Field of Science

Hydromantes: Salamanders in Different Places

There are times when biogeography is able to throw us some real puzzlers: organisms whose distribution seems to defy expectations. Among these mysteries, special mention must be made of the salamanders of the genus Hydromantes.

Gene's cave salamanders Hydromantes genei courting, copyright Salvatore Spano.


Hydromantes is a genus containing a dozen species from among the lungless salamanders of the family Plethodontidae. Plethodontids are the most diverse of the generally recognised families of salamanders, with over 450 known species found mostly in Central and South America. Hydromantes, however, is a geographically isolated genus in this family with its species found in two widely separated regions: California in western North America, and mainland Italy and Sardinia in Europe. Though some authors have advocated treating the species found on each continent as separate genera, both morphological and molecular studies have left little doubt that the group represents a discrete clade.

Distinctive features of Hydromantes compared to other plethodontids include feet with five, partially webbed toes and a weakly ossified, flattened skull (Wake 2013). Members of this genus capture prey with a projectile tongue which is the most extensive of any amphibian, extending up to 80% of the animal's total body length (Deban & Dicke 2004). There are some differences between North American and European species notable enough for the recognition of separate subgenera (there is something of a gigantic clusterfuck surrounding the names of said subgenera but the details are far too tedious to relate here). The three North American species of the subgenus Hydromantes have bluntly tipped tails that they use as a 'fifth leg' when navigating smooth and/or slippery surfaces, whereas the European species have unremarkable pointed tails. Historically, the North American Hydromantes species have been poorly known, being isolated to restricted ranges. Hydromantes shastae is found in limestone around Lake Shasta whereas H. brunus is found in a small area of mossy talus habitat along the Merced River in the foothills of the Sierra Nevada (Rovito 2010). The third species, H. platycephalus, is found at higher altitudes in the Sierra Nevada, well over 1000 m above sea level. Individuals found living on steep slopes are known to escape predators by tightly coiling their bodies and simply rolling down the slope (García-París & Deban 1995). A molecular analysis of H. platycephalus and H. brunus by Rovito (2010) identified the former species as derived from within the latter, and Rovito suggested that H. brunus may have originated in a remnant population from when H. platycephalus moved into lower altitudes during the Ice Age.

Mt Lyell salamander Hydromantes platycephalus, copyright Gary Nafis.


The seven or eight European species are mostly placed in the subgenus Speleomantes; a single species, Hydromantes genei, is divergent enough to be placed in its own subgenus Atylodes (though most recent studies have indicated that the European Hydromantes overall form a discrete clade). Hydromantes genei and three species of Speleomantes are found in caves on the island of Sardinia; the remaining Speleomantes species on mountains of mainland Italy. Molecular analysis suggests that H. genei became isolated on Sardinia about nine million years ago, with the ancestors of the Sardinian Speleomantes arriving later about 5.6 million years ago when the Mediterranean dried out during what is known as the Messinian Salinity Crisis (Carranza et al. 2008). The absence of any Hydromantes on neighbouring Corsica is something of a mystery, and it has been suggested that they may have been present there in the past before going extinct.

Extinction also seems the most likely explanation for Hydromantes' unusual distribution. The fossil record for the genus is minimal, and provides little information not already available from living species, but molecular dating attempts agree that the division between European and North American Hydromantes happened too recently to be related to the tectonic separation of the two continents. Such a scenario would also leave open the Hydromantes' absence in eastern North America. The description in 2005 of the Korean lungless salamander Karsenia koreana demonstrated the presence of plethodontids in eastern as well as far western Eurasia, and it seems possible that Hydromantes dispersed into Eurasia via the Bering Strait landbridge, becoming widespread across the continent before extinction reduced it to the isolated relicts it is today.

REFERENCES

Carranza, S., A. Romano, E. N. Arnold & G. Sotgiu. 2008. Biogeography and evolution of European cave salamanders, Hydromantes (Urodela: Plethodontidae), inferred from mtDNA sequences. Journal of Biogeography 35: 724–738.

Deban, S. M., & U. Dicke. 2004. Activation patterns of the tongue-projector muscle during feeding in the imperial cave salamander Hydromantes imperialis. Journal of Experimental Biology 207: 2071–2081.

García-París, M., & S. M. Deban. 1995. A novel antipredator mechanism in salamanders: rolling escape in Hydromantes platycephalus. Journal of Herpetology 29 (1): 149–151.

