Male Killing Research Articles

Modeling the indirect effect of Wolbachia on the infection dynamics of horizontally transmitted viruses.

Intracellular bacteria of the genus Wolbachia are widely distributed in arthropods. There is growing empirical evidence that Wolbachia directly interacts with viruses and other parasites inside the arthropod host, sometimes resulting in low or no pathogen replication. Previous theoretical studies showed that this direct effect of Wolbachia can result in a reduced virus prevalence (within the population), suggesting that Wolbachia could be used in the biological control of vector-borne diseases (e.g., dengue fever). However, Wolbachia might also indirectly affect virus dynamics because Wolbachia-induced reproductive phenotypes (cytoplasmic incompatibility or male killing) increase the larval mortality of hosts and thus alter the age structure of populations. We investigated this indirect effect using mathematical models with overlapping generations, and found the results to depend strongly on the host's life history. In general, the indirect effect can result in two different outcomes: (1) reduced virus prevalence and virus invasion ability, and (2) increased virus prevalence and virus invasion ability. The former occurs for host species with larval competition and undercompensation, the latter for hosts with either adult competition or larval competition and overcompensation. These findings suggest that the effect of Wolbachia on a specific virus is sensitive to the host's life history. We discuss the results with respect to biocontrol programs using Wolbachia.

English

Because of climate change and failure of the existing methods of control of vector borne diseases and vector are increasing. Mosquito species are the main vectors of human pathogens causing malaria, dengue, filariasis, chikungunya, yellow fever and West Nile. There are no well-organized methods and tools of controls of vector and vector borne diseases, since no efficient vaccines or drugs are available. Despite years of intense effort to control them, many of these diseases are increasing in prevalence, geographical distribution and severity, and options to control them are limited. Currently, efforts focused on the control of vector populations. During recent years, the endosymbiont bacterium has been well-documented and has led to suggestions that these could be used to control pests and therefore diseases. Wolbachia is perhaps the most renowned insect symbiont, primarily due to its ability to manipulate insect reproduction and to interfere with major human pathogens therefore providing new avenues for pest control. Wolbachia are common intracellular bacteria that are found in arthropods and nematodes. These alphaproteobacteria endosymbionts are transmitted vertically through host eggs and alter host biology in diverse ways, including the induction of reproductive manipulations, such as feminization, parthenogenesis, male killing and sperm–egg incompatibility. Wolbachia strains can invade and sustain themselves in mosquito populations, reduce adult lifespan, affect mosquito reproduction and interfere with pathogen replication. Wolbachia can also provide direct fitness benefits to their hosts by affecting nutrition and development, influencing fecundity or oogenesis and providing resist­ance to pathogens. For instance, infection of Anopheles gambiae with both wMelPop and wAlbB reduced the oocyst burden of Plasmodium falciparum, compared to uninfected control mosquitoes. In addition, similar study observed that the wMelPop strain inhibited development of Plasmodium berghei; however, the wAlbB strain was found to enhance development of P. berghei.   Key words: Malaria, Aedes aegypti, Chikungunya, dengue, drosophila, wolbachiapipientis, vectorborn diseases.

Population genetic structure and Wolbachia infection in an endangered butterfly, Zizina emelina (Lepidoptera, Lycaenidae), in Japan.

Zizina emelina (de l'Orza) is listed on Japan's Red Data List as an endangered species because of loss of its principal food plant and habitat. We compared parts of the mitochondrial and nuclear genes of this species to investigate the level of genetic differentiation among the 14 extant populations. We also examined infection of the butterfly with the bacterium Wolbachia to clarify the bacterium's effects on the host population's genetic structure. Mitochondrial and nuclear DNA analyses revealed that haplotype composition differed significantly among most of the populations, and the fixation index F ST was positively correlated with geographic distance. In addition, we found three strains of Wolbachia, one of which was a male killer; these strains were prevalent in several populations. There was linkage between some host mitochondrial haplotypes and the three Wolbachia strains, although no significant differences were found in a comparison of host mitochondrial genetic diversity with nuclear genetic diversity in Wolbachia-infected or -uninfected populations. These genetic analyses and Wolbachia infection findings show that Z. emelina has little migratory activity and that little gene flow occurs among the current populations.

