As I have stated before, polygamy plays a very crucial role in the sexy sons hypothesis as females will optimally mate with several males if “better sperm” is found. Females must be selective with the males they mate with and thus, if a more attractive male is found, it is better to mate with the new male instead of mating with previous less attractive males. A study was performed where rattlebox moths (Utetheisa ornatrix) were selected for either monandrous or polyandrous relationships and the offspring were then mated to test for increase in reproductive success (Egan, et al.2015).
The researchers acquired two size matched sister moths so that many factors in reproductive success may be accounted for. They then mated one moth with a single male three times and the other once with three different males. What they found was that sons produced from the polyandrous relationship had increased reproductive success. They produced around 81% of the total number of offspring including the monandrous line males. This translates into more than three times the amount of offspring than the monandrous offspring.
This study shows that males who came from polyandrous lineage were more reproductively successful and were able to produce a larger quantity of offspring. There are limitations, however, to this study as the offspring of the sister moths were not tested for attractiveness. Instead, they were tested only for number of offspring produced through an arranged mating. It would have been more informative if research was done such as creating a choice chamber for the second generation sons to test why they had greater reproductive success.
This study was helpful as previously stated, the purpose behind all life in an evolutionary perspective is to produce more offspring and the polyandrous lineage males were able to accomplish that goal. A more complete analysis was done in 2013 by Adam Nelson and 8 other researchers. Mice release certain proteins in their urine call MUPs (Major Urinary Proteins) as social pheromones for attracting females. This process has been studied for a long time with more and more evidence confirming its reliability as a measure of attractiveness (Kumar, et al. 2014).
It has been known that the higher the MUP concentration, the more attractive the male mouse is to females, so MUP concentrations were used as guidelines for the attractiveness of the males in the experiment. Nelson and his colleagues reintroduced them to free mate choice environments and allowed them to reproduce. On the other hand, he also mated monogamous non selective mice in a laboratory setting. What he found was that in the free mate choice scenario, the females produced offspring also had elevated MUP levels compared to the laboratory controlled mice.
Another very interesting thing to notice is that those sons were not only sexier, but they also had shorter life spans on average. This shows a possible tradeoff between attractiveness and viability. The mice were able to make this tradeoff because they simply had better genes,and in the end, being more attractive is more important in an evolutionary perspective as it increases the likelihood of producing offspring. This study provides more support for the Egan study as it demonstrates in mice, the increased reproductive success was due to having better genes.
It accomplishes what the Egan study did not because it goes a step further and demonstrates the reasoning behind the results and provides strong evidence for the sexy sons hypothesis. A 2007 study performed by Kirsten Klappert and Klaus Reinhold, analyzed the mechanisms behind the female grasshopper (Chorthippus biguttulus) preference towards showy traits, in this case, the quality of the male song. This quality was determined in a series of experiments using choice chambers. Females were placed in chambers and a recording of the male song would be played.
Based on the female reaction to the song, the males were given rankings of attractiveness and the moderately attractive males were removed from the experiment in order to analyze the extremes of attractiveness. The males were then placed independently with many females in enclosures in order to allow them to reproduce. Their larvae were then marked based on their father’s attractiveness and were allowed to grow up under constant conditions. Based on the sexy sons hypothesis, the offspring of the unattractive males should be less viable compared to those of the attractive males.
Additionally, it should be expected that the offspring descended from attractive males should also produce songs that were more attractive than those of descendants of unattractive males. However, both of these hypotheses appeared to be false. In fact, there appeared to be a negative correlation between attractiveness of the father and viability of the offspring as fewer attractive descended larvae reached adulthood compared to the unattractive descended larvae. Also, attractive descended grasshoppers did not manage to have more attractive songs compared to the unattractive ones.
This shows that the sexy sons hypothesis probably doesn’t apply to this particular species as the attractiveness of the first generation males did not translate into any particular benefits for the next generation. The major drawback to this study, however, was that the grasshoppers were not introduced into large community settings like the mice were in the 2013 Nelson study. In large communities, fitter individuals would most likely have dominated and produced the most offspring and possibly also the fittest.