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a la Lista de Antecedentes y Material de Investigación Assem, J. van den MALE COURTSHIP BEHAVIOUR, FEMALE RECEPTIVITY SIGNAL,
AND SIZE DIFFERENCES BETWEEN SEXES IN PTEROMALINAE (HYM., CHALCIDOIDEA
PTEROMALIDAE), AND COMPARATIVE NOTES ON OTHER CHALCIDOIDS. Netherlands Journal of Zoology
26(40): 535 -
548. 1976. Abstract. In the evolutionary history of the Pteromalinae, the
position of the courting male has moved from the rear (the area where
copulation will take place) to the front (the area where an exchange
of stimuli between partners may occur most efficiently).
The shift of position is related to
a number of other developments, one of which is the antennal
receptivity signal by the female. The
effect of this signal is that the male stops courting, leaves the frontal
position by backing up on the female, and establishes
a genital contact (van den Assem, 1974). In the present paper I have argued
that, once a frontal position for courtship has been realised, and female
receptivity can be perceived by the male at the front, a further reduction
of the size of the male seems advantageous. Small males are found in many groups of Chalcidoidea including the Pteromalinae. In several species of this subfamily the size
differences between the sexes are considerable. In a gregarious parasite, small
males take a smaller share of the host which leaves more food for their
sisters whose average reproductive success seems to be proportional
to their longevity (which, within limits, is proportional to body size
as adult). Small-sized males are likewise advantageous in solitary parasites:
a small host (e.g. a young instar) may be insufficient
as a food source for a female offspring to complete its development
but sufficient for a male. A
discriminative parasite will lay unfertilised eggs on small hosts more
succesfully. (It is true that a small instar will become larger with
time, if left undisturbed, but a delay of egg-laying will certainly
result in losses due to the competitive activity of other parasites,
conspecifics or otherwise). Additional advantages of small
males are the more rapid development, which ensures a timely presence
where females come to emerge a little later. Further, a smaller body
size had no effect on the duration of a courtship sequence required
to induce receptivity in virgin females. The reduction of male body size
also has negative effects: a limitation of the number of possible inseminations,
a reduction of longevity, and an increased vulnerability to competing
conspecific males (who may "steal" a copulation) are the most
obvious ones. The advantages
and disadvantages of size reduction were discussed. Courtship behaviour of Pteromalus
venustus was described and two other species, Pteromalus puparum and Muscidifurax
uniraptor were dealt with in detail because of their peculiarities.
In P. puparum the antennal movements made
by the receptive female no longer seem to serve a signal function (although
they are completely identical to those of other Pteromalinae). I argued
that this ineffectiveness is a secondary phenomenon, due to the peculiar
behaviour of the male which may be an adaptation to oppose strong competition
for females. In M. uniraptor males are extremely rare, and they no longer serve a
reproductive function. Virgin females lay diploid eggs which produce female
offspring exclusively. However, males (who may arise as progeny of females
who were exposed to high temperatures during oviposition) appear to have
retained a normal courtship. Conspecific females, however, were never
seen to respond to it, but females of a related species (M. raptorellus)
did signal receptivity when courted by uniraptor males. Fertilisation did not occur because uniraptor-mated raptorellus females produced only male offspring. A few courtship repertoires of
Encyrtidae were described. To
all appearances the evolution of courtship behaviour of Pteromalidae,
Encyrtidae, and Eulophidae exhibits parallel developments. Melittobia Species Mentioned: Melittobia acasta. Comments. Even though this
paper deals with the implications of having small size males as a normal
evolutionary trait in many parasitic wasps (one being that the smaller
the male size, the fewer numbers of females that it can inseminate),
the author mentions Melittobia
species as an exception to that "rule." This paper shows a figure with pupae of males and females of Melittobia acasta and mentions the species
as an example of an extremely efficient parasite. Regreso
a la Lista de Antecedentes y Material de Investigación |