Cytochrome P4501A1 expression in blubber biopsies of endangered false killer whales (Pseudorca crassidens) and nine other odontocete species from Hawai'i.

Odontocetes (toothed whales) are considered sentinel species in the marine environment because of their high trophic position, long life spans, and blubber that accumulates lipophilic contaminants. Cytochrome P4501A1 (CYP1A1) is a biomarker of exposure and molecular effects of certain persistent organic pollutants. Immunohistochemistry was used to visualize CYP1A1 expression in blubber biopsies collected by non-lethal sampling methods from 10 species of free-ranging Hawaiian odontocetes: short-finned pilot whale, melon-headed whale, pygmy killer whale, common bottlenose dolphin, rough-toothed dolphin, pantropical spotted dolphin, Blainville's beaked whale, Cuvier's beaked whale, sperm whale, and endangered main Hawaiian Islands insular false killer whale. Significantly higher levels of CYP1A1 were observed in false killer whales and rough-toothed dolphins compared to melon-headed whales, and in general, trophic position appears to influence CYP1A1 expression patterns in particular species groups. No significant differences in CYP1A1 were found based on age class or sex across all samples. However, within male false killer whales, juveniles expressed significantly higher levels of CYP1A1 when compared to adults. Total polychlorinated biphenyl (∑PCBs) concentrations in 84% of false killer whales exceeded proposed threshold levels for health effects, and ∑PCBs correlated with CYP1A1 expression. There was no significant relationship between PCB toxic equivalent quotient and CYP1A1 expression, suggesting that this response may be influenced by agonists other than the dioxin-like PCBs measured in this study. No significant differences were found for CYP1A1 expression among social clusters of false killer whales. This work provides a foundation for future health monitoring of the endangered stock of false killer whales and other Hawaiian odontocetes.

Recent genome reduction of Wolbachia in Drosophila recens targets phage WO and narrows candidates for reproductive parasitism.

Wolbachia are maternally transmitted endosymbionts that often alter their arthropod hosts’ biology to favor the success of infected females, and they may also serve as a speciation microbe driving reproductive isolation. Two of these host manipulations include killing males outright and reducing offspring survival when infected males mate with uninfected females, a phenomenon known as cytoplasmic incompatibility. Little is known about the mechanisms behind these phenotypes, but interestingly either effect can be caused by the same Wolbachia strain when infecting different hosts. For instance, wRec causes cytoplasmic incompatibility in its native host Drosophila recens and male killing in D. subquinaria. The discovery of prophage WO elements in most arthropod Wolbachia has generated the hypothesis that WO may encode genes involved in these reproductive manipulations. However, PCR screens for the WO minor capsid gene indicated that wRec lacks phage WO. Thus, wRec seemed to provide an example where phage WO is not needed for Wolbachia-induced reproductive manipulation. To enable investigation of the mechanism of phenotype switching in different host backgrounds, and to examine the unexpected absence of phage WO, we sequenced the genome of wRec. Analyses reveal that wRec diverged from wMel approximately 350,000 years ago, mainly by genome reduction in the phage regions. While it lost the minor capsid gene used in standard PCR screens for phage WO, it retained two regions encompassing 33 genes, several of which have previously been associated with reproductive parasitism. Thus, WO gene involvement in reproductive manipulation cannot be excluded and reliance on single gene PCR should not be used to rule out the presence of phage WO in Wolbachia. Additionally, the genome sequence for wRec will enable transcriptomic and proteomic studies that may help elucidate the Wolbachia mechanisms of altered reproductive manipulations associated with host switching, perhaps among the 33 remaining phage genes.

