Die genetische Grundlage der Monogenie bei der Schmei?fliege Chrysomya rufifacies (Calliphoridae, Diptera)

Summary Recently in our wild stock of the monogenic blowfly Chrysomya rufifacies a recessive mutation white (w) causing white instead of red-brown eyes spontaneously appeared (Fig. 1). This marker gene enabled us to clarify the genetic basis of monogeny in this species. F₁ offspring produced by reciprocal crossings between normal (+/+) and white-eyed (w/w) flies were phenotypically wildtype (Table 1). In F₂ offspring of female-producing (thelygenic) and male-producing (arrhenogenic) F₁ females wildtype and white-eyed flies appeared in the expected 3:1 ratio; in several crossings a slight deviation of this ratio indicated a reduced viability of the w/w individuals (Table 2). Examination of F₂ progeny of thelygenic F₁+/w females, which had received the w allele from their father, showed that most of the F₂+/+ females were thelygenic, whereas most of the F₂ w/w females were arrhenogenic; among F₂+/w females thelygenic and arrhenogenic individuals occurred in almost equal numbers (Table 3). On the other hand, when F₂ offspring of thelygenic F₁+/w females which had inherited the w allele from their mother were tested, most of the F₂+/+ females turned out to be arrhenogenic and most of the F₂ w/w females thelygenic; among F₂+/w females thelygenic and arrhenogenic flies also were found in almost equal frequencies (Table 4). the sex-linked inheritance of the factor w following from these results was also confirmed by an analysis of the progeny of thelygenic F₁+/w females backcrossed with w/w males. Among the R₁ offspring of F₁+/w females, which had received the w allele from their father, the +/w females were predominantly thelygenic compared to their predominantly arrhenogenic w/w sisters (Table 5). Analysis of R₁ progeny of F₁+/w females, which had inherited the w allele from their mother, yielded reciprocal results (Table 6).This mode of incomplete sex-linkage of the mutation white observed in C. rufifacies (Figs. 2–5) supports the hypothesis that thelygenic females are heterozygous for a dominant female sex realizer (F') with predetermined sex-determining properties, and that arrhenogenic females as well as the males are homozygous for the recessive allele f (Fig. 6). The recombination frequency between F'/f and the w-Locus was calculated to be 12.72±0.72 per cent.

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Mit Unterstützung durch die Deutsche forschungsgemeinschaft.     

Zur Ökophysiologie,Sexualität und Populationsgenetik litoraler Gammaridea — ein Überblick

Comparative investigations on the physiological capacities in the euryhaline amphipodsGammarus locusta, G. oceanicus, G. salinus, G. zaddachi andG. duebeni were reviewed. In order to assess the adaptations of these species to the abiotic conditions of their environment, the following criteria were examined: oxygen consumption in relation to ambient salinity and temperature levels, respiratory responses following osmotic stress, resistance capacities to oxygen deficiency, resistance to aerial exposure and the simultaneous presence of hydrogen sulphide. Covering the range from marine to typically brackish-water inhabitants, the 5 species show adaptive responses in the above-mentioned order. Respiration is less intensely modified by external factors, and oxygen consumption decreases. Accompanied by faster rates of acclimation to new steady states of performance, resistance capacities increase. The significance of the findings obtained is discussed in relation to the environmental requirements of the amphipods considered. Based on breeding experiments, the sex-determining systems reported thus far inGammarus species are outlined. As demonstrated inG. duebeni, a more or less pronounced influence of external factors such as photoperiod may become effective. A preponderance of males was noted when offspring were raised under long-day photoperiods, whereas females prevailed under short-day conditions. In terms of the critical daylength, the light per day was estimated as being between 13 and 14 h (Elbe estuary population). Feminizing microporidians (Octosporea effeminans, Thelohania herediteria), which are transovarially transmitted, can interfere with the system of sex determination and sex differentiation of the host. As reflected in variousG. duebeni populations, they cause a maternally transferred sex-ratio condition by the production of all-female broods, thereby mimicking extrachromosomal inheritance. An increase of the salinity level to 25–30‰ results in a disappearance ofO. effeminans. In both microsporidians, long exposure to low temperatures (≤4°C) produces eggs which are not all parasitized. Furthermore, intersexuality can be induced by changing environmental factors. Microsporidian species have no influence on sex differentiation inG. duebeni celticus, G. salinus, G. locusta andG. pulex. Patterns of relative electrophoretic mobilities of proteins and the distribution of allele frequencies at polymorphic gene loci can be utilized for species diagnosis and for the evaluation of the relationships between different taxa, particularly at and below the species level. As exemplified by studies on several gammarids from marine, brackish and freshwater environments, inter- and infraspecific gene-enzyme variation is described. Electrophoretic investigations on natural populations of the euryhaline amphipodsG. zaddachi, G. salinus, G. tigrinus and others from different geographic areas provided evidence of considerable biochemical genetic variation. InTalitrus saltator- andTalorchestia deshayesii-populations the extent of variability based on micro-and macrogeographic aspects is illustrated. The large-scale genetic divergence is demonstrated by comparison of samples obtained from the Baltic, North, Atlantic and northern Mediterranean Seas.      

