Sexual Selection In Spiders - Wikipedia

Size is a factor in the reproductive success of males with species such as Stegodyphus lineatus, Argiope aurantia and Argyroneta aquatica showing sexual dimorphism, beneficial for larger males, stronger and more aggressive, who fight off the smaller ones using their large chelicerae and forelegs.[1][8] This leads to a decrease in the paternal success for smaller males since they are unable to gain access to females.[9] Argiope aurantia males can lose legs in combat, with the loss more prevalent in smaller males, evidence that larger males are favored in male-to-male competition.[2] In the water spider Argyroneta aquatica, where males and females permanently live in the water[10] the males are larger, indicating sexual selective pressures for large body size. The large male water spiders are more mobile, helping them obtain more females.

Sexual selection provides benefits to smaller male spiders under certain conditions, such as Misumena vatia and Nephila clavipes, whose smaller males climb faster to reach their mates:[11][12] Explained by the gravity hypothesis,[11] outcompeting larger males thus having more reproductive success,[12] especially when females live in high patches of flowers,[12] whereas females live in low lying areas, larger males are favored.[2]

In spiders like Tetragnathidae, Araneidae, Thomisidae and Pholcidae[11] there is an optimal body size that favors climbing speed. Smaller males will have an advantage over the largest males of the species, however the smallest male will not be the fastest climber.[12] This optimal body size for climbing is observed in different males from the same species express phenotypes, weapons such as chelicerae, teeth or even legs to fight off competition are used to fight off oncoming rivals, with larger bodied spiders contained larger chelicerae.[8] In most cases body size correlated with mating success.[1] This is observed in Lyssomanes viridis, whose males display weapons that are very pronounced in comparison with females and selected to help males fight off competition.[8]

The time it takes to develop is crucial to the overall fitness of a spider. This idea is true, however does not mean that larger males will always have better fitness. In Latrodectus hasselti, larger males outcompete smaller males by getting to the females web first. However, these large male spiders have long development times, meaning that the larger male will need more time before being able to copulate. Smaller males tend to have a quick development time which gives them an advantage in mating with a female. This advantage correlates with high paternal success in the species Latrodectus hasselti. Larger males are able to outcompete smaller males, but not able to mate. Smaller males risk getting outcompeted, but are more likely to have paternal success.[13]