Sex Ratio Adjustment Research Papers (original) (raw)

Effects of Sodium and Potassium in diet to determine baby gender in high-sugar mammals have been investigated. Diabetes mellitus is a chronic, widely spread disease in living species. Sex determination has scientific basis for prevention of genetic diseases in addition to social backgrounds.60 rats (obtained from veterinary college Bangalore), were divided in to three groups in the ratio male to female 1:5. The first group was made diabetic with Na and K, the second group was non diabetic with Na and K, group third was control unit (Non-diabetic without Na and K). It was found that the delivered offspring male to female ratio were 4.3:1, 3.3:1 and 1.03:1 for the first, second and third groups respectively. Also, it was found that non diabetic rats fed with normal food yields maximum numbers of offspring (217), while non diabetic rat fed with Na and K yields 200 and diabetic rats with Na and K yield lowest numbers of offspring (144).

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Impact of calcium and magnesium in diet to determine the baby gender in high-sugar hamsters has been investigated. Diabetes mellitus is a chronic, widely spread disease in living species. Sex determination has scientific basis for prevention of genetic diseases in addition to social backgrounds.30 hamsters (obtained from veterinary college Bangalore), were divided in to three groups at the rate male to female 1:5. The first group was made diabetic with Ca and Mg, the second group was non diabetic with Ca and Mg, group third was control unit (Non-diabetic without Ca and Mg). It was found that the delivered offsprings female to male ratio were 3.6:1, 2.61:1 and 1.04:1 for the first, second and third groups respectively. Also, it was found that non diabetic fed with normal food yields maximum numbers of offspring (90), while non diabetic fed with Ca and Mg yields 83 and diabetic with Ca and Mg yield lowest numbers of offspring (70).

- by ashraf beirami
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Impacts of sodium and potassium in diet to determine offspring gender in hamsters have been investigated. Sex determination has scientific basis for prevention of genetic diseases in addition to social backgrounds.20 healthy hamsters chosen from the first generation of the previous experimental hamsters, were divided in to two groups in the hamsters male to female 1:5. The first group was Na and K, the second group was control unit without Na and K. It was found that the delivered offsprings male to female ratio were 2.06:1and 1:1, for the first and second groups respectively. Also, it was found that hamsters fed with (Na, K) food yields, numbers of offspring (135), while hamsters fed with normal food yields, numbers of male offspring (140).

- by ashraf beirami
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- by ashraf beirami
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- Endocrinology, Chemistry, Biology, Calcium

Impact of calcium and magnesium in diet to determine offspring gender in rats has been investigated. Sex determination has scientific basis for prevention of genetic diseases in addition to social backgrounds. 20 healthy rats chosen from the second generation of the previous experimented rats were divided into two groups in the ratio male to female 1:5. The first group was Ca and Mg, the second group was control unit without Ca and Mg. It was found that the delivered offspring male to female ratio were 2.7:1 and 1:1 for the first and second groups respectively. Also, it was found that rats fed with (Ca, Mg) food yields maximum numbers of female offspring 73, while rats fed with normal food yields lowest numbers of female offspring 50.

- by ashraf beirami
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- Biology, Calcium, Magnesium, Sugar Technology

Eusocial insect queens are remarkable in their ability to maximise both fecundity and longevity, thus escaping the typical trade-off between these two traits. In species exhibiting complex eusocial behaviour, several mechanisms have been proposed to underlie the remoulding of the trade-off, such as reshaping of the juvenile hormone pathway, or caste-specific susceptibility to oxidative stress. However, it remains a challenge to disentangle the molecular mechanisms underlying the remoulding of the trade-off in eusocial insects from caste-specific physiological attributes that have subsequently arisen due to their different life histories. Socially plastic species such as the orchid bee Euglossa viridissima represent excellent models to address the role of sociality per se in longevity as they allow direct comparisons of solitary and social individuals within a common genetic background. We present data on gene expression and juvenile hormone levels from young and old bees, from both ...

- by Klaus Hartfelder
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- Evolutionary Biology, Biology, Transcriptome, Longevity

Although adult longevity and fecundity are controlled genetically, the effect of environment is also significant. It has been determined that the developmental period and adult longevity of parasitoids in particular vary significantly according to temperature (1-5). In addition, developmental time and longevity are affected by: the type of species (6), the adult size (7, 8), mating status (mated or unmated) (7, 9), the frequency of mating in males (9), the sex of the parasitoid (2, 6, 7, 10-13), the amount and type of food consumed in the adult stage (3, 7, 11, 13-16) and, in those that complete their development on more than one host, the type of host (17, 18). Studies of different parasitoid species have demonstrated that adult parasitoid fecundity, sex ratio in progeny and the parasitization capacity of the female parasitoid vary according to temperature (1, 13). Additionally, fecundity, sex ratio in progeny and parasitization capacity of the female parasitoid are affected by: the age of the parasitoid (1,7, 11-13, 19-22), the host species (18, 23), the host stages (12, 20, 21), whether or not the host has been parasitized before (7, 24), the number of eggs laid by the female (1, 7, 20,

