Applied species concept

There exist a number of different ideas of how a species of organisms should be defined. A table of the most important species concepts is given by WÄGELE (2000: p. 57). In the practice of taxonomic work usually MAYR´s concept of a "biological species" is followed: "Species are groups of actually (or potentially) interbreeding natural populations which are reproductively isolated from other such groups" (MAYR, 1969). The advent of a precise methodology and theory of phylogenetics stimulated the formulation of other species concepts.HENNIG (1966) defines species as “Groups of individuals connected by tokogenetic [parental / genealogical] relationships”. HENNIG´s concept extends MAYR´s biological species into the fourth dimension by conceiving species as lineages with a distinct beginning (by speciation) and a distinct end (by speciation or by extinction). The concept of WILEY (e. g. 1981; as modified from SIMPSON, 1961) seems to go even further in being very generalized: "An evolutionary species is a single lineage of ancestor-descendant populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate". The advantage of this universality is that it can be applied also in problematic cases as exemplified by asexual organisms or the so called "chronospecies". Unfortunately, the trade-off is the clarity of the definition.

So far there are no records of fossil Euops species, nor is there an indication of the existence of parthenogenetic populations in attelabids. Thus, it is possible to restrict the conceptual base of the taxonomic work herein to MAYR´s biological species.

Since it was not possible to experiment in crossbreeding different populations of the species studied, what criteria were used in sorting the specimens at hand? First of all, series of similar specimens exhibiting discrete morphological characters ("morphospecies") were identified. If two or more such "morphospecies" had been found sympatrically, this was regarded a strong indication for a lack of gene-flow; i. e., reproductive isolation must be obtained and the specimens must belong to separate species. For example, three closely related species of Neosynaptops (E. punctaticeps, E. similis, E. waigeoensis) were collected near the village of Saporkren on Waigeo island. At least two species of the spinosus-group

(E. yali and E. armatus) occur sympatrically near the village of Kosarek.

It is more problematical to deal with specimens from different localities; in such cases there is the possibility of allopatric distributions without a "natural crossbreeding experiment" which is provided in the case of the sympatric populations. It was necessary to make a somewhat arbitrary decision if the observed morphological differences are sufficient to justify the status of a separate species. Nevertheless, in most groups some sympatric species

could provide a rough scale of the required morphological difference and the characters of importance. Concerning the examples above, it was found that male genital structures in the sympatric E. yali and E. armatus are very similar. However, the armature of the male profemur was completely different. As a consequence, this character was considered of major importance in the spinosus-group. When deciding about the status of other specimens of this group, differences of this character were first considered. In Neosynaptops, the situation is reversed. The three species occurring in Saporkren (Waigeo Island) are externally extraordinary similar, but the transfer apparatus of the male genitalia exhibits very distinct characters. Thus, comparable differences in genital characters were expected from other specimens of Neosynaptops to assign them specific status. In cases of doubt, the attitude of a "lumper" was preferred over the one of a "splitter". Local forms that may represent distinct species were described separately under "intraspecific variation". See for example the Biak-form of E. viridiceps, or the Mt.Kaindi-form of E. zimmermani. When additional material of these forms later suggests that they are indeed separate species, they can be named at that point. I have refrained categorically from naming subspecies. As outlined above, there is already some difficulty in defining species for which sound concepts exist. There is no reasonable concept for subspecies, an issue that was discussed in detail

byWILSON & BROWN (1953).

Generally, characters that seem to evolve under sexual selection were of great importance for defining the species. Judging from the diversity of male sexual characters, ranging from sophisticated structures of the genital transfer apparatus to all kinds of protrusions on legs and rostrum, there appear to exist strong pressures of sexual selection in

Euops. As outlined by STUBBLEFIELD & SEGER (1994) there is a positive correlation between

the difference in parental investment and the amount of sexual selection. Attelabid females have to prepare the nidi, a laborious task which is not supported by the males in any way. Therefore, in theory, strong pressures of sexual selection should rest on male Euops; in reality this becomes obvious in the diversity of sexual male characters as cited above. Considering MAYR´s species concept, which rests on reproductive ties between the individuals of populations, it appears reasonable to rely largely on such sexual characters when defining the Euops species herein. Characters of the transfer apparatus are of crucial importance in this context. They remind us of the lock-and-key hypothesis of genital morphology. However, as in many other groups of arthropods only the keys exist in Euops; the soft-walled and uniformly poach-like bursa copulatrix of most females does not appear to represent a corresponding lock. This issue was discussed extensively bySHAPIRO & PORTER (1989). The "female choice hypothesis" of EBERHARD (1985) explains the present situation without requiring a mechanical female "lock". It assumes a runaway coevolution between male genital structures and female neuronal properties. Such a coevolution could take place

if the female has some influence on the rate of fertilization after a copulation. This hypothesis explains equally well the rapid evolution of the male genital structures and their sophisticated specific structures.

All of the hypotheses regard these structures as critical for a successful insemination of the female and / or the fertilization of its egg-cells. Thus, the great practical value of male genital characters in sorting specimens and their importance in decision-making of which group of specimens to formally describe as a biological species is well-supported by evolutionary theory. Furthermore, it is well compatible with MAYR´s concept of a biological species.

For sorting the "morphospecies" (Euops, new species 1-108) male genital structures were also examined. The same rigorous criteria were applied as for the species which were formally described.