Blastocystis hominis: phylogenetic affinities determined by rRNA sequence comparison

In 1912 Blastocystis hominis was identified as a new species and classified as a yeast (Brumpt 1912). In the early 1920s several groups confirmed its classification as a yeast, specifically a member of the genus Schizosaccharomyces (discussed by Zierdt et al. 1967). Apart from an occasional case report, the classification of B. hominis and its role as a harmless intestinal yeast was not questioned for another 50 years. Then, Zierdt (1967) suggested that it should be classified in the phylum Protozoa, subphylum Sporozoa, and that it should be considered as a potential pathogen. The likely role of B. hominis as a human pathogen has recently become more firmly established (Garcia et al. 1984; Sheehan et al. 1986) and its classification has been changed. Although the classification of B. hominis as a protozoon was assumed widely, classification as a sporozoon was not accepted, and the most recent definitive classification of the Protozoa did not even list B. hominis (Lee et al. 1985). Then, based essentially on a review of the known characteristics of the organism, it was recently reclassified into the subphylum Sarcodina (Zierdt 1988). Clearly, the phylogeny of this emerging human pathogen needs definitive analysis (Mehlhorn 1988).

Evolutionary Relationships of Australian Marsupials as Assessed by Albumin Immunology

Current phylogenetic hypotheses of the relationships of Australian marsupials were tested by microcomplement fixation of albumin. The study involved antisera to albumins of 56 species, and cross- reactions to albumins of 199 species. The most notable and controversial features of the study were as follows. (1) Two major lineages are evident among the Australian marsupials- bandicoots-dasyuroids and diprotodontids; the marsupial mole represents a third lineage. (2) The honey possum Tarsipes is clearly a diprotodontid. (3) Acrobates and Distoechurus are monophyletic, but they are not burramyids; they are closely related to Tarsipes; moreover the Acrobates-Distoechurus-Tarsipes clade may be close to petaurids. (4) The New Guinean species of Antechinus are more closely related to the New Guinean Murexia than to Australian species of Antechinus. (5) The bandicoots fall into two groups-the New Guinean genera and the Australian genera; the bilby, Macrotis lagotis, is not clearly distinct from the bandicoots, and may be monophyletic with the New Guinean genera. (6) The banded hare-wallaby Lagostrophus is clearly the sister-group to all other extant macropodines, and may be monophyletic with potoroines rather than macropodines. (7) The genus Macropus may be paraphyletic. (8) The tree-kangaroos Dendrolagus may be closely related to the rock-wallabies and their allies (Petrogale, Peradorcas and Thylogale). (9) The genus Pseudocheirus (ringtail possums) is paraphyletic and its species are highly divergent at the molecular level. (10) The cuscuses (genus Phalanger) are probably a monophyletic assemblage.

Phylogenetic relationships of the apicomplexan protist Sarcocystis as determined by small subunit ribosomal RNA comparison

Reverse transcription of total cellular RNA was used to obtain the partial nucleotide sequence of the small subunit ribosomal RNA (srRNA) of Sarcocystis gigantea. The sequence was compared with the homologous sequences of 24 other eukaryotes. Phylogenetic analysis of the semiconserved regions by 4 different tree-building methods using bacteria as an outgroup all concur in showing monophyly of Sarcocystis gigantea and Toxoplasma gondii to the exclusion of all other taxa for which homologous sequences are available.

Identification of life cycle stages of the nematode Echinocephalus overstreeti by allozyme electrophoresis

Data presented in this study highlight the potential of allozyme electrophoresis in providing unequivocal genetic evidence for the identification of life cycle stages, particularly where species have complex life cycles. Adults of the nematode Echinocephalus overstreeti parasitize the elasmobranch Heterodontus portusjacksoni. The putative larval form which is morphologically dissimilar is found in two species of marine molluscs, Chlamys bifrons and Pecten albus. Electrophoretic analysis indicated that the adult and larval forms shared alleles at all of the 34 enzyme loci established. Furthermore, there were no fixed allelic differences between larval forms from different mollusc species.