- by Fevzi UÇKAN
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- Zoology, Biology, Hymenoptera, Photoperiodism

Achroia grisella and Galleria mellonella (Lepidoptera, Pyralidae) are two of the most common pests in apiaries worldwide since in their larval stage they feed on wax combs that bees use for their offspring, on bees' food, and on the wooden boxes. After finding some specimens of parasitoids associated to A. grisella cocoons in Tucum an, Argentina, our objective was to accurately identify the species and to study its oviposition habit as a basic biological aspect of the host-parasitoid association. We identified the parasitoid wasps as Apanteles galleriae (Braconidae, Microgastrinae) and herein report the species emerging from A. grisella for the first time in Argentina. Morphological and mitochondrial analyses of specimens coincided in their identification. Further studies on this parasitoid species will allow us to design strategies for the biological control of this important beehive pest.

- by ADRIANA SALVO
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- Zoology, Taxonomy, Biology, Molecular Genetics

The effects of the cytokinin hormone kinetin on the life history traits and hemocytes of the smaller wax moth Achroia grisella F. (Lepidoptera: Pyralidae) were examined in order to better understand the physiological impacts of plant growth regulators on insects. Based on the obtained results, it was found that kinetin did not lead to significant changes in larval mortality, development time, morphological disorders and egg fertility. Female and male longevity were almost unchanged when early instars were fed with a kinetin-added diet, and it tended to be higher for males when kinetin was applied at the egg stage, especially at 5 mg/L. The weight of females decreased significantly with 25 and 3000 mg/L of kinetin and that of males with 5 mg/L. The most striking effect was a considerable decline in the number of progeny, particularly at 400 and 3000 mg/L, as compared to the control. The injection of kinetin caused noticeable decreases in the number of hemocytes in the circulation at 3 and 24 h. This work presents the first evidence that kinetin adversely affects the development and the hemocyte counts of an economically-important host species, A. grisella.

- by Erinc Celik
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- Biology, Biological Sciences, Fecundity, Pyralidae

- by Eduardo Martin
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- Zoology, Taxonomy, Biology, Molecular Genetics

The tammar wallaby, Macropus eugenii, has a ruminant-like digestive system which may make a significant concentration of amino acids and fatty acids available to the blastocyst via uterine fluids. Fluorescent and radioisotope analyses were performed to determine the rate of glutamine and palmitate use by blastocysts recovered on day 0, 3, 4,5 and 10 after reactivation induced by removal of pouch young (RPY). Between day 0 and 4 glutamine uptake increased from 15.6 \m=+-\6.6 to 36.1 \m=+-\2.7 pmol per embryo h\m=-\1 (P < 0.01) and ammonium production increased from 8.2 \ m=+-\ 4.3 to 26.6 \ m=+-\ 3.0 pmol per embryo h\ m=-\ 1 (P < 0.01). Glutamine oxidation did not increase until day 10 after RPY (P < 0.01), but the percentage of glutamine oxidized increased from 4.5 \ m=+-\ 3.1% during diapause to 31.2 \ m=+-\ 12.6% (P < 0.01) by day 5 after RPY and increased further to 51.0 \ m= +-\ 15.8% (P < 0.01) by day 10 after RPY. Palmitate oxidation also increased from 0.3 \ m=+-\ 0.1 by day 0 blastocysts to 3.8 \ m=+-\ 1.7 pmol per embryo h\m=-\1 (P < 0.01) by day 4 blastocysts. This increase provides a greater potential for ATP production, possibly to supply increased demand due to the coincident resumption of mitoses. The ATP:ADP ratio within blastocysts had reduced by the time of the first measurement at day 3 (0.5 \m=+-\0.2 pmol per embryo h\ m=-\ 1; P < 0.01) compared with day 0 blastocysts (1.4 \ m=+-\0.3 pmol per embryo h\ m=-\ 1). It is likely that metabolism of amino acids and fatty acids contributes to the energy supply during reactivation of tammar wallaby blastocysts after embryonic diapause.

- by G. Shaw
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- Biology, Embryo, Biological Sciences, Glucose

Background and objectives. Despite growing interest in the role of maternal psychosocial stress as a determinant of preterm birth, no existing work has examined the relation between maternal stress and post-term birth (≥42 weeks). We hypothesize that prolonging gestation past term may represent an adaptive strategy to a suboptimal environment. Methodology. We examined the relationship between exposure to the September 2001 terrorist attacks and odds of post-term birth in California. We calculated the expected odds of post-term birth among conception cohorts of singleton gestations in California between October 1996 and November 2005. We used time series analysis to test for higher than expected odds of post-term birth among the 10 cohorts exposed to the attacks of September 2001 (those conceived from December 2000 to September 2001). Results. The observed odds of post-term delivery among gestations at 33-36 weeks in September 2001 were higher than statistically expected for all race...

