Sexual Host Research Articles

Cytosine methylation mediates sexual conflict

Transposons are infectious agents in sexual populations and can go to fixation even if they reduce the fitness of the host. Sexual hosts are therefore under selective pressure to evolve defensive functions that relieve the fitness penalty imposed by transposons. In mammals, this defensive function depends on transcriptional silencing through targeted cytosine methylation of transposon promoters in both germ-line and somatic tissues (with the probable involvement of some post-transcriptional gene silencing by pathways related to RNA interference). New families of transposons evolve in response to selective pressures imposed by host silencing mechanisms, with the result that the mammalian genome has suffered waves of transposon bombardment that have contributed the majority of the total sequence. Cytosine methylation defends the sexual genome against transposon damage even as it enforces a requirement for sexual reproduction through the phenomenon of genomic imprinting.

Phenotypic and genotypic structure of Phytophthora infestans populations on potato and tomato in France and Switzerland

A total of 134 isolates of Phytophthora infestans were collected from potato and 42 from tomato fields in Switzerland and France in 1996 and 1997, and compared with isolates from other countries. The structure of the populations was analysed phenotypically and genotypically, and associated to geographical, seasonal and host origin. Phenotype characteristics of the isolates included mating type; sensitivity to phenylamide fungicides; virulence on potato differentials; and pathogenic fitness. Genotypes were assessed for mitochondrial DNA haplotype with restriction fragment length polymorphism‐polymerase chain reaction (RFLP‐PCR) as well as amplified fragment length polymorphism (AFLP) and simple sequence repeats or microsatellites (SSR). The majority (96%) of isolates originating from potato were the A1 mating type, whereas half the isolates collected from tomato were A2 mating type. Isolates with sensitive, intermediate and resistant responses to the phenylamide fungicide metalaxyl‐M were detected in the populations. Isolates from potato represented races with highly complex virulence spectra, whereas those from tomato belonged to simple races. The pathogenic fitness of isolates was highest on the host of origin, and was significantly reduced for isolates from potato on tomato. One of the four haplotypes, Ia, dominated the population (93% of isolates). Among isolates collected from potato, 15 different SSR genotypes were detected of which two, A‐03 and A‐06, dominated the population. From tomato, 11 SSR genotypes were found of which four, A‐03, B‐03, D‐03 and F‐01, formed the major proportion of the population. Every ninth and fourth isolate from potato and tomato, respectively, represented a different SSR genotype. Four genotypes were isolated from both hosts, whereas 11 and seven genotypes, respectively, originated exclusively from either potato or tomato. The SSR genotype D‐02, represented by the ‘old’ Ib haplotype, was still detected in a few isolates in the current population, and in older reference isolates from different countries. The SSR genotype was not associated with mating type or sensitivity to phenylamide fungicides. A total of 40 AFLP genotypes were distinguished among the isolates, every second isolate representing another genotype. The diverse phenotypic and genotypic structure of the current field populations in Europe suggests that they may have evolved from local processes including sexual recombination, host preference and selection rather than through long‐distance migration.

The Ratchet and the Red Queen: the maintenance of sex in parasites

Abstract The adaptive significance of sexual reproduction remains as an unsolved problem in evolutionary biology. One promising hypothesis is that frequency-dependent selection by parasites selects for sexual reproduction in hosts, but it is unclear whether such selection on hosts would feed back to select for sexual reproduction in parasites. Here we used individual-based computer simulations to explore this possibility. Specifically, we tracked the dynamics of asexual parasites following their introduction into sexual parasite populations for different combinations of parasite virulence and transmission. Our results suggest that coevolutionary interactions with hosts would generally lead to a stable coexistence between sexual parasites and a single parasite clone. However, if multiple mutations to asexual reproduction were allowed, we found that the interaction led to the accumulation of clonal diversity in the asexual parasite population, which led to the eventual extinction of the sexual parasites. Thus, coevolution with sexual hosts may not be generally sufficient to select for sex in parasites. We then allowed for the stochastic accumulation of mutations in the finite parasite populations (Muller's Ratchet). We found that, for higher levels of parasite virulence and transmission, the population bottlenecks resulting from host–parasite coevolution led to the rapid accumulation of mutations in the clonal parasites and their elimination from the population. This result may explain the observation that sexual reproduction is more common in parasitic animals than in their free-living relatives.

