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H Ellegren

Publications and source records attributed to H Ellegren.

At least 37 records · Page 2Linked to original sources
PubMed2001

Evaluation of d2, a microsatellite measure of inbreeding and outbreeding, in wolves with a known pedigree.

We have evaluated a microsatellite measure proposed as an indicator of inbreeding and outbreeding using a captive wolf population with known inbreeding levels and founder sources. The measure, which is based on the difference in the repeat number for microsatellite alleles within an individual, was not more predictive of the known inbreeding coefficient than microsatellite heterozygosity (it was actually less predictive). We also found no support that the measure was predictive of the level of outbreeding. However, we could not determine if the measure was predictive of very low levels of inbreeding due to matings between remote relatives. Overall, it appears that the usefulness of this measure to identify individuals on the inbred-outbred continuum beyond that of heterozygosity and identify biologically important associations with fitness-related traits may be limited. We suggest that the measure be examined theoretically to determine when (and how much) the predictive value of the measure is different from that of heterozygosity for inbreeding or outbreeding levels in a variety of different scenarios.

Analysis of Variance↗
PubMed2000

Male-biased mutation rates revealed from Z and W chromosome-linked ATP synthase alpha-subunit (ATP5A1) sequences in birds.

Whether the mutation rate differs between sexes has been a matter of discussion for years. Molecular analyses of mammals have indicated that males mutate more often than females, as manifested by the faster rate of neutral sequence evolution on the Y chromosome than on the X chromosome. However, these observations can as well be interpreted as specific reduction of the X chromosome mutation rate, which would be adaptive because of reducing the number of slightly deleterious recessive mutations exposed in hemizygote males. Recently, data from birds have suggested that vertebrate mutation rates may indeed be male-biased. In birds, females are the heterogametic sex (ZW), and analyses of the Z-linked CHD1Z gene have shown that it evolves faster than its W-linked and thus female-specific homologue, CHD1W. We have now studied the second avian gene known to exist in a copy on the nonrecombining regions of both the Z and the W chromosome, viz., the ATP synthase alpha-subunit (ATP5A1). In independent comparisons of three pairs of bird species from divergent lineages, intron sequences of the Z-linked copy (ATP5A1Z) were consistently found to evolve faster than the W-linked copy (ATP5A1W). From these data we calculated male-to-female mutation rate ratios (alpha) of 1.8, 2.3, and 5.0 in Galliform, Anseriform, and Ciconiiform lineages, respectively. Therefore, this study provides independent support for a male-biased mutation rate in birds.

Animals↗
PubMed2000

Microsatellite mutations in the germline: implications for evolutionary inference.

Microsatellite DNA sequences mutate at rates several orders of magnitude higher than that of the bulk of DNA. Such high rates mean that spontaneous mutations that form new-length variants can realistically be seen in pedigree analysis. Data on observed mutation events from various organisms are now accumulating, allowing inferences on DNA sequence evolution to be made through an unusually direct approach. Here I discuss and integrate microsatellite mutation data in an evolutionary context. A striking feature of the mutation process is that it seems highly heterogeneous, with distinct differences between species, repeat types, loci and alleles. Age and sex also affect the mutation rate. Within genomes at equilibrium, the microsatellite-length distribution is a delicate balance between biased mutation processes and point mutations acting towards the decay of repetitive DNA. Indeed, simple repeats do not evolve simply.

Evolution, Molecular↗
PubMed2000

Evolution of the avian sex chromosomes and their role in sex determination.

Is it the female-specific W chromosome of birds that causes the avian embryo to develop a female phenotype, analogous to the dominance mode of genic sex differentiation seen in mammals? Or is it the number of Z chromosomes that triggers male development, similar to the balance mode of differentiation seen in Drosophila and Caenorhabditis elegans? Although definite answers to these questions cannot be given yet, some recent data have provided support for the latter hypothesis. Moreover, despite the potentially common features of sex determination in mammals and birds, comparative mapping shows that the avian sex chromosomes have a different autosomal origin than the mammalian X and Y chromosomes.

Journal Article↗
PubMed2000

Heterogeneous mutation processes in human microsatellite DNA sequences.

