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, 6 (11), 190743
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Social Context Alters Spatial Memory Performance in Free-Living Male Prairie Voles

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Social Context Alters Spatial Memory Performance in Free-Living Male Prairie Voles

Marissa A Rice et al. R Soc Open Sci.

Abstract

Spatial memory is crucial for mating success because it enables males to locate potential mates and potential competitors in space. Intraspecific competition and its varying intensity under certain conditions are potentially important for shaping spatial memory. For example, spatial memory could enable males to know where competitors are (contest competition), it could help males find mating partners (scramble competition) or both. We manipulated the intensity of intraspecific competition in two distinct contexts by altering the operational sex ratio of prairie voles (Microtus ochrogaster) living in outdoor enclosures by creating male- and female-biased sex ratios. After living freely under these contexts for four weeks, we compared males' performance in a laboratory spatial memory test. Males in the male-biased context demonstrated better spatial memory performance than males in the female-biased context. Notably, these data show that in spite of experiencing equally complex spatial contexts (i.e. natural outdoor enclosures), it was the social context that influenced spatial cognition, and it did so in a manner consistent with the hypothesis that spatial memory is particularly relevant for male-male interactions.

Keywords: cognitive ecology; intraspecific competition; operational sex ratio; social context; spatial memory.

Conflict of interest statement

A.G.O. is an Associate Editor of Royal Society Open Science.

Figures

Figure 1.
Figure 1.
(a) Satellite image and (b) side view image of the semi-natural outdoor enclosures used in this experiment. Each adjacent enclosure measured 40 × 20 m, and was constructed of aluminium sheet metal walls and powder-coated steel tube frames. The walls extended 60 cm above, and below ground, preventing subjects from escaping (above or below) the enclosures, and preventing any other animals from getting inside.
Figure 2.
Figure 2.
The apparatus of the Morris water maze test consisted of a 1000 l tank with a submerged platform. Quadrants and zones within the Morris water maze were used to analyse swimming performance. The zones we used were a ‘thigmotaxis zone’ (7.6 cm from wall, marked in light grey), which encompassed the outer edge, a ‘near platform zone’ (the area near the platform, 40.6 cm diameter) and a ‘platform zone’ (the area directly encompassing the platform itself, 11.5 cm diameter, marked in dark grey). Boundaries are superimposed over the image to outline the zones.
Figure 3.
Figure 3.
Marginal mean (±s.e.) latency in seconds (s) to reach the platform throughout all 10 learning trials for MB (grey circles, n = 16) males and FB (white squares, n = 6) males in the Morris water maze.
Figure 4.
Figure 4.
Memory trial performance. (a) Mean (±s.e.) time in seconds (s) subjects spent swimming in the platform-containing quadrant of the water maze, and (b) number of times subjects swam in the platform-containing quadrant of the water maze. (c) Mean (±s.e.) time in seconds (s) subjects spent swimming in the ‘near platform zone’, and (d) number of times subjects swam in the ‘near platform zone’ of the water maze. For (b,d), mean frequencies are presented; however, data were analysed using generalized linear models with a Poisson distribution and a log link (MB n = 16, FB n = 6). Dots represent individual data.
Figure 5.
Figure 5.
Mean (±s.e.) distance from of the swimming vole to the original location of the platform during the memory test (Trial 11) in the Morris water maze. Dots represent individual data.

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