title: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Animal Behaviour, University Bielefeld, P,O, Box 100 131, 33501 Bielefeld, Germany. melanie.kober@uni-bielefeld.de.
authors.forename: Melanie
authors.initials: M
authors.lastname: Kober
authors.forename: Fritz
authors.initials: F
authors.lastname: Trillmich
authors.forename: Marc
authors.initials: M
authors.lastname: Naguib
references.citation: Anim Behav. 1970 Feb;18(1):144-50
references.pmid: 5530113
references.citation: Psychosom Med. 1968 Sep-Oct;30(5):Suppl:576-607
references.pmid: 4303377
references.citation: Biol Reprod. 2003 Mar;68(3):929-36
references.pmid: 12604644
references.citation: Trends Ecol Evol. 1997 Jan;12(1):11-5
references.pmid: 21237955
references.citation: Physiol Zool. 1997 Sep-Oct;70(5):589-96
references.pmid: 9279926
references.citation: Psychoneuroendocrinology. 1988;13(1-2):189-212
references.pmid: 3287416
references.citation: Am Nat. 2006 Sep;168(3):412-20
references.pmid: 16947115
references.citation: Behav Processes. 2001 Sep 3;55(3):127-142
references.pmid: 11483351
references.citation: J Dairy Res. 1979 Nov;46(4):613-21
references.pmid: 536477
references.citation: J Endocrinol. 1984 Aug;102(2):251-6
references.pmid: 6747504
references.citation: Anim Behav. 1973 Feb;21(1):78-82
references.pmid: 4706768