Topic:Evolutionary Biology
Evolutionary biology and horses focus on the study of the evolutionary processes that have shaped the development, adaptation, and diversification of the Equus genus. This field examines the genetic, morphological, and ecological changes that have occurred over millions of years, leading to the modern horse. Researchers explore the transition from small, multi-toed ancestors to the large, single-toed horses of today, analyzing fossil records, genetic data, and environmental factors that influenced these changes. This page compiles peer-reviewed research studies and scholarly articles that investigate the evolutionary history, genetic adaptations, and ecological interactions of horses, providing insights into their development and survival strategies throughout history.
Optimization of the mammalian respiratory system: symmorphosis versus single species adaptation. Taylor and Weibel's principle of symmorphosis hypothesized optimal design of the mammalian respiratory system, with no excess structure relative to its maximal O2 flux, VO2max. Although they found symmorphosis not to be a general principle of design, it might apply to a highly adapted aerobic athlete, e.g. the Thoroughbred racehorse. Using a mathematical model based on empirical data of the equine O2 transport system at normoxic VO2max, the fraction of the total limitation to O2 flux contributed by each of the respiratory transport steps is calculated as either the fractional change (F) in VO2...
[Differentiation of domestic horse and Przewalskis horse using various DNA sequences]. The electrophoretic mobility of seven erythrocyte enzymes and spectra of fragments amplified by RAPD-PCR with primers UBC-85 and UBC-126 were comparatively analyzed in domestic horse and Przewalski's horse. All tested genetic markers were classified into two groups differing in their involvement in differentiation of the two closely related horse species. Markers from different groups differed neither in their type (a polymorphic protein or an amplification product) nor in their biochemical role (for enzymes).
[Are zoo Przewalski horses domesticated horses?]. Analysed were the brain case capacities and brain weights of wild przewalski horses, przewalski horses from zoological gardens and domesticated horses. Domesticated horses have about 14% less brain case capacity and 16% less brain weight than wild przewalski horses. Przewalski horses from zoological gardens also have about 14% less brain capacity than wild przewalski horses. The brain weight of przewalski horses from zoological gardens shows no difference to the brain weight of domesticated horses. If we look at the brain size, przewalski horses from zoological gardens are domesticated horses....
[Population genetic parameters of aboriginal Yakut horses as related to modern breeds of the domestic horse Equus caballus L]. This study was the first to analyze the polymorphic characteristics of a wide range of biochemical markers in aboriginal Yakut horses. A total of 124 alleles, including 48 alleles of seven blood-group loci and 76 alleles of ten loci for enzymes and other proteins, were studied. For these polymorphic systems, a computer analysis of the genetic distances between 85 horse breeds of different origin from all parts of the world was performed. The low level of hereditary variation in the Yakut horses confirmed that this breed is old and has long been an isolated population. Phylogenetic analysis dem...
An aspartic proteinase expressed in the equine placenta. This manuscript describes the cloning of a novel aspartic proteinase expressed in the placenta of the horse (order Perrisodactyla). Evidence for similar genes in the cat (Carnivora) and ruminants (Artiodactyla), indicates that these molecules have been conserved within widely divergent species with distinct types of placentation. Since ePAG is produced by the outer cell layer (trophoblast) of the placenta, it can tentatively be grouped with the pregnancy-associated glycoproteins (PAG) of cattle, sheep, and pig. The high sequence identity that ePAG shares with pepsinogens as well as the PAG, in...
Zoo-FISH with microdissected arm specific paints for HSA2, 5, 6, 16, and 19 refines known homology with pig and horse chromosomes. Microdissected arm specific paints (ASPs) for human (HSA) chromosomes (Chrs) 2, 5, 6, 16, and 19 were used as probes on pig (SSC) and horse (ECA) metaphase chromosomes. Regions homologous to individual human arms were delineated in the two species studied. Of the ten ASPs used, HSA6 and 16 ASPs showed complete synteny conservation of individual arms as single blocks/ arms both in pig and horse. A similar trend was, in general, also observed for HSA19 ASPs. However, contrary to these observations, synteny conservation of individual arms of HSA2 and HSA5 was not observed in pig and horse. The ar...
