Hypostomus cochliodon

Jonathan W. Armbruster, 2003, The species of the Hypostomus cochliodon group (Siluriformes: Loricariidae)., Zootaxa 249, pp. 1-60: 54-57

publication ID

z00249p001

publication LSID

lsid:zoobank.org:pub:DDFAA9D6-E4FA-4C3C-9749-CF0313D30F3C

persistent identifier

http://treatment.plazi.org/id/4CDB33DC-E60F-BFDF-63B6-C0B704425711

treatment provided by

Thomas

scientific name

Hypostomus cochliodon
status

 

[[ Hypostomus cochliodon  ZBK  Group ]]

Discussion

Delimiting the species of the Hypostomus cochliodon  ZBK  group is made difficult by the fact that the species vary little in morphometrics or meristics, and the species have a well developed ability to alter color pattern. However, the species can be divided into four groups and from those groups it is possible to distinguish the species. The four groups are the intermediate group ( H. hemicochliodon  ZBK  and H. sculpodon  ZBK  ), H. cochliodon  ZBK  with a unique color pattern, the odontodeless opercle group ( H. ericius  ZBK  , H. levis  , H. oculeus  , H. pyrineusi  , and H. taphorni  ), and an undifferentiated northern group ( H. hondae  , H. pagei  ZBK  , and H. plecostomoides  ). The odontodeless opercle group can be further subdivided into a highly keeled group ( H. ericius  ZBK  and H. oculeus  ) and a weakly to non-keeled group ( H. levis  , H. pyrineusi  , and H. taphorni  ). Once in these groups, it is fairly simple to separate the species. Principal components analysis is provided for each of the groups although H. levis  is excluded from the analysis because it lacks many of the measurements because of its absence of an adipose fin.

The PCA of the intermediate group showed a 100% separation of the species on principal component 2 (Fig. 10A). PC2 is most strongly and negatively effected by dorsal-anal length and anal-fin width and most strongly and positively effected by anal-fin length and folded dorsal-fin length. A ratio of dorsal-anal length to anal-fin length completely separates the two species from one another: average = 111.1 ± 8.4%, 92.5-132.6% in Hypostomus hemicochliodon  ZBK  and average = 79.2 ± 7.6%, 69.6-89.7% in H. sculpodon  ZBK  ).

The PCA of the odontodeless groups showed two trends, a complete or almost complete separation of H. taphorni  from H. ericius  ZBK  , H. oculeus  , and H. pyrineusi  and a complete separation of H. ericius  ZBK  and H. oculeus  on a graph of PC2 vs. PC3 (Fig. 10B). PC2 is most strongly and negatively effected by adipose-caudal length and mouth width and most strongly and positively effected by interdorsal length, eye-nare length and orbit length. PC3 is most strongly and negatively effected by base of anal-fin length, anal-fin length, and adipose-spine length and most strongly and positively effected by interdorsal length, adipose-caudal length, and postanal length. Although there is no morphometric evidence suggesting that H. ericius  ZBK  and H. oculeus  are distinct from H. pyrineusi  there are morphological differences (well-developed keels in H. ericius  ZBK  and H. oculeus  vs. no or weak keels in H. pyrineusi  ).

The PCA of the northern group showed some general trends separating H. hondae  and H. pagei  ZBK  from H. plecostomoides  and a complete separation of H. hondae  from H. pagei  ZBK  on PC2 vs. PC3 (Fig. 10C). PC2 is most strongly and negatively effected by eye-nare length and interorbital width and most strongly and positively effected by anal-fin length and interdorsal length. PC3 is most strongly and negatively effected by anal-fin length and folded dorsal-fin length and most strongly and positively effected by adipose-caudal length and interdorsal length.

For the most part, the species of the Hypostomus cochliodon  ZBK  group are allopatric (Figs. 8, 11, 17). It is only in the Amazon basin that several species coexist. Panaque  ZBK  , the other wood-eating genus of loricariid catfishes, also reaches its peak of diversity in the Amazon basin (Schaefer & Stewart 1993; Schaefer & Stewart 2002). In the upper Río Marañon drainage of Peru, there are at least nine species of wood-eaters: H. ericius  ZBK  , H. hemicochliodon  ZBK  , H. oculeus  , H. pyrineusi  , P. albopunctatus  , P. dentex  , P. gnomus  ZBK  , P. nocturnus  ZBK  , and probably at least one species of the P. nigrolineatus  clade (distributions based on this study and Schaefer & Stewart 1993). How these species subdivide the wood-eating niche is unknown, and ecological studies on wood-eating by fishes in the upper Río Marañon would represent a very interesting study.

