Male Anal Fin Research Articles

A new species of cloud fish of the genus Hypsolebias from Northeast Brazil (Cyprinodontiformes: Rivulidae)

Abstract A new species of cloud fish of the genus Hypsolebias is described from a temporary pool in the rio Trairi basin, Rio Grande do Norte State, Brazil. It is the first record of the genus Hypsolebias for the basin. The new speciesbelongs to the H. flammeus species-group, which is composed of the species H. alternatus, H. brunoi, H. delucai, H. fasciatus, H. longignatus, H. marginatus, H. multiradiatus, and H. flammeus. The new species differs from all other species of the group, except H. flammeus, H. multiradiatus,and H. brunoi, by male color pattern and the presence of a metallic blue sheen surrounding the black spots of females. It differs from H. flammeus, H. multiradiatus and H. brunoi by dorsal and anal fin shape (both rounded vs. pointed) and by the orientation of the reddish-brown bars on the body and anal fin of males (diagonal vs. vertical). The new species differs from its congeners of Northeast Brazil mainly by the higher number of dorsal fin rays in males and the higher number of scales in the longitudinal series.

Does Asymmetrical Gonopodium Morphology Predict Lateralized Behavior in the Fish Xenophallus umbratilis?

Why bilaterally symmetrical organisms express handedness remains an important question in evolutionary biology. In some species, anatomical asymmetries have evolved that accompany behavioral handedness, yet we know remarkably little about causal links between asymmetric morphological traits and behavior. Here, we explore if a dextral or sinistral orientation of the male intromittent organ predicts side preferences in male behaviors. Our study addresses this question in the Costa Rican livebearing fish, Xenophallus umbratilis. This fish has a bilaterally symmetrical body plan, with one exception—the male anal fin (gonopodium), used to inseminate females, terminates with a distinct left- or right-handed corkscrew morphology. We used a detour assay to test males for side biases in approach behavior when exposed to four different stimuli (predator, potential mate, novel object, empty tank control). We found that left morph males preferred using their right eye to view potential mates, predators, and the control, and that right morph males preferred to use their left eye to view potential mates and predators, and their right eye to view the control. Males of both morphs displayed no eye bias when approaching the novel object. Our results suggest that there is a strong link between behavior and gonopodium orientation, with right and left morph males responding with opposite directional behaviors when presented with the same stimuli. This presents the intriguing possibility that mating preferences—in this case constrained by gonopodial morphology—could be driving lateralized decision making in a variety of non-mating behaviors.

Sharply Angled Lateral Curvature Modification in Anal Fin of a Viviparous Fish, Xenotoca variata (Cyprinodontiformes: Goodeidae).

Almost all viviparous species possess male external genitalia; for example, the mammalian penis is an intromittent organ. Some live-bearing bony fish use their anal fins to assist in mating and internal fertilization. We previously reported a male-specific asymmetric curvature at the posterior end of the anal fin in Xenotoca eiseni, a viviparous fish of the family Goodeidae. However, three other goodeid species, Xenotoca melanosoma, Zoogoneticus quitzeoensis, and Chapalichthys pardalis, examined in that study possessed lesser anal fin curvature modifications as compared to those in the anal fin of X. eiseni. Here, we report the second case of acute-angled curvature modification of the male anal fin in the family Goodeidae. We obtained a dead specimen of the goodeid species Xenotoca variata from a city zoo in Japan, and the morphological and histological analyses indicated an acute-angled asymmetric curvature of the posterior end of the anal fin in X. variata, similar to that observed in X. eiseni in the previous study. However, in our previous report, obtuse-angled modification was only observed in one other Xenotoca species, X. melanosoma, and two species belonging to other genera, Z. quitzeoensis and C. pardalis. Therefore, our findings suggest that the acute-angled curvature in the male anal fin has been developed in the genus Xenotoca.

The direction of genital asymmetry is expressed stochastically in internally fertilizing anablepid fishes.