- by Ralph Catalano
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- Medicine, Pregnancy, Odds ratio, Odds

Sex ratio theory has been very successful in predicting under which circumstances parents should bias their investment towards a particular offspring sex. However, most examples of adaptive sex ratio bias come from species with well-defined mating systems and sex determining mechanisms, while in many other groups there is still an ongoing debate about the adaptive nature of sex allocation. Here we study the sex allocation in the mealybug Planococcus citri, a species in which it is currently unclear how females adjust their sex ratio, even though experiments have shown support for facultative sex ratio adjustment. Previous work has shown that the sex ratio females produce changes over the oviposition period, with males being overproduced early and late in the laying sequence. Here we investigate this complex pattern further, examining both the robustness of the pattern and possible explanations for it. We first show that this sex allocation behaviour is indeed consistent across lines from three geographical regions. Second, we test whether females produce sons first in order to synchronize reproductive maturation of her offspring, although our data provide little evidence for this adaptive explanation. Finally we test the age at which females are able to mate successfully and show that females are able to mate and store sperm before adult eclosion. Whilst early-male production may still function in promoting protandry in mealybugs, we discuss whether mechanistic constraints limit how female allocate sex across their lifetime.

- by Rohaa Langenhof
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- Evolutionary Biology, Conflict, Sex Allocation, Biology

In many insect societies, workers can manipulate the reproductive output of their colony by killing kin of lesser value to them. For instance, workers of the mound-building Formica exsecta eliminate male brood in colonies headed by a single-mated queen. By combining an inclusive fitness model and empirical data, we investigated the selective causes underlying these fratricides. Our model examines until which threshold stage in male brood development do the workers benefit from eliminating males to rear extra females instead. We then determined the minimal developmental stage reached by male larvae before elimination in F. exsecta field colonies. Surprisingly, many male larvae were kept until they were close to pupation, and only then eliminated. According to our model, part of the eliminated males were so large that workers would not benefit from replacing them with new females. Moreover, males were eliminated late in the season, so that new females could no longer be initiated, because matings take place synchronously during a short period. Together, these results indicate that workers did not replace male brood with new females, but rather reduced total brood size during late larval development. Male destruction was probably triggered by resource limitation, and the timing of brood elimination suggests that males may have been fed to females when these start to grow exponentially during the final larval stage. Hence, the evolution of fratricides in ants is best explained by a combination of ecological, demographic and genetic parameters.

- by Laurent Keller
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- Biology, Biological Sciences, Seasonality, Sex ratio

Sex allocation theory predicts that parents should bias their reproductive investments toward the offspring sex generating the greatest fitness return. When females are the heterogametic sex (e.g., ZW in butterflies, some lizards, and birds), production of daughters is associated with an increased risk of offspring inviability due to the expression of paternal, detrimental recessives on the Z chromosome. Thus, daughters should primarily be produced when mating with partners of high genetic quality. When female sand lizards (Lacerta agilis) mate with genetically superior males, exhibiting high MHC Class I polymorphism, offspring sex ratios are biased towards daughters, possibly due to recruitment of more Z-carrying oocytes when females have assessed the genetic quality of their partners. If our study has general applicability across taxa, it predicts taxon-specific sex allocation effects depending on which sex is the heterogametic one.

- by M. Olsson
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- Evolutionary Biology, Genetics, Economics, Polymorphism

In polygynous ants it has been proposed that the coexistence of several queens in a colony evolved as a response to ecological, social and genetic parameters. We present demographic, histological and genetic data showing that the plant-ant Petalomyrmex phylax is facultatively and secondarily polygynous. Polygyny is functional, lowers the reproductive output per queen, and is a kin-selected trait as new queens accepted in polygynous colonies are highly related females that never left their natal colony. The degree of polygyny varies according to a geographical gradient. Northern colonies can be strongly polygynous, while at the southern edge of the species' distribution, colonies are almost exclusively monogynous. However, ecological studies of the host-plant populations revealed that this cline could not be explained by variations in the degree of nest site limitation. We discuss selective costs and benefits associated with these social structures, and propose that this cline may result from historical processes such as selection of a more dispersive strategy along a colonization front.

- by Finn Kjellberg
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- Biology, Social insects, Cameroon, Biological Sciences

In bees, socially polymorphic species can either live solitary or in

- by Michael Lattorff
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- Evolutionary Biology, Zoology, Ethology, Psychology

Polygyny is common in social insects despite inevitable decreases in nestmate relatedness and reductions to the inclusive fitness returns for cooperating non-reproductive individuals. We studied the prevalence and mode of polygyny in the African acacia-ant Crematogaster mimosae. These ants compete intensively with neighboring colonies of conspecifics and with three sympatric ant species for resources associated with the whistling-thorn acacias in which they all obligately nest. We used the genotypes of alate males at ten microsatellite loci to reconstruct queen genotypes and found that C. mimosae colonies are frequently secondarily polygynous, in that they include multiple closely related (and sometimes full-sib) queens, and (more rarely) unrelated queens. We also found that individual queens in both monogynous and polygynous colonies had mated with multiple males, making C. mimosae an interesting example of simultaneous polygyny and polyandry. The presence of polygyny in C. mimosae and the intense competition for nest-sites between C. mimosae and its conspecifics support the association between nest-site limitation and polygyny. Polygyny may allow for increased worker populations and a competitive advantage, as intercolony conflicts are typically won by the colony with the larger number of workers.

