Effect of host size on male fitness in the parasitoid wasp Dinarmus basalis

The effect of host size on male fitness was tested in the parasitoid wasp Dinarmus basalis (Hymenoptera, Pteromalidae) using hosts of different fresh weight. Fitness was measured as the sperm stock in seminal vesicles, and the ability to access females in single or competition situations. Both body size and sperm in seminal vesicles increased with host fresh weight. Males from small hosts had a reduced size and sperm stock compared to those from larger hosts. In single situations, males from both small and large hosts had similar reproductive capacities, whereas in multiple mating or competition situations, males from small hosts were at a disadvantage, inseminating fewer females and copulating less frequently. However, females did not appear to choose between males, and no effect on sperm stored in the spermatheca was observed. Being small does not prevent a D. basalis male mating and producing progeny in single situations, although more offspring could be expected from larger males because of their better competitive abilities.     

Survival of Trichinella papuae muscle larvae in a pig carcass maintained under simulated natural conditions in Papua New Guinea

In Papua New Guinea, Trichinella papuae, a non-encapsulated species, is circulating among wild and domestic pigs and saltwater crocodiles. Since an important phase of the life cycle of nematodes of the genus Trichinella is the time of survival of infective larvae in decaying muscle tissues of the hosts, the carcass of a pig, experimentally infected with larvae of T. papuae, was exposed to the environmental conditions of Papua New Guinea to establish how long these larvae would survive and remain infective to a new host. Larvae retained their infectivity in the pig carcass up to 9 days after slaughtering, during which time the temperature within the carcass reached 35.0 degrees C on 2 days; the average relative humidity was 79.0%. A low number of larvae survived up to day 14 after the pig was killed, when the carcass temperature reached 38.0 degrees C, but they lost their infectivity to laboratory mice. This result suggests that the larvae of T. papuae can survive in a tropical environment for a time, favouring their transmission to a new host in spite of the lack of a collagen capsule.     

Stand tall and they still get you in your Achilles foot-pad.

The free-living first-instar larvae of Strepsiptera (Insecta) are the infective stage of the parasitoid. They normally enter the host via the abdominal cuticle, and there have also been reports of entry via the egg of the host. The first-instar larvae of Stichotrema dallatorreanum Hofeneder in Papua New Guinea were found to enter the host orthopteran via the tarsi. This is, to my knowledge, the first report of entry of first-instar larvae of Strepsiptera via the attachment pads (euplantulae) of the host.     

Morphology of the female Myrmecolacidae (Strepsiptera) including the apron, and an associated structure analogous to the peritrophic matrix

Development in the totally endoparasitic female Strepsiptera has been clarified by light and electron microscopy. At the end of the 4th instar the cuticle sclerotizes anteriorly to form the cephalothorax and collar, the former of which is later extruded through the host cuticle. Posteriorly, the cuticle remains unsclerotized, and this region is within the host. The moult to the neotenic adult takes place within the 4th instar cuticle, and the epicuticles of the previous instars are retained as persistent sheaths. The gut, which is present in the earlier endoparasitic stages, is lost after extrusion of the cephalothorax, and a novel structure develops on the ventral surface of the neotenic female. Due to the position of this novel structure in the neotenic female, this area is called an apron. The detailed structure of the membranes in the apron in Stichotrema dallatorreanum Hofeneder from Oro Province, and of another female myrmecolacid (which has a different host) from West New Britain in Papua New Guinea, is described. A dual function for the apron is proposed.     

Sex‐dependent infection causes nonadditive effects on kissing bug fecundity

The influence of parasites on host reproduction has been widely studied in natural and experimental conditions. Most studies, however, have evaluated the parasite impact on female hosts only, neglecting the contribution of males for host reproduction. This omission is unfortunate as sex‐dependent infection may have important implications for host–parasite associations. Here, we evaluate for the first time the independent and nonindependent effects of gender infection on host reproductive success using the kissing bug Mepraia spinolai and the protozoan Trypanosoma cruzi as model system. We set up four crossing treatments including the following: (1) both genders infected, (2) both genders uninfected, (3) males infected—females uninfected, and (4) males uninfected—females infected, using fecundity measures as response variables. Interactive effects of infection between sexes were prevalent. Uninfected females produced more and heavier eggs when crossed with uninfected than infected males. Uninfected males, in turn, sired more eggs and nymphs when crossed with uninfected than infected females. Unexpectedly, infected males sired more nymphs when crossed with infected than uninfected females. These results can be explained by the effect of parasitism on host body size. As infection reduced size in both genders, infection on one sex only creates body size mismatches and mating constraints that are not present in pairs with the same infection status. Our results indicate the fitness impact of parasitism was contingent on the infection status of genders and mediated by body size. As the fecundity impact of parasitism cannot be estimated independently for each gender, inferences based only on female host infection run the risk of providing biased estimates of parasite‐mediated impact on host reproduction.     