Adaptive significance of environmental sex determination in an amphipod

Environmental sex determination (ESD) permits adaptive sex choice under patchy environmental conditions, where the environment affects sex-specific fitness and where offspring can predict their likely adult status by monitoring an appropriate environmental cue. For Gammarus duebeni, an amphipod with ESD, it has been proposed that this flexible sex determination system is adaptive because males gain more from large size. Under ESD, young which are born earlier in the season become mostly males and, experiencing longer to grow, are therefore larger at breeding than females which are born later in the season. In order to test the hypothesis that ESD is adaptive for this species we investigated the relationship between size and fitness for both males and females, in a population of G. duebeni known to have ESD. We measured size related pairing success and fecundity, and used these two measures to calculate the relative fitness gains achieved through an increase in size for either sex. The fitness of both males and females increased with size, but males gained more from an increase in size than did females, throughout the breeding season. The data support the adaptive explanation for the evolution and maintenance of ESD in this species.     

Analysis of the predetermining effect of a sex realizer by ovary transplantations in the monogenic flyChrysomya rufifacies

Summary In the heterozygousF/f female-producing females of the strictly monogenic blowflyChrysomya rufifacies the gene product of the dominant or epistatic female sex realizerF which causes sexpredetermination is thought to be synthesized either by cells of the germ line (oocytes, nurse cells or oogonia) or by somatic cells and then transferred into the oocytes. To determine the possible site of synthesis, reciprocal transplantations were made of prepupal ovaries between female-producing (thelygenic; t) and male-producing (arrhenogenic; a) females ofChrysomya rufifacies. In another series of experiments prepupal host females of the wild t-type and a-type were each provided with one additional ovary either from a0type (f/f) or a t-type (F/f) prepupa (neither were distinguishable by their phenotypes). In all these experiments the donor females were marked by the recessive sex-linked mutation white (w/w); white eyes, white Malpighian tubules). In a considerable number of cases the implanted ovaries were in contact with the host's own oviduct and grew normally, but the rate of hatched adults was somewhat reduced. Crosses between such host females andw/w males (f/f) produced female or male offspring with white eyes from the eggs of the implantedw/w ovary, as well as flies with wild-type eyes (+/w) which had developed in the host's own ovaries. In all cases so far examined, the genetically thelygenic (or arrhenogenic) host females with an additional ovary implanted from an arrhenogenic (thelygenic) donor, produced progeny of both sexes: sons (daughters) from the eggs of the donor's ovary and daugthers (sons) from the eggs of the host's own gonads.These results demonstrate that the ovaries of the t-females ofChrysomya rufifacies at least from the early prepupal stage, are autonomous for the product of theF gene. Transplantations of the premordial germ cells (pole cells) are planned to find out whether the predeterminingF gene product is synthesized before the prepupal stage, by somatic cells outside the ovary or by somatic (follicle) cells of the ovary itself.Dedicated to Professor Dr. Hans Bauer with gratitude in commemoration of his 75th birthday     

Transfer of a parasitic sex factor to the nuclear genome of the host: A hypothesis on the evolution of sex-determining mechanisms in the terrestrial Isopod Armadillidium vulgare Latr.

In A. vulgare sex is usually determined either by a cytoplasmic feminizing factor (F symbiotic bacteria) or by another feminizing factor (f) which behaves like a mobile element of DNA and which seems to correspond to a fragment of bacterial DNA. By inhibiting the expression of male genes carried by the Z heterochromosome, these feminizing factors induce differentiation of neo-females [ZZ(+F) or ZZ(+f)]. Such a mechanism leads to the production of progenies whose sex ratio is highly female biased. In some populations in which F and/or f factors are present, genetic females (WZ) have disappeared and all individuals (males and females) are genetic males. However in other populations, cohabitation of ZZ(+f) neo-females and females in all points similar to genetic females is observed. Such a situation may be unstable and is not likely to be explainable only by migrations of individuals from distinct populations. Owing to certain types of crosses, in particular those which involve an artificial neo-male ( = female reversed into a functional male by an implant of androgenic gland) we show here that the f factor can be transmitted as a Mendelian gene. In these progenies Z_fZ females may appear: like WZ females, they breed broods whose sex ratio is unbiased. The hypothesis that the “F bacteria—A. vulgare” symbiosis may have led, after a complex co-evolutive process (F bacteria → f mobile element → insertion of f on Z heterochromosome), to the creation (from a male genotype) of a female genotype, is put forward. The consequences of such a phenomenon on the composition and the evolution of A. vulgare populations are examined.     