- by Maureen Stanton
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- Evolutionary Biology, Zoology, Biology, Hymenoptera

- by Fevzi UÇKAN
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- Zoology, Biology, Hymenoptera, Longevity
- by Eisuke Hasegawa
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- Evolutionary Biology, Zoology

MATERIALS AND METHODS showed that LMC should lead to constant male investment among mothers with variable amount of resources for reproduction. Frank (1987) argued that this constant male investment should cause sex-ratio variability among ant colonies. Assuming that LMC is unlikely in ants, sex-ratio variability in ants has been explained either by the "relative-relatedness asymmetry hypothesis" (RRA) (Boomsma and Grafen 1990, 1991) or the "resource-availability hypothesis" (RAH) (Nonacs 1986a), RRA predicts that if there is variability in the degree of genetic asymmetries among colony members, then workers-given that they can recognize asymmetry but cannot discriminate their full siblings-produce the sex to whom they are more closely related than the population average (Boomsma and Grafen 1990, 1991). Nonacs (1986a) argued that because female larvae of eusocial Hymenoptera can develop into either workers or sexual alates, colonies with abundant resources should produce many female reproductives. Accordingly, colonies with poor resources should produce mostly males and workers (the latter are not included in female sexual investment). Only a few empirical tests for these hypotheses exist (Backus and Herbers 1993; Queller et al. 1993b; Sundstrom 1994). Here we provide the first evidence of LMC in ants that conduct mass nuptial flights. This evidence contradicts a previous assumption that such competition does not occur in mating swarms of ants. We also present the first empirical data that support the existence of mating competition among related males as the main cause of the sex-ratio variability in an ant species.

- by Eisuke Hasegawa
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- Evolutionary Biology, Biology, Evolution, Medicine
- by bernard roitberg
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- Zoology, Biology, Competition, Ecological Applications
- by saadiya said
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- Academic Journals
- by William Brown
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- Genetics, Reproduction, Biology, Social insects

In the present work, laboratory and field strains of the greater wax moth, Galleria mellonella L. (Lepdoptera: Pyralidae) were reared on two food types (artificial diet for laboratory strain and wax frames for field strain) to study some biological aspects of the developmental stages of braconid wasp, Apanteles galleriae Wilkinson (Hymenoptera: Braconidae) the parasitoid of G. mellonella. Results of total developmental period, percentages of adults' emergence and longevity of females of the parasitoid are different when reared on two strains of G. mellonella. Total developmental period of the immature stages was shorter on field strain (47.26 days) than that reared on laboratory strain of G. mellonella recording 57.5 days. In contrast, no significant differences were observed between the longevity of adult females reared on the two strains, where the longevity period was 25.33 and 26.3 days in laboratory and field strains, respectively. Also, life cycle of immature stages, longevity of adults and reproductive parameters of the parasitoid A. galleriae were determined. The fecundity of A. galleria decreased when reared on laboratory strain of G. mellonella; it was 140 progeny/females and increased to 177.3 progeny/females when A. galleria was reared on G. mellonella field strain. On the other hand, the sex ratio of the parasitoid and longevity are different between the two strains. Results of the life tables for G. mellonella and the parasitoid, A. galleria strains, showed shortage in generation periods for that reared on the field strain. The present study was conducted to explore the effect of food types on some biological parameters of G. mellonella and its parasitoid, A. galleria.

- by saadiya said
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Host type choice and sex allocation were examined using the solitary parasitic wasp Dinarmus basalis (Pteromalidae, Hymenoptera) parasitizing larvae or pupae of the bean weevil Callosobruchus chinensis (Bruchidae, Coleoptera) within azuki beans (Vigna angularis). The wasps were offered two types of host; one was hard for the mother to lay eggs in, but was more beneficial for the offspring; the other was easy for the mother to lay eggs in, but was less beneficial for the offspring. The two types of host were one large host (17-day old host) in one bean and 6 small hosts (12-, or 13-day old hosts) in one bean. The same number of each host was presented at the same time to female wasps. The wasps accepted more 17-day old hosts than 12-day old hosts, and more 13-day old hosts than 17-day old hosts in each pair-wise choice experiment. The proportions of accepted host types were different from the proportions predicted by optimization models of random prey encounter with known or unknown prey densities. The wasps showed partial preference of host types. Incomplete information about prey densities, and about the costs and benefits of the two types of host may have generated the partial preference. Two predictions of host sizemodels, that (1) there should be a negative relationship between host size and offspring sex ratio (proportion of male offsprings), and (2) the sex ratio in each size host changes with the relative frequency of each size host utilized, were qualitatively supported.

