Download The squat lobster, Munida rugosa, has a chela

Thomas Claverie
Research Statement
Arthropods are incredibly diverse and morphologically disparate. In particular, they
possess some of the most morphologically variable and specialised appendages among living
creatures. What are the processes underlying the versatile evolution of these organisms? Has
morphological design evolved to comply with the animals’ requirements within their niches or
did the animals invade new niches based on the development of novel designs? How does
appendage diversity relate to species diversity? A growing knowledge exists on the genetic
control of arthropod development and the ecological significance of their morphology, thus I
propose to develop a research program that will investigate the driving evolutionary forces of
arthropods morphological disparity. My research focuses on how the relationship between
selection and function affects the evolution of appendage morphology across both populations
and species of crustaceans.
PREVIOUS RESEARCH: Sexual selection and appendage morphology
Identifying the function of particular morphologies and disentangling various selective
pressures acting on them requires an integrative approach. My dissertation work investigated
and identified the main selective pressures associated with the claws of a Squat lobster, Munida
rugosa (Fig.1A). This species possesses a strong sexual dimorphism in claw length (Journal of
the Marine Biological Association of UK, 2009) and a secondary dimorphism in shape (Aquatic
biology, 2010). Some animals develop enlarged chelae with arched “fingers” (the propodus and
dactylus) while others do not (Fig.1B). What could cause this species to evolve this
morphological variation?
A)
B)
Figure 1. A) Munida rugosa (A, Crustacea, Decapoda), possess a chela dimorphism
particularly pronounced in large males (B) with some chelae being straight (top) and
others arched (bottom). Arched morphologies are a better design for inflicting puncture
wounds on opponents during fights (they have a stronger and better grip on an
opponent’s claws). Scale bar, 1 cm.
Geometric morphometric techniques used to quantify the claw shape of captive and
tagged free-living animals (Fisheries Research, 2007) revealed that gradual changes in claw
shape occur during growth in both sexes, but only some mature males have an exaggerated
arched shape (Aquatic Biology, 2010). The prominence of exaggerated structures such as claws
in large males is often seen in the development of weapons. Could this claw dimorphism be the
evolutionary result of sexual selection?
In decapod crustaceans, claws are mainly used for feeding and fighting. I therefore
wanted to determine how the squat lobster claw morphology relates to these two functions.
Measurements of the maximum closing force in relation to claw shape revealed that arched
chelae were stronger and better designed to inflict puncture wounds on opponents than straight
chelae (Proceedings of the Royal Society B, 2007). Furthermore, gut content analyses showed
that feeding was not influenced by claw shape, while staged agonistic interactions showed that
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Thomas Claverie
males with longer chelipeds and more-arched chelae won more often during intra-specific
conflicts. These results suggested that the shape of arched claws confers an advantage as a more
efficient weapon while having no effect on feeding.
Field measurements were necessary to understand how selection acts on the evolution of
such weapons. I therefore investigated how males benefit from having more efficient weapons.
Measures of the relative abundance of various chelae morphologies within ten natural
populations showed that the proportion of males with arched chelae was positively correlated
with both the density of mature males and the proportion of males with fighting injuries.
Moreover, the survival rate of large males with arched chelae estimated from capture-recapture
data was higher than those with straight chelae. Consequently, it appeared that in a competitive
natural environment, males with arched chelae are favoured over those with straight chelae.
The cumulative evidence collected during my dissertation research allowed me to
conclude that arched chelae are more effective weapons in this particular species of squat
lobster, and that the evolution of this feature may be a consequence of sexual selection through
male competition. More broadly, this work showed how small morphological variations, in this
case a greater curvature of claws, can be exploited by selection forces during evolution. In
addition, this is a commercially exploited species in Great Britain and these studies provided
basic biological information that is being used to inform fisheries management.
PRESENT RESEARCH: Appendage specialisation and shape diversity
Various processes such as ecological specialisation or developmental mechanisms can
act in concert to influence morphological diversity in nature. In my Postdoctoral work, I
investigate the mechanisms that lead to the generation of morphological disparity in crustacean
appendages. Mantis shrimp (Fig. 2A, Crustacea, Stomatopoda) have highly specialised, poweramplifying raptorial appendages that are used to capture and kill prey and to fight conspecifics
or other intruders. Depending on the morphology of their appendages, they adopt different
predation strategies, either spearing fast-moving prey or smashing hard-shelled prey. These
appendages produce movements that are among the fastest ever recorded in animals, yet a wide
diversity of morphology is present across genera (Fig. 2B).
A)
B)
Figure 2. A) Peacock mantis shrimp possess prominent smashing appendages (bottom left
side on the picture). B) Three different appendage morphs used for spearing (left, centre) or
smashing (right) preys.
How can important morphological changes of such specialised structures occur without a
loss of mechanical performance? To answer this question, I investigated the morphological
development of appendages in one mantis shrimp species in relation to ontogenetic shape
changes and performances. I found that the appendage can be divided into three developmental
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modules that characterize the engine (muscle), amplifier (elastic energy storage), and tool
(hammer, used to break shelled prey) of the limb (Evolution, 2010). It is then possible that each
module could evolve independently, generating great diversity while maintaining performance.
