Name: natural selection patterns in populations
Uploaded: 2026-06-01T06:28:25.996Z
Duration: 1 min 46 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Biology

Biological Evolution- Unity and Diversity

LS.Bio.9.1

Types of Selection

- [Narratore] La selezione
naturale influenza la frequenza

di particolari alleli e fenotipi

all'interno della
popolazioni in svariati modi,

soprattutto attraverso
la selezione direzionale,

stabilizzante e diversificante.

Nella selezione direzionale,
un fenotipo estremo

subisce selezione positiva,
mentre l'altro negativa.

Per esempio, una specie di lucertole

si stabilisce su un'isola.

Senza competizione o predatori,

le femmine possono selezionare

maschi dai colori accesi
e vari, prestanti,

in un processo noto
come selezione sessuale.

Dato che le femmine si accoppiano

con maschi dai colori vari e brillanti,

la frequenza di quel fenotipo aumenta.

Tuttavia all'arrivo di un predatore

i maschi colorati diventano facili prede.

Dato che i maschi di colore opaco

non si accoppiano con frequenza elevata

e i maschi di colore vivace
vengono mangiati dai predatori,

il fenotipo intermedio
aumenta di frequenza.

Questo processo è noto come
selezione stabilizzante.

L'ultimo tipo di selezione,
quella diversificante,

accade quando vengono selezionati

entrambi i fenotipi estremi,

mentre quello intermedio
subisce selezione negativa.

Di nuovo, le lucertole arrivano
su un'isola senza predatori

e i maschi di colore vivace
sono selezionati dalle femmine

per via della maggiore prestanza.

Tuttavia i maschi di colore opaco

sono molto simili alle femmine

e riescono a inserirsi
negli accoppiamenti.

Questa azione incrementerà la frequenza

sia dei maschi di colore
vivace che di colore opaco,

mentre quelli di colore
intermedio diminuiranno.

Martin, Ryan A e David W Pfennig. "La diffusa selezione dirompente in natura è associata a un'intensa competizione per le risorse." BMC Evolutionary Biology 12 (2 agosto 2012): 136. [<a href="https://doi.org/10.1186/1471-2148-12-136" target="__blank">Sorgente</a>]

Podos, Jeffrey e Stephen Nowicki. "Becchi, adattamento ed evoluzione vocale nei fringuelli di Darwin". BioScience 54, n. 6 (1 giugno 2004): 501–10. [<a href="https://doi.org/10.1641/0006-3568(2004)054%5B0501:BAAVEI%5D2.0.CO;2" target="__blank">Source</a>]

tipi di selezione

La selezione naturale influenza le frequenze di particolari alleli e fenotipi all'interno delle popolazioni in diversi modi. Principalmente, la selezione naturale può essere direzionale, stabilizzante o dirompente. La selezione direzionale favorisce un tratto estremo e sposta la popolazione verso quel fenotipo mentre si seleziona contro gli individui che mostrano tratti alternativi. Stabilizzare la selezione favorisce un tratto intermedio con una gamma ristretta di variazioni. La deviazione dal fenotipo ottimale verso uno estremo è sfavorevole. Infine, la selezione dirompente favorisce entrambi gli estremi di un fenotipo, mentre i fenotipi intermedi vengono selezionati contro.

<h4>Selezione direzionale</h4>

La selezione direzionale favorisce un estremo di un fenotipo. Ad esempio, nel salmone di sockeye, la ricerca ha dimostrato che la selezione direzionale favorisce la migrazione stagionale prima. Si ritiene che ciò sia dovuto alla pressione predazione della pesca, poiché la pesca aumenta più avanti nella stagione migratoria. Pertanto, il pesce che arriva e depone le uova prima può avere maggiori possibilità di raggiungere la loro destinazione per riprodursi prima di essere catturato dai pescatori.

<h4>Stabilizzazione della selezione</h4>

Quando un particolare fenotipo non estremo è favorito, questo viene indicato come selezione stabilizzante. Ad esempio, in molte specie di uccelli, la dimensione della frizione (il numero di uova in una singola covata) è mantenuta all'interno di una finestra ottimale. Lapwings e pivieri dorati in genere depongono quattro uova. Questa ottimizzazione è un compromesso tra mantenere la dimensione della frizione abbastanza bassa da garantire risorse sufficienti per nutrire tutti i pulcini e avere abbastanza pulcini per garantire che almeno alcuni sopravvivano fino all'età adulta. Questo è un tema comune tra le specie di uccelli.

<h4>Selezione dirompente</h4>

In alcuni scenari, due estremi di un tratto possono essere più favorevoli nell'ambiente di un tratto intermedio. Lo schiaccianoci africano dal ventre nero (Pyrenestes ostrinus) mostra un impressionante polimorfismo per la dimensione del becco che non è determinato dal sesso, dalla dimensione del corpo, dall'età o dall'origine geografica. Esistono due principali polimorfismi distinti, dal becco piccolo e dal becco di grandi dimensioni. Questo tratto è controllato da un unico locus autosomico, con becco grande dominante. Queste due distinte morfologie del becco permettono ai frantumatori di semi di mangiare facilmente i semi di diverse erbe di carige. I soggetti dal becco piccolo mangiano principalmente specie di carige con semi più morbidi, mentre gli uccelli dal becco di grandi dimensioni possono rompere i semi più duri di altre specie di carige. Tuttavia, gli uccelli con becco di dimensioni intermedie non possono facilmente mangiarne entrambi i tipi e sono quindi raramente visibili.

