Males make mistakes but females call the shots: female resistance as a partial reproductive isolating mechanism in scorpions.

OVIEDO-DIEGO, MARIELA A.; MATTONI, CAMILO I.; PERETTI, ALFREDO V.

Davis, California

Congreso; American Arachnological Society Annual Meeting; 2022

American Arachnological Society

Courtship behavior is a critical component of pre-copulatory isolation. Both sexes exchange multiple signals to assess the specific identity and the mate’s quality, so courtship behaviors and the response to them may experience different selective pressures. In sympatric areas, the correct sexual recognition among conspecifics is critical to prevent heterospecific mating ensuring reproductive isolation. However, the recognition can fail, leading to heterospecific mating and processes like reproductive interference (RI). Scorpions have a wide repertoire of sexual courtship behaviors. Here we focused particularly on "female resistance" (FR) (pulling against the male or not moving in the male’s direction during the “promenade” phase). This behavior has been ruled out as a manifestation of sexual conflict in scorpions, being more likely to arise in a mate choice framework as a mechanism to assess male quality. However, to date, FR has not been analyzed in heterospecific courtships where this behavior can act as a barrier contributing to reproductive isolation. Here we assessed the FR in conspecific and heterospecific courtships of two sympatric scorpion species from central Argentina: Urophonius brachycentrus -UB- and Urophonius achalensis -UA-. Given that these species had RI in pheromone chemical attraction, a mating system with scramble competition, and that there is a high chance of encounters between heterospecifics, we expect that FR constitutes a selective filter to prevent the culmination of heterospecific mating. We predict that success in these mating is less likely than in conspecific mating due to behavioral filters as FR, which it’s related to interaction networks that are more disorganized and less linear. We collected specimens in the field and performed mating trials in the laboratory in arenas with randomly selected couples: (a) conspecific crosses: UA n=70 , UB n=41 ; (b) heterospecific crosses: ♂UA♀UB n=51 ; ♂UB♀UA n=25. We recorded sexual encounters and considered successful mating if sperm transfer is completed. We quantified the duration and frequency of FR and compared these parameters between conspecific and heterospecific courtships using GLMs in R. Complementarily, we performed an analysis of interaction networks with Gephi, analyzing the linearity and modularity of conspecific and heterospecific courtships and we compared these parameters with a Mann-Whitney U-test. We found that heterospecific mating was less successful than conspecific mating, with sperm transfer occurring in only 8% (♂UA♀UB) and 18% (♂UB♀UA) of sequences (p=0.004). Compared to conspecific ones, heterospecific courtships had almost three times more FR events (p=0.037) and a longer duration of these events (p=0.037). Consequently, heterospecific courtships were longer (p=0.041) and in many cases, the pair loosened their pedipalps and the courtship was finished or continued but in a disorganized way, giving rise to less linear and more modular interaction networks (p=0.036). We provide evidence that FR is a very plastic behavior, which can be modulated according to the mate's specific identity. Our results confirm that FR could be considered as a behavioral isolating mechanism in heterospecific mating. However, FR represents a partial barrier so we discuss the costs of RI and the use of multiple pre- and post-copulatory barriers in these species.