Rovito, S. M. 2010. Lineage divergence and speciation in the web-toed salamanders (Plethodontidae: Hydromantes) of the Sierra Nevada, California. Molecular Ecology 19: 4554–4571.

Wake, D. B. 2013. The enigmatic history of the European, Asian and American plethodontid salamanders. Amphibia-Reptilia 34: 323–336.

Leucicorus: FAKE EYES!

In an earlier post, I told you about the fishes known as brotulas. These are one of the most prominent groups of fish in the deep sea. They tend not to be attractive fish: their lack of outstanding dorsal and tail fins makes them look like something between an eel and a cod, and like many deep-sea fishes they look somewhat flabby and lumpish. There are numerous genera of brotulas out there; the individual in the photo below represents the genus Leucicorus.

Leucicorus atlanticus, from Okeanos Explorer.


Leucicorus belongs to the brotula family Ophidiidae, commonly known as the egg-laying brotulas though Leucicorus' own reproduction has (so far as I have found) not been directly observed. The feature that most immediately sets Leucicorus apart from other brotulas is the eyes: Leucicorus species have very large eyes but the actual lenses are rudimentary or absent (Cohen & Nielsen 1978). It almost looks like they grew bigger and bigger to cope with the low light of the deep sea before they just kind of gave up at some point.

Two species of Leucicorus are currently recognised, each known from separate parts of the world. Leucicorus lusciosus is found in the eastern Pacific, whereas L. atlanticus is known from around the Caribbean. The two species differ in meristic characters and proportions: for instance, L. lusciosus has more dorsal and anal fin rays, but fewer vertebrae and gill rakers, and has a deeper body (Nielsen & Møller 2007). Leucicorus has also been found in the vicinity of the Solomon Islands, but interestingly enough Nielsen & Møller (2007) identified the specimen found as L. atlanticus rather than L. lusciosus, despite the latter species' more proximate distribution. One wonders if perhaps a third species is involved, yet to be recognised.

REFERENCES

Cohen, D. M., & J. G. Nielsen. 1978. Guide to identification of genera of the fish order Ophidiiformes with a tentative classification of the order. NOAA Technical Report NMFS Circular 417.

Nielsen, J. G., & P. R. Møller. 2007. New and rare deep-sea ophidiiform fishes from the Solomon Sea caught by the Danish Galathea 3 Expedition. Steenstrupia 30 (1): 21–46.

Pontodrilus: Earthworms by Sea

Earthworms are primarily a terrestrial and freshwater group, sensitive to changes in the quality of their habitat. But there are some earthworm species that are tolerant of more saline environments. One such species is Pontodrilus litoralis, a widespread earthworm found in warm coastal habitats around the world, being recorded from such far-flung places as the Caribbean, the Mediterranean, Australia and Japan. The species is found in sandy or muddy soils in coastal habitats, including beaches, estuaries and around the roots of mangroves, and is able to tolerate salinities from 5 to 25 parts per thousand—that is, from fresh water to close to the standard salinity of sea water (Blakemore 2007).

Pontodrilus litoralis in its natural habitat, from here.


Pontodrilus litoralis is one of five species currently recognised in the genus Pontodrilus, though many more have been recognised in the past (Blakemore, 2007, listed eighteen species and subspecies now regarded as synonyms of P. litoralis). Characteristic features of the genus include an absence of nephridia in the anterior segments, and tubular prostrate organs opening to male pores on the eighteenth segment. The other Pontodrilus species have more restricted, non-coastal ranges; one, P. lacustris, is found free-swimming in Lake Wakatipu in New Zealand, whereas the other three are found in terrestrial habitats in Sri Lanka, China and Tasmania.

How P. litoralis achieved its wide distribution is currently unknown. If it arose prior to the separation of the land-masses on which it is now found then it would have had to have survived almost unchanged for hundreds of millions of years, which seems on the face of it unlikely. It seems more credible that it has dispersed more recently from its original point of origin, but while its green, spindle-shaped cocoons are often found attached to floating vegetation we do not know how long they can stand immersion in full-strength salt water. Nor do we know just where P. litoralis originated. It was first described in 1855 from the French Riviera so many authors have assumed the species is Mediterranean in origin. However, the distribution of related species seems to make an Indo-Pacific origin more likely. It may well be that P. litoralis was spread from its original home by humans, carried with rocks and sand used for ballast.