- by Kinya Nishimura
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- Evolutionary Biology, Sex Allocation, Biology, Ecology

Sex allocation theory describes how parents should bias investment in either sons or daughters when each gives a different fitness return. Over the past decades, social Hymenoptera have increasingly been used as models for testing the predictions of sex ratio theory. Their haplodiploid sex determining system gives mothers considerable control over the proportion of each offspring sex by selective fertilization of eggs. Moreover, the great diversity in life-history strategies and breeding systems has allowed detailed tests of quantitative predictions linking sex ratios to environmental or genetic factors at the colony and population levels. Nevertheless, the vast majority of theoretical and experimental treatments devoted to sex allocation in ants, bees and wasps have focused on sex ratio at emergence or adult stage, rather than primary sex ratio adjustment (the proportion of each sex at oviposition). Sex ratio at emergence may be adaptive, but it may also result from sex-specific di...

- by Serge Aron
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- Biology

The effect of parasitoid age on fecundity and sex ratio in Bracon hebetor Say (Hymenoptera: Braconidae) was examined at 26 ± 2 oC and 60 ± 5% relative humidity. Galleria mellonella (L.) and Ephestia kuehniella (Zell.) were used as host species. It was found that the fecundity of the female parasitoid did not change significantly during the first 5 days of the female's lifespan but afterwards it decreased significantly. Under laboratory conditions, the offspring sex ratio was male biased on both host species. The fecundity of the female parasitoids reared on late stage larvae of G. mellonella was higher than that of those reared on E. kuehniella.

- by Eylem Akman Gündüz
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- Biology, Fecundity, Host

Sex ratio is a subject of scientific interest but little is known about the factors that affect the sex ratio of humans. The aim of this study was to assess the effect of the Lebanese civil war on sex ratio. Data on all live births delivered at a large university hospital for the years 1977-2005 were used in this study. Study periods were defined as wartime (1977-1992) and postwar (1993-2005). The sex ratio in the study time period was calculated as the male proportion, i.e. males/males + females in live-born infants. Sex ratio during the war was compared with that of the postwar period. The sex ratio was similar in the war and postwar period (0.515 versus 0.513; OR = 1.007; 95% CI 0.98-1.04). The annual variation in the sex ratio during the study period did not show any significant change in any of the years. In conclusion, the Lebanese civil war did not cause a detectable change in sex ratio at birth. Factors that might have affected the sex ratio include the nature of the study population (civilians), the variable intensity of war in different periods, and the effect of stress and environmental toxins.

- by Anwar Nassar
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- Civil War, Lebanon, War, Pregnancy

Ant-associated microorganisms can play crucial and often overlooked roles, and given the diversity of interactions that ants have developed, the study of the associated microbiomes is of interest. We focused here on specialist plant-ant species of the genus Allomerus that grow a fungus to build galleries on their host-plant stems. Allomerus-inhabited domatia, thus, might be a rich arena for microbes associated with the ants, the plant, and the fungus. We investigated the microbial communities present in domatia colonised by four arboreal ants: Allomerus decemarticulatus, A. octoarticulatus, A. octoarticulatus var. demerarae, and the non-fungus growing plant-ant Azteca sp. cf. depilis, inhabiting Hirtella physophora or Cordia nodosa in French Guiana. We hypothesized that the microbial community will differ among these species. We isolated microorganisms from five colonies of each species, sequenced the 16S rRNA or Internal TranscribedSpacer (ITS) regions, and described both the alpha...

- by Alain Dejean
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- Insects

A model is constructed to study the effects of local mate competition and multiple mating on the optimum allocation of resources between the male and female reproductive brood in social hymenopteran colonies from the 'points of view' of the queen (parental manipulation theory) as well as the workers (kin selection theory). Competition between pairs of alleles specifying different sex investment ratios is investigated in a game theoretic frame work. All other things being equal, local mate competition shifts the sex allocation ratio in favour of females both under queen and worker control. While multiple mating has no effect on the queen's optimum investment ratio, it leads to a relatively male biased investment ratio under worker control. Under queen control a true Evolutionarily Stable Strategy (ESS) does not exist but the 'best' strategy is merely immune from extinction. A true ESS exists under worker control in colonies with singly mated queens but there is an asymmetry between the dominant and recessive alleles so that for some values of sex ratio a recessive allele goes to fixation but a dominant allele with the same properties fails to do so. Under multiple mating, again, a true ESS does not exist but a frequency dependent. region emerges. The best strategy here is one that is guaranteed fixation against any competing allele with a lower relative frequency. Our results emphasize the need to determine levels of local mate competition and multiple mating before drawing any conclusions regarding the outcome of queen-worker conflict in social hymenoptera. Multiple mating followed by sperm mixing, both of which are known to occur in social hymenoptera, lower average genetic relatedness between workers and their reproductive sisters. This not only shifts the optimum sex ratio from the workers' 'point of view' in favour of males but also poses problems for the kin selection theory. We show that kin recognition resulting in the ability to invest in full but not in half sisters reverts the sex ratio back to that in the case of single mating and thus completely overcomes the hurdles for the operation of kin selection.

