Host plant paper - genes

Question 1

What is parallel speciation?

Answer 1

A special form of parallel evolution where traits that determine reproductive isolation evolve repeatedly, in closely related populations, as by-products of adaptation to ecological conditions.

Question 2

Which organism is being studied?

Answer 2

Walking-stick insect
Timema cristinae
- wingless phytophagous insects inhabiting chaparral of California, western USA and northern Mexico.
- Patterns match host plants - unstriped common on C. spinosus, striped common on A. fasciculatum

Question 3

Why do the insects match the plant markings?

Answer 3

To avoid predation (by birds and lizards)
- exposed to intense divergent selection for crypsis
(cryptic)

Question 4

What does allopatric mean?

Answer 4

Geographically separated

Question 5

What did the study find?

Answer 5

Strong evidence of host-associated sexual isolation - across all populations, walking-stick insects were more likely to copulate if paired with an opposite sex member from the same host-plant species
- reproductive isolation was much stronger between individuals on different host plant species

Question 6

The degree of sexual isolation observed depended strongly on which pairs of populations were compared. Why may this be?

Answer 6

• Larger or smaller variation in the colour-patterns on the insects within a population
• Geographic distance between populations positively correlated with the degree of sexual isolation detected

Question 7

What processes limit gene flow between populations of insects using different hosts?

Answer 7

• Between-host migrants will be less cryptic an exhibit reduced survivorship owing to predation
• mating success of between-host migrants will be reduced because T. cristinae mates assortatively by colour morph within populations and the less cryptic morph is rare
• even if locally less cryptic migrants secure mates, they will produce a higher proportion of locally less cryptic offspring (as colour morph is genetically determined)

Question 8

Host adaptation…

Answer 8

promotes sexual isolation

Question 9

Where were the insects collected for this study?

Answer 9

Santa Ynez mountains, California

- 550 were measured (each trait measured twice)