Although microsatellite polymorphisms are one of the most commonly used tools in genetic analyses, it remains to be understood how microsatellite DNA has evolved as a ubiquitous and highly abundant class of repetitive sequences in eukaryotic genomes. On the basis of analyses of spontaneous human microsatellite mutations of germline origin, I show here that different mutation biases underlie the evolution of microsatellite repeats. The within-locus mutation rate increases with allele length, but is not affected by the size difference between an individual's two alleles (allele span). Within loci, long alleles tend to mutate to shorter lengths, thereby acting to prevent infinite growth. Expansions are more common than contractions among dinucleotide repeats, whereas no such trend is evident among tetranucleotide repeats. This observation is consistent with the longer repeat lengths and higher frequency of di- compared with tetranucleotide repeats. An excess of paternally transmitted mutations (male-to-female ratio of 4.9) supports a male-biased mutation rate in the human genome.

Alleles↗
PubMed2000

Sex ratio and fledging success of supplementary-fed Tengmalm's owl broods.

A nest box population of Tengmalm's owls (Aegolius funereus) in northern Sweden was studied to investigate the effects of extra food on the sex ratio between hatching and fledging in this sexually size-dimorphic species. The brood size and brood sex ratio of supplementary-fed and control broods were compared. Newly hatched nestlings were blood sampled and sexed by polymerase chain reaction (PCR) amplification of the sex-linked CHD1Z and CHD1W genes. The brood sex ratio at hatching was strongly male biased (65%); this was also the case in broods where all eggs hatched (72%). There was no relationship between hatch order and sex ratio, and hatching sex ratio did not vary significantly with laying date. Brood size decreased between hatching and fledging, but did not differ between fed and control broods at either stage. Brood sex ratio did not differ between hatching and fledging, and fledging sex ratio did not differ between fed and control broods. It was concluded that, at least during the year in which the study was carried out, feeding had no effect on brood reduction, and that male and female nestlings did not show any differential mortality. The mechanisms behind the male-biased sex ratio at hatching, and any possible adaptive reasons for it, are not known.

Animal Feed↗
PubMed2000

Molecular evolution of the avian CHD1 genes on the Z and W sex chromosomes.

Genes shared between the nonrecombining parts of the two types of sex chromosomes offer a potential means to study the molecular evolution of the same gene exposed to different genomic environments. We have analyzed the molecular evolution of the coding sequence of the first pair of genes found to be shared by the avian Z (present in both sexes) and W (female-specific) sex chromosomes, CHD1Z and CHD1W. We show here that these two genes evolve independently but are highly conserved at nucleotide as well as amino acid levels, thus not indicating a female-specific role of the CHD1W gene. From comparisons of sequence data from three avian lineages, the frequency of nonsynonymous substitutions (K(a)) was found to be higher for CHD1W (1.55 per 100 sites) than for CHD1Z (0.81), while the opposite was found for synonymous substitutions (K(s), 13.5 vs. 22.7). We argue that the lower effective population size and the absence of recombination on the W chromosome will generally imply that nonsynonymous substitutions accumulate faster on this chromosome than on the Z chromosome. The same should be true for the Y chromosome relative to the X chromosome in XY systems. Our data are compatible with a male-biased mutation rate, manifested by the faster rate of neutral evolution (synonymous substitutions) on the Z chromosome than on the female-specific W chromosome.

Amino Acid Sequence↗
PubMed1999

Microsatellite evolution: polarity of substitutions within repeats and neutrality of flanking sequences.

Though extensively used in a variety of disciplines, the evolutionary pattern of microsatellite sequences is still unclear. We addressed several questions relating to microsatellite evolution by analysing historically accumulated mutation events in a large set of artiodactyl (CA)n repeats, through sequence analysis of orthologous bovine and ovine loci. The substitution rate in microsatellite flanking sequences was not different from that in intron sequences, suggesting that if intron sequences in general are selectively neutral, sequences close to microsatellites are similarly so. This observation thus does not support the idea that successful heterologous amplification of microsatellites across distantly related taxa would be due to flanking sequences generally being under some form of selection. Interestingly, the substitution rate at the first nucleotide positions flanking repeats was significantly higher than in sequences further away. Moreover, the substitution rate in repeat units in the very end of microsatellites was significantly higher than that in the middle of repeat regions. Together these observations suggest a relative instability close to the boundary between repetitive and unique sequences. We present three models that potentially could explain such a feature, all involving inefficiency of mismatch repair systems.

Animals↗
PubMed1999

Sexual selection resulting from extrapair paternity in collared flycatchers.

