Topic 17: Mating Systems. Reproduction. How are natural, fecundity & sexual selection different? Why does sexual dimorphism evolve?

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1 Topic 17: Mating Systems Why does sexual dimorphism evolve? How are natural, fecundity and sexual selection different? What is fitness? How does each one work? Reproduction Mating Last lecture Development Last lecture Life history Last lecture Selecting mates Sexual selection Mating systems What are some examples of herp mating systems? Photos KP & K Bergmann Why does sexual dimorphism evolve? How are natural, fecundity & sexual selection different? Which is male and which is female? Why? Vipera berus Atelopus zetecki Triturus cristatus Natural selection Facilitates survival Escape from predators Obtaining prey Being efficient Fecundity selection _ mates _ mates Producing Chamaeleo calyptratus Platysaurus capensis Photos G Simpson, J Sevcik, FLchams.com, generalexotics.com,?? Pough et al. Fig 15-24,?? 1

2 Fecundity vs. Sexual Selection What is fitness? Vipera berus Female > Male developing offspring Phrynosoma cornutum Female > Male Males are Travel to find Hyla arenicolor Male > Female Males Call to The number of viable offspring that you produce Function of: How long you Natural Selection Number of Sexual Selection Number of per mate/clutch Fecundity Selection Quality of Photos G Simpson, aftfullbirds.com, KP Bergmann Photos??, KP Bergmann Often causes Can cause rapid divergence and speciation Often causes sexual dimorphism Can cause rapid divergence and speciation Intrasexual Sex that invests less typically competes Not always male-male Competing sex often has special structures Often relatively low cost Combat to establish dominance Ritualized Real Intersexual Sex that invests more is typically choosy Often results in strong selection for expensive phenotypes Non-choosy sex shows off to attract the choosy sex Nicholson et al. 2008; K Bergmann 2

3 Often includes Sperm competition Sometimes ritualized to avoid injury Other times can be dangerous Photos M Jones, D Endico, A Moussalli Pough et al. Fig Ambystoma maculatum sperm competition competition for females Male gains control over multiple females Polygyny, harem Pough et al. Fig. 14-5, photo M Graziano Photo J Dougherty Male defends resources in a territory Females have smaller territories within male territory Heterogeneous habitat When females are rare Polyandry Mating season is short Free-for-all Can be dangerous, especially to female Photo KP Bergmann Photo M Benard, R Taylor, T Crocetta 1

4 Females typically invest more resources in reproduction Look for good quality mates Females look for males with: calls Indications of What are the two types of sexual selection? Evolution of traits in males Require a lot of energy to produce Attract predators Prevent males from foraging, etc. Photos W Wells,?? All figures from Ryan 2010 Alternate hypotheses for what females are looking for Good genes Handicap principle (Zahavi 1975) What are the two types of sexual selection? Alternate hypotheses for what females are looking for Good genes Handicap principle (Zahavi 1975) Sexy sons (Weatherhead & Robertson 1979) Sensory bias Crotaphytus collaris Males with wider heads bite harder & run faster Have larger territories Get more matings Lappin & Husak 2005 Sexy sons (Weatherhead & Robertson 1979) Sensory bias Sceloporus virgatus Males with higher [T] Bite harder Run faster But have more mites Photo W Wells Photo PJB, graph: Cox & John-Alder 2007 What are the two types of sexual selection? a display area where males aggregate and compete to allow females to choose When female territories are large (hard to visit) get all the matings Frog choruses Physolaemus pustulosus Females prefer males that make more chucks What is a mating system? How a group is structured in relation to mating How many and which males mate with how many and which females A simple (and powerful) way to look at it: How Many? 1 Female > 1 Female 1 Male > 1 Male o Can be more specific and complicated as well o What mating systems have we already seen? Ryan

5 Type of monogamy Males are common Females are rare Often in interest of male, not necessarily female Copulation in some snakes can last 24 hrs Atelopus frog males stay with females for weeks or months Monogamy Tiliqua rugosa Males find females by scent Spend 6-8 weeks together before mating Pair bonding lasts multiple seasons Males are aggressive to other males Female produces small litters every 2-3 years Photo J Sevcik Photo PJB Polygyny Few males often get all matings Amblyrhynchus cristatus Males for leks Males also fight for territories Can lose 26% body mass by constantly displaying Females set up territories by males they choose Choose the largest males with most vigorous displays Polyandry Females like variety and call the shots Triturus vulgaris Elaborate courtship rituals Female chooses which males to mate with Fertilization occurs just before ovipostion sperm competition Photo J Dougherty,?? Pough et al. Fig 13-10, Photo J Bohdal Polyandry Thamnophis sirtalis Scramble competition and mating ball Male produce pheromone to decrease female interest in other males Also pheromone to make males look like females Sperm plugs used Photo R Taylor Cheating Ambystoma tigrinum Sneaker male goes between male and female Pretends to be female to the male Pretends to be male to the female Deposits spermatophore Pough et al. Fig Female Chosen Male Sneaker Male 3

6 Cheating: Rana temporaria Pirate male deposits sperm on a freshlyfertilized clutch Need external fertilization Multiple alternative mating strategies Uta stansburiana and Rock-Paper-Scissors Morph depends on [T] Does not change during life Morph fitness changes with Defend large territories In control of multiple females Usurp females from blue males _ No territories Look female Sneak copulations Not detected by orange males Defend small territories Guard females Detect and repel yellow males Photo: P Krasensky, Figure: Vieites et al Pough et al, Fig