A lot of secrets in a tiny spider: the peculiar sexual behavior and genital mechanics of a Ninetinae pholcid

IZQUIERDO, MATIAS A; DEDERICHS, TIM M; CARGNELUTTI, FRANCO; MICHALIK, PETER

Davis California

Congreso; American Arachnological Society 2022 Annual Meeting; 2022

Spider reproduction has remarkable characteristics among arachnids. The malecopulatory organs are not physically connected with their primary genital system.Instead, they are located in the pedipalps. In this unique way of reproduction, part ofthe male and female genitalia are visible externally during copulation. Thesecharacteristics place the spiders as excellent models for studying genital interaction.For example, how the different sclerites of the male pedipalps interact with the femalegenitalia and the placement of the delivered sperm at the first instances of copulation,among others. However, despite the advantages offered by spiders and theastonishing quantity of information related to genital morphology, these studies are stilllimited. Pholcidae is a diverse spider family, and the males have a unique projection ofthe pedipalp tarsus: the procursus. This pedipalp sclerite is inserted in the femalegenitalia in different stages of the copulation, evidencing a relevant role in this process.The subfamily Ninetinae has been proposed as the sister group of pholcids andpossesses interesting morphological characteristics. Although genital interactions havebeen studied in certain species of Pholcidae, this is not the case for the subfamilyNinetinae. Here, we describe for the first time the functional genital morphology ofGertschiola neuquena and summarize the main aspects of the copulatory behavior. Weperformed mating trials and recorded the mating behavior with a digital cameraattached to a stereomicroscope. For a detailed study of the genital interaction, asubset of mating pairs was fixed with liquid nitrogen. Selected samples were dried formicro-computed tomography, scanning electron microscopy, and histology. Ourprincipal results revealed that a hooked sclerite of the bulb is locked in a depression ofthe female epigastric fold and may serve to stabilize the bulb and as a pivot during thepedipalp movements. In addition, embolus and procursus are simultaneously insertedin the female genitalia. However, the long procursus is deeply inserted into anunpaired, blind-tortuous spermatheca, whereas the embolus reaches only the firstsection. Sperm cells were observed in the deepest parts of the spermathecae,indicating that the action of procursus movements may transport them to such places.In spiders, the sperm is deposited in the female genitalia by the embolus; our resultsmay indicate that the procursus partially performs this function by pushing the sperminto the spermathecae. Additionally, behavioral observations showed that males useonly one pedipalp to copulate, whereas other pholcids use both palps simultaneously.Our results deviate from the general rule in pholcids and allow us to ask differentquestions. In the first place, why do males insert only one pedipalp during copulationwhen most other pholcids insert both? In the second one, is the function of theprocursus a particularity of Gertschiola neuquena, or is it possible to extend it to otherNinetinae or pholcids? This work provides the first data on sexual behavior and finegenital morphology for a Ninetinae and performs the first steps to answering thesequestions.