Evidence of climatic adaptation in spontaneous torpor amoung Pouched mice Saccostomus campestris from southern Africa

Abstract

Ellison G. T. H. 1993. Evidence of climatic adaptation in spontaneous torpor among Pouched mice Saccostomus campestris from southern Africa. Acta theriol. 38: 49 -59.Spontaneous torpor was examined in 36 Pouched mice Saccostomus campestris Peters, 1846 from 6 localities in southern Africa. Fifteen .individuals displayed characteristic bouts of torpor in which oxygen consumption (VO2) fell below 50% of the resting levels of non-torpid pouched mice for more than 2 hr during the early morning. These bouts ended in an abrupt increase in VO2 which overshot resting levels during arousal to normothermia. Minimum oxygen consumption (VC>2min) was not correlated with the energy saved during torpor, but there was a significant positive correlation between V02min and the duration of torpor (Dt) and also between Dt and energy saved. In contrast, there was a negative correlation between the cost of arousal and energy saved which suggests that the cost of regaining homeothermy can limit the energetic efficiency of short bouts of torpor. Pouched mice from all 6 localities had the capacity to enter torpor and there were no significant geographical differences in the incidence of torpor. However, there were substantial differences in the expression of torpor, and Pouched mice from localities experiencing more variable temperatures underwent significantly longer bouts of torpor which suggests that selection for torpor had been greater in more energetically unpredictable environments.

Evolutionary history and species diversity ofAfrican pouched mice (Rodentia:Nesomyidae:Saccostomus)

“…The subspecies is known to inhabit remarkable variety of habitats from periodically flooded shrublands in southern Mozambique to semideserts in Namibia. Its ability to enter spontaneous torpor (Ellison ) and size variation (Ellison et al . ) were both linked to climatic variation.…”

“…These rodents are ecological opportunists, primarily granivorous, with high‐turnover population dynamics. During suitable periods with abundant food supply, they accumulate fat; when food is scarce during dry season, they enter torpor up to five hours long (Ellison ; Skinner & Chimimba ). The genus is morphologically well defined by heavily built bodies with short limbs and short tails as well as by the presence of cheek pouches (Carleton & Musser ; Ryan ).…”