First report of powdery mildew on mulberry caused by Phyllactinia guttata in the eastern Mediterranean region of Turkey

Mulberry (Morus spp.) is an increasingly importantcrop that is widely planted in the Hatay province,Turkey as a food source for silkworms. Production ofsilk products is the main source of income in thisprovince. Serious damage caused by powdery mildewwas discovered in the main mulberry production areasof Samandag and Harbiye regions in 2000. A diseaseincidence of 81–95% was recorded in affected orch-ards. Symptoms included white superficial myceliumwith abundant sporulation on lower leaf surfaces, andchlorotic spots on upper leaf surfaces. Mycelial growthwas observed on leaves, petioles and pedicels, but noton fruit and branches. Symptoms were apparent on eachplant, with disease severity ranging from a fewindividual spots to numerous lesions almost coveringwhole leaves.The white mycelium had lobed appressoria. Conidio-phores were straight and cylindrical. Single-celled, club-shaped conidia occurred usually singly on unbranchedconidiophores. Conidia ranged in length from 55 to85 mm (mean 68·25 ^2·88 mm), and in width from 15to 20 mm (mean 16·65 ^0·7 mm). Cleistothecia withtapering appendages and a bulbous base were yellowwhen young and turned black at maturity. Eachcleistothecium contained nine to 13 unitunicate asci,broadly oval to ellipsoid, short-stalked, and containingtwo ascospores. The size of cleistothecia ranged from225 to 255 mm in diameter (mean 235 ^3·27 mm).Asci were 68–95 mm long (mean 78·5 ^2·1 mm) and35–40 mm wide (mean 37·5 ^0·9 mm). Ascosporeswere 35–45 mm long (mean 40 ^1·29 mm) and 12·5–17·5 mm wide (mean 16 ^0·7 mm). The length ofappendages on cleistothecia ranged from 180 to285 mm (mean 242·6 ^6·7 mm).Pathogenicity tests were conducted on 1-year-old,healthy mulberry seedlings. These plants were inocu-lated by shaking conidia from powdery mildew-infectedleaves onto the leaves of healthy plants. Plants wereincubated in a growth chamber at 26 ^28C with a 16 hphotoperiod. Inoculated plants developed powderymildew symptoms after 9 days. The symptoms oninoculated plants and the morphological characteristicsof the pathogen were similar to those for naturallyinfected plants.Based on the characteristics of sexual and asexualstates and host specialization, the fungus was identifiedas Phyllactinia guttata (Webster, 1979; Hanlin, 1992).This is the first report of powdery mildew on mulberryin the eastern Mediterranean region of Turkey. Acombination of high inoculum pressure, low humidityand an unusually hot, dry summer during 2000favoured fungal infection and disease development.The disease is important as severe foliar lesions renderplants unacceptable for silkworm production.

Choosy females and indiscriminate males: mate choice in mixed populations of sexual and hybridogenetic water frogs (Rana lessonae, Rana esculenta)

For several decades, behavioral ecologists have studied the effects of the environment on the behavior of individuals; but only fairly recently they have started to ask the reverse question: how do the behavioral strategies of individuals affect the composition and dynamics of populations and communities? Although intuitively obvious, this feedback from individual to higher levels is difficult to demonstrate, except in systems with exceptionally fast and marked responses of the populations to the behavior of its members. Such a system exists in sperm-dependent species. In European water frogs, for instance, successful reproduction of a hybrid species (R. esculenta, genotype LR) requires mating with one of its parental species (R. lessonae, genotype LL), except in the rare cases where hybrids are triploid. The sexual host LL, however, should avoid matings with the sexual parasite LR, because the resulting LR offspring will eliminate the L genome from their germ line. In this study we investigate how this conflict is solved. Since water frog hybrids come in both sexes, rather than as females only like in other sperm-dependent systems, we performed the tests with both females and males. One individual was given a choice between two individuals of the opposite sex, one an LL and the other an LR. In both species, females showed the predicted preference for LL males, whereas males did not discriminate between LL and LR females. On the individual level, we interpret the sex difference in choosiness by the lower costs from mating with the wrong species (LR) and the higher benefits from mating with large individuals in males than in females. In normal species, male preference for large (i.e. more fecund) females is advantageous, but in this system such a choice can result in mating with the larger LR females. With respect to the structure and dynamics of mixed populations, we discuss that the observed female preference is consistent with the higher mating success of LL males found in nature. Hence, mate female choice is a strong candidate for a mechanism promoting coexistence of the sperm-dependent hybrid and its sexual host. This confirms predictions from previous theoretical models.

