Authors:	Jongepier, Evelien
Title:	Inter- and intraspecific variation in the host defence portfolios of Temnothorax ants
Online publication date:	6-Jan-2016
Year of first publication:	2016
Language:	english
Abstract:	A central theme in evolutionary biology is to explain why some species readily adapt to their environment while others apparently do not. Regarding the coevolutionary arms race between hosts and parasites, this question is fuelled by a large variety of host defence strategies against parasites, even between hosts experiencing very similar selection pressures. Recent theory predicts that the effectiveness of one defensive strategy modifies the selective regime for further lines of defence, which may affect the complexity of host defence portfolios. The evolution of host defences thus not only depend on attributes of parasites, such as parasite pressure or host preference, but also on the efficacy of other traits in the adaptive portfolios of the host. Here, we investigate the interplay between the different behavioural and chemical strategies in host defence portfolios and parasite prevalence. We focus on Temnothorax ant colonies, whose workforce is parasitically exploited by the social parasite and slavemaker ant, Protomognathus americanus. We studied up to 17 populations of two Temnothorax species, covering most of their geographic range. The first part of this thesis correlatively investigates the causes and consequences of variation in colony aggression. Despite the known advantages of aggressive defences, chapter 2 shows that Temnothorax populations exposed to high slavemaker prevalence were less aggressive towards the slavemaker than populations where the slavemaker was rare or absent. Instead, severely parasitized populations resorted to an alternative defence strategy in the form of nest evacuation. Chapter 3 shows that the decrease in host aggression with increasing slavemaker prevalence was not driven by variation in the aggressive potential of Temnothorax colonies. Instead, chapter 4 demonstrates that more aggressive populations were more resistant to manipulation of their aggressive responses by the slavemaker. Slavemakers benefitted from manipulating their hosts aggressive defences, as both the likelihood that slavemakers survived host encounter and slavemaker prevalence in ant communities increased with slavemaker-induced changes in host aggression. In addition, we show differences between host species in their expression of the different defence strategies, which had important implications for their level of exploitation by the slavemaker. Temnothorax longispinosus colonies were more susceptible to manipulation than T. curvispinosus colonies, which explains why T. curvispinosus responded with more aggression towards invading slavemakers, why they were less likely to let slavemakers escape and why they were less frequently parasitized by the slavemaker than T. longispinosus. The second part of this thesis focusses on two novel defence strategies against slavemakers: the host’s chemical adaptions involved in enemy recognition and their flexibility to respond to slavemaker attack. Specifically, chapter 5 investigates whether slavemakers can drive diversification in the host’s nestmate recognition cues. We show that T. longispinosus populations that co-occur with slavemakers are more variable in their chemical recognition cues. Larger variation between, but not within colonies, enables hosts to distinguish friend from foe and makes it impossible for slavemakers to adapt to any one recognition profile in their host population. In chapter 6, we experimentally investigate the fitness consequences of behavioural specialisation by T. longispinosus workers during slave raids. While specialized workers may be more efficient in the tasks they perform than generalists, they may also lack the flexibility to respond to rapid shifts in task needs. Such rigidity could impose fitness costs when societies face dynamic and unpredictable events, such as an attack by slavemaker ants. We indeed find that strict specialisation is disadvantageous for a colony’s annual reproduction and growth during slave raids. These fitness costs may favour generalist strategies in dynamic environments, as we also demonstrate that societies exposed ton slavemakers in the field show a lower degree of specialisation than those originating from slavemaker-free populations. Our findings thus provide an explanation for the ubiquity of generalists and highlight their importance for the flexibility and functional robustness of entire societies. In conclusion, this thesis demonstrates that ant colonies use a variety of strategies to cope with social parasites. The level of expression of these strategies varies across populations and species, depending not only on parasite prevalence but also on other strategies in the host’s defence portfolios. Hosts with efficient front line defences suffered lower parasite prevalence in the field. Nonetheless, hosts whose frontline defences were breached by the parasite were found to mount further lines of defence, providing empirical support that host defence portfolios can reach remarkable depths.
DDC:	570 Biowissenschaften 570 Life sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 10 Biologie
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-4197
URN:	urn:nbn:de:hebis:77-diss-1000000166
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	https://rightsstatements.org/vocab/InC/1.0/
Extent:	119 S.
Appears in collections:	JGU-Publikationen