The Vespertilionidae, vesper bats, are a cosmopolitan and speciose family of bats. Members of the family have a fairly generalised external appearance, but a distinctly derived wing structure with a greatly reduced ulna and only two bony phalanges present in the third finger (Miller 1907).
The Vespertilioninae are an assemblage of bats found worldwide. Most members of the group are fairly generalised, with relatively few characters separating the tribes. Members of the Plecotini (the long-eared bats) have the very large ears connected by a fold of skin at the base and touching each other when erect. The Vespertilionini have a more or less shortened face, with two pairs of upper and lower incisors and one or two pairs of upper and lower premolars. The Nycticeiini have only one pair each of upper and lower incisors. Species of Lasiurus, the hairy-tailed bats, have a greatly shortened face with only a single pair of upper and lower incisors and a broad rostrum.
The nominotypical subgenus of Rhogeessa contains the little yellow bats of Central and northern South America. Several species in this group are not distinguishable from external characteristics, and can only be identified from their karyotypes.
Little yellow bats
Published 16 August 2011
The Neotropical members of the genus Rhogeessa go by the incredibly imaginative vernacular name of ‘little yellow bats’. On the face of it, this would seem to sum up the salient features of these animals pretty succinctly: they’re small, they’re yellow, and they’re bats. Eleven species of Rhogeessa were recognised by Baird et al. (2008a), found from northern Mexico to southern Brazil. The species of Rhogeessa are rather difficult to distinguish from each other; in particular, the six species that referred by Baird et al. (2008a) to the ‘Rhogeessa tumida complex’ are all but indistinguishable. Nevertheless, recent authors have regarded them as good species, and it is because of the reasons why this is that the genus has attracted the most interest.
The only really reliable way to distinguish the species of the R. tumida complex is to take a look at their chromosomes. Despite their external similarity, the species have different chromosome numbers and arrangements from each other. This forms an interesting contrast to other bat genera, which may have more morphological variability but little chromosome variation. Comparison between Rhogeessa chromosomes has lead to the suggestion that the various species may have diverged as a result of a process called Robertsonian translocation.
To explain Robertsonian translocation, I have to indulge in a bit of background terminology of chromosomes (skip this if you know all this stuff). Think of the classic picture of an X-shaped chromosome (this is actually a doubled chromosome that develops during cell division: two copies, called chromatids, have been produced of the chromosome that will be separated when the cell divides). The point where the two chromatids are joined is a region of the chromosome called the centromere: it provides an attachment point for the spindle fibres that will draw each individual chromatid apart. The centromere is not always positioned at the midpoint of the chromosome: those chromosomes in which it is are called metacentric, while other acrocentric chromosomes have the centromere close to one end so the conjoined chromatids look closer to V-shaped than X-shaped.
Translocation is a process where a piece of genetic material breaks off one chromosome and becomes attached to another. Robertsonian translocation is a particular type of translocation where two acrocentric chromosomes, by breaking at the centromeres, effectively become fused to form a single metacentric chromosome (as shown in the diagram below from here):
Robertsonian translocation has been observed in many species; it even happens occasionally in humans. Where it becomes interesting for evolutionary studies is that the resulting metacentric chromosome continues to function in the same manner as the original acrocentric chromosomes, with little or no negative effects (the short bit from each acrocentric chromosome that is lost rarely contains any functioning genes). The individual carrying the fused chromosome even remains fertile, because when meiosis occurs in any individual with both the fused and unfused chromosomes, the two unfused chromosomes will each line up with their matching arm on the fused chromosome. However, imagine a situation where one individual in a population experiences a Robertsonian translocation between two chromosomes (call them 1 and 2), but another individual has a translocation between one of those chromosomes and another chromosome (say, 2 and 3). The individual that carries chromosomes 1-2 and 3 will produce fertile offspring if mating with an unfused individual, as will that carrying 1 and 2-3. However, if the 1-2 individual mates with the 2-3, their offspring will carry both fused chromosomes. Because these chromosomes and the unfused 1 and 3 cannot easily match up in a way that allows them to be separated effectively during meiosis, the hybrid offspring will have significantly reduced fertility. This has been practically shown to be the case between Robertsonian races of mice (Capanna et al. 1977). If the two fused chromosomes each become more predominant in a population than the original unfused chromosomes (either by drift or hitchhiking), then gene flow will be slowed or stopped between individuals carrying one or the other. Hey presto, speciation!
Speciation as a result of Robertsonian translocation also provides a counter-example to those who, when objecting to the taxonomic recognition of ‘cryptic’ species, raise the Biological Species Concept to defend their viewpoint. Contrary to popular assumption, there is no essential correlation between speciation and morphological divergence. Even under the Biological Species Concept, two populations may be good species (i.e. non-interfertile) and yet morphologically indistinguishable.
