Animal Behavior, 9E

The Evolution of Reproductive Behavior The female (left) and the male (right) of the gorgeous lizard Bowerbird courtship revolves around the bower Different bowers in different populations of the same bowerbird species Sexual Selection Traits that lower survival, but enhance the ability to mate are sexually selected traits. Elaborate costly traits exhibited by male birds Bower building may be an indicator of brain size Figure 7.4 Male mating success in the satin bowerbird is higher for birds with higher cognitive ability Variance in reproductive success is greater for males than for females in the satin bowerbird Male and female gametes differ greatly in size Operational Sex Ratio Alpine Newts Male sex drive is so intense that scientists were able to lure this male elephant seal to this area just by playing a tape recording of the call of a copulating female elephant seal Parental investment takes many forms males females Differences between the sexes in sexual behavior may arise from fundamental differences in parental investment Conventional Sex Roles • Male-Male Competition • Female Mate Choice Sex Role Reversal In those species where males make the larger parental investment we would expect: • the operational sex ratio to be biased towards females • competition among females • mate choice by males Male Pot-bellied seahorse giving birth Figure 7.10 A sex role reversal Long-tailed Dance Fly female Figure 7.11 Mormon cricket males give their mates an edible nuptial gift Clicker round-winged katydid Amblycorypha alexanderi Mating and spermatophore transfer Male (left) and Female (right) Clicker round-winged katydid Amblycorypha alexanderi Male (left) and female (right) immediately after copulation. The female has begun to eat the spermatophylax. When she finishes it, she will eat the spermatophore, which by that time will have moved its sperm into the female's sperm storage organ. Food supply affects sex roles in the Skinny Australian Katydid When food abundance is low, spermatophores are harder to produce and a more valuable nuptial gift to females. Males become choosy, females compete for access. Figure 7.13 Males of many species fight for females Figure 7.2 Elaborate costly traits exhibited by male birds Sexual selection involves trade-offs Figure 7.14 Convergent evolution in male weaponry Pecking Order = Dominance Hierarchy Dominance Hierarchy in Baboons Figure 7.16 Dominant male baboons do not control fertile females as completely as one would expect Options for subordinate males: • Female friendships • Male friendships Alternative Mating Tactics Conditional Strategy • Low ranking males can “make the best of a bad situation” • Higher fitness payoff by adopting an alternative then try to fight their dominant opponents Small males of the marine iguana must cope with sexual interference from larger rivals Attached Male Satellite Males Figure 7.19 A conditional strategy model of the relationship between male condition and reproductive success in the horseshoe crab Figure 7.20 Satellite male mating tactics (Part 2) Satellite Male Figure 7.21 A male Panorpa scorpionfly 1. Defend dead insects 2. Secrete saliva 3. Force copulation Environmentally based alternative forms of a marine amphipod of the genus Jassa Figure 7.23 Three different forms of the sponge isopod: the large alpha male, the female-size beta male, and the tiny gamma male Distinct genetically based strategies vs. Conditional strategy? If the 3 types represent 3 distinct strategies, then: 1. The differences between them should be genetic AND 2. The mean reproductive success of the 3 types should be equal Figure 7.24 Three different egg fertilization behaviors coexist in the bluegill sunfish Sperm Competition in the Black-winged Damselfly male Sperm transfer device female Lateral horn of the black-winged damselfly penis Mate Guarding Males Close-up of pedipalps Male Spider Mating spiders Mating Plug Severed male pedipalp in female genital pore Cannibalized male Female Mate choice leads to the evolution of nuptial gift giving Male dung beetle presents female with a dung ball Male hangingfly offers a moth Figure 7.31 Sperm transfer and the size of nuptial gifts Sexual cannibalism In some species, one sex (usually the female) consumes the other during sexual reproduction. Praying mantis Australian redback spider Scorpion Sexual suicide – the ultimate nuptial gift Australian Redback Spider Male somersaults his body right into her jaws Link to redback somersault video (Courtesy of Andrade Lab) Maydianne Andrade http://www.youtube.com/watch?v=F5WbtV GNpCI&feature=player_embedded#! 53 Good Parent Theory • Females prefer to mate with males that provide more paternal care • Male courtship is linked to his parental abilities 15-spined stickleback Healthy Mate or Good Genes • Bright colors can indicate good foraging ability, good health, stronger immune system (can help raise young, females avoid diseases and parasites if they choose them) • Male inherited good traits from his father (so he can pass them to offspring) Zebra finch Blue tit Do male ornaments signal good genes? Figure 7.38 Do male ornaments signal good genes? (Part 2) Figure 7.34 A sexually selected ornament Bird of Paradise Runaway Selection Theory • Female mate choice genes and genes for the preferred male attribute are inherited together. • Daughters inherit the genes for the mate preference, and sons inherit the preferred attribute (like bright tail in birds). • Males attract more females with the preference. • The mate preference “takes on a life of its own”. Runaway Selection in Stalk-eyed flies Chase-away selection theory (sensory exploitation) Sexual Conflict • Females resist matings, often have the control over which males get to mate • Males develop traits that enhance his ability to mate, even if it lowers female fitness (forced copulations, infanticide, transfer of toxic compounds during mating).

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