Individual Behaviors Dominate the Dynamics of an Urban Mountain Lion Population Isolated by Roads

Large carnivores can be particularly sensitive to the effects of habitat fragmentation on genetic diversity [1, 2]. The Santa Monica Mountains (SMMs), a large natural area within Greater Los Angeles, is completely isolated by urban development and the 101 freeway to the north. Yet the SMMs support a population of mountain lions (Puma concolor), a very rare example of a large carnivore persisting within the boundaries of a megacity. GPS locations of radio-collared lions indicate that freeways are a near-absolute barrier to movement. We genotyped 42 lions using 54 microsatellite loci and found that genetic diversity in SMM lions, prior to 2009, was lower than that for any population in North America except in southern Florida, where inbreeding depression led to reproductive failure [3-5]. We document multiple instances of father-daughter inbreeding and high levels of intraspecific strife, including the unexpected behavior of a male killing two of his offspring and a mate and his son killing two of his brothers. Overall, no individuals from the SMMs have successfully dispersed. Gene flow is critical for this population, and we show that a single male immigrated in 2009, successfully mated, and substantially enhanced genetic diversity. Our results imply that individual behaviors, most likely caused by limited area and reduced opportunities to disperse, may dominate the fate of small, isolated populations of large carnivores. Consequently, comprehensive behavioral monitoring can suggest novel solutions for the persistence of small populations, such as the transfer of individuals across dispersal barriers.

Preference for isolated host plants facilitates invasion ofDanaus chrysippus(Linnaeus, 1758) (Lepidoptera: Nymphalidae) by a bacterial male-killerSpiroplasma

Matrilinearly inherited endosymbiotic bacteria are estimated to occur in a third of all terrestrial arthropods. They include male killers, which are typically associated with organisms that lay their eggs in batches. Batch laying favours male-killing bacteria because infected female larvae can cannibalise dead brothers and do not have to compete with them for larval resources. This paper tackles the paradox of high male-killer infection rates in Danaus chrysippus (Linnaeus, 1758), a butterfly that lays its eggs singly rather than in batches, making the selective advantage of male killing for the bacterium hard to understand. The study was conducted in the Nairobi region of Kenya where two substantially allopatric but seasonally migratory semispecies of Danaus chrysippus overlap and hybridise. Within this hybrid zone, but apparently not outside it, D. chrysippus hosts the endosymbiotic male killer, Spiroplasma ixodetis. In Nairobi, this bacterium can infect up to 95% of females. Semispecies D. chrysippus chrysippus and its hybrid with D. chrysippus dorippus (form transiens) are heavily infected, unlike the parental pure D. chrysippus dorippus semispecies, which may be protected by a suppressor gene. We find that: (1) adult females oviposit preferentially on isolated host plants; (2) female larvae on isolated plants survive better than on plants growing in clumps; (3) female larvae survive in greater numbers on plants removed to the laboratory compared to plants left outside; (4) high Spiroplasma infection favours female survival; and (5) high egg/larval density adversely affects adult body size. We conclude that: (1) the butterflies' preference for isolated host plants creates high egg densities and hence enables invasion by Spiroplasma; (2) male killing favours female survival through cannibalism of male eggs and the extra food-plant resources so released; and (3) the butterfly's preference for isolated host plants may provide an enemy-free space that protects eggs and larvae from predators and parasitoids.

Young killer whale males learn dialect

![Figure][1] A young male killer whale vocalizing. Photo credit: J. Crance, HSWRI. If you travel through a country and you have an ear for dialect, you might notice odd words pop up that are particular to the location. Dialects are an occupational hazard of travel, and it turns out that

Distribution and evolutionary impact of wolbachia on butterfly hosts.

Wolbachia are maternally inherited endosymbiotic alpha-proteobacteria found in terrestrial arthropods and filarial nematodes. They are transmitted vertically through host cytoplasm and alter host biology by inducing various reproductive alterations, like feminization, parthenogenesis, male killing (MK) and cytoplasmic incompatibility. In butterflies, some effects especially MK and sperm-egg incompatibility are well established. All these effects skew the sex ratio towards female and subsequently favor the vertical transmission of Wolbachia. Some of the insects are also infected with multiple Wolbachia strains which may results in some complex phenomenon. In the present review the potential of Wolbachia for promoting evolutionary changes in its hosts with emphasis on recent advances in interactions of butterfly-Wolbachia is discussed. In addition to this, strain diversity of Wolbachia and its effects on various butterfly hosts are also highlighted.

Evidence for vocal learning in juvenile male killer whales, Orcinus orca, from an adventitious cross-socializing experiment.

