Download 2017_58: Convergent Evolution of Body Elongation

2017_58: Convergent Evolution of Body Elongation
Supervisors: Dr Mark Wilkinson ([email protected]) and Dr Arkhat
Abzhanov (Life Sciences)
Department: Natural History Museum / Life Sciences
Convergent evolution is both a problem (a confounding factor in phylogenetic
inference) and a blessing (the basis for statistical comparative methods for studying
adaptation) for evolutionary biologists. Increasingly, convergence is becoming of
interest in its own right as something that can help tell us whether there are general
rules and predictability in evolution. We have recently been examining whether the
propensity for convergent evolution is independent of phylogeney (our null hypothesis)
or whether the probability of convergence between taxa is positively correlated with
how closely related are the taxa. Using new methods, measures and tests we have
been able to reject the null hypothesis in about 40% of data sets culled from the
phylogenetics literature. This is quite exciting because it suggests, as many have
suspected, that evolution is not a markovian process. During this project we began
work on a case study in convergence, focussed upon the consequences of convergent
body elongation in eels. This preliminary study found evidence that convergent events
are underdispersed on the phylogeny. The PhD project seeks to build on this initial
work by investigating convergent evolution across a broader range of taxa that have
undergone evolutionary body elongation.
Elongation in body form has evolved many times in vertebrates, sometimes effecting
specific areas of the body, such as the elongated necks of sauropods or giraffes, other
times leading to the reduction or loss of limbs and cylindrical body plan that defines
entire clades, such as eels, caecilians, amphisbaenians and snakes. Body elongation
occurs also in many invertebrate groups (e.g. annelida, other “worms”, myriapoda).
Using comparative morphological data extracted from the literature or generated
during the course of the project the student will seek to determine if the pattern of
underdispersion of convergent events detected in eels is specific to eels, or is more of
a general trend in clades with an elongated body form. By extending analyses of the
consequences of elongation to other iconic clades of elongate vertebrates, caecilians,
snakes and amphisbaenians (and perhaps also some invertebrates) which exploit
various types of habit, including aquatic, fossorial and terrestrial, and each of which
have their own set of unique adaptations, the project aims to develop a deeper
understanding of the roles of selection and historical contingency in shaping
convergent adaptations.
For more information on how to apply visit us at www.imperial.ac.uk/changingplanet
Science and Solutions for a Changing Planet
Analyses will involve gathering detailed information on the anatomy of these
organisms to quantify the trends in organ position in these similar body forms adapted
to these different habitats, as well as build upon the wealth of count and morphometric
data currently available within the NHM collections. It is likely that the research will
also involve the further development of appropriate measures and statistical tests.
For more information on how to apply visit us at www.imperial.ac.uk/changingplanet