How do morphological changes affect strike mechanic across species? Numerous
components of appendage performance such as elastic energy storage (Journal of Experimental
Biology, 2009) and strike force have been measured across more than 15 species to precisely
analyse how morphological changes affect appendage function. These variables, currently being
analysed, will inform modelling of the appendage motion and will allow us to generate
predictions on the evolution of performances across species.
How did mantis shrimp’s appendages become so morphologically disparate? It appears
that a major switch in predation tactics (ambush vs active foraging) and habitat type, combined
with an evolutionary modular structure of the appendage could have promoted a great increase
in the diversity of shape while maintaining its power amplified performance. To answer this
question I measured the appendage morphology across most genera of mantis shrimp. Combined
with knowledge of performance and species ecology, these results will show how the
combination of patterned development with environmental pressure can lead to important
diversification of a highly specialised structure.
FUTURE DIRECTIONS: Morphological disparity and evolutionary processes
The roles of ecological specialisation and geographical isolation are often the only
processes taken into account to understand diversification. Recently, it was suggested that
developmental modularity of organisms could increase evolvability by reducing genetic
pleiotropy. A direct consequence of modularity is a rapid phenotypic change of organisms. This
could facilitate adaptation in changing environments and enhance rate of diversification. The
amazing diversity of arthropods, which are recognised as highly modular organisms, certainly
does give credence to this idea.
In the future, I will further investigate the relationship between modularity and
morphological disparity. Within arthropods, some clades are more morphologically disparate
than others, although they possess the same numbers of body segments (each being an
independent module). I intend to measure the degree of evolutionary and developmental
independence among modules and evaluate the evolutionary history of modularity in arthropods.
The correlation between morphological disparity and the degree of modularity of different
clades living in sympatry (to avoid any bias of ecological pressure on disparity) would be tested.
The degree of developmental modularity can be addressed using morphological variability
(methods mainly tested on mammal skull development).
More broadly, results of this research could provide invaluable insight into the
diversification of life and help to quantify the impact of rapidly changing environments on
biodiversity.
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Thomas Claverie
Teaching Statement
Philosophy
Students differ in their knowledge, motivation, and learning abilities. Therefore, to
captivate the group, I am highly enthusiastic about the subject that I teach, yet I remain attentive
to the needs some students might have. As a result, I am flexible to their different requests, such
as re-explaining a misunderstood concept. I also think that instruction should be clear, wellorganized, and to some extent repeated using different teaching methods. For instance, I use a
combination of exercises (theoretical and practical), discussions, and lectures with textual and
graphical support. Finally, knowledge is fundamental to human society, but is continually
evolving, and teaching content should be updated regularly in order to follow this trend.
Teaching experience
A challenging and instructive teaching experience for me was my first position as a
teaching assistant at the University Marine Biological Station in Millport. It was challenging not
only because it was my first time teaching, but also because it was a two week-long course with
a group of 70 third-year university students. It was an intensive Marine Biology course that
alternated theoretical lectures with practical exercises in the laboratory and in the field. I was in
charge of the practical component of the course, along with one other assistant. I had expected
that my enthusiasm would be enough to trigger student interest, but it was not. So, I explored
different communication approaches throughout the course. The most effective technique was to
give funny or surprising anecdotes about some of the animals or collecting methods. Once I got
the attention of the students, I oriented them toward the learning goal of the exercise by giving
precise directives. At the end of the week, numerous students became noticeably more interested
and even started arguing about relevant concepts presented in the course. From this experience, I
learned that teaching is not just about being enthusiastic and transferring knowledge, but also
about being able to adapt and communicate to a heterogeneous group of people. Subsequently, I
made the effort to adapt my communication approach to the dynamic of the class and I am
generally rewarded by a positive attitude from the students.
I mentored seven undergraduate students (from diverse ethnic and socioeconomic
backgrounds) that were doing research projects, two of whom became authors of scientific
publication and one who presented his results in an international conference. From these
experiences I realized that students learn better when they can explore a subject on their own
after an initial introduction. Lectures about a technical subject which explain everything, without
active involvement from the student, are generally quickly forgotten. I found that the best
compromise is to alternate guidance with individual work, either from books or exercises (e.g.,
practical research or training exercises). This approach has the benefit of letting the student
choose their personal learning rhythm while allowing me to identify potential gaps in knowledge
that could warrant further assistance.
Finally, my academic teaching experience was complemented with outreach experience
in public education to non-scientists at field research stations and in aquarium tours. These
experiences also helped me to learn how to communicate scientific information to a broader
audience, beyond the scope of a university.
Teaching subjects
My teaching and learning experiences, along with my research expertise in quantitative
biology and extensive marine field work, allow me to teach many quantitative biological
courses, full Organism Biology, Evolution, Animal Behaviour, Marine Ecology, Population
Biology, Invertebrate Zoology, and Morphometrics, as well as numerous other introductory
classes or field-based courses.
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