Lecture 7 Study Guide: Social Behaviours PDF

1 2 Evolution refers to the gradual change in the genetic composition of populations over successive generations. This process occurs over long periods and is driven by various factors, including natural selection, genetic drift, mutation, and gene flow. Domestication and intentional artificial sele...

1 2 Evolution refers to the gradual change in the genetic composition of populations over successive generations. This process occurs over long periods and is driven by various factors, including natural selection, genetic drift, mutation, and gene flow. Domestication and intentional artificial selection are examples of human-driven evolutionary processes that have resulted in significant changes in domestic animal species over relatively short periods. 3 4 Cells are the fundamental units of life, and they are organized into complex systems within an organism's body, including sensory, nerve, muscle, and gland cells. A species is defined as a group of organisms capable of interbreeding and producing fertile offspring. Each species exhibits unique characteristics and behaviors, with considerable variability between species. 5 6 Speciation is the evolutionary process by which new species arise from a single ancestral species. This process involves the splitting of a population into genetically independent lineages. Speciation can occur through various mechanisms, including allopatric, peripatric, parapatric, and sympatric speciation. 7 8 Reproductive isolation mechanisms prevent the interbreeding of different species and promote speciation. Pre-zygotic isolation mechanisms prevent mating or fertilization between species, while post-zygotic isolation mechanisms result in sterile or inviable offspring. Examples of pre-zygotic isolation mechanisms include spatial, temporal, mechanical, behavioral, and gametic isolation. 9 10 Mechanical isolation occurs when reproductive organs of two species are structurally incompatible, preventing successful interbreeding. Even if two species attempt to mate, differences in their reproductive anatomy prevent copulation. An example is the mechanical incompatibility of reproductive organs in bushbabies (galagos) in Africa, which prevents hybridization between closely related species. 11 Post-zygotic barriers occur after mating has taken place but result in reduced hybrid viability or fertility. Reduced hybrid viability may lead to developmental abnormalities or fragile offspring, while reduced hybrid fertility produces healthy but sterile offspring. Hybrid breakdown occurs when first-generation hybrids are viable but second-generation hybrids are weak or sterile. 12 13 Allopatric speciation occurs when populations of a species become geographically isolated from each other, leading to genetic divergence and the eventual formation of distinct species. An example is the Galápagos finches, where different species of finches evolved unique beak shapes adapted to different food sources on different islands in the archipelago. 14 15 Parapatric speciation occurs when adjacent populations of a species evolve into distinct species while maintaining contact along a common border or hybrid zone. An example is the Bullock's Oriole and Baltimore Oriole, which evolved different songs to attract mates despite living in close proximity. 16 Peripatric speciation is a special type of allopatric speciation that involves geographic isolation of a small population, often due to a severe bottleneck event. This small population may experience genetic drift, leading to the accumulation of rare alleles and ultimately the formation of a new species. 17 18 Sympatric speciation is a controversial concept where new species emerge from individuals inhabiting the same geographic location. Unlike other forms of speciation, there are no physical barriers preventing members of the same species from mating. Instead, reproductive isolation occurs through factors such as habitat preferences or behavioral differences. For example, cichlid fish in East Africa exhibit sympatric speciation, where different species arise despite inhabiting the same body of water. 19 Animals exhibit various sleeping behaviors, from roosting in nests or trees to sleeping in water or even while flying. Different species have adapted unique sleeping strategies to suit their ecological needs and ensure safety from predators. For example, birds may roost in cavities, trees, or even in water to protect themselves during sleep. 20 The development of complex biological systems involves the accumulation of genetic variation over time. Variability is essential for evolution, and genetic recombination during sexual reproduction introduces new sources of variation. Fossil studies provide insights into the anatomical structures of ancient organisms but do not reveal details about their color, texture, or behavior. 21 Allele frequency refers to the relative occurrence of specific alleles within a population. Several factors influence allele frequency, including selection, migration, mutation, and genetic drift. Selection involves the differential survival of certain alleles, while migration introduces new genetic material or reduces existing diversity. Mutation leads to changes in DNA sequences, contributing to genetic variation, while genetic drift causes random changes in allele frequencies, particularly in small populations. 22 23 Natural selection favors traits that enhance an organism's fitness for survival and reproduction in its environment. In contrast, artificial selection is imposed by humans to selectively breed individuals with desired traits. Both natural and artificial selection play significant roles in shaping the genetic composition of populations over time. 24 Migration refers to the movement of individuals between different populations or geographic areas. It can be influenced by geographical barriers or changes in environmental conditions. Gene flow, resulting from migration, can either increase or decrease genetic diversity within populations and contribute to speciation by promoting or preventing gene exchange. 25 Mutations are random alterations in DNA sequences that may lead to changes in an organism's characteristics. They occur spontaneously and can include base substitutions, deletions, or additions. While most mutations have little impact on an organism's phenotype, some may result in significant changes that affect its survival and reproductive success. 