Research
Using molecular and morphological data, my current research seeks to understand phylogenetic relationships among assassin spider species and among clades within the superfamily Palpimanoidea. To date there have been no comprehensive studies (using morphology and DNA) of species relationships among assassin spiders (but click here for a PDF of my work on a Malagasy clade). My work also seeks to document biodiversity through species descriptions, which are illustrated using SEM and AutoMontage images. I have described nine species of assassin spiders (click here for the monograph) and have more species still to describe for my dissertation research. To see images of assassin spiders from different parts of the world click here or the Images&Video link above.
Assassin 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 and could 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 assassin spiders were once more widespread, extant members occur only in the southern hemisphere: archaeids are in South Africa, Australia, and Madagascar; mecysmaucheniids are restricted to southern South America and New Zealand. A molecular clock applied to the phylogeny of this group will provide information on the age of the lineages in different geographic areas and will allow for comparison of the timing of speciation across areas (i.e., was diversification rapid due to key innovation or radiation into a new area, or was it a slower process due to allopatric speciation?). Preliminary data shows that Chilean assassin spiders have high morphological divergence, but very low molecular divergence (less than 2%) whereas among Malagasy assassin spiders even closely related sister taxa that are morphologically similar have much more molecular divergence (~15% among mitochondrial DNA). This may suggest that speciation in Chile was more recent and could be a radiation, while in Madagascar speciation may be much slower or older. I am interested in comparing speciation patterns of monophyletic clades on different land masses.
While living assassin spiders are found only in the southern hemisphere, fossil assassin spiders are known from Europe and Asia. The phylogenetic placement of fossil taxa is necessary to properly perform a biogeographic study. I will examine these fossils, which are housed in museums, and attempt to incorporate them into my phylogeny using morphological characters. Fossil taxa may also allow for calibration of a molecular clock, which can be used to estimate the divergence dates of different clades on a phylogeny. The image on the left is the species Eriauchenius workmani, which was the first living assassin spider discovered in the forests of Madagascar in 1881. Prior to this date, assassin spiders were only know as fossils.
Clades of assassin spiders have evolved two different predatory strategies. Click here to see animations and videos of these two different behaviors. Malagasy and South African assassin spiders will only prey on other spiders and the long 'neck' and jaws are used to attack at a distance. After the initial attack the prey is held away from the assassin spider's body and impaled on the fang until it dies. This attack strategy insures that the assassin spider is not injured by the spider prey.Alternatively, Chilean and New Zealand species seem to be generalists, and in these clades the jaws are employed in a trap-jaw mechanism. It remains to be seen what the behaviors are of the Australian clades and of closely related families, like huttoniids, palpimanids, stenochilids.
My research seeks to understand how these behaviors explain the morphology of the 'neck' and jaw and the evolutionary trade-offs of these two different predatory strategies. In general, assassin spiders that employ the trap-jaw mechanism have stouter shorter necks and jaws, while the clades that employ the alternate predatory strategy have thinner, longer necks and jaws. Given that there are two main types of predatory behaviors, why is there so much variation in the length and constriction of the 'neck' and which came first, the behavior or the morphology?
Carapace morphology is directly related to predatory behaviors. I am interested in understanding the muscular anatomy and biomechanical properties of the carapace and jaws in order to better understand the evolution of assassin spider predatory strategies.
The trap-jaw mechanism that evolved in some clades of assassin spiders may be an evolutionary strategy that allows for attack movements that are quicker than if muscles were acting on their own. The alternative predatory strategy (attack spider prey at a distance) insures that prey can't harm the predator. Comparing these two attack strategies is useful for understanding how morphology is constrained and shaped by evolution.
The image on the left is a basal view of the chelicerae in the species Eriauchenius lavatenda from Madagascar. The triangular sclerite in between the cheliceral bases has been modified into a structure that pops open the jaws in Chilean and New Zealand assassin spiders.
Assassin spider in Australia, Madagascar and South Africa are obligate araneophages, meaning they will only prey on other spiders, whereas clades from southern South America and New Zealand seem to be generalists. The araneophagic assassin spiders can sometimes take days to pursue and attack their prey. I have even observed them getting their prey to come to them by plucking on the prey's web. They also are capable of walking in the webs of their prey.I am interested in the specific way araneophagic spiders stalk and attack their prey. Of interest is knowing what cues (smell, sight, touch, movement) the spider uses to identify their prey. Do they have a search image that recognizes spiders in general, something truly amazing considering the amount of morphological diversity in all spiders, or alternatively, maybe they are only targeting specific families or types of spiders? This image is of a juvenile South African assassin spider that has just captured a cyatholipid spider as large as itself. (Image by J. Miller)
Assassin spiders are capable of communicating with members of the opposite sex by making tiny vibrations that are transmitted through the leaves and substrate. This is done by rubbing various structures on their pedipalps against a stridulatory file found on the chelicerae. In one species I have observed abdominal vibrating as well. These vibrations are used during courtship and mating by both the female and male. I would like to record these vibrations and examine if there is a phylogenetic signal in the song. I would like to compare the vibratory signals among sympatric and allopatric species. Also of interest are the various apophyses on the male palps that seem purposed to stimulate the female's abdomen (personal observation). Furthermore, in some species only the females have large sclerotized plates on the underside of their abdomen and in one species the female has a long protrusion origination from the ventral side of the petiole. In short, it seems various ways of stimulating the female's abdomen have evolved independently in assassin spiders. From a phylogenetic context, these data could be useful in understanding female choice and the evolution of sexually dimorphic traits.
•I would be interested in working on arthropod or invertebrate groups that have restricted distributions in the southern hemisphere, of particular interest are the montane rainforests in Africa, Australia and Chile. I would like to use biogeography and phylogenetics to compare how diversification takes place among different taxa on different land masses.
•I would like to study mating behaviors and communication systems in arthropods. Is there a phylogenetic signal in mating calls and how do the calls differ among allopatric and sympatric species?
•I have interest in the following evolution topics: sexual selection, female choice, speciation, and evolution at the genomic and molecular level.