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Accueil du site → Doctorat → Australie → Population genetics and mating system in the single remnant and translocated population of the endangered bridled nailtail wallaby, Onychogalea fraenata

University of Queensland (2005)

Population genetics and mating system in the single remnant and translocated population of the endangered bridled nailtail wallaby, Onychogalea fraenata

Sigg, Dominique Patricia

Titre : Population genetics and mating system in the single remnant and translocated population of the endangered bridled nailtail wallaby, Onychogalea fraenata

Auteur : Sigg, Dominique Patricia

Université de soutenance : University of Queensland. Integrative Biology

Grade : Doctor of Philosophy PhD 2005

Many species have suffered severe range contractions as a result of human impacts, and require careful management if they are to persist. An understanding of the ecology, population structure and mating system is important for the conservation of these endangered species. Translocation has become a widely used tool in the conservation of threatened species ; however, without proper planning and monitoring, many programmes end in failure. The bridled nailtail wallaby is one of the most endangered macropods in Australia, having suffered an extensive range contraction from the semi-arid region of eastern Australia to a single remnant population of 500 animals at Taunton National Park in Queensland. In 1996, a translocated population of bridled nailtail wallabies was established at Idalia National Park, on the western edge of the former range of this species. The aims of this study were to : 1) determine the factors underlying variation in reproductive success among animals released at Idalia ; 2) investigate the effects of a range decline on the genetic variation and population structure of the remnant population at Taunton ; 3) assess the impact of captive breeding and translocation on the genetic diversity and structure of the established population at Idalia ; and 4) investigate male and female mating strategies in this species. Chapter two investigated reproductive success among males released at Idalia National Park. The bridled nailtail wallaby is a sexually dimorphic, polygynous species and there is a large amount of variation in male reproductive success. Animals of different origin were released, including animals bred in captivity off the park, animals bred on-site in enclosures, and wild-caught animals from the remnant population that were moved directly to Idalia. There was significant variation in reproductive success among males released, but the origin of those animals did not explain this variation. Instead, large males were the most reproductively successful regardless of origin. Survival probability and release location were also important factors. This study highlighted the importance of considering mating system when choosing animals for translocation and suggests that, for polygynous species, a greater proportion of females and males of high breeding potential should be released. In Chapter three I investigated the genetic diversity and fine-scale genetic structure of the remnant population at Taunton. This last remaining population has been isolated for at least 60 years, corresponding to 30 generations for this species. Animals are patchily distributed in assemblages of different size that cover 10% of suitable habitat on the park. Genetic diversity was surprisingly high within the population remnant and this species showed one of the highest levels of heterozygosity and allelic diversity of any macropod. The three sub-populations of animals sampled over 10 km were significantly differentiated, and fine-scale spatial genetic structure was also observed within a continuous sub-population of animals covering just 750 ha. Females were more related to each other than expected from random, whereas males were less related to each other than expected. Fine-scale genetic structure was observed among females but not males, providing evidence for female philopatry and male-biased dispersal. I suggest that fine-scale population structure and restricted gene flow among females but not males may maintain genetic diversity in this remnant population. Chapter four assessed the effect of translocation of animals of different origin on genetic diversity in bridled nailtail wallabies. Both wild-caught and captive-bred animals were initially released, but subsequent releases consisted of captive-bred animals only. In this study, I compared genetic diversity of released animals to animals sampled in the remnant population. Heterozygosity did not differ between the remnant and translocated population, however allelic diversity was significantly reduced among all groups released. Animals bred in captivity were significantly differentiated from the source population, whereas animals moved directly from Taunton were not. Releasing more captive-bred animals into the population after the initial release resulted in a decline in overall heterozygosity and allelic diversity. This study highlights the importance of sourcing animals directly from remnant populations in order to maintain genetic diversity and minimize genetic drift between source and recipient populations. The bridled nailtail wallaby has a polygynous mating system and reproductive success is skewed toward large males. However unlike most polygynous, sexually dimorphic macropods, the bridled nailtail wallaby is highly solitary ; animals only associate to breed and males do not form stable dominance hierarchies. In Chapter five I investigated behavioural strategies used by males to secure matings, and mate choice among females. I found that males of different size adopted different mating strategies. Large males spent more time guarding females against other males and maintaining contact with them, whereas smaller males spent less time with guarded females in order to search for other females in oestrus. Females also preferred larger males and were more likely to engage in mate chases if there was a large number of males within the group.

Mots clés : population genetics • conservation • translocation • mating system • reproductive success • mammal


Page publiée le 5 mars 2006, mise à jour le 6 juillet 2017