REFERENCE

Blakemore, R. J. 2007. Origin and means of dispersal of cosmopolitans Pontodrilus litoralis (Oligochaeta: Megascolecidae). European Journal of Soil Biology 43: S3—S8.

The Asteiids: Overlooked Flies

Flies are incredibly diverse, but they may be one of the least appreciated of the major insect groups. There are many significant fly lineages whose presence goes all but unnoticed by a small number of afficionados.

Asteia amoena, copyright Mick E. Talbot.


One of the largest clades of flies is the Schizophora, including many such familiar animals as house flies, blowflies, and fruit flies (of both varieties). The most distinctive feature marking this lineage is the ptilinal fold, a groove that runs around the face of the flies along the inner margin of the eyes and across above the antennal insertions. This groove marks the position of a large fold of soft cuticle, the ptilinum, that is used by the fly when it emerges from the hardened case, the puparium, in which it metamorphoses from a larva. The ptilinum expands like a bellows as the fly pumps its head full of liquid until the pressure causes the cap of the puparium to pop open. After this, the excess cuticle is folded away inside the head, never to emerge again, but the mark of its presence remains.

House fly Musca domestica emerging from its puparium, showing the inflated ptilinum. Copyright Alex Wild.


Schizophorans have commonly been divided between two main groups, referred to as the calyptrates and acalyptrates. The basis of this division is the presence (calyptrates) or absence (acalyptrates) of the calypters, lobes at the base of the wings that help in controlling flight. This is not an entirely phylogenetic system: the calyptrates are a single clade but the acalyptrates are not. The most familiar flies belong to the calyptrates (which include house flies and blowflies) despite the fact that acalyptrate flies are considerably more diverse. This is in part because many acalyptrates are very small flies, easily overlooked by the casual observer.

The Asteiidae are one such group of overlooked flies. They are found pretty much world-wide and can be very abundant in some habitats. Nevertheless, they are apparently not common in collections: their soft-bodiedness makes them tricky to preserve, and Grimaldi (2009) noted that tropical species living on rolled leaves of herbs such as bananas and gingers were reluctant fliers and so unlikely to be collected by passive intercept traps. Noteworthy features of asteiids compared to similar flies include a reduced wing venation, and an antennal arista bearing alternating rays (Friedberg 2009). In two genera, Polyarista and Anarista, the arista is reduced or lacking, replaced by a collection of long setae arising from the first flagellomere (Papp 2013).

Diagnostic features of Asteia amoena, from Walker's Insecta Britannica Diptera.


Because of their low collection rates, the natural history of asteiids is poorly known. As already noted, a number of species are found in association with vegetation; others have been raised from fungi. Grimaldi (2009) described Asteia species running "over the surface of a leaf in all directions with uniform effort, including backwards and sideways, which gives them an appearance of floating over the surface". Some species have mating rituals involving trophallaxis, in which a male attempts to entice a female by offering her a regurgitated droplet. If his offering meets her standards, they will collaborate to produce a new generation that will carry on in the same obscurity as the last.

REFERENCES

Freidberg, A. 2009. Asteiidae (asteiid flies). In: Brown, B. V., A. Borkent, J. M. Cumming, D. M. Wood, N. E. Woodley & M. A. Zumbado. Manual of Central American Diptera pp. 1093–1096. NRC Research Press: Ottawa.

Grimaldi, D. A. 2009. The Asteioinea of Fiji (Insecta: Diptera: Periscelididae, Asteiidae, Xenasteiidae). American Museum Novitates 3671: 59 pp.

Papp, L. 2013. A new genus of Asteiidae with a key to the Old World genera (Diptera). Annales Historico-Naturales Musei Nationalis Hungarici 105: 199–205.

Scheloribates

Over the years, I've put up several posts about the diversity of oribatid mites. It's time for another one.

Scheloribates laevigatus, copyright R. Penttinen.


One of the largest genera of oribatids out there is the genus Scheloribates, for which well over 200 species have been described. Their distribution is pretty much worldwide; they are found in a range of microhabitats, such as in leaf litter, in pastures or marshes, or among rocks. Distinguishing features of the genus from other oribatids include well-developed, immobile pteromorphs, tridactylous (three-clawed) legs, and a notogaster with ten pairs of setae and three pairs of sacculi (little sac-shaped glandular openings) (Ermilov & Anichkin 2014).

