulnerable to ant predation during the period between flight and colony foundation. An experiment designed to compare the risk of alates and dealates to predation by a termite-hunting ant, Brachyponera chinensis Emery, showed that dealation reduced the predation risk during the period spent running on the ground.     

Oviposition and oogenesis in virgin fire ant females Solenopsis invicta are associated with a high level of dopamine in the brain

Abstract. In the fire ant Solenopsis invicta Buren, virgin females are capable of shedding their wings (dealation) and laying haploid eggs. However, dealation and reproduction are inhibited by a queen primer pheromone that depresses the release of Juvenile Hormone by the corpora allata. In an attempt to identify other neural signals that trigger the reproductive system, we measured the effect on brain biogenic amines of separation from the queen. Dopamine in the brain of virgin females increased from 552 ± 42 to 971 ± 65 fMol/brain when reproduction and dealation were stimulated by 15 days of separation. Octopamine and 5-hydroxytryptamine did not change significantly after the separation. Isolated virgin females fed with a tyrosine hydroxylase inhibitor 3-iodo- l -tyrosine mixed in sucrose for 15 days laid significantly fewer eggs and had fewer chorionated oocytes in their ovarioles than females fed with sucrose only. Restoring dopamine biosynthesis by adding l -dopa to the food also restored oogenesis and oviposition. Dealation was not affected by 3-iodo- l -tyrosine or l -dopa. The possible role of dopamine as the neural target of the queen pheromone regarding its potent allotoregulatory effect in other insects is discussed.     

Changes in juvenile hormone biosynthetic rate and whole body content in maturing virgin queens of Solenopsis invicta

Studies were conducted on the physiological and hormonal changes following the release of alates from developmentally suppressive pheromones produced by mature queens of the fire ant Solenopsis invicta Buren. Winged virgin queens were removed from the pheromonal signal and placed in colony fragments. The time for dealation, degree of ovarian development, and biosynthesis rate and whole body content of juvenile hormone (JH) were measured. The production rate and content of JH were highly correlated. Dealation and the initiation of oviposition corresponded to peak production of JH. JH production rose sharply following separation from the natal nest, peaking after 3 days. After 8 days of isolation, JH production gradually subsided to levels similar to that found in pre-release queens, but began to increase again after 12 days. Mature queens had highly elevated levels of JH relative to recently dealate females, probably reflecting the increased reproductive capability of these older females. The results support the hypothesis that the pheromone released by functional queens inhibits reproduction in virgin alates by suppressing corpora allata activity and the production of JH.     

Reproductive development and ontogeny of queen pheromone production in the fire ant Solenopsis invicta

Queens of the fire ant, Solenopsis invicta Buren, produce several releaser and primer pheromones. Using bioassays, the ontogeny of three of these pheromones related to reproductive development was investigated. Virgin queens, in which the process of wing-shedding (dealation) serves as an indicator of the initiation of reproductive development, were studied. First, the production of two queen pheromones produced in the poison gland was examined. The pheromone responsible for initiation and maintenance of retinue formation, a releaser effect, was found to be produced in detectable quantities 2 days after dealation, at which time queens showed significant ovary development and many (30%) had started laying eggs. A primer pheromone that inhibits alate virgin queens from dealating was detected in queens 3 days following wing-shedding, when 80% of the queens were ovipositing. Second, I examined the onset of a pheromone of unknown glandular origin produced by reproductively active virgin queens which leads to their destruction in queenright colonies by stimulating workers to attack and kill them. This pheromone is secreted in quantities detectable by bioassay 2 days after dealation. Thus, in S. invicta, the ontogeny of three distinct queen pheromones is tightly linked with ovary development and initiation of egg laying. These results demonstrate reproductive and communicative functions are closely associated during the transition from potential to functional queen.     