Studies with the dioecious angiosperm Mercurialis annua L. (2n=16): Correlation between genic and cytoplasmic male sterility, sex segregation and feminizing hormones (cytokinins)

Summary Male sterility in M. annua is controlled by a sterile S cytoplasm interacting with three nuclear genes: one inducer I and two fertility restorers R1 and R2. This system permits identification of the genotypes of the original sterile mutant (used as female after sex conversion by cytokinins), the constructed semi-sterile and restored fertile strains. Sex segregations in crosses between fertile strains selected for their various degree of sensitivity towards feminizing hormones make it possible to explain sex determinism and male plurality by a system of three complementary genes. Crosses between these strains show that the cytoplasmic factor and R1 gene involved in male sterility also affect sex distribution. Comparative data between endogenous cytokinin levels, phenocopies obtained by feminizing hormone, and crosses demonstrate that all these strains constitute a series of developmental mutants starting from strong males and continuing to weak , semisterile and sterile , and then females.     

The role of host sex in parasite dynamics: field experiments on the yellow-necked mouse Apodemus flavicollis

We investigated the role of host sex in parasite transmission and questioned: ‘Is host sex important in influencing the dynamics of infection in free living animal populations?’ We experimentally reduced the helminth community of either males or females in a yellow‐necked mice (Apodemus flavicollis) population using an anthelmintic, in replicated trapping areas, and subsequently monitored the prevalence and intensity of macroparasites in the untreated sex. We focussed on the dominant parasite Heligmosomoides polygyrus and found that reducing parasites in males caused a consistent reduction of parasitic intensity in females, estimated through faecal egg counts, but the removal of parasites in females had no significant influence on the parasites in males. This finding suggests that males are responsible for driving the parasite infection in the host population and females may play a relatively trivial role. The possible mechanisms promoting such patterns are discussed.     

rDNA magnification in D. melanogaster: state of rDNA copies following the first step.

Summary D. melanogaster males of bb/O genetic constitution undergoing rDNA magnification were mated singly to XXbb ⁺/O females, yielding bb/O male progeny, and to X_NO-w sn bb ⁺ fameles, yielding bb/X_NO- females. The male and female offspring were scored for the bb ⁺ phenotype.Results show that there is a higher percentage of bb ⁺ flies in the bb/O male progeny than in bb/X_NO- females progeny, in single crosses as well as in the combined data. rRNA/DNA hybridization experiments agree with this observation, by showing that the rDNA content in the progeny of premagnified flies was higher in the sons than in the daughters.These data indicate that the increase of ribosomal RNA genes is not due to a stable event such as an unequal mitotic sister exchange, whereas they do not contrast with the extracopy model.     

The effect of interspecific mating on sex ratios in the twospotted spider mite and the Banks grass mite (Acarina: Tetranychidae)

Mixed populations of the twospotted spider mite (TSM),Tetranychus urticae (Koch), and the Banks grass mite (BGM),Oligonychus pratensis (Banks), occur on corn and sorghum plants in late summer in the Great Plains. Interspecific matings between these arrhenotokous species occur readily in the laboratory but yield no female offspring. The effect of interspecific mating on female: male sex ratios was measured by examining the F₁ progeny of females that mated with both heterospecific and conspecific males in no-choice situations. TSM females that mated first with BGM males and then with TSM males produced a smaller percentage of female offspring than TSM females that mated only with TSM males (43.1±5.8 and 78.9±2.8% females, respectively). Similarly, BGM females mated with heterospecific males and then with conspecific males produced fewer female offspring than females mated only with BGM males (55.7±5.2 and 77.5±2.5%, respectively). Lower female: male sex ratios were produced also by BGM females that mated with TSM males after first mating with conspecifics (62.4±3.4%). In mixed populations containing males of both species, females also produced lower female: male sex ratios, but these ratios were not as low as expected based on mating propensities and progeny sex ratios observed in no-choice tests. These data suggest that interspecific mating may substantially reduce female fitness in both mite species by reducing the output of female offspring, but in mixed populations this effect is mitigated by unidentified behavioral mechanisms.     

