Contests Mate Choice - Armaments and weapons - Traits that confer advantage in fighting - Limited female choice - Ornaments and beauty - Traits that confer advantage in female choice - Very active female choice

“Where one sex invests considerably more than the other, members of the latter will compete among themselves to mate with members of the former” - Robert Trivers (1972) Females can only increase rep. success by turning food into eggs or offspring at a faster and/or more successful rate Females tend to be the choosier sex So are females choosy wrt to ‘ornamental’ traits?

Mean number of nests per male 2 1 Before after Anderson (1982) Mean number of nests per male 2 1 shortened III elongated Tail treatment After controls Control I – unmanipulated Control II – cut and glued back on

Question: What is the significance of mate choice by females in such species? And what is the significance of ornamental traits? 1)females choose mates at least in part based on traits that are indicators of parental care, e.g., courtship feeding (terns) or it is territory quality rather than the male per se. 2) Males tend to be highly ornamented with striking displays that appear to function in the choice of mates by females.

(1) Direct Selection is more important in monogamous relationships; male quality per se is not of interest, but rather his contribution or territory (2) In Arbitrary Mate Choice ornate traits do not signal male quality, rather they arise and become exaggerated through sensory bias/runaway selection (3) In contrast, the Good Genes Hypothesis males ornaments honestly signal their genetic quality and are used by females to choose quality males Fluctuating Asymmetry Handicap Principle Parasite Load (Hamilton-Zuk Hypothesis)

Direct Selection – Females are attracted to mates for reasons having to due with their own welfare or reproductive success. Laughing Gull – courtship feeding Male provision of resources, particularly the territory, probably the most common form of direct selection for territorial socially monogamous species – but clearly not the case in polygynous/ promiscuous species where males contribute only gametes

Male aggression and female choice may go hand in hand: Females choose males defending high quality territories - warm water for faster development - sparse vegetation so the eggs ball-up Preferred territories hotly contested for by males so that the strongest males end up in the best site

Hanging flies (Hylobittacus) and nuptial gifts females benefit through the reduced need to forage and direct energy gains

In Orthopterans, males produce their own nourishment via a spermatophore, which provides nutrition to the female This clearly benefits the female

The spermatophore may be so valuable that sex role reversal occurs Variance in reproductive success Environmental quality Males Females When food is common: spermatophores are easily produced and many males are available females are choosy When food is scare: spermatophores limit female reproduction and females should compete for males males are choosy

Direct Selection – Females are NOT selecting a male per se Relative lack of exaggerated or ornamental characters Blend of aggression among males (competition for territories) and female choice

Arbitrary Mate Choice – No underlying message of genetic quality conveyed by traits, rather an ornament is perceived as “attractive” and the more extravagant the more attractive 2 theories: Runaway Selection Sensory Bias Link between an exaggerated male trait and the preference for it – i.e., such a mating produces males with the trait and daughters with the preference for it

Sensory Bias (or Exploitation) may provide the proximate causation for Runaway Selection – i.e., preferences exist before the development a preferred trait

Zebra finches choose mates with artificial crests despite the fact that they lack an evolutionary history

Platyfish diverge from swordtails prior to the evolution of the sword tail.... Yet females show a strong preference for males with a sword tail ( after Basolo 1995 )

Female swordfish will respond to computer generated images

The neat thing about swords is they elicit the same response by females as body length, but are relatively easy to produce

Runaway-Selection predicts a genetic correlation between the male trait and female preference due to non-random mating

Males Females 50 males mate with 25 random females 10 males selected for next generation Test for a genetic correlation by offering females a choice between 2 males and recording either time spent with or number of copulations with male females – from treatments in which short male eye span was selected – preferred short eye stalk males Stalk-eyed flies - Cyrodiopsis Eye span Preference

Arbitrary Mate Choice – Link between male trait and female preference for it – Sensory Bias? Ornamental traits and strong female choice are correlated But no relationship between trait expression and males’ inherent quality

Good Genes – Females use male ornaments to gauge the genetic quality of males partners, e.g. genes of chosen males may provide their offspring w/inherited resistance to disease or parasites Females can enhance the well-being of her young (e.g., increased resistance) by choosing to mate with an individual with demonstrable health Females should focus on male features that honestly indicate physical condition and this promotes the evolution of those traits in males that signal their contribution to prospective mates Predicts: Ornaments/displays viewed as visible indicators of the underlying genetic quality of males 3 concepts: Handicap Principle Hamilton-Zuk Hypothesis Fluctuating Asymmetry