Novel and dynamic evolution of equine infectious anemia virus genomic quasispecies associated with sequential disease cycles in an experimentally infected pony. We have investigated the genetic evolution of three functionally distinct regions of the equine infectious anemia virus (EIAV) genome (env, rev, and long terminal repeat) during recurring febrile episodes in a pony experimentally infected with a well-characterized reference biological clone designated EIAV(PV). Viral populations present in the plasma of an EIAV(PV)-infected pony during sequential febrile episodes (18, 34, 80, 106, and 337 days postinfection) were amplified from viral RNA, analyzed, and compared to the inoculated strain. The comparison of the viral quasispecies showed that the ...
An introduction to mammalian interspecific hybrids. Haldane's law states that in interspecific hybrids, it is the heterogametic sex that is likely to be absent, rare, or sterile. In mammals, there is increasing evidence to suggest that this may be due to the high mutation rate of male sex-determining genes on the Y chromosome. The mule, humanity's first successful attempt at genetic engineering, provides some support for this concept. Interspecific hybrids may also shed new light on the importance of the maternal transmission of mitochondrial DNA and the phenomenon of genomic imprinting.
Stabilizing Selection and the Comparative Analysis of Adaptation. Comparative studies tend to differ from optimality and functionality studies in how they treat adaptation. While the comparative approach focuses on the origin and change of traits, optimality studies assume that adaptations are maintained at an optimum by stabilizing selection. This paper presents a model of adaptive evolution on a macroevolutionary time scale that includes the maintenance of traits at adaptive optima by stabilizing selection as the dominant evolutionary force. Interspecific variation is treated as variation in the position of adaptive optima. The model illustrates how phylog...
Repeated emergence of epidemic/epizootic Venezuelan equine encephalitis from a single genotype of enzootic subtype ID virus. Venezuelan equine encephalitis (VEE) epidemics and equine epizootics occurred periodically in the Americas from the 1920s until the early 1970s, when the causative viruses, subtypes IAB and IC, were postulated to have become extinct. Recent outbreaks in Columbia and Venezuela have renewed interest in the source of epidemic/epizootic viruses and their mechanism of interepizootic maintenance. We performed phylogenetic analyses of VEE virus isolates spanning the entire temporal and geographic range of strains available, using 857-nucleotide reverse transcription-PCR products including the E3 and ...
Characterization and phylogenetic significance of rhinoceros luteinizing hormone beta (LHbeta) subunit messenger RNA structure, complementary DNA sequence and gene copy number. The luteinizing hormone (LH) beta subunit gene is expressed in the pituitary glands of all mammals, whereas the closely related chorionic gonadotropin (CG) beta subunit genes have been identified only in primates and equids, and are expressed in placenta. In the case of horses, there is a single-copy equine (e) luteinizing hormone/chorionic gonadotropin hormone beta subunit gene (eLH/CGbeta) that (1) is expressed in both pituitary gland and placenta, (2) encodes a characteristic carboxyl terminal peptide (CTP) extension, and (3) transcribes an atypically elongated 5'-untranslated region (UTR) ...
Causes of natal dispersal and emigration and their effects on harem formation in Misaki feral horses. Misaki feral horses were separated into 2 herds and the difference between dispersal from natal group (natal dispersal) and dispersal from natal area (natal emigration) was studied. The causes of dispersal and emigration and their effects on harem formation were studied 1979-1994. The number of horses ranged from 73 (mature males: 8, mature females: 26, young males: 8, young females: 3, colt foals: 6, filly foals: 10 and geldings: 12) in 1979 and 86 (mature males: 14, mature females: 37, young males: 12, young females: 7, colt foals: 5, filly foals: 7 and geldings: 4) in 1994 when the present ...