26 27 enetic drift describes the random fluctuations in allele frequencies within populations due to chance events. It is more pronounced in small populations and can lead to the loss of alleles or fixation of others over time. Genetic drift has significant effects on genetic diversity and can influence the trajectory of evolution, particularly in isolated or bottlenecked populations. 28 The bottleneck effect occurs when a population undergoes a drastic reduction in size, leading to a loss of genetic diversity. In contrast, the founder effect occurs when a small group of individuals establishes a new population, resulting in a limited gene pool compared to the original population. Both phenomena can have significant consequences for genetic variation and evolutionary processes. 29 30 The founder effect and bottleneck effect are forms of genetic drift that can result in the loss of genetic diversity within populations. These events are particularly significant in small or isolated populations and can lead to the fixation of certain alleles or the loss of others over time. 31 Behavioral traits can also be influenced by genetic factors, as demonstrated by crossing experiments with lovebirds conducted by Dr. W.C. Dilger. Different species of lovebirds exhibit distinct behaviors related to gathering and carrying nesting material. When hybrids are produced from crosses between these species, they display intermediate behaviors, suggesting a genetic basis for these traits. 32 33 The observed behavioral differences between lovebird species suggest a genetic basis for nesting behavior. While hybrids exhibit a combination of behaviors from both parental species, these behaviors may not be as successful as those developed in purebred individuals. This suggests that natural selection may favor specific behavioral adaptations, leading to reproductive isolation between species. 34 The incomplete success of hybrid lovebirds in nesting behavior may contribute to species isolation by reducing their reproductive success. If hybrids cannot effectively carry nesting material, they may be less likely to produce viable offspring. This potential mechanism reinforces the genetic basis of behavioral traits and highlights their role in species divergence. 35 36 What is a Species? A species is a fundamental unit of biological classification representing a group of organisms that can interbreed and produce fertile offspring under natural conditions. It is defined as a category ranking below the genus or subgenus level and comprises closely related individuals capable of breeding with each other. Mechanisms of Speciation: Geographical and Genetic Models Speciation, the process by which new species arise, can occur through various mechanisms. Geographical models of speciation include allopatric, peripatric, parapatric, and sympatric speciation. These models involve different forms of geographic isolation or reproductive barriers that lead to the evolution of reproductive isolation between populations. Genetic models of speciation focus on genetic divergence and reproductive barriers within populations, such as chromosomal changes, polyploidy, and assortative mating. Examples of These Models in the Animal Kingdom Examples of geographical models of speciation include the evolution of polar bears from brown bears due to glaciation-induced isolation (peripatric speciation) and the divergence of Galápagos finches on different islands (allopatric speciation). Genetic models can be seen in cases of polyploidy in plants or the development of reproductive barriers within populations, such as differences in mating preferences or 37 behaviors. Reproductive Isolations: Types and Examples Reproductive isolation refers to mechanisms that prevent interbreeding between different species or populations, leading to speciation. Pre-zygotic barriers include spatial isolation (geographical separation), temporal isolation (different mating seasons), mechanical isolation (structural differences in reproductive organs), behavioral isolation (differences in mating behaviors), and gametic isolation (incompatibility of gametes). Post-zygotic barriers involve reduced hybrid viability or fertility, leading to unsuccessful or sterile offspring. How Animals Sleep Animals exhibit diverse sleeping patterns and behaviors adapted to their ecological niches and lifestyles. Some sleep in nests, caves, or burrows for protection, while others sleep while flying or floating in water. Sleep serves various functions, including restorative processes, thermoregulation, predator avoidance, and energy conservation. Factors Affecting Allele Frequency Allele frequency refers to the proportion of a particular allele in a population's gene pool. Factors influencing allele frequency include natural selection, migration, mutation, and genetic drift. Natural selection favors alleles that confer advantages for survival and reproduction, while migration introduces new alleles or reduces existing genetic variation. Mutation introduces new genetic variation, while genetic drift causes random changes in allele frequencies within populations, particularly in small populations. Mutation in Myostatin Gene Mutations in the myostatin gene can result in altered muscle development and increased muscle mass in animals. In certain cases, mutations that disrupt the function of myostatin can lead to enhanced muscle growth, known as double muscling, which has been observed in various livestock species. These mutations can have significant implications for animal breeding and agriculture. Crossing Experiments in Two Species of Lovebirds: Behavioral Outcomes Crossing experiments conducted with two species of lovebirds demonstrate the genetic basis of behavioral traits related to nesting behavior. Hybrids resulting from crosses between species exhibit intermediate behaviors, suggesting that nesting behavior is influenced by genetic factors. However, these hybrids may not display behaviors as successful as those of purebred individuals, highlighting the role of natural selection in shaping behavioral adaptations and species divergence. The Three-Toed Sloths: Most Important Facts Three-toed sloths are arboreal mammals known for their slow-moving and solitary lifestyles. They have specialized adaptations for their arboreal habitat, including long limbs with hooked claws for hanging from branches and a slow metabolic rate. Threetoed sloths feed primarily on leaves and spend most of their time in trees, descending to the ground only to defecate. Despite their slow movements, they have 37 evolved unique adaptations to survive in their environment, making them fascinating examples of evolutionary specialization. 37