Authors: Arild Johnsen Kim L Carter Kaspar Delhey Jan T Lifjeld Raleigh J Robertson Bart Kempenaers
Publish Date: 2011/10/05
Volume: 66, Issue: 2, Pages: 181-190
Abstract
In birds the number of sperm trapped between the perivitelline membranes around the ovum is an estimate of sperm numbers present at the time and place of fertilisation in the female reproductive tract Sperm numbers may vary among species and between eggs in a clutch and can provide information about sperm utilisation and mechanisms of sperm competition Here we describe patterns of variation in sperm numbers through the egglaying sequence in three passerines in which extrapair paternity is common but copulation behaviour differs Sperm numbers showed no systematic change across the laying sequence in blue tits Cyanistes caeruleus but decreased significantly with laying order in bluethroat Luscinia svecica and tree swallow Tachycineta bicolor clutches This is consistent with observations that blue tits regularly copulate throughout the laying sequence while bluethroats stop mate guarding and tree swallows reduce their copulation frequency once the first egg is laid Nevertheless cases of a sudden increase in sperm numbers in clutches of bluethroats and tree swallows suggest that successful inseminations also occurred after laying started In blue tits and bluethroats sperm numbers were not higher on extrapair sired eggs than on eggs sired by the social male suggesting that extrapair copulations are not timed to the period of peak fertility for each egg More extrapair offspring originated from eggs laid early in the sequence in blue tits while there was no systematic bias in bluethroats Our results suggest that copulations during the laying sequence are predominantly performed by withinpair males in our study speciesWe thank Cheryl Bishop Frode Fossøy Karin Hieke Terje Laskemoen Anne Peters Thomas Petitguyot Angelika Poesel Agnes Tuerk Emmi Schlicht and Mihai Valcu for assistance in the field and Frode Fossøy for lab assistance We are grateful to RaphaelThomas Klumpp and Alfred Fojt from the Institute of Silviculture Vienna for providing access to their facilities to Hans Winkler from the Konrad Lorenz Institute for Comparative Ethology Vienna for logistical support to the staff at the Queen’s University Biological Station for facilities and logistical support and to Chris Eckert at Queens’ University for letting us use his microscopy laboratory BK designed the study KC and BK conducted the blue tit field work AJ KC KD JTL and BK conducted the bluethroat fieldwork KC RJR and BK conducted the tree swallow fieldwork KC and BK counted the sperm on the egg membranes KC conducted the blue tit paternity analysis AJ conducted the bluethroat paternity analysis AJ and BK analysed the data AJ wrote the paper in collaboration with all other coauthors We thank Jim Briskie and two anonymous reviewers for thoughtful comments on the manuscript The work was funded by the Max Planck Society the Norwegian research Council the Natural History Museum of the University of Oslo and the Natural Sciences and Engineering Research Council of Canada
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