Life History and Reproductive Variation in the Spotted Skink, Niveoscincus Ocellatus
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Life History and Reproductive V ar ation in the Spotted S .. ink, Niveoscincus ocellatu_s (Gray 1845) T by Erik Wapstra BSc. (Hons) Life history variation · Niveoscincus ocella.tus Erik Wapstra "\ Declaration: This thesis contains no material which has been previously accepted for a degree or diploma by the University or any other institution, except by way of background information and duly acknowledged in the Thesis, and to the best of my knowledge and belief no material previously published or written by another person except where due acknowledgment is made in the text of the thesis. signed:~ , date: 'J-,.'3/;... /qg life history variation in Niveoscincus ocellatus Erik Wapstra This thesis may be made available for loan and limited copying in accordance with the Copyright Act 1968. Life history variation in Niveoscincus ocellatus Erik Wapstra Abstract Life history and reproductive variation in the spotted skink, Niveoscincus ocellatus The spotted skink, Niveoscincus ocellatus is a widely distributed small to medium size skink (3-12 g) which occurs throughout eastern and central Tasmania in a variety of climatic regimes. This thesis provides the first major ecological study of this species and describes in detail the life history and reproductive characteristics of two populations living at the climatic extremes of the species' distribution: a site on the Central Plateau represented the cold extreme and a site at Orford on the east coast represented the warm extreme. Niveoscincus ocellatus is a viviparous species that reproduces annually across its range. It shows an asynchronous gonadal cycle, with maximum male gonadal development in late summer and mating from April to June and August to September. Vitellogenesis occurs predominantly in autumn and continues through winter with ovulation in spring (September to October). Parturition occurs in January in the temperate Orford population, and in February in the subalpine Central Plateau population. In addition to minor variations in the timing of reproductive events between years at each site, N. ocellatus shows a degree of flexibility in the timing of reproductive events between sites. Ovulation and parturition occur approximately one month later at the Central Plateau, but there is little difference in the length of the gestation period between sites. An ability to show flexibility in the timing of reproductive events is undoubtedly responsible, in part, for the widespread distribution of Niveoscincus ocellatus in a range of climatic conditions. Niveoscincus ocellatus displays considerable geographic variation in life history traits. Maturity is delayed at the Central Plateau (3 years) Life history variation in Niveoscincus ocellatus Erik W apstra compared to Orford (2 years). As a result, indiv~duals from the Central Plateau mature at a large size and have a larger maximum size. Associated with their larger size and delayed maturity, Central Plateau females produce larger (mass and number of young) clutches than those from Orford. There is no trade-off between clutch size and size of offspring between populations, and females from the Central Plateau produce more (size adjusted) and larger offspring than females from Orforct. Through a series of experiments I show that life history traits of N. ocellatus are phenotypically plastic, and that observed differences in life history traits between sites, and annually within sites, may be explained, at least in part, by phenotypic responses to environmental variables. For example, growth rate of juveniles is positively correlated to basking opportunities in the laboratory and to thermal conditions in field enclosures, but is not influenced by any underlying genetic differences between populations. Offspring growth rate and phenotype are also influenced by other proximate factors, including the basking behaviour of their mothers prior to parturition in the laboratory. Phenotypically plastic responses allow a flexible approach to life history and reproductive strategies and are of adaptive significance to species such as N. ocellatus that occupy a wide geographic and/ or climatic range. Life history variation in Niveoscincus ocellatus Erik W apstra Acknowledgments: I thank all the people that assisted me with this project, especially the academics and staff of the Department of Zoology, University of Tasmania. I would especially like to thank: Associate Professor Roy Swain, my supervisor, for encouraging my interest in herpetology, for his advice in designing the study and his support throughout the entire study including the preparation of this thesis. I would also like to specifically thank other members of the Herpetology group for their help, advice