Principios de Taxonomia

4.6 Traits that are Used by the Species to Distinguish Themselvesj77
organisms that live in the same region have certain identifying traits to make the
correct partner choice. Females are especially picky. In most animal species, it is their
part to decide which particular individual is permitted sexual contact. Sexual
willingness of the female does not arise if the male does not display the correct
optical, acoustical or olfactory signals. Only if these traits fit do the females show the
necessary disposition required for reproduction. This biological phenomenon is
called female choice.
Signals such as these can be particular color traits. The female recognizes these
signals with a high degree of accuracy and distinguishes the conspecific male sexual
partner from foreign partners using these traits. Duck males, peacocks and birds of
paradise have especially impressive color signals that distinguish the species from
each other. In addition to optical partner identification signals, there are also
acoustical ones. Many bird songs are species-specific. They are presented by the
males and serve for the females to distinguish their own species from a foreign one.
Olfactory signals for species recognition are also widely distributed in the animal
kingdom, for example, in Clearwing Moths (Sesiidae) and the representatives of some
moth families. There are examples in which a single signal molecule sent by the
female is enough to unerringly attract the male for copulation.
Above, the use of traits for species classification was called into question because
traits are subjectively selected by humans for their own intentions for differentiation.
However, in the cases of partner recognition signaling, only traits play a role for which
the animals can recognize themselves as sexual partners. This seems to be a way out
of the dilemma because with partner recognition signals the species protect themselves
from false mating. The selection of those traits by which the members of a
species recognize each other for a taxonomic delimitation of species is without doubt
tempting. The exclusive application of only these traits for taxonomic classification
appears to be reliable. This approach seems to exclude the traits that have nothing to
do with species specificity.
Remarkably, one of the fathers of the species concept of the reproductive community,
Theodosius Dobzhansky, was already aware that there have to be two
different kinds of traits distinguished: those that are responsible for partner choice
and those that have nothing to do with partner recognition (Dobzhansky, 1937). The
genetic factors responsible for the production of the isolating mechanisms appear to
constitute rather a class of particular traits by themselves. He introduced the term
isolating mechanisms and defined them as an isolating traits or any trait that
hinders the interbreeding of groups of individuals. Those traits would make
interbreeding (with non-conspecifics) difficult or impossible.
Unfortunately, this assessment cannot be generalized. Several species live in
different geographical regions and overlap each other only within limited districts.
If, however, two species live in different geographical regions, in these regions, the
species-specific recognition signals are unnecessary. There is no selection pressure for
species distinction and, hence, for the development of species-specific recognition
signals. Only in the overlapping regions where two species live sympatrically and meet
eachotherdotheyhavetobeabletodistinguisheach otherina species-specificmanner.
In all of the other regions, species-specific recognition signals are unnecessary.