Reproductive strategies of the red-tailed phascogale (Phascogale calura).
Date
2008
Authors
Foster, Wendy Kay
Editors
Advisors
Taggart, David
Donnellan, Stephen Charles
Donnellan, Stephen Charles
Journal Title
Journal ISSN
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Type:
Thesis
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Abstract
This thesis examines the reproductive biology of red-tailed phascogales, an obligate male
semelparous dasyurid species, which is part of a captive breeding colony at Alice Springs
Desert Park. The red-tailed phascogale belongs to a group of dasyurids that shows an unusual
reproductive strategy amongst mammals, one which provides opportunity for understanding
means by which individuals maximise their reproductive success and the role of sperm
competition. The broad aim was to gain an understanding of the reproductive biology of red-tailed phascogales and explore means by which individuals can affect their reproductive
success.
Examination of the red-tailed phascogale reproductive biology showed that females mated
with multiple males and were capable of storing sperm in their oviducts for at least a five day
period. Captive female red-tailed phascogales showed greater plasticity in their breeding
season than has been observed in Antechinus, which exhibits the same life history strategy.
Females were observed to invest heavily into the production of young, producing almost
twice as many ova (15.1 ± 1.9) as young they can raise and 76% of females filling six to eight
of the eight available teats in a breeding attempt. A 63% male bias was observed in young
attaching to the teats, which could be produced through differential attachment of the sexes to
teats at birth. Of the 846 young born in the captive breeding colony, 68% were weaned, with
weaning occurring between 90-110 days of age and a 53% female bias observed in young
being weaned.
By weaning, a litter of young weighed 380% of the mothers mass with male young tending to
be heavier than females by weaning. No relationship was observed between maternal weight
and either litter sex ratio or sex biased growth of young. A positive relationship between
maternal body mass and body mass of offspring at weaning was observed, with the body mass
of young at weaning correlated with its body mass at maturity. Multiple paternity was
observed in more than half of the litters examined, with heavier males having increased siring
success compared to lighter males. Genotyping showed that the effective population size for
the captive colony was 1.9x that observed from the group managed studbook.
Male reproduction was also not as tightly constrained as in Antechinus, with spermatogenic
failure not occurring in captive populations until after mating had occurred, meaning males
are not reliant on epididymal stores alone for successful breeding. Scrotal diameter showed a positive relationship with testis and epididymal mass across male life, although this
relationship was not evident when analysis was restricted to the time of peak sperm
production. Captive males showed the opposite pattern of testosterone fluctuations to that
observed in wild animals, with lowest levels occurring during the mating period. Captive
animals were able to survive up to five years in captivity, in contrast to the obligate
semelparity observed in wild males.
Although most captive females can survive to breed in a second year and females are known
to breed in a second year in the wild, the reproductive strategy of females appears to be aimed
at maximising the returns on their first breeding attempt. In males, the need to maximise the
investment into the first breeding season is amplified through the complete absence of
opportunity to breed again; either through post-mating mortality in the wild or spermatogenic
failure in captivity.
The results of this study have implications for captive breeding of red-tailed phascogales, with
their reproductive biology; spermatogenic failure, restricted breeding season, teat number
limiting the number of young raised, high lactational investment into young, sex biases, the
need to maintain genetic diversity and biases in siring success; providing challenges for the
maintenance of a captive population. The results of this study also provide comparative
information that contributes to understanding the unusual life history strategy of Phascogale
and Antechinus, and contributes to the growing body of knowledge about mating strategies in
marsupials.
School/Discipline
School of Earth and Environmental Sciences
Dissertation Note
Thesis (Ph.D.) - University of Adelaide, School of Earth and Environmental Sciences, 2008
Provenance
Copyright material removed from digital thesis. See print copy in University of Adelaide Library for full text.