Ilyodon furcidens (incl. xantusi)

Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
Ilyodon furcidens
English Name: 
Goldbreast Splitfin
Mexican Name: 
Mexclapique (erronously: Mexcalpique) de Armería
Original Description: 

  JORDAN, D. S. & C. H. GILBERT (1882): Catalogue of fishes collected by Mr. John Xantus at Cape San Lucas, which are now in the U. S. National Museum, with descriptions of eight new species. Proceedings of the United States National Museum. No 5 (1882): pp 353-371

Holotype: 

  Collection-number: United States National Museum, Cat. No. USNM-9571 and USNM-30971.

  Many specimens in fair condition, the largest one of a total length of about 83mm (3.25 inches). In 1901, Carl H. Eigenmann described from Paraguay after two specimens (Cat. No. USNM-55642) mixed in with some Characiformes and "flattened out of shape as though they had been in a press" with Ilyodon paraguayense a new genus and species, correctly synonymized with the previous species by Hubbs & Turner in 1939. In the same paper in 1939 they described Balsadichthys xantusi with the Holotype (Cat. No. UMMZ-105997), an adult male of 78mm standard length, and 26 Paratypes, all from quiet pools in a small tributary of the Río Colima at (Hacienda) Los Limones, about 2km SW of Villa de Álvarez, Colima. Concening the validity of this species, go to Remarks.

Drawing of Ilyodon furcidens

Holotype of Balsadichthys xantusi

Terra typica: 

  Following the original description, the type locality should be the Cape San Lucas in Lower California (Baja California), which is definitely incorrect. Most probably there had been done mistakes when the types had been recorded: The item under "Locality " is blank for the cotype series (No. 30971) reported as from San Lucas, and someone assumed without warrant that this and nearby blanks signified dittos from an entry above of Cape San Lucas. Two series in the National Museum, all collected by Xantus, are cotype lots (No. 5093 and 35338), entered as from Colima, Mexico, so this seems be the right terra typica for the holotypes, too.  

Etymology: 

  This species epithet is derived from the Latin with the noun "furca" meaning fork, while the translation of "dens" is tooth. The Goldbreast Splitfin is named for its forked (bifid) teeth.

Synonyms: 

Characodon furcidens   Jordan & Gilbert, 1883

Ilyodon paraguayense   Eigenmann, 1907

Balsadichthys xantusi   Hubbs, 1926 (nomen nudum)

Balsadichthys xantusi   Hubbs & Turner, 1939

Ilyodon xantusi   Miller & Fitzsimons, 1971

Ilyodon furcidens amecae   Kingston, 1979 (nomen nudum)

Ilyodon furcidens furcidens   Kingston, 1979 (nomen nudum)

Ilyodon furcidens variabilis   Kingston, 1979 (nomen nudum)

Ilyodon xantusi xantusi   Kingston, 1979 (nomen nudum)

Ilyodon amecae   Radda, 1989 (nomen nudum)

Distribution and ESU's: 

  The Goldbreast Splitfin is endemic to the Mexican federal states of Jalisco and Colima. It occurs in the Río Salado, Lower Río Coahuayana basin, an affluent of the Río Naranjo named section of this river, furthermore in the ríos Purificación, Marabasco and Armería, the last ones with its main sources, the ríos Ayuquila and Tuxcacuesco. It inhabits additionally the Río Ameca basin including its big southern affluents, the ríos Mascota and Atenquillo and the Arroyo Jolapa. Affiliated to several separate river basins, five subpopulations can be inferred: The Río Armería subpopulation (type subpopulation), the Río Ameca subpopulation, the Río Purificación subpopulation, the Río Marabasco subpopulation and the Río Salado subpopulation. The underlined names are the ones officially used by the Instituto Nacional de Estadística y Geografía; nevertheless, other ones might be more often in use or better known and therefore prefered.

 

  ESU ist short for Evolutionarily Significant Unit. Each unit expresses an isolated population with different genetic characteristics within one species. ESU's can be defined by Molecular geneticsMorphology and/or Zoogeography and help in indicating different phylogenetic lineages within a species. The abbreviation for an ESU is composed of three letters of the genus, followed by the first two letters of the species name and an ongoing number in each species.

