Lecture 11 (Start of Test) - Social Behaviors PDF

1 MATING SYSTEMS (title) Mating systems refer to the patterns of sexual behavior within a species, particularly in terms of the number of sexual partners individuals acquire during a breeding season. Male: Monogamous: Individuals have only one sexual partner during the breeding season. Polygynous: M...

1 MATING SYSTEMS (title) Mating systems refer to the patterns of sexual behavior within a species, particularly in terms of the number of sexual partners individuals acquire during a breeding season. Male: Monogamous: Individuals have only one sexual partner during the breeding season. Polygynous: Males have multiple female sexual partners during the breeding season. Female: Monogamous: Females have only one male sexual partner during the breeding season. Polyandrous: Females have multiple male sexual partners during the breeding season. 2 MATING SYSTEMS AND SEXUAL DIMORPHISM (title) This slide discusses the relationship between mating systems and sexual dimorphism, which is the differences in appearance between males and females of the same species. Mating relationships vary from species to species. Promiscuous: There are no strong pair-bonds or lasting relationships; mating varies greatly. Monogamous: One male mates with one female, and individuals have similar external morphologies (monomorphy). Polygamous: Individuals of one sex mate with several individuals of the other sex. Polygyny/Polygynous: One male mates with many females, usually more showy and larger than the males. Polyandry/Polyandrous: One female mates with many males, often more showy than the females. 3 4 5 6 SEXUAL SELECTION (title) Sexual selection is a mechanism of evolution that acts on an organism's ability to obtain or successfully copulate with a mate. This slide highlights some key points about sexual selection: It is a "special case" of natural selection. Sexual selection can lead to features that may be harmful to an individual's survival, such as extravagant and colorful traits that also attract predators. Examples include peacocks (males) with elaborate tail feathers and peahens (females) choosing mates based on these traits. 7 MATING SYSTEMS (title) This slide delves deeper into how mating systems influence sexual selection by affecting the strength of sexual selection and the variance in mating success within a population: Monogamy: All males have the same mating success, usually having only one mate. Moderate polygyny: Some males have no mates, some have one mate, and some may have two mates. Strong polygyny: Most males have no mates, while one dominant male may have multiple mates. The example of elephant seals demonstrates different forms of polygyny, such as harem polygyny and territorial defense polygyny. 8 SEXUAL SELECTION (title) This slide explores the mechanisms of sexual selection, focusing on male competition and female choice: Male competition: Males compete for access to females, which can involve physical combat, displays, or other means. This competition determines which males get to mate, how much time they spend mating, and whose sperm fertilizes the female's eggs. Female choice: Females have the ability to choose which males to mate with, how long to mate, and even whose sperm will fertilize her eggs. Some females may even eject sperm from undesirable mates. 9 LEKKING POLYGYNY (title) Lekking polygyny describes a mating system where males congregate in a particular area, known as a lek, to display and compete for females. This slide highlights the combination of male competition and female choice within this mating system: Male competition: Males may engage in competitive behaviors to establish a dominant position within the lek, such as fighting for the center spot. Female choice: Females visit the lek and choose mates, often preferring dominant or centrally located males. Remember, reproductive success tends to be more variable in males compared to females within this system. 10 SEX ROLES (title) This slide addresses the question of why males and females exhibit typical roles in reproduction, focusing on reproductive success: Male blackbuck courting a female: This image likely illustrates typical mating behavior in blackbuck antelope, showcasing male courting behavior towards a female. 11 SEX ROLES (title) This slide introduces Angus John Bateman and his principle regarding sex roles and reproductive success: Bateman’s principle: It suggests that the sex which invests the most in offspring will become a limiting resource over which the other sex competes, leading to sexual selection. Males are under pressure to optimize offspring quantity (number of mating opportunities), while females optimize the quality of sperm (genetic contribution to the offspring). Bateman’s principle portrays females as the limiting factor of parental investment, over which males will compete to successfully mate. 12 SEX ROLES (title) This slide further explores reproductive success and its implications for males and females: Reproductive Success (RS): It refers to the production of independent offspring per breeding attempt or lifetime. Mating opportunities often limit male reproductive success, while fecundity (the ability to produce offspring) limits female reproductive success. 13 SEX ROLES (title) This slide outlines the differences in reproductive strategies and investment between males and females: Males: Sperm are limitless and fertile throughout life. Number of potential offspring is determined by the number of potential female partners. Required parental investment is low. Females: Eggs are much larger than sperm and released in limited numbers. Fertility is limited, and gestation periods are required. Nutrients for the fetus come from the mother's own supplies. Required parental investment is very high. Anisogamy refers to the difference in size between male and female gametes, with sperm being "cheaper" to produce than eggs. This leads to a greater level of parental investment in females. 