Diversity of Life in the Sea

• It would be virtually impossible to consider the breadth of organisms in the sea without some sort of classification system

Diversity of Life in the Sea

• Fortunately, there is a unifying concept that helps make this bewildering diversity of life comprehensible: EVOLUTION!

• Evolution describes the genetic changes in a population over time

• Organisms are adapted to their environment; a good fit (but not perfect!)

Natural Selection and Adaptation

• Evolution is descent with modification• Evolution occurs because individual organisms

have genetic differences in their ability to find food, mates, avoid being eaten, in their metabolism and in countless other attributes

• The best adapted individuals – those most successful at meeting the challenges of the environment – produce more offspring (on average) than those not so well-adapted.

Natural Selection

• Natural selection is the process by which favorable, inherited traits become more numerous in successive generations of a population of reproducing organisms

• Over time, natural selection leads to species that are well adapted (highly evolved) to their environments

• Populations either adapt to environmental changes or become extinct

The Principles of Natural Selection

King Penguin Rookery © Momatiuk - Eastcott/Corbis

• Struggle for existence/Competition – More offspring are produced than can be supported

by resources

The Principles of Natural Selection• Variation

– Some individuals, due to heredity or mutation, possess characteristics which make them better

adapted to their environment

The Principles of Natural Selection• Inheritance of Traits

– Best-suited organisms will survive to produce more individuals that share same adaptation

Population with varied inherited traits1

Elimination of individuals with certain traits2

Reproduction of survivors3

Certain individuals with a distinct, inherited characteristic will be selected against, while others with a (different) distinct, inherited trait will survive

Classifying Living Things• The adaptation of various populations to

different environments has produced a fantastic variety of life forms

• In order to properly study these organisms, it is necessary to classify them

• Must first identify what a “species” is exactly

What defines a species?

• Biological species concept: – A species consists of a population whose

members have the potential to interbreed with one another in nature to produce viable, fertile offspring, but who cannot interbreed with other such groups

– Species are based on their ability to interbreed; not on physical similarities!

Biological Species Concept• All domesticated dogs are the same species

because they can interbreed; a subspecies of the gray wolf, Canis lupus

Taxonomy

• Taxonomy is the practice and science of classification

• Taxonomy uses taxonomic units, or taxon• A taxon is a taxonomic unit at any level; for

example, Mammalia is a taxon at the Class level

• Domain Kingdom Phylum Class Order Family Genus Species

Domain

Kingdom

Phylum

Subphylum

Class

Order

Family

Genus

Species

Diversification

Scientific names

• Organisms are typically identified by 2 names; the name of their genus and their species = scientific name

• No two organisms can have the same scientific name and this name is the same everywhere in the world!

• Written as Genus species

Orcinus orca

Taxonomy• Scientific names are descriptive• May describe unique characteristic, region

where species is found, etc.• Ex. Humpback whale Megaptera novaeangliae

= “long-winged New Englander”• Common names

can be deceiving!!!– “dolphin”– “bear”

Phylogenetics

• Many hierarchies are being re-examined based on the results of molecular analysis (DNA, RNA)

• Binomial taxonomy does not take into account evolutionary relationships

• Enter phylogeny and systematics…• Reconstructs evolutionary relationships by

grouping organisms by their relatedness

Phylogeny and Systematics• Systematics is the reconstruction and study of

evolutionary relationships• Phylogeny – an evolutionary tree; species

grouped by how long they’ve shared a common ancestor

• Evidence for determining these relationships must come from body structure*, reproduction, embryological and larval development, and molecular characteristics

*homologous structures

http://www.edwardtbabinski.us/mpm/mpm_whale_limb.html

Homologous structures

Phylogenetic Tree: The Tree of Life

• Domain Archaea• Domain Bacteria

• Domain Eukarya

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No nucleus Have a nucleus