Assortative pairing with respect to parasite load in the beetle Timarcha maritima (Chrysomelidae)

Because of their effects on host reproductive behaviour, parasites are theoretically expected to create sometimes assortative mating among hosts, with heavily parasitized individuals pairing together and lightly parasitized ones pairing among themselves. We investigated the influence of protozoan gut parasites on the pairing pattern of the chrysomelid beetle Timarcha maritima. In the field, fecundity was negatively correlated with the parasite load of females, unpaired males were significantly more heavily infected than paired ones and, among pairs, males and females were matched for parasite load. Mate choice experiments in the laboratory showed that males have some ability to avoid heavily infected partners when given the choice between two females. Male competitiveness, measured as their mobility, was also negatively correlated with parasite load. These results indicate that parasite-related assortative pairing in this beetle could result from parasitized females being less fecund and parasitized males less competitive.     

Schistosoma mansoni, S. japonicum, S. haematobium: glycogen content and glucose uptake in parasites from fasted and control hosts

The glycogen content of male and female Schistosoma mansoni has been measured in flukes from normally fed hosts and those from fasted hosts. In infections from both the mouse and the hamster, a significant reduction in schistosomal glycogen of males is seen hours after food is withdrawn from the host. Reductions in protein content of the schistosomes were only observed in hamster infections fasted at least 72 hr. The livers of infected mice not only decrease in size during fasting, but there is a concomitant reduction in glycogen per unit wet weight. Comparisons of glycogen:protein ratios of mansonian males, females, and host livers indicate that the fasting-induced loss of liver glycogen is also observed in the male schistosome, but not the female. Studies of both S. mansoni and S. haematobium pairs from fed hosts suggest that the ratio of glycogen:protein contents in the male schistosome correlates with the glycogen:protein ratio of the female partner. Measurements of glucose uptake in vitro suggest that greater uptake rates may be observed in flukes perfused from fasted hosts. In S. japonicum from infected mice, a reduction in male glycogen was also detected as early as after a 6-hr fasting period, but changes in the females were not significant. Unmated male S. japonicum also exhibit a reduction in glycogen levels after fasting, but the quantity of worm glycogen present in these males remains higher than comparable mated males. In mice entrained to a regulated pattern of available food, fluctuations in glycogen content of the male schistosomes were observed, but in the female partners fluctuations were of a smaller magnitude.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of the acanthocephalan parasite Pomphorhynchus laevis on the lipid and glycogen content of its intermediate host Gammarus pulex

Besides conspicuous changes in behaviour, manipulative parasites may also induce subtle physiological effects in the host that may also be favourable to the parasite. In particular, parasites may be able to influence the re-allocation of resources in their own favour. We studied the association between the presence of the acanthocephalan parasite, Pomphorhynchus laevis, and inter-individual variation in the lipid and glycogen content of its crustacean host, Gammarus pulex (Amphipoda). Infected gravid females had significantly lower lipid contents than uninfected females, but there was no difference in the lipid contents of non-gravid females and males that were infected with P. laevis. In contrast, we found that all individuals that were parasitised by P. laevis had significantly increased glycogen contents, independent of their sex and reproductive status. We discuss our results in relation to sex-related reproductive strategies of hosts, and the influence they may have on the level of conflict over energy allocation between the host and the parasite.     

Water-seeking behavior in insects harboring hairworms: should the host collaborate?

We explored the idea that hosts infected with manipulative parasitesmight mitigate the costs of infection by collaborating withthe parasite rather than resisting it. Nematomorphs are usuallyconsidered to be manipulative parasites of arthropods becausethey cause hosts to seek an aquatic environment, which is neededby the adult parasite. We placed infected cricket hosts in situationsof forced noncompliance and compared some fitness parameters(life expectancy, gonad development, and reproductive behaviors)in noncompliant hosts and hosts allowed to express parasite-inducedbehavior. Compared to uninfected controls, reduced survivalwas observed in both males and females from the two categoriesof infected hosts, collaborative or not. A substantial proportionof collaborative females produced eggs or had developed ovarieswhile such phenomena were never observed among noncollaborativeones. Collaborative females retained a nymphal phenotype, butadult males nevertheless courted and produced spermatophoresto such females. However, collaborative females had difficultiesmounting males, taking spermatophores and/or ovipositing. Incontrast to females, all males were entirely castrated by theparasite regardless of their behavior, collaborative or not.Thus, bringing the parasite into water does not effectivelymitigate the costs of infection for the host.     

