Distinct genetic origins of eumelanin intensity and barring patterns in cichlid fishes.

Pigment patterns are incredibly diverse across vertebrates and are shaped by multiple selective pressures from predator avoidance to mate choice. A common pattern across fishes, but for which we know little about the underlying mechanisms, is repeated melanic vertical bars. In order to understand genetic factors that modify the level or pattern of vertical barring, we generated a genetic cross of 322 F2 hybrids between two cichlid species with distinct barring patterns, Aulonocara koningsi and Metriaclima mbenjii. We identify 48 significant quantitative trait loci that underlie a series of seven phenotypes related to the relative pigmentation intensity, and four traits related to patterning of the vertical bars. We find that genomic regions that generate variation in the level of eumelanin produced are largely independent of those that control the spacing of vertical bars. Candidate genes within these intervals include novel genes and those newly-associated with vertical bars, which could affect melanophore survival, fate decisions, pigment biosynthesis, and pigment distribution. Together, this work provides insights into the regulation of pigment diversity, with direct implications for an animal's fitness and the speciation process.

Genetic basis of ecologically relevant body shape variation among four genera of cichlid fishes.

Divergence in body shape is one of the most widespread and repeated patterns of morphological variation in fishes and is associated with habitat specification and swimming mechanics. Such ecological diversification is the first stage of the explosive adaptive radiation of cichlid fishes in the East African Rift Lakes. We use two hybrid crosses of cichlids (Metriaclima sp. × Aulonocara sp. and Labidochromis sp. × Labeotropheus sp., >975 animals total) to determine the genetic basis of body shape diversification that is similar to benthic-pelagic divergence across fishes. Using a series of both linear and geometric shape measurements, we identified 34 quantitative trait loci (QTL) that underlie various aspects of body shape variation. These QTL are spread throughout the genome, each explaining 3.2-8.6% of phenotypic variation, and are largely modular. Further, QTL are distinct both between these two crosses of Lake Malawi cichlids and compared to previously identified QTL for body shape in fishes such as sticklebacks. We find that body shape is controlled by many genes of small effect. In all, we find that convergent body shape phenotypes commonly observed across fish clades are most likely due to distinct genetic and molecular mechanisms.

Morphometric and Genetic Description of Trophic Adaptations in Cichlid Fishes.

Since Darwin, biologists have sought to understand the evolution and origins of phenotypic adaptations. The skull is particularly diverse due to intense natural selection on feeding biomechanics. We investigated the genetic and molecular origins of trophic adaptation using Lake Malawi cichlids, which have undergone an exemplary evolutionary radiation. We analyzed morphological differences in the lateral and ventral head shape among an insectivore that eats by suction feeding, an obligate biting herbivore, and their F2 hybrids. We identified variation in a series of morphological traits-including mandible width, mandible length, and buccal length-that directly affect feeding kinematics and function. Using quantitative trait loci (QTL) mapping, we found that many genes of small effects influence these craniofacial adaptations. Intervals for some traits were enriched in genes related to potassium transport and sensory systems, the latter suggesting co-evolution of feeding structures and sensory adaptations for foraging. Despite these indications of co-evolution of structures, morphological traits did not show covariation. Furthermore, phenotypes largely mapped to distinct genetic intervals, suggesting that a common genetic basis does not generate coordinated changes in shape. Together, these suggest that craniofacial traits are mostly inherited as separate modules, which confers a high potential for the evolution of morphological diversity. Though these traits are not restricted by genetic pleiotropy, functional demands of feeding and sensory structures likely introduce constraints on variation. In all, we provide insights into the quantitative genetic basis of trophic adaptation, identify mechanisms that influence the direction of morphological evolution, and provide molecular inroads to craniofacial variation.

Polygenic sex determination produces modular sex polymorphism in an African cichlid fish.