Animal genitalia vary considerably across taxa, with divergence in many morphological traits, including striking departures from symmetry. Different mechanisms have been proposed to explain this diversity, mostly assuming that at least some of the phenotypic variation is heritable. However, heritability of the direction of genital asymmetry has been rarely determined. Anablepidae are internally fertilizing fish where the anal fin of males has been modified into an intromittent organ that transfers sperm into the gonopore of females. Males of anablepid fishes exhibit asymmetric genitalia, and both left- and right-sided individuals are commonly found at similar proportions within populations (i.e. antisymmetry). Although this polymorphism was described over a century ago, there have been no attempts to determine if genital asymmetry has a genetic basis and whether the different morphs are accumulating genetic differences, as might be expected since in some species females have also asymmetric gonopores and thereby can only be fertilized by compatible asymmetric males. We address this issue by combining breeding experiments with genome-wide data (ddRAD markers) in representative species of the two anablepid genera with asymmetric genitalia: Anableps and Jenynsia. Breeding experiments showed that all offspring were asymmetric, but their morphotype (i.e. right- or left-sided) was independent of parental morphotype, implying that the direction of asymmetry does not have a strong genetic component. Consistent with this conclusion, association analyses based on approximately 25 000 SNPs did not identify markers significantly associated with the direction of genital asymmetry and there was no evidence of population structure between left- and right-sided individuals. These results suggest that the direction of genital asymmetry in anablepid fishes might be stochastic, a commonly observed pattern in species with antisymmetry in morphological traits.

A new species of Astyanax Baird amp; Girard (Characiformes: Characidae) from western Chapada Diamantina, Bahia, Brazil.

A new species of Astyanax from the upper rio Paraguaçu basin, Chapada Diamantina, Bahia, Brazil, is described. Astyanax sincora shares characters currently used to define the Astyanax scabripinnis species complex, as highest body depth approximately at vertical through pectoral-fin midlength and a low number of branched anal-fin rays (13-17). It differs from its congeners by a combination of characters, including eight branched dorsal-fin rays, six branched pelvic-fin rays, presence of bony hooks in pectoral and anal fins of males, dark midlateral line or stripe initiating posteriorly to the vertically elongate humeral blotch, and by the presence of 30-35 scales in the median longitudinal series. The generic positioning of the new species and some polymorphic morphological characters in Astyanax are briefly discussed. The degree of completeness of the lateral line in Hyphessobrycon balbus is discussed. [Species Zoobank registration: urn:lsid:zoobank.org:pub:D708FE7E-3FB5-4729-B438-779717F7ED1A].

Asymmetry in genitalia is in sync with lateralized mating behavior but not with the lateralization of other behaviors.

Asymmetries in bilateral organisms attract a lot of curiosity given that they are conspicuous departures from the norm. They allow the investigation of the integration at different levels of biological organization. Here we study whether and how behavioral and asymmetrical anatomical traits co-evolved and work together. We ask if asymmetry is determined locally for each trait or at a whole individual level in a species bearing conspicuous asymmetrical genitalia. Asymmetric genitalia evolved in many species; however, in most cases the direction of asymmetry is fixed. Therefore, it has been rarely determined if there is an association between the direction of asymmetry in genitalia and other traits. In onesided livebearer fish of the genus Jenynsia (Cyprinodontiformes, Anablepidae), the anal fin of males is modified into a gonopodium, an intromittent organ that serves to inseminate females. The gonopodium shows a conspicuous asymmetry, with its tip bending either to the left or the right. By surveying 13 natural populations of Jenynsia lineata, we found that both genital morphs are equally common in wild populations. In a series of experiments in a laboratory population, we discovered asymmetry and lateralization for multiple other traits; yet, the degree of integration varied highly among them. Lateralization in exploratory behavior in response to different stimuli was not associated with genital morphology. Interestingly, the direction of genital asymmetry was positively correlated with sidedness of mating preference and the number of neuromasts in the lateral line. This suggests integration of functionally linked asymmetric traits; however, there is no evidence that asymmetry is determined at the whole individual level in our study species.