Killer whales (Orcinus orca) are thought to learn their vocal dialect. Dispersal in the species is rare, but effects of shifts in social association on the dialect can be studied under controlled conditions. Individual call repertoires and social association were measured in three adult female killer whales and three males (two juveniles and an adult) during two periods, 2001-2003 and 2005-2006. Three distinct dialect repertoires were represented among the subjects. An adventitious experiment in social change resulted from the birth of a calf and the transfer of two non-focal subjects in 2004. Across the two periods, 1691 calls were collected, categorized and attributed to individuals. Repertoire overlap for each subject dyad was compared with an index of association. During 2005-2006, the two juvenile males increased association with the unrelated adult male. By the end of the period, both had begun producing novel calls and call features characteristic of his repertoire. However, there was little or no reciprocal change and the adult females did not acquire his calls. Repertoire overlap and association were significantly correlated in the first period. In the second, median association time and repertoire similarity increased, but the relationship was only marginally significant. The results provided evidence that juvenile male killer whales are capable of learning new call types, possibly stimulated by a change in social association. The pattern of learning was consistent with a selective convergence of male repertoires.

Basal metabolism of an adult male killer whale (Orcinus orca)

Marine Mammal ScienceVolume 30, Issue 3 p. 1229-1237 Notes Basal metabolism of an adult male killer whale (Orcinus orca) Graham A. J. Worthy, Corresponding Author Graham A. J. Worthy Hubbs-SeaWorld Research Institute, San Diego, California 92109, U.S.ACorresponding author: (e-mail: graham.worthy@ucf.edu).Search for more papers by this authorTamara A. M. Worthy, Tamara A. M. Worthy Hubbs-SeaWorld Research Institute, San Diego, California 92109, U.S.ASearch for more papers by this authorPamela K. Yochem, Pamela K. Yochem Hubbs-SeaWorld Research Institute, San Diego, California 92109, U.S.ASearch for more papers by this authorChristopher Dold, Christopher Dold SeaWorld Parks and Entertainment, Orlando, Florida 32821, U.S.ASearch for more papers by this author Graham A. J. Worthy, Corresponding Author Graham A. J. Worthy Hubbs-SeaWorld Research Institute, San Diego, California 92109, U.S.ACorresponding author: (e-mail: graham.worthy@ucf.edu).Search for more papers by this authorTamara A. M. Worthy, Tamara A. M. Worthy Hubbs-SeaWorld Research Institute, San Diego, California 92109, U.S.ASearch for more papers by this authorPamela K. Yochem, Pamela K. Yochem Hubbs-SeaWorld Research Institute, San Diego, California 92109, U.S.ASearch for more papers by this authorChristopher Dold, Christopher Dold SeaWorld Parks and Entertainment, Orlando, Florida 32821, U.S.ASearch for more papers by this author First published: 05 December 2013 https://doi.org/10.1111/mms.12091Citations: 10Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume30, Issue3July 2014Pages 1229-1237 RelatedInformation

Male killing Spiroplasma protects Drosophila melanogaster against two parasitoid wasps

Maternally transmitted associations between endosymbiotic bacteria and insects are diverse and widespread in nature. Owing to imperfect vertical transmission, many heritable microbes have evolved compensational mechanisms to enhance their persistence in host lineages, such as manipulating host reproduction and conferring fitness benefits to host. Symbiont-mediated defense against natural enemies of hosts is increasingly recognized as an important mechanism by which endosymbionts enhance host fitness. Members of the genus Spiroplasma associated with distantly related Drosophila hosts are known to engage in either reproductive parasitism (i.e., male killing) or defense against natural enemies (the parasitic wasp Leptopilina heterotoma and a nematode). A male-killing strain of Spiroplasma (strain Melanogaster Sex Ratio Organism (MSRO)) co-occurs with Wolbachia (strain wMel) in certain wild populations of the model organism Drosophila melanogaster. We examined the effects of Spiroplasma MSRO and Wolbachia wMel on Drosophila survival against parasitism by two common wasps, Leptopilina heterotoma and Leptopilina boulardi, that differ in their host ranges and host evasion strategies. The results indicate that Spiroplasma MSRO prevents successful development of both wasps, and confers a small, albeit significant, increase in larva-to-adult survival of flies subjected to wasp attacks. We modeled the conditions under which defense can contribute to Spiroplasma persistence. Wolbachia also confers a weak, but significant, survival advantage to flies attacked by L. heterotoma. The host protective effects exhibited by Spiroplasma and Wolbachia are additive and may provide the conditions for such cotransmitted symbionts to become mutualists. Occurrence of Spiroplasma-mediated protection against distinct parasitoids in divergent Drosophila hosts suggests a general protection mechanism.

