Seasonal reproduction in wild and captive male koala (Phascolarctos cinereus) populations in south-east Queensland
Allen, CD, de Villiers, DL, Manning, BD, Dique, DS, Burridge, M, Chafer, ML, Nicolson, VN, Jago, SC, McKinnon, AJ, Booth, RJ, McKee, JJ, Pyne, MJ, Peng Zee, Y, Lundie-Jenkins, G, Theilemann, P, Wilson, RJ, Carrick, FN & Johnston, SD 2010, Reproduction, Fertility and Development, vol. 22, no. 1, pp. 695-709.
Male koalas exhibit seasonal changes in anatomical and physiological characteristics relating to fertility and reproduction. These seasonal variations have implications for artificial insemination (AI) programmes, as semen samples collected from wild koalas during winter appear to retain the highest quality after thawing from cryopreservation.
A series of reproductive parameters were assessed for evidence of seasonal variation on a number of sampling occasions from three populations of wild, necropsied and captive koalas from the south-east Queensland region. The parameters investigated were body weight, coat score, sternal gland area and activity, testosterone secretion, reproductive anatomy volume and quality of semen, collected from live koalas via electroejaculation under anaesthesia, before and after cryopreservation. Koalas in all three sampling populations demonstrated evidence of seasonal variation for most reproductive parameters, though the parameters that varied seasonally differed somewhat between populations. The most significant finding in the context of assisted breeding programmes for the koala was that, of all semen samples collected from wild koalas throughout the sampling period, samples obtained in winter not only had the greatest initial rate of sperm movement but also retained the highest spermatozoa motility after cryopreservation. In winter wild males are also more likely to support a greater body weight and experience less stress during a capture event due to the cooler temperature. Similarly, during this period, the percentage of spermatozoa with intact plasma membranes after freezing and thawing was highest for captive koalas. Interestingly, the characteristics of spermatozoa collected from captive koalas indicated higher-quality samples than those obtained from wild koalas with regard to initial and post-thaw motility and percentage of spermatozoa with intact membranes after thawing. These differences may relate to the harsher environmental conditions faced by wild koalas that could affect spermatozoa survivability.
The success of AI programmes for the koala has grown considerably in recent years. The next step in refining AI techniques is to improve the logistics of obtaining semen samples from wild koalas. As repeated captures of individuals can be both stressful for the animal and impractical for the practitioner, identifying the reproductive parameters that change seasonally for koalas as in this study can inform the optimal timing of capture events to improve the likelihood of success of a subsequent AI procedure.
Although collecting semen samples from a wild koala on multiple occasions is possible, collection on fewer or a single occasion is much preferred. This study indicates that winter is the optimal time for this sampling to occur. Additionally, the finding that semen samples from wild koalas were generally of inferior quality to those from captive animals has important implications if genetic material from wild populations is sought. The authors suggest that a wild koala temporarily brought into captivity, where it can habituate to less demanding conditions, may produce a higher-quality sample than would be obtained in its natural habitat. Alternatively, retrieving semen samples from koalas brought into veterinary hospitals may be a feasible option for retrieving genetic material from the wild, so long as the disease status of such animals is carefully monitored.
Summarised by Joanna Horsfall
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