Palpimanoid Spiders
 
Hannah Marie Wood
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Research
 
   My research interests focus on trait evolution and comparative functional morphology, particularly in relation to biogeography, the timing and nature of diversification, and predatory behaviors. Palpimanoid spiders are a model group for understanding many aspects of evolution because of their novel morphological traits, unusual behaviors, restricted distributions and limited dispersal abilities.
Archaeid cephalothorax SEM male pedipalp Archaeid female genitalia
 
 
 
Biomechanics of the Carapace/Jaw Morphology, CT scanning

    Comparing the mechanical properties, anatomy and function of the chelicerae among different lineages of palpimanoid spiders is useful for understanding how novel traits evolve.
   
In several lineages of trap-jaw spiders, novel mechanisms have independently evolved that allow for extremely rapid predatory attack movements. However, the fastest trap-jaw spider species are very small. In fact, they are so tiny that they are difficult to dissect. Instead, I examine their internal anatomy by performing "virtual dissections" of 3D computer models. These 3D computer models are generated by synchrotron-based CT scanning. These 3D computer models can also be used in virtual kinematic simulations. I am also using CT scanning techniques to visualize internal anatomy of pelican spiders as well as other lineages of palpimanoid spiders.
     The image on the top left is a basal view of the chelicerae in the species Eriauchenius lavatenda from Madagascar. In trap-jaw spiders, the triangular sclerite in between the cheliceral bases has been modified into a structure that interacts with the chelicerae by locking them open (seen in the image on the right) and allowing for extremely rapid predatory attacks.

 
 
 
Evolutionary Relationships among Living and Fossil Palpimanoid Spiders
  Using molecular and morphological data, my research seeks to understand evolutionary relationships among different palpimanoid lineages, both living and extinct. Knowledge of these evolutionary relationships provides a context for understanding the evolution of different traits, such as predatory behaviors and functional morphologies. I also document biodiversity through species descriptions and species keys.
   While living pelican spiders are found only in the southern hemisphere, fossil pelican spiders are known from Europe and Asia. In fact, pelican spiders were initially known only as fossils and it was not until 1881 that the first living pelican spider was discovered in the forests of Madagascar. The phylogenetic placement of fossil taxa is necessary to properly perform a biogeographic study. I have examined many of these fossils and have incorporated them into phylogenies using morphological characters. It is important to incorporate fossil taxa directly into the phylogeny so that they can be used to help estimate the timing of lineage divergence. It is also crucial to incorporate fossils into biogeography analyses, particularly when fossils occur in different areas than the living lineages, and into analyses of character trait evolution, particularly when fossils have unique morphologies. The image on the lower left is a CT scan of the species Archaea paradoxa from Baltic amber, dated to be of Eocene age.
 
 
 
Biogeography, Diversification and Trait Evolution

Chilean Nothofagus Forests   Palpimanoid spiders are a model system for examining biogeographic patterns on different southern hemisphere landmasses because of their restricted distributions and low dispersal abilities.  These spiders are members of an ancient clade that appears to have originated before the breakup of Pangea.  This group is also of interest because it has a fossil record from Asia and Europe that extends into the Jurassic.  Although fossils suggest that these spiders were once more widespread, extant palpimanoid occur mostly in the southern hemisphere, occupying very restricted ranges. Estimating the timing of divergence among living and extinct lineages allows for comparison of the nature of speciation across different areas. My research also focuses on understanding how diversification patterns relate to predatory behaviors and chelicerae function, with an emphasis on ancient diversification patterns in Madagascar, Chile and New Zealand.

 
 
 
Evolution of Novel Predatory Behaviors and Araneophagy

   Palpimanoid spiders have evolved several unique predatory strategies. Pelican spiders are obligate araneophages, meaning they will only prey on other spiders and the long 'neck' and chelicerae are used to attack at a distance: their prey is held away from the body, impaled on the fang until it dies. Alternatively, trap-jaw species use their chelicerae for extremely rapid predatory attacks. Palpimanids are experts at invading spider retreats, using their first pair of legs to feel for and attack their prey. It remains to be seen what the behaviors are of other closely related families like huttoniids and stenochilids.
    My research seeks to understand the trade-offs between different predatory strategy and how this relates to specialization. Pelican spiders are highly specialized in their prey choice, but it is unknown whether they are targeting all spiders, or only preying on specific spider lineages. Most species of trap-jaw spiders appear to be generalists, however some species seem highly specialized. The species with the fastest predatory strikes seem to only feed on tiny soil arthropods that have rapid escape strategies, and there may even be a trap-jaw spider lineage that is araneophageous! The top image on the left is a trap-jaw spider that is about to capture a smaller theridiid spider; the bottom image is a juvenile pelican spider that has
just captured a cyatholipid spider (image by J. Miller).

 
 
 
Mating Behaviors
Archaeid mating   Palpimanoid spiders communicate with potential mates by making tiny vibrations that are transmitted through the substrate. This is done by rubbing various structures against stridulatory files. These vibrations are used during courtship and mating by both the female and male. A potential future research projects may be to examine courtship songs from a phylogenetic context. Another future research interest would be to examine how sexually dimorphic traits relate to diversification patterns.