Male Killing Spiroplasma Preferentially Disrupts Neural Development in the Drosophila melanogaster Embryo

Male killing bacteria such as Spiroplasma are widespread pathogens of numerous arthropods including Drosophila melanogaster. These maternally transmitted bacteria can bias host sex ratios toward the female sex in order to ‘selfishly’ enhance bacterial transmission. However, little is known about the specific means by which these pathogens disrupt host development in order to kill males. Here we show that a male-killing Spiroplasma strain severely disrupts nervous tissue development in male but not female D. melanogaster embryos. The neuroblasts, or neuron progenitors, form properly and their daughter cells differentiate into neurons of the ventral nerve chord. However, the neurons fail to pack together properly and they produce highly abnormal axons. In contrast, non-neural tissue, such as mesoderm, and body segmentation appear normal during this time, although the entire male embryo becomes highly abnormal during later stages. Finally, we found that Spiroplasma is altogether absent from the neural tissue but localizes within the gut and the epithelium immediately surrounding the neural tissue, suggesting that the bacterium secretes a toxin that affects neural tissue development across tissue boundaries. Together these findings demonstrate the unique ability of this insect pathogen to preferentially affect development of a specific embryonic tissue to induce male killing.

Hologenomic speciation: synergy between a male-killing bacterium and sex-linkage creates a ‘magic trait’ in a butterfly hybrid zone

Danaus chrysippus (L.) in Africa comprises four substantially isolated semispecies that are migratory and hybridize on a seasonal basis throughout the eastern and central part of the continent. In the hybrid zone (but not elsewhere), the butterfly is commonly host to a male killing endosymbiotic bacterium, Spiroplasma sp., which principally infects one semispecies, Danaus chrysippus chrysippus in Kenya. A W-autosome mutation, inherited strictly matrilinearly, links B and C colour gene loci, which have thus gained sex-linkage in chrysippus. We have monitored variation in sex ratio and genotype at the A and C colour gene loci for two extended periods of 18 months (2004–5) and 12 months (2009–10) in adults reared from wild eggs laid on trap plants in Kasarani, near Nairobi, Kenya. Additionally, in 2009–10, all surviving adult butterflies were screened for Spiroplasma infection. The hybridizing Kasarani population is highly atypical in three respects, and has apparently been so for some 30 years: first, the sex ratio is permanently female-biased (as expected), although subject to seasonal fluctuation, being lowest (male/female) when D. c. chrysippus (cc) peaks and highest when Danaus chrysippus dorippus (CC) predominates; second, the population is invariably dominated by Cc heterozygotes of both sexes but especially females; and third, cc males are always scarce because they are systematically eliminated by male killing, whereas the CC genotype is male-biased. It is this imbalance of sex versus genotype that determines the massive departure from Hardy–Weinberg equilibrium in the population, in part because cc females have little choice but to pair with C- males. We suggest that: first, Cc hybrids of both sexes fail to disperse in the company of either parental semispecies; second, Spiroplasma positive females carrying the W-autosome mutation have a selective advantage over females that lack the translocation; third, the endoparasite and the translocation create a ‘magic trait’ linkage group that underlies hologenomic reproductive isolation between two emerging species, D. c. chrysippus and D. c. dorippus; and, fourth, that the predominance of males in dorippus suggests that individuals must be protected by a male-killing suppressor gene. By contrast to the C locus, Aa heterozygotes are in substantial and permanent deficit, suggesting either assortative mating between AA (chrysippus and dorippus) and aa (Danaus chrysippus alcippus), or heterozygote unfitness, or both. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 92–109.

