Agelenidae C.L. Koch 1837

Bosco, Jennifer M. & Chuang, Angela, 2018, A new species of grass spider, Agelenopsis riechertii, from the Southwestern USA, with notes on its courtship behavior (Araneae: Agelenidae), Zootaxa 4442 (4), pp. 579-583 : 580-582

Agelenidae C.L. Koch 1837

Agelenopsis Giebel 1869

Agelenopsis lisa Gertsch , unpublished materials

Agelenopsis riechertii sp. nov

Type material: Female and male holotypes, USA: Texas: Balmorhea , Reeves Co., alt. 970m, 30.94° N, 103.79° W, 6 July 2014 (J.M. Bosco, S.E. Riechert, E. Beierschmitt, J.A. Dillon). Spiders were collected at dusk among buffalo grass ( Bouteloua dactyloides ) along a sloped ditch on the north side of Highway 17 between Balmorhea State Park and the city of Balmorhea.

Other material examined: Female and male paratypes from the same locality.

Etymology. This name honors Dr. Susan E. Riechert, a pioneering female ecologist ( Langenheim 1996), a “graybeard” within the field of arachnology, and a distinguished professor at The University of Tennessee in Knoxville, Tennessee. Her contributions to the fields of ecology, game theory, and animal behavior stem from decades of studying Agelenopsis spider populations, especially Agelenopsis aperta ( Hammerstein and Riechert 1988, Maupin & Riechert 2001, Riechert 1974, Riechert 1976, Riechert 1981, Riechert 1985, Riechert 1993, Riechert & Hedrick 1993, Riechert et al., 1973, Papke et al., 2001, Smith and Riechert 1984). With this description, we celebrate her substantial academic achievements, resilient attitude, and cheeky spirit.

Diagnosis. Males and females can be distinguished from other Agelenopsis spiders by features of the pedipalps and epigyna (Figs. 6–26). Specifically, A. riechertii males can be differentiated from A. aleenae , A. aperta , and A. spatula through variation in the embolus (Figs. 6–10). Agelenopsis riechertii has a loosely coiling embolus with a coiling diameter noticeably wider than the cymbium. This is unlike A. aleenae , which sports a tightly coiling and proportionally thicker embolus that obscures the view of the sides of the cymbium. Agelenopsis aleenae and A. spatula have embolic tips that significantly broaden at the tip into spatulate or spoon-like structures, whereas A. aperta and A. riechertii have narrower embolic tips (Figs. 11–14). The embolic tip of A. aperta is more uniformly cylindrical with a spur in the lateral view, whereas A. riechertii possesses a twisted tip with a small, convex edge in the lateral view.

Females of this species have a simple transverse opening of the epigynum and a thin and wide epigynal bridge that is characteristic of the other congeners (Figs. 15–18). Agelenopsis riechertii , A. aperta , and A. spatula all have widely set bursa openings, whereas A. aleenae have large bursa openings that are closely set together. Agelenopsis aleenae sports a strongly monolobed anterior atrial edge, while A. aperta possesses a bi-lobed anterior atrial edge. Agelenopsis riechertii and A. spatula and fall in between, with anterior atrial edges that possess indistinctive lobing. Unlike A. spatula , A. riechertii lacks a lip beneath the epigynal bridge.

Internally, A. riechertii has bursae that are longer than wide, stretching anteriorly before descending to the spermatheca at the base (Figs. 19–20). The spermatheca of A. riechertii fully sit at the center between the bursa openings. The spermatheca have an inverted comma shape, unlike A. spatula and A. aleenae , and are more elongate compared to those of A. aperta (Figs. 19–26).

Description. Females: We measured 13 individuals with the following lengths in mm (average; range): Cephalothorax length (6.16; 5.05–7.19), cephalothorax width (4.19; 3.05–4.86), abdominal length (7.94, 6.09– 9.32), abdominal width (4.93; 3.52–5.84), submarginal band (1.05; 0.73–1.38); median band (0.79; 0.57–1.06), sternum length (2.72; 2.3–3.2), sternum width (2.24; 1.62–2.5), posterior spinneret (0.95; 0.69–1.8); anterior spinneret (2.37; 1.98–2.85); chelicerae (2.45; 2.11–2.81). Leg measurements (femur-patella-tibia-metatarsustarsus): leg I [(5.27; 4.6–5.97)- (2.00; 1,64–2.31); (4.38; 3.5–5.31); (4.73; 3.96–6.03); (2.55; 2.11–3.03)]; leg II [(5.02; 4.28–5.98)- (1.98; 1.7–2.4)- (3.84; 3.31–4.57)- (4.29; 3.364–5.3)- (2.32; 2.03–2.78)]; leg III [(4.87; 4.22– 5.93)- (1.83; 1.5–2.28)- (3.61; 3.17–4.09)- (4.87; 4.2–5.73)-(2.28; 2.02–2.67)]; leg IV [(6.18; 5.00–6.81)- (1.99; 1.61–2.21)- (5.00; 4.52–5.54)- (7.03; 6.05–7.97)- (2.78; 2.44–3.43).

Copulatory organ: Epigynum width (1.67; 1.32–1.98), epigynum length (1.49; 1.27–1.71). The epigynum is a simple transverse oval without significant lobing at the anterior edge. The overall atrial opening is about 4- 5x as wide as long, with the center having a greater diameter than on the distal edges. The space between bursae openings has a width equal to or greater than the width of the bursa openings themselves. The fertilization ducts visibly wind around the base of the bursa twice.

