Evolutionary processes are critical
to understand how symbiotic relationships shape the natural history of species.
The fungus-growing ants (Formicidae: Attini, FGA) are part of a well-studied
symbiotic species network and have been the focus of innovative biological and
evolutionary research (Branstetter et al., 2017; Mehdiabadi & Schultz,
2010). Genomic studies demonstrate deep
phylogenetic splits, paralleling the ant-fungus symbiotic relationship (Branstetter et al., 2017; Nygaard et al., 2016). Furthermore, fungal
strain shifts are believed to have prompted the rapid radiation we see among FGA
lineages (Branstetter et al., 2017). However, FGA
species have maintained tight symbiont fidelity to single fungus cultivars for
millions of years (Mehdiabadi, et al., 2012). Although, these
evolutionary interactions with symbionts have likely influenced species
diversity, the array of non-fungal symbionts (e.g., bacteria, parasitoids,
social parasite ants) should also impact this species network (Adams et al., 2013; Currie, Mueller, & Malloch,
1999; Folgarait, 2013; Sen et al., 2009). Despite their
high prevalence, Diapriidae parasitoid wasps (Hymenoptera: Diapriinae) have
been the focus of only a single study on parasitism rates near Gamboa, Panama (Pérez-Ortega, et al., 2010). Thus, we lack a complete
understanding of the coevolutionary relationships in the FGA species network.
            To
address the gap in knowledge the long-term goal of my Master’s thesis is
to examine the influence of parasitoids on their FGA hosts through the lens of
established parasite theories (Box 1; Combes, 2005). The overall
objective of this application, which
is the first step towards attainment of my long-term goal, is to establish
a foundation in this system by (1) describing the genetic population
structure and colony densities of the host species and (2) determine chemical strategies of
parasitoids that attack the hosts. Preliminary data of the host FGA, Trachymyrmex sp. n. (T. fovouros sp. n., Cardenas, et al., in prep.), shows it is abundant in both
forested and creek habitats, yet it is only aggregated when found on creek
banks. Additionally, colonies are highly susceptibility to six parasitoid species
when aggregated on creek banks (Pérez-Ortega et al., 2010). In contrast, T. zeteki nests alone and are found less
often on creek banks and rarely in forests (per. comm. Jon Shik). Interestingly,
T. zeteki has only one documented
parasitoid species (Cardenas, et al., in
prep.). Because I can easily locate parasitized and unparasitized nests, focusing on both systems is logical and
feasible. The rational that
motivates the proposed research is to clearly describe aspects of host populations
for future research in compatibility filters of the parasitoid (Box 1). I am well prepared to undertake this proposed research, because colonies are easily
located, and I have collected the host T. spp. with their Diapriidae parasitoids (Pérez-Ortega et al., 2010); additionally,
Dr. Rachelle MM Adams, my advisor, is familiar with Panama field sites, and has
established relationships with Panamanian researchers and collaborators at the
Smithsonian Tropical Research Institute. By studying these two host species we
will begin to understand how parasitoids impact the evolution of fungus-growing
ants.

Proposed Research Aims:

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Populations
of Trachymyrmex spp. Hosts
            While
Trachymyrmex zeteki and T. sp. n. have been included in
biological and evolutionary research (see Overview and Objectives), what
constitutes a population and colony densities is unknown. Defining host FGA
populations and colony density is paramount for future studies of parasitoid host
relationships in this system. I intend to describe the population structure of T. zeteki and T. sp. n. in order to discriminate critical aspects of the host
species population. These
include: genetic drift, selection, and geneflow. Likewise, by studying the colony
density I also set out to interpret the population structure. The density of
organisms in their environment determines the patterns of genetic structure
seen within populations (Balkenhol, et al., 2015). Accounting for colony densities of populations
also serves to explain the natural history of the host FGA and the parasitoid
compatibility filters of hosts (Box 1). For
example, high and low colony densities have costs and
benefits for hosts and parasitoids. On one hand, high nesting densities could
represent a herd effect for the hosts. On the other, low nesting densities
could reduce the effectiveness of parasitoid host searching. The goal of this
first aim focuses on characterizing the population genetic structure and
nesting densities by employing land scape genetic principles (Balkenhol, et al., 2015). With this I will
establish the ecological context that influences the expected genetic variation
within the host species populations.