Temporal patterns of host availability, brown-headed cowbird brood parasitism, and parasite egg mass

I studied relationships between temporal patterns of host availability, brood parasitism, and egg mass for the parasitic brown-headed cowbird (Molothrus ater). At a study site consisting largely of edge habitat in north-eastern Illinois, I found 834 bird nests from 27 species. A total of 407 cowbird eggs and nestlings were found in these nests over three laying seasons. Nearly all (n= 379; 93%) were found in the nests of seven host species. For these species and all taken together, weekly nest availability generally decreased whereas parasitism frequency generally increased throughout the cowbird laying season, but the proportions of nests parasitized and the mean number of cowbird eggs in them did not. Additionally, no correlation was found between the proportions of nests parasitized and nest availability. Cowbird egg mass generally increased throughout the laying season, indicating that foraging conditions improved and that, early in the laying season, egg mass and quality may be less important than quantity. Consistently high weekly levels of parasitism indicate that cowbird reproduction was less limited by resources needed for egg production and more by the availability of suitable host nests. Fluctuating weekly host availabilities suggest that previously established, constant rates of cowbird egg laying would produce an excess of eggs during periods of low host availability. Further, the low frequency of parasitism (1%) of nests in stages too advanced for successful parasitism, and of abandoned nests, is consistent with the hypothesis that cowbirds' consistently high rate of egg production helps assure an egg is available when an appropriate nest is found. Frequently, nests were parasitized multiple times, raising the possibility that cowbirds were interfering with their own reproduction. A diverse host community increases the possibility that a decline of any one host species is unlikely to affect cowbird reproduction significantly. Received 11 July 1997 / Accepted: 31 March 1998     

The cost of being able to fly: a study of wing polymorphism in two species of crickets

Summary The widespread occurrence of wing polymorphisms in insects suggests that the possession of wings and ability to fly adversely affect components of the insect's life characteristics that contribute to its Darwinian fitness. This hypothesis was tested by an analysis of the differences in life history parameters of the macropterous and micropterous morphs of the two cricket species G. firmus and A. fasciatus. In both species there were no differences in development time or adult survival between the two morphs. Significant differences in head width were not consistent between the two species but in both sexes of G. firmus and females of A. fasciatus (insufficient males for analysis) long-winged individuals weighed more than short-winged individuals with the same head width. In both species egg production is delayed in macropterous females. The cumulative fecundity of the micropterous morph is greater than the macropterous morph in both species but only in G. firmus is the difference statistically significant. A. fasciatus frequently loose their wings but no such loss has been observed in G. firmus. There is a significant increase in egg production after the loss of the wings. These results are in accord with those of Tanaka (1976) for the cricket, Pteronemobius taprobanensis.Breeding experiments indicate that in G. firmus the wing polymorphism is under genetic control. The decrease in fecundity is sufficiently large that genotypes producing only macropterous offspring could only persist in highly unstable environments where continuous dispersal was imperative for survival. However, the reproductive cost of a genotype producing a small percentage of macropterous individuals is slight. The fitness that accrues to a genotype producing a few dispersing offspring is likely to offset the small reproductive cost and hence wing polymorphisms should be favoured.     

Body size and the timing of egg production in parasitoid wasps

In insects several key fitness-related variables are positively correlated with intraspecific variation in body size, but little is known about size-related variation in the timing of egg production within species. Female insects are known to vary in the degree to which they concentrate egg production into the early part of life. This variation has been quantified as the ovigeny index, defined as the proportion of the maximum potential lifetime complement of eggs that is mature following emergence from the pupa. We tested the hypothesis that the timing of egg production depends both on body size and on host availability, by means of a dynamic programming model that predicted optimal resource allocation to reproduction and survival together with the resulting ovigeny index, in non-feeding synovigenic parasitoids of different sizes. As body size increases, the proportionate increase in resource allocation to initial egg load is less than the proportionate increase in allocation to lifetime fecundity and potential life span, leading to a deferred investment in reproduction as shown by a decrease in ovigeny index. High habitat quality and high habitat stochasticity in reproductive opportunities have a significant effect on the optimal allocation of resources to reproduction and survival, and thus select for early reproduction, i.e. an increased ovigeny index. The ovigeny concept – ovigeny index together with its life-history correlates – enables understanding of the general occurrence of size-related deferment of reproductive investment in parasitoid wasps and also helps explain a significant part of the considerable life-history variation found among such insects.     