Females should focus on male features that honestly indicate physical condition and this promotes the evolution of those traits in males that signal their contribution to prospective mates

Signal intensity Fitness cost or benefit Cost – low quality Cost – high quality Benefit EQ low EQ high Handicap Principle – The size and conspicuousness of the males’s handicap is correlated to the phenotypic quality of the male. A very effective way to produce this is through costs that are disproportional to the males quality. Honest y arises through Costly signaling

Long-tailed widowbird Handicap Principle (Zahavi 1975) - The possession of ornamental traits is a Handicap in day-to-day-survival. Handicaps therefore are a reliable signal of male vigor (i.e., genetic quality). widowbird/euplectes-jacksoni/video- 00.html

Honest Signal?? – Testosterone influences the development of male secondary characters, e.g., song rate comb – jungle fowl tail length – barn swallow intensity of plumage, bare skin color Testosterone has a negative effect on the immune system – maximal elaboration of tes-driven traits simultaneous increases the risk of infection by disease/parasites It has to be COSTLY!! Advertises “I can survive & thrive despite suppression of the immune system”

Costly Signal Part III. – Carotenoid pigments (reds, yellows) must be consumed in the diet – therefore they are a signal to the quality of a territory, a male’s resource holding power, its forging aptitude, etc… e.g., brightness of red pigmentation of male House Finches used by females in mate choice, redder males are better parents, survive better, and that plumage color is related to dietary intake of cartenoids. - Signal nutritional status/health - May function in immune responses

Mates of sunscreened male produced fewer male offspring, supporting the notion that UV reflectance plays a role in male attractiveness Visible light UV light ControlSunscreen Male Blue Tits have a UV-reflecting crown patch

In Carolina wrens (Bewick’s wren is pictured) the BMR increases ~2-fold. Sage grouse displays: 2-4 fold increase in BMR Costly Signal Part IV. – Songs and displays are costly in terms of increased metabolic rate and missed opportunities – time allocated to singing is “lost”

Costly displays – Sage grouse 2 to 4 -fold increase in BMR

Honest Signals Part I – Fluctuating Asymmetry (NOT COST BASED): When normally bilaterally symmetric traits that are under the control of a single gene do not undergo identical development on both sides of the body

Considerable evidence exists that a large degree of FA in morphological characters indicates an individual has been unable to cope with stress during development of the trait

Sexually-selected traits are often displayed so as to “show-off” their degree of (a)symmetry. If low-quality males attempted to grow extravagant traits (e.g., long tails), they would possess a conspicuous degree of asymmetry

A role for asymmetry in humans?

Hamilton-Zuk Hypothesis (Parasite load hypothesis) – Relationship between ornamental traits and parasite load. 2 Components/predictions: (1) Interspecific (between spp) – in more heavily parasitized spp, females should discriminate more among males, sexual selection is more intense, and males become more ornamental Evidence is equivocal (2) Intraspecific (within spp) – Among males of a given spp, the less- parasitized (or non-parasitized) possess and display more highly developed ornamental traits. Females should prefer to mate with males that produce the most ornamental traits while simultaneously coping with and resisting the deleterious effects of parasites

Breeding plumage score 32.4% cestodes infection 12.2% Plumage variation in the male bar-tailed godwit # males captured # males seen in later years

true parents foster parents mites on offspring raised by foster parents (2) parasite load is heritable (3) parasite load is correlated w/tail length mites on offspring raised by foster parents Tail length tail treatment days between arrival to pairing (1)Female choice is based on male tail length S E after Møller (1990) # on parent

In conclusion: (1) Direct Selection - is most appropriate in monogamous relationships; male quality per se is not of interest, but rather his contribution or territory (2) In Arbitrary Mate Choice ornate traits do not signal male quality, rather they arise and become exaggerated through sensory bias/runaway selection (3) In contrast, the Good Genes Hypothesis females use male ornaments to honestly signal the genetic quality of males. Honest signals may arise thru testosterone-driven ornamentation and immune system suppression Carotenoid-based pigmentation Physical handicaps and predation risk Energetically-costly singing and displaying Expression of Fluctuating Asymmetry Hamilton-Zuk Hypothesis Ornamentation reveals Parasite Load and hence genetic quality Handicap Principle Ornamentation reveals male vigor (survivorship or energetic state) Fluctuating Assymetry Ornamentation reveals developmental stress