Coevolution Session 1f Evolution Meetings – Chico 2003.

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Presentation transcript:

Coevolution Session 1f Evolution Meetings – Chico 2003

Ancient Mariners & Recent Stowaways: the coevolution of seabirds & their lice Division of Environmental and Evolutionary Biology Institute of Biomedical and Life Sciences Graham Kerr Building University of Glasgow Scotland Vincent S. Smith & Roderic D.M. Page

Parasites… ancient associates or recent acquisitions? time Cospeciation Extinction In situ radiation Serial colonisation Recent colonisation Diversification by host switching Host Parasite Time is important!

The Hosts & Parasites Feather lice (Insecta: Phthiraptera) Tubenose seabirds (Aves: Procellariiformes)

Tubenose seabirds are very lousy! Ischnocera Charadriiformes Procellariiformes Number of louse species Procellariiformes Charadriiformes Ischnocera

Analysis ii.Rates smoothing nonparametric rate smoothing using r8s (Sanderson, 2003) perform on 100 trees drawn from Bayesian chain iii.Calibration assume that cospeciating host/parasites are likely to be the same age penalised likelihood to estimate the relative age of the other nodes i.Host/parasite phylogenies mitochondrial 12s rRNA, COI & Cyt. B Bayesian analysis (trees sampled every 1000 generations after burnin )

Albatross-louse cophylogeny Hosts: Albatrosses Parasites: Feather Lice Page et al (in press) Mol. Phyl. Evol.

Analysis v.Tree mapping identify comparable nodes in the host & parasite tree compare ages of nodes ii.Rates smoothing nonparametric rate smoothing using r8s (Sanderson, 2003) perform on 100 trees drawn from Bayesian chain iii.Calibration assume that cospeciating host/parasites are likely to be the same age penalised likelihood to estimate the relative age of the other nodes iv.Sensitivity analyses rate smoothing is sensitive to choice of smoothing parameter we varied the log of the parameter for each of the 100 bird/louse trees i.Host/parasite phylogenies mitochondrial 12s rRNA, COI & Cyt. B Bayesian analysis (trees sampled every 1000 generations after burnin )

Procellariiform-louse tanglegram Bayesian inference (12s rRNA, COI & Cyt. B)

Are procellariform lice as old as their hosts? Age estimates relatively constant across a range of smoothing parameters Radiation of procellariform lice is slightly more recent than that of their hosts log 10 smoothing Procellariiformes relative age Procellariform birds times older than albatrosses Feather lice log 10 smoothing relative age Feather lice times older than albatross lice

Bird-Louse Ages relative age

How do we account for this? ? Relative Age of Host-Parasite Clades Host Age Louse Age Petrels & Halipeurus Procellariformes & Philoceanus-complex Lice ¾ of the age of their hosts! i.e lice are slightly younger than we might expect if they are cospeciating

Conclusions i.Is this discrepancy real? Are the assumptions behind the calibration point correct

Calibration Correction? Hosts: Albatrosses Parasites: Feather Lice Host divergence Louse divergence Delayed cospeciation i.e. Paraclisis speciating slightly after their hosts

Conclusions iii.Do we need to redefine cospeciation Is the expectation of temporal congruence always correct in cospeciating lineages? i.Is this discrepancy real? Are the assumptions behind the calibration point correct ii.If it is real, what does it mean? Gene flow briefly persists between lice after speciation of the host? Failure of lice to speciate ( Johnson et al, 2003 ) Arent we really dating gene coalescent times anyway? ( Rannala & Michalakis, 2002 )

Acknowledgements Martyn Kennedy & Rob Cruickshank Wellcome Trust