A Review of Leg Ornamentation in Male Wolf Spiders, with the Description of a New Species from Australia, Artoria Schizocoides (Araneae, Lycosidae)
Total Page:16
File Type:pdf, Size:1020Kb
University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Eileen Hebets Publications Papers in the Biological Sciences January 2007 A Review of Leg Ornamentation in Male Wolf Spiders, with the Description of a New Species from Australia, Artoria schizocoides (Araneae, Lycosidae) Volker W. Framenau Western Australian Museum Eileen Hebets University of Nebraska - Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/bioscihebets Part of the Behavior and Ethology Commons Framenau, Volker W. and Hebets, Eileen, "A Review of Leg Ornamentation in Male Wolf Spiders, with the Description of a New Species from Australia, Artoria schizocoides (Araneae, Lycosidae)" (2007). Eileen Hebets Publications. 9. https://digitalcommons.unl.edu/bioscihebets/9 This Article is brought to you for free and open access by the Papers in the Biological Sciences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Eileen Hebets Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 2007. The Journal of Arachnology 35:89–101 A REVIEW OF LEG ORNAMENTATION IN MALE WOLF SPIDERS, WITH THE DESCRIPTION OF A NEW SPECIES FROM AUSTRALIA, ARTORIA SCHIZOCOIDES (ARANEAE, LYCOSIDAE) Volker W. Framenau: Department of Terrestrial Invertebrates, Western Australian Museum, Locked Bag 49, Welshpool DC, Western Australia 6986, Australia. E-mail: [email protected] Eileen A. Hebets: School of Biological Sciences, University of Nebraska, 348 Manter Hall, Lincoln, Nebraska 68588 USA. ABSTRACT. Morphological modifications of the first pair of legs in addition to widespread color var- iations of these legs among males of closely related species have been reported in a variety of spiders. Here, the evidence for sexual dimorphism in male foreleg morphology within wolf spiders (family Ly- cosidae) is reviewed and shown to occur in a number of species belonging to at least seven genera in five subfamilies: Alopecosa, Hogna, Schizocosa (all Lycosinae) Pirata (Piratinae), Evippa, (Evippinae), Par- dosa (Pardosinae) and Artoria (Artoriinae). These modifications, often in combination with distinct dark pigmentation, can be divided into three major groups: leg elongation, segment swelling and exaggerated setation (‘‘brushes’’). The latter two occur mainly on the tibial segment of the first leg. The function of these foreleg modifications has been studied most extensively in the genus Schizocosa. Since the courtship displays of all male Schizocosa incorporate a seismic component, foreleg ornamentation (namely pigmen- tation and associated ‘‘brushes’’) composes only one part of a multimodal courtship display. The function of this foreleg ornamentation appears to vary across closely related Schizocosa species and in some instances involves an interaction with the seismic signaling component. In most instances it appears to play a role in female mate choice and/or mate choice learning. In addition to reviewing lycosid foreleg modifications, we describe a new species of wolf spider, Artoria schizocoides from southwestern Western Australia that possesses sexually dimorphic modifications of the tibia of the first leg. Unique within the Artoriinae, males of this species carry spatulate setae on the ventral side of the tibia of the first leg that differ morphologically from other leg modifications in wolf spiders. Keywords: Courtship display, sexual dimorphism, sexual selection, secondary sexual traits Two main evolutionary processes that work rect aggressive encounters with members of independently or in combination are thought the same sex (generally males; intrasexual se- to explain sexual dimorphism or the morpho- lection), or used by members of the opposite logical differences between males and fe- sex to assess mate quality (generally females; males. One category relates morphological intersexual selection) (Darwin 1871; Anders- differences between males and females to a son 1994). reduction in intersexual competition for re- In wolf spiders, sexual dimorphism is evi- sources (ecological niche partitioning) (Shine dent in a multitude of forms and most differ- 1989; Fairbairn 1997). The second explains ences between males and females are attrib- sexual dimorphism by differences between the uted to differences in reproductive roles. With sexes in the relationship between a particular a few exceptions (e.g., Donacosa merlini Al- trait and reproductive fitness (sexual selection derweireldt & Jocque´ 1991) females are larger or differences in reproductive roles) (e.g., Se- than males. In most ground dwelling species, lander 1972; Hedrick & Temeles 1989; Reyn- these size differences are mainly explained by olds & Harvey 1994). Sexual selection arises a fecundity advantage of larger females (Pren- through competition between members of one ter et al. 1997, 1998, 1999). Sexual dimor- sex for reproduction with the other sex. Here, phism also exists with respect to differences dimorphic structures may either be used in di- in trophic morphology (i.e., the sizes of che- 89 90 THE JOURNAL OF ARACHNOLOGY licerae and venom glands); these differences ter two of which are most prevalent on the have been ascribed to the increased impor- tibial segment (Table 1). tance of foraging for females rather than an Elongation.