Female‐biased operational sex ratio of sexual host fish in a gynogenetic complex of Carassius auratus

To study the coexistence of sexual and gynogenetic forms, we examined the population structure of a gynogenetic complex of the Japanese crucian carp, Carassius auratus Temminck et Schlegel, during the April–June reproductive season by collecting 1225 mature fish that migrated from Lake Suwa to a tributary river for spawning. There were more sexual fish (about 80%) than gynogenetic fish in this complex, and the operational sex ratio in the sexual form was female biased (males were about 20%). Mean standard length and body weight of sexual females were larger than those of sexual males. Sex ratio was male biased in smaller fish (standard length, <8.5 cm) but female biased in larger fish (standard length, ≥8.5 cm). We determined age by scale ring marks; the average age of sexual females was higher than that of males, but there was no significant difference in the average age between sexual and gynogenetic females. Sex ratio in the sexual form was more female biased for old than for young fish, and the mean size of sexual females was larger than that of males of the same age. The clear female-biased sex ratio and age difference between sexual females and males can be explained either by (1) higher mortality of males or by (2) female-biased sex allocation. The latter process reduces the disadvantage of sex and contributes to the coexistence of sexual and gynogenetic forms.

SPECIFIC RESPONSES OF SEXUAL AND HYBRIDOGENETIC EUROPEAN WATERFROG TADPOLES TO TEMPERATURE

The European waterfrog, Rana esculenta, is a hemiclonal hybrid that must coexist with the parental species Rana lessonae in order to reproduce. It is not clear what allows the two morphologically, genetically, and ecologically similar forms to coexist, but differential success of the hybrid and its sexual host among environments suggests that these frogs may differ in their adaptive abilities, and that ecology plays an important role in determining the relative frequencies of the two related species. The objective of this study was to identify factors that may promote coexistence. We investigated the effect of temperature, food level, and food quality on a variety of life history traits in a laboratory experiment. Our results indicated that tadpoles of the two forms respond differently to temperature. Probability of metamorphosis and survival of R. lessonae were higher at 24°C, while the hybrid, R. esculenta, had a better survival rate and a much larger body mass at metamorphosis at 18°C. We then tested the results of our laboratory experiment by assessing the distribution of the hybridogen and the parental species in natural populations as a function of temperature, and found that the relative frequency of R. esculenta tadpoles declined with increasing temperature. We use these results to evaluate the applicability of the generalist and frozen niche variation models that had been proposed earlier as explanations for the coexistence of the sexual parental species, R. lessonae, and the hybridogen, R. esculenta.

Differential success in northwards range expansion between ecotypes of the marble gallwasp Andricus kollari: a tale of two lifecycles.

The Marble gallwasp Andricus kollari has a native range divided into two geographically separated lifecycles. In Eastern Europe and Turkey, the lifecycle involves a sexual generation on Turkey oak, Quercus cerris, while in Iberia and North Africa the sexual generation host is cork oak, Q. suber. Over the last 500 years, A. kollari has expanded its range into northern Europe, following human planting of Q. cerris from Italy and the Balkans. We ask: (i) what is the genetic relationship between eastern and western distributions of Andricus kollari? Can we determine which lifecycle is ancestral, and how long ago they diverged? (ii) To what extent have eastern and western native ranges contributed to northwards range expansion? (iii) Is there any evidence for hybridization between the two life cycle types? We present analyses of allozyme data for 13 polymorphic loci and of sequence variation for a 433 bp fragment of the mitochondrial cytochrome b gene. These show: (i) that four haplotype lineages (one in Spain, two in Hungary/Italy and one in Turkey) diverged more or less simultaneously between 1 and 2 million years ago, suggesting the existence of at least four refuges through recent ice age cycles. Our data cannot resolve which lifecycle type is ancestral. (ii) Populations north of putative refuges are divided into two sets. Populations in south-west France are allied to Spain, while all remaining populations in northern Europe have been colonized from Italy and the Balkans. (iii) The transition from one race to another in south-west France is marked by abrupt transitions in the frequency of refuge-specific private alleles and corresponds closely to the northern limit of the distribution of cork oak. Although hybrids were detected in north-west France, none were detected where the two lifecycles meet in south-western France. The biology of oak gallwasps predicts that any hybrid zone will be narrow, and limited to regions where Q. cerris and Q. suber meet. Our data suggest that eastern and western A. kollari are effectively separate species.

