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Sexual dimorphism in species of Schistura (Teleostei: Nemacheilidae) from the Mae Khlong basin and peninsular Thailand
Abstract
Sexually dimorphic characteristics are described for four species of Schistura from the Mae Khlong basin and peninsular Thailand. Males of S. mahnerti have a suborbital flap and rows of unculi on the upper surfaces of the pectoral-fin rays. Females of S. mahnerti have a suborbital groove. None of the morphological measurements differ significantly between males and females of S. mahnerti. In the other three species, S. aurantiaca, S. cf. aurantiaca, and S. sexcauda, all indi-viduals lack the flap or groove, but most males have a conspicuous black botch on the procurrent rays of the upper lobe of the caudal fin, a feature absent in most females. Some morphometric characteristics vary between sexes of these spe-cies. Sexually dimorphic traits presumably have a function related to reproduction; however, little is known about repro-duction in Schistura, and variation in morphology in relation to habitat or other environmental factors has not been studied.
... Even though the fin models do not mimic any fish species in particular, their geometries can be compared to caudal fins with low aspect ratios (AR=0.84 for shape A 1 , 1.03 for shape A 2 , 1.67 for shape B and 1.1 for shape C). Examples include the Schistura genus, the Oryzias genus, the zebrafish (Danio rerio) and the platy fish (Xiphophorus maculatus), as shown in figure 3 (Sambilay 2005;Offen et al. 2008;Parichy et al. 2009;Naruse et al. 2011;Plongsesthee et al. 2012;Bohlen et al. 2016;Kottelat 2017). ...
We address the fluid-structure interaction of flexible fin models oscillated in a water flow. Here, we investigate in particular the dependence of hydrodynamic force distributions on fin geometry and flapping frequency. For this purpose, we employ state-of-the-art techniques in pressure evaluation to describe fluid force maps with high temporal and spatial resolution on the deforming surfaces of the hydrofoils. Particle tracking velocimetry (PTV) is used to measure the 3D fluid velocity field, and the hydrodynamic stress tensor is subsequently calculated based on the Navier-Stokes equation. The shape and kinematics of the fin-like foils are linked to their ability to generate propulsive thrust efficiently, as well as the accumulation of external contact forces and the resulting internal tension throughout a flapping cycle.
... Even though the n models do not mimic any sh species in particular, their geometries can be compared to caudal ns with low aspect ratios (AR=0.84 for shape A 1 , 1.03 for shape A 2 , 1.67 for shape B and 1.1 for shape C). Examples include the Schistura genus, the Oryzias genus, the zebrash (Danio rerio) and the platy sh (Xiphophorus maculatus), as shown in gure 3 (Sambilay 2005;Oen et al. 2008;Parichy et al. 2009;Naruse et al. 2011;Plongsesthee et al. 2012;Bohlen et al. 2016;Kottelat 2017). ...
We address the fluid-structure interaction of flexible fin models oscillated in a water flow. Here, we investigate in particular the dependence of hydrodynamic force distributions on fin geometry and flapping frequency. For this purpose, we employ state-of-the-art techniques in pressure evaluation to describe fluid force maps with high temporal and spatial resolution on the deforming surfaces of the hydrofoils. Particle tracking velocimetry (PTV) is used to measure the 3D fluid velocity field, and the hydrodynamic stress tensor is subsequently calculated based on the Navier-Stokes equation. The shape and kinematics of the fin-like foils are linked to their ability to generate propulsive thrust effciently, as well as the accumulation of external contact forces and the resulting internal tension throughout a flapping cycle.
Schistura crocotula, a new species, is described from Khanan River, Prachuap Khiri Khan Province, southern Thailand. It is distinguished from other species of Schistura in Southeast Asia by a depressed head; 6-11 dark brown bars against an orange background; the first bar is the widest, two bars are under dorsal fin; interspaces are often indistinct on posterior part of body; a thick black bar at the base of the caudal fin.
A new nemacheiline fish, Schistura fasciata sp. nov. is described here from Barak River (Brahmaputra Drainage) of Manipur, India. The species is characterized by 11-13 dark brown transverse bars on the flank, moderately high adipose crest on dorsal and ventral side of caudal peduncle, three prominent dark spots at the base of dorsal fin, dorsal fin with 8.5 branched rays and an incomplete lateral line.
The aim of this study was to gain knowledge on the gonad morphology and to determine the stages of gonad maturation in Auchenoglanis occidentalis (Cuvier and Valenciennes), based on macroscopic and histological procedures. A total of 800 samples, of which 398 were females, 399 males and 3 with unidentified sex were examined between November 2005 and December 2008. The samples ranged in total length from 6.60 to 33.00 cm with a mean of 19.51±4.50SD and from 2.26 to 462.90 g total weight with a mean of 100.05±70.09 SD. In females, mean ovary weight was 2.74±0.23 SE, mean left ovary length 3.70±0.08 SE, mean left ovary width 0.59±0.03 SE, mean right ovary length 3.65±0.08 SE and mean right ovary width 0.57±0.02 SE. In males, mean testis weight was 0.17±0.03 SE, mean left testis length 2.75±0.06 SE, mean left testis width 0.20±0.01 SE, mean right testis length 2.74±0.06 SE and mean testis width 0.19±0.01SE. This shows that in both sexes, the left gonads were slightly larger than the right ones. Six stages of gonad maturation were established for the females and males namely, immature (I), maturing (II), mature (III), ripe and running (IV), spent (V) and resting (VI). Based on macroscopy, eggs of various sizes and colours were found in each ovary, while histologically, various stages of oocytes and spermatocytes developed in each ovary and testis, respectively, indicating multiple spawning in both sexes. Spawning of the species occurs during the peak of rainy season in River Rima, which is between July and September.