For many vertebrates, a single genetic locus initiates a cascade of developmental sex differences in the gonad and throughout the organism, resulting in adults with two phenotypically distinct sexes. Species with polygenic sex determination (PSD) have multiple interacting sex determination alleles segregating within a single species, allowing for more than two genotypic sexes and scenarios where sex genotype at a given locus can be decoupled from gonadal sex. Here we investigate the effects of PSD on secondary sexual characteristics in the cichlid fish Metriaclima mbenjii, where one female (W) and one male (Y) sex determination allele interact to produce siblings with four possible sex classes: ZZXX females, ZWXX females, ZWXY females, and ZZXY males. We find that PSD in M. mbenjii produces an interplay of sex linkage and sex limitation resulting in modular variation in morphological and behavioral traits. Further, the evolution or introgression of a newly acquired sex determiner creates additional axes of phenotypic variation for varied traits, including genital morphology, craniofacial morphology, gastrointestinal morphology, and home tank behaviors. In contrast to single-locus sex determination, which broadly results in sexual dimorphism, polygenic sex determination can induce higher-order sexual polymorphism. The modularity of secondary sexual characteristics produced by PSD provides context for understanding the evolutionary causes and consequences of maintenance, gain, or loss of sex determination alleles in populations.

Taxonomic revisions of Altigena laticeps and A. lippa (Cyprinidae: Labeoninae) from the Mekong River Basin.

Altigena laticeps, previously considered a junior synonym of A. lippa, is revalidated and re-described based on morphological examinations of type and non-type material. This species, found in the Upper Mekong River basin in China, can be distinguished from A. lippa based on higher numbers of lateral-line scales (40-42 vs. 34-39), predorsal scales (14-16 vs. 9-12), and circumpeduncular scales (20 vs. 16). Altigena lippa, from the Lower Mekong River basin in Lao PDR, Myanmar, Thailand, and Vietnam is also re-described. Four species of Altigena are herein recognized in the Mekong River basin: A. elegans, A. laticeps, A. lippa, and A. yunnanensis.

Papers on fishes of Asia, including those presented at international conferences of the Asian Society of Ichthyologists in Taipei, Taiwan in 2016, and in Ho Chi Minh City, Vietnam in 2017 (Cover Copytight page).

(Cover Copytight page).

Papers on fishes of Asia, including those presented at international conferences of the Asian Society of Ichthyologists in Taipei, Taiwan in 2016, and in Ho Chi Minh City, Vietnam in 2017 (Table of Contents).

(Table of Contents).

Preface.

The Asian Society of Ichthyologists (ASI) was established in February 2014 in Penang, Malaysia following organizational meetings in 2012 in Chiang Mai, Thailand and in 2013 in Bandar Seri Begawan, Brunei.

A new species of Lobocheilos (Teleostei: Cyprinidae) from East Kalimantan, Indonesian Borneo.

Lobocheilos aurolineatus, new species, is described from the Mahakam River basin in East Kalimantan, Indonesian Borneo. It is distinguished from all other species of Lobocheilos except for L. ixocheilos and L. tenura in having one pair of barbels (maxillary) and by the presence of a broad, black midlateral stripe, approximately ¾ scale height in thickness, extending from the operculum to the caudal-peduncle base. Lobocheilos aurolineatus differs from both species in possessing a thin cream to yellow stripe on the anterior ⅔ of the flank, separating the black midlateral stripe from the brown dorso-lateral scales, and by a smaller mouth width (23.5-29.9% head length in L. aurolineatus vs. 32.1-45.0% and 34.4-46.4% head length in L. ixocheilos and L. tenura, respectively).

Preference for conspecifics evolves earlier in males than females in a sexually dimorphic radiation of fishes.

