Boreonectes: Diversity Hidden Underwater

The beetle in the photo below (copyright Joakim Pansar) may or may not be Boreonectes griseostriatus. This small diving beetle, a few millimetres in length, has been regarded in the past as widespread with a distribution spanning the Holarctic region. However, in recent years it has become apparent that this single widespread species may actually be a number of more localised species in a skin.

This possibility had been considered for a while. In 1890, a Norwegian entomologist recognised distinct montane and coastal species, noting a tendency for the former to the neatly striped whereas the latter was more blotchy. Later authors, however, rejected this distinction. In 1953, a Russian author expressed the view that B. griseostriatus "varies markedly in many characters; all attempts to establish subspecies and varieties are unjustified, because almost all varieties are connected by transitions" (Angus et al. 2015). In its overall appearance, B. griseostriatus is a a fairly undistinguished small diving beetle. Most of the body surface is densely and finely punctate both dorsally and ventrally, and it lacks some of the modifications found in other diving beetles such as lateral grooves on the pronotum or sucker-hairs on the male tarsi (Angus 2010). This latter feature, offhand, is an adaptation that assists males who have it in clinging to the backs of females during mating. Their functionality would be much reduced in punctate species such as B. griseostriatus because the the uneven surface of the female would prevent the suckers from getting a grip, and phylogenetic studies suggest that their absence in Boreonectes may represent a secondary loss. I don't know if the Boreonectes males do anything to make up for their absence; maybe they just have to grip tighter.

Variation in parameres from male genitalia of the Boreonectes griseostriatus group, from Dutton & Angas (2007).

The complicated nature of B. griseostriatus' identity became really apparent in the 2000s when karyotypic studies on European specimens identified several different chromosomal races, distinct not only in chromosome topography but also in number, that may represent distinct species. The original B. griseostriatus of lowland Sweden possesses a karyotype of thirty pairs of autosomal chromosomes plus the X sex chromosome (sex is determined in this genus by an X0/XX system where males have one copy of the X chromosome and females have two, with no Y chromosome). Boreonectes multilineatus, the Scandinavian montane species, has 28 autosomal pairs. Other species have fewer. It appears likely that a similar thing is happening in Boreonectes to the situation I described in an earlier post for the bat genus Rhogeessa where mutations lead to chromosomes becoming fused or split. It is notable in this regard that Angus (2010) found several specimens of B. ibericus from Morocco that were heterozygous for a chromosomal fusion, so that a single fused chromosome was paired meiotically with distinct chromosomes 1 and 24.

Externally, however, these genetically distinct species remain all but indistinguishable. There may be a tendency for one species to be larger than another, or towards slightly different genital morphologies, but these differences are not distinct enough or consistent enough to provide a reliable guide to identification. Which, if you don't have access to fresh specimens allowing a karyotype spread, is a problem.

REFERENCES

Angus, R. B. 2010. Boreonectes gen. n., a new genus for the Stictotarsus griseostriatus (De Geer) group of sibling species (Coleoptera: Dytiscidae), with additional karyosystematic data on the group. Comparative Cytogenetics 4 (2): 123–131.

Angus, R. B., E. M. Angus, F. Jia, Z.-N. Chen & Y. Zhang. 2015. Further karyosystematic studies of the Boreonectes griseostriatus (De Geer) group of sibling species (Coleoptera, Dytiscidae)—characterisation of B. emmerichi (Falkenström, 1936) and additional European data. Comparative Cytogenetics 9 (1): 133–144.

Rhampsinitus Re-Redux

I've featured the African harvestman genus Rhampsinitus on this site twice before, but I'm going to have another dive into it today. There's still more I can say about this remarkable genus.

Male Rhampsinitus, possibly R. leighi, copyright Peter Vos. The individual ahead of the male is another Rhampsinitus, probably a female; there's also a short-legged harvestmen beneath the male.

There's more I could say about African phalangiids in general, in fact. There's never been a proper phylogenetic study of the long-legged harvestman family Phalangiidae, so we can't speak with confidence about the relationships between the African members of this group and their relatives elsewhere, but it would not be unexpected if the sub-Saharan phalangiids form an evolutionarily coherent group. Many of the family's most striking exemplars are to be found on the African continent: Cristina with their thick, spiky front legs; sleek, flattened Odontobunus, Guruia with their chelicerae like a pair of jar tongs held in a boxing glove. Rhampsinitus' current position as the best-known African harvestman genus is probably due not only to its diversity but also to its more temperate centre of distribution placing it closer to researchers than these other more equatorial genera.

As mentioned in my first post on the genus, there are currently over forty recognised species of Rhampsinitus. As alluded to in my second post, that number might be expected to change in the future. No reliable identification key is currently available for Rhampsinitus, nor is the information available for many species that would allow such a key to be written. A key to the southern African species was provided by Kauri (1961) but, while I did find this key invaluable when I conducted my own tentative foray into rhampsinitology, I couldn't recommend it to a novice. Kauri was simply unaware of the extreme variation that can be found among male Rhampsinitus belonging to a single species. There are only a handful of species for which both major and minor males have been described and, as I explained previously, minor males may not be identifiable to species without examining genitalia.

