Breeding behaviour of the foam nest frog, chiromantis xerampelina: sperm competition and polyandry.
Date
1992
Authors
Jennions, Michael Dawson
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Abstract
Breeding was observed in the foam nest frog, Chiromantis xerampelina,
over three breeding seasons The mating pattern was characterized by an
extended breeding season with a male-biased operational sex ratio and
asynchronous and unpredictable female arrival. At more than 90% of nests,
from one to seven unpaired males ('peripheral males') gathered around the
amplexing pair during nest construction. Those peripheral males closest to
the pair competed 'With each other, and with the amplexing male, to position
their cloacae against the female's cloaca during oviposition bouts. In a
detailed study of a single population, over 80% of males were observed as
peripheral males, and 57% of males were observed both in amplexus and as
peripheral males. Male mating success and participation at nests was
unrelated to size or weight. Chorus participation was the best predictor of
male, mating success and participation at nests.
The most plausible explanation for the presence of peripheral males was a
sperm competition hypothesis; namely that peripheral males compete with
the amplexing male for fertilizations by shedding sperm into the nest. I
collected data on body mass and testis mass for 13 African anurans. Using
additional published data on 19 Japanese anurans, an allometric relationship
between body mass and testis mass was calculated. using 16 genera as
independent data points. This revealed that C. xerampelina have testes
fourteen times heavier than predicted on the basis of body mass. This is
consistent with a trend seen in several taxa where testis size is related to the
intensity of sperm competition. An additional experiment, in which the
arnplexing male was prevented from shedding sperm into the nest, showed
that peripheral males are capable of fertilizing eggs. I conclude that
peripheral males are engaged in an opportunistic alternative mating tactic
involving sperm cosnpetition. More than half the observed females bred
polyandrously, some mating with up to three males, This was the result of
amplexing males dismounting between nesting sessions, and males displacing
one another from amplexus.
Description
Thesis submitted to the Faculty of Science,
University of the Witwatersrand, Johannesburg
in fulfilment of the requirements for the
degree of Master of Science.
Keywords
Chiromantis xerampelina., Frogs -- Reproduction., Frogs -- Breeding., Polyandry., Sexual behavior in animals., Sexual dimorphism (Animals)