Speciation: Basic Concepts

Speciation: Basic Concepts

Concepts Speciation is the origin of new species and is at the focal point of evolutionary theory Evolutionary theory must explain how new species originate and how populations evolve Biological Species Concept

Species is a Latin word meaning kind or appearance Archaeopteryx lithographica Morphology, physiology, biochemistry, and DNA sequences are compared when grouping organisms Definition of Species

Species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations Concept of Species Biological species concept:

reproductive barriers Ecological species concept: ecological niche Morphological species concept: unique features depending on the species Phylogenetic species concept: common ancestor Biological Species Concept:

Similarity and diversity Similarity between different species Diversity within a species Reproductive Isolation Reproductive isolation is the existence of biological factors (barriers)

that impede two species from producing viable, fertile offspring Hybrids are the offspring of crosses between different species Reproductive isolation can be classified by whether factors act before fertilization (prezygote) or after fertilization (postzygote). Prezygotic (before the zygote)

Prezygotic barriers block fertilization from occurring by: Impeding different species from attempting to mate Preventing the successful completion of mating Hindering fertilization if mating is successful

Barriers Habitat isolation Behavioral isolation Temporal isolation Mechanical isolation Gametic isolation Habitat isolation

One lives in water, the other on land Behavioral isolation The dancing and singing are completely different Temporal Isolation One is diurnal and the other is nocturnal

Mechanical isolation Spirals in opposite directions Gametic Isolation Gametes are not compatible Timing of gamete release may be different Conditions in the female womb of

a different species may not be ideal for the sperm Gamete recognition hampered due to molecules around the ovum Postzygotic Barriers Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown

Reduced hybrid viability Ensantia hybrid shows to be frail, may not survive Reduced hybrid fertility Mule: sterile hybrid of donkey and horse Hybrid breakdown

Hybrid (center sample) is stunted and may not survive or reproduce Speciation Based on Gene Flow (a) Allopatric speciation (b) Sympatric speciation Allopatric In allopatric speciation, gene

flow is interrupted or reduced when a population is divided into geographically isolated subpopulations The definition of barrier depends on the ability of a population to disperse

Separate populations may evolve independently through mutation, natural selection, and genetic drift Allopatric speciation in the Grand Canyon A. harrisi A. leucurus

Reproductive isolation between populations generally increases as the distance between them increases Barriers to reproduction are intrinsic; separation itself is not a biological barrier Mantellinae

(Madagascar only): 100 species Rhacophorinae (India/Southeast Asia): 310 species Other Indian/ Southeast Asian frogs 100

60 80 1 2 20

40 0 3 Millions of years ago (mya) 1 3

2 India Madagascar 88 mya 65 mya

56 mya Sympatric Speciation Sympatric means same country Speciation takes place in geographically overlapping populations Occurs because of Polyploidism

Habitat differentiation Sexual selection Polyploidism Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division 1. Autopolyploidy 2. Allopolyploidy

Autopolyploidy in plants 2n=6 4n=12 Failure of cell division after chromosome duplication gives rise to tetraploid cells, which may be viable and self-fertile

Allopolyploid An allopolyploid is a species with multiple sets of chromosomes derived from different species Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids Ancestral species:

AA Triticum monococcum (2n = 14) BB Wild Triticum (2n = 14)

Product: AA BB DD T. aestivum (bread wheat) (2n = 42) DD

Wild T. tauschii (2n = 14) Habitat differentiation Sympatric speciation can also result from the appearance of new ecological niches North American maggot fly can live

on native hawthorn trees as well as more recently introduced apple trees, so food preference may isolate the two populations Sexual selection Sexual selection can drive sympatric speciation

Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria Hybrid Zones region in which members of different species meet and mate Patterns

abnormal, more fragile offspring, less fit (mule is sterile) more fit than the parents for both environments (paco vicua) Reinforced Barriers less fit hybrids might show a reinforcement in the barriers

stronger in sympatric than allopatric species Fusion barriers are not strong enough hybrids are more likely murky water resulting in interspecies mating

Stability the hybrid production is stable barriers haven't happened or are too weak still hybrids are not the norm because the location where they occur are the extremes of the normal habitat where the original species exist

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