Social Spiders
In the Agnarsson lab work focuses on the systematics of social spiders, including the taxonomy and phylogenetics of Anelosimus worldwide. We use phylogenetic, behavioral, and ecological data to study the evolution of spider sociality and its causes and consequences on various levels and scales
Permanent non-territorial sociality (quasisociality) is found in only about 20-25 out of the over 41.000 described species. Most these instances of sociality are phylogenetically isolated, and spread throughout nine spider families:
Agelenidae
Agelena consociata (Pain 1964; Krafft 1970, 1975; Darchen 1980; Riechert 1985; Riechert et al. 1986; Tietjen 1986; Roeloffs & Riechert 1988; Furey & Riechert 1989, 1999)
Agelena republicana (Darchen 1967a, 1976, 1981).
Dictynidae
Aebutina binotata (Simon 1892; Avilés 1993a, 2000; Avilés et al. 2001)
Mallos gregalis (Diguet 1909; Burgess 1976, 1979a, b; Jackson & Smith 1978; Jackson 1979, 1980, 1982; Tietjen 1981, 1982, 1986a, b)
Eresidae
Stegodyphus dumicola (Kraus & Kraus 1988, 1990; Seibt & Wickler 1987, 1988a, b, 1990; Kraus 1988; Wickler & Seibt 1993; Henschel et al. 1995a, b, 1996; Henschel 1998; Seibt et al. 1998; Avilés et al. 1999; Ulbrich & Henschel 1999; Whitehouse & Lubin 1999; Amir et al. 2000; Schneider et al. 2001; Crouch & Malan 2002; Johannesen et al. 2002; Lubin & Crouch 2003)
Stegodyphus mimosarum (Ward & Enders 1985; Ward 1986; Seibt & Wickler 1987, 1988a, b, 1990; Kraus & Kraus 1988, 1990; Wickler & Seibt 1986, 1993; Crouch & Lubin 2000; Crouch & Lubin 2001; Bodasing, Slotow & Crouch 2001; Ainsworth et al. 2002; Bodasing, Crouch & Slotow 2002; Lubin & Crouch 2003)
Stegodyphus sarasinorum (Kraus 1988; Kraus & Kraus 1988, 1990; Kullmann et al. 1972; Bradoo 1972, 1983; Jacson & Joseph 1973; Willey & Jackson 1993; Smith & Engel 1994) Stegodyphus manaus Kraus & Kraus, 1992 (possibly social, see Kraus & Kraus 1992)
Nesticidae
Species not identified (Quintero & Amat 1995)
Oxyopidae
Tapinillus sp. (Aviés 1994; Avilés et al. 2001)
Sparassidae
Delena cancerides (Rowell 1987; Hancock & Rowell 1995; Rowell & Avilés 1995)
Theridiidae
Achaearanea disparata (Darchen 1968; Darchen & Ledoux 1978)
Achaearanea vervortii (Levi et al. 1982; Lubin 1982, 1991)
Achaearanea wau (Levi et al. 1982; Lubin 1982, 1991; Lubin & Robinson 1982)
Anelosimus domingo (Levi 1963; Levi & Smith 1982; Rypstra & Tirey 1989; Avilés et al. 2001)
Anelosimus eximius (Levi 1963; Vollrath 1982; Avilés 1992)
Anelosimus guacamayos (Avilés et al. 2007)
Anelosimus oritoyacu (Avilés et al. 2007)
Anelosimus puravida (Agnarsson 2006a)
Anelosimus lorenzo (Fowler & Levi 1979)
Anelosimus rupununi (Levi 1963; Rypstra & Tirey 1989; Levi 1972)
Theridion nigroannulatum (Avilés 1997; Avilés et al. 2001; Avilés et al. 2006)
Thomisidae
Diaea ergandros (Evans 1996)
Diaea megagyna (Evans 1996)
Diaea socialis (Evans 1996; Main 1988)
More than half of the social spiders are theridiids, even though the family represents less than 6% of spider diversity. Social theridiids occur in at least three genera: Theridion, Achaearanea, and Anelosimus and each genus has two or more social species with eight social species belong to Anelosimus. Strikingly, my phylogenetic results imply no less than 8 independent origins of sociality within Theridiidae, even within Anelosimus most instances of sociality are phylogenetically isolated (Agnarsson 2006, Agnarsson et al. 2006, 2007). This pattern parallels the three social Stegodyphus which each has a non-social sister species(Kraus & Kraus 1988, 1990; Seibt & Wickler 1988a, b, Wickler & Seibt 1993). It is thus evident that no social spider clade contains more than two species. The spindly, yet clustered, distribution of social spiders suggests a conflict between the short term (ecological) and long term (evolutionary) causes and consequences of sociality. The repeated evolution of sociality presumably stems from short term ecological benefits of group living such as access to larger prey. However, sociality appears to be accompanied with lowered speciation rates or higher extinction rates; in other words spider sociality may be best characterized as an evolutionary dead-end.