and support throughout the study. In particular I would like to thank Dr Sue Jones for her assistance and guidance during the course of this study. I am particularly grateful to Ashley Edwards for her support during the project, and the assistance she willingly supplied in various capacities, including in the Niveoscincus ocellatus "nursery" during several Christmas holidays. Dr Mats Olsson for many discussions on various subjects, herpetological and other, and for stimulating my further research interest in herpetology. More specifically, Mats provided valuable advice on the design of the investigation into juvenile growth rate and kindly provided facilities. This project could not have been carried out without the help of numerous field assistants and those who helped in rearing juveniles; Julianne O'Reilly, Kevin O'Reilly, Lollo Olsson, Mark Wapstra, Lorilee Yeates, Natasha Beveridge, Jane Melville, Colin McCoull, Adrian Smeilley, Ashley Edwards, Hans and Annie Wapstra, Sue Jones, Karen Bell, Ellen Bennett, Fiona Reardon, Jon Kudelka, Katherine Janney, Darren Sheen, Tamara Kincade, and Angus Sinclair (and sorry to those that I may have missed). Simon Hudson provided advice and references on the technique of skeletochronology and provided valuable assistance in "reading" the bones. The skeletochronology was carried out with the assistance of a grant from the WV Scott Bequest Fund and Julianne O'Reilly assisted in the preparation of samples and interpretation of results. Wayne Kelly provided specific equipment and reagents and advice on histology techniques. Life history variation in Niveoscincus ocellatus Erik W apstra Jane Melville designed the lizard racetrack I used to sprint lizards and Kit Williams constructed it. Kit also designed and constructed data loggers used at field sites. Dr. Mark Hindell and Associate Professor Alastair Richardson ·offered statistical advice. This work was carried out with the permission of Parks and Wildlife (permit numbers 95109, 95363. 96190) for work carried out in the Central Plateau World Heritage Area and was assisted by grants from the Zoology Department, Peter Rankin Trust Fund, Department of Park and Wildlife (World Heritage Fauna and Flora Grants Scheme) and the WV Scott Bequest Fund for animal research. The work on Mt Wellington (particularly the construction of the cages for growth rate experiments) was carried out by permit issued to Mats Olsson (Permit number 16/95). The cages used for growth rate analyses on Mt Wellington and Proctors Rd were supplied by Mats Olsson and Rick Shine. And finally I would like to thank those people who helped me survive the whole damn thing. Hans and Annie, Di and Al, Mats and Lollo, Katherine and Darren, Pas and Anna, Mark and Lorilee, Kevin and Helen and Ashley. They all provided support in many ways; encouragement, free feeds, advice and most importantly the reassurance that they believed in it too. In particular I would like to thank Jon Kudelka who dragged me "unwillingly" to the golf course to keep me sane and clear the brain during the thesis write-up. And finally to Julianne who was there in the beginning, then left me for three months to pursue her dreams but returned at the end to help me finish mine. Words cannot express how important her support, reassurance and love were to me during the stressful times, but I hope it was all worth it. Life history variation in Niveoscincus ocellatus Erik W apstra Contents Chapter 1 General Introduction 1 1.1 General overview 1 1.2 Life history theory 3 1.3 Variation in lizard life history traits 5 1.3.1 Intraspecific variation in life history traits of lizards 9 1.3.2 Approaches to studying life history variation 10 1.3.3 Biases in lizard life history studies 13 1.4 Australian lizards 14 1.5 Tasmanian reptiles 15 1.5.1 The genus Niveoscincus 19 1.5.2 Niveoscincus ocellatus 21 Chapter 2 Study sites 25 2.1 Location of study sites 25 2.2. D~scription of study sites 25 2.2.1 Orford study site 25 2.2.2 Central Plateau study site 27 2.3 Comparison of climatic conditions 31 2.3.1 Temperature profiles 31 2.3.2 Precipitation levels and cloud cover 35 2.4 Lizard capture and handling 38 Chapter3 Reproductive cycles in Niveoscincus ocellatus 40 3.1 Introduction 40 3.2 Methods 44 3.2.1 Lizard collection 44 3.2.2 Lizard autopsy 44 3.2.3 Hormone assays 46 3.2.4 Statistical analyses 46 3.3 Results 46 3.3.1 The female reproductive cycle 46 3.3.2 The male reproductive cycle 52 3.3.3 Annual variation in abdominal fat bodies 58 Life history variation in Niveoscincus ocellatus Erik W apstra 3.4 Discussion 61 3.4.1 Geographic and annual variation in the reproductive cycle 61 3.4.2 Male and female gonadal cycles 67 3.4.3 Annual variation in abdominal fat body weights 72 Chapter4 Geographic and annual variation in reproductive output in Niveoscincus ocellatus 75 4.1 Introduction