Pterolebias Garman

Wilson J. E. M. Costa, 2005, The Neotropical annual killifish genus Pterolebias Garman (Teleostei: Cyprinodontiformes: Rivulidae): phylogenetic relationships, descriptive morphology, and taxonomic revision., Zootaxa 1067, pp. 1-36 : 2-5

[[ Genus Pterolebias Garman ]]

Pterolebias Garman, 1895 , occurs over a vast area of South America, including the eastern and southern Amazon River basin and the ParanáParaguay River system (Costa, 1998a). It is a well defined clade of annual killifishes, supported both by morphological (Costa, 1998a) and molecular studies (Murphy et al, 1999; Hrbek & Larson, 1999). However, its taxonomy is still poorly known. It includes four nominal species: P. longipinnis Garman, 1895 ; P. bokermanni Travassos, 1969 ; P. luelingi (Meinken, 1969) ; and P. phasianus Costa, 1988 . Pterolebias longipinnis has been recorded over the entire geographic range of the genus, from Marajó Island in northern Brazil (about 1° S) to Corrientes in Argentina (about 28° S). Two nominal species from the Madeira River basin, P. bokermanni and P. luelingi , are insufficiently diagnosed and not distinguishable from P. longipinnis (Thomerson, 1984; Costa, 1988). Pterolebias phasianus is a distinctively slender species with a unique color pattern. Relationships of Pterolebias to other rivulid genera are also controversial. The hypothesis generated by morphological phylogenetic analysis indicates that Pterolebias is the sister group to Gnatholebias Costa, 1998 , an annual killifish genus occurring in the Orinoco River basin and adjacent coastal river basins in Venezuela and Colombia (Costa, 1998a). However, hypotheses derived from molecular studies support Gnatholebias as more closely related to other annual rivulid genera endemic to northern South America (i.e., Renova Thomerson & Taphorn, 1995 ; Terranatos Taphorn & Thomerson, 1978 ; Micromoema Costa, 1998 ; Rachovia Myers, 1927 ; and Austrofundulus Myers, 1932 ) than to Pterolebias (Murphy et al., 1999; Hrbek & Larson, 1999). The objectives of the present study are: 1) to provide a detailed description of morphological traits of Pterolebias , which in turn allows better morphological character analyses; 2) to identify informative characters useful for the diagnoses of species, based on large collections totaling over 400 specimens over the entire geographic range of the genus; and 3) to recognize and redescribe the valid species.

Taxonomic History

Pterolebias was first described to include a single species, P. longipinnis Garman , collected in the eastern Brazilian Amazon during the Thayer Expedition (1865-1866) (Garman, 1895). In Garman’s key to identification of cyprinodontiform genera, Pterolebias was distinguished from the other two rivulid genera known at that time, Rivulus Poey, 1860 , and Cynolebias Steindachner, 1876 , by having “body sharp-edged behind vent”. This condition was repeatedly listed as diagnostic for Pterolebias (e. g., Regan, 1912; Myers, 1927), but it was considered to be a possible artifact of preservation by Myers (in Weitzman & Wourms, 1967).

In the 20th century, nine new species over a wide area of South America, including the Orinoco, Amazonas and Paraguay river basins, were assigned to the genus Pterolebias : P. peruensis Myers , P. wischmanni Seegers , and P. rubrocaudatus Seegers , from the Peruvian Amazon (Myers, 1954; Seegers, 1983, 1984), P. bokermanni from the Madeira River drainage of Brazil (Travassos, 1955), P. zonatus Myers , P. maculipinnis Radda , and P. hoignei Thomerson from the Orinoco basin of Venezuela (Myers, 1935; Radda, 1964; Thomerson, 1974), P. staecki Seegers from the Brazilian central Amazon basin (Seegers, 1987), P. phasianus Costa from the Paraguay River basin, Brazil (Costa, 1988), and P. obliquus Costa, Sarmiento & Barrera from the Bolivian Amazon (Costa et al., 1996). When new collections of P. longipinnis were made in regions distant from the type locality, including the Paraná-Paraguay River basin of Argentina and Paraguay (Alonsode-Aramburu, 1961), this species became the most geographically widespread South American annual fish known.

During the 1970s, a new annual fish species of unknown South American origin was reported in the aquarium literature as Pterolebias NSC-1 (e. g., Terceira, 1973). Costa (1989) recognized it as an undescribed genus and species, which he described as Moema piriana Costa from the eastern Brazilian Amazon.

Thomerson (1984), following comparison of the original description of Rivulichthys luelingi Meinken , from the Chapare River floodplains, Madeira River drainage, Bolivian Amazon, with data obtained from the examination of type specimens of P. longipinnis , concluded that the former is a synonym of the latter. Costa (1988) examined the type specimens of P. bokermanni and did not find characters useful for distinguishing it from P. longipinnis , but preferred not to synonymize these species, since data on live color patterns were not available at that time. However, Huber (1995) identified Pterolebias sp. aff. longipinnis from the Paraguay River basin, thus suggesting it to be a distinct species, but he provided no justification for his opinion. Schindler & Staeck (1993a, b) provided data on recent collections of Pterolebias , and, in addition, Schindler (2004) recognized Pterolebias luelingi as a valid species, and reported diagnostic features for P. bokermanni and P. longipinnis .

