''Allocosa brasiliensis'' is a burrowing
wolf spider
Wolf spiders are members of the family Lycosidae (). They are robust and agile hunters with excellent eyesight. They live mostly in solitude, hunt alone, and do not spin webs. Some are opportunistic hunters, pouncing upon prey as they find it or ...
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
from southern
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...
. Long known to science, it remained almost unstudied until its
unusual sexual behavior was described in the early 21st century.
[BBC News 2011-APR-12]
Cannibal wolf spiders are ladykillers
/ref>
This ground-dwelling spider is native to mainly coastal areas, from southeastern Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
via Uruguay
Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...
and Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
to southern Chile
Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
, though its known occurrences are patchy. To what extent it is found on the Atlantic
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
coast south of the Río de la Plata
The Río de la Plata (, "river of silver"), also called the River Plate or La Plata River in English, is the estuary formed by the confluence of the Uruguay River and the Paraná River at Punta Gorda. It empties into the Atlantic Ocean and fo ...
remains largely unknown, for example. While the males have been known for over a century, the females were only described in 1980.
Description
''A. brasiliensis'' is a mid-sized cryptic light brown spider of robust build, with a body size of well over 1 cm (0.5 in and more) when fully grown, up to almost twice this size in the largest specimens. The cephalothorax has an inconspicuous darker stripe pattern reminiscent of that found in many lycosids, but the opisthosoma
The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma ( cephalothorax). It is a distinctive feature of the subphylum Chelicerata (arachnids, horseshoe crabs and others). Although it is similar in most respects to ...
is patterned with yellower and darker spots the approximate size of sand grains. Males and females look alike in color, but differ in size and genital
A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...
s.[Casanueva (1980), Capocasale (1990), Aisenberg ''et al.'' (2009)]
Adult females have a cephalothorax carapace some 4–5 mm wide and some 6–7 mm long on average. Quite unusually for spiders in general, adult males are about 20% larger. Still, as usual for wolf spiders the females are more robustly built, wider-bodied and shorter-legged. In both sexes the four middle legs are shortest, the hind pair longest and the front pair intermediate. Even the shortest four legs of the adult females usually measure more than 1 cm. The longest leg pair is usually 2 cm or more in adult males and may measure up to about 2.5 cm (1 in). In females, it may grow to almost 1 in, but is usually around 2 cm.
Taxonomy
''A. brasiliensis'' was first described to the New York Academy of Sciences
The New York Academy of Sciences (originally the Lyceum of Natural History) was founded in January 1817 as the Lyceum of Natural History. It is the fourth oldest scientific society in the United States. An independent, nonprofit organization wi ...
in 1909 by Russian-American arachnologist
Arachnology is the scientific study of arachnids, which comprise spiders and related invertebrates such as scorpions, pseudoscorpions, and harvestmen. Those who study spiders and other arachnids are arachnologists. More narrowly, the study of ...
A. Petrunkevitch; the description was based on a male from Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
and published in the Academy's annual volume released in 1910. Petrunkevitch placed the species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
in a new genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
''Moenkhausiana'', due to its unusual and distinct spinneret
A spinneret is a silk-spinning organ of a spider or the larva of an insect. Some adult insects also have spinnerets, such as those borne on the forelegs of Embioptera. Spinnerets are usually on the underside of a spider's opisthosoma, and a ...
s and leg proportions. Initially considered monotypic
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...
, C.F. de Mello-Leitão later described a presumed relative '' "M." argentinensis''.
But soon thereafter, when he studied spiders from northern Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
, he became so convinced of their distinctness as to consider them ant spiders (Zodariidae) and in 1945 re-described the present species as ''Glieschiella senex'', perhaps not recognizing it because he misidentified his specimen as a female (it was actually also a male, like the type specimen of ''A. brasiliensis''). In the supposed ant spider genus, it was associated with '' "G." alticeps'' (see below) and the type species of ''Glieschiella'', '' "G." halophila''.
Yet in 1951 Mello-Leitão, when studying some spiders caught at Maullin (Chile
Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
), again described ''A. brasiliensis'' anew, in yet another monotypic
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...
genus ''Araucaniocosa''. Subsequently it was mainly studied under the 1951 name – ''Araucaniocosa difficilis'' –, and affiliated closely with the "European tarantulas" (''Lycosa
''Lycosa'' is a genus of wolf spiders distributed throughout most of the world. Sometimes called the "true tarantula", though not closely related to the spiders most commonly called tarantulas today, ''Lycosa'' spp. can be distinguished from comm ...
