Key Evolution Research Projects

Our scientists regularly publish in the high-impact science journals.

Below are examples of key research projects that have provided new insights and understanding in the field of evolution. 

Snail speciation

snail-speciation-small.jpg Species definition and delimitation is a non-trivial problem in evolutionary biology. This is especially true of fossil organisms, as only a subset of the modern taxonomic toolkit is applicable. This problem is acute when considering the continuity of past and present species, because species defined in the fossil record are not necessarily equivalent to species defined in the living fauna. Correctly assigned fossil species are critical for sensitive downstream analysis (e.g. diversification studies and molecular-clock calibration). The marine snail genus Alcithoe exemplifies many of the problems with species identification. The paucity of discriminatory characters, prevalence of morphological convergence between species and considerable variability within species, observed in Alcithoe are typical of a broad range of fossilised organisms. Using a synthesis of molecular and morphometric approaches we show that two taxa currently recognised as distinct are morphological variants of a single species with shallow geneology. Furthermore, we validate the fossil record for one of these morphotypes by finding a concordance between the palaeontological record and divergence time of the lineage inferred from an independently calibrated molecular-clock analysis. This work demonstrates the utility of living species represented in the fossil record as candidates for molecular-clock calibration, as the veracity of fossil species assignment can be more rigorously tested.

References

Hills SFK, Crampton JS, Trewick SA, Morgan-Richards M. (2012). DNA and morphology unite two species and 10 million year old fossils. PLoS ONE 7(12):e52083

Hills SFK, Trewick SA, Morgan-Richards M. (2011). Phylogenetic information of genes, illustrated with mitochondrial data from a genus of gastropod molluscs. Biological Journal of the Linnean Society 104(4):770-785 


evolution-stick-insect.jpg Parthenogenetic reproduction in stick insects

Worldwide, parthenogenetic (asexual) reproduction has evolved many times in the stick insects (Phasmatidae). Many parthenogenetic sticks show geographic parthenogenesis; ie, live at higher altitude or latitude than their sexual relatives. We researched the distribution and evolutionary relationships ofsexual and asexual populations of the New Zealand stick insect, Clitarchus hookeri.

Males are common in the northern half of the species’ range but rare elsewhere, and most C. hookeri from putative-parthenogenetic populations share a common ancestor. Females from bisexual populations are capable of parthenogenetic reproduction, but those from parthenogenetic populations produced few offspring via sexual reproduction when males were available. It is often assumed that parthenogenetic populations have a reproductive advantage. However, we found similar fertility in mated and virgin females. Mated females map-geographic-parthenogenesis.jpg produced equal numbers of male and female offspring, hatching 9–16 weeks after laying. Most eggs from unmated females took 21–23 weeks, and most offspring were female. It appears that all C. hookeri females are capable of parthenogenetic reproduction, and could benefit from the numerical advantage. Nevertheless, our evidence shows that most all-female populations over a wide area originate from a single loss of sexual reproduction.

Reference

Morgan-Richards M, Trewick SA, Stringer IA. (2010). Geographic parthenogenesis and the common tea-tree stickinsect of New Zealand. Molecular Ecology 19: 1227-1238.

A: Distribution of sexual and parthenogenetic populations reveal a pattern of geographic parthenogenesis. Dotted line encloses sites where males have been recorded; colours represent distinct genetic clades as shown in B.

B: Unrooted Maximum Likelihood analysis of mtDNA haplotypes of Clitarchus hookeri.

C: Minimum spanning network of haplotypes from the parthenogenetic clade.

biodiversity-gradient.jpg Latitudinal Biodiversity Gradient

"Animal life is, on the whole, far more abundant and more varied

within the tropics than in any other part of the globe, and a great

number of peculiar groups are found there which never extend into

temperate regions."

—AR Wallace, 1876

Species density is higher in the tropics (low latitude) than in temperate regions (high latitude) resulting in a latitudinal biodiversity gradient (LBG). The LBG must be generated by differential rates of speciation and/or extinction and/or immigration among regions, but the role of each of these processes is stillunclear. Recent studies examining differences in rates of molecular evolution have inferred a direct link between rate of molecular evolution and rate ofspeciation, and postulated this as an important driver of the LBG. We are currently working to understand the effects of the different techniques used to estimate the rate of molecular evolution and how this might influence estimates of molecular evolution rates used when examining the LBG.

Figure 2 A multitude of hypotheses seek to explain the latitudinal biodiversity gradient (LBG). Each hypothesis aim torelate the LBG to processes that influence one or more of the three components controlling regional species diversity: immigration, extinction and speciation. The two key environmental parameters most frequently cited as underlying drivers of the LBG are area and energy (generally measured in the form of temperature). The inferred importance and directionality of effects varies among taxa, researchers and methods applied, with no clear consensus. Here we illustrate a subset of theories on the formation of the gradient that have gathered some empirical support (citations in figure) and, in particular, those that relate to molecular evolution (shaded area). A link between speciation rate and the rate of molecular evolution is widely shown, but which is the driver of the other is equivocal.

Fig2flow-diagram.jpg A latitudinal gradient in available energy may influence many traits but these are only tentatively associated with rates of extinction and/or speciation.


Reference

Dowle EJ, Morgan-Richards M, Trewick SA. 2013. Molecular evolution and the latitudinal biodiversity gradient. Heredity advance online publication 13 March 2013; doi: 10.1038/hdy.2013.4

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