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Heterogametic Sex (heterogametic + sex)
Selected AbstractsGENETIC DISSECTION OF HYBRID INCOMPATIBILITIES BETWEEN DROSOPHILA SIMULANS AND D. MAURITIANA.: III.EVOLUTION, Issue 11 2003AND IMPLICATIONS FOR HALDANE, DEGREE OF DOMINANCE, HETEROGENEOUS ACCUMULATION OF HYBRID INCOMPATIBILITIES Abstract The genetic basis of Haldane,rule was investigated through estimating the accumulation of hybrid incompatibilities between Drosophila simulans and D. mauritiana by means of introgression. The accumulation of hybrid male sterility (HMS) is at least 10 times greater than that of hybrid female sterility (HFS) or hybrid lethality (HL). The degree of dominance for HMS and HL in a pure D. simulans background is estimated as 0.23,0.29 and 0.33,0.39, respectively; that for HL in an F1 background is unlikely to be very small. Evidence obtained here was used to test the Turelli-Orr model of Haldane's rule. Composite causes, especially, faster-male evolution and recessive hybrid incompatibilities, underlie Haldane's rule in heterogametic male taxa such as Drosophila (XY male and XX female). However, if faster-male evolution is driven by sexual selection, it contradicts Haldane's rule for sterility in hetero-gametic-female taxa such as Lepidoptera (ZW female and ZZ male). The hypothesis of a faster-heterogametic-sex evolution seems to fit the current data best. This hypothesis states that gametogenesis in the heterogametic sex, instead of in males per se, evolves much faster than in the homogametic sex, in part because of sex-ratio selection. This hypothesis not only explains Haldane's rule in a simple way, but also suggests that genomic conflicts play a major role in evolution and speciation. [source] Sex allocation in black-capped chickadees Poecile atricapillaJOURNAL OF AVIAN BIOLOGY, Issue 2 2003Scott M. Ramsay Optimal sex allocation for individuals can be predicted from a number of different hypotheses. Fisherian models of sex allocation predict equal investment in males and females up to the end of parental care and predict brood compositions based on the relative costs of producing males and females. The Trivers-Willard hypothesis predicts that individual females should alter the sex ratio of their broods based on their own condition if it has a differential impact on the lifetime reproductive success of their sons and daughters. The Charnov model of sex allocation predicts that females should alter sex allocation based on paternal attributes that may differentially benefit sons versus daughters. Because females are the heterogametic sex in birds, many recent studies have focussed on primary sex ratio biases. In black-capped chickadees Poecile atricapilla, males are larger than females suggesting they may be more costly to raise than females. Female condition affects competitive ability in contests for mates, and thus may be related to variance in fecundity. Females prefer high-ranking males as both social and extrapair partners. These observations suggest that females might vary the sex ratio of their broods based on the predictions of any of the above models. Here, we report on the results of PCR based sex determination of 1093 nestlings in 175 broods sampled from 1992 to 2001. Population-wide, we found a mean brood sex ratio of 0.525±0.016, with no significant deviation from a predicted binomial distribution. We found no effect of clutch size, female condition, hatch date, parental rank or paternity. Our results reject the idea that female black-capped chickadees systematically vary sex allocation in their broods. [source] Haploid chromosomes in molecular ecology: lessons from the human YMOLECULAR ECOLOGY, Issue 7 2001Matthew E. Hurles Abstract We review the potential use of haploid chromosomes in molecular ecology, using recent work on the human Y chromosome as a paradigm. Chromosomal sex-determination systems, and hence constitutively haploid chromosomes, which escape from recombination over much of their length, have evolved multiple times in the animal kingdom. In mammals, where males are the heterogametic sex, the patrilineal Y chromosome represents a paternal counterpart to mitochondrial DNA. Work on the human Y chromosome has shown it to contain the same range of polymorphic markers as the rest of the nuclear genome and these have rendered it the most informative haplotypic system in the human genome. Examples from research on the human Y chromosome are used to illustrate the common interests of anthropologists and ecologists in investigating the genetic impact of sex-specific behaviours and dispersals, as well as patterns of global diversity. We present some methodologies for extracting information from these uniquely informative yet under-utilized loci. [source] Potential mechanisms of avian sex manipulationBIOLOGICAL REVIEWS, Issue 4 2003THOMAS W. PIKE ABSTRACT The aim of this review is to consider the potential mechanisms birds may use to manipulate the sex of their progeny, and the possible role played by maternal hormones. Over the past few years there has been a surge of reports documenting the ability of birds to overcome the rigid process of chromosomal sex determination. However, while many of these studies leave us in little doubt that mechanisms allowing birds to achieve this feat do exist, we are only left with tantalizing suggestions as to what the precise mechanism or mechanisms may be. The quest to elucidate them is made no easier by the fact that a variety of environmental conditions have been invoked in relation to sex manipulation, and there is no reason to assume that any particular mechanism is conserved among the vast diversity of species that can achieve it. In fact, a number of intriguing proposals have been put forward. We begin by briefly reviewing some of the most recent examples of this phenomenon before highlighting some of the more plausible mechanisms, drawing on recent work from a variety of taxa. In birds, females are the heterogametic sex and so non-Mendelian segregation of the sex chromosomes could conceivably be under maternal control. Another suggestion is that follicles that ultimately give rise to males and females grow at different rates. Alternatively, the female might selectively abort embryos or,dump lay'eggs of a particular sex, deny certain ova a chance of ovulation, fertilization or zygote formation, or selectively provision eggs so that there is sex-specific embryonic mortality. The ideas outlined in this review provide good starting points for testing the hypotheses both experimentally (behaviourally and physiologically) and theoretically. [source] | ||||||||||