Identifizierung der genetischen Geschlechtschromosomen bei der monogenen Schmeißfliege Chrysomya rufifacies (Calliphoridae,Diptera)

Previous investigations have shown the sex determination in the monogenic blowfly Chrysomya rufifacies to be controlled by a cytologically not discernible homogamety-heterogamety mechanism in the female. Female-producing (thelygenic) females are assumed to be heterozygous for a dominant female sex realizer (F′) with sex-predetermining properties, while male-producing (arrhenogenic) females as well as males are supposed to be homozygous for the recessive allele (f). In order to identify the genetic sex chromosomes of C. rufifacies among its five pairs of long euchromatic chromosomes (nos.1–5) plus one pair of small heterochromatic ones (no. 6), all chromosomes were marked by reciprocal translocations induced by X-ray treatment of adult males. The inheritance of thirteen different heterozygous translocations has been analyzed. All of the translocations (eleven) between two of the four longer chromosomes did not show sex-linked inheritance, thus demonstrating the autosomal character of the chromosomes nos 1, 2, 3 and 4. The same is true for the translocation T6 (2/6). Therefore the small heterochromatic chromosome no. 6, corresponding to the morphologically differentiated sex chromosomes within the amphogenic calliphorid species, remains without sex determining function in the monogenic fly. This could be confirmed by the analysis of monosomic (monosomy-6) and trisomic (trisomy-6) individuals, which resulted from meiotic non-disjunction in T6/+ translocation heterozygotes. Contrary to these translocations, the heterozygous 5/2 translocation (T14) exhibited sex-linked inheritance: There was but a very low frequency (0,76 per cent) of recombinants resulting from crossing-over between F′/f and the translocation breakage point in thelygenic F₁ T14/+ females. The sex-linked inheritance of T14 was confirmed by the progeny of a thelygenic F₁ T14/+ female crossed to a homozygous T14/T14 translocation male. Among the offspring of that F₁ T14/+ female, which had received the translocation from its father, all of the F₂ T14/+ females were thelygenic compared to their arrhenogenic T14/T14 sisters. These results prove that the chromosomes of pair no. 5 genetically act as X′X-XX sex chromosomes in C. rufifacies.     

X inactivation in a mammal species with three sex chromosomes

X inactivation is a fundamental mechanism in eutherian mammals to restore a balance of X-linked gene products between XY males and XX females. However, it has never been extensively studied in a eutherian species with a sex determination system that deviates from the ubiquitous XX/XY. In this study, we explore the X inactivation process in the African pygmy mouse Mus minutoides, that harbours a polygenic sex determination with three sex chromosomes: Y, X, and a feminizing mutant X, named X*; females can thus be XX, XX*, or X*Y, and all males are XY. Using immunofluorescence, we investigated histone modification patterns between the two X chromosome types. We found that the X and X* chromosomes are randomly inactivated in XX* females, while no histone modifications were detected in X*Y females. Furthermore, in M. minutoides, X and X* chromosomes are fused to different autosomes, and we were able to show that the X inactivation never spreads into the autosomal segments. Evaluation of X inactivation by immunofluorescence is an excellent quantitative procedure, but it is only applicable when there is a structural difference between the two chromosomes that allows them to be distinguished.     

Evolutionary consequences of cytoplasmic sex ratio distorters

Summary Computer simulations of diploid genetic models were used to examine the consequences of the spread of a cytoplasmic sex ratio distorter on the frequencies of nuclear sex-determination alleles and the spread of nuclear resistance alleles in female biased populations. The cytoplsmic elements considered here override the expression of the nuclear sex-determination genes, turning genetic males into females. When homozygous male genotypes are viable, a cytoplasmic sex ratio historter spreads in a population if the proportion of daughters produced by infected females exceeds the proportion of daughters produced by uninfected females. The equilibrium frequency of male phenotypes is the proportion of uninfected progeny produced by infected females. When homozygous male genotypes are lethal, the conditions for the spread of the cytoplasmic element are more stringent. The spread of a cytoplasmic sex ratio distorter causes an increase in the frequency of nuclear male sex-determination alleles as a result of the unusual combinations of genotypes which mate in infected populations. Eventually, a cytoplasmic element may replace the nuclear gene as the sex-determination mechanism. This occurs without selection. Nuclear genes conferring resistance to cytoplasmic sex ratio distorters generally increase in female biased populations and often restore a 11 sex ratio despite continual selection on the cytoplasmic element to increase its transmission efficiency.     

