Onymacris unguicularis

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Onymacris unguicularis
Onymacris unguicularis MHNT (cropped).jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Tenebrionidae
Genus: Onymacris
Species:
O. unguicularis
Binomial name
Onymacris unguicularis
Haag, 1875

Onymacris unguicularis, also known commonly as the fog-basking beetle, head-stander beetle, or the Toktokkies , is a species of darkling beetle that is native to the Namib Desert of southwestern Africa. At night, during foggy weather, these beetles climb sand dunes and stand on their forelegs in order to capture water droplets as they run down their vertical bodies and into their mouths [1] The behaviour is called "fog-basking" and is unique to Onymacris unguicularis and Onymacris bicolor.

Contents

Fog basking was first observed in the O. unguicularis in 1976. [1] The mechanism for this ability is still being discovered, but current research points towards the beetle’s elytra containing some hydrophobic component that can catch water droplets being blown in the wind. The idea of harvesting atmospheric moisture from early morning dew using special materials has been widely utilized in many parts of the world. [2]

This species has very often been confused with Stenocara gracilipes, another species of darkling beetle in the Namib Desert, due to their similar coloration and water capturing behaviour.

Geographic range

Onymacris unguicularis inhabits most of the Namib Desert and it is almost entirely restricted to this habitat. [2] [3] The species is confined to the major dune fields within the northern (Cunene, Skeleton Coast) and southern (Namib) sand seas of the desert. [4] The species’ migratory habits correlate very highly with the observed pattern for common fog occurrence in the region. [5]

Habitat

The coastal regions of the Namib Desert serve as the natural habitat of Onymacris unguicularis. The long and narrow desert hugs the southwestern coast of Africa, displaying a subtropical climate. [6] Due to cold water currents, the desert is extremely arid. The Namib Desert annually receives less than 50 mm of rainfall overall and in its western half between 0 and 12 mm. Humidity is low most of the year outside of fog events, with relative humidity daily dropping below 50%, with recorded lows below 20%. [7] A majority of the moisture is brought in by fogs blowing from the ocean, bringing water droplets that condensate across the environment. The phenomenon causes a gradient between “coastal” and “inland” faunas across the region as humidity decreases and temperature increases further inland. [3]

Appearance

Onymacris unguicularis Onymacris unguicularis in Namib Desert.jpg
Onymacris unguicularis

Onymacris unguicularis is a fully black beetle, with a fused elytra and no wings. The elytra are almost completely smooth, except for the back half which has large distinct grooves. These grooves are approximately 0.5 mm wide and are divided by narrow ridges. [8] Males have longer legs compared to females, as well as setose brushes on the anterior femora. Females tend to have wider elytra than their male counterparts. [4] There are differences between the two subspecies, with the northern Onymacris unguicularis schulzeae having shorter elytra when compared to the southern Onymacris unguicularis unguicularis. There are also notable differences in pronotal and prosternal shape. [4]

Behaviour

Onymacris unguicularis in headstand position Onymacris unguicularis.jpg
Onymacris unguicularis in headstand position

Fog-basking behaviour

One of the most distinguishing features of Onymacris unguicularis is its fog-basking behaviour. This behaviour is believed to have evolved independently in only two Tenebrionidae beetles, O. unguicularis and Onymacris bicolor [3] [9] O. unguicularis is normally active during the daytime and buries itself in sand dunes when night sets in. During periods of nocturnal fog in the desert, however, they will emerge from the sand and climb onto the slip face of a dune (the side of the sand dune not directly hit by the wind). Positioning themselves against the wind, they conduct a “headstand” posture, angling their heads toward the ground and lifting their dorsal side towards the wind. The angle from resting was observed to be 23 degrees from horizontal. [8] In this handstand position, fog water condenses on the surface of the beetle’s elytra and runs down their body into their mouth. The amount of water that can be collected by an individual beetle relative to their weight can vary greatly, with some beetles gaining little to no water while others have been recorded taking in 34% of their total body weight. [1]

The “headstand” posture is caused by high humidity caused by fog conditions. Low temperatures, observed to be below 20 degrees Celsius during nocturnal fog, [10] may play a role in modulating the behaviour, but low temperatures do not seem to be capable of triggering the “headstand” posture without high humidity conditions. [8]

