Theridion grallator

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Theridion grallator
Theridion grallator with happy face.jpg
Scientific classification edit
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae
Infraorder: Araneomorphae
Family: Theridiidae
Genus: Theridion
Species:
T. grallator
Binomial name
Theridion grallator
Simon, 1900[1]

Theridion grallator, also known as the Hawaiian happy-face spider, is a spider in the family Theridiidae that resides on the Hawaiian Islands. T. grallator obtains its vernacular name of “Hawaiian happy-face spider” from the unique patterns superimposed on its abdomen, specifically those that may resemble a human smiling face.[2] Its Hawaiian name is nananana makakiʻi (face-patterned spider).[3] The specific epithet grallator is Latin for "stilt walker", a reference to the species' long, spindly legs. T. grallator is particularly notable because of its wide range of polymorphisms that may be studied to allow a better understanding of evolutionary mechanisms.

Appearance[edit]

Female

T. grallator is a small spider with a body size less than 5 millimeters long. It has characteristically long and slender legs along with a translucent yellow body.[4] These distinctly long legs lead T. grallator to have the most divergent bodily morphology out of all the members of its clade - this unique characteristic likely occurred as a result of an ecological or behavioral shift.[4]

Its abdomen is often pale translucent yellow and can also contain a variety of red, white, and/or black superimposed patterns.[5] Certain morphs have a pattern resembling a smiley face or a grinning clown face on their yellow body. Each spider has a unique pattern, and the patterns differ from island to island. Some lack abdominal markings altogether.[6] Abdominal color has also been observed to change from translucent yellow to green or orange, depending on diet.[7]

Color morphs[edit]

A key characteristic of T. grallator is the presence of a large variety of abdominal color morphs.[7] Across all of the Hawaiian islands, there is a similar frequency of the discrete morphs;[8] however, there has been shown to be different genetic bases for these morphs between islands.[9] The various morphs have been assigned to a series of broad categories that characterize the abdominal color and/or its patterned patches; the categories include: Yellow, Red front, Red back, Red front and back, Red lines, Red ring, Black ring, Red/black ring, Red blob, Red/black blob, and White.[5] These color polymorphisms have been determined to follow simple Mendelian genetics. The most common morph is Yellow as it makes up 70 percent of populations.[9] Genetic studies of these morphs have shown that the Yellow morph, which is also known as the ‘unpatterned’ morph, is recessive to all patterned morphs. It has also been determined that within patterned morphs, the amount of pigment present in the abdomen is correlated with the dominance of the associated allele.[9] The alleles that are associated with black, red, or white pigments are arranged in a hierarchical structure and exhibit dominant effects.[9] In addition, it has been determined that unpatterned morphs are recessive to patterned morphs. Lastly, White is seen to be dominant to nearly all morphs.[9] The White morph is produced by a massive deposit of guanine below the hypodermis, which is a structure derived from the ectoderm.[10] Exceptions from simple Mendelian genetics have been observed; for example, White and Red lines exhibit codominance.[10] In regards to distribution of morphs amongst sexes, there appears to be no sex-linkage in these traits.[4]

Phylogeny[edit]

Upon analysis of genitalia patterns, at least nine species in the Hawaiian islands have been identified to be members of the T. grallator-clade.[2] This clade is believed to have been colonized from the Americas and is closely related to the genus Exalbidion.[2]

Most of the Hawaiian Theridion observed are believed to be closely related except for T. actitarase, which contains a number of common traits with the related Rugathodes genus. Similar traits include the palpal organ and certain genitalia features. There is another Theridion species, which remains unnamed, that also displays features that are distinct from most Hawaiian Theridion. However, this unnamed species does contains a few characteristics that resemble the T. grallator , namely, its long legs and abdominal shape. Thus, it is believed that this unnamed Theridion species may have evolved under similar evolutionary pressures as T. grallator.[2] Despite some variations in the bodily appearance of the Theridion species, it has been observed that there is a uniformity in sexual behavior. In addition, there is also a highly uniform web-building behavior and structure.[2] Overall, there has been much debate on how to organize clades and construct an appropriate phylogenetic structure of Theridiidae as work is still being done to properly classify these species.

Distribution[edit]

The colonization routes of Theridion grallator on the Hawaiian archipelago. Dark purple lines indicate colonization occurring in conjunction with island age. Light purple indicates a reverse colonization. T. grallator is not present on Kauai or Niihau so colonization may have occurred from there, or the nearest continent.