Demonstration of viability and fertility and development of a molecular tool to identify YY supermales in a fish with both genotypic and environmental sex determination

The pejerrey possesses a genotypic sex determination system driven by the amhy gene and yet shows marked temperature‐dependent sex determination. Sex‐reversed XY females have been found in a naturally breeding population established in Lake Kasumigaura, Japan. These females could mate with normal XY males and generate YY “supermale” individuals that, if viable and fertile, would sire only genotypic male offspring. This study was conducted to verify the viability, gender, and fertility of YY pejerrey and to develop a molecular method for their identification. Production of YY fish was attempted by crossing a thermally sex‐reversed XY female and an XY male, and rearing the progeny until sexual maturation. To identify the presumable YY individuals, we first conducted a PCR analysis using amhy‐specific primers to screen only amhy‐positive (XY and YY) fish. This screening showed that 60.6% of the progeny was amhy‐positive, which suggested the presence of YY fish. We then conducted a second screening by qPCR in order to identify the individuals with two amhy copies in their genome. This screening revealed 13 individuals, all males, with values twice higher than the other 30 amhy‐positive fishes, suggesting they have a YY complement. This assumption as well as the viability, fertility, and “supermale” nature of these individuals was confirmed in progeny tests with XX females that yielded 100% amhy‐positive offspring. These results demonstrate that qPCR can obviate progeny test as a means to identify the genotypic sex and therefore may be useful for the survey of all three possible genotypes in wild populations.     

A Neo-Sex Chromosome That Drives Postzygotic Sex Determination in the Hessian Fly (Mayetiola destructor)