Mating and Sexual Communication by Steinernema carpocapsae (Nemata: Steinernematidae)

Entomopathogenic nematodes are lethal insect parasites that reproduce exclusively inside their hosts in nature. Infection decisions made by the free-living infective-stage juveniles have an impact on reproductive success, but it is likely that mating decisions are made by adults while inside their host. We investigated sexual communication between male and female adult stages of Steinernema carpocapsae (Rhabditida: Steinernematidae) to assess whether mating is chemically mediated during the adult stage or results from incidental encounters between adults inside the insect host. To assess chemical communication, we measured the behavioral response of adult male S. carpocapsae to several different potential sources of chemical information. Male S. carpocapsae responded to virgin females only and were not influenced by mated conspecific females, conspecific males, or heterospecific females. These results show that species-specific communication takes place between adult entomopathogenic nematodes within the host cadaver just prior to mating.     

Acoustic defence in an insect: characteristics of defensive stridulation and differences between the sexes in the tettigoniid Poecilimon ornatus (Schmidt 1850)

Many insects exhibit secondary defence mechanisms upon contact with a predator, such as defensive sound production or regurgitation of gut contents. In the tettigoniid Poecilimon ornatus, both males and females are capable of sound production and of regurgitation. However, wing stridulatory structures for intraspecific acoustic communication evolved independently in males and females, and may result in different defence sounds. Here we investigate in P. ornatus whether secondary defence behaviours, in particular defence sounds, show sex-specific differences. The male defence sound differs significantly from the male calling song in that it has a longer syllable duration and a higher number of impulses per syllable. In females, the defence sound syllables are also significantly longer than the syllables of their response song to the male calling song. In addition, the acoustic disturbance stridulation differs notably between females and males as both sexes exhibit different temporal patterns of the defence sound. Furthermore, males use defence sounds more often than females. The higher proportion of male disturbance stridulation is consistent with a male-biased predation risk during calling and phonotactic behaviour. The temporal structures of the female and male defence sounds support a deimatic function of the startling sound in both females and males, rather than an adaptation for a particular temporal pattern. Independently of the clear differences in sound defence, no difference in regurgitation of gut content occurs between the sexes.     

Interspecific differences in growth of somatic and reproductive tissues during the breeding season in Menidia menidia and M. beryllina

The annual atherinid fishes, Menidia menidia and M. beryllina , are extremely similar morphologically, but appear to differ in their energetics and life histories. They emerge from winter in relatively emaciated condition. Menidia menidia males and females showed little change in carcass weight but significant increases in gonad weight in March and April prior to spawning in May. Female liver weight increased in March and remained high. Thus, this species had reached its reproductive size in the autumn and allocated its energy to gonadal growth during the spring. Menidia beryllina showed no significant increases in weight until early May, when carcass, liver and gonad all increased simultaneously, a pattern very different from its congener. The later spawning of M. beryllina is probably due both to its need for carcass growth in spring prior to spawning and to its apparent requirement for warmer water for growth. Females of both species invested more into liver and gonad than did males. Maximum gonadosomatic index was about twice as large for M. menidia males as for M. beryllina males, but the index was similar for females of both species.     

Effects of the sex-linked dwarf gene (dw) on the expression of the muscular dystrophy gene (am) in chicken.