Low Temperature Reveals Genetic Variability Against Male-Killing Spiroplasma in Drosophila melanogaster Natural Populations

Spiroplasma endosymbionts are maternally inherited microorganisms which infect many arthropod species. In some Drosophila species, it acts as a reproductive manipulator, spreading in populations by killing the sons of infected mothers. Distinct Drosophila melanogaster populations from Brazil exhibit variable male-killing Spiroplasma prevalences. In this study, we investigated the presence of variability for the male-killing phenotype among Drosophila and/or Spiroplasma strains and verified if it correlates with the endosymbiont prevalence in natural populations. For that, we analyzed the male-killing expression when Spiroplasma strains from different populations were transferred to a standard D. melanogaster line (Canton-S) and when a common Spiroplasma strain was transferred to different wild-caught D. melanogaster lines, both at optimal and challenging temperatures for the bacteria. No variation was observed in the male-killing phenotype induced by different Spiroplasma strains. No phenotypic variability among fly lines was detected at optimal temperature (23 °C), as well. Conversely, significant variation in the male-killing expression was revealed among D. melanogaster lines at 18.5 °C, probably caused by imperfect transmission of the endosymbiont. Distinct lines differed in their average sex ratios as well as in the pattern of male-killing expression as the infected females aged. Greater variation occurred among lines from one locality, although there was no clear correlation between the male-killing intensity and the endosymbiont prevalence in each population. Imperfect transmission or male killing may also occur in the field, thus helping to explain the low or intermediate prevalences reported in nature. We discuss the implications of our results for the dynamics of male-killing Spiroplasma in natural populations.

Life History Traits ofTalicada nyseus(Lepidoptera: Lycaenidae) Butterfly Under Laboratory Conditions

The butterfly Talicada nyseus G. (Lepidoptera: Lycaenidae) is abundant in India and Sri Lanka (Karunaratne, et al., 2002). In India, this butterfly is chiefly found in the peninsular area, Maharashtra, Karnataka, Punjab and foothills of the Himalayas (Singh, 2005). The host plants of this butterfly include Kalanchoe spp. (Saxifragales: Crassulaceae). Adult Talicada nyseus feed on nectar of surrounding flowering plants but are also reported to feed on lichens (Karunaratne, et al., 2002). Recently it has been discovered that Talicada nyseus is infected with maternally inherited Wolbachia bacteria (Ankola, et al., 2011; Salunke, et al., 2012) and exhibits a female biased sex ratio (Ankola, et al., 2011). It is suspected that the presence of the female biased sex ratio in this butterfly is caused by its endosybiont Wolbachia. As an endosymbiont, Wolbachia is known to cause female biased sex ratio in butterfly hosts by inducing two distinct reproductive anomalies: feminization of genetic males (Hiroki et al., 2004) and male killing (Jigginset al., 2001; Charlat et al., 2005). It is essential to record scientific data regarding the life history traits of Talicada nyseus naturally infected with Wolbachia. In the present report life history traits of Talicada nyseus which harbor Wolbachia infection were studied under controlled conditions. The individual Talicada nyseus specimens used for the study were collected from a laboratory reared population which was previously confirmed to be heavily infected with Wolbachia. Five individual mated pairs were used separately for the present study. The life cycle was analyzed at 28.09 ± 0.564° C. The data collected were statistically analyzed by paired t-test with the help of SPSS 7.5. Wolbachia infection in this butterfly was previously documented by Ankola etal. (2011). The fecundity of Talicada nyseus was found to be ranging from 61.6± 12.08 to 66.4 ± 17.75 (Table 1). The fecundity data obtained from the present study is in agreement with our previous report (Ankola et al., 2011). More than 95% hatchability was recorded during the present investigation indicating that there might not be male-killing induced by Wolbachia in Talicada nyseus (Jiggins et al., 2000; Charlat et al., 2007). The hatching time required for eggs ranged from 7.4 ± 1.83 to 9.6 ± 2.71 (Table 1). Furthermore, the time required for the

Male Killing Caused by a Spiroplasma Symbiont in the Small Brown Planthopper, Laodelphax striatellus