Two nonoverlapping autosomal inversions defined unusual neo-sex chromosomes in the Hessian fly (Mayetiola destructor). Like other neo-sex chromosomes, these were normally heterozygous, present only in one sex, and suppressed recombination around a sex-determining master switch. Their unusual properties originated from the anomalous Hessian fly sex determination system in which postzygotic chromosome elimination is used to establish the sex-determining karyotypes. This system permitted the evolution of a master switch (Chromosome maintenance, Cm) that acts maternally. All of the offspring of females that carry Cm-associated neo-sex chromosomes attain a female-determining somatic karyotype and develop as females. Thus, the chromosomes act as maternal effect neo-W''s, or W-prime (W′) chromosomes, where ZW′ females mate with ZZ males to engender female-producing (ZW′) and male-producing (ZZ) females in equal numbers. Genetic mapping and physical mapping identified the inversions. Their distribution was determined in nine populations. Experimental matings established the association of the inversions with Cm and measured their recombination suppression. The inversions are the functional equivalent of the sciarid X-prime chromosomes. We speculate that W′ chromosomes exist in a variety of species that produce unisexual broods.SEX chromosomes are usually classified as X, Y, Z, or W on the basis of their pattern of segregation and the gender of the heterogametic sex (Ohno 1967). However, when chromosome-based sex determination occurs postzygotically, the same nomenclature confounds important distinctions and may hide interesting evolutionary phenomena. The Hessian fly (Mayetiola destructor), a gall midge (Diptera: Cecidomyiidae) and an important insect pest of wheat, presents an excellent example (Stuart and Hatchett 1988, 1991). In this insect, all of the female gametes and all of the male gametes have the same number of X chromosomes (Figure 1A); no heterogametic sex exists. Nevertheless, Hessian fly sex determination is chromosome based; postzygotic chromosome elimination produces different X chromosome to autosome ratios in somatic cells (male A1A2X1X2/A1A2OO and female A1A2X1X2/A1A2X1X2, where A1 and A2 are the autosomes, X1 and X2 are the X chromosomes, and the paternally derived chromosomes follow the slash) (Stuart and Hatchett 1991; Marin and Baker 1998). Thus, Hessian fly “X” chromosomes are defined by their haploid condition in males, rather than by their segregation in the gametes.Open in a separate windowFigure 1.—Chromosome behavior and sex determination in the Hessian fly. (A) Syngamy (1) establishes the germ-line chromosome constitution: ∼32 maternally derived E chromosomes (represented as a single white chromosome) and both maternally derived (black) and paternally derived (gray) autosomes and X chromosomes. During embryogenesis, while the E chromosomes are eliminated, the paternally derived X chromosomes are either retained (2) or excluded (3) from the presumptive somatic cells. When the paternally derived X chromosomes are retained (2), a female-determining karyotype is established. When they are eliminated (3), a male-determining karyotype is established. Thelygenic mothers carry Cm (white arrow), which conditions all of their offspring to retain the X chromosomes. Recombination occurs during oogenesis (4). All ova contain a full complement of E chromosomes and a haploid complement of autosomes and X chromosomes. Chromosome elimination occurs during spermatogenesis (5). Sperm contain only the maternally derived autosomes and X chromosomes. (B) The segregation of Cm (white dot) on a Hessian fly autosome among monogenic families. Thelygenic females produce broods composed of equal numbers of thelygenic (Cm/−) and arrhenogenic (−/−) females (box 1). Arrhenogenic females produce males (box 2). (C) Matings between monogenic and amphigenic families. Cm (white dot) is dominant to the amphigenic-derived chromosomes (gray dot) and generates all-female offspring (box 3). Amphigenic-derived chromosomes are dominant to the arrhenogenic-derived chromosomes (no dot) and generate offspring of both sexes (box 4).An autosomal, dominant, genetic factor called Chromosome maintenance (Cm) complicates Hessian fly sex determination further (Stuart and Hatchett 1991). Cm has a maternal effect that acts upstream of X chromosome elimination during embryogenesis (Figure 1A). It prevents X chromosome elimination so that all of the offspring of Cm-bearing mothers obtain a female-determining karyotype. Cm-bearing females produce only female offspring and are therefore thelygenic. The absence of Cm usually has the opposite effect; all of the offspring of most Cm-lacking females obtain a male-determining karyotype. These Cm-lacking females produce only male offspring and are therefore arrhenogenic. Like a sex-determining master switch, Cm is usually heterozygous and present in only one sex (Figure 1B). Thus, thelygenic females (Cm/−) are “heterogametic,” as their Cm-containing gametes and Cm-lacking gametes produce thelygenic (Cm/−) and arrhenogenic (−/−) females in a 1:1 ratio. Collectively, thelygenic and arrhenogenic females are called monogenic because they produce unisexual families. However, some Hessian fly females produce broods of both sexes and are called amphigenic. No mating barrier between monogenic and amphigenic families exists (Figure 1C), but amphigenic females have always been found in lower abundance (Painter 1930; Gallun et al. 1961; Stuart and Hatchett 1991). In experimental matings, the inheritance of maternal phenotype was consistent with the segregation of three Cm alleles (Figure 1C): a dominant thelygenic allele, a hypomorphic amphigenic allele, and a null arrhenogenic allele (Stuart and Hatchett 1991).Here we report the genetic and physical mapping of Cm on Hessian fly autosome 1 (A1). Two nonoverlapping inversions were identified that segregated perfectly with Cm. The most distal inversion was present in all thelygenic females examined. The more proximal inversion extended recombination suppression. These observations suggested that successive inversions evolved to suppress recombination around Cm after it arose. The inversions therefore appear to have evolved in response to the forces that shaped vertebrate Y and W chromosomes (Charlesworth 1996; Graves and Shetty 2001; Rice and Chippindale 2001; Carvalho and Clark 2005). We therefore believe the inversion-bearing chromosomes may be classified as maternal effect neo-W''s.     

Feeding Behavior, Habitat Use, and Abundance of the Angelfish Holacanthus passer (Pomacanthidae) in the Southern Sea of Cortés

Feeding behavior and habitat use of the king angelfish, Holacanthus passer, was studied in the southern Sea of Cortés, México. H. passer fed on benthic communities (algae and sessile invertebrates) and in the water column (mainly feces from the damselfish Chromis atrilobata). Although there were not significant differences in feeding rate between sexes, coprophagy was more common in males, while grazing was more common in females. Spatial distribution of size classes followed a pattern of decreasing size with increasing depth. Feeding rate was significantly different among habitats: small females had a higher feeding rate on the bottom, big females and small males had similar feeding rates from the bottom to 3m above the bottom, and big males had higher feeding rates from 5m above the bottom to the surface. Habitat was clearly partitioned, and there was significant habitat overlap only between big females and small males. The abundance of H. passer was partly explained (34% of the total variance) by the abundance of the damselfish C. atrilobata. There was a clear trophic association between C. atrilobata schools and H. passer feeding damselfish feces in the water column. The sex ratio male:female of H. passer populations was >1 at several sites, an unusual pattern for a protogynous fish. The sex ratio on the H. passer water column stock was also biased towards males at most sites. Although there is a positive relationship between C. atrilobata abundance and H. passer, there are factors other than damselfish abundance which cause this dominance of males.     