Adaptive Evolution in an Avian Reproductive Protein: ZP3

Proteins involved in reproduction appear to be evolving adaptively across taxa. This rapid evolution is thought to be the result of forces involved in sexual selection. One of the most often suggested of these forces is sexual conflict involving sperm competition and polyspermy avoidance. Bird species offer a unique opportunity to test this hypothesis since the avian egg coat tolerates physiological polyspermy, or the penetration of multiple sperm during fertilization, without negative effects on later development. Despite this, and the extensive amount of data gathered on sexual selection in birds, there are limited studies on the patterns of evolution of avian reproductive proteins. Here we present an analysis of the pattern of evolution of Zona Pellucida 3 (ZP3), a protein present on the avian egg coat. We found that, across several galliform and a single anseriform species, ZP3 appears to be diverging by positive adaptive evolution. In an exploratory analysis of portions of the gene in Callipepla californica we also found evidence of a selective sweep at the putative sperm binding region of the protein. In sum, ZP3 in birds, like reproductive proteins in other species, appears to be adaptively evolving. This result suggests that polyspermy avoidance is not sufficient to explain positive Darwinian selection in reproductive proteins across taxonomic groups. Clearly, the inclusion of bird species in the study of reproductive proteins across taxa promises to add greatly to the discussion of the factors driving the widespread phenomenon of adaptive evolution in reproductive proteins. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Characterization of vitellogenin in the red imported fire ant, Solenopsis invicta (Hymenoptera: Apocrita: Formicidae)

Vitellin (VN) and vitellogenin (VG) profiles were analyzed in monogyne and polygyne colonies of the red imported fire ant, Solenopsis invicta. Non-denaturing and SDS-polyacrylamide gel electrophoresis (PAGE) analyses indicated that the native VN was likely 350 kDa and comprised of two subunits in the molecular size range of 170-185 kDa. SDS-PAGE of hemolymph showed that the relative mobilities and subunit patterns of VG and VN were similar. VG was present in the hemolymph of reproductive queens; alate, virgin queens; and workers, but not in males. Anti-VN, prepared from polygyne egg homogenates, reacted with egg homogenates and with hemolymph VG from reproductive, monogyne and polygyne queens and alate, virgin polygyne queens. Analysis of circulating VG and ovarian development in alate, virgin queens showed that low levels of VG appeared by five days following adult eclosion, but egg development was not observed until seven weeks. VG was evident in newly inseminated queens, and increased steadily for the first three weeks following dealation. VG levels declined slightly near eclosion of the first workers (= nanitics) and dropped sharply after nanitic emergence at five weeks following dealation. Oocyte maturation peaked at days 15-25 following dealation, but otherwise remained low but steady. These studies provide the basis for future investigations into endocrine regulations of vitellogenesis in S. invicta queens.     

ANTAGONISTIC PLEIOTROPY: AN INTERSPECIFIC DROSOPHILA COMPARISON

Wild-type flies of 12 Drosophila species and semispecies were examined to determine whether correlation patterns between early- and late-life fitness characters predicted for individuals within a population by the antagonistic-pleiotropy hypothesis are reflected in comparisons of related species and semispecies that are known to differ in lifespan. Our goal was to determine whether the hypothesis is relevant to the evolution of life-history differences beyond the population level. Two fitness traits, egg production and percentage mating success, were observed at three ages: onset of reproductive age, one week later, and one month later. Age-dependent patterns of these traits do not consistently conform to predictions of the hypothesis. Species or semispecies that show reproductive vitality early in life need not be short-lived, and long lifespan need not be accompanied by a cost in early reproductive vitality, as measured by mating success and egg production. The two fitness traits can show different age-dependent patterns in the same species or semispecies. Potential explanations for the frequent inconsistency of the data with predictions of the hypothesis are discussed. Results support the idea that the hypothesis is only relevant to the evolution of life-history differences among individuals in the same breeding population confronted by the same environmental constraints.     

