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The wisdom of the crowd: a crowd-sourcing task for character discovery from nematocyst ultrastructure
Marymegan Daly , Abigail Reft , Edith Law , Maureen O’Leary
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1,2
3
4
1 Dept. Evolution, Ecology & Organismal Biology, The Ohio State University; 2 Centre for Organismal Studies, Heidelberg, Germany; 3 Center for Research on Computation & Society, Harvard University; 4 Department of Anatomical Sciences, Stony Brook University School of Medicine
Non-scientists are drawn to the aesthetic beauty of organisms and curious about the evolution of form.
Focal problem: Nematocyst ultrastructure
How can we use the eyes and brains of students and natural history enthusiasts to expand our ability to
reconstruct and interpret the tree of life?
Nematocysts are microscopic structures produced uniquely by members
of Phylum Cnidaria (corals, sea anemones, jellyfish, and their kin).
These micro-machines are used by corals, jellyfish, Hydra, and other
cnidarians to capture prey, digest food, deter predators, and engage
in intraspecific competition.
Speeding the discovery and collection of
morphological characters for phylogenetics
Although DNA is now the primary means of building
phylogenetic trees, morphological attributes remain critical to
phylogenetics: morphological characters are often the focus of
explanations or interpretations of trees built with molecular
data, and are integral to the generation of tress that include
species known only from e.g., fossils or formalin-fixed museum
material. Although we have centuries’ worth of information
about anatomy and histology, the morphological data set for
any lineage tends to be replete with missing data: not all
characters have been assessed for all organisms in all lineages.
Furthermore, modern techniques like electron microscopy have
not been applied to questions of morphology in many groups,
in part because these techniques became widespread at the
same time that phylogenetics underwent a shift away from
morphology and towards DNA as the primary means of
assessing relationships.
Generating, extending, and completing morphological matrices
is critical to reconstructing and understanding the tree of life.
However, because these data require organismal and technical
expertise and tend to be time-intensive to collect, their
completeness and quality represent a major impediment to the
reconstruction of a detailed and comprehensive tree of life.
Through the “Assemble, Visualize, and Analyze the Tree of Life”
grant fromprogram of the US National Science Foundation, we
have developed interactive, web-based tools for discovering
and scoring phylogenetic characters from high-quality images.
These tools help to increase the speed and scale at which
morphological data can be collected and thus help to make
morphological data and tree reconstruction collection more
efficient and effective.
Curio: A platform for crowd sourcing character assessment
Curio (Law et al., 2013) is a citizen-science platform that harnesses the curiosity of
laypeople. Participants collect, annotate, and analyze e.g., images, audio, video, text,
time series, or spatial data to test hypotheses developed by content experts. Because
content experts need not have technical expertise in programming or experience with
crowd-sourcing to use Curio, new crowd-sourcing projects can be launched with minimal
effort.
We are implementing Curio to
develop new phylogenetic
characters for nematocysts.
Morphological matrices have
been made using attributes
visible with light microscopy
but this set of features is not
representative of the diversity
of nematocysts, as electron
microscopy (EM) reveals
attributes not visible with light
microscopy and light
microscopy fails to
differentiate structures
distinguishable with EM.
The participant is introduced to the broader question in an
easy-to-understand context. Images loaded for the project
can be used in multiple tasks and in multiple comparisons.
“What characteristics distinguish nematocysts of sea anemones?”
~ Professor Meg Daly
How do sea anemones manage to subdue and kill prey that moves when they themselves are stuck to the
substrate? The answer comes from within! Like all cnidarians, sea anemones make microscopic killing
machines called nematocysts.These are each smaller than a single cell, and are the most complex structure
micrograph of an un-discharged nematocyst. Only the
tubule is visible in the light micrograph.
Electron microscopy
of nematocysts
reveals structural
diversity unseen with
light microscopy: the
apex of the capsule varies from operculate, to cap-like, to
tri-flapped, and spines or tubules indistinguishable under light
microscopy can vary in shape and texture. The diversity of form has
largely been explored in a functional context, or remarked upon
anecdotally in studies of natural history, physiology, or taxonomic
diversity.
manufactured by any animal cell. Each nematocyst consists of a long tubule wound up and packed inside a
tiny capsule; when the tubule erupts from the capsule, the spines and barbs on it sick into the skin or wrap
around the body of the victim.
Nematocysts show a lot of variation in their size, shape, and function. Many of the attributes of nematocysts
visible under the 10,000 plus magnification of electron microscopy have not been described thoroughly for
Three nematocysts differing in the morphology of the tubule: note differences
in spine shape, spine arramgement, and tubule texture.
most species of sea anemone. We aim to use the attributes of the nematocyst capsule, tubule, and spines to
differentiate nematocysts from different species of sea anemone and to understand the ways in which these
highly complex, minute machines have changed over evolutionary time.
Meg Daly is an associate professor of Evolution, Ecology,
and Organismal Biology at Ohio State University.
We will develop new characters through an image comparison and annotation task, in
which participants are given two images asked to draw an outline around the same part
(e.g., “tubule,” “spine”, or “apex”) in each image and then describe, in plain language, the
most salient differences between the two examples of this part.
The Curio Interface for this project presents images of
nematocysts from two species and asks the participant to
differentiate them using non-technical language.
In an undischarged nematocyst, a spined tubule lies coiled inside the
capsule with which it is continuous. Upon stimulation, the tubule everts,
turning inside-out and revealing spines and harpoons that penetrate
the target.
A diagrammatic discharged nematocyst and a light
Annotation is especially helpful
because the micrographs can
contain multiple nematocysts
and orientation varies from
micrograph to micrograph. The
plain language descriptions are
helpful for the extension of
crowdsourcing tasks because
they provide non-technical
descriptions that can be used to
guide participants.
Our goal is to document this diversity and understand how it has
changed through evolution. Before we can reconstruct phylogenies
or interpret the evolution of nematocysts, we must:
1) Atomize the diversity of form into phylogenetic characters. This is
necessary to build trees of these attributes or to optimize the attributes
onto trees constructed using other data.
2) Assess the diversity of form across a meaningful sample of taxa.
Knowing a little bit about the attributes of few or incomparable sets of
species is insufficient to resolve the evolution of these complex
structures.
References and Acknowledgements
Edith Law, Conner Dalton, Nick Merrill, Albert Young, Krzysztof Z. Gajos. Curio: A Platform for Supporting
Mixed-Expertise Crowdsourcing. HCOMP 2013.
This project was supported by NSF DEB-1208523