Mechanism

The mechanism for water collection is still debated, but theories have been placed as to how Onymacris unguicularis collects fog water on its elytra. One theory posited for another darkling beetle, Stenocara gracilipes, claims that bumps on the elytra of the beetle function as hydrophilic peaks where water from the fog gathers into droplets before becoming heavy enough to roll off the peak and slide down the smooth hydrophobic regions between peaks and into the beetle’s mouth. [11] The theoretical mechanism, however, has some issues when applied to O. unguicularis. The mechanism requires bumpy elytra for the presence of hydrophilic peaks. O. unguicularis’s elytra is relatively smooth in its entirety, except for the back half which is compressed of grooves and ridges. While these aspects of O. unguicularis’s elytra could have functioned in a manner similar to the theoretical mechanism, hydrophilic regions on the beetle’s elytra were unable to be conclusively found. [8] Another theory posits that O. unguicularis’s smooth elytra is entirely hydrophobic, with no hydrophilic regions. [2] [7] The presence of hydrophobic regions on the elytra has been proven. A limitation that has plagued the ability to confirm any hydrophilic regions has been that most research has investigated the elytral properties of dead beetles. A live beetles may cause the surface properties of their elytra to change depending on the fog conditions. [12]

Function

Fog-basking is clearly an adaptation for obtaining water, but research has shown that it is the primary source of water intake for Onymacris unguicularis. [6] Moisture obtained from foraging detritus during the daytime is insufficient to maintain maximum foraging activity or egg production. Thus, fog-basking is a method that ensures that the beetle is capable of obtaining enough water to maintain an effective water balance that allows for daytime activity even in hot desert temperatures. The water obtained through fog-basking also seems to play a key role in O. unguicularis’s osmoregulation. [5] [13]

Physiology

Thermoregulation

Onymacris unguicularis is able to regulate its body heat at temperatures much lower than those experienced during normal daytime activity. O. unguicularis's body temperature has been recorded to be between 32-38 degrees Celsius. [5] During fog-basking activity, however, temperatures are much lower, falling as low as one degree Celsius. It has been shown that the beetle employs large amounts of glycerol and trehalose in its hemolymph, relative to other similar daytime-active beetles. [2] [13] These compounds are notable in nature for their antifreeze properties. It is understood that the presence of these compounds allows for O. unguicularis to counteract freezing during this fog-basking activity.

Mating

Female/male interactions

Copulation

In the events leading to copulation, male Onymacris unguicularis beetles will mount stationary or moving females and remain on top for extended periods of time. Forelegs and middle legs are primarily used to stay clung to the female while hindlegs are left limp and are mostly allowed to drag along. Females may attempt to throw off the mating male, but most efforts are unsuccessful. The whole copulation process may take anywhere from one to ten minutes. [14] Males directly transfer a spermatophore into the female through the insertion of a penile tube extending from the aedeagus into the bursa copulatrix of the female. [15]

Sperm competition

Female Onymacris unguicularis are known to practice a polyandrous mating system. If the female’s initial sperm supply has not been completely used for fertilizing her eggs before she mates with another male, there is sperm competition. The phenomenon is fairly common in female O. unguicularis, with the average number of matings for a female being three times in 35 days. [15] Aspects of sperm competition such as sperm displacement and sperm precedence have been observed in the species. In terms of the former, during copulation, the newly inserted spermatophore will push the old spermatophore out of the female’s body and into the sand. The old spermatophore, once ejected, appears as a bleb, consisting of the remains of the old spermatophore sac and coiled penile from the last male. [15] The latter phenomenon has been observed through experiments that use sterile male technique, indicating that not all old sperm is displaced during a new mating. In these experiments, females are allowed to mate with fertile males initially and lay eggs before the males are replaced with irradiated sterile males to do the same. The fertility rate between the fertile males and sterile males has shown substantial decrease in fertility rate, showing that the sterile sperm was unable to completely dislodge all of the former sperm. These observations indicate a possible mechanism involved in the long-term storage and maintenance of sperm. [15]

Subspecies [4]

Subspecies of Onymacris unguicularis include the following:

Confusion with Stenocara gracilipes

Due to the large variety of darkling beetle species in the Namib Desert, different beetles from the region have been confused with each other. Such is the case with Onymacris unguicularis and Stenocara gracilipes, which in non-scientific literature have both been called the “fog-basking beetle.” The confusion seems to originate from a paper [11] detailing a mechanism for S. gracilipes’s ability to capture water using hydrophilic bumps and hydrophobic troughs on the beetle’s elytra during fog-basking. Debate ensued as the only known beetles to display fog-basking behaviour were O. unguicularis and Onymacris bicolor. In a notable response, the notion of S. gracilipes’s fog-basking behaviour was challenged, and the photograph of S. gracilipes that was used in the original study was stated to have been misidentified, being a photo of another beetle, Physosterna cribripes . Additionally, it was noted that the tilting posture being identified as “fog-basking” was most likely a common alarm response found in many species of the Tenebrionidae family. [10] A later experiment would test the fog-basking behaviour and water-collecting efficiency between four Tenebrionidae beetles: O. unguicularis, Onymacris laeviceps, S. gracilipes and P. cribripes. Notably, only O. unguicularis displayed the behaviour. The study supported many of the points made in the response such as re-identifying the beetle as P. cribripes according to their own observations and noting no fog-basking behaviour in S. gracilipes. [8]

Related Research Articles

<span class="mw-page-title-main">Beetle</span> Order of insects

Beetles are insects that form the order Coleoptera, in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 described species, is the largest of all orders, constituting almost 40% of described insects and 25% of all known animal species; new species are discovered frequently, with estimates suggesting that there are between 0.9 and 2.1 million total species. Found in almost every habitat except the sea and the polar regions, they interact with their ecosystems in several ways: beetles often feed on plants and fungi, break down animal and plant debris, and eat other invertebrates. Some species are serious agricultural pests, such as the Colorado potato beetle, while others such as Coccinellidae eat aphids, scale insects, thrips, and other plant-sucking insects that damage crops. Some others also have unusual characteristics, such as fireflies, which use a light-emitting organ for mating and communication purposes.

<span class="mw-page-title-main">Namib</span> Desert in Southern Africa

The Namib is a coastal desert in Southern Africa. According to the broadest definition, the Namib stretches for more than 2,000 kilometres (1,200 mi) along the Atlantic coasts of Angola, Namibia, and northwest South Africa, extending southward from the Carunjamba River in Angola, through Namibia and to the Olifants River in Western Cape, South Africa. The Namib's northernmost portion, which extends 450 kilometres (280 mi) from the Angola-Namibia border, is known as Moçâmedes Desert, while its southern portion approaches the neighboring Kalahari Desert. From the Atlantic coast eastward, the Namib gradually ascends in elevation, reaching up to 200 kilometres (120 mi) inland to the foot of the Great Escarpment. Annual precipitation ranges from 2 millimetres (0.079 in) in the aridest regions to 200 millimetres (7.9 in) at the escarpment, making the Namib the only true desert in southern Africa. Having endured arid or semi-arid conditions for roughly 55–80 million years, the Namib may be the oldest desert in the world and contains some of the world's driest regions, with only western South America's Atacama Desert to challenge it for age and aridity benchmarks.

<span class="mw-page-title-main">Namib-Naukluft National Park</span> National park in Namibia

The Namib-Naukluft Park is a national park in western Namibia, situated between the coast of the Atlantic Ocean and the edge of the Great Escarpment. It encompasses part of the Namib Desert, the Naukluft mountain range, and the lagoon at Sandwich Harbour. The best-known area of the park and one of the main visitor attractions in Namibia is Sossusvlei, a clay pan surrounded by dunes, and Sesriem, a small canyon of the Tsauchab. The desert research station of Gobabeb is situated within the park.

<span class="mw-page-title-main">Darkling beetle</span> Family of beetles

Darkling beetle is the common name for members of the beetle family Tenebrionidae, comprising over 20,000 species in a cosmopolitan distribution.

<span class="mw-page-title-main">Sperm competition</span> Reproductive process

Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and variety of mates increases a female's chance to produce more viable offspring. However, multiple mates for a female means each individual male has decreased chances of producing offspring. Sperm competition is an evolutionary pressure on males, and has led to the development of adaptations to increase male's chance of reproductive success. Sperm competition results in a sexual conflict between males and females. Males have evolved several defensive tactics including: mate-guarding, mating plugs, and releasing toxic seminal substances to reduce female re-mating tendencies to cope with sperm competition. Offensive tactics of sperm competition involve direct interference by one male on the reproductive success of another male, for instance by mate guarding or by physically removing another male's sperm prior to mating with a female. For an example, see Gryllus bimaculatus.