The sex-linked dwarf gene (dw) was introduced into companion muscular dystrophic (am) and nondystrophic (Am+) New Hampshire chicken lines to investigate influences of the dwarf gene on breast muscle weights, muscle fiber area, and the histological expression of muscular dystrophy. Dystrophic and nondystrophic chickens within dwarf or nondwarf genotypes were similar in body and carcass weights. Pectoralis and supracoracoideus muscle weights (as a percentage of adjusted carcass weight) were similar in nondystrophic dwarf and nondwarf males and females. In addition, pectoralis weight was similar in dystrophic dwarf males and dystrophic nondwarf males and females. However, pectoralis weight was significantly smaller in dystrophic dwarf females than in dystrophic nondwarf females, whereas supracoracoideus weight was significantly larger in dystrophic dwarf males than in dystrophic nondwarf males. Supracoracoideus weight was similar in dystrophic dwarf males and females and dystrophic nondwarf females. Pectoralis muscle fiber area was influenced by sex and by dwarf and dystrophy genotype. Muscle fiber area was larger in females than in males, smaller in dwarfs than in nondwarfs, and smaller in dystrophic than in nondystrophic muscles. Muscle fiber degeneration and adipose infiltration was more extensive in dystrophic than in nondystrophic females and males, and it was more advanced in dwarfs than in nondwarfs. Excessive acetylcholinesterase staining patterns were characteristic of dystrophic muscle in both dwarf and nondwarf genotypes. Nondystrophic and dystrophic dwarf male and female chickens are comparable substitutes for nondwarfs as biomedical models with respect to pectoralis histology, acetylcholinesterase staining pattern, and pectoralis muscle hypertrophy.     

Adult size and reproduction in the ectoparasitoid Agrothereutes lanceolatus Walker (Hym., Ichneumonidae)

The effects of adult male and female size on reproductive performance in Agrothereutes lanceolatus Walker, a solitary ectoparasitoid of mature larvae and pupae of several pyralids and tortricids, were investigated. Females had a longer mean lifetime than males. Larger females lived longer, whereas the size of males did not influence the longevity. The number of ovarioles per female did not differ among females of different sizes but larger females carried a greater number of mature and immature eggs. When presented with host cocoons, large females parasitized a higher percentage of hosts than small females. This was due to the fact that larger females accepted more hosts for oviposition whereas smaller ones rejected more hosts. Small and large females used equal numbers of hosts for host-feeding, suggesting that large females removed a greater amount of materials from single hosts through host-feeding.     

Sexually differentiated flight responses of the Mexican bean beetle to larval and adult nutrition

Summary Flight of male and female Mexican bean beetle adults was examined in laboratory tests. The experimental design made it possible to examine flight behavior not only with respect to different types of hosts (young vs senescent common bean foliage) but also with respect to effects due to their utilization during particular stages of beetle development. The median flight time of males was significantly affected by the adult host, but not by the juvenile host; whereas, the median flight time of females tended to be more affected by the juvenile than by the adult host. These different effects of hosts on the flight times of males and females resulted in sexual dimorphism in flight when the sexes were fed senescent foliage as adults. Although age significantly affected the flight time of both males and females, the reproductive status of females did not affect their flight times. The significance of these results are discussed with respect to the influence of the nutritional complexity of habitats on life history strategies and population dynamics.     

Differences in Patterns of Reproductive Allocation between the Sexes in Nicrophorus orbicollis

Organisms are selected to maximize lifetime reproductive success by balancing the costs of current reproduction with costs to future survival and fecundity. Males and females typically face different reproductive costs, which makes comparisons of their reproductive strategies difficult. Burying beetles provide a unique system that allows us to compare the costs of reproduction between the sexes because males and females are capable of raising offspring together or alone and carcass preparation and offspring care represent the majority of reproductive costs for both sexes. Because both sexes perform the same functions of carcass preparation and offspring care, we predict that they would experience similar costs and have similar life history patterns. In this study we assess the cost of reproduction in male Nicrophorus orbicollis and compare to patterns observed in females. We compare the reproductive strategies of single males and females that provided pre- and post-hatching parental care. There is a cost to reproduction for both males and females, but the sexes respond to these costs differently. Females match brood size with carcass size, and thus maximize the lifetime number of offspring on a given size carcass. Males cull proportionately more offspring on all carcass sizes, and thus have a lower lifetime number of offspring compared to females. Females exhibit an adaptive reproductive strategy based on resource availability, but male reproductive strategies are not adaptive in relation to resource availability.     

The consequences of sexual selection in well‐adapted and maladapted populations of bean beetles†

Whether sexual selection generally promotes or impedes population persistence remains an open question. Intralocus sexual conflict (IaSC) can render sexual selection in males detrimental to the population by increasing the frequency of alleles with positive effects on male reproductive success but negative effects on female fecundity. Recent modeling based on fitness landscape theory, however, indicates that the relative impact of IaSC may be reduced in maladapted populations and that sexual selection therefore might promote adaptation when it is most needed. Here, we test this prediction using bean beetles that had undergone 80 generations of experimental evolution on two alternative host plants. We isolated and assessed the effect of maladaptation on sex‐specific strengths of selection and IaSC by cross‐rearing the two experimental evolution regimes on the alternative hosts and estimating within‐population genetic (co)variance for fitness in males and females. Two key predictions were upheld: males generally experienced stronger selection compared to females and maladaptation increased selection in females. However, maladaptation consistently decreased male‐bias in the strength of selection and IaSC was not reduced in maladapted populations. These findings imply that sexual selection can be disrupted in stressful environmental conditions, thus reducing one of the potential benefits of sexual reproduction in maladapted populations.     