Electrophoretic Identification of a New Species of Antechinus (Marsupialia, Dasyuridae) in Southeastern Australia

Two electrophoretically distinct but morphologically cryptic forms of Antechinus 'stuartii', designated 'northern' and 'southern', occur together at Kioloa on the southern coast of New South Wales. These forms are distinguished by fixed allele differences in three proteins (albumin, glycollate oxidase and mannosephosphate isomerase) and by differences in allele frequencies for transferrin, and are separated by a Nei D of 0.11. The two forms are reproductively isolated in sympatry at Kioloa by asynchrony in the timing of reproduction, and may be considered separate biological species. Northern form populations were identified by screening for albumin and transferrin in seven localities on the central coast of New South Wales north of Kioloa. Southern form populations were identified similarly in 13 localities south of Kioloa and inland along the Great Dividing Range, and at a further locality in southern Victoria. Ovulation occurs at different rates of change of photoperiod in the two species, and may ensure that reproductive isolation is maintained in all potential areas of sympatry. The northern form represents A. stuartii sensu stricto and ranges from Kioloa north into south-eastern Queensland. The southern form is an undescribed species of Antechinus that appears to be widely distributed throughout southern New South Wales and Victoria.

Electrophoretic Resolution of Species Boundaries in Australian Microchiroptera. IV. The Molossidae (Chiroptera)

Allozyme electrophoresis of 35 loci in 156 specimens of Australian bats belonging to the Molossidae was used to help elucidate the species-level taxonomy of the group in Australia. The electrophoretic data support the current species-level taxonomy of Tadarida australis and Chaerephon jobensis. However, for specimens currently allocated to the genus Mormopterus, the electrophoretic data fail to support any previous species-level account. On the electrophoretic data, a minimum of five species of the genus Mormopterus occur in Australia. A single specimen of a sixth species, whose generic affinities are undetermined, was also found.

The structure and evolution of immunoglobulin kappa chain constant region genes in the genus Rattus

We have cloned and sequenced the C-kappa (Ck) genes from seven species and subspecies of rats which have diverged over the past few million years in Australia. Comparisons of these sequences with each other and the Ck genes of the laboratory rat, Rattus norvegicus, indicate noncoding regions have accumulated fewer mutations than adjacent coding sequences, and amino acid replacing nucleotide substitutions in the coding regions have accumulated at a rate at least as great as silent changes. Exactly the opposite of both of these findings is observed when comparisons are made between Ck or other genes from more distantly related species, indicating that these features may be characteristic of Ck short-term evolutionary gene divergence. Changes in the coding regions of these genes result in a non-random distribution of amino acid substitutions on the three-dimensional alpha-carbon backbone of the Ck domain in the most serologically distinct forms of Ck. While phylogenetic relationships inferred from the Ck nucleotide sequences are in general agreement with those derived from other data, considerable differences are seen in rates of accumulation of Ck gene nucleotide substitutions vs rates of accumulation of enzyme polymorphisms.

Duplication of J kappa genes within genus Rattus

We have isolated a region containing the immunoglobulin kappa chain joining segments from a liver DNA library of the Australian rat Rattus villosissimus, and determined its nucleotide sequence. While the laboratory rat (Rattus norvegicus) had previously been shown to contain three recently duplicated copies of J kappa 2, R. villosissimus has only two. Furthermore, all three copies of J kappa 2 in R. norvegicus share an 11 bp deletion in their 5' flanking regions which is not evident in either copy of J kappa 2 in R. villosissimus. This suggests that the initial duplication events occurred separately in the two lineages, and were followed by a second duplication in R. norvegicus, all three duplications having occurred within the last 6-12 million years (although more complicated schemes involving gene conversion events cannot be excluded). These results indicate that there is a high degree of plasticity in this region of the genome, and that selective forces must exist which have maintained the number of expressible J kappa segments in humans (5) and rodents (4-6) within their narrow range.

Electrophoretic Resolution of Species Boundaries in Australian Microchiroptera. I. Eptesicus (Chiroptera: Vespertilionidae)

The technique of allozyme electrophoresis is used in the present study to define species boundaries in Australian Eptesicus. Until 1976, only one species of Eptesicus (E. pumilus) was recognized in Australia. More recently, a further four species have been recognised (E. vulturnus, E. regulus, E. sagittula and E. douglasl). Results obtained from an allozyme electrophoretic analysis of 35 loci in 182 individuals show that there are a minimum of nine species of Eptesicus in Australia. Moreover, in some geographic areas, up to four species occur sympatrically. These results highlight the applicability and significance of allozyme electrophoresis for the dissection of species complexes.

Electrophoretic Resolution of Species Boundaries in Australian Microchiroptera. II. The Pipistrellus Group (Chiroptera: Vespertilionidae)

Forty-four specimens of the Pipistrellus complex from Australia were analysed for 36 allozyme loci. The data show that four species were represented in the material, two of which are sympatric in the north, and two of which are allopatric in the south. The data are consistent with separate generic status for the two southern species.