Probably a male Rhampsinitus vittatus, copyright Nanna.

This, obviously, is a problem for the handful of species that have been described from what appear to be minor males. Some of these, such as Rhampsinitus fissidens and R. hewittius, are probably doomed to remain mysteries at least until someone redescribes their types. Others may be more recognisable. Rhampsinitus qachasneki is an unusually spiny species described from the mountains of Lesotho, with some of the denticles along the front edge of the body multi-pointed. These distinctive denticles, like repurposed muntjak antlers, might reasonably be expected to be present in any major males of this species, if they exist. The challenge may be even greater for the handle of species that have been described from females. Nevertheless, the known female of R. maculatus, another Lesotho mountain species, has a distinctive spotted colour pattern and thick, remarkably hairy pedipalps that might be expected to show their analogues in the unknown males (again, if they exist: we're kind of glossing over the point that some harvestmen species are known to be parthenogenetic, because harvestmen systematics is so heavily predicated on male genital morphology that the idea of an all-female harvestman species is a trifle intimidating*).

*I assume that this is precisely what Zappa had in mind when he got to the end of Thing-Fish.

Then, of course, there's the persistent question of Rhampsinitus lalandei. This was the first species included in Rhampsinitus in 1879 and as such represents the type or sine qua non of the genus. As was not unusual for the time, its author Eugene Simon was a bit vague about where his original specimen(s) had come from, giving the locality as simply 'Cafrerie'. Cafrerie, rendered in English as Kaffraria or Kaffirland, is a geographical designation that has fallen out of favour these days for reasons I would hope to be obvious, but was commonly used during the 1800s to refer to the area around the eastern coast of modern South Africa, particularly around Port Elizabeth. Unfortunately, Simon's description of R. lalandei is not definitive by modern standards—most of the features described could apply to any number of Rhampsinitus species—and Simon's original specimen appears to have been lost. This presents a problem for any who would suggest that this large genus should be divided up as it might become uncertain which division represents the true Rhampsinitus. Starega (2009) suggested that R. lalandei might be the same as R. crassus, a species definitely found in the Port Elizabeth region. However, it should be noted that Simon described R. lalandei as being irregularly armed with denticles dorsally. In the majority of Rhampsinitus species, the denticles on the opisthosoma form very neat transverse rows, but in others they are a bit more messily placed. Rhampsinitus crassus is one of the former species but the description of R. lalandei suggests it may have been one of the latter. So if anyone's looking at harvestmen from around that area, keep your eyes open.

REFERENCES

Kauri, H. 1961. Opiliones. In: Hanström, B., P. Brinck & G. Rudebeck (eds) South African Animal Life: Results of the Lund University Expedition in 1950–1951 vol. 8 pp. 9–197. Almqvist & Wiksells Boktryckeri Ab: Uppsala.

Staręga, W. 2009. Some southern African species of the genus Rhampsinitus Simon (Opiliones: Phalangiidae). Zootaxa 1981: 43-56.

Gar!

Apart from the mostly terrestrial radiation of the tetrapods, the vast majority of today's bony-skeletoned fishes belong to the clade of the teleosts. Way back in the Triassic, the ancestors of this clade went through a process of modification of the jaw skeleton to make it more mobile and adroit in catching small prey, and this together with a tendency towards the lightening of the skeleton and the body's covering of bony scales marked the beginnings of what is now well over 25,000 species. But while they may pale in comparison to this phylogenetic behemoth, there are still non-teleost (and non-tetrapod) bony fishes out there if you look in the right places.

Alligator gar Atractosteus spatula, copyright Stan Shebs.

Most studies on fish phylogeny in the last decade or so have agreed that the living sister group of the teleosts is the Holostei, a clade including only eight living species. One of these is the bowfin Amia calva, an elongate, cylindrical-bodied fish with a long dorsal fin running most of the length of its back. The other seven sepecies belong to the gar genera Lepisosteus and Atractosteus, forming the family Lepisosteidae*. Gars are also elongate like the bowfin, albeit without the long dorsal fin, and have elongate, flattened jaws (tending to be narrower in Lepisosteus than Atractosteus). The tail fin in both bowfins and gars is rounded, not forked. Living holosteans are restricted to North America (including Central America and the Caribbean)** but fossils show them to have been more widespread in the past. They are mostly found in fresh water; some species may tolerate brackish or even salt water but they do not stay there permanently. Bowfins and gars are able to breathe air directly as well as through their gills (indeed, gars are reported to drown if prevented from coming to the surface for several hours) and can therefore survive in more stagnant waters than many other fish. The bowfin averages about half a metre in length; the smaller gar species are also in this range. The largest species, the alligator gar Atractosteus spatula, reaches at least close to three metres. Larger sizes (up to six metres or more!) have been reported for this species but appear likely to be errors or exaggerations; as noted by one authority, "All fishes shrink under the tape measure" (Grande 2010).