- by Niranjan Joshi
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- Genetics, Sex Allocation, Kin Selection, Sex ratio

- by Mario X Ruiz-González
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- Insects

Nests of the primitively eusocial orchid bee Euglossa viridissima are generally founded
by a solitary female but can be reactivated by female offspring, in the presence or
absence of the mother. The population therefore exists of solitary and social nests
that co‐occur in an area. A female can stay as a subordinate helper under a dominant
female or disperse to become a solitary foundress. Yet, the costs and benefits of the
different social phenotypes are so far little understood. Here, we compared solitary
and social nests of orchid bees. We used offspring of solitary and social nests to
calculate offspring sex ratio, and applied molecular markers to calculate intranidal
relatedness, infer maternity and test whether sociality may have a genetic component.
We found that social nests had on average more brood than solitary nests.
The overall sex ratio in the population did not differ from 1:1. However, social nests
tended to produce a split sex ratio with some nests producing mainly males and others
mainly female offspring. Regardless of social phenotype, the number of offspring
was correlated with the sex ratio, with smaller nests having a more female‐biased
offspring. In social nests, not all offspring resulted from a single‐mated mother, which
was also the case for some solitary nests. This suggests shared reproduction in social
nests and may be an indication that intraspecific parasitism and nest takeover are not
uncommon. Structure analyses did not reveal different genetic background of the
two social phenotypes. Our results suggest that there is no clear benefit that favours
one of the two social phenotypes over the other and that the population is kept at
balance in terms of sex ratio.

- by Michael Lattorff
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- Social insects, Animal Behaviour, Sex Ratio Adjustment, Social behavior

Sex determination has scientific basis for prevention of genetic sex linked diseases in addition to social backgrounds. There are many methods for sex determination. This study was designed to investigate the effects of adding different ions to the drinking water of rats on determination of rats' offspring sexes. In total, 72 female Vistar rats were chosen and randomly divided into three groups. Group one (NaK) was supplied with sodium and potassium diet, group two (CaMg) was supplied with calcium and magnesium diet, and group (C) as the control group. After 15 days of special diet, the rats were mated with male rats and were separated after pregnancy. The newborn rats' sexes were determined after delivery. The data were entered and analyses by SPSS software using t. test. In CaMg group, 66 male and 97 female rats were born (sex ratio = 0.68), while these rates were 91 male and 73 female (sex ratio = 1.25) in the NaK group. In the control group, 72 male and 75 female rats were born (sex ratio = 0.96). The difference in the sex ratio between NaK and CaMg group was statistically significant (p-value = 0.007). While the differences between NaK group with control group (p-value = 0.251) and between CaMg group with control group (p-value = 0.133) were not statistically significant. Our results suggest that different amount of ions in the diet of rats can have significant effect on the sex ratio of delivered rats' offspring.

- by Mohammad Hasan Sheikhha
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- Genetics, Nutrition and Dietetics, Magnesium, Sex ratio

1. In haplodiploid organisms, virgin or sperm-depleted females can reproduce but are constrained to produce only male progeny. According to Godfray's constrained model, when p , the proportion of females constrained to produce only male progeny, is not null in a panmictic population, unconstrained females should bias their sex allocation towards females to compensate for the excess of males. These unconstrained females should be able to adjust the sex ratio in response to local variation of p .

- by Emmanuel Desouhant
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- Zoology, Ecology, Sex ratio, Offspring Sex Ratio

Seasonal population dynamics of Brevicoryne brassicae (L.) and Diaeretiella rapae (McIntosh) were studied in two canola (Brassica napus) fields with two different irrigation methods (flooding and sprinkler irrigations) from April to June 2010. Aphid and parasitoid (mummies) populations were sampled once a week. The highest aphid density was recorded on May 12th (792.5 ± 55.5) and on May 18th (1701.1 ± 195) in the sprinkler and flood irrigated fields, respectively. Parasitism rate recorded ranged from 0.4 to 19.5% and from 1.0 to 11.9% in sprinkler and flood irrigated fields, respectively. During the course of the study, there was no significant relationship between the weather values recorded and aphid populations observed in the field. However relationship with weather values was found in the case of D. rapae populations. Secondary parasitism was higher at the end of growing season and two hyperparasitoid species were dominant: Pachyneuron aphidis (Bouche) and Alloxysta fuscicornis...

- by Hossein Lotfalizadeh
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Effects of host species, stage and size on clutch size and sex ratio of the gregarious, idiobiont ectoparasitoid Dibrachys boarmiae were investigated at 25 ± 2°C and 70 ± 5% relative humidity. The greater wax moth, Galleria mellonella, small wax moth, Achroia grisella, and early stage solitary larvae of the endoparasitoid, Apanteles galleriae, were used as hosts. Clutch size was greatest from prepupae of the largest host, Galleria mellonella, with a mean of 40.07 offspring per host versus 14.73 and 2.93 for Achroia grisella and Apanteles galleriae, respectively. The mean clutch size from pupae was lower than from prepupae, being 17.27, 10.73 and 2.89 for Galleria mellonella, Achroia grisella and Apanteles galleriae, respectively. Within each host species and stage, heavier hosts resulted in larger clutches. The sex ratio of offspring (proportion of male) was approximately 0.20, with only minor differences among host species, stages and sizes.