''), even included there as a sub-genus. When the females were first described, they were also treated under the 1951 name, as they were also based on individuals from Chile.
Today, ''Moenkhausiana'' and ''Glieschiella'' are treated as junior synonym of the large genus '' Allocosa'', which is not considered to be very close to ''Lycosa'' as wolf spiders go. As regards the species which were historically affiliated with ''A. brasiliensis'', ''A. alticeps'' is generally considered valid, while ''"A. argentinensis"'' and ''"A. halophila"'' are apparently based on immature specimens and considered '' nomina dubia''. The former at least was described from outside the known range of ''A. brasiliensis'' – from Isla Tehuel Malal, Río Negro Province
Río Negro (, ''Black River'') is a province of Argentina, located in northern Patagonia. Neighboring provinces are from the south clockwise Chubut, Neuquén, Mendoza, La Pampa and Buenos Aires. To the east lies the Atlantic Ocean.
Its capi ...
, southeastern Argentina –, but restudy would be needed to determine whether any of them is a distinct taxon
In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...
. Whether the (possibly widely allopatric) Chilean population is a taxonomically distinct subspecies has not been studied in detail; certainly however, it does not seem to be a distinct species and has no conspicuous difference in size.
Ecology and behavior
''A. brasiliensis'' is nocturnal, resting at daytime in burrows in sand dunes along river mouths and the coast of at least part of the Southern Cone. The burrows of adults are quite exactly 1 cm wide and usually run steeply down, with a length of a few cm (1–3 in). Male burrows tend to be longer/deeper, up to 10 cm and more (4 in). The spiders are more frequently found on the land-side of dunes, which is better protected against strong winds, and prefer open habitat to vegetation when outside their burrows. The reproductive peak takes place in January (after midsummer), with the highest surface and foraging activity shown during Southern hemisphere summer.
In general, the habitat is cool and humid for its region, at best subtropical, the air being constantly moistened, usually by brine that is carried from the sea by the wind. In typical habitat at El Pinar, Uruguay, average air and ground temperatures were measured just around in November (early summer). Relative humidity
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.
Humidity dep ...
was almost 100%, even though the air was constantly exchanged even in the area of ground effect. The vegetation was rather monotonous, dominated by ragwort (''Senecio
''Senecio'' is a genus of flowering plants in the daisy family (Asteraceae) that includes ragworts and groundsels.
Variously circumscribed taxonomically, the genus ''Senecio'' is one of the largest genera of flowering plants.
Description
Mor ...
'') and ''Panicum
''Panicum'' (panicgrass) is a large genus of about 450 species of grasses native throughout the tropical regions of the world, with a few species extending into the northern temperate zone. They are often large, annual or perennial grasses, growi ...
'' grass. Potential ''A. brasiliensis'' prey that was commonly encountered were ''Acromyrmex
''Acromyrmex'' is a genus of New World ants of the subfamily Myrmicinae. This genus is found in South America and parts of Central America and the Caribbean Islands, and contains 33 known species.
Commonly known as " leafcutter ants" they compri ...
'' ants, '' Tetragonoderus'' ground beetle
Ground beetles are a large, cosmopolitan family of beetles, the Carabidae, with more than 40,000 species worldwide, around 2,000 of which are found in North America and 2,700 in Europe. As of 2015, it is one of the 10 most species-rich animal f ...
s and striped earwigs of genus '' Labidura''. Rhino beetles of the genus '' Thronistes'' were also common in that habitat, but presumably too tough for the spiders to eat. As a possible predator
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
of the spiders, a dune-adapted species of tree iguana (''Liolaemus'') was noted.
Owing to its harsh habitat, with high variability of weather conditions and prey availability, ''A. brasiliensis'' is a highly opportunistic free-roaming predator, feeding mostly on spider
Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...
s, beetle
Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
s, flies
Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced m ...
and ant
Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of ...
s. Altogether, the species prefers to feed on spiders, which make up about one-third of its diet; indeed, other ''Allocosa'' are typically eaten more often than any other kind of prey during the life of any wild-living ''A. brasiliensis''. But the mainstay food actually varies quite a lot between the seasons, and in general these spider's food choice is shaped by availability more than by preference. Less frequently other arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s are caught, e.g. true bug
Hemiptera (; ) is an order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They range in size from to around , ...
s (Hemiptera) or crickets, grasshoppers etc. ( Orthoptera). Ants such as ''Acromyrmex'' or '' Dorymyrmex'' are often caught on their trails or during their nuptial flight
Nuptial flight is an important phase in the reproduction of most ant, termite, and some bee species. It is also observed in some fly species, such as '' Rhamphomyia longicauda''.
