A redescription of Chrysso nigriceps (araneae, theridiidae) with evidence for maternal care.
Keywords: Chrysso, evolution of sociality, maternal care, taxonomy, South America
Chrysso nigriceps (Keyserling 1884) was described based on a female specimen from Colombia. In a revision of Chrysso O. Pick-ard-Cambridge 1882 from the Americas, Levi (1957) redescribed the female, but to date the male remains unknown. Here we redescribe C. nigriceps and provide a description of the male. We observed juveniles of C. nigriceps cohabitating in the female web (Fig. 1), suggesting some degree of maternal care. Kuntner (pers. comm.) also observed juveniles in adult webs of an Indonesian species, Chrysso nr. argyrodiformis (Yaginuma 1952). To our knowledge, these observations represent the first evidence of maternal care of juveniles reported in Chrysso. Although preliminary, our evidence for maternal care in Chrysso is consistent with Agnarsson's (2004) phylogenetic conclusion that maternal care is primitively present in the subfamily Theridiinae.
[FIGURE 1 OMITTED]
A growing body of evidence supports the "maternal care route" hypothesis to web sharing sociality (Aviles 1997; Agnarsson 2002, 2004). It states that social behavior evolved via temporal extension of maternal care (see Kullmann 1972; Aviles 1997 for reviews). Tolerance among juveniles is maintained over an increasing period of their life-span, culminating in permanent web sharing sociality (quasisociality) with extensive cooperation among adults. The optimization of maternal care (or simply the brief coexistence of mother and young in the web) on a phylogenetic tree is therefore an important step in reconstructing the evolutionary path from solitary to social lifestyle.
Agnarsson (2002, 2004) discussed the progression from solitary lifestyle to quasisociality in a phylogenetic context. In his phylogeny, maternal care optimized to the node leading to all instances of sociality (Anelosimus Simon 1891 plus Theridiinae, or the "lost colulus clade", see Agnarsson 2004, fig. 106). Based on this, he predicted that maternal care should be widespread within the lost colulus clade, a lineage containing hundreds of species. However, Agnarsson (2004) pointed out that the lack of behavioral data on many key taxa in the analysis limited the power of this argument. He noted that the lack of evidence for maternal care in many of these species is due to a poverty of studies on lost colulus clade species that might have discovered maternal care in the field, rather than failed attempts to document maternal care. Agnarsson's (2004) phylogeny of theridiid genera places Chrysso (based on an undescribed species called Chrysso nr. nigriceps) in a key phylogenetic position, sister to the remaining theridiines. Chrysso was scored as unknown for maternal care, as were several other basal theridiines. Evidence for maternal care in Chrysso corroborates the hypothesis that maternal care is primitively present in the lost colulus clade, and that maternal care precedes sociality in evolutionary time. Note that a molecular phylogeny of theridiids places Chrysso nr. nigriceps in a clade with Helvibis Keyserling 1884 and Theridula Emerton 1882, together sister to the remaining theridiines (Arnedo et al. 2004). Maternal behavior remains to be documented for Helvibis and Theridula and this alternative placement of Chrysso does not alter the significance of our finding.
Illustrations were modified from digital photographs taken using a Nikon DXM 1200 digital camera mounted on a Leica MZ16 A dissecting microscope. All measurements are in millimeters and were taken using a reticle in a LEICA MZ APO dissecting microscope. For further details on methods see Miller (in press) and Agnarsson (2004). Material used in this study was borrowed from the following institutions: The Natural History Museum, London (BMNH), Museum of Comparative Zoology, Harvard (MCZ), and National Museum of Natural History, Smithsonian Institution, Washington, D.C. (USNM).
Family Theridiidae Sundevall 1833 Genus Chrysso O. Pickard-Cambridge 1882 Chrysso nigriceps Keyserling 1884 Figs. 1-6
[FIGURES 2-6 OMITTED]
Chrysso nigriceps Keyserling 1884: 154, pl. 7, fig. 95 [??]; Levi 1957: 65, figs. 16, 32, 33 [??]; Platnick 2004. Holotype female from Bogota, Colombia, in BMNH, examined.