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Leucorchestris arenicola, commonly called the dancing white lady spider, is a huntsman spider in the family Sparassidae and genus Leucorchestris. It is commonly found in the Namib desert of Namibia. It is often mistaken with the similarly named Carparachne aureoflava, or more commonly known as the wheel spider from the same location. L. arenicola relies on seismic vibrations, called drumming, for communication. It taps its foremost legs on the sand to send messages to other white lady spiders. Male L. arenicola will travel over 50 m in one night searching for a mate. If they find a mate, they must be extremely careful, for drumming the wrong message can be deadly. One of the major features that characterizes its nocturnal behavior is its specialized vision, using eight eyes in different orientations to capture a panoramic view of the surroundings. L. arenicola spiders use temporal summation in order to be able to see dim lighting during night-time wanderings. The species was first described by Reginald Frederick Lawrence in 1962, who described all the species in the genus Leucorchestris.

<span class="mw-page-title-main">Tenebrionoidea</span> Superfamily of beetles

The Tenebrionoidea are a very large and diverse superfamily of beetles. It generally corresponds to the Heteromera of earlier authors.

<i>Pimelia</i> Genus of beetles

Pimelia is a genus of darkling beetles in the subfamily Pimeliinae.

<span class="mw-page-title-main">Namaqua chameleon</span> Species of lizard

The Namaqua chameleon is a ground-living lizard found in the western desert regions of Namibia, South Africa and southern Angola.

<i>Stenocara gracilipes</i> Species of beetle

Stenocara gracilipes is a species of beetle that is native to the Namib Desert in southern Africa. This is one of the most arid areas of the world, receiving only 1.4 centimetres (0.55 in) of rain per year. The beetle is able to survive by collecting water on its bumpy back surface from early morning fogs.

<i>Zophobas</i> Genus of beetles

Zophobas is a genus of beetles in the family Tenebrionidae, the darkling beetles. They occur in the Americas, from the Neotropics into southernmost United States. In Cuba beetles of this genus are known as blind click-beetles.

<i>Eleodes</i> Genus of beetles

Eleodes is a genus of darkling beetles, in the family Tenebrionidae. They are endemic to western North America ranging from southern Canada to central Mexico with many species found along the Mexico-United States border. Some species have been introduced to Colombia. The name pinacate is Mexican Spanish, derived from the Nahuatl (Aztec) name for the insect, pinacatl, which translates as "black beetle".

<i>Bolitotherus</i> Species of beetle

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<i>Physosterna cribripes</i> Species of beetle

Physosterna cribripes, the desert toktokkie or woestyntoktokkie, is a flightless species of desert-dwelling darkling beetle or Tenebrionid found along the West coast of Namibia and Angola. This species has a body length of some 18.4 mm (0.72 in) and a mass of 402 mg (6.20 gr).

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<i>Eleodes gigantea</i> Species of beetle

Eleodes gigantea is a species of desert stink beetle or darkling beetle in the family Tenebrionidae. They can be found from San Francisco California down to Tijuana Mexico, however they are more typically located in the lower half of California from Santa Cruz to San Diego.

