Lack of age-related mosaic loss of W chromosome in long-lived birds

Females and males often exhibit different survival in nature, and it has been hypothesized that sex chromosomes may play a role in driving differential survival rates. For instance, the Y chromosome in mammals and the W chromosome in birds are often degenerated, with reduced numbers of genes, and loss of the Y chromosome in old men is associated with shorter life expectancy. However, mosaic loss of sex chromosomes has not been investigated in any non-human species. Here, we tested whether mosaic loss of the W chromosome (LOW) occurs with ageing in wild birds as a natural consequence of cellular senescence. Using loci-specific PCR and a target sequencing approach we estimated LOW in both young and adult individuals of two long-lived bird species and showed that the copy number of W chromosomes remains constant across age groups. Our results suggest that LOW is not a consequence of cellular ageing in birds. We concluded that the inheritance of the W chromosome in birds, unlike the Y chromosome in mammals, is more stable.     

Linear differentiation of the C-band pattern of the W chromosome in snakes and birds

Evidence is presented from C-banding studies that the W chromosome of eleven species of snakes is not homogeneous in nature but is differentiated linearly into alternating lighter and darker C positive regions. The same is true of the W chromosome of at least some birds. There is evidence from the literature indicating a similar differentiation of the Y chromosome of some mammals and here the intermediate C positive regions are deficient in highly repetitive DNA. The significance of heterochromatinization as a means of generating differentiated sex chromosomes is discussed in the light of these findings.Dedicated to Professor M.J.D. White on the occasion of his 70th Birthday     

Low mitochondrial variability in birds may indicate Hill-Robertson effects on the W chromosome

Interference among loci subject to selection (the Hill-Robertson effect) may considerably reduce levels of adaptation and variability in genomic regions that lack recombination. Y- or W chromosomes are particularly vulnerable to such effects, since they represent large, non-recombining blocks of genetic material. In birds, the W chromosome and mitochondrial genomes are both maternally transmitted, and hence fail to recombine with each other, whereas in mammals the Y chromosome is paternally transmitted. We show here that mitochondrial DNA sequence diversity is reduced in non-ratite birds compared with mammals. After considering possible confounding factors, such as differences in generation times, mutation rates and demography, we conclude that Hill-Robertson effects associated with the W chromosome provide the most likely explanation for this difference.     

Karyological study of one charadriiform and two passerine Indian birds

The karyotypes of one charadriiform bird, Himantopus himantopus himantopus (Linnaeus) (Recurvirostridae) and two passerine birds, Chloropsis cochinchinensis jerdoni (Blyth) (Irenidae) and Melophus lathami (Gray) (Emberizidae), hithertho cytologically unknown have been studied. The diploid chromosome number (2n) is 82 ± in H. h. himantopus and 80 ± in both C. c. jerdoni and M. lathami. The Z and W chromosomes were identified except in H. h. himantopus. C-banding analysis in C. c. jerdoni shows almost the entire W chromosome and the short arm of the 5th chromosome to be completely heterochromatic. Possible karyological relationships among congeneric and confamilial species are discussed.     

Identification of the facultative heterochromatic X chromosome in females of 25 rodent species.

Treatment of the chromosomes of 25 rodent species with a 50 degrees C hypotonic solution and Giemsa staining permitted identification of the heterochromatic X chromosome in 24 species. With this technique, the facultative of the heterochromatic X chromosome or the facultative portion of large, composite-type X chromosoms is stained darker than the other chromosomes, allowing it to be distinguished from the homologous euchromatic X chromosome in female metaphase cells. Intense staining of the single X chromosome was not observed in male metaphase cells. It is suggested that this differential staining of one of the two X chromosomes might be due to qualitative differences in chromosomal proteins rather than to differences in the degree of chromosomal condensation or in DNA base sequence.     

Cytological analysis of constitutive heterochromatin in two species of birds

Two species of birds, the myna (Acridotheres tristis L.) and the jungle babbler (Turdoides malcolmi Sykes), have been studied cytologically. Their modal diploid numbers are 78±2 and 68±2 respectively. In T. malcolmi the heterochromatin is located on the centromeres of all the macros and most of the microchromosomes, heterochromatin comprises predominantly GC-sequences and at least one pair of microchromosomes is responsible for nucleolus organization. The occasional occurrence of silver deposition on more than one pair of microchromosomes suggests the possibility that more than one pair of micros may be associated with the synthesis of rRNA. The heterochromatin in A. tristis is AT-rich and restricted to the macro-chromosomes, though most of the micros are also C-band positive; no particular chromosome stains with silver nitrate, though when interphase cells are stained with acridine orange the nucleolus is surrounded by brightly fluorescing chromatin. Apparently unlike other species, the microchromosomes in the myna do not harbour NORs.     

