BIO151 UNIT 4 CH. 24 THE ORIGIN OF SPECIES

speciation

the process by which one species splits into 2 species

helps explain features that organisms share

microevolution

changes over time in allele frequencies in a population

macroevolution

the broad pattern of evolution above the species level

biological species concept

species is a group of populations whose members have the potential to interbreed in nature & produce viable, fertile offspring

they don’t produce viable, fertile offspring with those of other groups

members of a biological species are noted by being reproductively compatible

reproductive isolation

the existence of biological factors that impede members of 2 species from interbreeding & producing viable, fertile offspring

hybrids

offspring that are a result of interbreeding mating

habitat isolation

2 species occupying different habitats within the same area, they rarely encounter each other, if ever

temporal isolation

species that breed during different times of the day, different seasons, or different years; gametes can’t be mixed

behavioral isolation

courtship rituals that attract mates & other behaviors unique to a species are barriers to even closely related species

mechanical isolation

mating is attempted, but morphological differences (usually with reproductive organs/systems) prevent successful completion

gametic isolation

sperm of one species can’t fertilize the eggs of another species; sometimes the sperm can’t survive inside the reproductive tract or biochemical mechanisms prevent the sperm from reaching the egg

prezygotic barriers

impede mating or hinder fertilization if mating occurs

acts: impeding the attempts to mate, preventing attempted mating from being completed, or by hindering fertilization if mating is completed

types: habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation

postzygotic barriers

prevents a hybrid zygote from developing into a viable, fertile adult

other times, their chances of surviving long enough to reproduce are decreased (if fertile)

types: reduced hybrid viability, reduced hybrid fertility, hybrid breakdown

reduced hybrid viability

the genes of different parent species may interact in ways that impair the hybrid’s development or survival in its environment

reduced hybrid fertility

they can be sterile, if the chromosomes of the two parent species differ in number or structure, meiosis in the hybrids may fail to produce normal gametes

hybrid breakdown

some first-generation hybrids are viable & fertile, but when they mate with one another or with either parent species, offspring of the next generation are feeble or sterile

morphological species concept

distinguishes a species by body shape & other structural features

ecological species concept

defines a species in terms of its ecological niche, the sum of how members of the species interact with the nonliving & living parts of their environment

allopatric speciation

gene flow is interrupted when a population is divided into geographically isolated subpopulations

sympatric speciation

occurs in populations that live in the same geographic area

how can reproductive barriers develop in sympatric populations?

barriers will occur if gene flow is reduced by factors such as:

polyploidy - more than 2 complete sets of chromosomes

sexual selection - certain inherited traits are more successful than others

habitat differentiation - where subpopulations adapt to certain ecological niches within the same geographic area

allopolyploid

a sterile hybrid that turned into a fertile polyploid

only fertile when mating with each other, can’t interbreed with either parent species, making them a new biological species

how do infertile hybrids become fertile polyploids?

they can propagate themselves asexually (like most plants do)

this is due to an error in mitosis or meiosis, which doubles the chromosome number; what was originally a sterile hybrid zygote becomes a fertile diploid cell, forming a new species (no longer hybrid)