8.2 - Speciation

1. 8.2 - Speciation when is a species no longer a species? hybrids like mules, ligers, or grolar bear are not species because they are sterile the biological species concept includes members of a population or group of populations that breed naturally together and produce viable (i.e. fertile) offspring this definition does not include asexually reproducing organisms and it can only apply to those organisms still reproducing (i.e. not fossils)

2. Macroevolution • speciation describes the origin of new species and is the main focus of macroevolution microevolution explains how allele frequencies change in populations through adaptations, but not the origin of unique species, extinction of species, or the evolution of major new traits like wings or flowers

3. Reproductive Barriers Between Species • the effectiveness of a geographic barrier to maintain reproductive isolation is determined by the ability of an organism to bridge the gap (i.e. by size, flight, wind dispersal) the formation of a new species relies on reproductive isolation from similar species, either in the form of physical or behavioural barriers geographical isolation results from the rearrangement of the Earth’s surface through geological processes (i.e. orogenesis, island formation)

4. allopatric speciation usually involves a physical barrier (i.e. body of water, mountain range, dams, canals, highways) that is crossed by or isolates a founder population • any series of events that results in the reproductive isolation of two populations may also lead to the formation of a new species • any mutations and subsequent selection can no longer be shared with other populations  evolutionary change will result in the formation of two separate species

5. Habitat Isolation • some populations split into separate gene pools within the same geographical location • sympatric speciation results from a mutation that immediately results in reproductive (but not ecological) isolation, so that genetically similar species can occupy overlapping territories • occasionally, individuals or groups can become reproductively isolated within a large population (i.e. stickleback fish species that occupy different habitats within the same B.C. lakes)

6. Other Reproductive Barriers (see P. 227) • prezygotic mechanisms prevent successful reproduction by means of: • Prevention of Mating • ecological isolation (i.e. occupy separate habitats or niches) (i.e hoary marmot) • temporal isolation (i.e. reproductive cycles occur at different times) (i.e. Western spotted skunks) • behavioural isolation (i.e. specific mating ritual must be recognized) (i.e. Eastern meadowlarks) • Prevention of Fertilization • mechanical isolation (i.e. structural differences in reproductive organs prevent copulation) (i.e. lady’s slipperorchid) • gametic isolation (i.e. sperm and egg of same species recognize each other by molecular markers, or sperm dies within female)

7. postzygoticmechanisms are usually a chromosomal incompatability • prevent a hybrid zygote from developing into a fertile adult by: • dying at an early stage (zygotic mortality) • resulting in poor fitness and early death if born (hybrid inviability) • unable to produce gametes as adults (hybrid infertility) as in the case of mules

8. Divergent and Convergent Evolution the isolation and niche diversity of many islands create ideal conditions for speciation small, founding populations evolve rapidly through genetic drift and natural selection , the resulting diversity of species an example of adaptive radiation, or divergent evolution Darwin’s finches are a classic example of adaptive radiation

9. distantly related species that live in similar habitats develop similar adaptations (analogies) and the result is convergent evolution mammals that feed on ants and termites have evolved separately at least five times on different continents placental mammals have marsupial analogues for every niche they occupy

10. The Rate of Speciation • as discussed above, speciation can occur rapidly in small, founding populations such that fossil evidence shows “sudden” new and distinctive features Darwin was in the school of gradualism, in which species evolve through accumulation of genetic changes over geologic time the punctuated equilibrium model addresses the observation that species often diverge in spurts of relatively rapid evolutionary change after long periods of little evolutionary change

11. Human Effects on Biodiversity flight has been selected against for many island species predators introduced by European explorers have become invasive, finding easy prey in flightless birds and driving many to the brink of extinction leatherback turtles get caught in fishing nets, eat plastic bags they mistake for jellyfish, and suffer from human predation of their meat and eggs in breeding grounds many other Canadian species are at risk of extinction because of human activities