Evolution of net-spinning caddisflies: a hypothetical mechanisn for the reproductive isolation of conspecific competitors

Net-spinning caddisflies construct capture nets with a wide range of mesh s izes, although the ancestral net-spinner presumably spun large-meshed nets while inhabiting high current velocity microhabitats, Thorp proposed that t he evolutionary diversification of mesh sizes resulted from the competitive displacement of some net-spinners into lower flow microhabitats where less Hater and therefore less food passed through their nets. As a result, smal ler meshes were selectively advantageous because they captured smaller, mor e abundant food items. Although competition is often strongest between cons pecifics, Thorp did not present a mechanism by which reproductive isolation , and ultimately speciation. would be achieved between the competitively in ferior and superior individuals, One such mechanism may have been temporal isolation, Because the initially large-meshed nets of the competitively inf erior caddisflies would have been inefficient in the lower flow microhabita ts, these individuals would hare theoretically grown slow er and emerged as adults later than the competitively superior individuals, which in turn wo uld have led to reduced gene flow between the two populations, Although tem poral isolation may not have been their final reproductive isolating mechan ism, it may have opened the door to the evolution of other isolating mechan isms.