INTRODUCTION

SPECIATION

* A process regarding the formation of new species from the pre-existing species through evolution.

* It usually depends on the isolation of two polulations as well as their genetic divergence.

Types of speciation

                                                                 

Allopatric speciation

* When two populations are Geographically isolated from one another

* separated by distance or an impassable barrier 

Eg: rising sea level

Archipelago Island

* The vast expanse of ocean that isolated the island from the main land function as a

  geographical barrier to gene flow

* Thus, over generations, the island population diverges from the mainland species.

* Individuals of the diverging population may in turn colonize other islands in the

  archipelago.

* The Hawaiian archipelago includes 19 islands and more than 100 atolls that stretch 1500

  miles in the Pacific ocean.

* The habitats on the land masses of this archipelago range from lava beds, rain forest ,

  and grasslands to dry woodlands and snow-capped peaks.

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Parapatric speciation

* Occur when one population extends across a broad region encompassing diverse habitats.


* No specific extrinsic barrier to gene flow


* Population continuous but does not mate randomly


* Individuals more likely to mate with their same Geographic neighbors.

Although continuously distributed, different flowering times have begun to reduce gene flow between metal-tolerant plants and metal-intolerant plants.

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sympatric speciation

* Population inhabiting the same geographic region speciate in the absence of a physical barrier between them.

red fish

blue fish

pictures above : Mutations in genes that affect female's perception of color of ambient light in deeper or shallower regions of lake also affect their choice of mates. 

** Female cichlids prefer to mate with brightly colored males of their own species

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Hawaiian honeycreepers

Allopatric Speciation on an Archipelagos

Akepa

Akekee

Nihoa finch

Palila

Maui Parrotbill

Apapane

Pooli

Maui Alauahio

Kauai Amakihi

Akiapolaau

Akohekohe

Liwi

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