Mate choice in kaki (black stilts) : Does this highly managed and endangered species avoid inbreeding? : A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Science with Honours at Lincoln University

Abstract

In order to maximise individual fitness, animals would be expected to pair with a mate of the highest possible quality. One measure of mate quality is relatedness, or genetic similarity. Choosing an unrelated, genetically dissimilar mate enriches the genetic resources of the offspring and reduces the chances that detrimental recessive alleles will be brought into homozygosity, causing inbreeding depression. In order to avoid mating with close kin, it is necessary for animals to be able to recognise kin. The mechanisms suggested for kin recognition include learning the characteristics of kin by association with them, or learning a kin template, which other individuals are judged against. In small populations of endangered species, animals may be left with little choice of mates and as a result may be forced to breed with close relatives. One of the threats faced by small populations of endangered New Zealand birds, such as the kaki (Himantopus novaezelandiae), is that inbreeding will be detrimental to the population, reducing reproductive success or survival, or the ability of the population to adapt to environmental challenges. Kaki are a critically endangered endemic wader reduced to one population in the Mackenzie Basin. The population has been actively managed for the past 20 years, using a variety of management techniques. Since 1993 multiple clutching has been combined with captive rearing and pulse releases of kaki and dark hybrids. The practise of multiple clutching means that not all siblings from a season are raised together, a situation that does not occur naturally as kaki usually only lay a second clutch if the first fails. In addition, some clutches are intermingled in captivity, so that some kaki are raised with unrelated birds. If kaki learn to recognise close siblings by association with them, the practise of multiple clutching presents kaki with siblings that they will assume to be unrelated and clutch intermingling presents kaki with unrelated birds they will assume are related. Management therefore has the potential to increase inbreeding, depending on the kin recognition mechanisms used by kaki. By comparing the inbreeding levels in pairs involving released birds and wild-hatched birds, this study shows that management does not currently appear to be causing a high level of inbreeding. The tendency (although not statistically significant; P= 0.1597) for released birds to associate preferentially with siblings with whom they have been raised indicates that kin are probably learned primarily by association. Further work on kin recognition mechanisms in kaki is recommended to investigate the possibility that multiple clutching and clutch mixing will result in increased inbreeding and the relationship bern,een breeding pairs should be monitored to determine whether increased inbreeding occurs. Possible inbreeding can be minimised by aviary management and releasing siblings that have been raised separately into different sub-populations, although this may conflict with other management aims.

A short-term increase in inbreeding between full siblings may be justifiable to rapidly increase the population size. A larger population will then result in a reduced number of clutches from each pair being raised due to finite aviary space. Eventually the population should become large enough to eliminate the need for multiple clutching, and mating between full siblings will cease to be an issue. A short-term increase in sibling matings is therefore tolerable if it results in a long-term recovery of the species.