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References

  1. 1 2 3 Hamilton, William J.; Seely, Mary K. (1976). "Fog basking by the Namib Desert beetle, Onymacris unguicularis". Nature. 262 (5566): 284–285. Bibcode:1976Natur.262..284H. doi:10.1038/262284a0. S2CID   4192150.
  2. 1 2 3 4 Mitchell, Duncan; Henschel, Joh R.; Hetem, Robyn S.; Wassenaar, Theo D.; Strauss, W. Maartin; Hanrahan, Shirley A.; Seely, Mary K. (2020). "Fog and fauna of the Namib Desert: past and future". Ecosphere. 11 (1). Bibcode:2020Ecosp..11E2996M. doi: 10.1002/ecs2.2996 . ISSN   2150-8925.
  3. 1 2 3 Ward, David; Seely, Mary K. (1996). "ADAPTION AND CONSTRAINT IN THE EVOLUTION OF THE PHYSIOLOGY AND BEHAVIOR OF THE NAMIB DESERT TENEBRIONID BEETLE GENUS ONYMACRIS". Evolution . 50 (3): 1231–1240. doi:10.2307/2410663. JSTOR   2410663 – via Oxford Academic.
  4. 1 2 3 4 Lamb, Trip; Pollard, Rachel; Bond, Jason (2013-11-20). "Genetic variation corroborates subspecific delimitation in the Namib fog-basking beetle, Onymacris unguicularis (Haag) (Tenebrionidae, Coleoptera)". ZooKeys (353): 47–60. Bibcode:2013ZooK..353...47L. doi: 10.3897/zookeys.353.6228 . ISSN   1313-2970. PMC   3837484 . PMID   24294097.
  5. 1 2 3 Cooper, Paul D. (1982-01-01). "Water balance and osmoregulation in a free-ranging tenebrionid beetle, Onymacris unguicularis, of the Namib Desert". Journal of Insect Physiology. 28 (9): 737–742. doi:10.1016/0022-1910(82)90133-0. ISSN   0022-1910.
  6. 1 2 Seely, M. K. (1979-09-01). "Irregular fog as a water source for desert dune beetles". Oecologia. 42 (2): 213–227. Bibcode:1979Oecol..42..213S. doi:10.1007/BF00344858. ISSN   1432-1939. S2CID   31922146.
  7. 1 2 Henschel, Joh R.; Seely, Mary K. (2008-03-01). "Ecophysiology of atmospheric moisture in the Namib Desert". Atmospheric Research. Third International Conference on Fog, Fog Collection and Dew. 87 (3): 362–368. Bibcode:2008AtmRe..87..362H. doi:10.1016/j.atmosres.2007.11.015. ISSN   0169-8095.
  8. 1 2 3 4 5 Nørgaard, Thomas; Dacke, Marie (2010). "Fog-basking behaviour and water collection efficiency in Namib Desert Darkling beetles". Frontiers in Zoology . 7 (1): 23. doi: 10.1186/1742-9994-7-23 . ISSN   1742-9994. PMC   2918599 . PMID   20637085.
  9. ↑ Seely, Mary; Henschel, Joh R.; Hamilton III, William J. (2005). "Long-term data show behavioural fog collection adaptions determine Namib Desert beetle abundance: research letter". South African Journal of Science . 101 (11): 570–572. eISSN   1996-7489. ISSN   0038-2353 – via Sabinet African Journals.
  10. 1 2 Hamilton III, William J.; Henschel, Joh R.; Seely, Mary K. (2003). "Fog collection by Namib Desert beetles". South African Journal of Science . 99 (3): 181. eISSN   1996-7489. ISSN   0038-2353 – via Sabinet African Journals.
  11. 1 2 Parker, Andrew R.; Lawrence, Chris R. (2001). "Water capture by a desert beetle". Nature . 414 (6859): 33–34. Bibcode:2001Natur.414...33P. doi:10.1038/35102108. ISSN   1476-4687. S2CID   34785113.
  12. ↑ Malik, F T; Clement, R M; Gethin, D T; Krawszik, W; Parker, A R (2014-03-20). "Nature's moisture harvesters: a comparative review". Bioinspiration & Biomimetics. 9 (3): 031002. doi:10.1088/1748-3182/9/3/031002. ISSN   1748-3182.
  13. 1 2 Naidu, Strinivasan G. (2008-12-30). "Why does the Namib Desert tenebrionid Onymacris unguicularis (Coleoptera: Tenebrionidae) fog-bask?". European Journal of Entomology. 105 (5): 829–838. doi:10.14411/eje.2008.110.
  14. ↑ Rasmussen, J. L.; Seely, M. K.; Pietruszka, R. D. (1991-09-01). "The reproductive behavior of six species of Namib desert tenebrionid beetles (Coleoptera: Tenebrionidae)". Journal of Insect Behavior. 4 (5): 567–582. Bibcode:1991JIBeh...4..567R. doi:10.1007/BF01048071. ISSN   1572-8889. S2CID   26217276.
  15. 1 2 3 4 De Villiers, P.S.; Hanrahan, S.A. (1991). "Sperm competition in the Namib Desert beetle, Onymacris unguicularis". Journal of Insect Physiology. 37 (1): 1–8. doi:10.1016/0022-1910(91)90012-o. ISSN   0022-1910.
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