Question

1.What is the difference between genetic distance and reproductive isolation in allopatric and sympatric speciation

2. What is the modular organization of radiation in insects

Answer 1

ANSWER:

1)    Allotropic speciation is a mechanism to evolve reproductive isolation;it is caused by the accumulation of genetic differences between populations while they are geographically isolated.Here, we studied a simple stochastic model for the time until speciation caused by geographical isolation in fragmented populations that experience recurrent but infrequent migration between sub populations.We assumed that mating incompatibility is controlled by a number of loci that behave as neutral characters in the accumulation of novel mutations within each population.Genetic distance between populations was defined as the number of incompatibility-controlling loci that differ between them.If the number of invasive individuals relative to the resident population is not very large ,diffusion approximation provides an accurate prediction.There is an intermediate optimal rate of migration that maximizes the rate os species creation by recurrent invasion and diversification.

Sympatric speciation occurs when there are no physical barriers,and all members of a species from mating with another,and all members close proximity to one another.A new species,perhaps based on a different food source or characteristic,seems to develop spontaneously.The theory is that some individuals become dependent on certain aspects of an environment-such as shelter or food sources-while others do not.

               A possible example of sympatric speciation is the apple maggot, an insect that lays its eggs inside the fruit of an apple,causing it to rot.Asnthe apple falls from the tree,the maggots dig in the ground before emerging as flies several months later.

2)                          Speciation of plant -feeding insects is typically associated with host-plant shifts,with subsequent divergent selection and adaptation to the ecological conditions associated with the new plant.However, a few insect groups have apparently undergone speciation while remaining on the same host-plat species,and such radiations may provide novel insights into the causes of adaptive radiation.Within plant speciation of Asphondylia is thus appaently facilitated by the opportunity to partition the plant ecologically.One clade exhibits temopral isolation among species,which may have facilitated divergene via allochronic shifts.Using a novel method based on Bayesian reconstruction,we show that the rate of change in an ecomorphological trait,ovipositor length was significantly higher along branches with inferred shifts between host-plant organs than along branches without such shifts.