 

  In Ilyodon furcidens, no ESU's are distinguished, so all populations belong to Ilyfu1. However, phylogenetic studies from Beltrán-Lopez et al. (2017) had to admit some uncertainties in the taxonomy of the genus Ilyodon, so changes may follow in the future. Actually to keep it simple and follow a two species theory accepting only furcidens and whitei. In her classification, the Goldbreast Splitfin is summarized in Clade A.

 

  The ríos Coahuayana (green), Armería (yellow), Middle and Lower Ameca (pink), and Purificación/Marabasco (blue) drainages on a Mexico map:

ríos Armería, Coahuayana, Marbasco, Purificación, lower and middle Ameca

  Distribution of the Goldbreast Splitfin. Two subsequent detailed maps show the populated sub- and infrabasins. In all the maps, the bold red line encompasses the species' distribution, the thin red lines separate the infrabasins, partly even ESU's. For a more detailed distribution, see the map for the Maximum Extent of Occurence (EOO):

Ilyodon furcidens infrabasins

  Map A - Northern drainages: Within the Río Ameca basin, the species occurs in four infrabasins of two subbasins: It inhabits the Middle Río Ameca (MAM) and Río Atenguillo (ATE) infrabasins of the Middle, and the ríos Mascota (MAS) and Talpa (TAL) infrabasins of the Lower Río Ameca subbasin. It furthermore is known from the upper sections of the Río Armería subbasin, the ríos Tuxcacuesco (TXC) and Ayuquila (AYU) infrabasins. 

Ilyodon furcidens northern infrabasins

  Map B - Southern drainages: Subsequent to the upper sections of the Río Armería subbasin, it also occurs in the Río Armería infrabasin (ARM) and the Río Salado infrabasin (SAL) of the neighboring Río Coahuayana subbasin. In the southwest, the Goldbreast Splitfins also inhabits the ríos Marabasco (MAR) and Purificación (PUR) subbasins of the Purificación-Marabasco basin. 

Ilyodon furcidens southern infrabasins

  Maximum Extent of Occurence of Ilyodon furcidens:

Maximum EOO of Ilyodon furcidens

Status : 

  International Union for Conservation of Nature (IUCN): not assessed (assessment in process)

  Conservation status and population trends of Mexican Goodeids (Lyons, 2011): least concern/declining.: "As I define it, this species is widely distributed and common in the Armería, Marabasco, and upper Coahuayana river basins and uncommon in the upper Ameca River basin. Recent genetic analyses suggest that populations may also occur in parts of the Balsas River basin, although more specimens and analyses are needed to confirm this (Kyle Piller, personal communication). Because of this uncertainty about the identity of some Balsas populations, some authors consider I furcidens a synonym of (i.e., the same species as) I. whitei (Doadrio and Domínguez-Dominguez 2004). Two morphotypes of I. furcidens are present in many areas of the Armería, Marabasco, and Coahuayana basins (Lyons and Navarro-Pérez 1986), and these were long thought to be two different species, the narrow-mouthed form, I. furcidens and the wide-mouthed form, I. xantusi. However, work by Turner et al. (1983, 1985) and Grudzien and Turner (1984) demonstrated that narrow-mouthed females could produce both narrow-mouthed and wide-mouthed offspring, as could wide-mouthed females, proving that the two morphotypes were part of the same species. Ilyodon furcidens was the older of the two names and thus had priority, so the name I. xantusi is no longer considered valid. Some ichthyologists and aquarists consider populations from the upper Ameca River basin to be a separate species, I. “amecae” (Doadrio and Domínguez-Domínguez 2004). However, genetic and morphological differences between Ameca and Armería populations are small (Kyle Piller, personal communication), and I do not consider the Ameca populations worthy of separate species status. Furthermore, the name I. “amecae”has never been formally described in the scientific literature, and under the rules of scientific nomenclature it is therefore not appropriate for use in scientific or aquarium publications.