Effects of tapeworm infection on male reproductive success and mating vigor in the red flour beetle,Tribolium castaneum

Parasites may exert negative effects on host survivorship and reproductive success. The effects of parasites on female host fitness have been well documented; however, the effects of parasites on the reproductive success of male hosts and particularly the underlying mechanisms that alter male fitness are not well understood. Previous studies demonstrated that infection by rat tapeworm (Hymenolepis diminuta) reduced the fitness of male red flour beetles (Tribolium castaneum) in an environment of female mate choice and strong male-male competition. The present study determined the role of female mate choice and male insemination capacity on observed fitness reduction of male beetles by the tapeworm parasites. We found that infected males showed reduced mating vigor and consequently inseminated fewer females than did uninfected males. Specifically, tapeworm infection reduced the number of offspring sired by a male by 14-22% even when male-male competition and female mate choice were absent. Further, the insemination capacity of males diminished by 30% because of infection. Female beetles did not discriminate against infected males in precopulatory mate choice experiments. Copulatory courtship, a determinant of postcopulatory female choice, was not significantly different between infected and uninfected males. Hence, we concluded that female beetles did not show either pre- or postcopulatory choice against tapeworm-infected males. Therefore, tapeworm-induced reduction in the reproductive success of male beetles possibly results from altered reproductive biology, such as lower mating vigor and decreased sperm quantity or quality.     

Effects of larval diet on development rates and reproductive maturation of male and female Mediterranean fruit flies

Abstract Mediterranean fruit fly Ceratitis capitata (Diptera: Tephritidae) larvae are capable of developing in one of many hosts that may vary greatly in quality. We hypothesized that they will respond to the larval environment in a manner beneficial to their subsequent reproductive performance. Accordingly, we investigated the effects of various larval diets (varying in the amount of protein and sugar they contain) on the size, development time, nutritional status and reproductive maturation (ovarian development and onset of sexual behaviour) of females and males. We found that flies which undergo larval development in artificial host fruit that contain sugar and protein ('protein-fed') were larger, developed faster and emerged with more nutritional reserves than flies that were protein-deprived as larvae. Protein-fed males, regardless of their size, became sexually active before males that developed in hosts with no protein. Protein-fed females produced more mature eggs than protein-deprived ones. Moreover, protein-fed females tended to copulate sooner than females that developed in hosts with no protein. In addition, regardless of female larval diet, females with more mature eggs tended to copulate sooner than females with less mature eggs. In light of these results, the importance of the larval environment for adult reproductive success is discussed.     

Mating or ovipositing? A crucial decision in the life history of the cabbage aphid parasitoid Diaeretiella rapae (M’Intosh)

1. The reproductive fitness of a parasitoid depends on its mating and ovipositing success. Virgin haplodiploid females can reproduce, but produce only males, and may diminish fitness by producing more male offspring than required. Therefore, females must decide on whether to mate or oviposit first. 2. This study was conducted to assess the mating versus ovipositing decision and its impact on the reproductive fitness of Diaeretiella rapae (Hymenoptera: Aphididae), an endoparasitoid of the cabbage aphid Brevicoryne brassicae (Hemiptera: Aphididae). 3. When newly emerged females were given a choice between mating and ovipositing, about 62% of D. rapae females preferred to mate before ovipositing. Those females who oviposited before mating parasitised only 10% of the available aphids. After mating, females superparasitised their hosts with fertilised eggs, which resulted in a highly female‐biased sex ratio in the offspring. 4. Mating success was very high (91%) in the presence of hosts (cabbage aphid nymphs) compared with that in the absence of aphids. However, mating success was not influenced by the quality (size) of the hosts present in the mating arena, despite a parasitoid preference for larger hosts during oviposition. The time between pairing and mating was also shorter in the presence of host aphids. The mean number of aphids parasitised and the parasitism rate were significantly greater after mating.