Males: We measured 12 individuals with the following lengths in mm (average; range): Cephalothorax length (6.01; 4.81–6.83), cephalothorax width (4.08; 3.58–4.70), abdominal length (5.39; 4.35–7.72), abdominal width (3.19; 2.10–4.19), submarginal band (1.00; 0.81–1.29); median band (0.76; 0.52–0.90), sternum length (2.71; 2.30– 3.26), sternum width (2.17; 1.78–2.46), posterior spinneret (0.60; 0.49–0.84); anterior spinneret (2.20; 1.84–2.87); chelicerae (2.12; 1.78–2.51). Leg measurements (femur-patella-tibia-metatarsus-tarsus): leg I [(5.76; 4.87–6.93)- (2.09; 1.89–2.29); (5.28; 4.35–6.06); (6.02; 5.33–6.66); (3.27; 2.70–3.84)]; leg II [(5.35; 4.80–6.22)- (2.00; 1.70– 2.34)- (4.53; 2.80–4.97)- (5.60; 4.91–6.25)- (2.85; 2.43–3.27)]; leg III [(5.21; 4.62–5.75)- (1.85; 1.48–2.08)- (4.25; 3.66–5.67)- (5.96; 5.36–6.67)-(2.79; 2.42–3.25)]; leg IV [(6.64; 5.27–7.75)- (1.99; 1.67–2.33)- (5.60; 4.89–6.26)- (8.41; 7.29–9.70)- (3.54; 3.11–4.07).

Copulatory organ: Palp length (femur- patella- tibia- cymbium length- cymbium width): (2.53; 2.27–2.96)- (0.75; 0.6–0.9)- (0.96; 0.86–1.20)- (3.11; 2.71–3.41)- (1.40; 1.25–1.77). Agelenopsis riechertii has a coiling diameter that is wider than the cymbium. The embolus is thin and narrows into a twisted tip with a small, flat, crescent-shaped edge.

Distribution. Agelenopsis riechertii has been collected from the southwestern United States only, particularly in Texas. The species was the only agelenid in Balmorhea, Texas in March 2013, at 30.94° N; 103.79° W, near Balmorhea State Park. This species was also previously collected by Balmorhea Lake by Ayoub et al. (2005). Other Texas localities include the Basin Chisos Mountains in Big Bend National Park, Kerrville-Schreiner Park in Kerrville, and Elbow Canyon, Ft. Davis (Riechert, personal communication). Riechert also collected specimens in a desert grassland habitat within Capulin Volcano National Monument in New Mexico.

Ecology. Agelenopsis riechertii appears to mature in late spring (mid-April to early May). It is found in dry desert scrub habitats, including irrigation drainage ditches on roadsides. Individuals can be found sparingly at the base of desert scrub plants and human-made rock wall structures. Individuals were found in the highest abundance in irrigation ditches and other places where water regularly passes through, possibly due to increased prey abundance at these sites.

Courtship behavior. Male Agelenopsis riechertii exhibit courtship patterns that are similar to A. aleenae , A. aperta , and A. spatula in the use of web pulses, abdomen waggling, and web flexing. The courtship sequence in males starts with a series of web pulses, followed by the characteristic abdomen waggle, and ends with the male flexing the web ( Table 1, Fig. 17). This sequence repeats until the male contacts the female. Females are generally not active during this sequence, but some occasionally move or retreat in response to males. Catalepsis or quiescence of females is known in multiple Agelenopsis species (Gehring 1953), and is thought to result from the release of airborne male pheromones, as evidenced in A. aperta males ( Becker et al. 2005). Female quiescence typically occurs if males contact females. If the courtship ritual progresses until the female is immobilized, copulation occurs almost 100% of the time.

A nominal logistic model revealed significant whole model effects (X2 189,23=251.19, P <0.0001) and significant effects of inter-bout interval, waggle duration and number of flexes after waggle (X2 41,1=41.92, P <0.0001; X2 46,1=422.55, P <0.0 0 0 1 and X2 46,17=131.74, P <0.0 0 0 1, respectively) on whether a particular courtship bout succeeded or failed. Successful courtship sequences had less time between bouts (26.04 ± 6.93 s), longer time spent waggling (2.62± 0.45s), and fewer web flexes (8.85 ± 1.34) than unsuccessful courtships, which were characterized by longer inter-bout intervals (76.64 ± 13.29s), shorter waggling durations (1.73 ± 0.28s), and more web flexes (16.39 ± 3.01) (mean ± SE). In general, the longer the period of rest between courtship bouts, the less likely copulation was to occur between the pair. This supports Singer et al.’s findings in A. aperta , which suggest that males that take shorter rest periods between courtship sequences have a higher copulation success rate (2000).

While courtship behaviors are superficially indistinguishable between A. riechertii and its congenerics, Galasso found that finer-scale analysis of courtship behaviors in A. aperta , A. aleenae , and A. spatula were distinguishable in discriminant analysis space (2012). A. aperta spends proportionally less time resting during courtship, and more time spent waggling its abdomen and flexing the web than A. aleenae and A. spatula . Deeper analysis of courtship sequences and vibratory signals are needed to determine whether interspecific differences in courtship rituals may mediate hybridization in the overlapping geographic ranges of these closely related spiders. Whether pheromone signals differ as well, is worth investigation, although only the pheromone of female A. aperta spiders has been identified to date ( Papke et al., 2001).