Anyway, I have a vague memory that somewhere along the line I was talking about bats. The known karyotype numbers for Rhogeessa vary from 30 (in three species: R. alleni, R. gracilis and R. io) to 52 (in a specimen from Suriname that Baker et al. 1985 assigned to R. tumida but which almost certainly represents an undescribed species). The phylogeny for the genus that was recovered by Baird et al. (2008a, b) could be consistent with both Robertsonian fusions and fissions taking place during the genus’ history. In an attempt to test whether the different karyotypes truly function as isolating mechanisms (and hence whether the chromosomal ‘species’ are actually species), Baird et al. (2008b) could only find genetic indicators of possible recent hybridisation between the two apparently least divergent species, R. tumida (34 chromosomes) and R. aeneus (32 chromosomes); all other species maintained reciprocal monophyly in each of the three gene types (mitochondrial, Y-chromosome and somatic chromosome) tested. Baker et al. (1985) referred to another 32-chromosome karyotype (’32N’) that differed from R. aeneus (assuming, on the basis of geography, that R. aeneus corresponds to Baker et al.‘s ’32B’) in terms of exactly which chromosomes had been fused and so would be reproductively incompatible with R. aeneus. However, this 32N form appears to be assigned by Roots & Baker (2007) to R. io, otherwise with 30 chromosomes. As 30-chromosome R. io and the 32N form differ only in a single pair fusion in the former (Baker et al. 1985), they would probably remain interfertile by the principles described earlier. In contrast, despite their apparent difference in chromosome number of only two, R. tumida and R. aeneus actually differ in five chromosome fusions (three on one side, two on the other), meaning their interfertility should be considerably lower.
And if you’ve gotten this far and you’re still not sick of bats, Darren Naish covered Rhogeessa and its relatives as part of his mammoth series on vesper bats earlier this year.
Systematics of Vespertilionidae
Characters (from Miller 1907): Humerus with trochiter very noticeably larger than trochin and projecting distinctly beyond head, its surface of articulation on scapula decidedly more than half as large as glenoid fossa, distinctly concave and sharply outlined, epitrochlea obsolete, capitellum scarcely out of line with shaft; ulna usually fused with radius at head, shaft reduced to a scarcely ossified fibrous strand; second finger with fully developed metacarpal and one small bony phalanx; third finger with three phalanges, of which the distal is cartilaginous throughout except at extreme base, where distinct joint is formed with middle phalanx ; shoulder girdle strictly normal in its general structure, the seventh cervical vertebra free; presternum small, with forward-projecting, variously developed median lobe, mesosternum flat and scarcely keeled, usually slender; foot normal; fibula thread-like, complete or with upper extremity cartilaginous, extending to head of tibia; pelvis normal, boundaries of sacral vertebrae distinct, ischia widely separated posteriorly, symphysis pubis in males; lumbar vertebrae free; skull without postorbital processes; premaxillaries without palatal branches, palate widely emarginate anteriorly; palate abruptly narrowed behind toothrows, the sides of its posterior extension parallel or nearly so; teeth usually normal, though in a few genera showing a tendency to reduction of cusps; ears usually though not invariably separate, anterior border with distinct basal lobe; tragus usually well developed, simple; muzzle without distinct leaf-like outgrowths; tail well developed, extending to edge of wide interfemoral membrane.
