Mechanisms of Sexual Selection in the Sand Goby, Pomatoschistus Minutus

Mechanisms of Sexual Selection in the Sand Goby, Pomatoschistus minutus Nuutti Kangas Department of Ecology and Systematics Division of Population Biology University of Helsinki Finland Academic dissertation To be presented, with permission of the Faculty of Science of the University of Helsinki, for public criticism in the lecture room of the Department of Ecology and Systematics, P. Rautatiekatu 13, on December 16, 2000, at 12 o’clock noon. Helsinki 2000 © Nuutti Kangas (Summary and II, IV, V) © Oxford university press (I) © Academic press (III) Technical editing by Johan Ulfvens Author’s address: Department of Ecology and systematics Division of Population Biology P.O.Box 17 (Arkadiankatu 7) 00014 University of Helksinki Finland ISBN 952-91-2870-3 (printed) ISBN 952-91-2871-1 (pdf) Oy Edita Ab Helsinki 2000 Mechanisms of Sexual Selection in the Sand Goby, Pomatoschistus minutus Nuutti Kangas Department of Ecology and Systematics Division of Population Biology P.O.Box 17 (Arkadiankatu 7) 00014 University of helsinki Finland The thesis is based on the following articles: I Lindström, K. and Kangas, N. 1996. Egg presence, egg loss, and female mate preferences in the sand goby (Pomatoschistus minutus). – Behavioral Ecology 7, 213–217. II Kangas, N. and Haldin, C. The effects of egg age on mating success in the sand goby, Pomatoschistus minutus. – Submitted manuscript. III Kangas, N. and Lindström, K. Male interactions and female mate choice in the sand goby, Pomatoschistus minutus. – In press (Animal Behaviour). IV Kangas, N. Sexual selection and male colour in the sand goby, Pomatoschistus minutus. – Submitted manuscript. V Kangas, N. and Viitasalo, M.Predation affects nest site colonisation, courtship and mate choice in the sand goby, Pomatoschistus minutus. – Submitted manuscript. These are referred to by their numerals in the text. 4 Contributions Contributions The following table shows the major contributions of authors to original articles I II III IV V Initiative KL NK NK NK NK Experimental planning NK & KL NK NK & KL NK NK & MV Data gathering NK NK & CH NK NK NK Analysis NK & KL NK NK & KL NK NK Manuscript preaparation NK & KL NK NK & KL NK NK Supervised by Dr. Kai Lindström, University of Helsinki Finland Reviewed by Prof. Liselotte Sundström University of Helsinki Finland Dr. Johanna Mappes University of Jyväskylä Finland Examined by Prof. Arja Kaitala University of Oulu Finland Contents 5 Contents 0. Summary ........................................7 Introduction .......................................8 Sexual selection ...................................8 The focus of the thesis..................................9 Natural history .....................................10 General methods ....................................12 Main results ......................................13 Study I .......................................13 Study II .......................................13 Study III ......................................13 Study IV ......................................14 Study V .......................................15 Discussion .......................................16 1. Factors affecting mate choice and male-male competition............16 2. Habitat constraints on sexual selection......................20 3. Conclusions ...................................21 References .......................................22 I. Egg presence, egg loss and female mate preferences in the sand goby (Pomatoschistus minutus)...............................29 Materials and methods .................................30 Egg choice experiments...............................30 Effect of nest success ................................30 Results .........................................30 Discussion .......................................31 References .......................................33 II. The effect of egg age on mating success in the sand goby, Pomatoschistus minutus................................37 Material and methods .................................38 Natural history ...................................38 Egg age and mating success in the wild ......................39 Standardation of the egg mass area .........................39 Male condition and egg age in the wild.......................39 The effect of egg age on female choice .......................40 Results .........................................42 Egg age and mating success in the wild ......................42 Standardation of the egg mass area .........................42 Male condition and egg age in the wild.......................42 The effect of egg age on female choice .......................42 Discussion .......................................43 Literature ........................................45 6 Contents III. Male interactions and female mate choice in the sand goby, Pomatoschistus minutus................................49 Material and methods .................................50 Phase 1 .......................................51 Phase 2 .......................................52 Results .........................................53 Female preference .................................53 Male-male interaction................................53 Courtship ......................................54 Discussion .......................................55 References .......................................57 IV. Sexual selection and male colour in the sand goby, Pomatoschistus minutus . 61 Material and methods .................................62 Natural history ...................................62 Aquarium experiment................................62 Experiment with non-manipulated males – males interacting ...........62 Mate choice experiment – interactions prevented .................64 Experiment with manipulated males – males interacting ..............64 Ornament size and mating success in the field ...................65 Results .........................................65 Non-manipulated males interacting and mate choice ................65 Mate choice when interactions prevented......................66 Manipulated males interacting and mate choice ..................66 Ornament size and mating success in the wild ...................67 Discussion .......................................67 Literature ........................................69 V. Predation affects nest site colonisation, courtship and mate choice in the sand goby, Pomatoschistus minutus ......................73 Materials and methods .................................74 Natural history ...................................74 Bird predation and nest colonisation in the field ..................74 Field experiment on fish predation .........................75 Nest colonisation under predation risk .......................76 Predation avoidance with and without female ...................77 Mate choice experiment ..............................77 Results .........................................77 Bird predation and nest colonisation in the field ..................77 Field experiment on fish predation .........................78 Nest colonisation under predation risk .......................79 Predation avoidance with and without female ...................79 Mate choice experiment ..............................80 Discussion .......................................80 Literature ........................................83 7 Mechanisms of Sexual Selection in the Sand Goby, Pomatoschistus minutus Abstract This thesis describes five basic mechanisms of sexual selection in the sand goby, Pomatoschistus minutus, a small fish with paternal care. These are: (1) the female preference for eggs in the nest, (2)the effect of brood age on mating success, (3) the effect of male–male interactions on mate choice, (4) sexual selection of male colour and (5) the effect of predation on sexual selection. All the studies test in the laboratory and in the field, factors that may give direct benefits to females in terms of offspring survival. The studies show that females avoid nests were potential of egg survival is poor. Also, females spawn with strong males, which might be able to carry the costs of hard male–male competition. Furthermore, in all of the studies the constraints of mate choice are tested. Male interactions are shown to affect mate choice and dominant males may some- times override female choice. Besides this, predation is shown to reduce female activity towards potential mates. Also, in all the studies, factors affecting male– male competition are tested. It is shown that mate choice may affect the result of male–male competition. Parental stage of the male, nest size and predation affect the competition for mates among males. Furthermore, it is shown that males avoid high predation risk nest sites during colonisation, increasing competition for safe sites. Female choice is not necessarily always operating in the same direction as male–male competition. Either one may outweigh the other, but which one is stronger may be dependent on local ecological conditions. For example, it is shown that brood age variation may affect competition for spawnings and con- sequently female spawning patterns. Furthermore, this spawning pattern may constrain female choice in the wild, when most males are guarding old eggs. Yet, male interactions may outweigh mate choice but not in cases where males differ clearly in ornamentation. I also show that under certain conditions female choice may constrain male–male competition. For example females may choose males that are weaker in physical fights between males. These results suggest that different

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