Sexual selection in an isopod with Wolbachia‐induced sex reversal: males prefer real females

A variety of genetic elements encode traits beneficial to their own transmission. Despite their ‘selfish’ behaviour, most of these elements are often found at relatively low frequencies in host populations. This is the case of intracytoplasmic Wolbachia bacteria hosted by the isopod Armadillidium vulgare that distort the host sex ratio towards females by feminizing the genetic males they infect. Here we tested the hypothesis that sexual selection against Wolbachia‐infected females could maintain a polymorphism of the infection in populations. The infected neo‐females (feminized males) have lower mating rates and received less sperm relative to uninfected females. Males exhibited an active choice: they interacted more with uninfected females and made more mating attempts. A female behavioural difference was also observed in response to male mating attempts: infected neo‐females more often exhibited behaviours that stop the mating sequence. The difference in mating rate was significant only when males could choose between the two female types. This process could maintain a polymorphism of the infection in populations. Genetic females experimentally infected with Wolbachia are not exposed to the same sexual selection pressure, so the infection alone cannot explain these differences.     

Strahlenbiologische Untersuchungen an Gammariden (Crustacea,Amphipoda)

Zusammenfassung 1. Der Einfluß einmaliger Röntgenbestrahlungen auf die Überlebenszeiten der euryhalinen AmphipodenGammarus duebeni Lilljeborg,Gammarus salinus Spooner undGammarus zaddachi Sexton wurde bei einer konstanten Temperatur von 15⁰ C und einem Salzgehalt von 10 untersucht.2. Bestrahlungen mit Dosen von 625 und 1250 R führen beiG. duebeni zum vorzeitigen Tod von nur einigen Versuchstieren, Bestrahlungen mit 2500 R und höheren Dosen zum vorzeitigen Tod aller Versuchstiere.3. BeiG. duebeni sind die strahlenempfindlicher als die , die Jungtiere strahlenempfindlicher als adulte Individuen.4.G. salinus undG. zaddachi sind strahlenempfindlicher alsG. duebeni.5. Die LD₅₀-Kurven lassen drei Bereiche erkennen. Bei mittleren Dosen ändert sich die Zeitspanne, in der 50% der Versuchstiere sterben, nur wenig oder gar nicht mit der Dosis. Bei hohen und niedrigen Dosen ist die Überlebenszeit dosisabhängig.6. Die Strahlenempfindlichkeit vonG. duebeni war im ersten Quartal des Jahres 1967, in dem die Temperaturen über den langfristigen Monatsmitteln lagen, geringer als bei Flohkrebsen, die zu einem späteren Zeitpunkt gefangen wurden oder aus Laboratoriumszuchten stammten.7. Die Häutungsvorgänge, deren Beeinflussung nur beiG. duebeni untersucht wurde, werden durch Bestrahlungen mit 1250 R oder geringeren Dosen nicht beeinflußt.8. Nach einer Bestrahlung mit 20 000 R sind 2 Tage nach der Bestrahlung nur wenige oder gar keine Häutungen möglich. Nach Bestrahlungen mit 10 000 und 5000 R erfolgen die Häutungen verspätet.9. Als Folge von Bestrahlungen mit letalen Dosen nimmt die Zahl der Häutungen um den 30. Tag nach der Bestrahlung ab.10. Die Häutungsvorgänge waren bei Tieren, die im ersten Quartal 1967 gefangen und bestrahlt wurden, weniger beeinflußbar als bei Tieren, die aus Laboratoriumszuchten stammten oder zu einem späteren Zeitpunkt gefangen wurden.11. Nach Bestrahlungen mit letalen Dosen treten zwei kritische Phasen auf. Ein Teil der mit mittleren und der größte Teil der mit hohen Dosen bestrahlten Tiere stirbt bereits in der ersten kritischen Phase. Die zweite kritische Phase wird von allen mit niedrigen Dosen bestrahlten Tieren erreicht. Tiere, die sich in der ersten kritischen Phase häuten, haben eine geringe Lebenserwartung.12. Die Überlebenszeit des einzelnen Individuums hängt außer von der Bestrahlungsdosis von dem Zeitpunkt ab, zu dem es sich innerhalb der Versuchszeit häutet.

