Erica Todd
I am a molecular biologist interested in ecological and evolutionary questions that can be addressed with genetic and genomic approaches. My current work in the Gemmell Lab at the University of Otago explores the molecular basis of sex reversal in sequentially hermaphroditic fishes. Using state-of-the-art gene expression analyses and comparative genomic approaches, we aim to identify both the primary trigger and subsequent genetic cascade that results in female to male sex reversal in protogynous wrasses. For my PhD, I investigated how climatic and landscape processes have shaped current patterns of freshwater biodiversity, working with Australian freshwater turtles within a population genetic and phylogenetic framework. I also have past research experience and a continued interest in mating system biology.
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not yet well understood. Australia’s eastern coastal margin provides an ideal
setting for examining the relative influence of landscape development, sea level
fluctuation, and cyclic climatic aridity on the evolution of freshwater biodiversity.
We examined the impact of climatic oscillations and physical biogeographic
barriers on the evolutionary history of the wide-ranging Krefft’s river turtle
(Emydura macquarii krefftii), using range-wide sampling (649 individuals representing
18 locations across 11 drainages) and analysis of mitochondrial
sequences (~1.3-kb control region and ND4) and nuclear microsatellites (12
polymorphic loci). A range of phylogeographic (haplotype networks, molecular
dating), demographic (neutrality tests, mismatch distributions), and population
genetic analyses (pairwise FST, analysis of molecular variance, Bayesian clustering
analysis) were implemented to differentiate between competing demographic
(local persistence vs. range expansion) and biogeographic (arid corridor
vs. drainage divide) scenarios. Genetic data reveal population genetic structure
in Krefft’s river turtles primarily reflects isolation across drainage divides. Striking
north-south regional divergence (2.2% ND4 p-distance; c. 4.73 Ma, 95%
higher posterior density (HPD) 2.08–8.16 Ma) was consistent with long-term
isolation across a major drainage divide, not an adjacent arid corridor. Ancient
divergence among regional lineages implies persistence of northern Krefft’s populations
despite the recurrent phases of severe local aridity, but with very low
contemporary genetic diversity. Stable demography and high levels of genetic
diversity are inferred for southern populations, where aridity was less extreme.
Range-wide genetic structure in Krefft’s river turtles reflects contemporary and
historical drainage architecture, although regional differences in the extent of
Plio–Pleistocene climatic aridity may be reflected in current levels of genetic
diversity.
Location: Northern and Eastern Australia and New Guinea.
Methods: Phylogenetic relationships were inferred for all extant species of Elseya plus two putative species not yet described, from molecular data comprising mitochondrial (control region, ND4 and 16S) and nuclear (R35 intron) loci, using maximum likelihood and Bayesian inference methods. A calibrated relaxed molecular clock was used to estimate divergence times. Intraspecific lineage structure and diversity were investigated using control region sequences analysed via haplotype networks and AMOVA.
Results: Elseya species exhibited a striking degree of local endemism across their range. Four divergent clades corresponded geographically to New Guinea, southern New Guinea plus northern Australia, north-eastern Australia, and south-eastern Australia. These arose in the late Miocene (c. 5.82–9.7 Ma),
diversifying further in the early Pleistocene (c. 2.2–2.43 Ma and 1.36–1.66 Ma), coincident with major phases of aridity and climatic upheaval.
Main conclusions: The genus Elseya has a long vicariant history in Australia, closely tied to disconnection of fluvial habitat through landform evolution, sea-level rise and ongoing aridification. Our analysis paints a more complete picture of Australian freshwater biogeography, including evidence for periodic connectivity with New Guinea, important regional biogeographical barriers, and the location of potential freshwater refugia. Congruence with patterns
described for terrestrial groups implies a collective response of the Australian fauna to aridification."
not yet well understood. Australia’s eastern coastal margin provides an ideal
setting for examining the relative influence of landscape development, sea level
fluctuation, and cyclic climatic aridity on the evolution of freshwater biodiversity.
We examined the impact of climatic oscillations and physical biogeographic
barriers on the evolutionary history of the wide-ranging Krefft’s river turtle
(Emydura macquarii krefftii), using range-wide sampling (649 individuals representing
18 locations across 11 drainages) and analysis of mitochondrial
sequences (~1.3-kb control region and ND4) and nuclear microsatellites (12
polymorphic loci). A range of phylogeographic (haplotype networks, molecular
dating), demographic (neutrality tests, mismatch distributions), and population
genetic analyses (pairwise FST, analysis of molecular variance, Bayesian clustering
analysis) were implemented to differentiate between competing demographic
(local persistence vs. range expansion) and biogeographic (arid corridor
vs. drainage divide) scenarios. Genetic data reveal population genetic structure
in Krefft’s river turtles primarily reflects isolation across drainage divides. Striking
north-south regional divergence (2.2% ND4 p-distance; c. 4.73 Ma, 95%
higher posterior density (HPD) 2.08–8.16 Ma) was consistent with long-term
isolation across a major drainage divide, not an adjacent arid corridor. Ancient
divergence among regional lineages implies persistence of northern Krefft’s populations
despite the recurrent phases of severe local aridity, but with very low
contemporary genetic diversity. Stable demography and high levels of genetic
diversity are inferred for southern populations, where aridity was less extreme.
Range-wide genetic structure in Krefft’s river turtles reflects contemporary and
historical drainage architecture, although regional differences in the extent of
Plio–Pleistocene climatic aridity may be reflected in current levels of genetic
diversity.
Location: Northern and Eastern Australia and New Guinea.
Methods: Phylogenetic relationships were inferred for all extant species of Elseya plus two putative species not yet described, from molecular data comprising mitochondrial (control region, ND4 and 16S) and nuclear (R35 intron) loci, using maximum likelihood and Bayesian inference methods. A calibrated relaxed molecular clock was used to estimate divergence times. Intraspecific lineage structure and diversity were investigated using control region sequences analysed via haplotype networks and AMOVA.
Results: Elseya species exhibited a striking degree of local endemism across their range. Four divergent clades corresponded geographically to New Guinea, southern New Guinea plus northern Australia, north-eastern Australia, and south-eastern Australia. These arose in the late Miocene (c. 5.82–9.7 Ma),
diversifying further in the early Pleistocene (c. 2.2–2.43 Ma and 1.36–1.66 Ma), coincident with major phases of aridity and climatic upheaval.
Main conclusions: The genus Elseya has a long vicariant history in Australia, closely tied to disconnection of fluvial habitat through landform evolution, sea-level rise and ongoing aridification. Our analysis paints a more complete picture of Australian freshwater biogeography, including evidence for periodic connectivity with New Guinea, important regional biogeographical barriers, and the location of potential freshwater refugia. Congruence with patterns
described for terrestrial groups implies a collective response of the Australian fauna to aridification."