The rise of internal fertilization in the Anablepidae (Teleostei, Cyprinodontiformes): two new genera and species from the Miocene of Tucumán, Argentina

AbstractTwo new genera and species of Cyprinodontiformes from the Miocene of Tucumán, Argentina, are described: Tucmanableps cionei and Sachajenynsia pacha. Both exhibit sexual dimorphism, indicated by the modification of the male anal fin into an intromittent organ; tricuspid teeth in the jaws; abdominal pelvic fins and other features that demonstrate a relationship with the family Anablepidae. Males of Sachajenynsia pacha gen. et sp. nov. present modifications of the anal fin, herein interpreted as an incipient gonopodium, whereas the anal fin of Tucmanableps cionei gen. et sp. nov. is modified into a complex gonopodium with a median distal plate, which is unique among the Anablepidae. In extant genera of the family, modification of the anal fin into an intromittent organ is related to internal fertilization; this condition is inferred for S. pacha but was clearly the reproductive mode of T. cionei. In our phylogenetic analysis, S. pacha is recovered as the sister group of all anablepids with evident internal fertilization, while T. cionei forms a clade with Anableps species. The occurrence of two new anablepid genera showing distinct and unique morphologies suggests that the fossil diversity of the Anablepidae may be higher than the extant one. Also, the new taxa were found in open lake deposits with coastal and inner lake sediments of the Río Salí Formation associated with the Miocene Entrerrian–Paranense Marine Ingression, supporting the idea that coastal environments and brackish waters are related to the generic diversification of the Anablepidae, as was suggested for the species of Jenynsia.

Two new seasonal killifishes of the Austrolebias adloffi group from the Lagoa dos Patos basin, southern Brazil (Cyprinodontiformes: Aplocheilidae)

Morphological characters and phylogenetic trees generated by analyses of a segment of the mitochondrial gene cytochrome b support two new species from the Lagoa dos Patos basin, in southern Brazil. The phylogenetic analyses indicate that the two new species are each other’s respective closest relatives among species of A. adloffi group. The clade comprising the two new species is supported as being more closely related to A. adloffi than to A. nigrofasciatus that is endemic to the same area. Austrolebias pelotapes Costa & Cheffe n. sp. is distinguished from all other species of the A. adloffi group by having the urogenital papilla base attached by a thin membrane to the anterior margin of the anal fin in males; it is endemic to an area containing temporary pools and swamps associated to small streams tributaries to the northern margin of the São Gonçalo channel, just about 10 km from the area inhabited by A. nigrofasciatus. Austrolebias pongondo Costa & Cheffe n. sp., from temporary pools and swamps in the floodplains south of the São Gonçalo channel, and A. pelotapes are distinguished from all other species of the A. adloffi group by a combination of character states, including the presence of a transverse row of small spots on the middle portion of the dorsal fin in males, unpaired fins with a single row of light blue spots on their basal portion in males, a distinctive dark grey zone on the posterior portion of the dorsal and anal fins, and caudal peduncle in males predominantly dark brownish grey or dark grey to black, with narrow vertical light blue zones.

Three new species of the killifish genus Melanorivulus from the central Brazilian Cerrado savanna (Cyprinodontiformes, Aplocheilidae).

Three new species are described from the Neotropical region comprising the Cerrado savannas of the central Brazilian plateaus, which is among the most important biodiversity centres in the world. These species are considered closely related to Melanorivulus dapazi from the same region, with which they share the presence of a rudimentary interarcual cartilage and a dark reddish brown distal margin on the male anal fin. The group comprising Melanorivulus dapazi and the three new species is here named as the Melanorivulus dapazi species group. Melanorivulus ignescens sp. n., from the upper Rio Araguaia basin, is distinguished from all other species of the Melanorivulus dapazi group by the anal-fin colour pattern in males; Melanorivulus flavipinnis sp. n. and Melanorivulus regularis sp. n. from the Rio Paraguai basin are distinguished from all other congeners of the Melanorivulus dapazi group by the colour pattern of the caudal fin and number of scales in the longitudinal series, respectively. All the new species are further unambiguously diagnosed by unique combinations of morphological characters, including meristic and morphometric data, and colour patterns. This study reinforces the importance of using live colour patterns to diagnose species and species groups of the genus Melanorivulus, but also indicates that osteological characters may be informative for species diagnosis. This study confirms the high diversity of species of Melanorivulus in the central Brazilian Cerrado plateaus already reported in previous studies, indicating that endemic species are often restricted to short segments of a single river drainage.

