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4 Posts tagged with the bryozoa tag
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Wednesday 22nd May 11:00
Sir Neil Chalmers seminar room, Darwin Centre LG16 (below Attenborough studio)

 

 

Polyembryony and unexpected gender roles in hermaphroditic colonial invertebrates

 

 

Helen Jenkins - PhD student, Aquatic Invertebrates, Dept. of Life Sciences, NHM

 

 

Polyembryony – the production of multiple genetically identical embryos from a single fertilised egg – is a seemingly paradoxical combination of contrasting reproductive modes that has evolved numerous times and persists in a diverse range of taxa including rust fungi, algae, plants and animals. Polyembryony is thought to characterise an entire order of bryozoans, the Cyclostomata. A molecular genetic approach was used to confirm this widely cited inference, based on early microscopy, and to test the apparently paradoxical nature of this reproductive mode in relation to cyclostomes, and will be reported here. Additional research, also presented here, has revealed further insights into the mating systems of this relatively understudied group of hermaphroditic colonial invertebrates. Mating  trials indicated a greater degree of female investment in the presence of allosperm in Tubulipora plumosa and produced evidence of separate-sex colonies in Filicrisia geniculata. If not a complete transition to gonochorism, the situation in F. geniculata indicates at least very pronounced gender specialisation. Further investigations into mating systems of this group may reveal more examples, with implications for our understanding of hermaphroditism and its related traits.

 

For additional details on attending this or other seminars see http://www.nhm.ac.uk/research-curation/seminars-events/index.html

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Bryozoans are widespread aquatic colonial animals living both in the sea (sea mats) and fresh waters, with an extensive marine fossil record over almost 500 million years. Collaborating research groups in the NHM Departments of Zoology and Palaeontology represent arguably the strongest concentration of bryozoan research expertise anywhere in the world.

 

NaturalHistoryMuseum_026159_IA.jpg

 

Wilbertopora woodwardi (Brydone) from the Upper Cretaceous Chalk, Hampshire

 

Andrea Waeschenbach (NERC Postdoctoral Fellow, Zoology), Paul Taylor (Palaeontology) and Tim Littlewood (Zoology) have had accepted for publication the most comprehensive molecular phylogeny of bryozoans to date, using mitochondrial and ribosomal genes.

 

This has resulted in a well supported topology (the shape of the phylogenetic tree), providing unambiguous evidence for the interrelationship of the taxonomic classes.  It also provides strong evidence that several presently recognized taxonomic units at various hierarchical levels are each in fact of more than one origin in evolutionary terms - they are non-monophyletic (a monophyletic group has a single ancestor)

 

Using this topology, the work tried to establish the likely larval form and strategy of the ancestral bryozoans, but this gave ambiguous results.  It seems most likely that multiple shifts have occurred between different types of larval nutrition – dependency on yolk provided to the egg (lecithotrophy) and feeding by the bryozoan larva on phytoplankton (planktotrophy).

 

This result, combined with their long fossil record, promises bryozoans to be a suitable phylum to studying links between reproductive strategy and large scale evolutionary patterns, such as speciation rates. This paper is a significant contribution for assessing the interrelationships in a relatively neglected group that offers much promise as an evolutionary model. This work was funded by NERC (NE/E015298/1).

 

Waeschenbach, A., Taylor, P.D., Littlewood, D.T.J. (2011) A molecular phylogeny of bryozoans, Molecular Phylogenetics and Evolution. http://dx.doi.org/10.1016/j.ympev.2011.11.011

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Just over one hundred years ago in Feburary 1911, Captain R.F. Scott RN received news from Roald Amundsen that he was intending to make a bid for the South Pole in competition with Scott’s. Scott’s expedition had a range of important scientific goals: the race for the Pole for which he is best known was only one of the objectives. The science involved resulted in a number of Antarctic collections, some of which are in the Museum today.

 

These collections have been used to show a dramatic doubling in the growth of bryozoans in Antarctic seas in the last twenty years. Bryozoans are tiny colonial animals that encrust rocks, algae and other objects beneath the sea, filtering food from the water.  It is another use of older collections that could never have been anticipated at the time of collection, but shows the value and importance of these collections to modern science and current concerns.

 

Dr Piotr Kuklinski, a Scientific Associate of the Museum who works for the Polish  Academy of Sciences Institute of Oceanography, has collaborated with other scientists from the British Antarctic Survey and US institutions to examine collections to tell how growth has changed over time and to suggest reasons why this might be happening.

 

They looked at a whole series of Antarctic collections in the Museum from 1909 to the 1930s, and other collections in the US and New Zealand up to the present day.  The species Cellarinella nutti from the Ross Sea was used – it shows annual growth lines as the colony expands and so yearly growth can be measured. The growth measurements showed no particular change in rates of growth from 1890 to 1970, but there was a rapid increase in growth from the 1990s to the present day.

 

Why is this happening?  Growth seems to be increasing because of increased availability of food – tiny single-celled plants known as phytoplankton. This increase would result from higher concentrations of phytoplankton or a longer growing season. Climate change?  Probably not - the scientists point out that there is little evidence of changes to sea ice or water temperatures in the Ross Sea.

 

However, they do suggest that this may be linked to depletion of stratospheric ozone – the ozone holes that occur in the Antarctic summer.  This could be causing stronger west winds that result in currents bringing in more nutrients to the area, in turn resulting in higher growth of plankton and higher growth of bryozoans.  Our understanding of the detail of these questions helps refine our understanding of the Earth’s carbon cycle, which is closely linked to our climate system.

 

The authors conclude ‘Amundsen claimed that Scott's “..British expedition was designed entirely for scientific research. The Pole was only a side-issue…”. Being first to reach the pole was foremost in fundraising and probably in Scott's thinking but coming second in the ensuing ‘race’ and dying there completely overshadowed the many scientific achievements of the expedition. However, the baselines that they established and crucial subsequent curation may prove key to interpretation of trends with significance way beyond the polar regions.’

 

David K.A. Barnes, Piotr Kuklinski, Jennifer A. Jackson, Geoff W. Keel, Simon A. Morley, Judith E. Winston (2011) Scott's collections help reveal accelerating marine life growth in Antarctica.  Current Biology - 22 February 2011 (Vol. 21, Issue 4, pp. R147-R148) doi:10.1016/j.cub.2011.01.033

 

 

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Bryozoans are colonial invertebrates, commonly found attached to hard surfaces from the shallow subtidal zone to the deep sea. Bryozoan colonies increase in size by the budding of the numerous individuals (zooids) that make up the colony.

 

A collaborative team, including Professor Beth Okamura, Dr Tanya Knowles and Dr Paul Taylor from the NHM, explored how the size of zooids in fossil bryozoans varied as temperature changed.  This enabled them to use bryozoans to deduce the annual ranges of temperature during the Early Pliocene (around 4 million to 5.5 million years ago) in the Weddell Sea off the coast of  Antarctica.

 

Their results show that during this period the climate was warmer than that of the present day, suggesting an ice-free environment in that part of Antarctica.

 

The research shows the value of fossil bryozoans from shallow seas as a tool for reconstructing seasonal variation in climate in near-polar latitudes in past periods of the Earth's history.  This helps to understand how climates have changed naturally in the past - knowledge that in turn enables present-day changes in climate to be understood and predicted.

 

Clark, N., Williams, M., Okamura, B., Smellie, J., Nelson, A., Knowles, T., Taylor, P., Leng, M., Zalasiewicz, J. & Hayward, A. 2010. Early Pliocene Weddell Sea seasonality determined from bryozoans. Stratigraphy 7: 199-206.