14 POLYANDRY IN JACANAS (title) This slide discusses polyandry, a mating system where females have multiple male mates, focusing on jacanas, a type of bird. Key points include: Harem polyandry and "sex role reversal": Males maintain small territories and perform all parental care, while females mate with multiple males and leave eggs with males. Reproductive success: The number of males a female mates with determines her reproductive success, as she does not care for the eggs herself. Sexual dimorphism: Unusually, females are larger than males by 60% in mass. Females aggressively fight other females and may even kill their own chicks (infanticide). 15 Saddleback Tamarins, Spotted Sandpipers, Red-necked Phalaropes: Polyandry species This slide lists examples of species known for practicing polyandry, where females have multiple male mates. 16 MATING SYSTEMS (title) This slide explores when polyandry is favored as a mating system and its consequences: When is polyandry favored? Polyandry is favored when males become limiting resources for reproduction, often due to low offspring survival requiring male parental care. Consequences: In such cases, sexual selection is stronger on females than males. 17 Wild Saddle-back Tamarins (Saguinus fuscicollis) (title) This slide presents a specific example of polyandry in wild saddle-back tamarins in southeastern Peru: Monogamy vs. Polyandry: Adults mate monogamously only if they have nonreproductive helpers (older offspring) to assist with infant rearing. Without helpers, both male and female reproductive success is higher, on average, if they mate polyandrously. Cooperatively polyandrous groups: These are groups in which two or more females copulate with a single male during a single breeding season and then cooperate to raise the offspring. 18 19 SEXUAL DIMORPHISM AND SEXUAL SELECTION (title) This slide discusses sexual dimorphism and its relationship with sexual selection: Sexual dimorphism: It refers to differences in external appearance between males and females of a species. Sexual selection: Most sexual dimorphism is thought to have evolved through sexual selection, where traits are favored based on their attractiveness to the opposite sex. Fecundity selection: Selection on female fecundity, or the number of offspring produced, is often linked to sexual dimorphism. In species where females produce more eggs, sexual dimorphism tends to favor larger females, reflecting fecundity selection. 20 MATE CHOICE BY FEMALES (title) This slide discusses the phenomenon of mate choice by females, particularly in relation to intersexual competition and its implications: Female choice as intersexual competition: Females choose mates based on certain traits, driving sexual selection. Ornaments: Traits or features that often correlate with health and vitality, which females may prioritize when selecting mates. 21 THE WALRUS (title) Here, the focus is on walruses and their distinctive features and behaviors: Walrus tusks: Found in both males and females, with males typically having longer and wider tusks. Tusks play roles in masculinity, fighting, and helping walruses walk on land. Pharyngeal pouches: After diving, walruses can inflate throat pouches with air, using them to rest at the surface or make loud bell-like sounds during the breeding season. 22 THE WALRUS (title) Continuing with walruses, this slide details their mating behavior and reproductive patterns: Territorial behavior: Mature males claim aquatic territories (harems) near groups of females, where courting occurs. Mating dynamics: Each female chooses one male, with the strongest males securing the best territories. Females may mate with several males each season, but males typically mate with only one female. Reproductive rate: Walruses have a low reproductive rate, with females giving birth to only one calf every 2-3 years. Babies stay with their mothers for over 2 years. 23 MATE CHOICE BY FEMALES: ZEBRA FINCHES (title) This slide shifts focus to zebra finches and their mate choice behavior: Imprinting and mate choice: Female chicks that imprint on ornamented fathers are more likely to select ornamented mates. Role in evolution: Experiments suggest that mate choice by female zebra finches has played a significant role in the evolution of ornamentation in male zebra finches. 24 25 AVIAN ORNAMENTS: EXTRAVAGANT CHARACTERS DUE TO SEXUAL SELECTION (title) This slide discusses extravagant traits in birds and their implications: Examples: Long-tailed widowbirds and barn swallows with elongated tails. Reproductive success vs. costs: These traits can attract mates and increase reproductive success but may also incur costs, such as flight deficiencies or vulnerability to predators. 26 MALE ORNAMENTS: SEXUAL SELECTION (title) Here, Fisher's "runaway" hypothesis is introduced to explain the evolution of male ornaments: Fisher's hypothesis: Mate choice initially evolved to facilitate selection for traits conferring a survival advantage but later led to the preference for extravagant traits. Inheritance: Sons inherit traits that make them sexually attractive, while daughters inherit the majority of mate preferences. 