—An elongation of the front avoidance of intersexual competition for food pair of legs can be either subtle (e.g., Alope- (Walker & Rypstra 2001, 2002). Across many cosa cuneata (Clerck 1757) (Kronestedt 1990) wolf spider species, especially those with sed- or very conspicuous (e.g., Artoria flavimana entary females, males also possess compara- Simon 1909) (Framenau 2002). For example, tively longer legs than females. This leg di- in the Palaearctic Alopecosa cuneata, the ratio morphism is thought to have evolved through of the length of tibia I to tibia IV is higher an advantage of more mobile males to en- than in a related species of similar size, A. counter females occupying permanent bur- pulverulenta (Clerck 1758) (Kronestedt 1990). rows (Framenau 2005a). While the above This elongation of the forelegs has been re- forms of dimorphism refer mainly to differ- lated to male courtship displays (Kronestedt ences in body shape or size, dimorphic color 1990), as there is direct contact between the patterns to augment body size and condition forelegs of a male and female A. cuneata in have also been argued to play an important the form of the female grasping the swollen role in the mating behavior of wolf spiders tibial segment of the male with her chelicerae (Moya-Laran˜o et al. 2003). (Kronestedt 1990, for more detail see below). Dimorphic patterns of foreleg pigmentation Male Alopecosa taeniata (C. L. Koch 1835) appear to be one of the most widespread and also have longer legs as compared to the conspicuous form of sexual dimorphism closely related A. aculeata (Clerck 1758) among wolf spiders (Framenau, pers. obs.) (Kronestedt 1990). In this case however, the and these differences in foreleg ornamentation elongation is not restricted to the forelegs and appear to be driven mostly by sexual selec- increased species-specific mobility of males tion. Male foreleg ornamentation commonly during courtship is suggested to explain this involves extremely dark pigmentation or very pattern (Kronestedt 1990), although there is distinct light coloration on individual foreleg currently no experimental evidence to support segments or covering the entire front pair of this hypothesis. legs. In some species, males possess an ex- In almost all wolf spiders the fourth pair of aggerated form of foreleg ornamentation in- legs is the longest, followed by leg I, and then volving morphological modifications of the II and III, or less commonly III and II (ex- pressed in the ‘‘leg formula’’: IV Ͼ I Ͼ II Ͼ first pair of legs. These morphological modi- Ͼ Ͼ Ͼ fications occur in a variety of forms in most III or IV I III II). However, in males of the Australian A. flavimana mentioned currently recognized subfamilies of wolf spi- above, the front pair of legs is extremely elon- ders. Our study aims to review the evidence gated and much longer than the fourth pair of for sexual foreleg dimorphism within the spi- legs. In females of A. flavimana the fourth leg der family Lycosidae by compiling morpho- is the longest, similar to both sexes of all other logical information from the taxonomic liter- species in this genus (Framenau 2002, 2004, ature. In addition, we describe a species with 2005b, also this study). The elongation is not a novel form of male tibial ornamentation— restricted to a single segment as in A. cuneata ventral spatulate modified setae. This species, but concerns all segments. The behavioral Artoria schizocoides n. sp., belongs to the mating sequence of A. flavimana is not known Australasian/Pacific subfamily Artoriinae and and therefore the function of this morpholog- is the only species within this subfamily ical modification remains unclear. In male known to the authors with excessive setation orb-weaving spiders, an elongation of the first on the first pair of legs. pair of legs has been argued to be beneficial to avoid sexual cannibalism (Elgar et al. MORPHOLOGICAL MODIFICATIONS IN 1990). THE FIRST LEG OF WOLF SPIDERS Swelling.—The tibia of the first leg of male Morphological modifications of the first A. cuneata is not only elongated (see above) pair of legs in male wolf spiders belong to but also distinctly swollen (Fig. 1). The swol- three major categories: (1) elongation,