- by Adnan SARIKAYA
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- Sex Ratio Adjustment, Clutch Size, Parasitoids, Host Size

The control of reactivation from embryonic diapause in the tammar wallaby, 20

- by Jane Fenelon
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- Physiology, Reproduction, Pregnancy, Progesterone

Embryonic diapause, the temporary suspension of development of the embryo, is a fascinating reproductive strategy that has been frequently exploited across the animal kingdom. It is characterized by an arrest in development that occurs at the blastocyst stage in over 130 species of mammals. Its presumed function is to uncouple mating from parturition, to ensure that both occur at the most propitious moment for survival of the species. Diapause can be facultative, i.e. induced by physiological conditions, or obligate, i.e. present in every gestation of a species. In the latter case, the proximal signals for regulation are related to photoperiod. Three diverse models, the mouse, the mustelid carnivores and the wallaby have been studied in detail. From these studies it can be discerned that, although the endocrine cues responsible for induction of diapause and re-initiation of development vary widely between species, there are a number of commonalities. Evidence to date indicates that the uterus exercises the proximal regulatory influence over whether an embryo enters into and when it exits from diapause. Some factors have been identified that appear crucial to this regulation, in particular, the polyamines. Recent studies indicate that diapause can be induced in species where it does not exist in nature. This suggests that the potential for diapause in mammals to be due to a single evolutionary event, to which control mechanisms adapted when the trait was beneficial to reproductive success. Further work at the molecular, cellular and organismic levels will be required before the physiological basis of diapause is resolved.

- by Jane Fenelon and +1
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- Reproduction, Biological Sciences, Mice, Blastocyst

- by Xy nobody
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We examined the effect of facultative sex allocation by workers on queen fitness in a Furnish population of the ant Formica truncorum. Workers rear female-biased broods in colonies headed by a singly mated queen and male-biased broods in colonies headed by a multiply mated queen. As a result, multiply mated queens have a 37% fitness advantage over singly mated queens. Neither reproductive output nor worker population of colonies varied with queen mating frequency. We suggest that singly mated queens persist in the population because fitness benefits to multiply mated queens via sex allocation are balanced by costs of additional mating*. Alternatively, singly mated queens may persist simply because some queens lack opportunities to mate multiply or because male control sometimes prevents additional matings by queens. Kty words: eusodah'ty, Formica, queen fitness, sex allocation, social insects, worker-queen conflict. [Behav Ecol 9:116-121 (1998)]

- by Xy nobody
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Variable queen mating frequencies provide a unique opportunity to study the resolution of worker-queen conflict over sex ratio in social Hymenoptera, because the conflict is maximal in colonies headed by a singly mated queen and is weak or nonexistent in colonies headed by a multiply mated queen. In the wood ant Formica exsecta, workers in colonies with a singly mated queen, but not those in colonies with a multiply mated queen, altered the sex ratio of queen-laid eggs by eliminating males to preferentially raise queens. By this conditional response to queen mating frequency, workers enhance their inclusive fitness.

- by Xy nobody
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Social Hymenoptera have become key organisms for tests of sex-ratio theory. We assess the role of resources for explaining sex-ratio variation in a highly male-biased population of the ant Formica exsecta. Key predictions of two of the three leading hypotheses invoking an effect of resource availability on sex ratios in social insects are not upheld. One prediction of the multifaceted parental-investment hypothesis is that colonies with greater brood production will rear a greater proportion of their diploid offspring as reproductive females (gynes), rather than workers. This study shows the positive correlation between female-biased sex ratio and the production of brood by female-producing colonies was not the outcome of a trade-off in the production of workers vs. gynes. The main prediction of the constant-female hypothesis is that investment in gynes should be constant. We found extreme variation among colonies in the number of gynes produced. By contrast, all the predictions of the queen-replenishment hypothesis were supported. The queen-replenishment hypothesis predicts that colonies produce gynes only when queen number is so low that colony production of brood is reduced, or colony survival threatened. We found that, as predicted by this hypothesis, female-producing colonies had fewer queens and produced a lower biomass of brood than male-producing colonies. In contrast, male-producing colonies had lower production per queen, and were more likely to be limited by external resources. This suggests that queen number limits production in female-producing colonies. These data provide evidence of adaptive adjustment of resources to worker, gyne, and male brood.

- by Xy nobody
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Wolbachia is a maternally inherited bacterium that may manipulate the reproduction of its arthropod hosts. In insects, it is known to lead to inviable matings, cause asexual reproduction or kill male offspring, all to its own bene® t, but to the detriment of its host. In social Hymenoptera, Wolbachia occurs widely, but little is known about its ® tness effects. We report on a Wolbachia infection in the wood ant Formica truncorum, and evaluate whether it in¯uences reproductive patterns. All 33 colonies of the study population were infected, suggesting that Wolbachia infection is at, or close to, ® xation. Interestingly, in colonies with fewer infected workers, signi® cantly more sexuals are produced, indicating that Wolbachia has deleterious effects in this species. In addition, adult workers are shown to have signi® cantly lower infection rates (45%) than worker pupae (87%) or virgin queens (94%), suggesting that workers lose their infection over life. Clearance of Wolbachia infection has, to our knowledge, never been shown in any other natural system, but we argue that it may, in this case, represent an adaptive strategy to reduce colony load. The cause of ® xation requires further study, but our data strongly suggest that Wolbachia has no in¯uence on the sex ratio in this species.

