xiii
Sex was a key novelty in the evolutionary history of the Eukaryota, and for most Metazoa a
combination of sex and replication is the only way of reproducing (Barnes et al. 2001; CavalierSmith 2002). Sexual reproduction typically involves gonadogenesis, gametogenesis, fertilization, embryogenesis (often accompanied by incubation of the embryos) and, in species with a
larval stage, larval ontogenesis and metamorphosis. These reproductive stages are implemented by means of various provisional and permanent structures, such as gonads, gonoducts
and associated glands, organs responsible for gamete release into the environment, their transfer to the partner and for their storage, incubation chambers and various larval organs. Although
having a general similarity in different metazoan groups, the reproductive stages vary greatly
in their phenomenology as do the organs in their structure. This diversity is expressed in: (1)
gender (unisexuality or gonochorism vs. different variants of hermaphroditism), (2) the structure of gonads as well as the sources, ways, timing and sites of their origin and fi nal location,
and their maturation time and duration of functioning, (3) gametic structure and development,
(4) place, time and methods of insemination and fertilization and the structures ensuring these
processes, (5) incubation modes and structures, (6) modes of embryogenesis, (7) larval types,
and (8) modes of metamorphosis (reviewed in Franzén 1956; Raven 1961; Adiyodi and Adiyodi
1983, 1989, 1990; Wourms 1987; Giese et al. 1987; Eckelbarger 1994; McEdward 1995;
Ivanova- Kazas 1995; Drozdov and Ivankov 2000; Schmidt-Rhaesa 2007; etc.). This broad
range of diversity indicates that sexual reproduction has been evolving in concert with the
organisms themselves. Being stable in the essentials, sexual reproduction has been constantly
changing in its details.
Various combinations of the reproductive characters listed above can be taken as representing particular reproductive patterns – specifi c variants or stable complexes of the sexual traits
characteristic of a species or a group of living organisms. Note, however, that in biological
literature the term “reproductive pattern” is often not quite correctly understood as a synonym
of “reproductive strategy.” In general, a reproductive strategy is a method of energy input into
the offspring defi ned by the amount of resources allocated for the production and parental care
of a single offspring (Vance 1973). These methods may be quite different, representing the socalled r–K continuum (MacArthur and Wilson 1967; Pianka 1999). Besides, each strategy is
characterized by a specifi c set of features ensuring reproduction, that is, by the reproductive
pattern, and similar strategies may have different patterns. For instance, during lecithotrophic
and placentotrophic development, the offspring obtains the necessary resources in different
ways and at different stages. The result, however, is very much the same. To sum up, the term
“reproductive strategy” describes the general character of resource allocation (for which data on
seasonal dynamics of reproduction are usually necessary; see, for instance, Dyrynda and Ryland
1982), whereas the term “reproductive pattern” refers to a specifi c complex of reproductive
traits, including the mode of oogenesis, method of gamete manipulation (spawning, copulation),
time and site of syngamy, incubation mode, larval type, etc. It should be noted that marine invertebrates are sometimes said to possess larval (planktotrophic and lecithotrophic) and embryonic
(lecithotrophic and placentotrophic) reproductive strategies (Thorson 1950; Mileikovsky 1971;
Kasyanov 1989; Levin and Bridges 1995). This classifi cation is based on the ways in
which the embryos and larvae obtain resources during different phases of their development.
Introd uction
Sex was a key novelty in the evolutionary history of the Eukaryota, and for most Metazoa a
combination of sex and replication is the only way of reproducing (Barnes et al. 2001; CavalierSmith 2002). Sexual reproduction typically involves gonadogenesis, gametogenesis, fertilization, embryogenesis (often accompanied by incubation of the embryos) and, in species with a
larval stage, larval ontogenesis and metamorphosis. These reproductive stages are implemented by means of various provisional and permanent structures, such as gonads, gonoducts
and associated glands, organs responsible for gamete release into the environment, their transfer to the partner and for their storage, incubation chambers and various larval organs. Although
having a general similarity in different metazoan groups, the reproductive stages vary greatly
in their phenomenology as do the organs in their structure. This diversity is expressed in: (1)
gender (unisexuality or gonochorism vs. different variants of hermaphroditism), (2) the structure of gonads as well as the sources, ways, timing and sites of their origin and fi nal location,
and their maturation time and duration of functioning, (3) gametic structure and development,
(4) place, time and methods of insemination and fertilization and the structures ensuring these
processes, (5) incubation modes and structures, (6) modes of embryogenesis, (7) larval types,
and (8) modes of metamorphosis (reviewed in Franzén 1956; Raven 1961; Adiyodi and Adiyodi
1983, 1989, 1990; Wourms 1987; Giese et al. 1987; Eckelbarger 1994; McEdward 1995;
Ivanova- Kazas 1995; Drozdov and Ivankov 2000; Schmidt-Rhaesa 2007; etc.). This broad
range of diversity indicates that sexual reproduction has been evolving in concert with the
organisms themselves. Being stable in the essentials, sexual reproduction has been constantly
changing in its details.
Various combinations of the reproductive characters listed above can be taken as representing particular reproductive patterns – specifi c variants or stable complexes of the sexual traits
characteristic of a species or a group of living organisms. Note, however, that in biological
literature the term “reproductive pattern” is often not quite correctly understood as a synonym
of “reproductive strategy.” In general, a reproductive strategy is a method of energy input into
the offspring defi ned by the amount of resources allocated for the production and parental care
of a single offspring (Vance 1973). These methods may be quite different, representing the socalled r–K continuum (MacArthur and Wilson 1967; Pianka 1999). Besides, each strategy is
characterized by a specifi c set of features ensuring reproduction, that is, by the reproductive
pattern, and similar strategies may have different patterns. For instance, during lecithotrophic
and placentotrophic development, the offspring obtains the necessary resources in different
ways and at different stages. The result, however, is very much the same. To sum up, the term
“reproductive strategy” describes the general character of resource allocation (for which data on
seasonal dynamics of reproduction are usually necessary; see, for instance, Dyrynda and Ryland
1982), whereas the term “reproductive pattern” refers to a specifi c complex of reproductive
traits, including the mode of oogenesis, method of gamete manipulation (spawning, copulation),
time and site of syngamy, incubation mode, larval type, etc. It should be noted that marine invertebrates are sometimes said to possess larval (planktotrophic and lecithotrophic) and embryonic
(lecithotrophic and placentotrophic) reproductive strategies (Thorson 1950; Mileikovsky 1971;
Kasyanov 1989; Levin and Bridges 1995). This classifi cation is based on the ways in
which the embryos and larvae obtain resources during different phases of their development.
Introd uction