Extrapair paternity has been suggested to represent a potentially important source of sexual selection on male secondary sexual characters, particularly in birds with predominantly socially monogamous mating systems. However, relatively few studies have demonstrated sexual selection within single species by this mechanism, and there have been few attempts to assess the importance of extrapair paternity in relation to other mechanisms of sexual selection. We report estimates of sexual selection gradients on male secondary sexual plumage characters resulting from extrapair paternity in the collared flycatcher Ficedula albicollis, and compare the importance of this form of sexual selection with that resulting from variation in mate fecundity. Microsatellite genotyping revealed that 15% of nestlings, distributed nonrandomly among 33% of broods (N=79), were the result of extrapair copulations. Multivariate selection analyses revealed significant positive directional sexual selection on two uncorrelated secondary sexual characters in males (forehead and wing patch size) when fledgling number was used as the measure of fitness. When number of offspring recruiting to the breeding population was used as the measure of male fitness, selection on these traits appeared to be directional and stabilizing, respectively. Pairwise comparisons of cuckolded and cuckolding males revealed that males that sired young through extrapair copulations had wider forehead patches, and were paired to females that bred earlier, than the males that they cuckolded. Path analysis was used to partition selection on these traits into pathways via mate fecundity and sperm competition, and suggested that the sperm competition pathway accounted for between 64 and 90% of the total sexual selection via the two paths. The selection revealed in these analyses is relatively weak in comparison with many other measures of selection in natural populations. We offer some explanations for the relatively weak selection detected. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Report of the International Equine Gene Mapping Workshop: male linkage map.

The goal of the First International Equine Gene Mapping Workshop, held in 1995, was the construction of a low density, male linkage map for the horse. For this purpose, the International Horse Reference Family Panel (IHRFP) was established, consisting of 12 paternal half-sib families with 448 half-sib offspring provided by 10 laboratories. Blood samples were collected and DNA extracted in each laboratory and sent to the Lexington laboratory (KY, USA) for dispatch in aliquots to 14 typing laboratories. In total, 161 markers (144 microsatellites, seven blood groups and 10 proteins) were tested for all families for which the sire was heterozygous. Genealogies and typing data were sent for analysis to the INRA laboratory (Jouy-en-Josas, France) according to a specific format and entered into a database with input verification and output processes. Linkage analysis was performed with the CRIMAP program. Significant linkage was detected for 124 loci, of which 95 were unambiguously ordered using a multipoint analysis with an average spacing of 14.2 CM. These loci were distributed among 29 linkage groups. A more comprehensive analysis including synteny group data and FISH data suggested that 26 autosomes out of 31 are covered. The complete map spans 936 CM.

Animals↗
PubMed1999

Mitochondrial DNA phylogeography and population history of the grey wolf canis lupus

The grey wolf (Canis lupus) and coyote (C. latrans) are highly mobile carnivores that disperse over great distances in search of territories and mates. Previous genetic studies have shown little geographical structure in either species. However, population genetic structure is also influenced by past isolation events and population fluctuations during glacial periods. In this study, control region sequence data from a worldwide sample of grey wolves and a more limited sample of coyotes were analysed. The results suggest that fluctuating population sizes during the late Pleistocene have left a genetic signature on levels of variation in both species. Genealogical measures of nucleotide diversity suggest that historical population sizes were much larger in both species and grey wolves were more numerous than coyotes. Currently, about 300 000 wolves and 7 million coyotes exist. In grey wolves, genetic diversity is greater than that predicted from census population size, reflecting recent historical population declines. By contrast, nucleotide diversity in coyotes is smaller than that predicted by census population size, reflecting a recent population expansion following the extirpation of wolves from much of North America. Both species show little partitioning of haplotypes on continental or regional scales. However, a statistical parsimony analysis indicates local genetic structure that suggests recent restricted gene flow.

Journal Article↗
PubMed1999

Inbreeding and relatedness in Scandinavian grey wolves Canis lupus.

Management of small and threatened populations may require detailed knowledge about the genetic status of individuals and the genetic relatedness between individuals. I show here that individual heterozygosity at a set of 29 microsatellite loci correlates closely to the degree of inbreeding in a captive grey wolf population. Microsatellite allele sharing similarly correlates closely to known relatedness between pairs of individuals. Genotyping the same markers in a small (60-70 individuals) natural population of grey wolves in Sweden, low individual heterozygosities and high values of allele sharing between some animals were found. Since inbreeding depression has been documented in a captive grey wolf population of Scandinavian origin, the results point out an additional risk for the small Swedish wild population.