Ilyodon furcidens is often the most common species at the localities where it occurs. However, numbers appear to be decreasing since the 1990’s. Populations have declined or disappeared from several streams in the Ameca River basin because of shrinking water levels and invasions of non-native species. Within the Armería River basin, the expansion of the non-native largemouth black bass, a top predator, has apparently resulted in the near elimination of the I. furcidens from long stretches of the Ayuquila River (Norman Mercado-Silva, Universidad de Guadalajara, Autlán, Mexico, personal communication)."

  NOM-059-SEMARNAT-2010: categoría de riesgo (category of risk): amenazada (threatened)

Habitat: 

  The habitats are pools and riffles of streams and rivers over substrates of sand, gilt, gravel, rocks, bedrocks and boulders in depths to 1.5m. The water is usually clear to murky with no vegetation or with green algae, Potamogeton and Nasturtium. The currents are not homogeneous, going from none to slow to fairly swift.

Arroyo Dávalos

Río de las Bolas

Río Jiquilpan

Barranca de la Tía Barragana, Comala

Effluent of the Agua Fría spring, Río Armería drainage

Río Hondo, Río Salado drainage

Arroyo El Limón, Río Atenguillo drainage

Río Atenguillo

Río Ayuquila at Zenzontla bridge

Arroyo Mazantlán

Río La Lumbre

Río Colima

creek in San Rafael

Biology: 

  Following Miller, young are born from February to July (possibly through autumn) as indicated by captures. The adult fish prefer swimming in a strong current, the young fish can be found in pools near the shore.

Diet: 

  Teeth, gut and dentition is similar to its congener, so the feeding habits are most probably identical, means mainly herbivorous, grazing from aufwuchs and algae and collecting insects from the surface. The gut is long and suggests herbivorous feeding habits. Two trophic types can be distinguished (by their mouth) in this species: one with a narrow mouth (being suggested to be insectivore or planktivore), and one with a broad mouth (being suggested to feed from aufwuchs and algae). Both types have been seen feeding in the habitat from aufwuchs, the narrow-mouthed form additionally from the surface (Kingston, 1979).

Size: 
The maximum known standard length is 103mm (Miller et al., 2005).
Colouration: 

  Hubbs & Turner pointed 1939 at the much variation in the colouration of this species, with age, sex and individuals. Typical for young fish is a lateral row of irregular blackish spots and bars crossing an inconspicuous axial streak as well as an irregular dorsolateral row of smaller spots and traces of other dark markings. These bars are occasionally lacking in larger young, rarely fused into a lateral band, faint to intense, small and roundish to high and narrow, often restricted to the anterior, posterior or median section. As these several variations are independent, many types of pattern are developed. In the males the bars fade out more or less completely at a length of about 35mm and are then replaced by rather dense speckling, which is strongest forward. In the females, the bars show the same variations but can be seen faintly in even the largest specimens. The dorsolateral spots usually become obsolete in the smaller females, but occasionally persist rather strongly to a length of at least 56mm. The speckling is usually little developed in smaller females, but gradually increases in intensity. Nevertheless, females are more faintly and in a finer pattern speckled than males. The ground colouration of both sexes is mainly greenish or grayish-brown on the back, becoming darker with age, and yellow to orange on the belly. This can be overwhelmed with grayish-green or brown in old individuals. The fins are normally coloured yellow to orange, the males show a dark submarginal band in the dorsal and a (most times broad) submarginal or marginal band in the caudal fin with 1 to 3 additional vertical rows of spots. Females show a narrow to wide submarginal band on the anal fin as well as in the caudal fin, where is becomes disrupted with age and fades in older females. Pelvic and Pectoral fins are usually yellow. All in all, both sexes display a very striking colouration. 

Remarks: 

  The confusion about the origin of this species is not alone shown in the original description and the wrongly assigned type locality (see above in Terra typica), but also in the description of Ilyodon paraguayense by Eigenmann in 1907: The two (crushed) types of Ilyodon paraguayense were assigned to Paraguay because they were mixed in with some Characins, collected by E. Palmer in this country. Hubbs & Turner examined in 1939 these types, and stated, that they "agree very closely not only in characters but also in superficial appearance with the types of Characodon furcidens, and it is probable that they were part of the same material, collected by Xantus in Colima." 