In quasisocial species juveniles typically never leave the natal colony and therefore sociality is accompanied by a switch in breeding system from outbred panmictic to inbreeding. Inbreeding and consequent low genetic variability (Agnarsson et al. in prep.), accompanied with unstable population structure ('boom and bust', see Avilés 1997; Wickler & Seibt 1993), may be the primary cause of the apparent long-term failure of sociality. Although independent, social instances in theridiids are non-randomly clustered within a relatively distal clade, suggesting a common cause (preadaptations). Maternal care is likely one; theridiid sociality evolved as an extension of maternal care, where juvenile tolerance and cooperation is maintained to adulthood (e.g. Shear 1970; Kullmann 1972; Brach 1975, 1977; Burgess 1978; Krafft 1979; Cangialosi & Uetz 1987; Avilés 1997; Jones & Parker 2002; Schneider 2002; Agnarsson 2002, 2006, 2011; Miller & Agnarsson 2005, Agnarsson et al. 2006). The origin of quasisociality from maternal care and intermediate subsociality is corroborated phylogenetically (Agnarsson 2004, 2006). A three-dimensional web has also been frequently considered as a preadaptation for sociality (e.g. Shear 1970; Krafft 1979, 1982; Buskirk 1981; D'Andrea 1987; Cangialosi & Uetz 1987). Across spiders sociality seems indeed to be limited to lineages with maternal care, and in theridiids sociality occurs where maternal care and a three dimensional web overlap (Agnarsson 2004, 2006). Interestingly, corroborating data comes from the other group of spiders with multiple origins of quasisociality (the distantly related, non-orbicularian Stegodyphus, see Kraus & Kraus 1988, 1990) where maternal care and three dimensional webs also overlap. My work seeks understanding of sociality through molecular and morphological methods. Currently the aim is to revise the genus globally, and to obtain molecular data to reconstruct gene trees for several loci in all extant Anelosimus species. Across species, these represent the phylogeny, which will reveal independent origins of sociality and whether diversification or reversals to less social states have occurred. Within species, these will indicate whether sociality represents a watershed event in the genetic history of the species and whether populations in social species exhibit slow clonal divergence or frequent and widespread replacement/turnover of lineages.
Permanent non-territorial sociality (quasisociality) is found in only about 20-25 out of the over 41.000 described species. Most these instances of sociality are phylogenetically isolated, and spread throughout nine spider families:
Agelenidae
Agelena consociata (Pain 1964; Krafft 1970, 1975; Darchen 1980; Riechert 1985; Riechert et al. 1986; Tietjen 1986; Roeloffs & Riechert 1988; Furey & Riechert 1989, 1999)
Agelena republicana (Darchen 1967a, 1976, 1981).
Dictynidae
Aebutina binotata (Simon 1892; Avilés 1993a, 2000; Avilés et al. 2001)
Mallos gregalis (Diguet 1909; Burgess 1976, 1979a, b; Jackson & Smith 1978; Jackson 1979, 1980, 1982; Tietjen 1981, 1982, 1986a, b)
Eresidae
Stegodyphus dumicola (Kraus & Kraus 1988, 1990; Seibt & Wickler 1987, 1988a, b, 1990; Kraus 1988; Wickler & Seibt 1993; Henschel et al. 1995a, b, 1996; Henschel 1998; Seibt et al. 1998; Avilés et al. 1999; Ulbrich & Henschel 1999; Whitehouse & Lubin 1999; Amir et al. 2000; Schneider et al. 2001; Crouch & Malan 2002; Johannesen et al. 2002; Lubin & Crouch 2003)
Stegodyphus mimosarum (Ward & Enders 1985; Ward 1986; Seibt & Wickler 1987, 1988a, b, 1990; Kraus & Kraus 1988, 1990; Wickler & Seibt 1986, 1993; Crouch & Lubin 2000; Crouch & Lubin 2001; Bodasing, Slotow & Crouch 2001; Ainsworth et al. 2002; Bodasing, Crouch & Slotow 2002; Lubin & Crouch 2003)
Stegodyphus sarasinorum (Kraus 1988; Kraus & Kraus 1988, 1990; Kullmann et al. 1972; Bradoo 1972, 1983; Jacson & Joseph 1973; Willey & Jackson 1993; Smith & Engel 1994) Stegodyphus manaus Kraus & Kraus, 1992 (possibly social, see Kraus & Kraus 1992)
Nesticidae
Species not identified (Quintero & Amat 1995)
Oxyopidae
Tapinillus sp. (Aviés 1994; Avilés et al. 2001)
Sparassidae
Delena cancerides (Rowell 1987; Hancock & Rowell 1995; Rowell & Avilés 1995)
Theridiidae
Achaearanea disparata (Darchen 1968; Darchen & Ledoux 1978)
Achaearanea vervortii (Levi et al. 1982; Lubin 1982, 1991)