Alleles↗
PubMed1998

Evolution of the avian sex chromosomes from an ancestral pair of autosomes.

Among the mechanisms whereby sex is determined in animals, chromosomal sex determination is found in a wide variety of distant taxa. The widespread but not ubiquitous occurrence, not even within lineages, of chromosomal sex determination suggests that sex chromosomes have evolved independently several times during animal radiation, but firm evidence for this is lacking. The most favored model for this process is gradual differentiation of ancestral pairs of autosomes. As known for mammals, sex chromosomes may have a very ancient origin, and it has even been speculated that the sex chromosomes of mammals and birds would share a common chromosomal ancestry. In this study we showed that the two genes, ATP5A1 and CHD1, so far assigned to the female-specific W chromosome of birds both exist in a very closely related copy on the Z chromosome but are not pseudoautosomal. This indicates a common ancestry of the two sex chromosomes, consistent with the evolution from a pair of autosomes. Comparative mapping demonstrates, however, that ATP5A1 and CHD1 are not sex-linked among eutherian mammals; this is also not the case for the majority of other genes so far assigned to the avian Z chromosome. Our results suggest that the evolution of sex chromosomes has occurred independently in mammals and birds.

Animals↗
PubMed1998

Identification of a mutation in the low density lipoprotein receptor gene associated with recessive familial hypercholesterolemia in swine.

Elevated blood plasma cholesterol (hypercholesterolemia) is a major risk factor for coronary artery disease (CAD) in humans. Genetic dissection of polygenic lipid and lipoprotein disorders in swine, a key animal model for the study of familial hypercholesterolemia (FH) and CAD, led to the isolation of a monogenic subphenotype (FH-r), that is inherited in the recessive (r) manner. A genome scan mapped the FH-r locus close to the centromere of chromosome 2. Comparative mapping showed that this region shares homology with a part of human chromosome 19 that harbors the low density lipoprotein receptor (LDLR) locus, and therefore suggested LDLR as the prime candidate gene for FH-r. Cloning and sequencing of hepatic LDLR cDNA from two FH-r/r and one normal (N/N) animals disclosed a single missense mutation (R84C) in a region that corresponds to human exon 4. The C84 mutation cosegregates invariantly with hypercholesterolemia, which strongly suggests that this mutation is responsible for the observed hyperlipidemia.

Amino Acid Sequence↗
PubMed1998

Experimentally reduced paternity affects paternal effort and reproductive success in pied flycatchers

The question of whether, and how, male birds should change their parental effort in response to reduced paternity is a controversial issue among behavioural ecologists. We report a study on pied flycatchers, Ficedula hypoleuca, in which paternity was manipulated through experimentally induced mate switching during the female's fertile period. The paternity of care-giving males ranged from 0 to 100% of the brood. The number of parental males per nest varied between zero and two, and the amount of male assistance in nestling provisioning had a marked effect on female reproductive success. For 17 monogamous males, provisioning effort and the body mass of nestlings on day 12 were reduced at low levels of paternity. However, the shape of the effort function was not unambiguously determined. Male provisioning effort showed a curvilinear decline, whereas nestling body mass showed a linear decline. Two important assumptions of the theory of optimal parental effort seem to be fulfilled in this case: that males had reliable cues to their paternity, and that paternity is likely to be increased in future (normal) breeding attempts. The fact that males reduced their effort at the expense of the welfare of the offspring suggests that there are significant costs of parental care in this species. Whether a similar response to cuckoldry occurs in unmanipulated breeding situations remains to be studied.Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

Sex biases in the mutation rate.

Men have more germ-line cell divisions than women. Does this lead to a higher mutation rate in males? Most estimates of the proportion of mutations originating in men come either from direct observation of disease-inducing mutations or from analysis of the relative rate of evolution of sex-linked and autosomal genes in primates. The latter mode of analysis has also been applied to other mammals, birds and files. For unknown reasons, this method produces contradictory results. A majority of estimates using the best direct methods in humans indicate a male bias for point mutations, but the variance in estimates is high. It is unclear how the evolutionary and direct data correspond and a consensus as to the extent of any male bias is not presently possible. While the number of germ-line cell divisions might contribute to differences, this by no means accounts for all of the data.

Aging↗