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Sexual Dimorphism

Nephila pilipes displays sexual dimorphism, where there is distinct difference between male and females of the species. This can be seen in Nephila pilipes as the female spiders are much larger than their male counterparts. Some research, such as that done by Dr. Kuntner, Dr. Zhang, Dr. Gregorič, and Dr. Li suggests that the females are able to become larger than males is due to their continued molting, shedding and outgrowing of skin to make way for new skin after growth. Males have been observed to have less frequent molts after reaching maturity while females continue to molt at a higher frequency. These molting continue to occur in females as they age except during times of high copulation where it may be a non-advantageous to continue to grow as sperm is fertilizing eggs.

Sexual dimorphism appears to be a shared feature of Nephila pilipes spiders of different populations as examinations of populations in Southeast Asia as well as the continent of Australia and the island of Papua New Guinea have shown the trait to be a shared characteristic but, large spiders are see to persist in these populations. This has led many researchers in the field to decide to characterize and label the species as a whole with regards to sexual dimorphism as a species where the males are “4–10 times smaller than females.” While there may not be variation in size, with regards to males of a population vs. males on another and the same for the comparison of females, variation could be seen in other traits due to environmental factors. This includes they protein characteristics of the silk produced based on the food ingested by the spider.

Another explanation for the dimorphism observed in the population is that it may have been a part of a coevolution with another trait and, may have continued to persist as part of the female spider’s response to male spider’s use of mating plug. , the evolution of plugs occurred in a coevolution with female gigantism earlier in the Nephila species phylogenetic tree leading to the persistence of female gigantism despite the ineffectiveness of the male plug. This makes this theory one with a genetic basis as the continued presence of the trait is due to the passing of the genes coding for the alleles of these traits from the ancestral species to the extant species N. pilipes Female gigantisms persisted despite plugging losing its effectiveness as the female spiders with their larger bodies the “embolic plugs” inserted in the N. pilipes females genitalia became to thin to effectively seal the spider’s genitalia and, gigantisms also proved to be a positive adaption as it increased the fitness of the larger female spiders.

An alternative reason for the displayed sexual dimorphism is that the dimorphism is due to male dwarfism instead of female giganticism and, one theory for this is due the scramble competition. Through experimentation on N. pilipes spiders specifically that the male spiders that were able to find the female spiders first often fertilized a greater percentage of her eggs than others. And, as female N. pilipes spiders often did not remain on their webs the smaller, more agile spiders were able to reach them first versus the slower, larger males who often waited at the web of the female in advantageous spots. This explanation would mean that smaller males had a greater fitness due to the behavior of the female spider to move around in maturity and when molting