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Radiobiological investigations on gammarids (Crustacea, Amphipoda)

Effects of single exposures of X-radiation on survival were studied inGammarus duebeni, G. salinus andG. zaddachi under constant conditions of temperature (15⁰ C) and salinity (10 ). Effects on moulting were investigated inG. duebeni. The amphipods were irradiated with doses between 625 and 20,000 R.G. salinus andG. zaddachi are equally radioresistant (LD_50/30 : 1,700 R) but less resistant thanG. duebeni (LD_50/30(males) : 3,900 R; LD_{50/30(females)} : 3,500 R). At high doses, half of the test individuals die within a few days; at medium doses survival time is dose-independent; at lower doses survival time again increases with decreasing doses up to dose-ranges (below 1,250 R forG. duebeni, 1,000 R forG. salinus andG. zaddachi), at which only a few individuals die before their natural death. Subadult gammarids are less resistant;G. duebeni of 4 to 7 mm body length have a LD_50/30 of 2,200 R. Death distribution after medium doses indicates that at least two mechanisms are involved in acute mortality. A first mortality maximum occurs shortly after irradiation; subsequently, mortality decreases for a few days, and is followed by another maximum. At lower doses no individual dies during the first critical period. Shortening of survival time at higher doses results from survival of fewer individuals to the second critical period. Few or no moults occur inG. duebeni irradiated with 20,000 R following the second day after irradiation and after the 30th day in those individuals irradiated with 2,500 to 10,000 R; moulting is delayed after exposure to 5,000 to 10,000 R. Individuals ofG. duebeni taken from the field during the mild winter 1966/67 were more resistant to radiation, and moulting was less affected, than in laboratory-reared amphipods, or in those collected in the field during other seasons. Besides on irradiation dose, survival time of an individual depends on the time of its moulting in the course of an experiment.

     

Parthenogenesis in the Two Races of Radopholus similis from Florida

Single larval inoculations of both the citrus and banana races of Radopholus similis from Florida indicate parthenogenetic reproduction is possible. These races normally reproduce amphimictieally. Both races produced all-female populations from single larva inoculations after 80 d and male-female populations after 180 d. The all-female populations produced female progeny with viable eggs, but no spermatozoa were present in the spermatheca, indicating tychoparthenogenesis occurred. Uninseminated females in the latter study produced both male and female progeny. Approximately 95% of the female progeny of the male-female populations were inseminated, indicating that cross-fertilization had occurred. The proportion of males to females was as expected in a normal bisexual population. No intersex males were observed. The mechanism of sex determination is not fully understood but assumed to be enviromnentally induced.     

Morphological and sexual traits in Atlas and Iberian Pied Flycatchers Ficedula hypoleuca speculigera and F. h. iberiae: a comparison

Capsule: There are significant biometric differences between Pied Flycatchers from Iberian and north African populations which are consistent with proposals to classify the two forms into separate species.

Aims: To determine the similarities and differences in the main biometrical and plumage sex traits between populations of the Iberian Pied Flycatcher Ficedula hypoleuca iberiae and the Atlas Flycatcher Ficedula hypoleuca speculigera.

Methods: Biometric and plumage traits of 193 breeding individuals of Iberian Pied Flycatchers and 43 Atlas Flycatchers were measured in 2014 with standardized protocols.

Results: Both sexes of Atlas Flycatchers were larger than Iberian Pied Flycatchers in skeletal (tarsus) and wing size and also differed in bill morphology, which was wider but shallower in speculigera than iberiae, with females (but not males) having shorter bills than iberiae females. Males differed in mantle colour and forehead patch size, with speculigera males being darker and displaying larger forehead patches than iberiae males. As in populations of iberiae, some speculigera females also expressed a white forehead patch.

Conclusion: We demonstrate significant phenotypic differences between Iberian Pied Flycatchers and Atlas Flycatchers with respect to size and traits of ecological and evolutionary relevance, supporting the recently proposed scenarios on their independent evolution.     

Population structure of pierid butterflies

Summary Mark-release-recapture techniques were used to study alfalfa pest populations of Colias philodice eriphyle. Two new methods for estimating relative catchability and residence rates were used to compare males to females. The results show that: (1) both sexes had limited dispersal, with mean individual ranges less than 100 m; (2) males were more abundant than females; (3) males and females had similar residence times; (4) males were more catchable than females in uncut fields, but not in cut fields. Explanations for the differences between the sexes are considered. Females may be less catchable in uncut fields because they spend less time in flight than males. Males may be more abundant than females because they develop faster, and may have lower pre-adult mortality. The differences between the sexes are discussed with respect to reproductive strategy. Comparisons with non-pest C.p. eriphyle show differences between pest and non-pest populations. Pest C.p. eriphyle were more sedentary. The residence times were similar for pest and non-pest populations, but pest C.p. eriphyle probably have longer reproductive life-spans. Mid-summer broods of the pest population were partially overlapping; the non-pest population has discrete broods. Pest population density varied less between years than non-pest population density. The differences between pest and non-pest C.p. eriphyle support the idea of ecological diversity among conspecific populations.