Testes mass, but not sperm length, increases with higher levels of polyandry in an ancient sex model

VRECH, D.E.; OLIVERO, P.A.; MATTONI, C.I.; PERETTI, A.V.

PLOS ONE

PUBLIC LIBRARY SCIENCE

Lugar: San Francisco; Año: 2014 vol. 9413 p. 1 - 10

1932-6203

There is strong evidence that polyandrous taxa have evolved relatively larger testes than monogamous relatives. Sperm sizemay either increase or decrease across species with the risk or intensity of sperm competition. Scorpions represent anancient direct mode with spermatophore-mediated sperm transfer and are particularly well suited for studies in spermcompetition. This work aims to analyze for the first time the variables affecting testes mass, ejaculate volume and spermlength, according with their levels of polyandry, in species belonging to the Neotropical family Bothriuridae. Variablesinfluencing testes mass and sperm length were obtained by model selection analysis using corrected Akaike InformationCriterion. Testes mass varied greatly among the seven species analyzed, ranging from 1.661.1 mg in Timogenes dorbignyi to16.364.5 mg in Brachistosternus pentheri with an average of 8.465.0 mg in all the species. The relationship between testesmass and body mass was not significant. Body allocation in testes mass, taken as Gonadosomatic Index, was high inBothriurus cordubensis and Brachistosternus ferrugineus and low in Timogenes species. The best-fitting model for testes massconsidered only polyandry as predictor with a positive influence. Model selection showed that body mass influenced spermlength negatively but after correcting for body mass, none of the variables analyzed explained sperm length. Both bodymass and testes mass influenced spermatophore volume positively. There was a strong phylogenetic effect on the modelcontaining testes mass. As predicted by the sperm competition theory and according to what happens in other arthropods,testes mass increased in species with higher levels of sperm competition, and influenced positively spermatophore volume,but data was not conclusive for sperm length.