Savory - Arachnida 1977

312 V. HETEROGRAPHIA
With the approach to the second question, why is there any courtship,
Platnick sees in it an important factor in evolution. This follows
Mayr's opinion that a change of behaviour accompanies any entry into
a new environmental niche, and that other adaptations "particularly
the structural ones", are acquired subsequently. Thus it is suggested
that courtship methods may be valuable in arranging the genera of a
family; for example they may produce a better method of dividing the
Salticidae than a system which depends on the number of chelicera!
teeth.
If, however, the courtship of spiders marks the crown of the evolutionary
tree, the lower branches should be considered in an attempt to
present the phenomena in a logical order.
The scorpions set the pattern. In their courtship the male first
grasps the pedipalpi of the female in his own, and then, tails raised, there
follows the well known "promenade a deux". This, interspersed with
the actions described as "kissing" and "juddering", last until the pair
have reached a place where the ground is smooth. Here the male
deposits a loaded spermatophore. The female is then moved so that the
drop of spermatozoa is absorbed by her body andfertilizationisinternal.
The essential steps are therefore:
( i) the seizing of the female;
(ii) the long, preliminary dancing;
(iii) the depositing of the spermatophore;
(iv) the entry of the sperm-packet.
Reference to the skeleton classification printed among the preliminary
pages of this book will show that the scorpions are followed by the
Palpigradi and then by the orders formerly included in the "Pedipalpi".
Of the courtship of the Palpigradi little or nothing is known, but the
Uropygi, which tend to "repeat the scorpion pattern" (see Chapter 15),
adopt a courtship that is very similar to that just described. There is
the same grasping of the female by the male, the same prolonged
dancing which leads to the depositing of a spermatophore.
The Schizomida's courtship closely resembles this, but the next step,
which takes us to the Amblypygi, shows a difference. The male does not
take hold of the female; instead he touches her long first legs with his
own; he even turns his back on her before placing a spermatophore on
the ground and leading her to it.
The order most closely related to the Amblypygi is that of the spiders,
which have already been fairly fully described. They continue the process
begun by the Amblypygi in that there may be less actual contact
37. COURTSHIP IN ARACHNIDA 313
between the sexes, and the use of the spermatophore has been
abandoned.
In the classification just mentioned the Araneae arc followed by five
orders that are now extinct and can therefore supply no data by which
an interpretation of arachnid courtship might be strengthened. Hence
the next orders to be considered arc the Opiliones and the Ricinulci.
The former, the harvestmen, are most interesting. An order with an
impressive list of adaptations, they are clearly one of the oldest members
of the class, and they have had time to produce a complete change in the
reproductive behaviour. There is no courtship, no appeasement, no
dancing, no spermatophore, no delay. l\Iating normally follows
immediately on the meeting of the sexe-s, when the male makes use of
an intromittent organ, a true penis that is found only in the related
Acari.
The Ricinulei are less we-ll known. Pollock (1967) has stated that the
male grasps the- female, whether or not any courtship has taken place
is still uncertain, but the essential fact is that sperm arc introduced
into the female's body by the third leg of the male and there is no
spermatophore.
The position that is thus developing presents first, close contact
between the- individuals and the use of the spermatophore; then the
spermatophore with less physical contact; and lastly the use of a limb
or male organ to transfer the spermatozoa.
The fourth sub-class contains but two orders, the Pseudoscorpione-s
and the Solifugae. One could wish for more orders at this stage of
evolution, which may at some distant time have seen some of the missing
combinations of characteristics deplored in Chapter 12. However, the
data available seem closely to agree with the outline suggested above.
Among false scorpions there arc genera in which the traditional
clutching of the female occurs, there is a rhythmic walking to and fro,
the appearance of a spermatophore, and the impaling of the female
upon it. Again, there are genera in which there is lack of close association,
and the male abandons the spermatophore, which is later found
by the female and all romance has vanished from the insemination.
\Vhen, finally, we move to the Solifugae, we find that again the
spermatophore has been abandoned, and the packet of spermatozoa
is placed in the female orifice by the chelicerae of the male.
Two questions now arise. V\'hat is the significance of the dropping of
the spermatophore, and, is the courtship of the Arachnida related to the
courtship behaviour of other invertebrate-s?
Courtship is of general occurrence throughout the animal kingdom,
and has be-e-n fully expounded by Bostock ( 1969), whose conclusions
may be summarized as follows.