Alternative reproductive tactics and their consequences in the ant genus Cardiocondyla Alexandra Schrempf Oktober 2005 Alternative reproductive tactics and their consequences in the ant genus Cardiocondyla DISSERTATION ZUR ERLANGUNG DES DOKTORGRADES DER NATURWISSENSCHAFTEN (D R. RER . NAT .) DER NATURWISSENSCHAFTLICHEN FAKULTÄT III – BIOLOGIE UND VORKLINISCHE MEDIZIN DER UNIVERSITÄT REGENSBURG vorgelegt von Alexandra Schrempf aus Ergoldsbach 10/2005 Promotionsgesuch eingereicht am: 29.09.2005 Die Arbeit wurde angeleitet von Prof. Dr. J. Heinze Prüfungsausschuss: Vorsitzender: Prof. Dr. S. Schneuwly 1. Prüfer: Prof. Dr. J. Heinze 2. Prüfer: Dr. J. Korb 3. Prüfer: Prof. Dr. P. Poschlod CONTENTS TABLE OF CONTENTS GENERAL INTRODUCTION..................................................................................................... 1 CHAPTER 1: Proximate mechanisms of male morph determination in the ant Cardiocondyla obscurior ..................................................................................... 12 Introduction ............................................................................................................................. 14 Materials and Methods ............................................................................................................ 15 Results ..................................................................................................................................... 17 Discussion ............................................................................................................................... 21 CHAPTER 2: Alternative reproductive tactics in males of the ant Cardiocondyla obscurior .............................................................................................................. 24 Introduction ............................................................................................................................. 26 Materials and Methods ............................................................................................................ 27 Results ..................................................................................................................................... 30 Discussion ............................................................................................................................... 35 CHAPTER 3: Back to one: consequences of secondary monogyny in an ant with polygynous ancestors .......................................................................................... 39 Introduction ............................................................................................................................. 41 Materials and Methods ............................................................................................................ 42 Results ..................................................................................................................................... 44 Discussion ............................................................................................................................... 48 CHAPTER 4: Inbreeding and local mate competition in the ant Cardiocondyla batesii .................................................................................................................. 51 Introduction ............................................................................................................................. 53 Materials and Methods ............................................................................................................ 54 Results ..................................................................................................................................... 58 Discussion ............................................................................................................................... 63 CHAPTER 5: Exclusion of complementary sex determination, inbreeding depression and sex ratio adaptation in the ant Cardiocondyla obscurior ............................. 68 Introduction ............................................................................................................................. 70 Materials and Methods ............................................................................................................ 71 Results ..................................................................................................................................... 74 Discussion ............................................................................................................................... 80 CHAPTER 6: Sexual cooperation: mating increases longevity in ant queens............................ 86 Introduction ............................................................................................................................. 88 Materials and Methods ............................................................................................................ 89 Results and Discussion............................................................................................................ 89 CONTENTS GENERAL DISCUSSION.......................................................................................................... 94 SUMMARY .............................................................................................................................. 101 ZUSAMMENFASSUNG.......................................................................................................... 103 ACKNOWLEDGEMENTS ...................................................................................................... 105 REFERENCES.......................................................................................................................... 106 GENERAL INTRODUCTION 1 GENERAL INTRODUCTION “One of the greatest problems facing Darwin´s (1859) theory of evolution by natural selection concerned conspicuous male traits, (….). These and other extravagant male characters would seem to reduce survival, and so should be opposed by ordinary natural selection” (Andersson, 1994). To solve the problem, Darwin (1871) developed his theory of sexual selection as a special case of natural selection, of which a key aspect is the competition between males over access to females, which can increase the variance in the reproductive success of individual males and thus the opportunity for sexual selection. As a consequence, alternative reproductive behaviours of males can evolve, for example, small, weak or young males that have low competitive abilities do better using completely different tactics. Frequently used alternatives are "sneaking" matings without paying the cost of fighting, or, mimicking females to avoid being attacked by territorial males (Andersson, 1994; Neff, 2001; Shuster and Wade, 1991a; Shuster and Wade, 2003). The expression of alternative reproductive tactics is known from a variety of taxa, including mammals, fish, birds and arthropods (for reviews see Alcock, 1998; Andersson, 1994; Austad, 1984; Brockmann, 2001; Dominey, 1984; Gadgil, 1972; Neff, 2001). They are often accompanied by morphological correlated traits such as the development of weapons (e.g. mandibles in the coleopteran Dendrobias mandibularis, Goldsmith, 1987, forelegs in the thrips Hoplothrips pedicularis , Crespi, 1986, and cerci in the earwig Forficula auricularia , Eberhard and Gutierrez, 1991; see also below), and can be either genetically or environmentally determined. In case of genetic polymorphism, the fitness of the different phenotypes is expected to be on average equal, otherwise, the most successful genotype would spread and replace the others (Dominey, 1984; Gadgil, 1972; Gross, 1996). The different strategies can be maintained for example due to environmental heterogeneity, accompanied by the occupation of different niches (Dominey, 1984). Most often, however, they are maintained by negative frequency dependent selection (Gadgil, 1972; Gross, 1996; Maynard Smith, 1982). Thus, male fitness depends on the frequency of rival male types, and each morph has a fitness advantage when rare (Alonzo and Warner, 2000; Henson and Warner, 1997). However, such alternative strategies are rare in nature but do exist e.g. in fish (Zimmerer and Kallman, 1989), a bird (Lank et al., 1995), lizards (Sinervo and Lively, 1996; Zamudio and Sinervo, 2000) and the marine isopod Paracerceis sculpta. In the latter, three phenotypes correlate with three alleles at a single GENERAL INTRODUCTION 2 autosomal locus. Big fighter males occur alongside of intermediate-sized males which mimic females and also, alongside of small males which "sneak" matings (Shuster and Wade, 1991b). Conversely, alternative tactics within a conditional strategy are frequent in nature (Gross, 1996). Under the conditional strategy, individuals are genetically monomorphic. Theory predicts that the “decision", which tactic is expressed, is dependent on the status of the individual and will result in higher fitness for the individual (Gross, 1996). Individuals naturally differ in their status, e.g. because of environmental influences or because they differ in their developmental stages. The fitness of the alternative tactics are different, and are maintained by status-dependent selection (with or without frequency-dependent selection). A switch-point in status exists at which the fitness from the alternatives are equal (intermediate status; Repka and Gross, 1995). For example, individuals with a status above the switch-point will adopt a territorial tactic, whereas individuals