T. grallator is endemic to the Hawaiian archipelago, and sparsely distributed populations have been reported from Oʻahu, Molokaʻi, Maui and the island of Hawaiʻi in rainforests at elevations of 300–2,000 m (980–6,560 ft).[4]

Although abdominal color morphs have a nearly identical appearance throughout all the Hawaiian islands, there are genetic differences between the populations residing on different islands. On Maui, the color morphs of T. grallator were shown to have originated from one locus while those on Hawai’i were shown to have at least two unlinked loci involved in the color polymorphisms. In addition, on Maui, all polymorphisms are attributed to individual alleles while on Hawai’i, there are two pairs of color morphs that are believed to depend on one single locus that is differentially expressed in males and females.[10] One pair of these differentially expressed morphs are the Yellow and Red fronts, where the morph manifests phenotypically as Yellow in females but Red in males. Similarly, the Red blob and Red ring in Hawai’i populations are shown to have a varied manifestation between the sexes with the Red blob in females and Red ring in males.[9] In addition, these differences in phenotypes are most likely due to differential expression and not sex-linkage.[11]

Diet[edit]

T. grallator spiders may change color depending on their diet. This color change may occur because of the translucent quality of their abdomens. Experimental studies have shown that color pigments can be retained in the abdomen for two to six days, and the color generally shifts from translucent yellow to orange.[7] Once the food is digested and excreted, the color of the abdomen returns to its original translucent pale yellow.

Reproduction & life cycle[edit]

Molting[edit]

During the last molt of a female T. grallator, a mature male may be found to share a leaf with her. Once the female completes its molt, the male will copulate with her.[9]

Reproduction[edit]

A few weeks after copulation, a female will deposit her egg sacs and will remain closely attached to the egg sacs by a short silk thread until the eggs have hatched. When the egg sacs are ready to hatch, the maternal female T. grallator will loosen the silk that is wrapped around the eggs to allow the spiderlings to emerge.[12]

Growth[edit]

T. grallator populations seasonally fluctuate in terms of spider size and sex make-up. During winter months, specifically October to March, there is a higher proportion of smaller sized and immature spiders. In the spring, specifically May to August, there is an increased number of adults in the population with the majority of these adults being maternal females. In fact, it has been observed that up to 85% of a population can consist of maternal females with egg sacs in these later months.[12]

Mating[edit]

Female/male interactions[edit]

Mature males actively move through forest vegetation seeking out females, which tend to be more sedentary. Courtship depends primarily on vibrations and olfaction.[9] For example, males may carry out a courtship dance that involves somatic movements and web-plucking; these vibrations during the courting performance are assessed by potential female mates. Copulation occurs at night, while both spiders hang from the underside of the leaf. Males die soon after mating, but females live longer, and guard their eggs until they hatch, and catch prey for their young.[12]

In addition, there has been observed to be a rare-male advantage phenomenon during mating. Females may prefer a rarer male morph due to many reasons; for example a less common morph may better evade predation. This rare morph may then be selected for and will increase in number until it no longer provides the inconspicuous advantage from predators - an example of negative frequency-dependent selection.[9]

Parental care[edit]

Egg guarding[edit]

A maternal female T. grallator is notably aggressive against intruders right after the birth of her young while she is guarding her egg sac.[12] She must protect her young from predation, parasitic wasps, and the possibility of the resident leaf dropping. Once the spiderlings have hatched, the maternal female will continue to defend and care for her young. The mother will demonstrate exceptional maternal care as she communally feeds all the spiderlings and protects them from predators; spiderlings remain on the same leaf with their mother for approximately 40 to 100 days. Spiderlings are unable to catch their own prey during this first period of their life and will die in the absence of the mother.[12]  The mother wraps all prey that she catches in her silk and is never observed to consume the prey itself.

Adoption[edit]

Mothers take on foster egg sacs with acceptance. When spiderlings are transferred between broods, the new mothers are observed to ‘adopt’ these spiderlings into their family and care for them as if they were their own.[12] In nature, adoption of spiderlings may occur if the related mother has been lost.

Parent-offspring conflict[edit]

Parent-offspring conflict, an idea first introduced by Robert L. Trivers in 1974, may be observed in the costs of mothers guarding their spiderlings. When a maternal female T. grallator has a second brood, she must remain with the first brood for a period of time after hatching because of the spiderlings' inability to feed themselves. Thus, the second brood may be compromised due to the need for parental investment by the first brood.[12]

Social behavior[edit]

Adult females are usually found to be sedentary and located on the underside of leaves while males are often more mobile as they may move about in the search of mates. Thus, due to male mobility, they often become more conspicuous to predators.[9]

Cooperative brood care[edit]

There has been no observation of competition for food resources between members of the same brood. Siblicide and cannibalism have not been observed either.[12]

Protective color & predation[edit]

It has been hypothesized that the variety of polymorphisms present in T. grallator allows an evolutionary benefit to evade predation. Spiders with depigmentation or polymorphic colors and patterns can avoid predation by birds that use a search image, when scanning for prey. A search image may be a particularly abundant color morph, and predators will use this as an identification of possible prey.[7]

Webs[edit]

T. grallator lives beneath the leaves of plants, where they spin a much reduced web.[7] Instead of using the web as a prey-detection medium, it has been demonstrated that vibrations of prey transmitted through the residence leaf are detected by the spiders and guides their orientation toward potential prey.

