Sagehen Creek Field Station

09 Jun, 04 PM - 27 Jun, 01 PM

Formica aserva is one of the Nearctic facultative slave-makers found across North America with concentrated populations in Northern California. As a group, researchers know very little about the evolution of this form of parasitism and the mechanisms that parasites employ during the founding, raid, capture and integration of a host species. I propose answering the questions, (1) Why does Formica aserva parasitize the host species it does and not other potential hosts, (2) What chemical strategies do facultative parasites use during the acquisition of a host species and (3) How behaviorally dependent are parasites on their hosts? During my time at Sagehen Creek, I will be collecting data for my first and second chapter on the evolution and chemical ecology of social parasites. The evolutionary origins of social parasites have long been tested using Emerys rule, which states that social parasites are close relatives to their hosts6. This rule has been applied to the diversity of social parasites within Hymenoptera with strong support of this pattern in the ants6. The evolution of host specificity in facultative slave-making ants has yet to be clearly understood. I will test the predictions of Emerys rule in three ways: by (1) making a phylogenetic reconstruction of sympatric species that represent the Formica diversity in a parasites community, (2) conducting a comparative analysis of cuticular hydrocarbons used for species and colony recognition for the Formica species found in that community, and (3) measuring Formica species abundance as a potential ecological explanation for host specific relations in Formica aserva. EVOLUTION Hypothesis 1: Formica aserva parasitizes its closest relative in a geographic range Study system: F. aserva occupies two vastly different habitats in Northern California. These regions are distinct in the Formica diversity they comprise and populations of F. aserva specify on different species depending on which geographic range they inhabit. In Central California, F. aserva parasitizes F. moki, which is an abundant species in dry, arid habitats. Montane populations of F. aserva are found with host species, F. argentea. Methods: I will collect parasite and host workers from mixed nests in the central valley and montane field sites. Formica species diversity will be determined using transects of pitfall traps for surveying ant activity in a given habitat range. Hypothesis 2: Formica aserva is more chemically similar to its host species than to other Formica species in a geographic range Methods: Only free-living host workers will be collected for these chemical analyses because enslaved workers would presumably share certain compounds with F. aserva as part of their colony gestalt. I will collect candidate individuals from each Formica population in a given geographic range. Hypothesis 3: Formica aserva parasitizes the most abundant species in a geographic range F. aserva may not exhibit a discriminatory strategy for selecting hosts based on Emerys predictions of common ancestry and/or chemical similarity. Rather, availability of a potential host in a community may drive host selection in this facultative system. Methods: I have mapped two field sites containing focal F. aserva nests and the Formica species residing within the parasites range. To conduct a Formica species diversity survey for each site, I will census ants in a 150x150 meter area around each colony using pitfall traps and visual surveys of nest proximity within the mapped sites9. Formica species abundance quantified and used to determine whether or not F. aserva is choosing the most abundant species in its range. CHEMICAL ECOLOGY Nestmate recognition cues are crucial for discriminating against non-members that might otherwise exploit a colonys resources10. Social parasites with an exploitative nature must therefore find a way to manipulate such cues for their own benefit. Here, I will investigate the proximate cause of (1) host integration by parasite workers and (2) host usurpation by newly mated parasite queens. Hypothesis 1: Parasite workers label enslaved hosts with their own recognition cues Methods: I will sample individuals from three distinct nests at each field site, (1) mixed nest with F. aserva and host, (2) free-living host nest and (3) free-living F. aserva nest. I will use a solvent (hexane) to dissolve the hydrocarbons from the ant bodies of each sample of pooled individuals. Concentrated hydrocarbons will be analyzed using a Gas Chromatograph/Mass Spectrometer, which splits up the chemical mixture from the pooled samples into identifiable peaks, each peak representing a chemical compound that was present on the ant body. Hypothesis 2: Founding parasite queens chemically evade host attacks during usurpation Relative to the research that exists on facultative parasite worker manipulation of host recognition cues, very little work has been done to investigate what types of strategies the parasite queens use to establish their nest within an existing host colony8. The strategy used by the newly mated queens may be evidence for more sophisticated chemical mimicry since this dependent-founding behavior is risky for a queen who might otherwise face potentially fatal interactions upon entering a foreign nest without such camouflage. The force of selection is most likely stronger in this scenario and thus may have resulted in adaptations to queen pheromones and/or denovo biosynthesis of host-specific odors. Methods: Preliminary work: The initial field collection, lab establishment and chemical extraction of a free-living host colony are prerequisites for the following design. Queen collection and chemical analysis: Newly mated queens will be collected in late June-July when F. aserva conducts mating flights. Hydrocarbons will be extracted from parasite queens before and after introduction to a host colony.

Visit #51158 @Sagehen Creek Field Station

Approved

Under Project # 35290 | Research

Chapter 1: A Test of Emerys Rule: Ultimate causes of host specificity in a facultative slave-making ant

graduate_student - University of California, Berkeley

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Kelsey Scheckel Jun 9 - 27, 2017 (19 days)

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Cabin 34 Jun 9 - 27, 2017