During the flight, virgin queens mate with males and then land t ...
s, and the nimble and well-camouflaged spiders manage to surprise Lepidoptera (butterflies and moths) resting on the ground surprisingly often. As regards cannibalism, the adult female ''A. brasiliensis'' are if anything less prone to eat conspecific
Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species.
Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...
s than spiders in general, let alone the adult females which in many species are famous for habitually feeding on their mates. In ''A. brasiliensis'' by contrast, immatures are voraciously cannibalistic on each other and even more often eat females of the smaller sympatric relative '' A. alticeps''. Most remarkably however, the adult males include a considerable number of conspecific females in their diet.[Aisenberg ''et al.'' (2009)]
Adults reach maturity at around 9–10 months of age and after around 10 (up to one dozen) moult
In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...
s; females grow up somewhat faster than males, and often have one moult less. On average females tend to be slightly shorter-lived than males at least in captivity, where the latter typically live for almost 500 days. An extreme age of almost 2 years has been recorded in a captive female; generally the species seems to be semelparous
Semelparity and iteroparity are two contrasting reproductive strategies available to living organisms. A species is considered semelparous if it is characterized by a single reproductive episode before death, and iteroparous if it is characteri ...
.[Aisenberg & Costa (2008)]
In captivity, these spiders have been maintained from wild-collected eggs to maturity and senescence in petri dishes, one spider per dish. A thin layer of sea sand and a watered lump of clean cotton wool create a favorable microclimate
A microclimate (or micro-climate) is a local set of atmospheric conditions that differ from those in the surrounding areas, often with a slight difference but sometimes with a substantial one. The term may refer to areas as small as a few squ ...
and allow the spiders to drink. Spiderlings fared well in dishes of 3.5 cm diameter and about 1 cm height; as they grow (around the third to fourth instar
An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ...
) they will need to be housed in larger dishes (about 10 cm in diameter and over 1 cm in height). As captive-bred food, ''Drosophila
''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many speci ...
'' flies up to the fourth instar and subsequently '' Tenebrio'' mealworm
Mealworms are the larval form of the yellow mealworm beetle, ''Tenebrio molitor'', a species of darkling beetle. Like all holometabolic insects, they go through four life stages: egg, larva, pupa, and adult. Larvae typically measure about or ...
s of appropriate size, and for adults also small Orange-spotted Cockroaches (''Blaptica dubia''), were used with success. Adults will need three such food items per week. Captive breeding attempts require sizeable terraria
''Terraria'' is an action-adventure sandbox game developed by Re-Logic. The game was first released for Windows on May 16, 2011, and has since been ported to several other platforms. The game features exploration, crafting, building, painting ...
due to the spiders' burrowing and cannibalistic habits; a 15-cm (>5 in) sand bottom with 5 cm (2 in) air above has been found to work; the base area should not be much less than 450 cm2 (0.5 ft2). The mating terrarium needs to be divided by a barrier, the above ground part of which is removed when male and female have constructed their burrow.
Sexual role reversal
''A. brasiliensis'' males use pheromones to attract females, in contrast to most other burrowing wolf spiders, where the females attract the males. Males have been observed to specifically cannibalize on older females that were lured into the male's burrow, while preferring mating with virgins. The first egg sac of ''A. brasiliensis'' females contains more eggs than later ones, which, together with the harsh habitat, gives this behavior an evolutionary advantage.
The smaller and stronger-marked relative '' Allocosa alticeps'', which lives sympatrically in the same habitat, seems to show a similar sexual role reversal. Although cannibalism is not rare among spiders, the selective hunting of females by males is as of 2010 unknown in any other spider species; even ''A. alticeps'' does not seem to be conspicuously cannibalistic.
