Fish in the desert: behaviour, genes, and persistence in a changing world

2017-02-23T23:57:43Z (GMT) by Mossop, Krystina
Organisms inhabit a variable world. Indeed, the spectacular variation exhibited by natural environments has long captured the attention of biologists, and raises a multitude of questions about how individuals and populations persist when their habitats vary or change. In this thesis, I have used an overarching conceptual framework of different scales of variation – both spatial and temporal – to guide three research foci (connectivity, refugia, and conservation) aimed at better understanding the ways in which animals interact with environmental variation. Australia’s aridification forms a dynamic setting in which the continent’s interior shifted from the warm, wet climates of 20 million years ago, to its current, arid state; vast, dry places in which freshwater is rare and fragmented. I have capitalised on the modern and historic variation captured in this iconic landscape to gain new insights into the evolution and persistence of part of its desert-dwelling fish fauna: the Chlamydogobius gobies. In taking a molecular perspective (via phylogenetic and phylogeographic investigations; Chapters 2 and 3 respectively), my work has provided a perspective on how arid connectivity underpins fish diversification and persistence. I begin by exploring the origin of the group; a highly resolved molecular phylogeny enabled me to infer evolutionary relationships, speciation patterns, and the environmental drivers that led to diversification of these small, benthic fishes. I focus in on one part of that biogeographic range to explore the genetic structure and phylogeography of C. eremius populations in the artesian springs and ephemeral rivers surrounding the massive salt lake, Kati Thanda-Lake Eyre. There are recurring concepts in results at both coarse (e.g. regional, Chapter 2) and more local (Chapter 3) levels of variation. The existence of permanent water sources in the arid zone is unsurprisingly crucial to fish persistence: it has been a source both of persistence, and the generation of biodiversity. However, these findings also illustrate that species-specific traits (such as the ability to opportunistically exploit temporary hydrological connections) can override or delay the effect of potential terrestrial barriers to dispersal. I build on this context of connectivity and refuge by examining the behavioural responses of contemporary populations and individuals to variable conditions. Here, my experimental investigations of populations in the ecologically disparate habitats of permanent springs and temporary rivers found that despite a complex picture of ecological variation, key components of landscape heterogeneity – hydrological connectivity, and habitat “type” (permanent spring or temporary river) – did indeed predict the behavioural responses of fish, providing insights into how fish exploit diverse habitats (Chapter 4). Finally, at a finer, within-habitat level (Chapter 5), I discovered that individual C. eremius males in either a simple or complex habitat were able to adjust their behaviour with the visual environment, but that mating outcomes were robust to the variation. Overall, my thesis contributes to our understanding of arid zone biodiversity, evolution, and conservation. In a contemporary setting, the findings inform perspectives on connectivity, persistence, and management of threatened desert fishes in isolated relict habitats that are increasingly and urgently threatened by anthropogenic change.