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 similar to midshipmen – Large, dominant males with horns defend burrows – Small, hornless males with “big balls”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