Spiroplasma-mediated late male killing was found in the small brown planthopper, Laodelphax striatellus. Female-biased colonies (maternal lines, N = 4) were established from planthoppers collected in Taiwan and Japan. This sex ratio distortion was maternally inherited (sex ratio of total number of progenies [female:male]: 488:0 in F1, 198:7 in F2, 407:0 in F3; likelihood ratio test of all generations, P < 0.0001) and caused by male death during nymphal stages. The female-biased colonies were doubly infected with Spiroplasma and Wolbachia, and the non-biased colonies were infected solely with Wolbachia. Antibiotic treatment resulted in a normal sex ratio, strongly suggesting that bacteria are manipulating host reproduction. Spiroplasma-singly-infected planthopper colonies created by the antibiotic treatment produced progeny with strongly female-biased sex ratios (181:2; likelihood ratio test, χ(2) = 231.6, P < 0.0001). This is the first report of Spiroplasma-mediated male killing in hemimetabolous insects.

The direct effects of male killer infection on fitness of ladybird hosts (Coleoptera:Coccinellidae)

Male killing bacteria are common in insects and are thought to persist in host populations primarily by indirect fitness benefits to infected females, whereas direct fitness effects are generally assumed to be neutral or deleterious. Here, we estimated the effect of male killer infection on direct fitness (number of eggs laid, as a measure of fecundity, together with survival) and other life-history traits (development time and body size) in seven ladybird host/male killer combinations. Effects of male killers on fecundity ranged, as expected, from costly to neutral; however, we found evidence of reduced development time and increased survival and body size in infected strains. Greater body size in Spiroplasma-infected Harmonia axyridis corresponded to greater ovariole number and therefore higher potential fecundity. To our knowledge, this is the first report of direct benefits of male killer infection after explicitly controlling for indirect fitness effects. Neutral or deleterious fitness effects of male killer infection should not therefore be automatically assumed.

Asymmetry in male lethal fight between parapatric forms of a social spider mite

Closely related species often show adjacent geographic distributions, albeit with some overlap. This contiguity is thought to result from secondary contact between (spatially separated) diverging groups or from parapatric speciation. Fights between males of closely related species will affect their chance to mate with females of the other species, which in turn may promote their spatial segregation and drive their speciation. Stigmaeopsis miscanthi is a social spider mite that lives in a group within self-woven nests on leaves of Chinese silver grass. This mite shows lethal male-male fight as a means to maintain a harem, and has two forms showing differences in the levels of male-male aggression, diapause intensity in females and the relative length of the first to third legs. The two forms show parapatric distributions. We found that males of one form readily engage themselves in lethal fight with males of the other form, thereby acquiring the nests and gaining access to females of this other form. Males of the aggressive form tend to win the fights with males of the other form. Their first legs are longer which may provide them with a better weapon and which also indicate a larger body width. However, another determinant of who wins the fight is the length of the third legs which can be a proxy for body length. Based on these results, we hypothesize that male killing behavior is one of the mechanisms maintaining parapatry (instead of sympatry) of the two spider mite forms apart from difference in diapause attributes.

Wolbachia Infection in Populations of Ostrinia furnacalis: Diversity, Prevalence, Phylogeny and Evidence for Horizontal Transmission

Wolbachia are maternally inherited endosymbiotic bacteria infecting a wide range of arthropods and filarial nematodes. They can induce various reproduction alterations in their hosts, including thelytokous parthenogenesis, cytoplasmic incompatibility (CI), feminization of genetic males and male killing. Here we investigated diversity and prevalence patterns of Wolbachia infection in 43 geographical populations of the Asian corn borer, Ostrinia furnacalis, in China and one population in North Korea. Based on Wolbachia surface protein gene (wsp) sequences, nine strains of Wolbachia (wFur1-wFur9), belonging to supergroups A and B, were identified in populations of O. furnacalis with an average infection rate of 10.5%. Superinfection commonly appeared in individuals of O. furnacalis and coinfection patterns were very complex. There was no specific pattern for the prevalence and distribution of the nine Wolbachia strains suggesting an intricate evolutionary history of Wolbachia infection in this species. The genetic similarity of the wFur1-wFur9 strains with those detected in two parasitoids of O. furnacalis, Macrocentrus cingulum and Lydella grisescens, strongly suggests host-parasitoid horizontal transmission.