Male vocalization and female choice in the hybridogenetic Rana lessonae/Rana esculenta complex

In many species, females can improve their fitness by preferring particular males over others. In Palaearctic water frogs of the Rana lessonae/R.esculenta complex the consequences of such mate choice are particularly pronounced. To produce viable offspring, the hybrid R.esculenta (genotype RL) must mate with the parental species R.lessonae (LL); but R.lessonae should avoid mating withR.esculenta , because the resulting hybrid offspring will eliminate the L genome from the germline (hybridogenesis). Hence, there exists a conflict between the sexual parasite (RL) and its sexual host (LL) over the best mating partner. Previous studies have shown a preference for LL males in LL and RL females; but they have also shown that females cannot usually realize their choice when in close proximity to males, because the males forcefully and indiscriminately amplex them. We tested whether females use male vocalizations as a long-distance signal to increase their chances of mating with the preferred LL males. We exposed female R.lessonae and R.esculenta to playbacks of single LL and RL mating calls (experiment 1) and to choruses with a 3:1 excess of LL and RL calls, respectively (experiment 2). In experiment 1, both female types were attracted more by the LL than by the RL calls. In experiment 2, no discrimination between LL- and RL-dominated choruses was observed. The results suggest that females do not use distant male vocalization to approach preferentially ponds or arenas within a pond that hold an excess of LL males. But once they have arrived in a chorus, mating calls from nearby males can direct them to the preferred LL mates. We discuss possible reasons for the failure to discriminate between choruses and the chances for successful choice between individuals within choruses.

Factors influencing the composition of mixed populations of a hemiclonal hybrid and its sexual host

Abstract Hemiclonal/hybridogenetic hybrids combine demographic superiority of asexuals and genetic diversity of sexuals, but their need for backcrossing with a parental species tightly couples them with this sexual host. How can systems like this persist in ecological and evolutionary time? Two discrete-time mathematical models describing the complex life cycle and mating system of hybridogenetic waterfrogs (Rana esculenta) identified four factors and their interactions as important. Although female mating preferences, in combination with differences in fecundity, determine species coexistence, differences in larval competitiveness seem to be more important for the hybrid‘s actual frequency. However, coexistence is possible even when host and hybrid are equally fecund and competitive. Dispersal and competition interact in their influence on species composition, but ecological and reproductive dispersal has opposing effects. In ecological terms our results explain the remarkable stability of observed species ratios over time within natural hybridogenetic populations, and indicate why the species composition can vary so widely between localities. In evolutionary terms they explain the old age of these and other hybridogenetic systems. They also suggest interesting consequences for other tightly coupled systems.

The Effect of Assortative Mating on the Coexistence of a Hybridogenetic Waterfrog and Its Sexual Host

In central Europe, the hybridogenetic waterfrog Rana esculenta, a hybrid between Rana ridibunda and Rana lessonae, lives in sympatry with one of its parental species, the poolfrog Rana lessonae. As R. esculenta has to backcross constantly with R. lessonae in order to produce viable offspring, this coexistence is obligatory for R. esculenta. Since R. esculenta has a higher primary fitness than R. lessonae, a mechanism is required that prevents the hybrid from driving the parental species, and hence itself, to extinction. Here, we present an analytical model and a computer simulation that investigate whether assortative mating can operate as a such a control mechanism. Our results show that assortative mating is very effective in regulating coexistence in such a hybrid-host system. This is particularly true when choice is affected by the proportion of the two male types in the population. Furthermore, we could show that even if the species composition in a mixed hybrid-host population may be largely influenced by differences in life-history parameters, assortative mating still plays a very important role by stabilizing coexistence. Thus, mating behavior turns out to be more important for the populations dynamics of hybridogenetic waterfrog systems than previously assumed.

