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March 4, 2011

Charles Darwin spent much of his later life at Downe in Kent: thinking, writing and experimenting in an emphatically rural landscape.  But he retained an interest in marine animals, a fascination that developed in his early years at university and during his extended voyage around the world on HMS Beagle.

Professor Phil Rainbow (Keeper of Zoology) has published a keynote presentation in the journal Marine Ecology on the influence of marine biology on Charles Darwin - and the influence of Darwin on marine biology.


Darwin made his first forays into the world of marine biology as a medical student in Edinburgh from 1825 to 1827. He came under the influence there of the Lamarckian Robert Grant, and developed an understanding of the simple organisation of the early developmental stages of marine invertebrates. Yet Darwin could not accept Lamarckian transmutation - a complex set of ideas on evolution that preceded the idea of natural selection.  (Lamarck was a French scientist who, among other ideas, argued that a characteristic [such as larger muscles as a result of frequent exercise] acquired during an organism's life would be passed on to descendants and resulted in evolutionary change: Darwin's later development of natural selection as an explanation for evolution discredited Lamarck's ideas.)


The voyage of the Beagle gave him intense exposure to a wide range of marine environments around the world and led to Darwin's perceptive theory on the origin of coral reefs, an origin still mainly accepted today. This theory was linked closely to the uniformitarianism (gradual geological change over millions of years) of the geologist Charles Lyell, depending on the slow, gradual growth of billions of coral polyps keeping pace at sea level with slow sinking of land to produce an atoll.


Darwin's interest in variation in animals and plants led him to examine many different organisms, both wild and domestic. However, he was aware that his unusual scientific background meant that he had not developed a his reputation on the basis of detailed scientific study in a particular area.  Therefore, from 1846 to 1854 Darwin focused on barnacle diversity and revolutionised understanding of barnacles, producing the monographs Living Cirripedia that are still relevant today.



Capitulum mitella


Darwin's barnacle studies gave him the credibility to pronounce on the origin of species; he found great variation in morphology, and a series of related species with remarkable reproductive adaptation, culminating in the presence of dwarf males. Barnacles laid out an evolutionary narrative before him, and contributed greatly to his qualification and confidence to write with authority on the origin of species by 1859.

PS Rainbow (2011) Charles Darwin and marine biology. Marine Ecology. doi:10.1111/j.1439-0485.2010.00421.x



Worm Sperm and Evolution

Posted by John Jackson Mar 4, 2011

Drs Tim Littlewood and Andrea Waeschenbach (Zoology) have collaborated with colleagues from Switzerland and Japan on a paper, recently published in the Proceedings of the National Academy of Sciences, that attracted widespread media attention from the science and popular press. Headlines such as “‘Worm porn’ sheds light on evolution of sperm” (MSN Science) and “X-rated worm movies reveal sex secrets” (Nature News) reflect the more restrained coverage.


It is a continuing challenge in science to explain why sex evolved in different species in such a variety of forms - internal or external fertilisation; separate sexes or hermaphrodites; mate selection; number of offspring; number of mates; timing of reproduction; and many other questions.  Sperm in particular are intriguing - these are highly specialised cells with the function of exchanging genetic material, evolved to survive and function in quite different situations in different species.  The huge variety of different sorts of sperm cells reflects the variety of different reproductive strategies in various groups of organism.


This study looked at a number of related species of a small transparent flatworm - Macrostomum. The team used a robust molecular phylogeny (developed by TL and AW) using DNA to define evolutionary history of the worms.  They then looked at mating strategies, the morphology of the bodies and the types of sperm in different species.


They found that one group of worms had very complex sperm with spines and a pattern of hermaphrodite exchange of sperm cells.  However, a different strategy had evolved in one member of this group and in four worms in another group in which the sperm is injected by one worm into the body of another. In these injecting species, the form of the sperm has evolved to become simpler, losing certain characteristics such as spines: the form of sperm seems to be related to mating techniques. It seems possible that the hypodermic injection gives certain advantages in some species - this might be to avoid competition from the sperm of rivals, or to avoid female rejection of sperm, but more work will be needed to answer this question.


The team was led by Dr Lukas Scharer (University  of Basel, Switzerland) and included Dr Dita Vizoso (Basel) and Dr Wataru Yoshida (Hirosaki University,  Japan).


Schärer, L., Littlewood, D.T.J., Waeschenbach, A., Yoshida, W. & Vizoso, D.B. (2011). Mating behaviour and the evolution of sperm design. Proceedings of the National Academy of Sciences USA 108:1490-1495.