Timema
Timema | |
---|---|
Timema genevievae on the leaves of chamise (Adenostoma fasciculatum). | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Insecta |
Order: | Phasmatodea |
Family: | Timematidae |
Genus: | Timema Scudder, 1895 |
Species | |
21, and see text | |
Geographical distribution of Timema species in North America (Law & Crespi, 2002). T. morongense is found west of T. chumash but the extent of its full range is unknown.[1] |
Timema is a
Compared to other stick insects (order Phasmatodea), the genus Timema is considered basal; that is, the earliest "branch" to diverge from the phylogenetic tree that includes all Phasmatodea. To emphasize this outgroup status, all stick insects not included in Timema are sometimes described as "Euphasmatodea."
Five of the twenty-one species of Timema are parthenogenetic, including two species that have not engaged in sexual reproduction for one million years, the longest known asexual period for any insect.[5]
Description
Timema spp. differ from other
Cryptic coloration and camouflage
Timema walking sticks are night-feeders who spend daytime resting on the leaves or bark of the plants they feed on. Timema colors (primarily green, gray, or brown) and patterns (which may be stripes, scales, or dots) match their typical background, a form of crypsis.[7][8]
In 2008, researchers studying the presence or absence of a dorsal stripe suggested that it has independently evolved several times in Timema species and is an adaptation for crypsis on needle-like leaves. All of the eight Timema species with a dorsal stripe have at least one host plant with needle-like foliage. Of the thirteen unstriped species, seven feed only on broadleaf plants. Four (T. ritense, T. podura, T. genevievae, and T. coffmani) rest during the day on the host plant's trunk rather than its leaves and have bodies that are brown, gray, or tan. Only two species (T. nakipa and T. boharti) have green unstriped morphs that feed on needle-like foliage; both are generalist feeders that also feed on broadleaf hosts.[7]
The species Timema cristinae exhibits both striped and unstriped populations depending on the
These characteristics are genetically inherited and has been interpreted as the early stages of the speciation process. The two ecotypes will eventually become separate species once reproductive isolation is achieved. At the moment, both ecotypes are still capable of interbreeding and producing viable offspring, as such they are still considered a single species.[9][10]
Life cycle and reproduction
Timema eggs are soft, ellipsoidal, and about two mm long, with a lid-like structure at one end (the operculum) through which the nymph will emerge.[11] Timema females use particles of dirt, which they have previously ingested, to coat their eggs.[12]
The eggs of many stick insects, including Timema, are attractive to ants, who carry them away to their burrows to feed on the egg's capitulum, while leaving the rest of the egg intact to hatch.[13][14] The emerging nymph passes through six or seven instars before reaching adulthood.[14]
Timema males, in sexual species of Timema, show a consistent pattern of courting behavior. The male climbs onto the back of the female and, after a short display of vibrating and waving, they proceed to mate. (Rejection by the female is possible but uncommon.) The male then rides on the female's back for up to five days, a behavior often referred to as "guarding" the female.[15]
Several species of Timema are parthenogenetic:[16] that is, females can reproduce asexually, producing viable eggs without male participation.
According to Tanja Schwander, "Timema are indeed the oldest insects for which there is good evidence that they have been asexual for long periods of time."[5] She heads a team of researchers who found that five Timema species (T. douglasi, T. monikense, T. shepardi, T. tahoe and T. genevievae) have used only asexual reproduction for more than 500,000 years, with T. tahoe and T. genevievae reproducing asexually for over one million years.[5][17]
Genetic analysis, published in 2023, of four asexual Timema species suggested that males, which are rare but not entirely absent, do in fact engage in sexual reproduction with some females.[18]
Habitat
The geographic range of Timema is limited to mountainous regions of western North America between 30° and 42° N.
Host plants of the different Timema species include
Phylogeny
General
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Classification
Timema is the only extant member of the
Twenty-one species have been described; in addition there are at least two undescribed species known to exist:[7]
- Timema bartmani
- Timema boharti
- Timema californicum
- Timema chumash
- Timema coffmani
- Timema cristinae
- Timema dorotheae
- Timema douglasi
- Timema genevievae
- Timema knulli
- Timema landelsense
- Timema monikense
- Timema morongense
- Timema nakipa
- Timema nevadense
- Timema petita
- Timema podura
- Timema poppense
- Timema ritense
- Timema shepardi
- Timema tahoe
- Timema sp. nov. on limber pine
- Timema sp. nov. on Sargent cypress
See also
References
- ^ S2CID 45314005.
- ^ Brock, P.D. "Species Timema californicum Scudder, 1895". Phasmida Species File Online. Retrieved 19 July 2011.
- ^ Hebard, M. (1920). "The genus Timema Scudder, with the description of a new species, (Orthoptera, Phasmidae, Timeminae)" (PDF). Entomological News. 31: 126–132. Retrieved 19 July 2011.
- ^ About Timemas | Timema Discovery Project
- ^ a b c Davies, Ella. "Sticks insects survive one million years without sex". BBC. Retrieved 19 July 2011.
- ISBN 0-395-91170-2.
Timema small, stout-bodied, earwig-like forms occurring in the far West
- ^ . Retrieved 21 July 2011.
- ISBN 978-1-4443-3036-6.
... many stick insects look very much like sticks and may even move like a twig in the wind.
- ^ a b Lorraine Scanlon (2009). "Timema cristinae" (PDF). Eukaryon. 5: 87–90. Retrieved July 22, 2011.
- .
- ^ a b Jintsu, Yoshie; Toshiki Uchifune; Ryuchido Machira (2010). "Structural Features of Eggs of the Basal Phasmatodean Timema monikensis Vickery & Sandoval, 1998" (PDF). Arthropod Systematics & Phylogeny. 68 (1): 71–78. Retrieved 23 July 2011.
The genus Timema Scudder, 1895 (Timematidae), endemic to western North America, is usually considered the basalmost clade of Phasmatodea, i.e., the sister group of the remaining Phasmatodea
- ^ ISBN 978-0-521-82149-0. Retrieved 23 July 2011.
..the importance of this group is recognized today by its placement into a separate suborder, Timematodea, versus all other families (i.e. the Euphasmatodea)
- JSTOR 2389958.
- ^ a b "Phasmids" (PDF). Grzimek’s Animal Life Encyclopedia. Retrieved 24 July 2011.
- ^ PMID 20456561. Retrieved 24 July 2011.
- ^ . Retrieved 19 July 2011.
- S2CID 2053974.
- ^ These Male Stick Insects Aren’t ‘Errors’ After All Scientific American
- S2CID 13787599.
External links