The Effect of Assortative Mating on the Coexistence of a Hybridogenetic Waterfrog and Its Sexual Host

In central Europe, the hybridogenetic waterfrog Rana esculenta, a hybrid between Rana ridibunda and Rana lessonae, lives in sympatry with one of its parental species, the poolfrog Rana lessonae. As R. esculenta has to backcross constantly with R. lessonae in order to produce viable offspring, this coexistence is obligatory for R. esculenta. Since R. esculenta has a higher primary fitness than R. lessonae, a mechanism is required that prevents the hybrid from driving the parental species, and hence itself, to extinction. Here, we present an analytical model and a computer simulation that investigate whether assortative mating can operate as a such a control mechanism. Our results show that assortative mating is very effective in regulating coexistence in such a hybrid‐host system. This is particularly true when choice is affected by the proportion of the two male types in the population. Furthermore, we could show that even if the species composition in a mixed hybrid‐host population may be largely influenced by differences in life‐history parameters, assortative mating still plays a very important role by stabilizing coexistence. Thus, mating behavior turns out to be more important for the populations dynamics of hybridogenetic waterfrog systems than previously assumed.

Genetic variation of geminiviruses: comparison between sexual and asexual host plant populations

One of the most promising hypotheses for the evolution of sex is that sexual reproduction is advantageous because it increases the rate of adaptive evolution in response to parasites. To investigate this advantage of sex, we compared genetic variation of geminiviruses infecting sexual and asexual populations of Eupatorium (Asteraceae). The infection frequency was 37.5% in the sexual population and 87.8% in the asexual population. The lower infection frequency in the sexual population might be the result of higher genetic diversity of host plants. If geminiviruses have diverged to counter defence systems of genetically variable hosts, genetic diversity of viruses is expected to be higher in sexual host populations than in asexual host populations. To test this expectation, we used single‐strand conformation polymorphism (SSCP) analysis to examine genetic diversity of the geminiviruses in a DNA region containing the open‐reading frame (ORF) C4 gene, which is known to function as a host range determinant. As predicted, higher genetic diversity of viruses was observed in the sexual population: three SSCP types were found in the asexual population while six types were found in the sexual population. Sequencing of the polymerase chain reaction (PCR) products revealed further genetic diversity. Phylogenetic analysis of the sequences showed that the SSCP types belonged to four different clades. Several SSCP types from the same clade were found in the sexual population, whereas the asexual population included only one SSCP type from each clade. Amino acid replacements of ORF C4 are suggested to be accelerated in the sexual population. This evidence supports the hypothesis that sexual reproduction is advantageous as a defence against epidemic disease.

Evolutionary genetics and ecology of sperm‐dependent parthenogenesis

AbstractSperm‐dependent (or pseudogamous) forms of parthenogenetic reproduction occur in a wide variety of animals. Inheritance is typically clonal and matroclinous (of female descent), but sperm are needed to initiate normal development. As opposed to true parthenogenesis (i.e., sperm‐independent reproduction), pseudogamous parthenogenetic lineages must coexist with a ‘sperm donor’— e.g., males from a conspecific sexual lineage, conspecific hermaphrodites, or males from a closely related sexual species. Such sperm donors do not contribute genetically to the next generation. The parasitic nature of sperm‐dependent parthenogenesis raises numerous ecological and evolutionary questions. How do they arise? What factors help stabilize coexistence between the pseudogamous parthenogens and their sperm donors (i.e., ‘sexual hosts’)? Why do males waste sperm on the asexual females? Why does true parthenogenesis not evolve in pseudogamous lineages and free them from their dependency on sperm donors? Does pseudogamous parthenogenesis provide compensatory benefits that outweigh the constraints of sperm‐dependence? Herein, we consider some genetic, ecological, and geographical consequences of sperm‐dependent parthenogenesis in animals.

Genetic Analysis of Predatory Efficiency in Natural and Laboratory Made Hybrids of Poeciliopsis (Pisces: Poeciliidae)

AbstractMultiple hybridization events between females of Poeciliopsis monacha and males of P. lucida have produced a genetic diversity of all-female biotypes in Sonora, Mexico. All-females depend on the sperm of their sexual ancestors. Strong competition among all-females and their coexistent sexual host take place. The frozen niche-variation model was proposed to explain how such coexistence is possible and how the genetic diversity of all-female biotypes arose. According to this model, the hybrids have multiple origins, freeze and replicate unique genotypes, and produce phenotypic differences with reduced ecological overlap with one another and their sexual ancestors. The objective of the study was to test whether differences in predatory efficiency of all-females are 'frozen' from the sexual ancestor which possessed phenotypic diversity for that behavioural trait. I investigated predatory efficiency in nine strains of Poeciliopsis (P. monacha, two natural hybrids, and six laboratory made hybrids). First, I analysed the variation in average performances of each strain for time spent in capture and handling of two prey species (Artemia salina and Daphnia magna). Second, I offered both prey simultaneously to test if preference affects the average time spent to handle prey. Preference for prey species was analysed using the order of capture as reference. Handling time and prey preference differed among laboratory made hybrids, supporting frozen niche-variation model assumptions.

