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Optimal outbreeding : mate choice of mallards (Anas platyrhynchos) and consequences to breeding success Calogeros, Artemis Eva


This study was undertaken to determine if mallards (Anas platyrhynchos) use kin recognition during mate choice as a means to achieve optimal outbreeding and to examine the consequences of inbreeding on breeding success. Mallards hatched from eggs collected in the wild were raised and bred to produce ducklings that were either inbred (parents were sibs) or outbred (parents not sibs). Ducklings were raised in isolated subfamily groups so that when sexually mature, they could be tested for mate preference among 4 choices: 1) a sib that was a brood mate, 2) a sib that the subject had not seen before, 3) a first cousin not previously seen, 4) an unrelated individual not previously seen. The initial preference test was inconclusive. In the second mate choice test when the subject and the four choice objects were allowed to interact for 22 hours, neither inbred, outbred females, nor outbred males showed any consistent preference. Inbred males, however, significantly avoided the familiar sister. The results provided no strong support for mallards using kin recognition to achieve optimal outbreeding, but rather suggested kin recognition as a mechanism for severe inbreeding avoidance. Optimal outbreeding in mallards may be achieved via other mechanisms such as female natal site fidelity. Comparison of mate compatibility between pairs of siblings (inbred matings) and pairs of unrelated individuals (outbred matings) indicated that males paired with a sister performed significantly less pre-copulatory head-pumping and were significantly more aggressive to their mates than males paired with an unrelated female. Breeding success was examined by comparing the laying characteristics and fertility of these pairs and comparing the morphological measurements of the resulting ducklings. While fertility was not affected, there was a 50% reduction in hatchability of eggs from inbred matings. Inbred ducklings also had significantly lighter body mass and shorter extremities at days 15, 30 and 45 post-hatch compared to outbred ducklings. Although inbreeding depression was clearly evident after only one generation of full-sib mating, an occasional brother-sister mating may not seriously reduce the fitness of the population as a whole.

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