Implications of mate choice for the management of small populations : experimental studies using the guppy (Poecilia reticulata) as a model species
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- Institutt for biologi 
This thesis aims to investigate the implication of mate choice for individual fitness in small populations. Specifically I address Allee effects, inbreeding and outbreeding by using the guppy (Poecilia reticulata) as a model organism. Human activities during the last century have exerted major impact on habitats, species and populations. Many species have gone extinct and many more are highly endangered. Concern has been raised that we are in a phase of mass extinction which, without proper conservational action, could surpass any of the mass extinctions of the prehistoric past. Of particular concern is the habitat loss and overexploitation of species and populations which results in a negative population growth rate. Small populations face threats like inbreeding which could give inbreeding depression in offspring, and also of negative effects due to the reduced possibility of interactions among individuals. These last effects are termed Allee effects and include all effects that exert a negative influence on per capita growth rate with diminishing population sizes or densities. Several mechanisms have been proposed as being responsible for such a reduced growth rate with reduced population size, but the most sited is perhaps the difficult task of finding a partner in the right reproductive stage in small populations. A conservation action used as a means to rescue threatened populations from extinction is the translocation of individuals for the supplementation of populations both in and ex situ. Furthermore, society is encouraging the movement of goods and persons which implies that also living animals and plants, in increasing numbers, cross borders and habitats. Both deliberate translocations and accidental introductions may result in interactions among individuals of genetically divergent origin. Crosses between such individuals could result in outbreeding depression in offspring. In this thesis, four specific questions were raised: (1) Do limitations in the opportunity for mate choice due to small population size affect various individual fitness components of mothers and offspring? (2) Does time together with a randomly assigned male influence a female’s willingness to reproduce? (3) Do individuals have the ability to recognize and avoid close kin as mating partners? And finally, (4) do individuals have an innate ability to recognize and avoid partners of differing phenotype and do offspring of such crosses experience signs of outbreeding depression? These studies show that; (1) female guppies who were assigned a random partner had lower fitness than females who could choose among several potential partners. (2) Female guppies were, however, under a no-choice regime, able to compensate by investing more in the reproduction when costs of searching for better partners were high. On the other hand, (3) there were no signs of female guppies having the ability to recognize and avoid kin, but (4) there was a trend for a female preference against males from a differing phenotype, and such crosses resulted in a decrease in female fertility. Thus, in the management of endangered natural populations, attempts should be made to keep population size large enough for individuals to be able to choose among several potential partners. In captive breeding programmes, giving individuals a choice of partner among several individuals of an intermediate genetic distance (optimal outbreeding) and thereby preventing the possibility of inbreeding and outbreeding, may give a positive individual fitness effect and a higher success of ex situ management of species.