Morphological and biochemical correlates in the characterization of Sarcocystis spp

Isoenzyme electrophoretic techniques were applied to the characterization of seven Sarcocystis spp. that had been identified by conventional morphological studies. Cystozoites were harvested from macroscopic cysts from sheep, cattle, and mice and from microscopic cysts from sheep, cattle, and goats. Soluble cystozoite extracts were subjected to cellulose acetate gel electrophoresis and characterized at 15 of the 39 enzyme loci examined. Genetic relationships among isolates were examined by simple phenetic clustering. Two different morphological types of macroscopic cysts from sheep, identified as S. gigantea (syn. S. ovifelis) and S. medusiformis, consistently differed at 40% of the loci examined. Such genetic divergence confirms their separate morphotypic classification. Both differed from microscopic cyst isolates from sheep at 87% of the loci examined; however, two different morphotypes of microscopic cysts were found in the sheep sampled (thick-walled and thin-walled cysts). Until sufficient numbers of each type can be isolated and examined separately, both were regarded as belonging to the species S. tenella (syn. S. ovicanis). Macroscopic and microscopic cysts from cattle consistently differed at 80% of the loci thereby supporting their separate classification as S. hirsuta (syn. S. bovifelis) and S. cruzi (syn. S. bovicanis), respectively. Isolates from goats (microscopic cysts identified as S. capracanis) differed from S. tenella and S. cruzi at 20% and 47% of the loci, respectively. All macroscopic cyst isolates from the various host animal species (including S. muris from mice) differed from each other at nearly all loci. Isoenzyme electrophoretic techniques therefore provided genetic evidence supporting the classification of these various Sarcocystis spp. by their morphological characteristics.

Biochemical differentiation in bile duct cestodes and their marsupial hosts

Isozyme electrophoresis was used to assess possible cospeciation of parasites (cestodes of the Progamotaenia festiva complex) and their hosts (Australian diprotodont marsupials) and to compare the extent of interspecific genetic diversity of the parasites and their hosts. On the basis of morphology, there are three species in the complex, although electrophoresis revealed 14 distinct genetic types, most of which were host specific, although there were three cases of apparent host switching. The evolutionary relationships among the parasites were only partially concordant with those among the hosts. Moreover, the extent of electrophoretic diversity among the parasites was much higher than that among hosts.

Kappa-chain constant-region gene sequences in genus Rattus: coding regions are diverging more rapidly than noncoding regions

We have determined the nucleotide sequence of a 1,200-base pair (bp) genomic fragment that includes the kappa-chain constant-region gene (C kappa) from two species of native Australian rodents, Rattus leucopus cooktownensis and Rattus colletti. Comparison of these sequences with each other and with other rodent C kappa genes shows three surprising features. First, the coding regions are diverging at a rate severalfold higher than that of the nearby noncoding regions. Second, replacement changes within the coding region are accumulating at a rate at least as great as that of silent changes. Third, most of the amino acid replacements are localized in one region of the C kappa domain--namely, the carboxy-terminal "bends" in the alpha-carbon backbone. These three features have previously been described from comparisons of the two allelic forms of C kappa genes in R. norvegicus. These data imply the existence of considerable evolutionary constraints on the noncoding regions (based on as yet undetermined functions) or powerful positive selection to diversify a portion of the constant-region domain (whose physiological significance is not known). These surprising features of C kappa evolution appear to be characteristic only of closely related C kappa genes, since comparison of rodent with human sequences shows the expected greater conservation of coding regions, as well as a predominance of silent nucleotide substitutions within the coding regions.

Enzyme markers in inbred rat strains: genetics of new markers and strain profiles

Twenty-six inbred strains of the laboratory rat (Rattus norvegicus) were examined for electrophoretic variation at an estimated 97 genetic loci. In addition to previously documented markers, variation was observed for the enzymes aconitase, aldehyde dehydrogenase, and alkaline phosphatase. The genetic basis of these markers (Acon-1, Ahd-2, and Akp-1) was confirmed. Linkage analysis between 35 pairwise comparisons revealed that the markers Fh-1 and Pep-3 are linked. The strain profiles of the 25 inbred strains at 11 electrophoretic markers are given.

