Chapter #8 Life History Patterns (pg. 164 – 180) 8.1 – Reproduction May Be Sexual or Asexual

What are the goals for living organisms? 8.2 – Sexual Reproduction Takes Many Forms

Parthenogenesis – born w/o fertilization

Dioecious – Separate Males and Females

Hermaphroditic – Individual organisms with both male and female organs.

Monoecious – separate male and female flowers on the same plant. 8.3 – Mating Systems Describe the Pairing of Males and Females

Mating Systems Range from Monogamy to Promiscuity 8.3 – Mating Systems Describe the Pairing of Males and Females

Polygamy – the acquisition by another individual of two or more mates, none of which is mated to other individuals. A pair bond exists between the individuals and the individual having multiple mates is generally not involved in caring for the young. - Size of group depends upon synchrony of fertility and receptivity.

- Small time period – fewer individuals. - Longer time period – more individuals. 8.3 – Mating Systems Describe the Pairing of Males and Females

Polygyny – Where an individual male pairs with two or more females.

Polyandry – Where an individual female pairs with two or more males (exception rather than the rule)

Access to Parental resources Investment 8.3 – Mating Systems Describe the Pairing of Males and Females Relevance to Population Ecology

• Life-history characteristics determine – Organization of individuals in space and time • Examples… – How the population perpetuates itself • discretely vs. continuously; rapidly vs. slowly, etc… – Which characteristics will be selected for and persist within the population (due to sexual selection) • Conversely, selective pressures (abiotic factors, distribution of resources, etc..) will affect the life- history patterns observed . 8.4 – Acquisition of a Mate Involves Sexual Selection

What is the advantage to the individual and species by this display? 8.4 – Acquisition of a Mate Involves Sexual Selection Sexual Selection involves: -Intrasexual selection: male:male competition or female:female competition for access to potential mates. The maintenance of traits that assist in competition within the gender Æ successful mating.

- Intersexual selection: differential attractiveness of males to females and vice versa. The maintenance of traits that are attractive to the opposite gender. Which gender determines the “winner”? Intersexual Selection: A Focus on Female Choice • Material benefits: Nutrition Ex: hangflies) – Length of mating time depends on quality and size of “courtship gift” Intersexual Selection: A Focus on Female Choice • Material benefits: Anti-predator substances – Defensive compounds in arctiid moths

Photo: butterfly-conservation.org Intersexual Selection: A Focus on Female Choice

• Ability of males to provide sufficient sperm – Female fruit flies (some species) choose virgin males.

Photo: San Francisco Exploratorium Intersexual Selection: A Focus on Female Choice

• Parental Ability – Cannot assess directly – May be correlated with other features of the male – Example 1: Redwing blackbirds • “Epaulettes” correlated with nest defense • Courtship effort correlated with feeding effort Photo: Vancouverislandbirds.com Intersexual Selection: A Focus on Female Choice

• Parental Ability (Ex: sedge warbler) – Size of song repertoire correlates with chick weight at fledging The Sedge Warbler (cont.)

• Female sedge warblers choose on the basis of repertoire size. – Thus they choose the “most fit”males. Intersexual Selection: A Focus on Female Choice

• Health/Genetic Quality – Example: song repertoire in great reed warbler where: – Females chose males with larger repertoires. – This was correlated with greater offspring survival (unrelated to parental care). Intersexual Selection: A Focus on Female Choice

• Health/Genetic Quality – Example: Bright coloration of sticklebacks negatively correlated with low parasite loads Intersexual Selection: A Focus on Female Choice