 

  In 1939, Hubbs & Turner described Balsadichthys xantusi in honour of John Xantus, who collected the first specimens. Even in the original description - though they pointed at the narrow relationship with Balsadichthys whitei - they discussed hybrids between Ilyodon furcidens and the new described species. They mentioned an intimate relationship of the both genera, "as indicated by their common ovarian and trophotaenial characters and evidenced by the discovery that these genera commonly hybridize in nature." They wrote furthermore: "This circumstance might even be considered a reason for synonymizing Balsadichthys and Ilyodon, but to do so would violet the consistent judgement of authors that the species with weak teeth movably set in loosely conjoined jaws of a wide, transverse mouth should be separated generically from those with stronger teeth tightly set in the firmly joined jaws of narrower mouths with better-developed lateral gape." and "It is not all improbable that it will be found expedient to synonymize Balsadichthys and Ilyodon...". So Hubbs & Turner recognized instinctively the narrow relationship of all these forms, they decided to let the consistent system of judging the fish after their teeth-structure persist, maybe because they saw no other, or better way to judge the fish. However, they saw this judgement not very pleasable. Nevertheless, it took another 30 years till this synonymizing had been done finally (Miller & Fitzsimons, 1971), mainly because both trophic forms can be found at the same locations, but not always. Sometimes there is only the furcidens-type represented, sometimes the xantusi-type, and sometimes both with many intermediates, so hybridisation seemed to be very likely.

 

  In 1979, Kingston who did her doctor thesis on Ilyodon, added another subspecies to Ilyodon furcidens, calling it Ilyodon furcidens amecae. Though this subspecies had never described officially, Radda took over this name and gave it species rank in 1989. Domínguez (pers. comm. 2010) values the population from the Río Ameca as belonging to Ilyodon furcidens without subspecies status. 

 

  In 1980, Turner & Grosse hypothesized that Ilyodon furcidens and xantusi are conspecific, representing different trophic forms as they sampled a dichotomous population in the Río Armería and one in the Río Coahuayana and discovered little or no allozyme differentiation between the presumptive species in either location. They suggested intraspecific polymorphism. In 1984, Grudzien et al. collected Ilyodon at four locations along the Río Terrero and one of its tributaries, the Río del Tule, and examined 36 gene loci. They detected 15 loci being polymorphic, but the detected variation has not been connected with one of the both trophic forms. In contrary: they varied independently from both forms in the same value, so there could not been detected any genetic difference between furcidens and xantusi. A similar result gave the examination of the kind of chromosomes in Ilyodon through Turner et al in 1985: surprisingly they found a different number of metacentric chromosomes in fish of the Río Coahuayana basin, so-called cytotypes, starting with 0-2 up to 16! Such a variation is very rare among teleosteen fish at all. However, genic and chromosomal divergence are clearly uncoupled in Ilyodon and a certain number of metacentric chromosomes is not typical for one of the both trophic forms. So finally, it is neither genetically nor by the number of metacentric chromosomes possible to distinguish furcidens from xantusi. Considering that in many habitats both trophic forms can be found (even in the type material of furcidens), the final consequence had to be to see both forms as members of one species.

 

  Hieronimus (1989) sampled Ilyodon furcidens in a small creek above San Antonio, finding differences mouth forms in the colour of their caudal fin (orange without markings = furcidens; yellow with black makings = xantusi). Keeping the fish in tanks, the differences disappeared and the fish looked similar to each other. 

 

  Comparing all Ilyodon-forms (including whitei and the former cortesae), there is not much difference (even phylogenetically) between them all. The genetic distances (intraspecific pairwise uncorrected "p" distances) comparing the Cytochrom b gene between Ilyodon furcidens, the former xantusi and whitei is low, only p=0.3 to 1.7% (Domínguez et al, 2004). This value is even lower than between some populations of Ilyodon whitei (1.5 to 1.7%, which is still very low)! This genus is definitely in a specification process, which makes it very difficult for scientists to classify the different forms.