27 RUNAWAY SELECTION HYPOTHESIS (title) This slide delves deeper into the runaway selection hypothesis: Trait preference: Some traits become so strongly preferred by females that only males with the strongest expression of the trait successfully mate. Consequences: Over time, offspring are more likely to possess the physical trait and preference for it, leading to extreme sexual dimorphism. However, this does not necessarily equate to higher quality in terms of survival or fitness. 28 29 MALE ORNAMENTS (title) This slide focuses on Zahavi's "handicap" hypothesis regarding extravagant male ornaments: Zahavi's hypothesis: Extravagant traits are costly to develop and maintain, serving as honest signals of genetic quality. Only males in good condition, with "good genes," can fully develop and maintain such ornaments. Costly signals: Males evolve costly signals to indicate their underlying genetic quality for survivorship. Amotz Zahavi: The scientist who proposed this hypothesis. 30 ZAHAVI’S HANDICAP HYPOTHESIS (title) Here, Zahavi's hypothesis is further explained, emphasizing female preference for males with handicaps: Female preference: Females prefer males with handicaps because these handicaps serve as indicators of heritable viability, suggesting the presence of good genes. Traits as indicators: Traits that encumber the owner are physiologically costly and indicate genetic quality, such as symmetry, bright color signaling immunocompetence, dominance, and parasite/disease resistance. 31 MATING SYSTEMS AND PARENTAL CARE (title) This slide addresses how the needs of offspring influence mating systems and parental care: Asymmetry in parental investment: Males typically have small gametes and provide minimal parental care, while females have large gametes and invest more energy in care. Effect on mating systems: The type of parental care needed by offspring influences mating systems, with monogamy favored when chicks require continuous care and polygyny favored when chicks can care for themselves early. 32 33 MATING SYSTEMS AND PARENTAL CARE (title) Continuing from the previous slide, this one emphasizes how certainty of paternity influences parental care and mating behavior: Certainty of paternity: Females are certain that their offspring carry their genes, but paternal certainty depends on mating behavior. Infanticide and heteropaternal superfecundation: These phenomena are discussed in relation to the uncertainty of paternity, particularly in species with internal fertilization. 34 MATING SYSTEM AND PARENTAL CARE IN BIRDS AND MAMMALS (title) This slide contrasts mating systems and parental care between birds and mammals: Mammals: Typically polygynous, with over 90% of species exhibiting this mating system. Male parental care is rare due to internal gestation and lactation. Birds: Mostly monogamous, with over 90% of species exhibiting this mating system. Male parental care is often essential because eggs must be incubated and chicks must be fed in most species. 35 Mating systems and sexual dimorphisms: This topic explores the relationship between mating systems (such as monogamy, polygyny, polyandry) and sexual dimorphisms (physical differences between males and females of a species). It investigates how different mating strategies influence the evolution of traits that enhance reproductive success and may lead to differences in appearance between males and females. Sexual selection: Sexual selection refers to the evolutionary process driven by competition for mates and choices made by one sex (usually females) regarding the other sex's traits. It can lead to the development of characteristics that increase an individual's chances of mating and reproducing, even if those traits may be detrimental in other aspects of life. Sex roles: Sex roles refer to the behaviors and activities typically associated with each sex within a species. These roles can vary widely between species and can include responsibilities related to courtship, mating, parental care, and other aspects of reproduction. Bateman’s Principle: Bateman's Principle, proposed by Angus John Bateman, suggests that the sex with the greater investment in offspring (typically females) will be more selective when choosing mates, leading to stronger sexual selection on that sex. This principle highlights the importance of parental investment in driving the 36 evolution of mating strategies and sexual behaviors. Male ornaments: Male ornaments are traits or characteristics that males develop to attract mates, often through sexual selection. These ornaments can include bright colors, elaborate displays, or physical features that enhance the male's attractiveness to females. Fisher’s “runaway” hypothesis: Fisher's runaway hypothesis proposes that certain traits become preferred by one sex (usually females) to such an extent that they are exaggerated over time, even if they are not directly beneficial for survival. This can lead to the development of extravagant or exaggerated traits that are favored solely because they are preferred by the opposite sex. Zahavi’s “handicap” hypothesis: Zahavi's handicap hypothesis suggests that extravagant traits or displays in males serve as honest indicators of genetic quality. These traits are costly to develop and maintain, so only males with good underlying genetic quality can afford to invest in them. Therefore, females choose mates with these traits as a signal of their genetic fitness. Parental care (investment): Parental care refers to the investment of time, energy, and resources by parents in the care and upbringing of offspring. This can include behaviors such as feeding, protecting, and teaching offspring. Parental care can vary greatly between species and sexes, with some species exhibiting extensive care from one or both parents, while others provide little to no care after offspring are born or hatched. 36