Page 88 - University of Pretoria RESEARCH REVIEW 2016

NATURAL environments
PARTY AFTER DARK
A TALE OF TWO SHREWS
Light and the day-night transition is crucial in the reproductive and life history processes of many organisms and particularly mammals; and so do activity patterns linked to seasonal changes make possible sympatric coexistence.
Carol Hoole, under the supervision of Professors Nigel Bennett and Andrew McKechnie in the Department of Zoology and Entomology, has been unravelling how the natural environment can shape the reproduction and activity patterns of two shrew species in the eastern Cape.
Photoperiodism is the process by which organisms use both absolute measures of day length, and the direction in which day length is changing, as a cue for regulating
seasonal changes in physiology and behaviour so that birth and lactation arise with optimal resource availability, thus increasing offspring survival. Two sympatric shrew species were studied to assess how the length of a day affects the reproductive biology of males: the Red musk shrew, Crocidura flavescens (±40g) and the Forest shrew, Myosorex varius (±10g). Interestingly, the Red musk shrew, an insectivore with a longer lifespan than the heterospecific Forest shrew, was found to exhibit reproductive activation on a short day, where males exhibited greater testicular volume and seminiferous tubule diameter following exposure to a short day, but long night cycle. This suggests that these animals may have breeding peaks that correspond to short days. In
direct contrast, the short-lived Forest shrew was found to show increased testicular volume and seminiferous tubule diameter on a long day.
The day-night cycle is also important for dictating
the locomotory activity patterns of organisms. Again, the two sympatric species of shrew placed in the laboratory on a 12-hour light/12-hour dark light cycle exhibited a strictly nocturnal activity pattern with polyphasic periods of activity occurring in the dark phase of the light cycle. The smaller Forest shrew exhibited greater frequency of polyphasic energy due to higher energy demands. When the shrews were trapped throughout the year in the field, the smaller Forest shrew were found to be captured mainly at night well after sunset in the summer, spring and autumn months, whereas captures in the winter months were at dawn and dusk, with individuals avoiding the very cold nights. In direct contrast,
the larger Red musk shrew maintained a very strict nocturnal activity pattern with captures occurring well into the night. These studies again show that the smaller shrew maintains its activity to avoid times that could result in hypothermia, and potentially to avoid competition as the larger Red musk shrew will feed on the smaller Forest shrew.
These two studies elegantly demonstrate how two species of differing lifespan and body size organise their reproductive biology and locomotory activity patterns in unison with the changes in day length and seasonal changes in temperature to enable a sympatric coexistence.
A TRIBUTE TO A LIFETIME’S RESEARCH
The legacy of scientific research at the Prince Edward and Marion Islands, and the many individuals who have contributed to research in this remote context, is captured in a book compiled and edited by Nico de Bruyn and Chris Oosthuizen, Pain forms character: Doc Bester, cat hunters and sealers (Antarctic Legacy of South Africa, 2017). The book is dedicated to Professor Marthán N Bester for his contribution to science and conservation, and his influence on generations of young and fellow researchers. Bester’s 40-year ‘island research’ career, through the South African National Antarctic Programme (SANAP), and the Marion Island Marine Mammal Programme (MIMMP) which he started in 1983, provides rich context for this tribute to his life’s work. The book does what the substantial scientific literature and research outcomes do not: it provides personal accounts of the harsh working and living conditions, and the marvelous camaraderie, of the Marion Island ‘cat-hunters’ and ‘sealers’.
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Forest shrew – Marietjie Oosthuizen