How to fool a virgin: Artificial dealation triggers oviposition in virgin Lasius niger queens

Once inseminated, ant queens rapidly shed their wings and start to lay eggs. Here we test whether there is a causal link between dealation and oviposition in the ant Lasius niger. We show that artificially dealated virgin queens start to lay eggs shortly after wing removal, whereas winged virgin queens hardly ever lay eggs. Dealate virgins do, however, produce fewer eggs than mated queens. These findings indicate that dealation does induce egg-laying, and that other factors, such as mating and/or insemination, further stimulate oviposition under natural conditions. Received 2 January 2006; revised 8 February 2006; accepted 4 April 2006.     

THE EVOLUTION OF OVIPARITY WITH EGG GUARDING AND VIVIPARITY IN LIZARDS AND SNAKES: A PHYLOGENETIC ANALYSIS

This paper investigates the evolution of viviparity and of egg guarding in lizards and snakes in which three modes of reproduction can be described: oviparity without egg guarding, oviparity with egg guarding, and viviparity. All possible transitions of reproductive modes were detected in each taxon using Maddison's method. We then tested two specific hypotheses. First, egg guarding can be regarded as an alternative to viviparity. A relatively frequent association of egg guarding and viviparous species in the same taxon may be due to similar environmental conditions or species characteristics leading to two different solutions. Second, egg guarding may facilitate the evolution of viviparity. This hypothesis is supported by the high frequency of viviparous species in taxa containing egg guarding species and by a tendency for prolonged uterine retention of eggs in brooding squamates. Our analyses demonstrate that the first hypothesis is the best supported. Egg guarding and viviparity most often evolved independently. If a major benefit of egg guarding is the repulsion of potential predators, size is one of the most obvious morphological characters that should be correlated with the evolution of reproductive modes. The two reproductive traits were correlated to a reduction in body size for viviparous species and an increase in body size for egg guarding species. This could partly explain why the evolution of these reproductive modes seems almost antagonist.     

Evolution and physiological consequences of de-alation in crickets

Wing shedding or de-alation is a common phenomenon among crickets. Its significance and effects on other traits were examined based on the results from experiments using artifical or natural de-alation. Artificial de-alation at adult emergence induces rapid egg production and flight muscle histolysis in several species examined. However, natural de-alation does not always shorten the pre-ovipositional period because it does not occur immediately after adult emergence and because oviposition starts before de-alation. In some cases, naturally de-alated females produce more eggs than to intact females during early adult life, but peak ovipositing activity occurs before de-alation. Therefore, retention of the hindwings does not suppress high ovipositing activity in such cases. It appears that de-alation is a result rather than a causal factor in ending migration. Ovarian development and flight muscle histolysis, which can be stimulated by de-alation, are controlled by the jevenile hormone, but the mechanism inducing de-alation remains unknown. The possible factors leading to the evolution of de-alation are discussed.     

A cost of reproduction in Drosophila melanogaster: stress susceptibility

Little is known about physiological mechanisms that underlie the cost of reproduction. We tested the hypothesis that stress susceptibility is a cost of reproduction. In one test of our hypothesis, Drosophila melanogaster females were exposed to a juvenile hormone analog (methoprene) to stimulate egg production followed by stress assays. A sterile stock of D. melanogaster was employed as a control for reproduction. Exposure of fertile females to methoprene resulted in an increase in female reproduction and increased susceptibility to oxidative stress and starvation (compared to solvent controls). Sterile females did not exhibit a decrease in stress resistance. Mating also stimulated egg production. As a second test of our hypothesis, mated females were compared to virgin females. Mated fertile females were relatively susceptible to oxidative stress, but this relationship was not evident when mated and virgin sterile females were compared. The results of the present study support the hypothesis that stress susceptibility is a cost of reproduction.     