Contribución al estudio de los peces Cheirodontinae (Familia Characidae) de Costa Rica y Panamá. Géneros Compsura y Pseudocheirodon

The present paper defines the taxonomic position of Compsura gorgonae. The genus Pseudocheirodon is maintained tentatively distinct from Cheirodon. Compsura gorgonae is distinguished from Pseudocheirodon affinis by the presence of spines on the anal fin of males, fewer maxillary teeth and longer maxillary bone. A key is pravided to distinguish the genera Compsura, Cheirodon, Odontostilbe and Pseudocheirodon. Over 2,800 specimens from 54 Panamanian and Costa Rican collections were utilized. The number of lateral line pores of C. gorgonae increases in a westward direction and this may be related to the shorter rivers of steeper gradient and more turbid waters in the rainy season in western Panama. The number of lateral line pares of P. affinis , also quite variable (7-3 3), showed a random rather than clinal variation. Both the above species, when sympatric, exhibit nearly the same average number of lateral line pares, which suggests an adaptation to the same enviranmental factors. The length of the maxillary bone of C. gorgondo decreased from east to west, whereas in P. affinis the situation was reversed. No hypothesis could be offered for this latter relationship.

A Middle Triassic stem-neopterygian fish from China sheds new light on the peltopleuriform phylogeny and internal fertilization

Internal fertilization and viviparity are easily observed and well studied in living neopterygian fishes (14 teleostean families), but they are difficult to identify in extinct taxa due to the limitation of the fossil record. The Peltopleuriformes from the Middle to Late Triassic of Europe and South China are a stem group of Neopterygii that may have first evolved internal fertilization and viviparity in this clade because they show a highly modified anal fin in presumed males resembling the intromittent organ in living viviparous teleosts. Until recently, Peltopleurus lissocephalus and P. rugosus from the Ladinian/Anisian boundary (~242Ma) of Monte San Giorgio area in Switzerland and Italy represent the oldest record of Peltopleuriformes, and the phylogenetic interrelationships of this group remain controversial. Here, we report the discovery of a new peltopleuriform, Peltopleurus nitidus sp. nov., based on eleven well-preserved specimens from the early Middle Triassic (Pelsonian, Anisian, ~244Ma) of Luoping, eastern Yunnan, China. The discovery documents the oldest convincing peltopleuriform, extending the geological range of this clade by proximately two million years. Results of the phylogenetic analysis recover P. nitidus at the base of Peltopleuridae, and provide robust support for the sister-group relationships of Peltopleuridae with Thoracopteridae within the Peltopleuriformes. The male anal fin of P. nitidus shows a primitive condition unknown in other peltopleuriforms. Comparative studies of the male anal fin in P. nitidus and other peltopleuriforms shed new light on the internal fertilization in this group.

Comparative morphology and classification of South American cynopoeciline killifishes (Cyprinodontiformes: Aplocheilidae), with notes on family-group names used for aplocheiloids