Tipi di selezione

La selezione naturale influenza le frequenze di particolari alleli e fenotipi all'interno delle popolazioni in diversi modi. In primo luogo, ...

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Education

Didattica

JoVE Core

Biologia

Evolution

Evoluzione

Natural Selection

Selezione naturale

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

natural selection patterns in populations

Natural selection can change how alleles and traits appear in a population. The main patterns are directional selection, stabilizing selection, and disruptive selection. Each pattern favors a different range of phenotypes, or observable traits.

Directional selection favors one extreme of a trait. In sockeye salmon, selection appears to favor earlier migration in the season. Later in the migration season, fishing pressure is higher. Fish that arrive and spawn earlier may have a better chance to reproduce before being caught.

Stabilizing selection favors an intermediate trait. A common example is clutch size, which is the number of eggs in one brood. Many bird species, including lapwings and golden plovers, typically lay four eggs. This number seems to balance the need for enough chicks with the need to provide enough resources for them.

Disruptive selection favors both extremes of a trait while against the intermediate form. The African black-bellied seedcracker shows this pattern in beak size. Small-billed birds eat softer sedge seeds, and large-billed birds crack harder seeds. Birds with intermediate bills do not feed well on either seed type, so they are seen less often.

Natural Selection Patterns in Populations

natural-selection-patterns-in-populations

what is natural selection?

Natural Selection and Adaptive Evolution

Natural selection is an evolutionary process that changes populations over time. Individuals with traits that help them survive and reproduce tend to leave more offspring. As those favorable traits are passed on, they become more common in the population or species. These helpful traits usually begin with random genetic mutations. Natural selection can act only when a population shows variation, the trait is heritable, and the variation gives an evolutionary advantage. In other words, the...

types of selection

Natural selection can change how alleles and traits appear in a population. The main patterns are directional selection, stabilizing selection, and disruptive selection. Each pattern favors a different range of phenotypes, or observable traits. Directional selection favors one extreme of a trait. In sockeye salmon, selection appears to favor earlier migration in the season. Later in the migration season, fishing pressure is higher. Fish that arrive and spawn earlier may have a better chance to...

frequency-dependent selection

Common vs Rare Trait Selection

Common vs rare trait selection describes how a trait’s fitness can change based on how often it appears in a population. This process is called frequency-dependent selection. It can happen between species or within a single species. The effect may be positive, where common phenotypes do better, or negative, where rare phenotypes do better. Positive frequency-dependent selection gives an advantage to the most common phenotype. This is often seen in mimicry systems. In Central America,...

limits to natural selection

Why Natural Selection Has Limits

Natural selection has limits, even when a trait would seem helpful. Organisms that fit their environment better are more likely to survive and reproduce. But evolution does not always produce perfectly adapted organisms. One limit is that natural selection can only work with genetic variation that already exists. For example, red tusks might help elephants by discouraging ivory-seeking poachers. If no allele, or gene variant, for red tusks is present, natural selection cannot raise its...

key terms and concepts

Explore directional, stabilizing, and disruptive selection with real examples from salmon, birds, and seedcrackers. Learn how natural selection shapes populations.

Natural Selection Patterns in Populations | JoVE K12

JoVE Core series brings biology to life through over 300 concise and easy-to-understand animated video lessons that explain key concepts in biology, plus more than 150 scientist-in-action videos that show actual research experiments conducted in today’s laboratories.

biology

JoVE Core Biologia illustra i concetti chiave della biologia grazie a oltre 300 video-lezioni animate, concise e di facile comprensione. Inoltre, negli oltre 150 video di "scienziati in azione", i concetti scientifici vengono applicati e dimostrati da ricercatori attraverso esperimenti in laboratorio.

LS.Bio.9.3

Pennsylvania State Academic Standards

Life Science

Natural Selection and Evolution

3.1.9-12.T

3.1.9-12.U

3.1.9-12.W

Louisiana Student Standards for Science

High School

Life Sciences

Biological Evolution: Unity And Diversity

HS-LS4-2

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Mechanisms

Virginia  Standards of Learning

HIgh School

BIO.7

BIO.7.c

LS.11

LS.11.a

LS.11.c

Minnesota Academic Standards in Science

3.2.1 9L.3.2.1.3

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

Biological Evolution: Unity and Diversity

HS-LS4-4

Arizona Science Standards

HS+B.L4

HS+B.L4U1.14

Alabama Course of Study Science

Unity and Diversity

9-12.B.4.14

Next Generation Science Standards

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance and Variation of Traits

HS-LS3-3

HS-LS4-3

HS-LS4-5

Florida Department of Education

SC.912.L.15

SC.912.L.15.13

Texas Essential Knowledge and Skills

BIO.10

BIO.10.A

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

B-LS4-2.

B-LS4-3.

B-LS4-4.

new-york-state-science-learning-standards

New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS3-3.

HS-LS4-3.

HS-LS4-4.

Georgia Standards of Excellence

Ecology

SEC2.

SEC2.c

SB6.d

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Frequency-dependent Selection

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LS.Bio.9.2

Use models to illustrate the conditions required for natural selection, including the overproduction of offspring, inherited variation, and the struggle to survive.

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LS.Bio.9.4

Extinction

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LS.Bio.10.1

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LS.Bio.10.2

Understand natural selection as a mechanism for biological evolution.

Natural Selection Patterns in Populations

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