Ilyodon whitei (incl. cortesae & lennoni)

Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Original Description: 

  MEEK, S. E. (1904): The fresh-water fishes of Mexico north of the Isthmus of Tehuantepec. Publication. Field Columbian Museum 93, Zoological Series 5: pp 137 - 138

Etymology: 

  This species is named for E.A. White of the city of Mexico, in recognition of many favours, Meek received through his courtesy.

Holotype: 

  Collection-number: Field Columbian Museum, Cat. No. FCM-4547.

  The Holotype is 71.5mm TL long.

English Name: 
Balsas Splitfin
Mexican Name: 
Mexclapique cola partida
Synonyms: 

Goodea whitei   Meek, 1904

Balsadichthys whitei   Hubbs, 1926

Ilyodon lennoni   Meyer & Förster, 1983

Ilyodon cortesae   Paulo-Maya & Trujillo-Jiménez, 2000

Karyotype: 

  The Karyotype describes the number and appearance of chromosomes during the phase of condensation, classified by the position of the centromere (Levan et al., 1964).

The following abbreviations are employed:

 

M = large metacentric chromsome (a result of Robertsonian fusion)

m = small metacentric chromsome (centromere at medium position)

sm = submetacentric chromsome (centromere at submedian position)

smst = submetacentric-subtelocentric chromosome (continous series)

st = subtelocentric chromosome (centromere at subterminal region)

stt = subtelocentric-acrocentric chromosome (continous series)

t = acrocentric chromosome (centromere at terminal region)

 

The Karyotype of Ilyodon whitei, following Uyeno, Miller & Fitzsimons, 1983:

2n = 48    8st/ 40t

Size: 
The maximum known SL is 101mm (Miller et al, 2005).
Terra typica: 

  The Holotype comes from upper tributaries of the Río Balsas near Yautepec in Morelos.

Status : 

  International Union for Conservation of Nature (IUCN): critically endangered

 

  Conservation status and population trends of Mexican Goodeids (Lyons, 2011): vulnerable/declining – As I define it, this species is limited to the Balsas River basin, where it occurs in about 12 different areas. Specimens from a tributary to the Balsas River near Ciudad Altamirano in the state of Guerrero were described as a separate species, I. lennoni (Meyer and Forster 1983), but I and most other ichthyologists (e.g., Doadrio and Domínguez-Domínguez 2004; Domínguez-Domínguez et al. 2005b; Miller et al. 2005) do not consider this name to be valid. Many populations of I. whitei have declined or disappeared over the last 25 years, largely because of predation by or competition from non-native fish species (e.g., Contreras-MacBeath et al. 1998). Non-native species now dominate many areas of the Balsas River basin.

Ilyodon cortesae: critically endangered/stable? – This species was recently described (Paulo-Maya and Trujillo-Jimenez 2000), and is known from only three nearby locations in the Tacámbaro River drainage in the upper Balsas River basin. However, some ichthyologists question the validity of this species and suggest that it may be merely a variant of I. whitei (Miller et al. 2005; Omar Domínguez-Domínguez, personal communication). Little is known about the overall distribution and abundance of I. cortesae, which is found in a remote and difficult-to-access area, but known populations are small and localized.

 

  NOM-059-SEMARNAT-2010: no categoría de riesgo (no category of risk)

Distribution and ESU's: 

  The Balsas Splitfin is distributed on the Pacific Slope in the upper tributaries of the ríos Coahuayana and Balsas in the states Colima, México, Michoacán and Morelos.

 

  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 genetics, Morphology and/or Zoogeography and help in indicating different phylogenetic lineages within a species. The abbreviation for an ESU is composed of the first 3 letters of the genus, followed by the first 2 letters of the species name and an ongoing number in each species.