Growth and reproduction of fungal feeding Collembola as affected by fungal species,melanin and mixed diets

Fungal feeding soil invertebrates feed on a wide spectrum of fungal species suggesting that mixed diets increase fitness. We investigated relationships between food preferences for seven saprophytic fungal species/forms and fitness parameters (mortality, growth, time to reproduction, reproduction, egg size) in two Collembola species, Folsomia candida and Protaphorura armata. The fungal species/forms studied included the wild type and a melanin-deficient form of Aspergillus fumigatus to investigate the role of melanin in collembolan nutrition. Also, three mixed diets consisting of a preferred fungal species (Cladosporium cladosporioides) and species of intermediate or low food quality were investigated. Both Collembola species preferred similar fungal species/forms as food. Food preference generally matched fitness parameters, i.e. growth and reproduction of Collembola was at a maximum when feeding on preferred fungi. This was not the case for A. fumigatus. The wild type and the melanin-deficient form ranked among the least preferred fungi. Growth and reproduction of Collembola were low when feeding on the wild type but high when feeding on the melanin-deficient form indicating that the Collembola misjudged the food quality of the latter in the preference tests. The results show for the first time that genes driving melanin syntheses (pksP) strongly affect the food quality of fungi for fungal feeding invertebrates. Feeding on mixed diets generally increased growth and reproduction of Collembola except when the diets included toxic species (Penicillium sp.). The results support the nutrient balance hypothesis and also show that the detection of toxic species in the diet is important. They indicate that the widespread generalist feeding mode of Collembola maximizes fitness if toxic fungal species are avoided. The fitness parameters growth, reproduction and time until onset of reproduction were correlated closely but egg volume, which also varied with fungal diet, correlated poorly with the other fitness parameters. Variation in egg size with fungal diet shows that the diet of Collembola may have transgenerational effects.     

Terminal investment strategies following infection are dependent on diet

When future reproductive potential is threatened, for example following infection, the terminal investment hypothesis predicts that individuals will respond by investing preferentially in current reproduction. Terminal investment involves reallocating resources to current reproductive effort, so it is likely to be influenced by the quantity and quality of resources acquired through diet. Dietary protein specifically has been shown to impact both immunity and reproduction in a range of organisms, but its impact on terminal investment is unclear. We challenged females from ten naturally derived fruit fly (Drosophila melanogaster) genotypes with the bacterial pathogen Pseudomonas aeruginosa. We then placed these on either a standard or isocaloric high‐protein diet, and measured multiple components of reproductive investment. As oogenesis requires protein, and flies increase egg production with protein intake, we hypothesized that terminal investment would be easier to observe if protein was not already limiting. Oral exposure to the pathogen triggered an increase in reproductive investment. However, whereas flies feeding on a high‐protein diet increased the number of eggs laid when exposed to P. aeruginosa, those fed the standard diet did not increase the number of eggs laid but increased egg‐to‐adult viability following infection. This suggests that the specific routes through which flies terminally invest are influenced by the protein content of the maternal diet. We discuss the importance of considering diet and natural routes of infection when measuring nonimmunological defences.     

