Diana Fisher

Evolution of semelparity

A handful of animals (some arthropods and Australian marsupials) have iteroparous females- that reproduce repeatedly, but semelparous males- that inevitably die during or soon after mating. This ARC-funded project is using multi-species comparative tests, museum specimens and arthropod collections, behavioural ecology, population ecology methods, and quantitative modelling to test evolutionary explanations. Multiple projects are available on the causes and cnsequences of semelparity in animals and plants. Rob Salguero-Gomez at the University of Oxford, UK will be a co-supervisor

One aspect is Sexual selection in animals with male-only semelparity

An analysis in this paper https://www.pnas.org/doi/10.1073/pnas.1310691110 tested if semelparous marsupials have larger testes and longer mating duration than iteroparous marsupials in the same families. They did- this is evidence that intense post-mating male competition is a component of the evolution of life history in these taxa. All other animals with male-only semelparity are arthropods. This project would analyse species in Families of ants, bees, mantids and spiders that contain some species with male-only semelparity, to test if greater semelparity (fewer males surviving after mating) is associated with indices of higher male reproductive investment in sperm volume and mate guarding, that indicate intense sperm competition. This project would involve 1) measuring body parts of museum specimens (pedipalp size and body size) as well as specimens of insects and spiders that you collect in the field (pedipalp size, body size, testes size of mature males / spermatophore volume where available), 2) measuring body parts of digital images of insects and spiders from published sources, 3) using published data on testes size in mature males and the loss of body parts during mating, to calculate male investment in mating (testes size accounting for body size, proportion of body mass lost, time). The main analyses are phylogenetic regressions. This project is part of an ARC grant, there is a PhD student and a postdoc in my group working on other aspects of the evolution and implications of animal semelparity. There would be a co-supervisor who is a specialist in behavioural and evolutionary ecology of spiders and insects (at Macquarie University, Sydney).

A visual lure for small mammals- do Australian species use running wheels in the wild?

(Masters project, potentially part of a larger project on mammal detectability). Worldwide only two studies have been published on how wild animals are attracted to and use running wheels in nature, in the Netherlands and Paraguay (Meijer & Robbers 2014 http://dx.doi.org/10.1098/rspb.2014.0210 and Van Lunteren et al. 2021 https://doi.org/10.1007/s10211-020-00359-2). Small mammals were surprisingly enthusiastic in two environments in the Netherlands, but rarely used wheels in Paraguay. It was suggested that the lower interest in running wheels by wildlife in South America was because of the different taxonomic groups of rodents there, or the more remote environment. Running wheels in the wild have never been tested in Australia. There are reasons to suspect that wild Australian small mammals would respond to a wheel lure: Australian rodents are murids (like the Netherlands) and experience shows that dasyurids including antechinus and dunnarts very readily use wheels when temporarily in captivity. To attract small mammals to camera traps, running wheels would have advantages over scent lures such as peanut butter: the visual lure of a wheel does not degrade over time, whereas the strength of scent inevitably declines; food lures can attract larger non-target species that would could not use a mouse-sized running wheel, such as feral foxes; and a mammal using a running wheel can be positioned so that identifying features are visible to the camera and in focus. This project would test if running wheels are effective as lures for small mammals in Australia, if wheels and traditional peanut butter bait differ from unbaited cameras in effectiveness, and if these effects depend on habitat type and remoteness.

Identifying causes of initial bias to improve the Threatened Species Index

(Masters project) Overall Threatened Species Index (TSX) curves and individual time series and taxa show a glitch in the first two or three years- the curve drops or rises before it settles into a more consistent trajectory (https://tsx.org.au/tsx2024/?type=all&tgroup=All&group=All&subgroup=All&state=All&statusauth=Max&status=NT_VU_EN_CR&management=All&refyear=1990). This project would test the potential reasons for this.

These glitches might be due to a sampling bias artefact related to the choice of initial sampling site. Many studies have addressed spatial bias, such as surveying mainly near roads. Few studies have addressed bias that comes from sampling at certain times in the trajectory of a fluctuating population. Over-sampling of one phase of a fluctuating population (e.g. at a time and place of maximum abundance) is demographic sampling bias.

Demographic sampling bias comes from researchers typically choosing thriving populations to study (so that their projects are feasible, or because these are most likely to be detected). In these cases most short term studies will report declines, because fluctuating populations with stable long-term means tend to decline in the short term following a peak (this is 'regression to the mean'). Overestimated declines are also expected if researchers preferentially monitor populations in steady decline and ignore stable ones- this might also be likely in the TSX time series. However, regression to the mean implies that underestimates of decline will ensue if studies focus on recently-declined populations, as these are likely to be in a short term increase phase.

This project can use aggregated data to find which curves have which pattern, and understand why this initial glitch occurs. We might expect that single-species studies might be more likely to initially decline from a peak, and community studies that have not chosen a site based on single species abundance might not show this pattern, as the site was not chosen based on that species. Birds and mammals would be good data sets to test this.