9.2 Sympatric speciation and ecological divergence
2 min read•july 25, 2024
Speciation mechanisms are the processes that lead to the formation of new species. occurs within the same area, while happens when populations are geographically isolated. Both involve genetic divergence and reproductive isolation.
plays a crucial role in speciation. Populations can adapt to different niches, leading to and . Examples like the and show how and can drive sympatric speciation.
Speciation Mechanisms
Sympatric vs allopatric speciation
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- Sympatric speciation occurs within same geographic area populations diverge without physical barriers requires strong selective pressures or assortative mating (apple maggot fly)
- Allopatric speciation occurs when populations geographically isolated physical barriers prevent gene flow and lead to divergence (Galápagos finches)
- Key differences geographic context same area vs separate areas gene flow reduced vs completely prevented time frame typically faster in allopatric speciation
Ecological divergence in speciation
- Resource partitioning populations exploit different niches within same habitat reduces competition between subpopulations (Darwin's finches)
- Adaptive radiation rapid diversification to fill various ecological roles (Hawaiian honeycreepers)
- Reproductive isolation mechanisms:
- preferential use of different microhabitats
- different breeding times or seasons
- changes in mating preferences or rituals
- accumulation of adaptive mutations for specific niches reduced gene flow between ecologically divergent populations
Examples and Mechanisms
Examples of sympatric speciation
- Apple maggot fly (Rhagoletis pomonella) host shift from hawthorn to introduced apple trees temporal isolation due to different fruiting times genetic differences in host preference and emergence time
- Cichlid fish in African lakes rapid speciation in Lake Victoria and Lake Malawi divergence in feeding structures and mating colors ecological specialization for different depths and habitats
- Palms on Lord Howe Island (Howea forsteriana and Howea belmoreana) soil type preferences led to reproductive isolation
- Orcinus orca (killer whales) ecological divergence based on prey specialization resident transient and offshore ecotypes
Disruptive selection in sympatric speciation
- Disruptive selection favors extreme phenotypes over intermediate forms leads to bimodal distribution of traits in population
- Mechanisms promoting divergence:
- Assortative mating preference for similar phenotypes
- Reduced hybrid fitness intermediate phenotypes less adapted
- Reinforcement of reproductive barriers selection against hybrids strengthens isolation mechanisms
- Examples of traits under disruptive selection beak size in Galápagos finches body size in stickleback fish
- Frequency-dependent selection rare phenotypes may have higher fitness maintains diversity and promotes divergence
Key Terms to Review (20)
Adaptive Radiation: Adaptive radiation is the rapid evolution of diversely adapted species from a common ancestor in response to new environmental challenges and opportunities. This process often leads to the exploitation of various ecological niches, resulting in a wide variety of forms and functions among the descendant species.
Allopatric speciation: Allopatric speciation is the process by which new species arise from a common ancestor due to geographic isolation, leading to reproductive isolation as populations diverge over time. This phenomenon emphasizes the importance of physical barriers, like mountains or rivers, that separate populations, preventing gene flow and allowing evolutionary changes to accumulate independently in each group.
Apple maggot fly: The apple maggot fly (Rhagoletis pomonella) is a species of fruit fly that lays its eggs in apples, leading to significant agricultural damage. This insect is a classic example of sympatric speciation, as it evolved into two distinct forms based on host plant preferences, contributing to ecological divergence within overlapping populations.
Assortative mating: Assortative mating is a mating pattern where individuals select partners based on specific traits or characteristics, leading to non-random mating within a population. This behavior can influence the genetic structure of populations by increasing the frequency of certain traits and reducing genetic diversity. It can also contribute to reproductive isolation, which is essential in understanding processes like speciation.
Behavioral isolation: Behavioral isolation is a reproductive isolation mechanism that occurs when two populations develop differences in mating behaviors or rituals, preventing them from interbreeding. This type of isolation helps maintain the genetic distinctiveness of species by ensuring that individuals mate only with those that share similar behaviors, ultimately affecting gene flow between populations.
Cichlid fish: Cichlid fish are a diverse group of freshwater fish known for their remarkable evolutionary adaptations and speciation events, particularly in isolated ecosystems like the African Great Lakes. These fish exhibit an incredible range of forms, colors, and behaviors, often resulting from ecological divergence and competition for resources within their habitats.
