In summary, among the arthropods, x are by far the most abundant - a great majority of these are x, and obviously some have secondarily x
insects - mostly winged, some secondarily lose wings
x and x have select winged forms for only a short period of time in the life cycle
ants and termites
****(ON EXAM)How did insects get their wings? 2 hypothesis and the model organisms that are providing clues
Big debate. The arboreal bristletails bridge the gap between Insecta and Entognatha, they are the most primitive and wingless of Insecta clade and are ORDER THYSANURA. Their habitat is up high on tree and they exhibit a behavior called DIRECTED AERIAL DESCENT. The two main hypotheses for how insects got their wings are 1. INSECT wings evolved terrestrially, as extensions of the thoracic pleura of primitive hexapods gliding from tall vegetation (as evidenced by flying silverfish). 2. Insect wings evolved in an aquatic setting,derived from gills or gill plates of primitively aquatic forms. STONE FLY IS THE BIG EXAMPLE FOR THIS ONE.
So we see that flying silverfish provide evidence for the first hypothesis about why insects got their wings. What evidence is there for the other hypothesis?
stone flies are winged but flightless (larvae are aquatic) and they skim the water.
winged but flightless, larvae are aquatic. They skim the water and ask us the question - could ancestral insects possessing a trace of a wing ( a nub, perhaps highly modified from gills have an advantage that could eventually give rise to wings used for flight?
experiment done with stoneflies to show flight progression
speed increases as the amount of contact with water decreases in stoneflies that use their wings to move across the surface of water.