10-on-10: The Chronicle of Evolution
S.E.A. Aquarium Singapore May 23rd, 2017
John A. Long Strategic Professor in Palaeontology Flinders University, South Australia
Reproduction 1) Asexual –cloning, budding Advantage –uses less energy, low risk, 100% genetic material of parent passed on Disadvantage-proliferates single genetic population
2) Sexual –by sharing genetic material Advantage-more variation in gene pool. Disadvantage- high energy, more risk, only 50% genetic material shared
Shark (male) clasper
The Evolution of Fish-500 million years of change
From ancient simple jawless fishes (“Agnatha”)
To primitive jawed forms like Placoderms
To modern bony fishes (Osteichthyes)
Oldest fossil fish Metaspriggina (c 520myo) No bone developed Cyclostomes- the living jawless fishes
Hagfish (Eptatretus) (spawning? Not sure)
Lamprey (Petromyzon) (spawning)
Arthrodires
Ptyctodontids Antiarchs Entelognathus (Zhu et al. Nature Sept 25, 2013) Earliest placoderms from China (425 mya) Placoderms gave us jaws and teeth
(Long 2016, Science 354:280-281) GOGO
1 cm
1 cm 1 cm Micro CT scan of fossil umbilical cord Looped to placoderm embryo (Vizlab, ANU, Canberra Australia)
1 cm
(Long et al. 2009, Nature)
Phyllolepid arthrodires
Phyllolepid sexual dimorphism (left) and copulation (right) (artwork by Peter Trusler, Monash University)
Trinajstic et al. 2015 Biological Reviews 90
A serendipitous discovery in Tallinn, Estonia, late 2013
Single posterior ventrolateral plate (PVL) of Microbrachius
clasper? PVL plates
Geological Institute, Tallinn University of Technology (length c.2 cm) Microbrachius ‘clasper’showed similar structure to claspers of ptyctodontid placoderms
Microbrachius sp, from Essi Farm, d-g, ptyctodontid Estonia (a-c) claspers from Gogo (Western Australia) Eday Flags, Middle Devonian, Orkney islands, Scotland collecting expeditions 2014, 2016 First discovery of male claspers in antiarch placoderms
Male clasper development
Long, J.A. et al. Nature 517 (2015) Earliest record of a female (vertebrate)
Female Pterichthyodes (above) Microbrachius and Bothriolepis (right)
Microbrachius female with genital plates Long, J.A. et al. Nature 517 (2015)
This discovery had profound implications
Internal fertilisation must have evolved several times within vertebrates
(previously thought to be impossible!)
Long, J.A. et al. Nature 517:196-199 (2015) Did jaws evolve for reproduction not feeding? • Shh (sonic hedgehog) signalling necessary for male clasper development and female pelvic cartilages • Androgen response element (ARE) in HAND 2 locus identified
= genetic circuit for appendage development evolved an androgen regulory input, drove clasper skeletogenesis Leucoraja (skate) Males (left) female (right)
Same clasper cartilages develop in females as in males but to lesser degree
O’Shaughnessy et al. 2015. Nature Communications 10.1038/ncomms7698 Freitas et al PLOS One 2(8) e754 (2007) Cohn, M. (2004) Adv. Exp. Med. Biol. 545 MALE GENITAL EVOLUTION From placoderms to people The Rise of Fishes - 500 Million Dawn of the Deed – Years of Evolution The Prehistoric Origins of Sex Johns Hopkins University Press, University of Chicago Press, 2012 2011, 288 pp. PB 2014, 280pp