For almost 60 years after Garmans paper, no additional diagnostic data were provided for the genus Pterolebias and no hypothesis of relationships was erected. Myers (1954) suggested Pterolebias as being closely related to Rachovia , due to the common occurrence of a short pelvic fin in Rachovia and in P. peruensis . However, a short pelvic fin is the primitive condition for rivulids, occurring in most aplocheiloid taxa, and does not, by itself, indicate a close relationship between Pterolebias and Rachovia .

Weitzman & Wourms (1967) hypothesized that Rachovia , Pterolebias and Austrofundulus (including Terranatos ) form a natural assemblage, based on their common geographic distribution in northern South America and presence of scales on the caudal fin. However, although both Rachovia and Austrofundulus have scales extensively covering the caudal fin, this condition does not occur in Pterolebias , but is present in other rivulid genera (i. e., Neofundulus Myers and Trigonectes Myers ); therefore, it does not support monophyly of the group including Rachovia , Pterolebias and Austrofundulus . Weitzman & Wourms (1967) also proposed a group including Cynolebias , Cynopoecilus Regan , Pterolebias , Rachovia , Austrofundulus , Leptolebias Myers , and Simpsonichthys de Carvalho , based on the possession of thickened rays on the anterior half of the anal fin in females. According to Parenti (1981), however, this derived condition is not present in Pterolebias .

Thomerson (1974) suggested that Pterolebias is an artificial assemblage, but provided no justification for this conclusion. In contrast, Parenti (1981) considered Pterolebias to be a monophyletic group diagnosed by the absence of an interarcual cartilage, based on examination of cleared and stained specimens of P. longipinnis and P. zonatus . However, Costa (1990) noted that the interarcual cartilage is present in Pterolebias , although very reduced, a condition later considered a synapomorphy for the genera Pterolebias and Gnatholebias (Costa, 1998a). Parenti (1981) recognized Pterolebias and Trigonectes as sister to a clade including Neofundulus , Rachovia , Austrofundulus , and Cynolebias , the latter including Terranatos , Leptolebias , Cynopoecilus , and Simpsonichthys , which were considered synonyms of Cynolebias .

Costa (1989, 1990) hypothesized Pterolebias to be the sister group of Pituna Costa based on a reduced interarcual cartilage and widened proximal radiais of the anal fin, and Pterolebias was diagnosed by the possession of eight pelvic-fin rays and a lengthened caudal fin in males. Thomerson & Taphorn (1992) criticized the employment of eight pelvic-fin rays to diagnose Pterolebias , since Rivulichthys luelingi (then considered as a synonym of P. longipinnis ) and P. hoignei may sometimes have fewer pelvic-fin rays. However, Costa (1998a) asserted the non-variability of this character state in all material examined, which is in accordance with the present study.

Costa (1998a) analyzed morphological traits, including osteology, laterosensory system, fin morphology and color patterns, and some sexual behavior patterns. This analysis indicated that Pterolebias was a paraphyletic assemblage, and consequently it was divided into four genera: Pterolebias , including P. longipinnis and P. phasianus ; Gnatholebias , including G. zonatus and G. hoignei ; Aphyolebias Costa , including A. peruensis , A. wischmanni , A. rubrocaudatus , and A. obliquus ; and Micromoema Costa , including M. xiphophora (also see Table 1, which shows the present generic placement of all species previously assigned to Pterolebias ). Pterolebias was accordingly diagnosed by an anteriorly expanded ventral tip of the autopalatine, constricted dorsal portion of metapterygoid, long process of quadrate, narrow and long basihyal, reduced number of vertebrae, rounded pectoral fin, metallic orange humeral spot, and black bars on the pectoral fin in males. A sister group relationship between Pterolebias and Gnatholebias was supported by large teeth on premaxilla and dentary laterally directed, long pelvic fins, and enlarged caudal fin with filaments on posterior margin in males. Pterolebias and Gnatholebias were placed in a clade that also includes Aphyolebias , Micromoema , Moema , Renova , Trigonectes and Neofundulus .

Subsequently, monophyly of both Pterolebias (sensu Costa, 1998a) and Gnatholebias were supported by molecular data published in two independent papers (Murphy et al., 1999; Hrbek & Larson, 1999). However, these studies contained unexpectedly different hypotheses of relationships involving Pterolebias and Gnatholebias . Murphy et al. (1999) analyzed four segments of the mitochondrial genome, generating an hypothesis based on parsimony analysis, in which Pterolebias would be the sister group to a clade including Renova , Terranatos , Gnatholebias , Micromoema , Rachovia , and Austrofundulus . Hrbek & Larson (1999) also analyzed mitochondrial DNA and found a most parsimonious tree, in which Pterolebias would be the sister group to Renova , and the clade Pterolebias plus Renova , the sister group to a clade including Terranatos , Gnatholebias , Micromoema , Rachovia , and Austrofundulus .