Lecture 8

Question 1

explain hybrids

Answer 1

• show mixtures of traits from crossing of 2 different species

Question 2

explain niches

Answer 2

• the range of ecological resources and conditions a species needs and uses

Question 3

review the fitness of hybrids

Answer 3

Expectation: natural selection should adapt species to different ecological niches, where a species is successful (fit), but individuals do not compete significantly with other species

• it is not the “habitat” where a species, but more like its “profession” or functional role
• when 2 different related species hybridize, it makes sense to expect that the intermediate traits of hybrids are not well adapted to compete with either parental species niche in their habitats, and hybrids should ultimately be eliminated by competition. Natural selection should favor REINFORCEMENT; selection for traits that keep species apart (since hybrids are “wasted” offspring)
• but not always! if a suitable but different environment exists nearby, the hybrids might be more successful than either parental species and evolve into a third species, sometimes very rapidly

Question 4

Hybridization between animal species usually acts like what?

Answer 4

• acts like a species barrier
• keeping species distinct: since hybrid offspring are not optimally adapted to the environment of their parents and thus not expected to persist… (same expectation as for plants)

Question 5

What is allopolyploidy?

Answer 5

• unreduced gametes from 2 different species can fuse and give rise to new reproductively isolated species with a mix of characteristics

Question 6

what is the problem with all odd chromosome numbers?

Answer 6

• cannot pair evenly during meiosis since pairs need even numbers

ex. triploids have 3 copies of each chromosome

Question 7

What is adaptive radiatoin

Answer 7

• the diversification of a phyletic line into many different species

Question 8

What can adaptive radiation result from

Answer 8

• ecological opportunity
  ex. new habitat or new resources, or reduced competition or predation: environmental changes
• morphological innovation
  ex. the evolution of a significant new trait, like jaws, feathers, flowers, seeds, eyes, defensive chemicals

Question 9

give an example of ecological opportunity using adaptive radiation in galapagos finches

Answer 9

• adaptive radiation of Galapagos finches is an example of ecological opportunity. The islands provided new habitats, including new resources (ex. new food sources). The finches diversified to specialize or take advantage of these different food sources. Islands increase reproductive isolation which can accelerate allopatric speciation.

Question 10

Where do most of the Earth’s history fall into?

Answer 10

• falls within Precambrian time, and the fossil record begins around 3.5 billion years ago with prokaryotes (stromatolites)
• history of familiar multicellular organisms begins after the Precambrian, the so-called Phanerozoic or “flowering of life” (although real flowers do not appear until much later)

Question 11

review the earliest major adaptive radiation

Answer 11

• during the early to mid Cambrian period, animal diversity diversified in many ways, producing many new innovations (hard parts, legs, eyes, genetic sequences, mobility) and ecological lifestyles.
• major radiation of animals