V. Haukisalmi et al., VARIABILITY OF SEX-RATIO, MATING PROBABILITY AND EGG-PRODUCTION IN ANINTESTINAL NEMATODE IN ITS FLUCTUATING HOST POPULATION, International journal for parasitology, 26(7), 1996, pp. 755-763
Haukisalmi V., Henttonen H. & Vikman P. 1996. Variability of sex ratio
, mating probability and egg production in an intestinal nematode in i
ts fluctuating host population, International Journal for Parasitology
26: 755-764, In dioecious parasites, the chances of co-occurring with
the opposite sex depend on the sex ratio, abundance and distribution
pattern of parasites within the host population. Theory suggests that
if the abundance and degree of aggregation are very low, mating probab
ility may decrease so much that the parasite population is vulnerable
to extinction, Our aim is to determine the factors affecting the matin
g probability and egg production in Heligmosomum mixtum (Heligmosomida
e), an intestinal nematode of the bank vole, Clethrionomys glareolus,
at Pallasjarvi, Finnish Lapland. We also search for factors responsibl
e for the persistence of H. mixtum in its fluctuating host population.
The results showed that during high parasite abundance practically al
l nematode females co-occurred with males, but during a phase of very
low abundance only 15% of females had a chance to mate, Comparison of
observed mating probabilities and those predicted by a theoretical mod
el (May & Woolhouse, 1993) showed that deviation from the assumption o
f complete aggregation between males and females results in underestim
ation of the mating probability. Sex ratio and the degree of aggregati
on showed a minor effect on mating probability, The sex ratio (proport
ion of females) of H. mixtum, which was female-biased (0.58), showed a
negative correlation with the mean intensity of infection in the mont
hly samples (decreasing female-bias at high mean intensity), but no si
gnificant relation to the intensity of infection (number of worms in a
host individual). The long-term persistence of H. mixtum in its stron
gly varying host population seems to be due to the high transmission e
fficiency and long life-span of the parasite. Copyright (C) 1995 Austr
alian Society for Parasitology.