Agriculture Reference
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ending) and seemingly a polytypic species; and (2) endemic species, like
Octodrilus frivaldszkyi
or
Octodrilus aporus
, which are confined to small and distinct habitats mainly on Mesozoic limestone
and which appear to be monotypic species with a limited variability of characters.
T
D
I
O
S
N
AXA
ISCRIMINATION
AND
DENTIFICATION
OF
CTODRILUS
PECIES
BY
UMERICAL
T
AXONOMY
Taxa identifications have to be based on a thorough examination of the variability of the diagnostic
characters in local populations. The high constancy in some sexual characters, like the number and
position of the spermathecae, the position of the tubercula pubertatis, and, to a certain extent, the
position of the clitellum were confirmed statistically and were considered the major diagnostic
characters at the species level (Pop 1989, 1991).
The position of the tubercula pubertatis seems to have a particularly good diagnostic value at
the species level. We have never found any local species population with variable positions of the
tubercula pubertatis, as occurs in other lumbricid genera. When differences of even one segment
in the position of tubercula pubertatis occurred in the same sample, there were other differences
as well, which allowed the separation of the individuals into distinct taxa. On the basis of a study
of the variability of characters in more than 1500 individuals, it is justifiable to recognize as many
Octodrilus
species as there are different positions of tubercula pubertatis (Figure 7.3).
Subspecies discrimination presents yet another difficult taxonomic task. Subspecies in lumbri-
cids have so far been recognized on classical criteria. According to Mayr (1971), Ña subspecies is
an aggregate of phenotypically similar populations of a species inhabiting a geographic subdivision
of the range of the species and differing taxonomically from other populations of the species.Ò That
is, a subspecies has a character of spatial unity, a subdivision of a species in the dimensions of
longitude and latitude.
However, habitat differences may occur over small distances in the case of insular distributions
of biotopes in mountain regions. In many areas of the Carpathians, patchy distribution patterns of
biotopes are evident. Islands of soils developed on limestone are surrounded by soils developed on
acid parent material, and there are grassland areas that surround forest islands. Soils, valleys, and
vegetation act as barriers, so there is scope for allopatric, accelerated, insularlike speciation.
FIGURE 7.3
Pattern of
Octodrilus
taxa discrimination by the main diagnostic characters.