Disruptive Selection: Disruptive selection is a type of natural selection that favors individuals at both extremes of a trait distribution while selecting against the average or intermediate phenotypes. This process can lead to increased genetic variance and may promote speciation, especially when the extremes have distinct advantages in their environment. Over time, disruptive selection can contribute to the emergence of new species by enhancing ecological divergence and altering allele frequencies in populations.
Ecological divergence: Ecological divergence refers to the process where populations of a species evolve different adaptations to exploit varying ecological niches, leading to reduced competition and increased specialization. This process is crucial for understanding how new species can arise from a common ancestor, particularly in environments where multiple habitats or resources are available, allowing populations to adapt to their specific surroundings.
Ecological Niche: An ecological niche refers to the role and position a species has within its environment, encompassing its habitat, resource use, and interactions with other organisms. It includes everything from where an organism lives to how it obtains food, interacts with competitors, and contributes to its ecosystem. This concept is crucial in understanding species coexistence, biodiversity, and the processes that drive both speciation and extinction.
Experimental evolution: Experimental evolution is a scientific approach that involves manipulating environmental conditions or genetic factors to observe evolutionary changes in organisms over time. This method allows researchers to study the processes of natural selection, adaptation, and speciation in real-time, providing valuable insights into how species evolve in response to ecological pressures.
Genetic differentiation: Genetic differentiation refers to the process by which distinct genetic variations emerge between populations of a species due to factors such as natural selection, genetic drift, and gene flow. This differentiation can lead to the development of unique traits and adaptations in different environments, affecting the potential for speciation and the maintenance of genetic diversity within populations. Understanding genetic differentiation is key to comprehending how species evolve and adapt in their respective habitats.
Genetic drift: Genetic drift is the random fluctuation in allele frequencies within a population due to chance events, leading to changes in genetic variation over time. This process can significantly impact small populations where random events can lead to large changes in allele frequencies, affecting evolution and the overall genetic diversity of populations.
Habitat isolation: Habitat isolation is a form of reproductive isolation that occurs when two species occupy different habitats within the same geographic area, preventing them from mating. This type of isolation can lead to speciation as populations adapt to their specific environments, often resulting in ecological divergence where species evolve unique traits suited for their distinct habitats.
Host race hypothesis: The host race hypothesis suggests that populations of a species can diverge into distinct races or ecotypes due to specialization on different host organisms. This divergence can lead to reproductive isolation and eventually speciation, especially in situations where multiple host types coexist in the same geographic area, promoting ecological differentiation among populations.
Lande's Model: Lande's Model is a theoretical framework that describes how genetic variation in a population can lead to adaptive divergence and speciation, particularly in the context of ecological differences among populations. This model emphasizes the role of natural selection and genetic drift in shaping the evolution of traits that allow organisms to exploit different ecological niches. It suggests that when populations experience different selective pressures due to their environments, they can evolve distinct adaptations, potentially leading to sympatric speciation.
Natural Selection: Natural selection is the process through which organisms better adapted to their environment tend to survive and produce more offspring. This concept is a key mechanism of evolution, linking genetic variation, adaptation, and the survival of the fittest in the dynamic interplay of species and their environments.
Phylogenetic Analysis: Phylogenetic analysis is a method used to infer the evolutionary relationships among various biological species or entities based on their genetic, morphological, or behavioral traits. This analysis allows scientists to construct evolutionary trees, known as phylogenies, which depict the lineage and divergence of species over time. Understanding these relationships is crucial in studying how species adapt to their environments and diversify, particularly in relation to geographical distributions and ecological interactions.
Resource partitioning: Resource partitioning refers to the process where competing species utilize different resources or use the same resource in different ways to minimize competition. This allows species to coexist in the same habitat by reducing direct competition for food, nesting sites, or other essential resources. Through this mechanism, resource partitioning can lead to ecological divergence and ultimately contribute to sympatric speciation, as species adapt to their unique ecological niches.
Sympatric speciation: Sympatric speciation is the process by which new species evolve from a single ancestral species while inhabiting the same geographic region. This type of speciation occurs without physical barriers, often driven by factors such as behavioral changes, ecological shifts, or variations in mating preferences that lead to reproductive isolation within populations.
Temporal isolation: Temporal isolation is a form of reproductive isolation that occurs when two populations breed at different times, preventing them from interbreeding. This can happen due to variations in mating seasons, daily activity patterns, or other timing factors, leading to a divergence in species even if they occupy the same habitat. It plays a critical role in maintaining genetic separation and can contribute to the process of speciation.