Characterization of the Lancefield group C streptococcus 16S-23S RNA gene intergenic spacer and its potential for identification and sub-specific typing. The 16S-23S RNA gene intergenic spacers of isolates of Streptococcus equi (n = 5), S. zooepidemicus (n = 5), S. equisimilis (n = 3) and S. dysgalactiae (n = 2) were sequenced and compared. There were distinct regions within the spacer, arranged in the order 1-9 for all S. equi and one S. zooepidemicus isolate and 1,2 and 4-9 for the remaining isolates. Region 4 was identical to the tRNA(ala) gene found in the 16S-23S intergenic spacers of other streptococci. Regions 1, 5, 6 and 7 had distinct variations, each conserved in different isolates. However, amongst the intergenic spacers there were d...
Localization of the U2 linkage group of horses to ECA 3 using chromosome painting. The U2 linkage group of horses includes the genes albumin (ALB), vitamin D binding protein (GC), mitochondrial glutamate oxaloacetate transaminase 2 (GOT2), and haptoglobin (HP) which are found on two human chromosomes, namely, 4 (HSA 4) and 16 (HSA 16). Likewise these genes are also found on two different chromosomes in mice, rats, and cattle. Chromosome painting demonstrated that only horse chromosome 3 (ECA 3) hybridized with whole chromosome paints for both HSA 4 and HSA 16. This indicated that the equine U2 linkage group occurs on ECA 3, spanning the centromere. This technique will be use...
The hemoglobin polymorphism of the Sardinian wild dwarf horse and the oxygen binding properties of the four different horse hemoglobins. A study was made of the Hb phenotype of the Sardinian dwarfhorse (Equus caballus jara), one of the last surviving wild horse species in Europe. Hb haplotypes and their frequencies were found to be similar to those described in the Arabian horse (BI = 0.551, BII = 0.389, A = 0.036, V = 0.015), which suggests possible introduction onto the island from North Africa. The oxygen binding properties of the whole hemolysates and of the four different horse Hbs, separated by ion-exchange chromatography, were considered with regard to the effect of chloride, 2,3-bisphosphoglycerate and lactate. Results ...
The complete mitochondrial DNA (mtDNA) of the donkey and mtDNA comparisons among four closely related mammalian species-pairs. The nucleotide sequence of the complete mitochondrial genome of the donkey, Equus asinus, was determined. The length of the molecule is 16,670 bp. The length, however, is not absolute due to pronounced heteroplasmy caused by variable numbers of two types of repetitive motifs in the control region. The sequence of the repeats is (a) 5'-CACACCCA and (b) 5'-TGCGCGCA, respectively. The order of (a) and (b) can be expressed as {n[2(a)+(b)]+m(a)}. In 32 different clones analyzed the number of n and m ranged from 0 to 9 and 1 to 7. The two rRNA genes, the 13 peptide-coding genes, and the 22 tRNA gene...
[Wild horse or domesticated horse? Horse remains from the neolithic settlement in Pestenacker, Bavaria]. The bone finds from the neolithic settlement in Pestenacker (near Landsberg am Lech) date back to the second half of the 4th millennium BC (Altheim). Like in any other late neolithic horse bones, the question we have to deal with is whether they represent the remains of wild horse or early domestic horse, as we do not know for certain yet the date of the earliest domestic horses' occurrence in Middle Europe. The post pleistocene distribution of the wild horse is described. For a long time people thought that hardly any wild horses existed in post pleistocene Middle Europe any longer, due to th...
Zoo-FISH delineates conserved chromosomal segments in horse and man. Human chromosome specific libraries (CSLs) were individually applied to equine metaphase chromosomes using the fluorescence in situ hybridization (FISH) technique. All CSLs, except Y, showed painting signals on one or several horse chromosomes. In total 43 conserved chromosomal segments were painted. Homoeology could not, however, be detected for some segments of the equine genome. This is most likely related to the very weak signals displayed by some libraries, rather than to the absence of similarity with the human genome. In spite of divergence from the human genome, dated 70-80 million yea...
