Sperm uptake and release in male spiders: a functional, biomechanic and neurobiological perspective.

• Applicants: Professor Dr. Stanislav Gorb; Professorin Dr. Gabriele Beate Uhl
• Subject Area: Systematics and Morphology (Zoology) ; Evolution, Anthropology
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 578631514

Animals with internal fertilization have evolved diverse structures for sperm transfer from males to females. These include spermatophores deposited externally and taken up by females, as well as specialized body parts, such as penes connected to testes. Some species have developed secondary sperm transfer devices from modified appendages. Sperm transfer structures are highly complex and species-specific, and go beyond simple sperm delivery. This complexity makes the male genitalia important for species identification and a focus of evolutionary biology research on sexual selection, sexual conflict, and speciation. This research project aims to elucidate the mechanisms of sperm uptake and transfer in male spiders using specialized palpal organs (POs). Despite nearly two centuries of observation, the functioning of spider POs remains unclear. This study will focus on two species representing major spider clades: Pholcus phalangioides (Synspermiata) and Pisaura mirabilis (Entelegynae). The project will employ advanced imaging techniques, biomechanical testing, and experimental manipulations to investigate the following: 1. Structural and material properties of POs, including sclerites, membranes, and sperm-bearing spermophors. 2. Roles of muscles, hemolymph pressure, glandular secretions, and innervation in sperm uptake. 3. Dynamics of sperm release from PO to female during mating. For 2 and 3. we posultate that P. phalangioides POs may be primarily secretion-driven, whereas P. mirabilis POs may be mainly hemolymph-driven. The research will be divided into four work packages: WP1: Examine the PO structure, material composition, and biomechanical properties. WP2: Investigate sperm uptake mechanisms through behavioral observations and experimental manipulation. WP3: Study of sperm release dynamics during mating using various imaging and biomechanical techniques. WP4: Synthesizing findings to understand how PO mechanisms shape spider mating systems and sexual selection strategies. The project combines expertise in spider mating behavior, ultrastructural anatomy, and functional morphology of copulatory organs in the Uhl lab (Greifswald) with state-of-the-art methods of micromechanics in the Gorb lab (Kiel). We apply for two doctoral researchers who will focus on morphological/behavioral and biomechanical aspects and who will work closely together. By elucidating the intricate mechanisms of spider sperm transfer in spiders, this study will significantly advance our understanding of arachnid reproductive biology and may inspire novel technological applications in microfluidics and related fields.

• DFG Programme: Research Grants
• Co-Investigator: Professor Peter Michalik, Ph.D.