- by Xy nobody
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The genetic basis of morphological traits in social insects remains largely unexplored. This is even true for individual body size, a key life-history trait. In the social insects, the size of reproductive individuals affects dispersal decisions, so that small size in queens is often associated with reduced dispersal, and large size with long-range dispersal and independent colony founding. Worker size is connected to division of labour when workers specialize in certain tasks according to their size. In many species, variation in worker size has been shown to increase colony performance. In this study, we present the first evidence of an additive genetic component to queen size in ants, using maternal half sib analysis. We also compared intra-colony size variation in colonies with high (queen doubly mated) versus low (queen singly mated) genetic variability. We found a high and significant heritability (h 2 =0.51) for queen size in one of the two study years, but not in the other. Size variation among queens was greater in colonies headed by a doubly mated queen in one of the study years, but not in the other. This indicates that genetic factors can influence queen size, but that environmental factors may override these under some circumstances. The heritability for worker size was low (h 2 =0.09) and non-significant. Increased genetic diversity did not increase worker size variation in the colonies. Worker size appeared largely environmentally determined, potentially allowing colonies to adjust worker size ratios to current conditions.

- by Xy nobody
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A model is constructed to study the effects of local mate competition and multiple mating on the optimum allocation of resources between the male and female reproductive brood in social hymenopteran colonies from the 'points of view' of the queen (parental manipulation theory) as well as the workers (kin selection theory). Competition between pairs of alleles specifying different sex investment ratios is investigated in a game theoretic frame work. All other things being equal, local mate competition shifts the sex allocation ratio in favour of females both under queen and worker control. While multiple mating has no effect on the queen's optimum investment ratio, it leads to a relatively male biased investment ratio under worker control. Under queen control a true Evolutionarily Stable Strategy (ESS) does not exist but the 'best' strategy is merely immune from extinction. A true ESS exists under worker control in colonies with singly mated queens but there is an asymmetry between the dominant and recessive alleles so that for some values of sex ratio a recessive allele goes to fixation but a dominant allele with the same properties fails to do so. Under multiple mating, again, a true ESS does not exist but a frequency dependent region emerges. The best strategy here is one that is guaranteed fixation against any competing allele with a lower relative frequency. Our results emphasize the need to determine levels of local mate competition and multiple mating before drawing any conclusions regarding the outcome of queen-worker conflict in social hymenoptera. Multiple mating followed by sperm mixing, both of which are known to occur in social hymenoptera, lower average genetic relatedness between workers and their reproductive sisters. This not only shifts the optimum sex ratio from the workers' 'point of view' in favour of males but also poses problems for the kin selection theory. We show that kin recognition resulting in the ability to invest in full but not in half sisters reverts the sex ratio back to that in the case of single mating and thus completely overcomes the hurdles for the operation of kin selection.

- by Raghavendra Gadagkar
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- Genetics, Sex Allocation, Kin Selection, Sex ratio

Sex allocation data in eusocial Hymenoptera (ants, bees and wasps) provide an excellent opportunity to assess the eectiveness of kin selection, because queens and workers dier in their relatedness to females and males. The ®rst studies on sex allocation in eusocial Hymenoptera compared population sex investment ratios across species. Female-biased investment in monogyne ( with single-queen colonies) populations of ants suggested that workers manipulate sex allocation according to their higher relatedness to females than males (relatedness asymmetry). However, several factors may confound these comparisons across species. First, variation in relatedness asymmetry is typically associated with major changes in breeding system and life history that may also aect sex allocation. Secondly, the relative cost of females and males is dicult to estimate across sexually dimorphic taxa, such as ants. Thirdly, each species in the comparison may not represent an independent data point, because of phylogenetic relationships among species. Recently, stronger evidence that workers control sex allocation has been provided by intraspe-ci®c studies of sex ratio variation across colonies. In several species of eusocial Hymenoptera, colonies with high relatedness asymmetry produced mostly females, in contrast to colonies with low relatedness asymmetry which produced mostly males. Additional signs of worker control were found by investigating proximate mechanisms of sex ratio manipulation in ants and wasps. However, worker control is not always eective, and further manipulative experiments will be needed to disentangle the multiple evolutionary factors and processes aecting sex allocation in eusocial Hymenoptera.

- by Laurent Keller
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- Evolutionary Biology, Genetics, Genomics, Sex Allocation

- by Michel Chapuisat
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- Science, Multidisciplinary, Kin Selection, Sex ratio

- by Michel Chapuisat
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- Evolutionary Biology, Genetics, Genomics, Sex Allocation