• Health/Genetic quality (bright color negatively correlated with parasite load) – Advantages to females choosing these males • Avoid getting parasites while mating Æ • Avoid transferring parasites to young • Are choosing healthier males; their health status may be related to “genetic quality” Origin/maintenance of Mate Choice for “Exaggerated” Characteristics • In some species, why do males develop what appear to be extreme traits that actually can hamper their survival? – Example: Peacock’s tail Origin/maintenance of Mate Choice for “Exaggerated” Characteristics • Hypothesis 1: Runaway selection (R.A. Fisher - early 20th Century) – Directional that takes on a life of its own • Starts as an “honest signal” Æ more extreme. • Mechanism: Females choose males with large tails, multiple eyespots. Æ the next generation has a higher proportion of these males. – Will work even if his traits are not honest signals of quality. Why? – Evidence of arbitrary choices by females (bird band example) Origin/maintenance of Mate Choice for “Exaggerated” Characteristics • Hypothesis 2: Handicap or “good genes” hypothesis (R.A. Fisher) – Exaggerated trait might decrease chance of survival, only males with superior genes can survive despite the handicap. • Example: peacock tail as a handicap. – In this case, a female choosing a male with these traits would be improving her fitness. (His signal is an “honest signal” of fitness.) Distinguishing Between Runaway Selection and “Good Genes”(Petrie) • Methods – Males of different ornamentation/tail length randomly bred with females • Why random? – Young raised under identical conditions and then released • Results – Offspring of the “attractive” males weighed more at day 84. – Offspring of the attractive males were more likely to be alive after two years • Which hypothesis is supported by this data? Marion Petrie’s Peacock Data

Source: http://blog.lib.umn.edu/denis036/thisweekinevolution/2008/06/guest_blogger_the_peacocks_tal.html Origin/maintenance of Mate Choice for “Exaggerated” Characteristics

• How extreme can a characteristic become? Under what conditions will directional selection stop? (Think about costs vs. benefits…) Intrasexual Selection - Adaptations to Gain Access to Females –

• Dominance behavior & characteristics – Example 1: sexual dimorphism in elephant seals Male-male competition and sexual dimorphism (seals) NOTE: Each point represents a species Intrasexual Selection - Adaptations to Gain Access to Females –

• Weaponry for fighting with other males.

• Example: dung beetle!

Male dung beetle, Phanaeus vindex (Rattlebox photography) Intrasexual Selection - Adaptations to Gain Access to Females –

• Sneaker strategies – Example: Plainfin midshipmen • Dominant male features and behavior – Nest building, singing, guarding • Sneaker male features and behavior – No nest, no singing, just sex… – Small fish, big balls! Dung Beetles - Two Morphs

• Behavioral and morphological differences similarballs to midshipmen – Large, dominant males with horns defend burrows – Small, hornless males with “big ”sneak • Midshipmen – Genetically-based differences • Dung beetles – Nutritionally-based differences Intrasexual Selection - Adaptations Favoring Use of Sperm - • Displacing or inactivating rival sperm – Damselfly “scooper” penis Intrasexual Selection - Adaptations Favoring Use of Sperm - • Displacing or inactivating rival sperm – Example: Chemical sperm inactivation in fruit flies

Photo: San Francisco Exploratorium Intrasexual Selection - Adaptations Favoring Use of Sperm - • Mechanisms to avoid sperm displacement – Mate guarding (Example: many crab species) Intrasexual Selection - Adaptations Favoring Use of Sperm - • Mechanisms to avoid sperm displacement – Prolonged mating and cannibalism (example: redback spider) • Female less likely to mate with another if she eats him • He has low likelihood of finding a new mate (high predation) – Andrade, 1996 Intrasexual Selection - Adaptations Favoring Use of Sperm - • Mechanisms to avoid sperm displacement – Anti-aphrodisiac (Example: Heliconius erato) 8.5 – Females May Acquire Mates Based on Resources

In sexual Selection, the female will select mate(s) based on their physical characteristics, because this is an indirect measure of their health OR their (their mate’s) ability to acquire and defend resources (e.g., food and space).

Territoriality - Monogamy Sexual Selection

• Defined: – Selection for characteristics/behaviors that maximize chances of mating and producing the most, and highest quality, offspring. – A category within “natural selection” • General pattern: Male-male competition and female choice – Common pattern with many exceptions! Example: Satin bowerbird mating behavior • Each male builds an elaborate bower where he conducts his courtship display • Bowers located near each other • Each female visits several times, finally chooses a mate Bowerbird Males: # of Mates

• Some males are much more successful than others. Bowerbird Females: # of Mates Only ~1/3 of females have >1 mate. Why Do Males Usually Compete, While Females Choose?