Persistent High Levels of Tetraploidy in Salamanders of the Ambystoma jeffersonianum Complex

Almost all unisexual members of the Ambystoma jeffersonianum complex of salamanders are triploid, although occasional tetraploid individuals have been observed in a few populations. A population characterized by a high percentage of tetraploids (7-27%) exists at Kickapoo State Park, Vermilion Co, Illinois. This high frequency of tetraploids has been maintained over a period of 12 years. Tetraploids in this population were originally formed by fertilization of unreduced A. platineum ova by A. texanum sperm. Tetraploids at Kickapoo State Park are, however, capable of obtaining sperm from the sexual host, Ambys- toma texanum, and producing tetraploid offspring. Because tetraploids can be produced two ways, they might be expected to out-reproduce and replace triploids. However, these tetraploids also produce abundant pentaploid offspring as a result of fertilization of their ova by A. texanum sperm. A high incidence of physical abnormalities among pentaploid larvae and their scarcity as breeding adults suggests that penta- ploids have reduced viability. Production of pentaploid larvae may thus be the selective mechanism that prevents tetraploids from replacing triploids in this population. Higher than normal water temperature may be causing increased fertilization rates in this population; this would account for its higher frequency of tetraploids compared to other populations, as well as for the high number of pentaploid larvae that tetra- ploids produce.

MATERNAL ANCESTRY OF THE RUTILUS ALBURNOIDES COMPLEX (TELEOSTEI, CYPRINIDAE) AS DETERMINED BY ANALYSIS OF CYTOCHROME b SEQUENCES.

Cytochrome b (cyt b) sequences from specimens of the Rutilus alburnoides unisexual complex and five bisexual species were compared to examine hypotheses regarding the origin and maternal ancestry of this complex. Phylogenetic analysis revealed a monophyletic relationship among unisexuals and Leuciscus pyrenaicus, clearly identifying this species as the maternal ancestor. Considerable mtDNA diversity exists among R. alburnoides populations, with many localities exhibiting unique haplotypes. The topology recovered from analysis of cyt b variation among populations suggested that R. alburnoides is polyphyletically derived from their sympatric L. pyrenaicus populations, indicating that unisexual lineages have been generated through multiple hybridization events. Although much less abundant, R. alburnoides is present outside the range of L. pyrenaicus, suggesting that it may have dispersed from the Tejo drainage into the northern basins. In this region, Leuciscus carolitertii is most likely the sexual host for the unisexual complex.

GYNOGENETIC REPRODUCTION IN HYBRID MOLE SALAMANDERS (GENUS AMBYSTOMA).

Ambystoma platineum, a unisexual clonal triploid taxon of mole salamander, originated by hybridization between the Mendelian species A. jeffersonianum and A. laterale. Studies of lampbrush chromosomes indicated that A. platineum reproduces gynogenetically, that is, sperm from a sexual host species is required to activate egg development but makes no genetic contribution to the developing embryo. Nevertheless, electrophoretic diversity in populations of some hybrid Ambystoma suggested continual in situ recreation of unisexual hybrids and bidirectional gene exchange between the parental species and the hybrids. A. platineum usually lives with, and is sexually dependent on, one of its parental species, A. jeffersonianum. In central Indiana, however, A. platineum populations have shifted their host dependency to A. texanum. Such A. texanum-dependent populations of A. platineum provide an almost ideal system for studying reproductive mode in A. platineum, because both replacement of a jeffersonianum or laterale genome of A. platineum by a texanum genome, and movement of genes from A. platineum to the host species, A. texanum, would be readily detected by electrophoretic markers. Our samples of A. texanum provided no evidence for the transfer of jeffersonianum or laterale genes into A. texanum. Similarly, among 32 A. platineum sampled from six localities in east-central Illinois and central Indiana, we find no texanum alleles, and thus no evidence for genome replacement. The one diploid hybrid individual contained only a jeffersonianum and a laterale genome; because of the absence of either parental species from these populations, this hybrid could only have come from a diploid ovum produced by A. platineum. Both morphometric and electrophoretic results for the two tetraploid individuals indicate that they resulted from fertilization of triploid oocytes of A. platineum by sperm of A. texanum. Because genome replacement in A. texanum-dependent populations of A. platineum is irreversible, the persistence of A. platineum in A. texanum-dependent populations demonstrates conclusively that the major mode of reproduction in A. platineum populations is clonal: A. platineum produces mainly triploid eggs that develop gynogenetically.