 

  In Ilyodon whitei, we have the situation, that the five ESU's we distinguish do not match with the last phylogenetic results (Beltrán-Lopez et al., 2017). We try here to bring together both systems until the situation is cleared. Ilywh1 is one ESU with a polyphyletic origin. Fish from the lower Río Coahuayana basin (including Ilyodon xantusi) represent Ilyodon furcidens, whereas fish from the upper Coahuayana river Ilyodon whitei.  This population forms Clade D within Ilywh1, whereas fish from the western Balsas present Clade E within the same ESU. So these both populations represent different phylogenetic lineages. Additionally, the ESUs Ilywh2 from the Río Tacambaro ("cortesae") and Ilywh3 from the Río Chacembero ("lennoni") belong phylogenetically to Clade E. Confusing situation, we have to confess. Anyway, we prefer to keep these two populations as separate ESU's due to situation, they were kept as distinct species for a while. Ilywh4 encompasses fish from the middle Balsas - basin (ríos Amacuzac, Cuautla, Cuernavaca and Cútzmala), subclade B2 sensu Beltrán-Lopez, whereas Ilywh5 the ones from the eastern Balsas - basin (Río Atoyac and creeks in vicinity) subclade B1respectively .

Habitat: 

  The habitats are similar to the ones of Ilyodon furcidens, means pools and riffles of clear to turbid streams, over substrates of sand, silt, mud, gravel, rocks and boulders. The currents are usually slight to swift. Vegetation can be absent or made of green algae, Potamogeton and Ceratophyllum. The preferred depth is less than 1.3m.

 

Río Tamazula I

Río Tamazula II

 

Río Tamazula III

Río Tamazula IV

 

Puente ContlaArroyo Contla

 

 

Colouration: 

  The ground colouration of Ilyodon whitei is mostly light brown or grey, in some populations tending to yellow. The upper part of the body is darker than the lower part, the scales have its posterior portion darker giving the fish a finely speckled appearance. A narrow blackish lateral band, extending from above the opercle nearly to the base of the caudal fin, is composed of a lot of small dark dots in males, females often have this band splitted into the single dots. Both sexes have no or very few dots in the fins, but darker areas can be found sometimes, mainly as a short bar in the anal fin. The base of the caudal fin is dotted with several transverse rows of dark dots and the caudal fin itself shows a dark submarginal band followed by a yellowish terminal band in the male gender. Males show a metallic-yellowish or bluish mirror on the sides, sometimes even females can show a hint of it. Many fins show iridescent light parts.  

Biology: 

  Miller (2005) wrote, that the occurrence of young in collections suggests that the reproduction occurs during the latter part of the dry season in March and April.

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. 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). The broad mouth form was originally described as Ilyodon xantusi. The gut of both types is long and suggests herbivorous feeding habits.

Remarks: 

  This species is widely distributed. Its eastern habitats are reaching nearly the height of Mexico City, westwards this species reaches even the Río Tamazula. Looking at its distribution along the Río Balsas basin, it is conspicuous, that it inhabits only the right tributaries of this river. This might be caused by river piracy of the Río Balsas, taking over waters from a river originally flowing much more northwards of the Balsas to the Río Coahuayana basin. Strata movement may have raised a new mountain range with redirecting former waters of this ancient river being now tributaries of the Balsas river, that is (mainly) free of Ilyodon.

 

  In 1983, Meyer and Förster described Ilyodon lelloni in honour of the famous British musician and former member of the "Beatles", John Lennon. Following the describers, this species should be forming a complex with Ilydodon xantusi in contrast to a complex formed by furcidens and whitei. However, the noticed differences in dentition and trophotaenial structure are not big enough to separate lennoni from whitei. Furthermore, a described gender related pair of chromosomes seemed to rather reflect differences that can be found routinely in condensation and fixation of chromosomes than a real chromosomal heteromorphism (Turner, 1985).

 

 Ilyodon cortesae,  that was described by Paulo-Maya & Trujillo-Jiménez is differing from other populations of Ilyodon whitei by its strongly convex cephalic profile, its small size, the thinner caudal peduncle, more scales in the longitudinal series, form and size of the neural prezygapophyses of the caudal vertebrae, the strongly bifid teeth and the disposition of the pores of the lateral line of the preorbital system. Nevertheless phylogenetical results are clear, that the populations from the Río Tacambaro belong to whitei, too.