The Importance of Different Paternity Guards in the Polygynandrous Penduline Tit (Remiz Pendulinus)

It is well documented that extra-pair copulations are a strategy by which males can increase their reproductive success and females may obtain genetic benefits. Whereas in monogamous species extra-pair copulations are the only way for both sexes to increase their reproductive success, in polygamous systems both partners can benefit from mating with several individuals. Here we examine the intensity of sperm competition and the rate of extra-pair fertilizations in relation to male anti-cuckoldry tactics in a small passerine, the polygynandrous penduline tit (Remiz pendulinus), where both sexes have the opportunity to become polygamous. The results revealed rather low rates of extra-pair paternity for this species: 6.9% (14 out of 201) of young being sired by an extra-pair male. Males build elaborate nests to attract females and because of this high initial investment, one would expect males to evolve anti-cuckoldry tactics to ensure paternity. However, male mate guarding intensity as well as within-pair copulation frequency were rather low in comparison to other polygynandrous species, and hence both strategies are unlikely to ensure paternity. In fact our results show that those males which deserted their females early in their fertile cycle (already before the second egg is laid) did not lose paternity, whereas those males which tended to guard their females throughout their whole fertile period were more likely to be cuckolded. Thus, although no obvious anti-cuckoldry tactics exist in this species, extra-pair paternity is very low. This indicates a tendency in females to cooperate with their pair-males rather than seek extra-pair copulations.

Timing and Use of Paternity Guards By Male Chaffinches

I studied the relative timing and extent to which male chaffinches used two alternative paternity guards, frequent copulation and mate guarding by close following. Males guarded their mates strongly, and guarding peaked in intensity on day -2 relative to laying. Male mate guarding intensity varied predictably with the value of the female to the male in three ways: (a) guarding intensity increased from day to day as laying approached, as does the risk of a single EPC fertilizing an egg. (b) Males reduced their level of guarding when their females laid the penultimate egg of the clutch and were therefore no longer fertile. (c) The diurnal pattern of guarding varied with respect to whether laying had begun, which might represent a male response to an 'insemination window', when sperm would be less likely to fertilize an egg. Males also copulated frequently with their mates, with a peak rate of 4.4 copulation attempts per hour on day -3 relative to laying, with an estimated total of 207 copulation attempts (83 successful) per clutch. The peak in copulation frequency occurred earlier than the peak in mate guarding intensity. Males did not show any behavioural response to an increased risk of extra-pair copulations, assessed by the proportion of neighbouring males that were free to seek extra-pair copulations. I propose that in chaffinches frequent copulation is a relatively 'low-cost, high-risk' paternity assurance mechanism compared to mate guarding, and that the mechanism males employ depends upon the amount of information that males have about whether the female is going to lay, which represents the value of the female to the male. Fine-tuning of male behavioural mechanisms with the female value as a resource provides good evidence that the mechanisms are adaptations to sperm competition.