ribosomes of eukaryotic cells are normally larger (80S)
than prokaryotic ones (70S). Within chloroplasts and
mitochondria, ribosomes are of the 70S-type, which is consistent with the prokaryotic origin of these organelles.
Sexual reproduction, which is absent in prokaryotes, was
an early and pivotal evolutionary innovation of eukaryotic
cells. It is characterized by two opposite events, fertilization
(fusion of two gametes that doubles the number of
chromosomes), a process where the conditions are highly
taxon-dependent and varied, and meiosis, a special type of
cell division (that divides the number of chromosomes by
two). Fertilization, meiosis, and some associated processes
constitute a series of transitions between generations and
phases whose succession represents the life cycle (cf.
Sect. 7.3). Patterns of life cycle are highly diverse and may
constitute a biological marker characteristic of some highlevel taxa. Sexual reproduction is however absent from some
eukaryotic taxa, either because it never emerged (which is
highly unlikely), or because it was secondarily lost, or finally
because it is pending discovery.
Another pivotal evolutionary innovation in eukaryotes
was the phagotrophy, the capability for an organism, either
unicellular or multicellular, to engulf a particulate food, e.g.
a prey, a process unknown in prokaryotes (Cavalier-Smith
1987a). Phagotrophy made possible a major process in early
eukaryote evolution, endosymbiosis with Bacteria at the
origin of mitochondria and chloroplasts (cf. Sect. 5.4). Its
absence, e.g. in Fungi (kingdom Opisthokonta) is probably a
loss and therefore a derived character.
7.3
Life Cycles
7.3.1 Why Is It Important to Use a Simple
and Standardized Terminology?
Disciplinary boundaries, which were set in the eighteenth
century, have been the source of a terminological proliferation. Botanists, zoologists, and bacteriologists created different terms to refer to the same notion while, at the same time, a
given term was used with very different meanings. The same
process of terminological proliferation occurred within each
of these branches. Within botany, specialists in fungi (customary meaning), algae, mosses, ferns, and flowering plants
created their own jargon. Sometimes, this confusing terminology can be found within a given family, even a given genus of
the customary complexes called “fungi” (not the taxon named
hereafter Fungi), “algae,” and “protozoans” (cf. Sect. 5.5.3).
Many teachers around the world are guilty of perpetuating old
terminological customs and so spreading false similarities that
mask the real similarities. In short, their teaching leaves much
to be desired.
A given term, e.g. spore*, refers to a kaleidoscope of
meanings from one taxon to another. The specialists of a
taxon (sometimes a particular species) have added a multitude
of prefixes to account for highly redundant shades: aplanospore,
ascospore, autospore, basidiospore, carpospore, chlamydospore, conchospore, conidiospore, ecidiospore, endospore,
exospore, megaspore, meiospore, microspore, mitospore,
monospore, oospore, paraspore, perispore, probasidiospore,
seirospore, sporangiospore, teliospore, tetraspore, unispores,
urediospore, zoospore, zygospore, etc. Conversely, the male
gamete, a clear and simple notion, was named spermatozoon,
antherozoid, or spermatium. Is it really useful or necessary to
designate a filament consisting of cells, “trichome” in
Cyanobacteria and “hypha” in Fungi?
Here it was decided to replace the customary terms stemming from the partitioning of the taxonomy by a single term,
despite the risk of surprising, or even shocking, some
experts. The choice of one term rather than another (there
was often a choice) may seem arbitrary: the point is that this
term has a precise definition, and that it facilitates the understanding of the real similarities and differences between
taxa. When necessary, the correspondence to traditional
terms is indicated. A little known book by a professor at
the University of Montpellier (France), Jean Motte (1971),
who tried to “groom” the customary terminology, served in
part as the basis for the terminology used here.
Some figures which illustrate the present chapter are
based upon multicellular organisms. The reasons are either
that some multicellular eukaryotes are traditionally taken
into account by microbiologists or because they help in
understanding some of the concepts used here.
7.3.2 What Are the Differences Between
Spores, Gametes, Conidia, Cuttings,
Carpoconidia, and Zygotes?
A gamete* is a haploid (n) sexual cell that fuses with
another gamete to produce a diploid (2n) zygote. Gametes
contain only one set of dissimilar chromosomes, while
zygotes contain two sets of (paired) chromosomes
(Fig. 7.2). The fusion of gametes is called fertilization*
and can be summed up in the form: n + n ! 2n. When
more or less anthropomorphic criteria make the distinction
possible, male and female gametes are distinguished: the
male gamete is the smaller and/or more mobile, whereas
the female is the larger and/or less mobile. When such
criteria do not apply, gametes of opposing mating type are
referred to by “+” and “À”.
A spore*
3 is a haploid (n) cell produced by meiosis.
Meiosis begins with one diploid cell containing two copies
of each chromosome. The cell divides twice (a reductional
and an equational division), potentially producing up to
3 Spore, from the ancient Greek word spora (meaning ‘seed’, ‘sowing’).
198
C.-F. Boudouresque
than prokaryotic ones (70S). Within chloroplasts and
mitochondria, ribosomes are of the 70S-type, which is consistent with the prokaryotic origin of these organelles.
