morphologically indistinguishable groups of animals living in the same biotope are sexually isolated, i.e. represent "true" species (sibling species), or whether gene flow exists between given
species (hybrid species). Enzyme electrophoresis
allows the process of species formation (speciation) to be followed directly. The initial expectation that molecular analysis of relationships
would bring a breakthrough in systematics and,
for example, the phylogenetic relationships
between the animal phyla would be clearly
defined, has not proved to be the case. Nevertheless, compared with morphological characters,
proteins and nucleic acids possess certain advantages for the analysis of relationships and the
reconstruction of phylogeny (p.11l). Furthermore, the comparison of molecular characters has
provided insights into the early phases of evolution; these are amongst the most fantastic results
of molecular biology but can only be listed, and
not dealt with in depth in a book on the comparative biochemistry of animals. They are as follows:
1. The mitochondria and plastids of the eukaryotes have their origins in symbiotic prokaryotes.
2. In addition to the two classical organism kingdoms of the (Eu-)bacteria and the Eukaryotes, there is at least one more kingdom, that of
the Archaebacteria.
3. The unicellular organisms possess a heterogeneity that had been unimaginable before the
era of molecular biology and which cannot be
described by the traditional concepts of fungus, plant or animal.
In the following, a few examples will serve to
illustrate the different possibilities for the molecular analysis of evolutionary relationships.
4.7.1 Molecular Phylogenetic Trees
Amino acid sequences have been more-or-less
systematically collected since the 1960s and used
for the construction of phylogenetic trees; particularly extensive comparative material is available for the globins, cytochrome c, a-crystallin,
immunoglobulins, pancreas RNases and fibrinopeptides. The knowledge of phylogenetic development gained in this way will be presented in
each case by the individual proteins. Phylogenetic
considerations must, of course, be restricted to
the evolution within single protein super-families;
how these came into being in the early phases of
life on earth is at present beyond our knowledge.
4.7.2 Species Systematics
165
The analysis of DNA sequences, which began in
the 1980s and has constantly increased in intensity, has already made available, in terms of the
total length of analysed sequences, more extensive material than protein sequencing did; however, comparative data on homologous sequences
from a large number of species is required for the
analysis of relationships and, as yet, is only available for the globin genes as well as for the rRNAs
and the tRNAs and their genes.
4.7.2 Species Systematics
For species diagnosis, i.e. the assignment of
single individuals to a certain species or a taxon
below the species level, biochemical characters
can be applied just as well as morphological or
other characters. Here also, macromolecular
materials appear particularly suitable because of
their high information content, but low molecular
weight substances are also used, although more
frequently in botanical than in zoological systematics. The substance used need not necessarily
be identified chemically, e.g. unidentified spots
on a chromatogram can also have taxonomic
value so long as they are only "diagnostic", i.e.
exclusively present in the members of a particular
species and preferably also in all individuals.
Because, in general, the analysis of biochemical
characters requires a greater technical effort, they
are usually only taken into account for species
diagnosis when suitable morphological features
are unavailable. This applies in particular to animal groups, like amoebae, trypanosomes, sporozoans or nematodes, that are relatively poor in
characters, to eggs and early developmental
stages, and, finally, to isolated tissues whose origin is of interest, for example, in the fields of
foodstuffs or crime. Numerous such examples are
presented in the book by Ferguson [115], and
recent investigations have been carried out, for
example, on the protozoans and the muscle tissue
of fish [27, 432].
Even in animals that are rich in characters, species may be so similar to each other that they are
indistinguishable using morphological features
alone (sibling species). In such cases, the method
of enzyme electrophoresis has been used with
particular success, e.g. to subdivide several
groups of sibling species of Drosophila [25, 90],
and for the separation of the brachyuran Uca speciosa and U. spinicarpa [359], the nematodes Caenorhabditis elegans and C. briggsae [51], the sea
species (hybrid species). Enzyme electrophoresis
allows the process of species formation (speciation) to be followed directly. The initial expectation that molecular analysis of relationships
would bring a breakthrough in systematics and,
for example, the phylogenetic relationships
between the animal phyla would be clearly
defined, has not proved to be the case. Nevertheless, compared with morphological characters,
proteins and nucleic acids possess certain advantages for the analysis of relationships and the
reconstruction of phylogeny (p.11l). Furthermore, the comparison of molecular characters has
provided insights into the early phases of evolution; these are amongst the most fantastic results
of molecular biology but can only be listed, and
not dealt with in depth in a book on the comparative biochemistry of animals. They are as follows:
1. The mitochondria and plastids of the eukaryotes have their origins in symbiotic prokaryotes.
2. In addition to the two classical organism kingdoms of the (Eu-)bacteria and the Eukaryotes, there is at least one more kingdom, that of
the Archaebacteria.
3. The unicellular organisms possess a heterogeneity that had been unimaginable before the
era of molecular biology and which cannot be
described by the traditional concepts of fungus, plant or animal.
In the following, a few examples will serve to
illustrate the different possibilities for the molecular analysis of evolutionary relationships.
4.7.1 Molecular Phylogenetic Trees
Amino acid sequences have been more-or-less
systematically collected since the 1960s and used
for the construction of phylogenetic trees; particularly extensive comparative material is available for the globins, cytochrome c, a-crystallin,
immunoglobulins, pancreas RNases and fibrinopeptides. The knowledge of phylogenetic development gained in this way will be presented in
each case by the individual proteins. Phylogenetic
considerations must, of course, be restricted to
the evolution within single protein super-families;
how these came into being in the early phases of
life on earth is at present beyond our knowledge.
4.7.2 Species Systematics
165
The analysis of DNA sequences, which began in
the 1980s and has constantly increased in intensity, has already made available, in terms of the
total length of analysed sequences, more extensive material than protein sequencing did; however, comparative data on homologous sequences
from a large number of species is required for the
analysis of relationships and, as yet, is only available for the globin genes as well as for the rRNAs
and the tRNAs and their genes.
4.7.2 Species Systematics
For species diagnosis, i.e. the assignment of
single individuals to a certain species or a taxon
below the species level, biochemical characters
can be applied just as well as morphological or
other characters. Here also, macromolecular
materials appear particularly suitable because of
their high information content, but low molecular
weight substances are also used, although more
frequently in botanical than in zoological systematics. The substance used need not necessarily
be identified chemically, e.g. unidentified spots
on a chromatogram can also have taxonomic
value so long as they are only "diagnostic", i.e.
exclusively present in the members of a particular
species and preferably also in all individuals.
Because, in general, the analysis of biochemical
characters requires a greater technical effort, they
are usually only taken into account for species
diagnosis when suitable morphological features
are unavailable. This applies in particular to animal groups, like amoebae, trypanosomes, sporozoans or nematodes, that are relatively poor in
characters, to eggs and early developmental
stages, and, finally, to isolated tissues whose origin is of interest, for example, in the fields of
foodstuffs or crime. Numerous such examples are
presented in the book by Ferguson [115], and
recent investigations have been carried out, for
example, on the protozoans and the muscle tissue
of fish [27, 432].
Even in animals that are rich in characters, species may be so similar to each other that they are
indistinguishable using morphological features
alone (sibling species). In such cases, the method
of enzyme electrophoresis has been used with
particular success, e.g. to subdivide several
groups of sibling species of Drosophila [25, 90],
and for the separation of the brachyuran Uca speciosa and U. spinicarpa [359], the nematodes Caenorhabditis elegans and C. briggsae [51], the sea