Recombination in the X chromosome of Drosophila melanogaster females heterozygous for two autosomal translocations

X chromosome recombination was measured in females carrying two 2; 3-translocations. Total X chromosome recombination values varied according to the amount of structural heterozygosity between the two translocations. The results support the hypothesis that the observed effects of autosomal translocation homozygosity on recombination in the X chromosome are due to homozygosity for position effects of the translocation breakpoints and are not due to chromosome discontinuity.     

On the occurrence of two new species of Trichophyton in Indian soils

Summary Two new species ofTrichophyton, T. indicum andT. evolceanui, isolated from soil in India by the hair baiting technique, are described.T. indicum is characterized by its flat colony and delicately roughened microconidia. It is common and widely distributed in soil in India. T. evolceanui can be distinguished fromT. indicum by its heaped and folded colony on tomato juice agar and its echinulate and obovate microconidia which are consistently wider than those ofT. indicum on the various culture media tested.T. evolceanui also differs fromT. indicum in producing perforating organs on hair in vitro soil culture. It has restricted occurrence in Indian soils.     

A comparison of the reproductive parameters of females of two reptile tick species

In comparisons of females of two reptile tick species Aponomma hydrosauri and Amblyomma limbatum, Ap. hydrosauri was initially larger, and after mating on the host engorged faster and remained attached for a shorter time before completing engorgement and detaching. Amb. limbatum had a longer period of engorgement, and achieved a greater engorged weight. Engorged Amb. limbatum females laid significantly more eggs than equivalent sized Ap. hydrosauri. Although the two species are ecologically similar and were collected from the same site for this study, their reproductive differences probably reflect adaptations to different conditions in their largely allopatric ranges.     

Evidence of a neo-sex chromosome in birds

Neo-sex chromosomes often originate from sex chromosome–autosome fusions and constitute an important basis for the study of gene degeneration and expression in a sex chromosomal context. Neo-sex chromosomes are known from many animal and plant lineages, but have not been reported in birds, a group in which genome organization seems particularly stable. Following indications of sex linkage and unexpected sex-biased gene expression in warblers (Sylvioidea; Passeriformes), we have conducted an extensive marker analysis targeting 31 orthologues of loci on zebra finch chromosome 4a in five species, representative of independent branches of Passerida. We identified a region of sex linkage covering approximately the first half (10 Mb) of chromosome 4a, and associated to both Z and W chromosomes, in three Sylvioidea passerine species. Linkage analysis in an extended pedigree of one species additionally confirmed the association between this part of chromosome 4a and the Z chromosome. Markers located between 10 and 21 Mb of chromosome 4a showed no signs of sex linkage, suggesting that only half of the chromosome was involved in this transition. No sex linkage was observed in non-Sylvioidea passerines, indicating that the neo-sex chromosome arose at the base of the Sylvioidea branch of the avian phylogeny, at 47.4–37.6 millions years ago (MYA), substantially later than the ancestral sex chromosomes (150 MYA). We hypothesize that the gene content of chromosome 4a might be relevant in its transition to a sex chromosome, based on the presence of genes (for example, the androgen receptor) that could offer a selective advantage when associated to Z-linked sex determination loci.     

Assessing the reproductive behavior of on- and off-reservation American Indian females: characteristics of two groups in Montana

Only limited fertility and general reproductive health data exist on American Indians. Using data from the 1987 Montana American Indian Health Risk Assessment, we found that the fertility of American Indians in Great Falls and on the Blackfeet Reservation was similar to blacks in the U.S. and relatively high when compared with fertility of whites in the United States. The influence of the direct determinants of fertility (nuptiality, contraceptive use, and lactation) was very different for the populations examined in this study. Great Falls American Indians and the U.S. black population were similar regarding age at first sexual intercourse (very young), breastfeeding (low prevalence and short duration), planning status of pregnancies (high unplanned), and contraceptive use (only moderate use). In contrast, Blackfeet women on the reservation and the U.S. white population married relatively late, had very high contraceptive use, used effective methods of contraception, and had moderately high levels of breastfeeding. However, Blackfeet fertility was much higher than that of whites. Three interrelated reasons are suggested as possible explanations. Blackfeet couples either wanted high fertility, were relatively poor users of family planning methods, or used less effective methods until they had exceeded their desired family size after which time they turned to sterilization. These finds raise numerous questions concerning the social and economic factors that may account for these group similarities and differences. Further studies with much larger data sets are needed to address these issues adequately.     