Sexual reproduction, which is absent in prokaryotes, was
an early and pivotal evolutionary innovation of eukaryotic
cells. It is characterized by two opposite events, fertilization
(fusion of two gametes that doubles the number of
chromosomes), a process where the conditions are highly
taxon-dependent and varied, and meiosis, a special type of
cell division (that divides the number of chromosomes by
two). Fertilization, meiosis, and some associated processes
constitute a series of transitions between generations and
phases whose succession represents the life cycle (cf.
Sect. 7.3). Patterns of life cycle are highly diverse and may
constitute a biological marker characteristic of some highlevel taxa. Sexual reproduction is however absent from some
eukaryotic taxa, either because it never emerged (which is
highly unlikely), or because it was secondarily lost, or finally
because it is pending discovery.
Another pivotal evolutionary innovation in eukaryotes
was the phagotrophy, the capability for an organism, either
unicellular or multicellular, to engulf a particulate food, e.g.
a prey, a process unknown in prokaryotes (Cavalier-Smith
1987a). Phagotrophy made possible a major process in early
eukaryote evolution, endosymbiosis with Bacteria at the
origin of mitochondria and chloroplasts (cf. Sect. 5.4). Its
absence, e.g. in Fungi (kingdom Opisthokonta) is probably a
loss and therefore a derived character.
7.3
Life Cycles
7.3.1 Why Is It Important to Use a Simple
and Standardized Terminology?
Disciplinary boundaries, which were set in the eighteenth
century, have been the source of a terminological proliferation. Botanists, zoologists, and bacteriologists created different terms to refer to the same notion while, at the same time, a
given term was used with very different meanings. The same
process of terminological proliferation occurred within each
of these branches. Within botany, specialists in fungi (customary meaning), algae, mosses, ferns, and flowering plants
created their own jargon. Sometimes, this confusing terminology can be found within a given family, even a given genus of
the customary complexes called “fungi” (not the taxon named
hereafter Fungi), “algae,” and “protozoans” (cf. Sect. 5.5.3).
Many teachers around the world are guilty of perpetuating old
terminological customs and so spreading false similarities that
mask the real similarities. In short, their teaching leaves much
to be desired.
A given term, e.g. spore*, refers to a kaleidoscope of
meanings from one taxon to another. The specialists of a
taxon (sometimes a particular species) have added a multitude
of prefixes to account for highly redundant shades: aplanospore,
ascospore, autospore, basidiospore, carpospore, chlamydospore, conchospore, conidiospore, ecidiospore, endospore,
exospore, megaspore, meiospore, microspore, mitospore,
monospore, oospore, paraspore, perispore, probasidiospore,
seirospore, sporangiospore, teliospore, tetraspore, unispores,
urediospore, zoospore, zygospore, etc. Conversely, the male
gamete, a clear and simple notion, was named spermatozoon,
antherozoid, or spermatium. Is it really useful or necessary to
designate a filament consisting of cells, “trichome” in
Cyanobacteria and “hypha” in Fungi?
Here it was decided to replace the customary terms stemming from the partitioning of the taxonomy by a single term,
despite the risk of surprising, or even shocking, some
experts. The choice of one term rather than another (there
was often a choice) may seem arbitrary: the point is that this
term has a precise definition, and that it facilitates the understanding of the real similarities and differences between
taxa. When necessary, the correspondence to traditional
terms is indicated. A little known book by a professor at
the University of Montpellier (France), Jean Motte (1971),
who tried to “groom” the customary terminology, served in
part as the basis for the terminology used here.
Some figures which illustrate the present chapter are
based upon multicellular organisms. The reasons are either
that some multicellular eukaryotes are traditionally taken
into account by microbiologists or because they help in
understanding some of the concepts used here.
7.3.2 What Are the Differences Between
Spores, Gametes, Conidia, Cuttings,
Carpoconidia, and Zygotes?
A gamete* is a haploid (n) sexual cell that fuses with
another gamete to produce a diploid (2n) zygote. Gametes
contain only one set of dissimilar chromosomes, while
zygotes contain two sets of (paired) chromosomes
(Fig. 7.2). The fusion of gametes is called fertilization*
and can be summed up in the form: n + n ! 2n. When
more or less anthropomorphic criteria make the distinction
possible, male and female gametes are distinguished: the
male gamete is the smaller and/or more mobile, whereas
the female is the larger and/or less mobile. When such
criteria do not apply, gametes of opposing mating type are
referred to by “+” and “À”.
A spore*
3 is a haploid (n) cell produced by meiosis.
Meiosis begins with one diploid cell containing two copies
of each chromosome. The cell divides twice (a reductional
and an equational division), potentially producing up to
3 Spore, from the ancient Greek word spora (meaning ‘seed’, ‘sowing’).
198
C.-F. Boudouresque