These ''Allocosa'' are the only known wolf spiders adapted to living on the Uruguay
Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...
an coastline (though see above for possible relatives). Sexual size dimorphism seems to be more pronounced in ''A. brasiliensis'', while ''A. alticeps'' females and males are often enough about the same size. Both sexes of the present species are usually found equally frequently; in ''A. alticeps'' females appear to outnumber males by far. Reproductive isolation is ultimately achieved via behavior and genital
A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...
anatomy
Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...
, but quite often inspecting the differently-sized and differently-smelling burrow entrance will already allow these spiders to identify conspecific
Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species.
Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...
s. In addition, the species also seem to have different microhabitat
In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
preferences.[Aisenberg & Costa (2008), Aisenberg ''et al.'' (2009), Aisenberg ''et al.'' (2010a)]
Footnotes
References
* (2008): Reproductive isolation and sex-role reversal in two sympatric sand-dwelling wolf spiders of the genus ''Allocosa''. ''Canadian Journal of Zoology'' 86(7): 648-658. PDF fulltext
* (2009): Reversed Cannibalism, Foraging, and Surface Activities of ''Allocosa alticeps'' and ''Allocosa brasiliensis'': Two Wolf Spiders from Coastal Sand Dunes. '' J. Arachnol.'' 37(2): 135-138
PDF
* (2010a): Behavioural evidence of male volatile pheromones in the sex-role reversed wolf spiders ''Allocosa brasiliensis'' and ''Allocosa alticeps''. '' Naturwissenschaften'' 97(1): 63-70. PDF fulltext
* (1990): Las especies de la subfamilia Hippasinae de America del Sur (Araneae, Lycosidae) The South American species of subfamily Hippasinae" '' J. Arachnol.'' 18: 131-141 panish with English abstractbr>PDF fulltext
* (2001): Review of the South American species of the genera ''Aulonia'' and ''Allocosa'' (Araneae, Lycosidae). '' J. Arachnol.'' 29: 270-272
PDF
* (1980): Los licosidos de Chile. Estudio biologico y taxonomico por los metodos de sistematica alfa y taxonomica numerica (Araneae: Lycosidae) The wolf spiders of Chile. Biological and taxonomic study by means of alpha and numerical taxonomy" ''Gayana Zoologia'' 42: 1-76 panishbr>Fulltext
at Internet Archive
The Internet Archive is an American digital library with the stated mission of "universal access to all knowledge". It provides free public access to collections of digitized materials, including websites, software applications/games, music, ...
* (1945): Arañas de Misiones, Corrientes y Entre Ríos Spiders of Misiones, Corrientes and Entre Rios provinces" ''Revista del Museo de La Plata Sección zoología'' 4: 213-302 panish
* (1951): Arañas de Maullin, colectadas por el ingeniero Rafael Barros V. Spiders of Maullin, collected by Engineer R. Barros V." '' Rev. Chil. Hist. Nat.'' 51-53: 327-338 panish
* 910 Some new or little known American Spiders. '' Ann. N.Y. Acad. Sci.'' 19(1): 205-224. (First page image)
* (2010): World Spider Catalog
The World Spider Catalog (WSC) is an online searchable database concerned with spider taxonomy. It aims to list all accepted families, genera and species, as well as provide access to the related taxonomic literature. The WSC began as a series of ...
&ndash
Lycosidae
Version 11.5, 2010-DEC-15. Retrieved 2011-APR-12.
Further reading
* (2007): Daring females, devoted males, and reversed sexual size dimorphism in the sand-dwelling spider ''Allocosa brasiliensis'' (Araneae, Lycosidae). ''Behavioral Ecology and Sociobiology'' 62(1): 29-35. (HTML abstract and first page image)
* (in print): Male sexual cannibalism in a sand-dwelling wolf spider with sex role reversal. '' Biol. J. Linn. Soc.'', in print. (HTML abstract)
* (2010b): Sexual dimorphism in chelicerae, forelegs and palpal traits in two burrowing wolf spiders (Araneae: Lycosidae) with sex-role reversal. '' J. Nat. Hist.'' 44(19-20): 1189-1202. (HTML abstract)
* (2011): Spatial distribution, burrow depth and temperature: implications for the sexual strategies in two ''Allocosa'' wolf spiders. '' Studies on Neotropical Fauna and Environment'' 46(2): 147–152.
External links
Photo of an ''A. brasiliensis''
{{Taxonbar, from=Q2661205
Lycosidae
Spiders of South America