THE EFFECTS OF SPERM COMPETITION ON TESTES SIZE AND INTROMITTENT ORGAN MORPHOLOGY IN WATERFOWL by CHRIS R. COKER B.Sc. (hon.), Trent University, 1993 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Animal Science) We accept this thesis as conforming to the required standard THE: UNIVERSITY OF BRITISH COLUMBIA April 1998 © Chris R. Coker, 1998 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver, Canada DE-6 (2/88) Abstract Waterfowl are one of very few avian taxa that possesses an intromittent organ (10). This thesis examines the adaptive significance of the 10 in waterfowl by determining the relationships between 10 morphology and the intensity of sperm competition (as reflected by frequency of extra-pair copulations (EPCs)). Intromittent organ morphological characteristics, including length and circumference (adjusted for body size), number of ridges and/or knobs (per unit area), ridge/knob height, ridge/knob length, and % area covered by ridges/knobs were measured from scaled museum drawings of freshly killed, sexually mature, specimens of 57 waterfowl species (across 33 genera). Thirty of which were ranked by frequency of EPC (1= monogamous, 2= rare EPC, 3= frequent EPC, 4= promiscuous). Testes sizes were also investigated in relation to EPCs, where testes masses (adjusted for body size) from 47 species (across 24 genera) were obtained (32 species with mating strategies). The size of the testes, the size (length) of the 10, the size (height) of the 10 ridges/knobs and the % area covered by ridges/knobs increased significantly with the frequency of EPC. These relationships exist even after the removal of phylogenetic constraints. These results are consistent with the hypothesis that waterfowl 10s are involved in sperm competition. Further research into the actual mechanism by which the 10 is involved with sperm competition would be worthwile. TABLE OF CONTENTS Page Abstract ii Table of Contents iii List of Tables v List of Figures •. '.. vi Acknowledgements vii Chapter 1 Introduction and Background 1 Intromittent Organs 2 Male Genitalia in Animals 2 Male Genitalia in Birds 4 Why Do Some Birds Possess or Lack an IO? 5 Male Genitalia in Waterfowl 10 Female Genitalia in Birds 11 Extra-Pair Copulation 14 Sperm Competition 16 Chapter 2 The relationship between testes size and mating strategy in waterfowl 21 Avian Testes 21 Materials and Methods 23 Results 29 Discussion 32 Chapter 3 The relationship between intromittent organ morphology and mating strategy in waterfowl 37 Sperm Competition 37 Hypothesis 38 Materials and Methods 39 Results 43 Discussion 55 iii Chapter 4 Conclusions and Future Directions 59 Conclusions 59 Study Limitations 59 Future Directions 61 A Final Thought 62 References 65 Appendix A Intromittent Organ Model 73 iv List of Tables Page Table 2.1 Table of testes masses, body masses, mating strategies, and testes data sources 25 Table 3.1 Principal components analysis 43 Table 3.2 List of species categorized according to mating strategy 46 Table 3.3 Correlation matrix of morphological characteristics 50 Table 3.4 Correlation matrix of morphological characteristics after phylogenetic constraints removed 52 v List of Figures Page Figure 2.1 The relationship between testes mass and mating strategy 29 Figure 2.2 The relationship between body mass and testes mass 30 Figure 2.3 The relationship between testes size and IO size 31 Figure 2.4 The relationship between testes size and IO size (removal of phylogenetic effects) 32 Figure 3.1 Sample of Harlequin duck and Ruddy duck intromittent organ drawings showing various characteristics 40 Figure 3.2 Principal components analysis of morphological measurements......... 45 Figure 3.3 PCA of initial 18 species categorized according to mating strategy 49 Figure 3.4 PCA with newly added species' mating strategies 51 Figure 3.5 The relationship between IO length and mating strategy 53 Figure 3.6 The relationship between the number of ridges and knobs (per unit) and mating strategy 54 Figure 3.7 The relationship between the area covered by ridges and/or knobs and mating strategy 54 Figure 3.8 The relationship between the height of the ridges/knobs and mating strategy... 