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Abstract

The Eastern quoll, Dasyurus viverrinus, is one of the larger
members of the family Dasyuridae and is found only in Tasmania. The quoll
has a short breeding period with mating occupying two to three weeks of every
year. Males display seasonal cycles of body weight and testes size. Both
parameters are maximal prior to breeding then decline during and after
mating.
LH and testosterone concentrations fluctuate at basal levels for
much of the year. A gradual rise in LH and testosterone occurs in April, two
to three months before breeding. This probably functions to initiate
spermatogenesis and to prepare the gonads and accessory glands for
reproduction. Male quoll produce a peak in LH (mean 13.9 ng per ml) and
testosterone (mean 5.0 ng per ml) during the mating period. This peak
coincides with maximimi number of animals in the area and is associated
with an increase in activity and mobility of males at this time. The highest
testosterone level occurs just prior to mating and declines during copulation.
By the time the young are born, approximately 19 days after copulation, most
males have basal levels of hormones.
Juvenile quoll increase in weight with age and have comparatively
high levels of LH and testosterone when entering the population after
weaning. These levels may be associated with the processes of maturation and
also with agonistic behaviour encountered during dispersal.
LH, progesterone and prolactin secretion in the female quoll
conform to the patterns shown by other marsupials. LH and progesterone
levels are highest near the time of oestrus and ovulation while prolactin
concentration increases throughout the lactation period. The endocrine cycles
and pouch development of pregnant and non-pregnant females appear to be
similar.
Experimental evidence suggests that photoperiod is the likely
proximate cue regulating the breeding cycle of the male quoll. Males exposed
to a long daylength increase in weight and have lower LH concentrations
compared to control animals. Testosterone secretion and testes size appear
unaffected by a change in photoperiod and may require either a longer
exposure time or additional factors to influence these cycles. Males in captivity generally have lower LH and testosterone levels
compared to males in the wild. The hormonal profiles of captive male quoll
are related to the degree of physical contact with the female. When males are
housed with females, LH and testosterone levels are significantly higher than
when males are housed near, or isolated from females. A cue fi-om the female
may be the stimulus initiating a peak in androgens in the male and therefore
females may be responsible for the S5mchrony of the breeding cycle.
Cortisol levels are significantly lower in captive animals when
physical contact is prevented. There is no evidence of an androgen dependent
decrease in plasma CBG during breeding nor is there any increase in free
Cortisol associated with a decrease in MCBC. The breeding season did not
appear to be a period of high stress nor was it characterised by major changes
in plasma protein, albumin or triglyceride levels. This is consistent with the
Eastern quoll being one of the long lived members of the Dasyuridae.
This project proposes that the seasonal breeding activity in the male
quoll is broadly regulated by photoperiod. However, the androgen rise prior to
mating is triggered by additional cues, mainly from the female. The
synchrony of this rise is directly related to interspecific male aggression
probably involving physical interaction. High androgen levels occur just before
mating, enabling males to establish their dominance and position in the social
hierarchy before pairing with females. This reproductive pattern enables the
Eastern quoll to intensify its reproductive effort and the relatively short, sharp
rise in androgens and free cortisol does not impose immediate constraints on
the life expectancy of the animal. The role of the male throughout the breeding
cycle therefore contributes much to the life history classification of this species.

Item Type:	Thesis - PhD
Authors/Creators:	Bryant, SL
Additional Information:	Copyright the Author
Item Statistics:	View statistics for this item

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