Considering their abundance in soil habitats, Scheloribates probably have a significant role to play in decomposition and nutrient cycling. Studies on the diet of one of the better-known species, S. laevigatus, have found that it will eat almost any type of vegetable or fungal matter, though its preferred diet is microscopic algae (Hubert et al. 1999). Indeed, they are most abundant in damper habitats that would provide good conditions for the growth of such algae.

Scheloribates species may impact on human lives in other ways too. They are an intermediate host for the larvae of anoplocephalid tapeworms that infect livestock when the mites are accidentally ingested during grazing. S. laevigatus is a known host for at least eight tapeworm species in North America. Rates of tapeworm infestation in Scheloribates can be quite high; over 60% of the individuals of one species at a particular locality in Australia were infected (Lee & Pajak 1990). Scheloribates species are also noteworthy as a likely source of the toxic alkaloids found in the skin of arrow-poison frogs. The alkaloids are likely to be synthesised by the mites (as suggested by their presence in adults but not in juveniles, despite no known difference in diet between the two life stages) and then sequestered by the frogs after they eat the mites (Saporito et al. 2011). And if they eat enough mites, they end up becoming dangerous even to something the size of a human.

REFERENCES

Ermilov, S. G., & A. E. Anichkin. 2014. A new species of Scheloribates (Scheloribates) from Vietnam, with notes on taxonomic status of some taxa in Scheloribatidae (Acari, Oribatida). International Journal of Acarology 40 (1): 109–116.

Robert, J., V. Šostr & J. Smrž. 1999. Feeding of the oribatid mite Scheloribates laevigatus (Acari: Oribatida) in laboratory experiments. Pedobiologia 43: 328–339.

Lee, D. C., & G. A. Pajak. 1990. Scheloribates Berlese and Megascheloribates gen. nov. from southeastern Australia, with comments on Scheloribatidae (Acarida: Cryptostigmata: Oriopodoidea). Invertebrate Taxonomy 4: 205–246.

Saporito, R. A., R. A. Norton, N. R. Andriamaharavo, H. M. Garraffo & T. F. Spande. 2011. Alkaloids in the mite Scheloribates laevigatus: further alkaloids common to oribatid mites and poison frogs. Journal of Chemical Ecology 37: 213–218.

A Parasitic Eel?

The following post was inspired by an e-mail that I was sent recently by Sebastian Marquez. He told me about a friend of his catching a trevally when fishing, then cutting it open to find a snake eel inside the body cavity (but outside the stomach), wrapped around the trevally's internal organs. According to Sebastian, the lead suspicion for what had happened was that the eel had somehow burst out of the trevally's stomach before it was caught, and he wanted to know if I'd ever heard of anything similar. I didn't have an explanation for him, but his story did get me thinking about the snub-nosed eel.

Snub-nosed eel Simenchelys parasitica, from Jordan (1907).


The snub-nose eel Simenchelys parasitica is a small deep-sea eel, about 20 to 35 centimetres long. It has attracted note by being found a number of times burrowed into the body cavity of larger fishes with perhaps the most renowned case being two juveniles that were found nested inside the heart of a mako shark. This lead to the description of S. parasitica as an endoparasite (hence the species name). However, acceptance of this tag has been far from universal. The snub-nosed eel has been caught free-living more regularly than it has been found in other fish and because of its deep-sea habitat it has never been observed in life. An alternative suggestion has been that Simenchelys is normally a scavenger; because many of its recorded 'hosts' have been collected through non-targeted methods such as trawls, it is not impossible that the snub-nosed eels may have burrowed into their body cavity after they were already deceased.

It was with this conundrum in mind that the cranial anatomy of the snub-nosed eel was described by Eagderi et al. (2016). The jaws of Simenchelys are relatively short and muscular (hence its 'snub nose'). It also has teeth arranged in such a way that they form an even cutting edge (in contrast to the more spaced and uneven teeth of other eels). Eadgeri et al. came to the conclusion that the snub-nosed eel probably feeds by biting out plugs of flesh, in a similar manner to a cookie-cutter shark. Simenchelys also resembles a cookie-cutter in having large, fleshy lips that are probably used to form a seal between jaws and food source. A large hyoid ('tongue') apparatus probably works to provide suction to maintain the seal. The snub-nosed eel may also rotate while biting, a behaviour known from both cookie-cutters and other eels.