Habitat & ecology[edit]

T. grallator inhabits wet and mesic environments.[4] Wet environments are defined as having an annual rainfall from 200 to 350 centimeters and mesic are defined as having an annual rainfall of 100 to 200 centimeters. These spiders are found in the forests of the Hawaiian Islands.[4] More specifically, they have been recorded to be found on the islands of O’ahu, Moloka’i, Maui, and Hawai’i.[13] They prefer to reside on the underside of plant leaves such as the native Broussaisia arguta and Clermontia arborescens and the introduced Hedychium coronarium. H. coronarium is a particularly tactical plant to reside on as its large, slippery leaves allow T. grallator to better evade predation.[4]  

Red front morph

T. grallator hunts mainly from dusk, through the evening, to dawn. By day, the spiders assume a remarkable posture that flattens the body against the residence leaf, with legs splayed out and all joints held flat against the leaf.

Evolution[edit]

The closest relatives of T. grallator are other Hawaiian species, such as T. posticatum and T. kauaiense. This "T. grallator clade" may be more closely related to the genus Exalbidion than to any other species currently classified in the genus Theridion.[14]

References[edit]

  1. ^ "Taxon details Theridion grallator Simon, 1900", World Spider Catalog, Natural History Museum Bern, retrieved 2016-01-30
  2. ^ a b c d e Arnedo, Mquel A.; Agnarsson, Ingi; Gillespie, Rosemary G. (July 2007). "Molecular insights into the phylogenetic structure of the spider genus Theridion (Araneae, Theridiidae) and the origin of the Hawaiian Theridion-like fauna". Zoologica Scripta. 36 (4): 337–352. doi:10.1111/j.1463-6409.2007.00280.x. ISSN 0300-3256.
  3. ^ Hawaiian Dictionaries
  4. ^ a b c d e f g Gillespie, Rosemary G; Tabashnik, Bruce E (August 1990). "Maintaining a happy face: stable colour polymorphism in the spider Theiridion grallator (Araneae, Theridiidae)". Heredity. 65 (1): 67–74. doi:10.1038/hdy.1990.71. ISSN 0018-067X.
  5. ^ a b Gon, Samuel M. (1985). Comparative Behavioral Ecology of the Spider Theridion Grallator (Araneae: Theridiidae) in the Hawaiian Archipelago. University of California, Davis.
  6. ^ Rosemary G. Gillespie & Bruce E. Tabashink (1989). "What makes a happy face? Determinants of colour pattern in the Hawaiian happy face spider Theridion grallator (Araneae, Theridiidae)". Heredity. 62 (3): 355–363. doi:10.1038/hdy.1989.50.
  7. ^ a b c d e Gillespie, Rosemary G. (1989). "Diet-Induced Color Change in the Hawaiian Happy-Face Spider Theridion grallator, (Araneae, Theridiidae)". The Journal of Arachnology. 17 (2): 171–177. ISSN 0161-8202.
  8. ^ Gillespie, Rosemary G.; Oxford, Geoffrey S. (June 1998). "Selection on the Color Polymorphism in Hawaiian Happy-Face Spiders: Evidence from Genetic Structure and Temporal Fluctuations". Evolution. 52 (3): 775. doi:10.2307/2411271.
  9. ^ a b c d e f g h i j Oxford, Geoff S.; Gillespie, Rosemary G. (2001). "Portraits of Evolution: Studies of Coloration in Hawaiian Spiders". BioScience. 51 (7): 521. doi:10.1641/0006-3568(2001)051[0521:POESOC]2.0.CO;2. ISSN 0006-3568.
  10. ^ a b c Oxford, G S; Gillespie, R G (March 1996). "Quantum shifts in the genetic control of a colour polymorphism in Theridion grallator (Araneae: Theridiidae), the Hawaiian happy-face spider". Heredity. 76 (3): 249–256. doi:10.1038/hdy.1996.38. ISSN 0018-067X.
  11. ^ Knoflach, Barbara (April 1998). "Mating in Theridion varians Hahn and related species (Araneae: Theridiidae)". Journal of Natural History. 32 (4): 545–604. doi:10.1080/00222939800770301. ISSN 0022-2933.
  12. ^ a b c d e f g h Gillespie, Rosemary G. (April 1990). "Costs and Benefits of Brood Care in the Hawaiian Happy Face Spider Theridion grallator (Araneae, Theridiidae)". American Midland Naturalist. 123 (2): 236. doi:10.2307/2426552.
  13. ^ Oxford, G S; Gillespie, R G (March 1996). "Genetics of a colour polymorphism in Theridion grallator (Araneae: Theridiidae), the Hawaiian happy-face spider, from Greater Maui". Heredity. 76 (3): 238–248. doi:10.1038/hdy.1996.37. ISSN 0018-067X.
  14. ^ Miquel A. Arnedo, Ingi Agnarsson & Rosemary G. Gillespie (2007). "Molecular insights into the phylogenetic structure of the spider genus Theridion (Araneae, Theridiidae) and the origin of the Hawaiian Theridion-like fauna" (PDF). Zoologica Scripta. 36 (4): 337–352. doi:10.1111/j.1463-6409.2007.00280.x.

External links[edit]