<==Vespertilionidae (see below for synonymy) |--+--Eudiscopus denticulusFS15 | `--CistugoMJ11 | |--C. lesueuriBP87 | `--C. seabraeFS15 `--+--‘Rhogeessa’ gracilisFS15 `--+--+--‘Rhogeessa’ hussoniFS15 | `--‘Rhogeessa’ io Thomas 1903FS15, C57 `--+--+--ScotophilusFS15 | `--+--‘Rhogeessa’ genowaysiFS15 | `--Baeodon Miller 1906 [=Baedon (l. c.)]RB07 | `--*B. alleni (Thomas 1892)RB07 [=Rhogeessa (*Baeodon) alleniFS15, RB07] `--+--+--MyotisFS15 | `--+--KerivoulinaeFS15 | `--+--MurininaeFS15 | `--HarpiolaFS15 | |--H. griseaFS15 | `--H. isodonFS15 `--+--+--Idionycteris phyllotisFS15 | `--Nycticeius Rafinesque 1819FS15, M07 (see below for synonymy) | |--*N. humeralis (Rafinesque 1818)M07, B75 [=Vespertilio humeralisB75] | |--N. balstoniIT07 | |--N. cubanusM07 | |--N. greyiiIT07 | |--N. rueppelliiIT07 | |--N. sanborniIT07 | `--N. schlieffeni [=Scoteinus schlieffeni]B78 `--+--VespertilioniniFS15 `--+--+--LasiurusFS15 | `--Euderma Allen 1892FS15, M07 [incl. Histiotus Allen 1891 non Gervais 1856M07] | `--*E. maculatum [=Histiotus maculatus]M07 `--+--+--PlecotusFS15 | `--+--Otonycteris Peters 1859FS15, M07 | | |--*O. hemprichiiM07 | | `--O. petersiM07 | `--Corynorhinus Allen 1865FS15, M07 (see below for synonymy) | | i. s.: *C. macrotis [=Plecotus (*Corynorhinus) macrotis]M07 | |--C. rafinesquei (Lesson 1827)FS15, K92 [=Plecotus rafinesqueiK92] | `--+--C. mexicanusFS15 | `--C. townsendii (Cooper 1837)FS15, K92 [=Plecotus (Corynorhinus) townsendiiG69] | |--C. t. townsendiiFS15 | |--‘Plecotus’ t. australis (Handley 1955)MB86 | |--‘Plecotus’ t. ingensBP87 | `--‘Plecotus’ t. virginianusBP87 `--+--Barbastella Gray 1821FS15, M07 [incl. Synotus Keyserling & Blasius 1839M07] | |--*B. barbastellus [=Vespertilio barbastellus]M07 | `--B. leucomelasI92 | |--B. l. leucomelasI92 | `--B. l. darjilingensis (Hodison 1855)I92 `--+--Antrozoidae [Antrozoinae, Antrozoini]ST01 | |--AnzanycterisKJ70 | |--Bauerus dubiaquercusRB07 (see below for synonymy) | `--Antrozous Allen 1862FS15, M07 | |--*A. pallidus [=Vespertilio pallidus]M07 | | |--A. p. pallidusMB86 | | `--A. p. packardi Martin & Schmidly 1982MB86 | |--A. minorM07 | `--A. pacificusM07 `--Rhogeessa Allen 1866FS15, RB07 [=Rhogoessa (l. c.)RB07] | i. s.: R. velilla Thomas 1903C57 |--+--R. miraFS15 | `--R. parvula Allen 1866FS15, RB07 [=Vesperugo parvulusRB07] | |--R. p. parvulaRB07 | |--R. p. bombyx Thomas 1914C57 | `--R. p. major Goodwin 1958 [=R. tumida major]RB07 `--+--R. minutilla Miller 1897FS15, C57 `--+--*R. tumida Allen 1866RB07, FS15, RB07 [=R. parvula tumidaC57] `--R. aeneusFS15 Vespertilionidae incertae sedis: Registrellus Troughton 1943R64 `--*R. regulus (Thos. 1906) [=Pipistrellus regulus]R64 Rhinopterus Miller 1906M07 `--*R. floweri (Winton 1901)M07, W01 [=Glauconycteris floweriM07] Scoteinus Dobson 1875M07 |--*S. emarginatus [=Scotophilus (*Scoteinus) emarginatus]M07 |--S. balstoniR64 | |--S. b. balstoniR64 | `--S. b. caprenus Troughton 1937R64 |--S. greyiiM07 |--S. pallidusM07 `--S. sanborni Troughton 1937R64 Pterygistes Kaup 1829 [incl. Noctulinia Gray 1842, Panugo Kolenati 1856]M07 |--*P. noctula [=Vespertilio noctula, Panugo noctula; incl. Noctulinia proterus]M07 |--P. azoreumM07 |--P. lasiopterusM07 |--P. leisleri [=Panugo leisleri]M07 |--P. madeiraeM07 |--P. maximaM07 |--P. montanusM07 `--P. stenopterusM07 Stehlinia Revilliod 1919SM93 OligomyotisKJ70 SuaptenosKJ70 MiomyotisKJ70
Bauerus dubiaquercusRB07 [=Antrozous dubiaquercusRB07; incl. Baeodon meyeri Pine 1966G69]
Corynorhinus Allen 1865FS15, M07 [=Corynorhynchus Peters 1865M07; incl. Synotus Allen 1864 non Keyserling & Blasius 1839M07]
Nycticeius Rafinesque 1819FS15, M07 [=Nycticea Le Conte 1831M07, Nycticejus Temminck 1827M07, Nycticeus Lesson 1827M07, Nycticeyx Wagler 1830M07; Nycticeina]
Vespertilionidae [Myotinae, Myotini, Nycticeiini, Plecotinae, Plecotini, Vespertilioneae, Vespertiliones, Vespertilionina, Vespertilioninae]
*Type species of generic name indicated
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