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. 2009 Jun 29;4(6):e6070.
doi: 10.1371/journal.pone.0006070.

Cool Sex? Hibernation and Reproduction Overlap in the Echidna

Free PMC article

Cool Sex? Hibernation and Reproduction Overlap in the Echidna

Gemma Morrow et al. PLoS One. .
Free PMC article


During hibernation there is a slowing of all metabolic processes, and thus it is normally considered to be incompatible with reproduction. In Tasmania the egg-laying mammal, the echidna (Tachyglossus aculeatus) hibernates for several months before mating in mid-winter, and in previous studies we observed males with females that were still hibernating. We monitored the reproductive activity of radio-tracked echidnas by swabbing the reproductive tract for sperm while external temperature loggers provided information on the timing of hibernation. Additional information was provided by camera traps and ultrasound imaging. More than a third of the females found in mating groups were torpid, and the majority of these had mated. Some females re-entered deep torpor for extended periods after mating. Ultrasound examination showed a developing egg in the uterus of a female that had repeatedly re-entered torpor. The presence of fresh sperm in cloacal swabs taken from this female on three occasions after her presumed date of fertilization indicated she mated several times after being fertilized. The mating of males with torpid females is the result of extreme competition between promiscuous males, while re-entry into hibernation by pregnant females could improve the possibility of mating with a better quality male.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Figure 1
Figure 1. Ultrasound image showing an egg in the uterus of echidna 5D5E on July 23 2008.
Fertilization probably occurred on July 9, but she had fresh sperm in her reproductive tract and was also torpid. Distance between the two markers showing the structure within the egg is 0.35 cm.
Figure 2
Figure 2. External temperature logger record from female echidna 0118.
She entered hibernation in March, and her final arousal was on July 27 (arrow 2), when temperature variability increased. The subsequent reduction in variability (arrow 3) is associated with entry into the nursery burrow and egg-laying. Periodic arousals can be seen between April and July. In mid-July she shows an extended arousal (July 10–21), and we presume fertilization occurred at the time indicated by arrow 1.
Figure 3
Figure 3. Time between final arousal from hibernation and egg-laying for 23 reproductive events from 13 echidnas, as estimated from internal (red circles), and external (blue circles) temperature loggers.
The reported gestation period for echidnas is 20–24 days . Although three animals (3A61, 4057, 2753) were active for periods of up to 3 weeks before becoming pregnant, the majority of points lie between 20 and 24 days after the end of hibernation. In these cases the females must have become pregnant nearly immediately after the final arousal from hibernation, or were already pregnant. Echidna 0118 must have become pregnant during the previous euthermic period (see Figure 2), as was probably also the case for three of 5D5E's pregnancies.

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