• Hypothesis 1, A.J. Bateman: “Eggs are expensive, sperm is cheap!”

• Amount of energy invested in a single gamete is much greater for females (eggs) than for males (sperm) – Female bird may invest up to 30% of body weight in eggs. “Eggs Are Expensive, Sperm is Cheap.”

• Difference in investment per gamete – Example: Fairy wrens • Males have 8 billion sperm in testes at once • Females lay six eggs maximum per clutch • Female limited by egg production, • Male limited by number of mates only (presumably unlimited sperm) • Operational sex ratio skewed toward males But, Is Sperm Really Cheap?

• It often takes a large number of sperm to fertilize a single egg, due to – Hostile environment within female • Acid • Attacks by the immune system But, Is Sperm Really Cheap?

• Sperm competition among males – Occurs when females have multiple mates • Possibly the predominant situation • Fitness advantages for female (will explore in next lecture) – Some males may actually run out of sperm… • Garter snakes, zebra finch, blue crabs, rams… What if there is No Sperm Competition? • In sea horses, eggs are deposited into pouches, and there is not sperm competition. – Why not? • Male sea horses have relatively low sperm counts! But, Is Sperm Really Cheap?

• Drosophila bifurca: one sperm with long tail – Sperm tail is 20x length of his body. – His testes make up 11% of his body mass. Why Do Males Usually Compete, While Females Choose?

• Hypothesis 2 (R. Trivers): Competition vs. choice is based on individual with the most total parental investment – Often the female (example: mammals) – But in some species, male makes a greater total investment. Gulf Pipefish

• While male cares for a single brood, a female can produce two clutches of eggs Æ male has greater total parental investment – Operational sex ratio skewed toward females. • Males choose large, ornamented females over small, drab ones.

Female

Male Overview

• A mating system includes – how members of a particular species (or population) choose and bond with mates – how many mates per individual – how parental care (if it occurs) takes place. • Types of mating systems – Monogamy: One male mates with one female – Polygyny: One male mates with several females – Polyandry: One female mates with several males • “Social” vs. “genetic” monogamy Key Principles

• The system that evolves depends upon the individual interests of each gender. • Male and female interests are often in conflict. Why? – Differences in gamete investment and/or total parental investment – Male “default” system = ______. Why? – Is there a female default system? Why? • Interests/behavior of one gender serve to constrain options available to the other gender. Polygyny callipterus • Resource defense polygyny – Example: African cichlid fish, Lamprologus

• Defended resource = shells in which females lay eggs Polygyny

• Female defense polygyny – Example: Elephant seals (females aggregate)

Photo: www.driftersister.com Polygyny • Female defense polygyny – Example: Elephant seals (males compete for beachmaster status)

Photo: www.wetasschronicles.com Polygyny

• Lek polygyny – Males clump, but not due to another resource • Males become the clumped resource! – Example 1: satin bowerbirds Satin Bowerbirds: multiple signals of health and fitness (and good genes?) Polygyny • Lek polygyny – Males clump, but not due to another resource • Males become the clumped resource! – Example 2: sage grouse (filoplumes and sound in central area of lek determines mate preference) Polygyny

• Lek polygyny – Example 3: bullfrogs • Females choose males with longest, loudest and deepest calls • But don’t forget the sneaky f--kers

www.tc.umn.edu Polygyny: benefits/costs

• Male: – number of offspring (+) • Female: – gets a high-quality male (+) – gets less of the male’s time and attention for • raising young • being defended against predators Monogamy

• Common or rare? • In which group of animals is it most common? • What hypotheses would account for it?

www.magicmud.com Monogamy: alternate hypotheses

• Mate assistance: it takes two parents to raise the offspring – Example: Adelie penguins – Both parents needed for chick survival

Photo: Karen Haberman Monogamy: alternate hypotheses

• Mate guarding: guarding assures paternity; not guarding jeopardizes it. – Especially critical if females are rare or receptive for a limited time – Example: many crab species Monogamy: alternate hypotheses

