Speciation

More about change over time…

All organisms have adaptations that help them survive and thrive. Some adaptations are structuralStructural adaptations are physical features of an organism like the beak or feet on a bird, that help them to survive long enough to reproduce in their environment. • Opposable

Thumb• Binocular and Monocular Vision

• Camouflage and mimicry

Mimicry is a structural adaptation that is a form of camouflage that enables one species to resemble another species.

Other adaptations are behavioralBehavioral adaptations are the things organisms do to survive. For example, bird song, feeding patterns, and migration are behavioral adaptations.

Courtship and mating rituals are also behavioral adaptations

Bird of Paradise

Dispersal of parent organisms occurs by a variety of mechanisms:

Passive: (slowly alters gene pool over time)

• Migratory Random Walks • Continental Drift

• Mountain Building • Climate Changes

• Millions of years timescale

Active: (catastrophic "overnight" change in ecosystem)

• Asteroid Impacts • Large Floods • Volcano eruption • massive earthquake • the rapid emergence of 6 billion humans

The key is that basically, organisms become

ISOLATED.

DISPERSAL…CONTINUED

In nature, physical barriers can break large populations into smaller ones. Geographic isolation occurs whenever a physical barrier divides a population.

Whenever a new species evolves due to geographic isolation…

Reproductive isolation can occur when populations become increasingly distant, and are no longer able to mate and produce fertile offspring.Types of Prezygotic Isolation

Behavioral Isolation:

Temporal Isolation:

Mechanical Isolation:

The female is pre-wired to recognize certain mating rituals

Time of year for mating and reproduction separates speciesSpecies just become incompatible due to differences between body parts

Ecological Isolation:

Gametic Mortality:

Populations may adapt to different microenvironments in the same habitat, like the Manzanita Shrub.

Gametes of different species don’t recognize one another.

Postzygotic Isolation:While the embryo is developing, certain genetic combinations aren’t compatible, causing death to the embryo. Hybrids are usually weak, or sterile if they do survive. Mules (hybrid offspring between female horse and male donkey) are like this.

• Sympatric speciation occurs when there is no physical barrier, but populations still diverge (with slight ecological isolation…like the Cichlids)

• crater Lake Apoyo in Nicaragua was seeded once by the ancestral benthic species the Midas cichlid (Amphilophus citrinellus) 10,000 years ago. The most common cichlid species in the area;

• a new elongated limnetic species, the Arrow Cichlid (Amphilophus zaliosus) evolved in Lake Apoyo from the ancestral species (A. citrinellus) within less than 10,000 yr;

• the two species in Lake Apoyo are reproductively isolated

Parapatric Speciation• Neighboring populations become distinct

species while maintaining contact along a common border.

– Bordering individuals produce hybrids in a region called a “hybrid zone”

– These may eventually become a “subspecies”

Bullock’s Oriole and Baltimore Oriole

Gradualism vs. Punctuated Equilibrium

Gradualism is the idea that species originate through a gradual, slow and steady change of adaptations.

Punctuated Equilibrium is a hypothesis that argues that speciation occurs relatively quickly, in rapid bursts, with long periods of genetic equilibrium in between.Which do scientists accept? There is no reason why both scenarios can’t be true!

When an ancestral species evolves into an array or a “burst” of species (speciation) to fit a number of diverse habitats, the result is called adaptive radiation, or divergent evolution.

Founder Species

Fruit and seed eaters

Insect and nectar eaters

A pattern of evolution in which distantly related organisms evolve similar traits is called convergent evolution.This occurs when unrelated species occupy similar environments in different parts of the world. They evolve to look

similarly, but they may be genetically unrelated.

A bottleneck occurs whenever there has been a severe reduction in population size due to some calamity.• Contagious disease• Habitat loss• Hunting pressure

Oak WiltDue to human mining interestDeforestation in the Amazon

Founder Effect is a type of bottlenecking that occurs when a few organisms leave a population to establish a new one elsewhere. Speciation may occur rapidly due to chance

allelic frequencies of the “founder” organisms that differ from the original population.

The problem that all endangered or threatened species encounter is this tendency to be forced to “inbreed”. Within large populations, the tendency for this to occur is inconsequential. However, when there are only 100 of a species left, and they are forced to inbreed…then the tendency is for genetic diversity to diminish even further.

So what??? Why is genetic diversity important?

Another consequence of inbreeding in small populations is that recessive and possibly fatal combinations of alleles becomes greater.

Ethiopian Wolf

Genetic diversity gives species the chance to evolve. It provides enough variation for possible positive evolutionary outcomes. If certain allelic combinations produce organisms that are more susceptible to diseases, there would still be those individuals left to carry on the species who had the beneficial allelic combinations. The smaller the population, the less likely that is to occur.