Saturday, May 19, 2018

[Ichthyology • 2018] Austrolebias wichi • An Endangered New Species of Seasonal Killifish of the Genus Austrolebias (Cyprinodontiformes: Aplocheiloidei) from the Bermejo River Basin in the Western Chacoan Region, northwestern Argentina


Austrolebias wichi

 Alonso, Terán, Calviño, García, Cardoso & García, 2018
  
Abstract
Austrolebias wichi, new species, is herein described from seasonal ponds of the Bermejo river basin in the Western Chacoan district in northwestern Argentina. This species was found in a single pond, a paleochannel of the Bermejo River, which is seriously disturbed by soybean plantations surrounding it. Despite intensive sampling in the area, this species was only registered in this pond where it was relatively scarce. Therefore, we consider this species as critically endangered. This species is the sister species of A. patriciae in our phylogenetic analyses and is similar, in a general external aspect, to A. varzeae and A. carvalhoi. It can be distinguished among the species of Austrolebias by its unique color pattern in males. Additionally, from A. varzeae by presenting a supraorbital band equal or longer than the infraorbital band (vs. shorter) and from A. patriciae by the convex dorsal profile of head (vs. concave). Further diagnostic characters and additional comments on its ecology and reproduction are provided.

Fig 1. Live pictures of males in left lateral view.
(A-B) 
Austrolebias wichi sp. nov. (C) Austrolebias varzeae, picture by Matheus Volcan;
D) 
Austrolebias patriciae from type locality, not preserved, picture by Daniel W. Fromm. 

Fig 2. Live pictures of females in left lateral view.
(A)
 Austrolebias wichi sp. nov. (B) Austrolebias varzeae, picture by Matheus Volcan;
(C) 
Austrolebias patriciae from type locality, not preserved, picture by Daniel W. Fromm.

Austrolebias wichi, new species

Diagnosis: Distinguished from all other congeners except from Austrolebias patriciae by a supraorbital bar longer or equal than infraorbital bar (vs. always shorter than infraorbital bar). Austrolebias wichi can be distinguished from Austrolebias patriciae by head dorsal profile on lateral view concave (vs. convex), the absence of filamentous rays markedly overpassing the interradial membrane distal margin of dorsal and anal fin in adult males (vs. present), by presenting small numerous whitish dots on unpaired fins in males (vs. fewer and bigger), infraorbital and supraorbital bands thinner than pupil and pointed distal portion (vs. equal or wider than pupil and rounded distal portion), dorsal-fin origin posterior to anal fin origin in females (vs. anterior) (Fig 1).

Female colour pattern similar to A. patriciae, with grey pinkish background having irregular grey blotches and some dark blue blotches over the caudal peduncle and body flank and differing from A. varzeae, which presents an orange background with minute black and grey relatively rounded, irregular blotches (Fig 2), and from A. araucarianus which presents a yellowish brown pale flank, with vertically elongated dark grey to black spots, often forming short narrow bars [Costa, 2014].
Fig 1. Live pictures of males in left lateral view. (A-B) Austrolebias wichi sp. nov. (C) Austrolebias varzeae, picture by Matheus Volcan; D) Austrolebias patriciae from type locality, not preserved, picture by Daniel W. Fromm.

 Fig 2. Live pictures of females in left lateral view. (A) Austrolebias wichi sp. nov. (B) Austrolebias varzeae, picture by Matheus Volcan; (C) Austrolebias patriciae from type locality, not preserved, picture by Daniel W. Fromm.

Etymology: The name wichi is a reference to the occurrence of the new species in the Western Chacoan region where the Wichí indigenous people inhabits in several settlements very close to the type locality.

Ecology: The ponds in the region have marked dry and wet seasons; the rains are concentrated during the summer, with about 75% of the total rains concentrated from December to March, and almost no rains from May to September [Arias, 1996] (Table 2). This determines that the seasonal ponds present water approximately from December to April, depending on the pond and the variability among years, (persobs.) (Fig 6).

The seasonal aquatic environment where the new species was collected is part of a long paleochannel which is interrupted by a road. Despite intensive sampling efforts in this area and in the Western Chacoan region we were only able to collect this species in the portion of the paleochannel immediately next to the road. Physicochemical parameters measured on January 2006 where pH 6,9 and a conductivity of 70 μsiemens/cm. This environment generally presents abundant aquatic vegetation. Other syntopic killifish species are: Papiliolebias bitteri (Costa 1989) and Trigonectes aplocheiloides Huber, 1995, which are the most abundant species, followed in abundance by Austrolebias vandenbergi (Huber, 1995) and A. wichi, which is very scarce in this environment, and some years we could not even collect a single specimen of this species while there were other annual fishes in the pond. Also, very few Neofundulus paraguayensis (Eigenmann & Kennedy, 1903) were collected in this pond. Nearby, a couple of hundred of metres from this environment there is another pond where we collected Austrolebias monstrosus (Huber, 1995) but this species was not found syntopically with A. wichi. There are many seasonal ponds in this area where annual fish are very abundant; nevertheless, the only place where we found A. wichi is the type locality. The only noticeable difference between this environment and other seasonal ponds in the area may be that this is a very profound (about 1 meter depth) and big environment.

From mid autumn, winter, and spring the pond is completely dry and the top layer of substrate, which consist of slime with some vegetal rests, is very dry (Fig 7). The presence of domestic cattle in this area is evident in the bottom of the dry pond and the impact of this alteration in the bottom structure over the killifish populations is unknown.

Fig 6. Type locality of Austrolebias wichi sp. nov. (A) January 2006. (B) January 2014. (C) April 2017. (D) August 2012. 

Fig 7. Detail of the bottom of the pond where Austrolebias wichi n. sp. is found. August 2012. Picture courtesy of Marcos Mirande.


Felipe Alonso, Guillermo Enrique Terán, Pablo Calviño, Ignacio García, Yamila Cardoso and Graciela García. 2018.   An Endangered New Species of Seasonal Killifish of the Genus Austrolebias (Cyprinodontiformes: Aplocheiloidei) from the Bermejo River Basin in the Western Chacoan Region. PLoS ONE. 13(5): e0196261.  DOI: 10.1371/journal.pone.0196261

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