Weber and Montoya-Burgos (2002) recently described Hypostomus fonchii  ZBK  and suggested that the species was derived from the H. cochliodon  ZBK  group. The teeth described for H. fonchii  ZBK  are elongate and unicuspid and it is suggested that the unicuspid teeth represent a synapomorphy for H. fonchii  ZBK  and the H. cochliodon  ZBK  group. This is problematic in that I have not observed truly unicuspid teeth in any members of the H. cochliodon  ZBK  group. In all specimens of the H. cochliodon  ZBK  group that I have examined, the medial cusp remains present, but is generally fused with the lateral cusp. The mesial cusp remains visible as a slightly darker, thicker ridge on the medial side of the tooth. I have not examined any specimens of H. fonchii  ZBK  , and I cannot determine whether or not this is the case with this species. The only truly unicuspid teeth that have been reported for the Hypostominae  are the teeth found in nuptial male Aphanotorulus  ZBK  (Armbruster & Page 1996). I do not consider H. fonchii  ZBK  as a member of the H. cochliodon  ZBK  group as its body shape is that of a generalized, fast-water dwelling Hypostomus  ZBK  and not the derived shape of H. cochliodon  ZBK  . Exact placement of H. fonchii  ZBK  awaits an analysis of its diet, osteology, and external anatomy for the synapomorphies of the H. cochliodon  ZBK  group.

Recent expeditions into poorly collected regions where no members of the Hypostomus cochliodon  ZBK  group have been reported from in the past are finding more species of the H. cochliodon  ZBK  group. Two undescribed species are now known from the Essequibo and Takutu River drainages of Guyana (pers. obs.) and one species from the Rio Tocantins in Brazil (Reis, pers. comm.). These species and a revised key will be presented in future publications.

Phylogeny

Character 1: Teeth - 0: elongate (Fig. 1A); 1: intermediate throughout life (Fig. 1B); 2: spoon-shaped at least in adults (Fig. 1C).

Character 2: Maxilla - 0: straight to moderately curved (Fig. 3A); 1: greatly curved, almost forming right angle (Fig. 3B).

Character 3: Odontodes on opercle - 0: 11+ (Fig. 2A); 1: 0-10 (Fig. 2B).

Character 4: Longitudinal ridge formed from bone and slightly enlarged odontodes on pterotic-supracleithrum - 0: present (Fig. 5A); 1: absent (Fig. 5B).

Character 5: Nuptial body odontodes - 0: absent (Fig. 2A); 1: present (Fig. 2B).

Character 6: Notch between the hyomandibula and metapterygoid - 0: present (Fig. 3A); 1: absent (Fig. 3B).

Character 7: Buccal papilla - 0: present (Fig. 4A); 1: absent or extremely small (Fig. 4B).

Character 8: Dentary angle - 0: averaging greater than 90°; 1: averaging less than 80°.

Character 9: Sharp keel odontodes - 0: present; 1: absent.

Character 10: Body shape deep and narrow with the head taller than wide - 0: absent; 1: present.

Very few morphological characters are useful in elucidating the relationships of the species of the Hypostomus cochliodon  ZBK  group. Based on the ten characters found, a phylogeny is produced for the species of the H. cochliodon  ZBK  group (Fig. 23). The single tree found has 12 steps and CI = 1.00. Character state data is in Table 8. No skeletal material is available for H. sculpodon  ZBK  or H. ericius  ZBK  ; however, external evidence does provide information as to the potential relationships of these species with other members of the H. cochliodon  ZBK  group. Considering there are so few characters available for analysis, the phylogeny should be considered tentative.

Also providing support for the basal position of Hypostomus hemicochliodon  ZBK  and H. sculpodon  ZBK  is diet. In all of the specimens of the H. cochliodon  ZBK  group examined, almost the entire intestine is filled with small wood chips suggesting that the fishes consume little other than wood. In H. hemicochliodon  ZBK  and H. sculpodon  ZBK  the intestine mostly contains wood, but other organic matter makes up a major portion of the diet (not greater than 50%). It is apparent that H. hemicochliodon  ZBK  and H. sculpodon  ZBK  are wood eaters but not wood specialists.