Effects of diet and host access on fecundity and lifespan in two fruit fly species with different life‐history patterns

The reproductive ability of female tephritids can be limited and prevented by denying access to host plants and restricting the dietary precursors of vitellogenesis. The mechanisms underlying the delayed egg production in each case are initiated by different physiological processes that are anticipated to have dissimilar effects on lifespan and reproductive ability later in life. The egg‐laying abilities of laboratory‐reared females of the Mediterranean fruit fly (Ceratitis capitata Wiedmann) and melon fly (Bactrocera cucurbitae Coquillett) from Hawaii are delayed or suppressed by limiting access to host fruits and dietary protein. In each case, this is expected to prevent the loss of lifespan associated with reproduction until protein or hosts are introduced. Two trends are observed in each species: first, access to protein at eclosion leads to a greater probability of survival and a higher reproductive ability than if it is delayed and, second, delayed host access reduces lifetime reproductive ability without improving life expectancy. When host access and protein availability are delayed, the rate of reproductive senescence is reduced in the medfly, whereas the rate of reproductive senescence is generally increased in the melon fly. Overall, delaying reproduction lowers the fitness of females by constraining their fecundity for the remainder of the lifespan without extending the lifespan. © 2013 The Royal Entomological Society     

Male-biased sex ratios,female promiscuity,and copulatory mate guarding in an aggregating tropical bug,Dysdercus bimaculatus

The ecological and social bases of the mating system of the seed-feeding bug, Dysdercus bimaculatus(Hemiptera: Pyrrhocoridae), were studied in the lab and in aggregations at the host tree, Sterculia apetala(Malvales: Malvaceae), in Panama. On theoretical grounds, two factors are predicted to be of importance in determining the evolution of male mating tactics in Ms species: the operational sex ratio and the probability that undefended females will mate with other males, subjecting the gametes of deserters to sperm competition. Results of a study of a related species suggested that sperm displacement is probably substantial. Adult sex ratios at numerous sites were significantly male biased, and females whose mates were removed remated before oviposition (i. e., sperm utilization). These results predict that a mate defense tactic is likely to be superior to a nondefense tactic. The biological significance of the parameters is supported by observations that captive pairs often remained in copulafor several days, until just before oviposition. However, substantial variation in copulation duration was also observed, and possible causes of this variation are considered. Causes of male biased adult sex ratios were investigated by monitoring demographic changes within a single aggregation over 2 months. Both female juvenile and adult mortality rates were greater than male. In addition, dissections of reproductive adults showed that the flight muscles of females, but not males, had histolyzed, so that female reproduction is physiologically limited to a single site. Greater rates of immigration among both mature and young males suggests that an excess of males may also be found in the populations of bugs that subsequently colonize other host plants, so that female scarcity is typical of aggregations in all stages of development. The evolution of sex-limtied flight muscle histolysis may be explained by greater patchiness of females than males as mating resources, plus a lower energetic benefit/cost ratio of histolysis for males.     

Reproductive strategy of the snapping shrimp Alpheus armillatus H. Milne-Edwards, 1837 in the South Atlantic: fecundity,egg features,and reproductive output

Summary

The family Alpheidae, composed by shrimps of relatively small size, popularly known as snapping shrimps, is the one of the most diverse decapod groups. These shrimps are found worldwide and occur in tropical and subtropical waters, from the intertidal zone to great depths. We investigated reproductive aspects of Alpheus armillatus, in order to gather information on egg production, aiming to enhance knowledge of its reproductive strategies in a population in an intertidal area of the South Atlantic. Ovigerous females were collected under rocks, in May and July 2006 (dry season) and in November 2006 and March 2007 (rainy season). Egg production and reproductive output were analyzed and compared seasonally and during the period of embryonic development. Females measured on average 11.28 mm CL, with a mean of 763 eggs and 0.10 mm3 egg volume. The egg volume of this population was smaller than previous estimates for other species of snapping shrimps, but the mean egg number was higher. The volume of eggs doubled during the incubation period, but despite this increase, no significant loss of eggs was observed. Alpheus armillatus invests on average about 12% of body weight in reproduction. The proportional investment in egg production is significantly higher in the rainy season when compared with the dry season (17.9% vs 4.8%), correlated with higher temperatures and increased food availability at this time. Our results corroborated the hypothesis of a pattern of egg production influenced by environmental conditions and intraspecific variability among the family Alpheidae, as a function of the biogeographic region.