• Female-enforced monogamy – Similar to mate-guarding, but done by female. – Example: Burying beetles – A female would lose resources, and possibly her offspring if she allows her male to mate again. www.royalbertmuseum.ca Monogamy: alternate hypotheses

• Danger “theory” – Leaving Æ increases chance of dying if predation rates are high. – Example: The mantis shrimp Lysiosquilla sulcata

Lysiosquilla sp. Opencage.info Mantis shrimp (another type) Monogamy: alternate hypotheses

• Pop ‘em out “theory” – Highly fertile mate – Not worth time/energy to seek another. – Example: Djungarian hamsters

bbs.petsky.com.cn Social Monogamy and extra-pair copulations • Extra-pair copulations can increase fitness of participants. • Males: More mates Æ more offspring possible. • Females: – Historical (not current) ideas: no advantage for females – Observational/experimental evidence: clear fitness benefits documented for some species • Example: Yellow-toothed cavy Yellow-toothed cavy: Offspring survival as a function of multiple mates for females Social Monogamy and extra-pair copulations • Direct fitness benefits: genetically based – Good genes • What does this mean? – Genetic compatibility • What does this mean? – Genetic variability among offspring • Why important? Social Monogamy and extra-pair copulations • Other benefits that may improve fitness for females: – More resources hypothesis • Example: Orange-rumped honeyguides swap food for sex. – Better protection/care hypothesis • Example: Dunnocks (European song bird) – Mate with two males Æ both care for young – Infanticide reduction hypothesis • Example: chimpanzees (who’s dad?) Polyandry (w/o polygyny)

• Spotted sandpipers: near-complete sex-role reversal – Females arrive on breeding grounds; compete with other females for territories. – Initial male arrives, mates, cares for her first clutch. – Second male arrives later, mates, and cares for her second clutch. What Circumstances Promote Polyandry? • Female: only lays 4 eggs at once – Add eggs (experimentally) Æ decrease the total young successfully raised • Related to incubation effort and protection – Female can ↑ reproductive success by laying a second broodÆ • Needs second mate • Reproductive success limited by mates rather than gametes in this case What Circumstances Promote Polyandry? • Why would males “comply?” – Operational sex ratio biased toward males (related to absolute ratio for this species) – She abandons Æ • He stays Æ offspring survive • He leaves Æ offspring die – Male 1: Certain of paternity for clutch 1; possibility of paternity for clutch 2 • How is this possible? – Male 2: Later arrivals less dominant, but still have a chance of paternity if they stay. What Circumstances Promote Polyandry? • Food fluctuation hypothesis – In food-poor years, females put all energy into eggs and have no energy left for care of eggs/young. • Mate assistance (by male) essential Æ monogamy – In food-rich years (i.e. many mayflies), the female “recovers” her body mass and can lay another batch • Monogamy Æ Polyandry What Circumstances Promote Polyandry? • Heavy predation pressure on nests – Multiple nests assure that at least some young will survive. • Male is needed to prevent predation • Young will all be lost if he doesn’t stay. Patterns of Reproductive Effort Variations • Numbers of young produced at a time – More young = less parental investment/individualÆ high mortality among young • Care of eggs/larvae – Variability in parental investment • Type of young produced – Precocial vs. altricial offspring (What is the difference?) Patterns of Reproductive Effort Variations • Number of reproductive events in a lifetime – Semelparous: one big reproductive event in lifetime/many offspring • Many are relatively short-lived (squid, annual plants) • But some are long-lived (periodical cicadas) – Itoparous: many reproductive events in lifetime/ fewer offspring per event. • Common especially birds and mammals • Timing is an issue: – begin early Æ materials/energy into reproduction, – Begin later Æ materials/energy into survival and growth “r ” vs. “K”strategists

“r”-strategists “K”-strategists Semelparous Itoparous Many offspring Few offspring Little/no parental investment High levels of investment per per individual offspring individual offspring Relatively short lifespan Relatively long lifespan Begin to reproduce relatively Begin to reproduce relatively early in life later in life Good colonizers of newly Not usually colonizers, but available habitat, but often arrive later in succession, not effective competitors compete successfully