The roles of aridification and sea level changes in the diversification and persistence of freshwater fish lineages

Abstract

20While the influence of Pleistocene climatic changes on divergence and speciation 21 has been well-documented across the globe, complex spatial interactions between 22 hydrology and eustatics over longer timeframes may also determine species 23 evolutionary trajectories. Within the Australian continent, glacial cycles were not 24 associated with changes in ice cover and instead largely resulted in fluctuations from 25 moist to arid conditions across the landscape. Here, we investigate the role of 26 hydrological and coastal topographic changes brought about by Plio-Pleistocene 27 climatic changes on the biogeographic history of a small Australian freshwater fish, 28 the southern pygmy perch Nannoperca australis. Using 7,958 ddRAD-seq (double 29 digest restriction-site associated DNA) loci and 45,104 filtered SNPs, we combined 30 phylogenetic, coalescent and species distribution analyses to investigate the relative 31 roles of aridification, sea level and tectonics and their associated biogeographic 32 changes across southeast Australia. Sea-level changes since the Pliocene and 33 reduction or disappearance of large waterbodies throughout the Pleistocene were 34 determining factors in strong divergence across the clade, including the initial 35 formation and maintenance of a cryptic species, N. 'flindersi'. Isolated climatic 36 refugia and fragmentation due to lack of connected waterways maintained the 37 identity and divergence of inter-and intraspecific lineages. Our historical findings 38 suggest that predicted increases in aridification and sea level due to anthropogenic 39 climate change might result in markedly different demographic impacts, both 40 spatially and across different landscape types. 41 42

Variation in intraspecific demography drives localised concordance but species-wide discordance in responses to Plio-Pleistocene climatic change

“…This disjunction was attributed to potential historical connections from Mount Emu Creek into more western populations [35], although short branch lengths and low genetic diversity across the species may also indicate incomplete lineage sorting as a factor [63]. For both species, we denote two major clades: one of Murray-Darling Basin populations and another of coastal populations in N. australis, as suggested elsewhere [43], and two clades each containing two previously identified ESUs in N. obscura [37].…”

“…The temperate zone of southeast Australia has undergone significant environmental change since the Pliocene, owing to a combination of continent-wide aridification [24], eustatic changes [28] and major hydrological rearrangements [62]. These various aspects likely had significant impacts on the persistence and connectivity of freshwater lineages across the region [43]. This was supported by the high level of phylogenetic structure within N. australis, and the inferred migration pathways that correspond well to those previously suggested through ancient hydrological conduits [62].…”

“…The distribution of both species spans the southwest Victoria biogeographic province and the lower reaches of the Murray-Darling Basin [31]. Nannoperca australis is more widely distributed and is also found across eastern Victorian drainages, northern Tasmania and the upper reaches of the southern Murray-Darling Basin [43].…”

Historical biogeography and phylogeography ofIndoplanorbis exustus

“…Hence, it is highly likely that even older events might have affected the stem lineages in similar fashion and brought about the speciation events. Aridification is a known driver of allopatric separation in freshwater organisms (Beheregaray et al, 2017; Buckley et al, n.d.). In the Indian subcontinent aridification-driven allopatric speciation was documented in Ichthyophid caecilians (Gower et al, 2016).…”

“…which is dependent on freshwater sources which were likely to have depleted during the aridification cycles. A lot of freshwater species groups exhibit such patterns in response to the Pleistocene glaciation driven aridification events (Bagley et al, 2013; Buckley et al, n.d. ; Guzik et al, 2012; Klunzinger Manuel Lopes-Lima Andre Gomes-dos-Santos Elsa Froufe A J Lymbery L Kirkendale, n.d.…”