Amblypygids, colloquially known as whip spiders, are a charismatic order of arachnids
that a characterised a unique pair of spined pedipalp appendages. Amblypygid pedipalps
are hypothesised to primarily function as a prey capture device. However, the pedipalp is
also used in several other functions including territorial contest and courtship, opening
the possibility that the appendage could also be under the influence of sexual selection.
There exists a vast degree of morphological diversity within the pedipalp, with relative
length spanning nearly an order of magnitude across the group and spination varying
markedly both within- and between species. The amblypygid pedipalp is therefore subject
to multiple selective pressures, and both its external morphology and kinematics likely
reflect this. Thus, the amblypygid pedipalp provides an ideal structure through which to
study the evolution of morphological traits subject to multiple selective pressures, and
the potential evolutionary trade-offs that may arise. Despite this, amblypygid pedipalp
morphology and kinematics remains poorly quantified and little comparative work has
been carried across the group. Here, I aim to quantify intra- and interspecific trends in
amblypygid pedipalp shape and prey capture kinematics for the first time, using modern
morphometric techniques and high-speed videography. In this work I present a
comprehensive review of sexual dimorphism in arachnids and identify the common
drivers behind this phenomenon. Building on this, I quantify sexual dimorphism in
pedipalp size and shape in a single species of amblypygid using a novel geometric
morphometric approach. This is followed by an broad analysis of intraspecific and
interspecific trends in shape complexity of pedipalps using Elliptical Fourier Analysis.
Finally, I draw a link between form and function by quantifying and comparing prey
capture kinematics in a morphologically diverse set of amblypygids, using high-speed
videography and motion analysis. This work provides new insights into amblypygid
8
pedipalp diversity and posits the possibility of an evolutionary trade-off between
increased pedipalp length, for use in display in courtship and territorial contest, and strike
performance during prey capture