55 Figure 3.9 Intromittent organ of the Ruddy duck, Oxyurini jamaicensis (left), and it's features compared to the Mealworm beetle, . Tenebrio molitor (right) 58 vi Acknowledgements This thesis could not have been completed without the efforts of Helen Hays from the American Museum of Natural History (New York). The unpublished illustrations of waterfowl intromittent organs were drawn and are owned by her; she kindly let me use them for the purpose of this study. I would like to thank my supervisory committee, Kim Cheng, Frank McKinney (University of Minnesota), Wayne Vogl, Harold Kasinsky, and Raja Rajamahendran for their support and tutelage. There are also many people who were involved in helping me on certain aspects of my thesis. I would like to express gratitude to Kevin Johnson at the University of Utah, for his help on the phylogenetic analysis; Wayne Vogl for assisting in the dissections and model casting, and Gary Bradfield for his guidance on the statistical analysis. I would also like to acknowledge Frank McKinney, Dan Brooks (Texas A & M University), and Peggi Rodgers (Wildlife Rehabilitator) who provided information on mating behaviours; and Sue Briggs (CSIRO, Canberra), Brad Millen (Royal Ontario Museum), Maryanne Hughes (UBC), and Trevor Pitcher (York University), who helped supply testes data, I would also like to thank my family and friends who showed their love and support (and tried not to snicker at my topic of research). Finally, I would like to thank my wife, Anne Hepplewhite, who was there all the way and never doubted my ability to achieve excellence. vii Chapter 1 Introduction and Background Rapid and divergent evolution in male genital morphology is expected in animals with internal fertilization (Eberhard 1985). This is due to a variety of adaptive pathways that enhance the success of self's ejaculate relative to rival ejaculates (i.e. to ensure paternity). The theory that the evolution of male genitalia results from sexual selection has been examined in the book, Sexual Selection and Animal Genitalia (Eberhard 1985), which extensively reviewed numerous studies of male genitalia in a vast array of vertebrates and invertebrates. The class Aves, however, is seldom mentioned in this book. Except for general descriptions of anatomy and physiology (e.g. Barkow 1829, Eckhard 1876, Muller 1908, Liebe 1914, Lake 1981, King 1981), studies on the function or adaptive significance of the intromittent organ (IO) are extremely rare in birds. Perhaps this is due to the fact that the majority of avian species do not have an IO, and consequently there has been little interest in carrying out research in this area. The majority of IO studies that have been carried out are on mammals, or insects. Mammals have external lOs and domestic and farm mammals are abundant and easily accessible for research. IO studies began in insects in association with sperm competition studies (e.g. Waage 1979, Michiels 1989, Miller 1991). Though most avian species lack an IO, some species do have one. This study attempts to examine the evolution and adaptive significance of the IO in waterfowl. I Intromittent Organs It has long been recognized that among closely related species with internal fertilization, the genitalia often show clear morphological differences (Eberhard 1985). This is particularly accentuated in the male of the species and is widespread throughout numerous animal groups. For example, species-specific IO are found in flatworms, nematodes, oligochaete worms, insects, spiders, millipedes, sharks and rays, some lizards, snakes, mites, opilionids, crustaceans, molluscs, and mammals (including rodents, bats, armadillos, and primates) (Eberhard 1990). In contrast, animals that have external fertilization, such as most fish, do not have species-specific genital morphology. External fertilizing groups of animals include echinoderms, most polychaete worms, hemichordates, brachiopods, sipunculid worms, frogs, few insects, and most fish (Eberhard 1990). Even as recently as 1990, birds have been categorized as not having an IO, and in fact, have even been classified as having external fertilization! (Eberhard 1990, pp. 134). Any structure that has evolved both rapidly and divergently (i.e. it acquires a new form in each new species) is a useful taxonomic character at the species level (Eberhard 1985). The universality of this pattern can be demonstrated below with a review of the genitalia from a variety of animal groups together with an examination of the complexity of many genitalia. Male Genitalia in Animals When fertilization is internal, the male, with few exceptions, develops intromittent 2 or copulatory organs for introducing sperm into the female reproductive tract. For example, the 10 of elasmobranchs are grooved, finger-like appendages of the pelvic fins known as claspers (Kent 1987) and in the anuran genus Ascaphus, the IO is a permanent tubular tail-like extension of the cloaca (Taylor & Guttman 1977). Male turtles, crocodilians, a few birds and mammals exhibit an unpaired erectile penis. In its simplest form, the penis is a thickening of the floor of the cloaca that consists chiefly of spongy erectile tissue, the corpus spongiosum, which bears a urethral groove on its dorsal surface and ends in a glans penis (Fox 1977).