Achaearanea wau (Levi et al. 1982; Lubin 1982, 1991; Lubin & Robinson 1982)
Anelosimus domingo (Levi 1963; Levi & Smith 1982; Rypstra & Tirey 1989; Avilés et al. 2001)
Anelosimus eximius (Levi 1963; Vollrath 1982; Avilés 1992)
Anelosimus guacamayos (Avilés et al. 2007)
Anelosimus oritoyacu (Avilés et al. 2007)
Anelosimus puravida (Agnarsson 2006a)
Anelosimus lorenzo (Fowler & Levi 1979)
Anelosimus rupununi (Levi 1963; Rypstra & Tirey 1989; Levi 1972)
Theridion nigroannulatum (Avilés 1997; Avilés et al. 2001; Avilés et al. 2006)
Thomisidae
Diaea ergandros (Evans 1996)
Diaea megagyna (Evans 1996)
Diaea socialis (Evans 1996; Main 1988)
More than half of the social spiders are theridiids, even though the family represents less than 6% of spider diversity. Social theridiids occur in at least three genera: Theridion, Achaearanea, and Anelosimus and each genus has two or more social species with eight social species belong to Anelosimus. Strikingly, my phylogenetic results imply no less than 8 independent origins of sociality within Theridiidae, even within Anelosimus most instances of sociality are phylogenetically isolated (Agnarsson 2006, Agnarsson et al. 2006, 2007). This pattern parallels the three social Stegodyphus which each has a non-social sister species(Kraus & Kraus 1988, 1990; Seibt & Wickler 1988a, b, Wickler & Seibt 1993). It is thus evident that no social spider clade contains more than two species. The spindly, yet clustered, distribution of social spiders suggests a conflict between the short term (ecological) and long term (evolutionary) causes and consequences of sociality. The repeated evolution of sociality presumably stems from short term ecological benefits of group living such as access to larger prey. However, sociality appears to be accompanied with lowered speciation rates or higher extinction rates; in other words spider sociality may be best characterized as an evolutionary dead-end.
In quasisocial species juveniles typically never leave the natal colony and therefore sociality is accompanied by a switch in breeding system from outbred panmictic to inbreeding. Inbreeding and consequent low genetic variability (Agnarsson et al. in prep.), accompanied with unstable population structure ('boom and bust', see Avilés 1997; Wickler & Seibt 1993), may be the primary cause of the apparent long-term failure of sociality. Although independent, social instances in theridiids are non-randomly clustered within a relatively distal clade, suggesting a common cause (preadaptations). Maternal care is likely one; theridiid sociality evolved as an extension of maternal care, where juvenile tolerance and cooperation is maintained to adulthood (e.g. Shear 1970; Kullmann 1972; Brach 1975, 1977; Burgess 1978; Krafft 1979; Cangialosi & Uetz 1987; Avilés 1997; Jones & Parker 2002; Schneider 2002; Agnarsson 2002, 2006, 2011; Miller & Agnarsson 2005, Agnarsson et al. 2006). The origin of quasisociality from maternal care and intermediate subsociality is corroborated phylogenetically (Agnarsson 2004, 2006). A three-dimensional web has also been frequently considered as a preadaptation for sociality (e.g. Shear 1970; Krafft 1979, 1982; Buskirk 1981; D'Andrea 1987; Cangialosi & Uetz 1987). Across spiders sociality seems indeed to be limited to lineages with maternal care, and in theridiids sociality occurs where maternal care and a three dimensional web overlap (Agnarsson 2004, 2006). Interestingly, corroborating data comes from the other group of spiders with multiple origins of quasisociality (the distantly related, non-orbicularian Stegodyphus, see Kraus & Kraus 1988, 1990) where maternal care and three dimensional webs also overlap. My work seeks understanding of sociality through molecular and morphological methods. Currently the aim is to revise the genus globally, and to obtain molecular data to reconstruct gene trees for several loci in all extant Anelosimus species. Across species, these represent the phylogeny, which will reveal independent origins of sociality and whether diversification or reversals to less social states have occurred. Within species, these will indicate whether sociality represents a watershed event in the genetic history of the species and whether populations in social species exhibit slow clonal divergence or frequent and widespread replacement/turnover of lineages.
