Evolution of Ornamentation and Courtship Behavior in Schizocosa: Insights From a Phylogeny Based on Morphology (Araneae, Lycosidae)

Abstract

A phylogenetic analysis for the North American Schizocosa species was undertaken by scoring 49 morphological characters for 31 taxa representing all of the Nearctic species of Schizocosa plus individuals that are hybrids between S. ocreata and S. rovneri. Rabidosa rabida, Allocosa georgicola and Gladicosa pulchra were used as outgroups. Three clades are recognized: a large clade from eastern North America (Clade A) within which is nested the S. ocreata clade; Clade B, which includes the widespread S. avida and the western 5'. mccooki, and a smaller, third clade, Clade C. Sexual ornamentation occurs on the first legs of mature males of several species within the Schizocosa and takes the form of pigmentation and or bristles primarily on the tibia of leg I; there is at least one species with bristles in each of the three main clades. Mapping the occurrence of male ornamentation on the preferred phylogeny suggests that ornamentation evolved 5 or 6 separate times and was subsequently lost 2 or 3 times. The ornamentation is concentrated in the S. ocreata clade, a clade defined by a finger like projection on the paleal process of the male pedipalp. Courtship behavior is known for 20 of the 3 1 taxa. All species studied utilize chemical communication and seismic signals for communication; some species also have distinct visual signals. Seismic signals are produced by palpal drumming (as is seen in several species within Clade B), or by stridulation (seen in Clade A). Visual signals consisting of movements of the first pair of legs are common in species that are distinctly ornamented. This study provides the first phylogenetic study of a North American genus of wolf spider and provides morphometric comparisons of the North American species in Schizocosa.

Enigmatic ornamentation eases male reliance on courtship performance for mating success

“…Although S. stridulans was originally described as lacking foreleg brushes (Stratton 1991), a more recent morphological analysis indicates that tibial bristles are present (Stratton 2005). None the less, foreleg brushes are undetectable without the use of magnifying equipment, and thus, the present study focuses on pigmentation only.…”

“…Like many other animal taxa, males of several species of Schizocosa wolf spider engage in active, ritualized movements during courtship, often involving waving and tapping of ornamented forelegs (reviewed in Stratton 2005). While early Schizocosa studies focused on the relationship between ornamentation and female choice (McClintock and Uetz, 1996;Scheffer et al, 1996;Hebets and Uetz, 2000;Uetz and Roberts, 2002;Hebets et al, 2006;Uetz and Norton, 2007), more recent studies have highlighted the importance of these active displays, as courtship rate has been shown to influence male mating success across multiple species of wolf spider (Kotiaho et al, 1998a;Parri et al, 2002;Rypstra et al, 2003;Delaney et al, 2007;Gibson and Uetz, 2008;Lomborg and Toft, 2009;Shamble et al, 2009;Rundus et al, 2010Rundus et al, , 2011.…”

“…McClintock and Uetz, 1996;Scheffer et al, 1996;Hebets and Uetz, 2000;Hebets, 2003. Additionally, extensive variation exists among species in terms of the complexity of their courtship displays and associated secondary sexual traits (reviewed in Stratton, 2005;Framenau and Hebets, 2007), making them ideal focal taxa for studies exploring female choice and its influence on male reproductive behavior and associated morphologies.…”

“…In S. stridulans Stratton 1991, upon sexual maturation, males develop black coloration on their foreleg tibiae, patellae, and a portion of their foreleg femora, and very small black brushes of hair on their foreleg tibiae (Stratton, 1991(Stratton, , 2005. This foreleg pigmentation is fixed at maturation (Foelix 1996) and is lacking in mature females.…”

Temporal patterns of nutrition dependence in secondary sexual traits and their varying impacts on male mating success

“…Mature males possess dark pigmentation on the first pair of walking legs (forelegs), which covers both the tibia and patella and can extend as far as halfway up the femur (Stratton, 1991). The foreleg tibiae also have short brushes of black hair (Stratton, 2005), further enhancing the visual contrast between the pigmented and unpigmented leg segments. During courtship, males tap their first pair of legs repeatedly and vigorously in front of the female (Stratton, 1991).…”