*The incorrect alternative spellings Lepidosteus and Lepidosteidae (as well as Lepidosteiformes) have often appeared in the past.

**References to a supposed Chinese gar have long persisted in the literature, based on a description of a "Lepidosteus sinensis" from 1873. This description was based on a drawing rather than an actual specimen, and it is now thought that the fish depicted was probably a belonid (an unrelated long-jawed teleost) rather than a gar.

Bowfin Amia calva sharing a tank with largemouth basses, copyright Bemep.

Modern holosteans are ambush predators, feeding on other fish or aquatic invertebrates. In general, larger species tend to prefer a diet of fish whereas smaller species focus on invertebrates, but all appear to be happy to take whatever they may, whether alive or dead. The alligator gar has been claimed to attack humans but no such attacks seem to have been authenticated; Grande (2010) stated that "swimmers probably have very little to fear from them". As well as their sheer size, this accusation may have been fueled by the alligator gar's apparent tendency in some areas to hang around wharves scavenging garbage. Neither bowfins nor gars are of high importance as food fish for humans though their size and strength gain them some attraction as sport fish*. An industry for the production and marketing of bowfin roe has arisen in recent years following the decline in availability of caviar from Russian sturgeon species; no such market exists for gar eggs, which are toxic to humans. Historically, the thick armour of scales covering the skin of gars was used by Caribbean Indians for making breastplates while individual scales could be used for arrowheads.

*Grande (2010) quotes Eberle (1990) to the effect that gars have "a poor reputation among anglers, who believe [they] would have been better suited as land dwellers had they been able to stand their own reflections in the water".

Shortnose gar Lepisosteus platostomus, copyright Rufus46.

Reproductive habits are best known in the bowfin and the longnose gar Lepisosteus osseus. Male bowfins construct a nest in mats of fibrous vegetation, into which they attempt to induce passing females to spawn. Guarding of the eggs after spawning is the duty of the male alone; the female moves on, perhaps to spawn in another male's nest (the male himself may also court more females). The eggs are adhesive and take about a week and a half to hatch. Following hatching, the fry attach themselves to nearby vegetation by an adhesive organ at the end of their snout and spend some time being nourished by the remains of their yolk sac beofre beginning to forage. The male will continue to guard his fry until they reach about a month of age. Reproduction in longnose gars is similar in the production of adhesive eggs and the early sessile, snout-attached period of the life cycle, but differs in that there is no nest construction or parental care. There is a record of gar eggs being deposited in the nest of a smallmouth bass and the fry being subsequently raised cuckoo-wise by the nest's owner, but it is unclear whether this reflects any deliberate action by the parental gars or simply a fortuitous accident. Gars take up to six years to reach maturity, with males maturing a couple of years earlier than females.

Semionotus bergeri, copyright Ghedoghedo.

The fossil record of holosteans extends back to their divergence from the teleosts in the early to mid-Triassic, with the bowfin and gar lineages apparently diverging from each other not long afterwards. As noted above, both lineages include a diversity of extinct members that somewhat belies their current paucity, such as Macrosemiidae and Semionotidae in the gar lineage, and Ophiopsidae, Ionoscopidae, Caturidae and Sinamiidae in the bowfin lineage. The greatest diversity in both lineages was during the Jurassic and Cretaceous (Brito & Alvarado-Ortega 2013; Cavin 2010) and the two modern gar genera appear to have been separate lineages at least since the late Cretaceous (Grande 2010). Holosteans were also more ecologically diverse in the past. Masillosteus, a gar genus from the Eocene of Europe and North America, had a shorter jaw and flatter teeth than modern jaws, and probably fed on harder-shelled animals such as molluscs and/or crustaceans. The Mesozoic 'Semionotidae', suggested by Cavin (2010) to be paraphyletic to the gars, were even more diverse, including marine as well as freshwater forms, and forms that may have plant feeders or detritivores. In the early Jurassic of eastern North America, one group of semionotids underwent a lake-based radiation that has been compared to the modern cichlids of African rift lakes. Adequately covering the diversity of fossil holosteans would make this post considerably longer than it already is; perhaps one day, I'll get to it.

REFERENCES

Brito, P. M. & J. Alvarado-Ortega. 2013. Cipatlichthys scutatus, gen. nov., sp. nov. a new halecomorph (Neopterygii, Holostei) from the Lower Cretaceous Tlayua Formation of Mexico. PLoS One 8 (9): e73551.

Cavin, L. 2010. Diversity of Mesozoic semionotiform fishes and the origin of gars (Lepisosteidae). Naturwissenschaften 97: 1035–1040.

Grande, L. 2010. An empirical synthetic pattern study of gars (Lepisosteiformes) and closely related species, based mostly on skeletal anatomy. The resurrection of Holostei. Copeia 2010 (2A): iii–x, 1–871.