Antigenic and genetic evolution of equine H3N8 influenza A viruses. Evolution of equine influenza a H3N8 viruses was examined by antigenic and genetic analysis of a collection isolates from around the world. It was noted that antigenic and genetic variants of equine H3N8 viruses cocirculate, and in particular that variants currently circulating in Europe and the USA are distinguishable from one another both in terms of antigenic reactivity and genetic structure of the HA1 portion of the haemagglutinin (HA) molecule. Whilst the divergent evolution of American and European isolates may be due to geographical isolation of the two gene pools, some mixing is believ...
Cloning and analysis of the cDNA for the common alpha-subunit of the donkey pituitary glycoprotein hormones. Reverse transcription-PCR was used to clone the coding region of the donkey (Equus asinus) glycoprotein hormone alpha-subunit transcript from pituitary gland RNA. The donkey alpha-subunit sequence demonstrated considerable identity with the horse (97% at the nucleotide level), confirming the very close evolutionary linkage between these two species. The predicted amino acid sequence revealed that the donkey alpha-subunit has the same unusual C-terminus as the horse alpha-subunit, when compared with all other mammalian alpha-subunits, including a Tyr-His transposition between positions 87 and 9...
The gyrification of mammalian cerebral cortex: quantitative evidence of anisomorphic surface expansion during phylogenetic and ontogenetic development. Describing the shapes of 3D objects has proved to be as problematical in biology as in other areas. In an attempt to tackle this problem, established stereological methods (the Cavalieri principle and vertical sectioning) have been used to estimate a 3D shape-dependent quantity which can detect anisomorphic changes and is related to the degree of cortical convolution or gyrification. This isomophy factor is employed to assess phylogenetic and ontogenetic changes in the mammalian cerebral cortex. Gross anatomical differences between cerebral hemispheres of adult domestic mammals (horses, oxen, ...
Nucleotide sequence of exons 5 to 9 of the p53 tumour-suppressor gene of the horse (Equus caballus). An evolutionary conserved 1.3 kb fragment corresponding to the horse p53 tumour suppressor gene was PCR amplified, cloned and the nucleotide sequence determined. The p53 fragment encoded exons 5 to 9 and the intervening introns. The nucleotide sequence and the predicted aminoacid sequence showed a high level of homology with human and donkey p53 sequences.
Mitochondrial DNA sequences of various species of the genus Equus with special reference to the phylogenetic relationship between Przewalskii’s wild horse and domestic horse. The noncoding region between tRNAPro and the large conserved sequence block is the most variable region in the mammalian mitochondrial DNA D-loop region. This variable region (ca. 270 bp) of four species of Equus, including Mongolian and Japanese native domestic horses as well as Przewalskii's (or Mongolian) wild horse, were sequenced. These data were compared with our recently published Thoroughbred horse mitochondrial DNA sequences. The evolutionary rate of this region among the four species of Equus was estimated to be 2-4 x 10(-8) per site per year. Phylogenetic trees of Equus species demo...
Cloning and analysis of the cDNA encoding the horse and donkey luteinizing hormone beta-subunits. The coding regions of the horse (Equus caballus) and donkey (E. asinus) luteinizing hormone (LH) beta-subunit transcripts were cloned from pituitary gland RNA, in order to investigate their relationships to the corresponding equine chorionic gonadotropin (CG) beta-subunits and to further understand the unusual receptor-binding properties of equine LH and CG. The horse and donkey LH beta-subunit sequences were very similar (97% identity at the nucleotide (nt) level; 93% at the amino acid (aa) level), confirming their very close evolutionary linkage and also indicating that the C-terminal extens...
At least four MHC class I genes are transcribed in the horse: phylogenetic analysis suggests an unusual evolutionary history for the MHC in this species. Nineteen horse MHC class I specificities have been serologically identified previously at a single locus (ELA-A), and two other specificities appear to be coded at other loci. Biochemical studies indicate that there are at least two expressed loci. In order to establish the number of transcribed horse MHC class I genes, we made a cDNA library from a heterozygous animal (ELA-A3/A7), and screened for positive clones using a bovine class I probe. More than 200 class I clones were isolated in this way, and so far seven unique full length sequences have been identified. All of the sequences are pre...