Biochemical Systematics of the Australian Cockatoos (Psittaciformes: Cacatuinae)

The genetic and evolutionary relationships of the Australian cockatoos (excluding Probosciger) and of the cockatiel, Nymphicus hollandicus, were examined by the technique of isozyme electrophoresis. A cladistic analysis of data from 28 loci showed that Nymphicus is more closely related to cockatoos than to any ofthe non-cockatoos; accordingly Nymphicus should be included within the Cacatuinae, but in a monotypic tribe. The other genera form two well defined groupings. One comprises all of the white cockatoos (Cacatua) and the gang gang Callocephalon fimbriatum, and the other, the black cockatoos (Calyptorhynchus). Within the white cacatuine cockatoos there seem to be at least two minor groups. One, clearly indicated by the electrophoretic data, comprises the galah Cacatua roseicapilla and Australo-Papuan corellas, all of which have short plain crests and usually coloured periophthalmic skin. The other, neither denied nor confirmed biochemically, is a looser assemblage characterized by coloured up-curving crests and plain periophthalmic skin; it included the sulphur-crested cockatoo Cacatua galerita and the pink cockatoo Cacatua leadbeateri, and their allospecies on islands north of Australia. Isozyme electrophoresis of the loci examined in this study could not differentiate members of the Calyptorhynchus funereus superspecies, nor of the Cacatua tenuirostris-pastinator group of corellas. The results are therefore in accord with other studies that show that isozyme electrophoresis has limited application in elucidating species boundaries in birds.

Electrophoretic Resolution of Species Boundaries in the Sminthopsis murina Complex (Dasyuridae)

Isozyme electrophoresis of 30 loci was used to characterize 52 individuals in 20 populations of the Sminthopsis murina complex. The populations fell into six groups within which there was genetic uniformity but among which there were extensive differences. These groups correspond to the species S. murina, S. ooldea, S. leucopus, S. dolichura, S. gilberti and S. caniventer.

GENETIC DIFFERENTIATION AMONG KARYOTYPIC FORMS OF THE BLACK RAT, RATTUS RATTUS

The black rat, Rattus rattus, consists of five karyotypic forms—2n = 42 (high C-banding); 2n = 42 (low C-banding); 2n = 40; 2n = 38; 2n = 42 Mauritius. Here, we use isozyme electrophoresis and microcomplement fixation to elucidate the genetic distance and phylogenetic relationship among each of the various karyotypic forms of R. rattus and R. norvegicus. The results show that (1) the 2n = 42 Mauritius black rat (2n = 42Mau) is genetically very similar to the 2n = 38 form, suggesting that this island population has undergone very rapid chromosomal evolution; (2) the 2n = 40 form from the highlands of Sri Lanka is genetically distinct from the 2n = 38 form from the lowlands; the genetic difference is probably insufficient, however, to prevent future introgression; (3) the level of genetic differentiation occurring between the 2n = 42 forms on the one hand and the 2n = 38, 2n = 40 and 2n = 42 Mau forms on the other support the hybrid incompatability data in suggesting that the two groups are either full species or incipient species; (4) in contrast to data from amino acid composition of transferrin and from restriction endonuclease digests of mtDNA, the present data suggest that the various karyotypic forms of R. rattus are phylogenetically more closely related to each other than any is to R. norvegicus, and that they are related by a series 2n = 42 → 2n = 40 → 2n = 38; (5) the R. rattus/R. norvegicus divergence occurred 2-8 million years ago, whereas the various chromosomal forms of R. rattus diverged over the last 4 million years.

An Electroporetic and Chromosomal Study of the Dasyurid Marsupial Genus Ningaui Archer

Isozyme electrophoresis of 28 loci was used to characterize 30 specimens of Ningaui from four States of Australia. The specimens fall into three genetic groups, with large differences between groups (21-32% fixed differences) and genetic homogeneity within groups. One group, from the Pilbara of Western Australia, is referable to N. timealeyi; a second group, extending from the Kalgoorlie area of Western Australia to the far west of South Australia and north to the Tanami Desert of the Northern Temtory, is referable to N. ridei; and a third group extends from the Kalgoorlie area of Western Australia (where it is sympatric with N. ridei) across southern South Australia and into north-westem Victoria. Because the third group maintains its genetic uniqueness despite being sympatric with N. ridei, it clearly represents a different species, N. yvonnae Kitchener, Stoddart & Henry. This species is distinguishable from N. ridei on skull characters, but indistinguishable on external characters. In contrast to most dasyurids, ningauis display considerable karyotypic diversity involving a pericentric inversion, a reciprocal translocation and addition of constitutive heterochromatin to the X-chromosome.