Reproductive Seasonality in Nesticus (Araneae: Nesticidae) Cave Spiders

Abstract

Spiders of the family Nesticidae are members of cave communities around the world with cave-obligate (troglobiotic) species known from North America, Europe, Asia and the Indo-Pacific. A radiation of Nesticus (Araneae: Nesticidae) in the southern Appalachians includes ten troglobiotic species. Many of these species are of conservation interest due to their small ranges, with four species being single-cave endemics. Despite conservation concerns and their important role as predators in cave communities, we know little about reproduction and feeding in this group. We addressed this knowledge gap by examining populations of two species on a monthly basis for one year. We made further observations on several other species and populations, totaling 671 individual spider observations. This more than doubled the reported observations of reproduction and feeding in troglobiotic Nesticus. Female Nesticus carry egg sacs, facilitating the determination of the timing and frequency of reproduction. We found that Nesticus exhibit reproductive seasonality. Females carried egg sacs from May through October, with a peak in frequency in June. These spiders were rarely observed with prey; only 3.3% (22/671) of individuals were observed with prey items. The frequency at which prey items were observed did not vary by season. Common prey items were flies, beetles and millipedes. Troglobiotic species constituted approximately half of all prey items observed. This result represents a greater proportion of troglobiotic prey than has been reported for various troglophilic spiders. Although our findings shed light on the life history of troglobiotic Nesticus and on their role in cave ecosystems, further work is necessary to support effective conservation planning for many of these rare species.

Spiders in caves

“…A reduced number of eggs/cocoons (less than 10) was also documented for several troglobionts [28,50,[65][66][67]. For comparison, a number of eggs/eggsacs one order of magnitude higher was documented for troglophile species able to disperse outside the cave habitat [68,69].…”

“…Documented observations in spiders-mostly anecdotal [27]-primarily refer to reproductive behaviour [13,66,68,72]. Complex courtships were documented in troglophiles [13,68], whereas maternal care was observed in troglobiont Nesticidae [66,73]. Sociality in cave spiders was never documented [14].…”

Population genomics in two cave-obligate invertebrates confirms extremely limited dispersal between caves

“…Their tendency to live in dark, moist habitats has led to numerous instances of cave habitation, with roughly one third of species in the group either troglophiles (frequent cave dwellers that are also found on the surface) or troglobionts 17 . N. barri demonstrates typical troglomorphic features, lacking eyes and with reduced pigment, although it still possesses reproductive seasonality 18 . The genus Ptomaphagus includes about 60 species in North America, again with roughly one third either troglophiles or troglobionts 4 .…”

Occurrence of the Black lace-weaver spider, Amaurobius ferox, in caves

“…Spiders are among the most abundant predators in caves (Mammola & Isaia 2017). Numerous studies have been performed on cave spiders in recent years (Novak et al 2010;Carver et al 2016;Mammola & Isaia 2016;Lipovšek et al 2018). However, these studies largely focus on species dependant on cave habitats and poorly adapted species are frequently overlooked.…”