The ecology of two West Indian species of mud-wasps (Eumenidae: Hymenoptera)

Factors affecting the distribution and numbers of the neotropical mud-wasps Zeta abdominale (Drury) in Jamaica and Z. canaliculatum (Oliv.) in Trinidad are discussed. Rainfall was a limiting factor in both aspects of the ecology of the two species. In Jamaica, Z. abdominale was virtually absent from rainfall zones >2540 mm m.a.p. (mean annual precipitation), whereas in Trinidad, Z. canaliculatum hardly inhabited those localities of > 2250 mm m.a.p. Furthermore, the local populations were progressively smaller and more scattered in wetter areas, because consistent rainfall and overcast conditions may result in reduced nesting activity. However, in a favourable locality, numbers may be temporarily increased after rainfall which boosts food supply (caterpillars).
Developmental mortality, at 57.68% and 57.2896 respectively was remarkably similar in Z. abdominale and Z. canaliculatum . The important predators within the cells were Melittobia sp. ( hawaiiensis complex) (Eulophidae) and Amobia fioridensis Townsend (Miltogramminae). In Zeta abdominale total developmental mortality was positively correlated with log,₀ (no. of cells) at different sites; averaging only 33.3% for small populations, but 77.4% for large ones.
Regulation at low numbers ( Z. abdominale ) was probably achieved by harsh physical factors, causing low fecundity, but great survival in the cells and high emigration rate. Where Z. abdominale was numerous, the physical environment was favourable, but developmental mortality was so high, that it is necessary to postulate the immigration of many nesting females.     

On the sex chromosome trivalent in some Lepidoptera females

In four of the moth species investigated, viz. Witlesia murana, Scoparia arundinata (Pyraloidea), Bactra furfurana and B. lacteana (Tortricoidea) the metaphase plates of the first meiotic division of their oocytes show a trivalent in addition to the normal bivalents. It evidently has its rise in a transverse break in one of the conjugated chromosomes. Two sex chromatin bodies can be seen in the female somatic cells of three of these species, whereas other species with a normal XY bivalent have only one. These two sex chromatin bodies are unequal in size, and their sizes bear approximately the same relation to each other as do those of the two smaller chromosomes of the trivalent. The broken chromosome is evidently the Y chromosome. The sex chromosome designation for the four above-mentioned species is thus XY₁Y₂ for the females and XX for the males. The sex chromosomes of the four species are among the biggest of the respective complements. This supports the view that the big chromosome to be found in several Lepidoptera species is the sex chromosome. It seems that in animals with holokinetic chromosomes an excessive fragmentation is hindered, at least in the case of the sex chromosomes, by its deleterious effect on the balance of sex-determining genes.Dedicated to Doctor Sally Hughes-Schrader on the occasion of her seventy-fifth birthday.     

Triploidy in a sexually dimorphic passerine provides new evidence for the effect of the W chromosome on secondary sexual traits in birds

In birds, there are two main models for the determination of sex: the ‘Z Dosage’ model in which the number, or dose, of Z chromosomes determines sex, and the ‘Dominant W’ model which argues that a specific gene in the W chromosome may influence Z gene expression and determine sex. The best evidence for W determination of sex comes from birds with 2 copies of the Z chromosome paired with a single W (e.g. ZZW) which are nonetheless females. Here, we expand the species where such a mechanism may operate by reporting a case of a triploid Neotropical passerine bird with sexually dimorphic plumage, the São Paulo marsh antwren Formicivora paludicola. Evidence from 17 autosomal unlinked microsatellite loci, and CHD1 sex‐linked locus, indicate that this individual is a 3n ZZW triploid with intermediate plumage pattern. This example expands our knowledge of sex determination mechanisms in birds by demonstrating that both the W and the two Z chromosomes affect the expression of morphological secondary sexual traits in a non‐galliform bird.     

Diffuse migratory connectivity in two species of shrubland birds: evidence from stable isotopes

Connecting seasonal ranges of migratory birds is important for understanding the annual template of stressors that influence their populations. Brewer’s sparrows (Spizella breweri) and sagebrush sparrows (Artemisiospiza nevadensis) share similar sagebrush (Artemisia spp.) habitats for breeding but have different population trends that might be related to winter location. To link breeding and winter ranges, we created isoscapes of deuterium [stable isotope ratio (δ) of deuterium; δ ²H] and nitrogen (δ ¹⁵N) for each species modeled from isotope ratios measured in feathers of 264 Brewer’s and 82 sagebrush sparrows and environmental characteristics at capture locations across their breeding range. We then used feather $\delta^{2} {\text{H}}_{\text{f}}$ and $\delta^{15} {\text{N}}_{\text{f}}$ measured in 1,029 Brewer’s and 527 sagebrush sparrows captured on winter locations in southwestern United States to assign probable breeding ranges. Intraspecies population mixing from across the breeding range was strong for both Brewer’s and sagebrush sparrows on winter ranges. Brewer’s sparrows but not sagebrush sparrows were linked to more northerly breeding locations in the eastern part of their winter range. Winter location was not related to breeding population trends estimated from US Geological Survey Breeding Bird Survey routes for either Brewer’s or sagebrush sparrows. Primary drivers of population dynamics are likely independent for each species; Brewer’s and sagebrush sparrows captured at the same winter location did not share predicted breeding locations or population trends. The diffuse migratory connectivity displayed by Brewer’s and sagebrush sparrows measured at the coarse spatial resolution in our analysis also suggests that local environments rather than broad regional characteristics are primary drivers of annual population trends.