A comparative morphological study involving all cynopoeciline killifishes indicates that Leptolebias marmoratus is more closely related to species of the genera Campellolebias and Cynopoecilus than to other species of Leptolebias, and that Mucurilebias leitaoi is the sister group of a clade comprising all other cynopoecilines. Leptopanchax, new genus, is described to place species that share urogenital papilla in males separated from the anal-fin origin by broad interspace, basal portion of the urogenital papilla in males not forming a pronounced wide structure, absence of thickened tissue on the basal portion of the anal fin in males, caudal fin oval and symmetrical in males, anterior proximal radials of the anal fin not placed in close proximity in males, presence of a broad iridescent golden stripe on the distal zone of the dorsal fin in males, and caudal fin with vermiculate dark red marks in males. Poecilopanchax, new subgenus of Cynopoecilus, is diagnosed by having the basihyal narrow, about rectangular, the interarcual element of the dorsal branchial arch ossified, the uncinate process of the third epibranchial distinctively widened, a long filamentous ray on the tip of the anal fin in males, caudal fin lanceolate in males, dark bars on the flank in females, branchiostegal region with intense red pigmentation in males, a brownish red stripe on the basal portion of the dorsal fin in males, and dark red marks extending to the antero-distal margin of the dorsal fin in males. This study follows an old classificatory scheme in which all aplocheiloids are placed in a single family, the Aplocheilidae.

Comparative morphology of bony hooks of the anal and pelvic fin in six neotropical characid fishes (Ostariophysi: Characiformes)

The morphology of bony hooks on anal-fin and pelvic-fin rays in six neotropical characid fish (Astyanax fasciatus, A. lacustris, Hyphessobrycon bifasciatus, H. itaparicensis, Compsura heterura and Serrapinnus heterodon) representing different reproductive modes (inseminating and externally fertilizing) was analysed with a particular focus on the form, distribution, development and orientation of bony hooks of the male anal-fin and pelvic-fin rays.When present bony hooks of the anal-fin and pelvic-fin rays in adult males represented a permanent structure and its development is likely closely related to the reproductive phase. Bony hooks were found on anal-fin and pelvic-fin rays in A. lacustris, C. heterura, H. itaparicensis and S. heterodon whereas A. fasciatus and H. bifasciatus showed bony hooks only on the anal-fin rays. The absence of pelvic-fin rays may be related to hormonal factors and linked to the courtship behavior. Despite their reproductive mode, the bony hooks on anal-fin and pelvic-fin rays were positioned along the posterolateral border. On pelvic-fin rays, the distal tips of the bony hooks were directed towards the anterior fin ray border in inseminating or non-inseminating species. On the anal-fin rays, the distal tips of the hooks were morphologically different in inseminating and externally fertilizing species. Inseminating characids such as C. heterura exhibited a distinct morphological arrangement of hooks exclusively present on pelvic-fin rays similar to the structures found in inseminating species. The number of bony hooks on anal-fin rays was higher only among the Cheirodontinae such as C. heterura and S. heterodon regardless of their reproductive mode. Apparently the presence and morphology of bony hooks on fin rays represent an important data source for phylogenetic, reproductive and behavioral studies of characid fish.

Molecular phylogeny and evolution of internal fertilization in South American seasonal cynopoeciline killifishes

Internal fertilization is a widespread mode of reproduction in chondrichthyans and tetrapods, but uncommon in actinopterygian fishes. In killifishes of the suborder Aplocheiloidei, internal fertilization is restricted to two genera, Campellolebias and Cynopoecilus, both containing species adapted to life in seasonal pools of subtropical South America and exhibiting elaborated inseminating structures. Phylogenetic studies involving these genera are scarce and limited to morphological characters and fragments of mitochondrial DNA sequences available for a few taxa, providing incongruent results and thus impeding hypotheses on the evolution of insemination and related morphological traits. We analyzed three nuclear loci (GLYT1, ENC1, Rho) for 13 aplocheiloid taxa obtaining the first well-supported phylogeny for cynopoecilines, thus providing a significant background to interpret evolutionary changes within the group. Like in killifishes of the suborder Cyprinodontoidei, the evolution of internal fertilization in aplocheiloids is associated with deep changes in the structure of male anal fin. The phylogenetic analyses indicate that internal fertilization corresponds to a single evolutionary event during the evolution of aplocheiloid killifishes. The analyses also indicate that male specialized muscle characters, comprising a muscular ejaculatory pump in the urogenital region and hypertrophied inclinatores and depressores anales, arose in the ancestor of the clade comprising Campellolebias and Cynopoecilus. On the other hand, anal fin specialized structures including the male inseminating tube of Campellolebias and the male inseminating fan of Cynopoecilus evolved independently in each genus.

