The paper started with a premise that insects did evolve from being simple organisms that move by crawling and other usual means of mobility, to one with wings and having the ability to fly. According to the proponents of the study the ability to fly was needed to increase their access to resources, locate mates and escape predators and by doing so has undoubtedly contributed to their tremendous success (McCulloch, Wallis, & Waters, 4073).
Then based on review of literature they went on to say that even if it was advantageous for insects to fly this ability was lost repeatedly (McCulloch, Wallis, & Waters, 4073). The process of flight loss was attributed to the reduction in wing length and it was believed to be due to the high energy expenditure required to produce and maintain wings. The proponents of the study went on further to say that insects had to evolve once again into a simpler organism – minus flight – in order to increase their ability to reproduce while at the same time flightless males are known to acquire more mates and thus father more offspring (McCulloch, Wallis, & Waters, 4073).
The assumption regarding evolution to more complex insects and then going back again to being flightless must be accepted first before this study can proceed. Based on this idea and the observation that the absence of flight is beneficial to some species of stoneflies the researchers asked the question if insects lose flight before they lose their wings.
The problem is complicated by the fact that there are three kinds of flightless stoneflies. The first group is comprised of those who have fully formed wings (macropterous). The second group is comprised of those with smaller-sized wins (micropterous). And the third group is comprised of stoneflies that do not have wings (apterous). One can only be certain of one thing at this point and it is the conclusion that the presence of wings does not determine flight. Thus, the researchers hypothesized that the deterioration of flight muscle is the reason why these species of stoneflies lost its ability to fly. The greater challenge is to devise the methodology to find out with certainty that this is the case.
The research design required a lot of work but the goal was relatively simple. It is to compare the genetic differentiation between those that have strong flight capacity (Z. deocrata) and those that are flightless or have reduced flight (Z. pennulata, and Z. fenestrata). At this point the researchers went a little further and stated that due to high rate of dispersal of flight-capable insects their genetic variation is less compared to those with limited dispersal capability (McCulloch, Wallis, & Waters, 4075). These groupings were simplified into two: 1) the Z. decorata group and 2) the fenesrata species group. They followed standard protocol when it comes to collecting insects belonging to each group making sure that each group is well represented.
DNA was extracted, amplified and sequenced for further analysis (McCulloch, Wallis, & Waters, 4075). They also used standard software and other laboratory procedures used to achieve accurate DNA sequencing. Based on this methodology the proponents of the said study were able to determine that for the Z. decorata there was “no obvious phylogeographic partitioning of genetic variation” and that there is one “common haplotype that was identified from 25 sampling locations” (McCulloch, Wallis, & Waters, 4077). This is as expected; the ability to fly allowed this group to reproduce offspring without significant evidence of genetic variation.
When it comes to the second group – the fenestrata species group – it was observed that there was more sequence diversity, especially among clades (McCulloch, Wallis, & Waters, 4077). It was also revealed those macropterous specimens were recorded at 313 meters above sea level, while micropterous specimens were at 808 and apterous specimens were at 790 meters above sea level (McCulloch, Wallis, & Waters, 4079). In other words the higher the altitude the smaller is the wing-size and in other cases the wings disappear completely.
Discussion
The proponents use two major results to justify their conclusion that flight was lost first before wings. Firstly, they pointed out the significant genetic variation within the fenestrata species group and compared it to the results that say there is no significant genetic variation in the Z. decorata group. Secondly, they used the data regarding the length of wings and the corresponding altitude where this type of wing-size can be located. In other words the genetic variation that can be found in the fenestrata species group was attributed to evolution or changes required to become flightless or to acquire limited capability for flight.
This is a very problematic conclusion because there are other factors that can be causing the genetic variation. The inability to fly resulted in more mating opportunities and most probably with other species, including those that are macropterous and apterous. It was not also clarified if they can differentiate offspring that were able to cross-breed with Z. decorata. If the strong-flight species mated with the wing-less species then it is possible to produce stoneflies that have wings, reduced wings that cannot fly or have limited ability to fly. This is no clear proof that stoneflies evolved form winged organisms to flightless insects.
In order to be accurate with their results there seems to be no other way than to redesign the methodology and create a more sophisticated experimental procedure – one that maybe beyond the capability of the researchers. In order to be certain the experiment should determine the gene that enabled Z. decorata to fly. If the same gene is present in semi-flightless fenestrata and absent in flightless species of stoneflies then they can begin their study to find out if flight muscle deteriorated first before wings were completely lost. Otherwise the differences can be attributed to the cross-breeding of two different species that originally existed as flightless and strong-flight stone flies. This cross-breeding produced different kinds of stoneflies that are macropterous and micropterous and have two kinds of abilities – flight and non-flight.
On top of that the cross-breeding will also produce the offspring of the original pair that mated a long time ago and these are:
- macropterous stoneflies that can fly and
- apterous flies that cannot fly.
In other words these two species existed a long time ago and not the by-product of evolution. The proponents were eager to prove that it is high-altitude that prompted the evolution but at this point they cannot prove that this is the case, they simply used too many assumptions and they merely jumped to conclusions.