Theridion keyserlingi Petrunkevitch 1911: 198 (un-justified replacement name for C. nigriceps; see Levi 1957; Platnick 2004); Mello-Leitao 1941: 250; Roewer 1942: 494.
Type material.--Holotype female: COLOMBIA: Cundinamarca: Bogotd, Keyserling (BMNH, BM1818.104.22.16850).
Other material examined.--COLOMBIA: Cundinamarca: Silvania, Res. Agua Bonita (off Carretera Sibate--Fusagasuga; 15 km from Sibate), 4[degrees]26'N, 74[degrees]20'W, 2440-2560 m, 1 February 1998, G. Hormiga (USNM), 1 [??]; same data, J. Miller (USNM), 1 [??]; La Calera, Cerro del Chocolatero, ca. 5 km NE of Bogotd, 4[degrees]42'N, 73[degrees]58'W, 3000-3145 m, 31 January 1998, G. Hormiga, J. Miller, J. Barriga, J.C. Bello, A. Sabagal (USNM), 1 [??]; Valle del Cauca: Yotoco, 1600 m, December 1976, W Eberhard (MCZ, del. B. Opell), 2 [??], 1 [??], 1 juvenile [??]; Saladito above Cali, 1800 m, 3 January 1977, fog forest, H. Levi (MCZ, 57413), 1 [??]; arriba de Saladito, 1800 m (MCZ, 57412), 5 [??], 3 egg cases; Saladito, 1800 m, 20 March 1970 (MCZ, 57417, det. Levi), 1 [??]; Saladito, 1800 m [no date] (MCZ, 57411), 1 [??], eggs and embryonic juveniles; near Saladito, 12 October [no year] (MCZ, 57418), 4 [??], eggs and embryonic juveniles; Cali [no date] (MCZ, 57414), 1 [??]; near Pance, P.N.N. Farallones de Cali, Res. Nat. Hato Viejo, 3[degrees]20'53"N, 76[degrees]40'07'W 2300 m, 12 February 1998, G. Hormiga (USNM), 1 d ; Putumayo: Cauda-Pu-tumayo, road between Mocoa and Silbundoy, ca. 71,500 m [sic], August 1973, W Eberhard (MCZ, 57416, del. Levi), 1 [??].
Additional records.--ECUADOR: Banor, Runtun Trail, 2000 m, 26 November 1939, E M. Brown, 1 [??] (see Levi 1957).
Diagnosis.--Chrysso nigriceps differs from most American Chrysso by the coloration of the abdomen, bright orange (light gray in alcohol) with black posterior lobe (Figs. 1, 2 & 4). Females further differ by the presence of a trapezoidal plate on the posterior margin of the epigynum (Fig. 3). Males can be diagnosed by the shape of the median apophysis in prolateral view (Fig. 6).
Description.--Female (from Agua Bonita, Cundinamarca, Colombia): Total length 4.40, carapace length 1.55, carapace width 1.29, sternum length 0.88, sternum width 0.87. Carapace dusky orange, darker around eyes. Sternum orange. Chelicerae orange with two promarginal teeth. Palpi dusky orange; palpaltibia with one prolateral, one retrolateral trichobothrium. Coxae, trochanters, and basal half of femora orange; distal half of femora and distal leg segments dusky orange. Leg I: femur 2.71, patella 0.58, tibia 1.85, metatarsus 2.02, tarsus 0.95, total 8.12; leg II: femur 1.87, patella 0.50, tibia 1.09 metatarsus 1.20, tarsus 0.73, total 5.40; leg III: femur 1.28, patella 0.42, tibia 0.70, metatarsus 0.78, tarsus 0.58, total 3.76; leg IV. femur 2.22, patella 0.51, tibia 1.40, metatarsus 1.33, tarsus 0.69, total 6.14. Leg formula: 1-4-2-3. Abdomen extends posteriorly beyond spinnerets, bright orange (light gray in alcohol) with black posterior tip and two white guanine patches, posterior patch larger than anterior (Figs. 1, 2). Colulus absent. Area between booklungs covered with smooth orange sternite continuous with epigynum; spermathecae separated by less than their width; epigynum with median trapezoidal plate at posterior margin (Fig. 3).
