Adaptive_Radiations_in_Chondrichthyes_and_Actinopterygii[1].pptx

Adaptive Radiations in Chondrichthyes
and Actinopterygii
Dr Showkat Ahmad Wani

Introduction
• Adaptive radiation refers to the diversification of a single ancestral lineage into
a variety of species, each adapted to a specific niche or environment.
• This process is driven by ecological opportunities, morphological innovations,
and environmental changes.
• Chondrichthyans, with their ancient evolutionary history and remarkable
diversity, provide an excellent case study for understanding adaptive radiations.

Overview of Chondrichthyes
• Chondrichthyes are a class of cartilaginous fishes that first appeared over 400
million years ago during the Silurian period.
• They are characterized by their cartilaginous skeletons, placoid scales, and
well-developed sensory systems.
• The group includes two subclasses: Elasmobranchii (sharks, rays, and skates)
and Holocephali (chimaeras).

What is Adaptive Radiation?
• Adaptive radiation occurs when a single lineage rapidly diversifies into
multiple species, each occupying a distinct ecological niche.
• Key drivers include:
• Ecological opportunity: Availability of new habitats or resources.
• Morphological innovations: Evolution of new traits that enable exploitation of new
niches.
• Environmental changes: Shifts in climate, sea levels, or competition.

Historical Context of Chondrichthyan Radiations
• Chondrichthyans have undergone multiple adaptive radiations throughout
their evolutionary history.
• The first major radiation occurred during the Devonian period, when early
chondrichthyans diversified into various marine environments.
• A second significant radiation took place during the Mesozoic era, coinciding
with the rise of modern sharks and rays.

Case Studies of Adaptive Radiations in
Chondrichthyes – Sharks
• Sharks are a prime example of adaptive radiation, with over 500 extant
species occupying diverse niches.
• Examples:
• Pelagic sharks (e.g., great white shark, Carcharodon carcharias): Adapted for open-ocean
hunting with streamlined bodies and powerful tails.
• Benthic sharks (e.g., wobbegong sharks, Orectolobidae): Camouflaged for life on the
seafloor, with flattened bodies and cryptic coloration.
• Deep-sea sharks (e.g., lantern sharks, Etmopteridae): Bioluminescent adaptations for life
in the dark depths.

Case Studies of Adaptive Radiations in Chondrichthyes – Rays and Skates
• Rays and skates have evolved flattened bodies and enlarged pectoral fins for
benthic life.
• Examples:
• Manta rays (Mobula): Filter feeders adapted to pelagic environments.
• Electric rays (Torpediniformes): Possess electric organs for predation and defense.
• Stingrays (Dasyatidae): Adapted for life on the seafloor, with venomous spines for
protection.

Case Studies of Adaptive Radiations in Chondrichthyes –
Chimaeras
• Chimaeras, or ghost sharks, represent a more basal lineage within
Chondrichthyes.
• They have adapted to deep-sea environments, with elongated bodies and
specialized sensory systems.

Key Adaptations Driving Radiations
• Feeding strategies: Diversification of jaw morphology and dentition (e.g.,
crushing plates in rays, serrated teeth in sharks).
• Locomotion: Variations in body shape and fin structure for different
swimming styles (e.g., fast pelagic swimmers vs. slow benthic cruisers).
• Sensory systems: Enhanced electroreception, olfaction, and vision for
detecting prey in diverse environments.
• Reproductive strategies: Evolution of oviparity, viviparity, and ovoviviparity to
suit different ecological niches.

Ecological and Evolutionary Significance
• Chondrichthyans play critical roles as apex predators and mesopredators in
marine ecosystems.
• Their adaptive radiations have contributed to the stability and complexity of
marine food webs.
• Studying their evolutionary history provides insights into the processes of
speciation and adaptation.

Conclusion
• Adaptive radiations in Chondrichthyes illustrate the remarkable ability of life
to diversify and thrive in response to changing environments.
• From the open ocean to the deep sea, sharks, rays, and chimaeras have
evolved an incredible array of adaptations that underscore their evolutionary
success.
• By studying these radiations, we gain a deeper appreciation for the
complexity of life and the importance of conserving these ancient and
fascinating creatures

Overview of Actinopterygii
• Actinopterygii, or ray-finned fishes, are characterized by their bony rays supporting
the fins, as opposed to the fleshy lobes found in lobe-finned fishes (Sarcopterygii).
• They first appeared in the fossil record during the Silurian period (~420 million years
ago) and have since diversified into a wide array of habitats, including freshwater,
marine, and brackish environments.
• The group includes familiar fishes such as salmon, tuna, seahorses, and clownfish, as
well as lesser-known species like deep-sea anglerfish and freshwater electric eels.

