Male sexual rest affects litter sex ratio of newborn Norway rats
Article Abstract:
The pairing of female Rattus norvegicus with males copulated to satiety three weeks previously or recently copulated males shows that litters sired by rested males have higher sex ratios. The sex ratio bias exists only in litters conceived during a cycling estrus and is negatively associated with the time of mating completion. A relationship between sex ratio and rest-influenced mating behavior exists only in litters with fewer pups at birth than at implantation. The bias is probably due to adaptive litter decrease as post-implantation losses occur when uterine horns are crowded.
Publication Name: Animal Behaviour
Subject: Zoology and wildlife conservation
ISSN: 0003-3472
Year: 1996
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Sex ratios are multiply determined: a reply to James
Article Abstract:
James argues that post-implantation loss may not be the reason for sex-ratio biases in rats. He argues, instead, that maternal hormone levels can influence whether ovum are likely to be fertilised by sperm carrying Y chromosomes. Such a mechanism prior to conception could occur but there may be other mechanisms affecting sex ratios following conception. There is a great deal of theory relating to sex ratio biases but less correlation and almost no explanation of mechanisms relating to such biases.
Publication Name: Animal Behaviour
Subject: Zoology and wildlife conservation
ISSN: 0003-3472
Year: 1997
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Can microhabitat selection or differences in 'catchability' explain male-biased sex ratios in overwintering populations of monarch butterflies?
Article Abstract:
A study of monarch butterflies reveals that their sex ratio is male-biased throughout the overwintering season due to female-biased mortality during summer and autumn migration. Monarch butterflies found in California sites have a male-biased sex ratio. Male monarchs can be distinguished from females by their higher speed of movement and a patch of black scales on their hind wings.
Publication Name: Animal Behaviour
Subject: Zoology and wildlife conservation
ISSN: 0003-3472
Year: 1993
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