A new species of Hemigrammus Gill, 1858 (Characiformes: Characidae) from the central and western Amazon and rio Paraná-Paraguai basins.

A new species of Hemigrammus is described from the middle rio Solimões/Amazonas and tributaries, upper and middle rio Madeira, and rio Paraná-Paraguai basins in Brazil and Paraguay. The new species is most similar among congeners with Hemigrammus marginatus, with which it shares similar caudal-fin pigmentation pattern. The new species can be distinguished from Hemigrammus marginatus by possessing two conspicuous dark patches of pigmentation on caudal fin, occupying most of caudal-fin lobes, except the tips, by having two dark narrow stripes along anal-fin base, and by possessing 5-8 pored lateral line scales. The new species differs from Hyphessobrycon diancistrus, which is similar in color pattern and general body shape, by the presence of small scales on caudal-fin lobes, occupying approximately its basal third, by the presence of two narrow stripes along anal fin base, and by the absence of bony hooks on analfin in mature males. The occurrence of the new species in both Amazon and rio Paraná-Paraguai basins is discussed in order to clarify and expand recent discussions on the biogeographical relationships between both river systems.

A new genus of miniature cynolebiasine from the Atlantic Forest and alternative biogeographical explanations for seasonal killifish distribution patterns in South America (Cyprinodontiformes: Rivulidae)

The analysis of 78 morphological characters for 16 species representing all the lineages of the tribe Cynopoecilini and three out-groups, indicates that the incertae sedis miniature species ‘Leptolebias’ leitaoi Cruz & Peixoto is the sister group of a clade comprising the genera Leptolebias, Campellolebias, and Cynopoecilus, consequently recognised as the only member of a new genus. Mucurilebias gen. nov. is diagnosed by seven autapomorphies: eye occupying great part of head side, low number of caudal-fin rays (21), distal portion of epural much broader than distal portion of parhypural, an oblique red bar through opercle in both sexes, isthmus bright red in males, a white stripe on the distal margin of the dorsal fin in males, and a red stripe on the distal margin of the anal fin in males. Mucurilebias leitaoi is an endangered seasonal species endemic to the Mucuri river basin. The biogeographical analysis of genera of the subfamily Cynolebiasinae using a dispersal-vicariance, event-based parsimony approach indicates that distribution of South American killifishes may be broadly shaped by dispersal events. The analysis supports south-eastern Brazilian coastal plains as the centre of dispersal for cynolebiasine killifishes. Alternative biogeographical explanations are compared and possible dispersal routes and means of dispersal are discussed.

Rhodeus albomarginatus, a new bitterling (Teleostei: Cyprinidae: Acheilognathinae) from China.

Rhodeus albomarginatus, new species, is described from the Lvjiang River, a tributary flowing into Poyang Lake of Yangtze River basin, in Anhui Province, China. It is distinguished from all congeneric species by unique combination of characters: branched dorsal-fin rays 10; branched anal-fin rays 10-11; longest simple rays of dorsal and anal fins strong and stiff, distally segmented; pelvic fin rays i 6; longitudinal scale series 34-36; transverse scale series 11; pored scales 4-7; vertebrae 33-34; colour pattern of adult males (iris black, belly reddish-orange, central part of caudal fin red, dorsal and anal fins of males edged with white margin).