What is Adaptive Radiation?
• Adaptive radiation occurs when a single ancestral lineage rapidly diversifies into
multiple species, each adapted to a specific ecological niche.
• Key drivers include:
• Ecological opportunity: Availability of new habitats or resources (e.g., colonization of freshwater
systems or coral reefs).
• Morphological innovations: Evolution of new traits that enable exploitation of new niches (e.g.,
jaw protrusion, specialized fin structures).
• Environmental changes: Shifts in climate, sea levels, or competition that create new selective
pressures.

Historical Context of Actinopterygian Radiations
• Actinopterygii have undergone several major adaptive radiations throughout
their evolutionary history:
• Devonian period: Early radiation of primitive ray-finned fishes in marine environments.
• Carboniferous to Permian periods: Diversification into freshwater habitats.
• Mesozoic era: Rise of modern teleosts, the most diverse and successful group of
Actinopterygii.
• Cenozoic era: Explosive diversification in response to the formation of new habitats, such
as coral reefs and river systems.

Adaptive Radiations in Actinopterygii – Teleost Fishes
• Teleosts account for over 95% of all Actinopterygii and represent one of the most
spectacular examples of adaptive radiation.
• Examples:
• Coral reef fishes (e.g., wrasses, parrotfish, clownfish): Adapted to the complex and competitive reef
environment with bright coloration, specialized feeding structures, and symbiotic relationships.
• Pelagic predators (e.g., tuna, marlin): Streamlined bodies, high-speed swimming, and advanced
sensory systems for open-ocean hunting.
• Deep-sea fishes (e.g., anglerfish, gulper eels): Bioluminescence, elongated bodies, and expandable
stomachs for life in the dark, nutrient-scarce depths.

Adaptive Radiations in Actinopterygii – Freshwater Radiations
• Freshwater systems have been hotspots for actinopterygian diversification due to
their isolated and diverse habitats.
• Examples:
• Cichlids (e.g., African Rift Lake cichlids): Over 2,000 species with diverse feeding strategies
(herbivores, carnivores, planktivores) and morphological adaptations (jaw shapes, body sizes).
• Characins (e.g., tetras, piranhas): Adapted to riverine environments with varied feeding and
reproductive strategies.
• Catfishes (e.g., Siluriformes): Bottom-dwelling species with sensory barbels and armor-like plates.

Adaptive Radiations in Actinopterygii – Extreme Environments
• Actinopterygii have radiated into some of the most extreme environments on
Earth.
• Examples:
• Desert pupfish (e.g., Cyprinodon): Adapted to high salinity and temperature fluctuations
in isolated desert springs.
• Cavefish (e.g., Astyanax mexicanus): Evolved loss of pigmentation and eyesight in
response to life in complete darkness.

Key Adaptations Driving Radiations
• Feeding strategies: Evolution of specialized jaws, teeth, and pharyngeal structures
for diverse diets (e.g., crushing mollusks, grazing algae, or filter-feeding plankton).
• Locomotion: Variations in fin shape and body form for different swimming styles
(e.g., fast pelagic swimmers, slow benthic cruisers, or maneuverable reef dwellers).
• Reproductive strategies: Diverse modes of reproduction, including external
fertilization, live-bearing, and mouthbrooding.
• Sensory systems: Enhanced vision, electroreception, and lateral line systems for
detecting prey and navigating complex environments.

Ecological and Evolutionary Significance
• Actinopterygii play critical roles in aquatic ecosystems as predators, prey, and
ecosystem engineers.
• Their adaptive radiations have contributed to the biodiversity and stability of
freshwater and marine ecosystems.
• Studying their evolutionary history provides insights into the processes of
speciation, adaptation, and ecological interactions.

Challenges and Conservation
• Many actinopterygian species are threatened by habitat destruction,
overfishing, pollution, and climate change.
• Understanding their adaptive radiations can inform conservation strategies by
highlighting their ecological roles and evolutionary uniqueness.

Conclusion
• Adaptive radiations in Actinopterygii illustrate the remarkable ability of life to
diversify and thrive in response to changing environments.
• From coral reefs to deep-sea trenches, ray-finned fishes have evolved an
incredible array of adaptations that underscore their evolutionary success.
• By studying these radiations, we gain a deeper appreciation for the complexity
of life and the importance of conserving these diverse and fascinating creatures.

Adaptive_Radiations_in_Chondrichthyes_and_Actinopterygii[1].pptx

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