So is Simenchelys a parasite? It is probably not a habitual endoparasite, lacking as it does any clear adaptations to the endoparasitic lifestyle. There are fish that could be described as ectoparasites, in that they habitually feed on live animals larger than themselves in a manner that does not normally lead to the host's death. The cookie-cutter is one such fish; another is the candiru Vandellia cirrhosa, a small freshwater catfish from the Amazon basin that feeds on blood from the gills of other fish. It is possible that the snub-nosed eel could have a similar lifestyle to one of these. However, recorded evidence of its habits is even more consistent with scavengers such as hagfish and the candiru-açu Cetopsis candiru (another South American catfish) that tear flesh from the submerged bodies of dead animals, and may often burrow their way into the corpse's body cavity as they do so.

Of course, the two modes of feeding are not mutually exclusive. The only difference between predator and parasite in this scenario is whether the attacked animal is alive or dead, and the thing about flesh-feeders is that they're not always picky. A habitual scavenger may easily choose the opportunity to take a nibble from a still-living host, especially is said host is in some way incapacited (as a result of being swept up by a trawl, for instance). The snub-nosed eel may not be a habitual parasite, but it may be an opportunistic one.

REFERENCE

Eagderi, S., J. Christiaens, M. Boone, P. Jacobs & D. Adriaens. 2016. Functional morphology of the feeding apparatus in Simenchelys parasitica (Simenchelyinae: Synaphobranchidae), an alleged parasitic eel. Copeia 104 (2): 421–439.

Of Shrimp Plants and Bear's Breeches

For today's semi-random post, I drew the plant subfamily Acanthoideae. As recognised by Scotland & Vollesen (2000), the Acanthoideae is the largest of the subfamilies of the Acanthaceae by a considerable margin, including about 95% of the family's 2500+ species. Though perhaps not hugely familiar to readers in more temperate climes, the Acanthoideae are one of the dominant groups of herbs and shrubs in tropical parts of the world.

Golden shrimp plant Pachystachys lutea, copyright Dryas.


The Acanthoideae have been recognised as a morphological group since the late 1800s and their integrity has been confirmed by more recent molecular studies. They are distinguished from related plants (within the Lamiales, the order that also includes such plants as the mints and snapdragons) by having capsular fruits that dehisce explosively when mature to scatter their seeds. The seeds are attached within the capsule by hook-shaped stalks called retinacula that presumably play a role in determining how the seeds are released. A classification of Acanthaceae published in 1965 by Bremekamp restricted the family to species with explosive fruits and retinacula, dividing them between two subfamilies, the Acanthoideae and Ruellioideae, based on the absence or presence, respectively, of cystoliths. These are outgrowths of the epidermal cell walls that are impregnated with calcium carbonate. They are visible in the stems and leaves, at least in dried specimens, as hard white streaks. As phylogenetic studies have supported division of Acanthoideae in the broad sense between a cystolith-possessing and a cystolith-lacking clade, the decision whether to recognise 'Ruellioideae' as a separate subfamily comes down to a ranking choice only. At lower levels, the classification of Acanthoideae is less straightforward. Over two hundred genera of Acanthoideae are recognised but just three of those—Justicia, Strobilanthes and Ruellia—account for about half the total number of species. Each of these mega-genera is morphologically diverse and likely to be para- or polyphyletic with regard to related taxa, raising the distinct likelihood of future revisions.

Spiny bear's breeches Acanthus spinosus, copyright Magnus Manske.

Economically, few of the Acanthoideae are of great significance except for a number of species being grown ornamentally. One such species is Acanthus mollis, which goes by the vernacular name of 'bear's breeches' (why, I have absolutely no idea). Acanthus was a popular decorative motif in classical Greece and forms the basis for the design of Corinthian columns. Its use as an ornamental has lead to it becoming regarded as an invasive weed in some regions, largely because this is one of those garden plants that Just Will Not Die, spreading easily from seeds and tubers. We've got some in a pot outside that is currently flourishing despite having been burnt down to a nub by the searing Perth summer sun, metaphorically shouting its defiance at an uncaring world.

REFERENCE

Scotland, R. W., & K. Vollesen. 2000. Classification of Acanthaceae. Kew Bulletin 55 (3): 513–589.