Speciation by sexual selection is generally modeled as the coevolution of female preferences and elaborate male ornaments leading to behavioral (sexual) reproductive isolation. One prediction of these models is that female preference for conspecific males should evolve earlier than male preference for conspecific females in sexually dimorphic species with male ornaments. We tested that prediction in darters, a diverse group of freshwater fishes with sexually dimorphic ornamentation. Focusing on the earliest stages of divergence, we tested preference for conspecific mates in males and females of seven closely related species pairs. Contrary to expectation, male preference for conspecific females was significantly greater than female preference for conspecific males. Males in four of the 14 species significantly preferred conspecific females; whereas, females in no species significantly preferred conspecific males. Relationships between the strength of preference for conspecifics and genetic distance revealed no difference in slope between males and females, but a significant difference in intercept, also suggesting that male preference evolves earlier than females'. Our results are consistent with other recent studies in darters and suggest that the coevolution of female preferences and male ornaments may not best explain the earliest stages of behavioral isolation in this lineage.

Comment on "On Gonorynchus, Gonorhynchus, Gonorinchus, Gonorhinchus, and Gonorrhynchus, and some other names of labeonine fishes (Teleostei: Gonorhynchidae and Cyprinidae)" by Kottelat (2016).

Kottelat (2016) noted that 'Gonorhynchus McClelland, 1838,' the name used for a South Asian cyprinid genus recognized by Yang et al. (2012) and revised by Ciccotto & Page (2016), does not exist or is a junior homonym of Gonorhynchus Cuvier, 1816. He further noted that Tariqilabeo Mirza & Saboohi, 1990 is the valid genus name for the species recognized in Gonorhynchus by Yang et al. (2012) and by Ciccotto & Page (2016). Kottelat also rejected the placement of Epalzeorhynchus bicornis Wu, 1977 in this genus by Yang et al. (2012), instead placing it in the monotypic Akrokolioplax Zhang & Kottelat, 2006, and questioned the validity of the designation of the neotype of Cyprinus latius Hamilton, 1822 by Ciccotto & Page (2016). While we are in agreement with the validity of Tariqilabeo, we disagree with the use of Akrokolioplax and defend the designation of the neotype for C. latius.

Revised diagnosis of the genus Gonorhynchus McClelland (Teleostei: Cyprinidae: Labeonini) with redescription of G. latius (Hamilton) and revalidation of G. wattanah (Sykes).

A new diagnosis of the genus Gonorhynchus McClelland 1838 from South Asia is proposed. Seven species are contained in the genus: G. latius (Hamilton 1822), G. diplochilus (Heckel 1838), G. wattanah (Sykes 1839), G. macmahoni (Zugmayer 1912), G. burmanicus (Hora 1936), G. bicornis (Wu 1977), and G. periyarensis (Menon & Jacob 1996). Gonorhynchus latius, a senior synonym of the type species G. brevis M'Clelland 1839 is redescribed. Crossocheilus gohama (M'Clelland 1839) and Crossochilus rostratus Günther 1868 are considered junior synonyms of G. latius, and a neotype is designated for G. latius. Gonorhynchus wattanah (Sykes 1839) from the Krishna and Godavari River basins in western India is revalidated and redescribed with the designation of a neotype. Akrokolioplax Zhang & Kottelat 2006 is a junior synonym of Gonorhynchus.

The ecological drivers of nuptial color evolution in darters (Percidae: Etheostomatinae).

Closely related animal lineages often vary in male coloration, and ecological selection is hypothesized to shape this variation. The role of ecological selection in inhibiting male color has been documented extensively at the population level, but relatively few studies have investigated the evolution of male coloration across a clade of closely related species. Darters are a diverse group of fishes that vary in the presence of elaborate male nuptial coloration, with some species exhibiting vivid color patterns and others mostly or entirely achromatic. We used phylogenetic logistic regression to test for correlations between the presence/absence of color traits across darter species and the ecological conditions in which these species occur. Environmental variables were correlated with the presence of nuptial color in darters with colorful species tending to inhabit environments that would support fewer predators and potentially transmit a broader spectrum of natural light compared to species lacking male coloration. We also tested the color preferences of a common darter predator, largemouth bass, and found that it exhibits a strong preference for red, providing further evidence of predation as a source of selection on color evolution in darters. Ecological selection therefore appears to be an important factor in dictating the presence or absence of male coloration in this group of fishes.