Life in the “dead heart” of Australia: The geohistory of the Australian deserts and its impact on genetic diversity of arid zone lizards

Abstract

Aim The Australian deserts are home to a remarkable diversity of taxa that might appear to have evolved in the absence of topographic and physical barriers to dispersal. In fact this is a biogeographical illusion, as the dunefields of the modern arid zone obscure the fossil landscapes of the wet desert that existed for much of the Cenozoic. As the geohistory of Australia's arid zone is not widely understood by biologists, we review its geological development and contemporary landscapes in an accessible way, and describe eight biogeographical hypotheses centred on how geomorphology, evolutionary history and contemporary ecological factors interact to shape diversification patterns in the desert lowlands. Location Australia. Taxon Lizards. Methods We review the arid zone landscapes before and after the development of the vast dunefields. As lizards represent a significant component of genetic studies that sample widely across the arid biome, we focus on this taxonomic group to establish emerging patterns. Results Recent geological work suggests that the dunefields never formed extensive mobile landscapes such as in the Sahara, but rather were a mosaic of vegetated and stable dune surfaces with scattered bare, mobile patches. Large fluvial systems in the eastern arid zone during the Pleistocene also are at odds with the general perception of an arid landscape during this time. Incorporating this geohistorical insight, understanding where landscape heterogeneity is greatest within the arid zone, and where relative homogeneity might facilitate connectivity and gene flow, are at the heart of our biogeographic hypotheses. Main conclusions Patterns are emerging that reflect the underlying influence of geomorphological processes on the genetic structure of Australian desert taxa. Quantifying finer‐scale edaphic complexity across the arid zone, widespread genetic sampling from disparate taxonomic groups, and a more detailed understanding of species ecology and life history will greatly improve our understanding of the ecological and historical drivers of diversity gradients in the Australian deserts.

Geographic range size and speciation in honeyeaters

“…Among Australian continental vertebrates, including birds, patterns of vicariant speciation associated with changing climates in particular, but also landform evolution, have played a major role in species diversification [ 61 – 63 ]. Diversification patterns and their outcomes are similar among mammals, amphibians, and birds [ 64 ] and our findings for continental honeyeaters are congruent with these patterns (Fig.…”

Genetic variability and the ecology of geographic range: A test of the central‐marginal hypothesis in Australian scincid lizards

“…Also, the different biomes of Australia have experienced dynamic histories that might differentially affect patterns of genetic diversity. In particular, species endemic to the deserts likely experienced rapid population growth and range expansion as the deserts expanded in the late Miocene‐early Pliocene (Pepper & Keogh, 2021). We included biome as a factor by determining which biome the majority of an OTU's geographic range spanned (Olson et al, 2001).…”

Variation in intraspecific demography drives localised concordance but species-wide discordance in response to past climatic change

“…Despite intense inland aridification during glacial maxima, run-off in many southeast Australian rivers were likely much greater during the LGM [ 74 ]. These increased river flows have been attributed to seasonal snow melt of periglacial regions in the highlands and reduced vegetation cover, creating large rivers with enhanced run-off [ 31 , 74 ]. Colder conditions and strong flows may have facilitated the observed concordant expansion in populations at this time, with the steep decline in flows during the early Holocene (14–7 Kya) potentially contributing to their more recent contraction [ 75 ].…”

“…[ 28 , 29 ]). For example, intense inland aridification during the Miocene and Pliocene has been associated with major coastward contractions in mesic species [ 30 , 31 ], and rising post-glacial sea levels have driven the isolation of coastal and island populations of several terrestrial species (e.g., [ 27 , 32 , 33 ]).…”