Trebouxiophyceae, Chlorophyta - (S)FTP hesla na Botany

General introduction
More variable markers, such as the gene introns, provide high resolution in phylogenetic
studies and they are useful in identifying and delimiting cryptic and phylogenetic species
and for use in population genetic studies. One such variable marker, the actin type I intron,
was reported by Liss et al. (1997), who observed high levels of its variation in Chlamydomonas
and Volvox (Fig. 10). Afterwards, actin introns were used to investigate the cryptic
diversity in lichen photobionts Trebouxia s. str. (Kroken & Taylor 2000) and Asterochloris
(Nelsen & Gargas 2006, 2008).
Fig. 10. Diagram illustrating the organisation of the actin genes of Chlamydomonas reinhardtii with respect to exons
(shaded boxes) and introns (open boxes) (After Liss et al. 1997).
1.4 Species concepts
All the above-mentioned morphological and molecular markers are frequently applied
for description and delimitation of particular species of coccal green algae. However, given
two organisms, how can we distinguish, whether they belong to the same species or not? The
answer may be straightforward for two divergent organisms, but it can be extremely difficult
and laborious in closely related ones. That is why many different concepts of species have
been and are held by biologists.
According to the morphological
species concept, species are the
smallest groups that can be repeatedly
defined by structural characteristics
that are relatively easy to distinguish
(Fig. 11). However, some morphological
species have been observed to
undergo seasonal succession or distinct
morphological variability depending
on environmental conditions
(Luo et al. 2006; Stoyneva et al. 2007;
van Holthoon et al. 2003; Verschoor
et al. 2004). Therefore, frequently
observed intraspecific morphological
variation avoids the descriptions of
species based solely on the morpho-
logical differences. Moreover, traditional morphological species concept alone is not sufficient
for species descriptions, since it does not recognize cryptic or sibling species (Behnke et
al. 2004). However, due to its long tradition, previously published morphological investigations
represent valuable information sources about morphological variability, uniqueness and
distribution of particular green algal species.
Fig. 11. Morphological species concept. Distinguishing Chlamydomonas
species according to the chloroplast morphology (after Ettl
1983).
The biological species concept, the most widely accepted concept among the biologists,
defines species in terms of interbreeding. According to this concept, species are groups
of interbreeding natural populations that are reproductively isolated from other such groups
(Mayr 1948). This is generally useful formulation for scientists working with living examples
of the higher taxa like mammals, fish, and birds, but meaningless for organisms that do not
reproduce sexually. In the majority of green microalgal genera, sexual reproduction has never
been observed (Ettl & Gärtner 1995) and thus wide application of the biological concept is
hard to imagine. However, indirect evidences on the interbreeding processes within the bio-
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