DR SIMON GRIFFITH
Focusing primarily on wild and captive populations of passerine birds we use a combination of traditional approaches and new techniques (e.g. optical spectrometry, transponder tagging, PCR-based molecular tools) to focus on a number of areas in the field of evolutionary ecology.
1) Sexual signalling and coloration
From the classic example of the peacock to the widely under-rated house sparrow, birds have evolved a profusion of colourful plumages primarily for the purposes of attracting mates and maximising reproductive success.
What processes drive the diversity of ornamental colour found across the birds? Why are so many different colours used? One idea is that various colours signal subtly different things to receivers and that, for example, a female might learn about the diet of a male from a yellow plumage (based on carotenoid pigments), and his dominance status from a black plumage (based on melanin pigments). To address these questions we need to investigate sources of variation in the expression of different types of colour in the context of sexual selection. We are using optical spectrometry to make quantitative measurements of reflectance spectra; investigating the quantitative genetics of colour based sexual ornaments in the wild; conducting mate choice trials; using microsatellite genotyping to relate actual reproductive success to variation in colour expression, and conducting experiments to determine the extent to which condition and the environment are responsible for variation in the colour produced by individuals. This work is being conducted on the blue tit,
Zebra finch, and Gouldian finch.
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2) The evolution of mating systems
Over ninety percent of avian species form socially monogamous bonds, with a male and female pairing for at least the duration of the breeding season. In the Victorian era birds were upheld as examples of fidelity and virtue. In fact, although it had been predicted in the 1970's it was only in the late 1980's that molecular techniques began to reveal the true picture of widespread genetic polyandry. Both males and females participate in extra-pair copulations in the majority of species and in passerine birds on average 13% of all offspring are fathered by an extra-pair male and therefore not the one who invests so much in their care.
However, even within the passerine birds there is great variation in the level of extra-pair paternity across species. Silvereyes (breeding on Heron Island, Queensland), remain completely faithful to one another and invest a lot of time maintaining a very strong social bond with their partners. In the superb fairy wren nearly 80% of offspring are fathered outside the pair bond. How can we explain this diversity?
The study of extra-pair paternity in birds has largely been done by proxy through post-hoc molecular screening of families. As a result, despite over fifteen years research on over 100 species we still know very little about the function of extra-pair paternity and even whether it is driven primarily by females or males.
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To date there have been less than a handful of experimental studies investigating the source of variation in levels of extra-pair paternity. We are using comparative studies in addition to experimental work in wild populations (with microsatellite genotyping) in four species of passerine bird (and a live-bearing fish species) to investigate this area.
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3) Direct benefits and the evolution of parenting strategies
Almost all birds exhibit a relatively high level of parental care in contrast with other animals. For example, whilst in mammals males very rarely make any post-fertilisation contribution to reproduction, in most birds males and females bring a similar amount of food to their chicks. Why is parental care so important in birds compared with other taxa? What are the consequences to the evolution of life-history and the process of sexual selection of such high levels of direct parental effects on offspring? We are using comparative studies and experimental manipulation of direct benefits in wild and aviary based populations to explore questions in this area.
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A more extreme form of parental care occurs in cooperatively breeding birds in which direct benefits are also accrued from helpers at the nest - individuals who forego their own reproduction and assist in rearing offspring belonging to other individuals. In the ecologically harsh arid zone of Australia, cooperative breeders actually out-number non-cooperative species, one of the few places in the world where the avian community contains such a high level of cooperative breeders. Why? In addition to addressing this central question we are conducting a highly manipulative study of the importance of direct benefits and maternal effects in such systems.
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4) Sexual selection and population processes
Sexual selection is a fundamental evolutionary process and as such would be expected to drive the dynamics of populations. For example, very strong sexual selection will affect the effective population size. However it is clearly a two way process and there is increasing evidence that the dynamics of a population will also affect the operation of sexual selection. For example, classically, the operational sex ratio should affect the level of competition between individuals of the same sex within a population. In a similar way, the levels of genetic variation within populations are predicted to affect levels of polyandry and ultimately sexual selection.
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Again the comparative method will be used to explore this new direction in sexual selection in addition to population level experiments in the wild (with birds) and captivity (other taxa). This area has particular relevance to the field of conservation genetics as threatened populations are often highly fragmented, genetically impoverished and subject to greater stochastic dynamics.
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COLLABORATORS
Postdoctoral Fellows based in my lab