Male (from Hato Viejo, Valle del Cauca, Colombia): Total length 2.77, carapace length 1.21, carapace width 1.06, sternum length 0.73, sternum width 0.70. Carapace orange. Sternum orange. Chelicerae orange with two promarginal teeth. Palpi dusky orange. Coxae, trochanters, and basal half of femora orange; distal half of femora and distal leg segments dusky orange. Leg I: femur 2.43, patella 0.49, tibia 1.76, metatarsus 1.83, tarsus 0.91, total 7.41; leg II: femur 1.65, patella 0.37, tibia 1.02, metatarsus 1.09, tarsus 0.66, total 4.78; leg III: femur 1.18, patella 0.33, tibia 0.69, metatarsus 0.73, tarsus 0.51, total 3.43; leg IV: femur 1.97, patella 0.41, tibia 1.28, metatarsus 1.24, tarsus 0.66, total 5.56. Leg formula: 1-4-2-3. Abdomen extends posteriorly slightly beyond spinnerets, light gray (in alcohol) with black posterior tip; guanine patches absent (Fig. 4). Colulus absent. Area between book-lungs covered with smooth orange sternite. Palp as in Fig. 5; median apophysis diagnostic (Fig. 6).
Distribution.--Colombia and Ecuador.
Remarks.--During an expedition to Colombia, Chrysso nigriceps was collected from two regions, the male from near Cali, females near Bogotd. An undescribed Chrysso species was also collected on this same expedition. Both males and females of this undescribed species were collected from the S.F.F. Iguaque, Boyoca, Colombia. The undescribed species was included as the exemplar representing Chrysso in recent phylogenetic analyses of theridiid genera, where it was referred to as Chrysso nr. nigriceps (Agnarsson 2004; Arnedo et al. 2004).
Manuscript received S February 2004, revised 12 May 2004.
Mark Harvey, Barbara Knoflach, Matjaz Kuntner, and an anonymous reviewer, provided comments that helped improve the manuscript. Thanks to Janet Beccaloni (BMNH), Jonathan Coddington and Dana De Roche (USNM), and Gonzalo Giribet and Laura Leibensperger (MCZ) for the loan of specimens. Matjaz Kuntner generously shared unpublished data on Chrysso in Indonesia. Colombian field assistance provided by Jonathan Coddington, Gustavo Hormiga, Eduardo Florez, Valeria Rodrfguez, Darfo Correa, Javier Barriga, Juan Carlos Bello, Fernando Ferndndez, Claudia Medina, A. Sabogal, and the Instituto von Humboldt, Instituto de Ciencias Naturales. Institutional support was provided by the National Museum of Natural History (Smithsonian Institution) and the George Washington University. This work was supported in part by an NSF-PEET (9712353) grant to Hormiga and Coddington and the USIA Fulbright program. Special thanks to Cynthia Zujko.
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Manuscript received 5 February 2004, revised 12 May 2004.
Jeremy Miller (1,3) and Ingi Agnarsson (1,2,4):
(1) Department of Entomology, National Museum of Natural History, NHB-105, Smithsonian Institution, PO Box 37012, Washington, DC 20013-7012, U.S.A.;
(2) Department of Biological Sciences, George Washington University, 2023 G Street NW, Washington, D.C. 20052, USA
(3) Current address: Department of Entomology, California Academy of Science, 875 Howard Street, San Francisco, CA 94103, USA. E-mail: jmiller@Calacademy.org
(4) Current address: Department of Botany and Zoology, The University of British Columbia, 3529-6270 University Blvd., Vancouver, BC. V6T 1Z4, Canada.
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|Author:||Miller, Jeremy; Agnarsson, Ingi|
|Publication:||The Journal of Arachnology|
|Date:||Sep 1, 2005|
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