Vocal mother-offspring communication in guinea pigs: females adjust maternal responsiveness to litter size

Abstract

Background: In parent-offspring communication, vocal signals are often used to attract attention and offspring might call to induce parental behaviour. In guinea pigs (Cavia aperea f. porcellus) mothers wean larger litters later than small ones, but it is unknown whether this difference depends on processes induced during pregnancy or is influenced post-natally by the number of pups present. We here tested with playback-experiments using pup separation calls whether mothers with cross-fostered large experimental litters (four-pup-litters) were more responsive to offspring calls and maintained responsiveness for longer than mothers with small experimental litters (two-pup-litters). Mothers were tested when two pups were suckling i.e. when both teats were occupied.

Results: Mothers of four-pup litters responded stronger to broadcast pup separation calls than those with two-pup litters. Additionally, we tested the mothers' responsiveness to pup separation calls in the absence of their pups on day 8 and 20 of lactation. Mothers of four-pup litters responded stronger and showed no decrease in responsiveness from day 8 to 20, whereas mothers of two-pup litters responded less and decreased responsiveness from day 8 to 20. Mothers of four-pup litters also weaned their pups 5 days later than those of two-pup litters.

Conclusion: Measured by their response to pup calls and by time to weaning, guinea pig mothers adjust maternal responsiveness to litter size. This behaviour is likely to be an adaptive strategy in resource allocation during reproduction.

Figure 1

Sound spectrogram of a series of pup separation calls. Calls shown were recorded from an eight days old individual.

Figure 2

Experimental setup for experiment 1: The test-arena was equipped with huts for shelter on both sides of the test-arena and a loudspeaker placed on each hut. The zone closest to the loudspeaker that was used in a given trial was labelled as zone one and the most distant zone as zone four. Mother and pups could lie down for suckling anywhere in the arena. Stimuli were broadcast from the loudspeaker opposite to the animals' position.

Figure 3

Responses of two-pup (N = 13) and four-pup (N = 15) mothers; (a) frequency to abandon the suckling pups, and (b) latency to abandon the suckling pups (10 sec intervals) during playback of another pup's calls (experiment 1). Each boxplot depicts median with inter-quartile range; whiskers extend to max. 1.5 times the inter-quartile range, outliers are shown as circles.

Figure 4

Responses of two-pup (N = 11) and four-pup litter (N = 11) mothers; (a) intervals spent in zone 4 (closest to the loudspeaker) and (b) intervals with vocalizations during playback of unfamiliar pup calls on day 8 and day 20 of lactation (experiment 2). Each box plot depicts median with inter-quartile range; whiskers extend to max. 1.5 times the inter-quartile range, outliers are shown as circles.