Altered reproductive behaviours in male mosquitofish living downstream from a sewage treatment plant

Freshwater environments are common repositories for the discharge of large volumes of domestic and industrial waste, particularly through wastewater effluent. One common group of chemical pollutants present in wastewater are endocrine disrupting chemicals (EDCs), which can induce morphological and behavioural changes in aquatic organisms. The aim of this study was to compare the reproductive behaviour and morphology of a freshwater fish, the mosquitofish (Gambusia holbrooki), collected from two sites (wastewater treatment plant (WWTP) and a putative pristine site). The mosquitofish is a sexually dimorphic livebearer with a coercive mating system. Males inseminate females using their modified anal fin as an intromittent organ. Despite this, females are able to exert some control over the success of male mating attempts by selectively associating with, or avoiding, certain males over others. Using standard laboratory assays of reproductive behaviour, we found that mosquitofish males living in close proximity to WWTP showed increased mating activity compared to those inhabiting a pristine site. More specifically, during behavioural trials in which males were allowed to interact with females separated by a transparent divider, we found that WWTP-males spent more time associating with females. Concordant with this, when males and females were subsequently allowed to interact freely, WWTP-males also spent more time chasing and orienting towards the females. As a result, females from both sites showed more interest towards the WWTP-site males. Male anal fin morphology, however, did not differ between sites. Our study illustrates that lifetime exposure to WWTP-effluents can greatly affect male behaviour. The results underscore the importance of behaviour as a potential tool for investigating unknown contaminants in the environment.

Retinoic Acid Is Involved in the Metamorphosis of the Anal Fin into an Intromittent Organ, the Gonopodium, in the Green Swordtail (Xiphophorus hellerii)

In poeciliid fish the male anal fin has been transformed into a gonopodium, an intromittent organ required for internal fertilization. Elevated testosterone levels induce metamorphosis of a subset of anal fin rays to grow and form the specialized terminal structures of the gonopodium. The molecular mechanisms underlying these processes are largely unknown. Here, we investigated whether retinoic acid (RA) signaling is involved in gonopodium development in the swordtail Xiphophorus hellerii. We showed that aldh1a2, a RA synthesizing enzyme, and the RA receptors, rar-ga and rar-gb, are expressed in anal fins during metamorphosis. aldh1a2 expression is regulated by testosterone in a concentration-dependent manner and is up-regulated in both hormone-induced and naturally developing gonopodia. Androgen receptor (ar), a putative regulator of gonopodial development, is co-expressed with aldh1a2 and the RA receptors in gonopodial rays. Importantly, experimental increase of RA signaling promoted growth of the gonopodium and increased the number of new segments. Based on gene expression analyses and pharmacological manipulation of gonopodium development, we show that the RA signaling pathway is activated in response to androgen signaling and promotes fin ray growth and development during the metamorphosis of the anal fin into the gonopodium.

Species limits and phylogenetic relationships of red-finned cryptic species of the seasonal killifish genusHypsolebiasfrom the Brazilian semi-arid Caatinga (Teleostei: Cyprinodontiformes: Rivulidae)

Members of the Hypsolebias antenori species group comprise a diverse clade of morphologically similar seasonal killifishes occurring in a vast region of the semi-arid savannah of northeastern Brazil. The present paper focuses on an assemblage of three allopatric cryptic species (H. antenori from isolated coastal river drainages, Hypsolebias igneus from the São Francisco River basin and Hypsolebias coamazonicus sp. nov. from the Parnaíba River basin) sharing almost identical colour patterns, including the presence of an orangish red anal fin in males, thus herein named as the red-finned assemblage. A tree-based approach using mt-DNA (cytochrome b) supports delimitation of all three species, but indicates that the red-finned assemblage is paraphyletic – H. igneus and H. coamazonicus are closely related to Hypsolebias nudiorbitatus, whereas H. antenori is the sister group to a clade comprising all 13 species of the H. antenori group included in the analysis. Morphological characters are useful to diagnose species, but are not informative for most clades highly supported by molecular data. H. coamazonicus is distinguished from all other congeners by the possession of a dark grey or black stripe on the dorsal fin in males. The basal position of H. antenori is related to uplift episodes involving the Araripe-Borborema plateau during the Miocene, which isolated the coastal area inhabited by H. antenori from the remaining areas of the Caatinga. The sister group relationship between H. igneus and H. coamazonicus is attributed to a past connection between the São Francisco and Paranaíba River until the Tertiary.