Morphological evidence for limited sperm production in the enigmatic Tasmanian cave spiderHickmania troglodytes(Austrochilidae, Araneae)

Abstract

The male reproductive systems of spiders are highly diverse in structure across all major spider taxa. Little is known about this organ system in basal araneomorph spiders, especially Austrochiloidea; such knowledge is necessary for a more complete understanding of the evolutionary morphology of the male reproductive system in spiders. In the present study, we describe the male reproductive system of an austrochilid spider, the enigmatic troglophilic Tasmanian cave spider Hickmania troglodytes, using light and electron microscopic techniques. The male reproductive system consists of tubular testes leading into convoluted deferent ducts, which are fused close to the genital opening to an unpaired ejaculatory duct. Spermatogenesis occurs only in the subadult testes, whereas adult testes showed neither spermatogenic stages nor any generative tissue in all investigated specimens. The testes of adult males are drastically reduced in size compared with those of subadult males, but the deferent ducts are filled with large numbers of mature spermatozoa. Thus, our data suggest that males of H. troglodytes are sperm‐limited, but not necessarily sperm‐depleted as described for certain orb‐weaving spiders. Due to the absence of generative tissue, limited sperm production is permanent (PSL) and probably has an influence on the reproductive strategies in this species. As nearly no data are available on the life history of H. troglodytes, and in particular information on the phenology of males is lacking, implications of the evolution of PSL in this species are unclear. Nonetheless, our data on other representatives of Austrochilidae (Austrochilus forsteri, Thaida chepu) and Gradungulidae (Progradungula otwayensis) suggest that PSL evolved within Austrochiliodea only in H. troglodytes and might be an adaptation to its troglophilic lifestyle.

Ultrastructure of spermatozoa of orsolobidae (Haplogynae, Araneae) with implications on the evolution of sperm transfer forms in Dysderoidea

“…Nevertheless, STF are abundantly present in the lumen of the deferent ducts of all investigated specimens. Thus, the production of sperm in these species might be terminated as recently suggested for the Tasmanian cave spider, Hickmania troglodytes (Austrochilidae) (Michalik et al, 2014). However, because we do not have a reasonable sample size and cannot exclude age or teratological effects no further conclusions can be drawn.…”

Continental data on cave-dwelling spider communities across Europe (Arachnida: Araneae)

“…They are distinctive for their key ecological role as predators and for the variety of functional adaptations, representing therefore ideal model organisms for exploring a variety of ecological and evolutionary topics (Mammola and Isaia 2017). For example, different spider species have been used for studying silk's mechanical and structural properties (Lepore et al 2012, Piorkowski et al 2017), for exploring a range of morphological, metabolic and behavioural adaptations (Cardoso and Scharff 2009, Doran et al 2001, Doran et al 2017, Hadley et al 1981, Lipovšek et al 2018, Lipovšek et al 2017, Miller 2005, Yancey et al 2018, Chiavazzo et al 2015, Michalik et al 2014,Hesselberg et al 2019), for shedding light on the mechanisms of speciation and the processes underpinning biological radiations (Arnedo et al 2007, Hedin 2015, Růžička et al 2013, Yao et al 2016, Zhang and Li 2013), as well as for testing ecological hypotheses (Cardoso 2012, Mammola et al 2016, Mammola et al 2019, Novak et al 2010, Lunghi 2018).…”