Comparison of Glass and Plastic McPhail Traps in the Capture of the South American Fruit Fly, Anastrepha fraterculus (Diptera: Tephritidae) in Brazil

McPhail traps have been used throughout the new world for many decades to detect and monitor for fruit flies of genus Anastrepha. Since no sexual lures or host attractant have been developed for Anastrepha spp., a food lure containing protein hydrolysate, torula yeast and carbohydrate has been used for bait in McPhail traps (Lopez & Hernandez Bacerril 1967, Lopez et al. 1971, Malavasi & Morgante 1981). Many modifications in the original design of McPhail have been proposed in recent years but none have substantially increased effectiveness. The traditional glass McPhail has two problems. First, it is expensive when compared with polyethylene made traps, and second, it is fragile, heavy and difficult to handle. Its lifetime is short compared with other models. Under extreme conditions, for example when the temperature reaches over 40?C inside the trap, spontaneous breakage is common. In regions where large Anastrepha spp. monitoring and detection programs have been conducted for certification of fruit fly-free areas, the large number of traps required is a major expense. In an attempt to replace the original glass McPhail trap with a more economical plastic model of identical shape and similar size, we tested the efficiency of both models in trapping the South American fruit fly, Anastrepha fraterculus (Wiedemann). The experiments were conducted in a non-commercial grove, where previous studies had determined large populations of A. fraterculus were found (Malavasi & Morgante 1980, Amaral 1987). The experiment was conducted in Itaquera, 30 Km east Sao Paulo city where there are more than 15 species of Anastrepha host trees. Traps were suspended in guava (Psidium guajava), Surinam cherry (Eugenia uniflora) and loquat (Eryobotrya japonica) during 8 consecutive weeks in March-May 1989. Two traps models were tested. The traditional McPhail glass trap was made in Mexico, and the plastic model made in Brazil. Both were similar in shape, the glass trap with 19 cm diameter and the plastic trap with 17 cm diameter. Both traps were the same height (14 cm) and had a similar entrance hole (glass 4.5 cm, plastic 4.0 cm diameter). All traps were baited with 250 ml of 3% protein hydrolysate solution with borax added to prevent decomposition. Two traps (one of each model) were placed in opposite quadrants of each tree. Traps were hung at 1.7 to 2.0 m high, in the peripheral canopy with a minimum of 2.0 m between each trap. Trap positions were alternated, the bait was changed and the adults were collected and counted weekly. Ten sets of the two traps were hung up in 5 loquat, 3 guava, 1 grumixama and 1 Surinam cherry trees. Statistical comparisons of means were made with t tests, and by analysis of variance (ANOVA) (SAS Institute 1987). A total of 7,148 A. fraterculus flies were caught in the grove. No statistical difference between glass and plastic traps was observed using t test analysis (F = 1.18; df = 15; p > 0.7450) (Table 1). There were no significant differences in the sex ratios of the trap catches between trap models. More females were captured than males. Females may require more frequent feeding than males and so may be captured in greater numbers in food-baited traps (Davis et al. 1984).

The evolutionary significance of incest rules

Evolutionary theory predicts that humans should avoid incest because the behavior depresses individual fitness through production of defective offspring. Selection for avoidance of close-kin mating has resulted in a developmental mechanism that promotes voluntary incest avoidance. If avoided, why are social rules constructed in most cultures to regulate incest? The suggestion in this article is that incest do not regulate close-kin mating, but instead regulate inbreeding between more distant kin and sexual relations between nonkin. Inbreeding (e.g., cousin marriage) is hypothesized to be regulated because if it occurs, it can concentrate wealth and power within families threatening the powerful positions of rulers in the society. The hypothesis was supported using a worldwide sample of 129 societies, whereas two other alternative hypotheses (one dealing with coadapted genomes, and the other with sexual reproduction and host/ parasite coevolution), were not.