Schistura udomritthiruji, new species, is described from streams draining to the Andaman Sea in southern Thailand between Takua Pa and Ranong. It is distinguished from congeners by the following characters: dark bars on the body much thinner in the anterior half of the body than in the posterior half; 9+8 branched rays in the caudal fin; males with suborbital flap; lateral line ends above base of anal fin; caudal fin hyaline and dark bars on posterior half of body more than twice as wide as interspaces.
Schistura callidora, new species, is described from the Myitnge River drainage, Irrawaddy basin (Myanmar). It is distinguished by dark bars on the body much thinner in the anterior half of the body than in the posterior half; a high dorsal crest on the caudal peduncle; 8 1 /2-10 1 /2 branched dorsal-fin rays; and the lateral line reaching behind the base of the anal fin. Pteronemacheilus, new genus, is characterised by the presence of elongated skinfolds on the dorsal side of the second and third branched pectoral-fin rays in males. Pteronemacheilus lucidorsum, new spe-cies, is described from the Myitnge River drainage, Irrawaddy basin (Myanmar). It differs from its only congener, P. meridionalis, by having the dorsal midline without pigmentation and usually 8 + 8 branched caudal-fin rays.
Information about sexual dimorphism is essential for understanding the ecology, behavior, and life history of a species, as well as for making morphological comparisons between populations. Furthermore, in order to understand the evolution of sexual dimorphism, it is important to know whether sexual dimorphism is genetically determined or the result of phenotypic plasticity. To this end, we have characterized patterns of sexual dimorphism in the threespine stickleback (Gasterosteus aculeatus). These fish are widely distributed throughout the temperate Northern Hemisphere, and their behavior, ecology, and evolution have been extensively characterized. We first examined sexual dimorphism in morphometric and meristic characters of wild-caught threespine sticklebacks from multiple populations that demonstrate different life history strategies in order to understand general patterns of sexual dimorphism in the threespine stickleback. Next, we made several crosses by in vitro fertilization and raised them in the laboratory to investigate developmental and genetic contributions to sexual dimorphism. Morphological analysis of wild-caught breeding males and females from four North American and six Asian populations revealed that adult males have larger heads and mouths than adult females in all populations. In contrast, adult females were longer in standard length and had longer pelvic girdles than adult males in many populations. Sexual dimorphism in dorsal-spine length was variable among popula- tions. Except for body size, sexual dimorphism in most external morphological traits was similar between wild-caught and lab-reared fish. However, sexual dimorphism was only observed after the fish became reproductively mature. These results suggest that general features of secondary sexual characters are shared across different threespine stickleback populations and that sexual dimorphism in some morphological traits may have a genetic basis.
The different reproductive roles of the sexes can predict the direction and magnitude of sexual dimorphism of external and internal morphology. Males should have enlarged structures that enhance the acquisition of mating opportunities, whereas females are predicted to have enlarged organs that are associated with the production of eggs. We tested these predictions in male and female lake whitefish, a species in which both sexes have similar overall body size and shape. After controlling for body size, male lake whitefish had significantly longer jaws and pectoral and pelvic fins, larger hearts, and more muscle than females. Sexual dimorphism in relative muscle mass may be one of the most fundamental morphological differences between males and females. Females had relatively heavier livers than males. Because the liver is important for the breakdown of fats and vitellogenesis, selection should favour an enlarged liver in females for the processing of energy and the production of large numbers of eggs.
Current and traditional research on sexual selection focuses largely on explaining the evolution (gain) of elaborate male traits and of female preferences for these traits. However, recent phylogenetic studies have revealed a surprising trend: that losses of these elaborate male traits are widespread and can be much more common than are gains. Furthermore, recent studies also show that female preferences for these male traits can be reduced, lost, or even reversed. These losses of traits and preferences could have important implications for competing models of sexual selection. Integrated phylogenetic, experimental and theoretical studies are needed to explain these unexpected patterns.
This study examined sexual dimorphism of head morphology in the ecologically diverse three-spined stickleback Gasterosteus aculeatus. Male G. aculeatus had longer heads than female G. aculeatus in all 10 anadromous, stream and lake populations examined, and head length growth rates were significantly higher in males in half of the populations sampled, indicating that differences in head size increased with body size in many populations. Despite consistently larger heads in males, there was significant variation in size-adjusted head length among populations, suggesting that the relationship between head length and body length was flexible. Inter-population differences in head length were correlated between sexes, thus population-level factors influenced head length in both sexes despite the sexual dimorphism present. Head shape variation between lake and anadromous populations was greater than that between sexes. The common divergence in head shape between sexes across populations was about twice as important as the sexual dimorphism unique to each population. Finally, much of the sexual dimorphism in head length was due to divergence in the anterior region of the head, where the primary trophic structures were found. It is unclear whether the sexual dimorphism was due to natural selection for niche divergence between sexes or sexual selection. This study improves knowledge of the magnitude, growth rate divergence, inter-population variation and location of sexual dimorphism in G. aculeatus head morphology.
The gametogenesis and reproduction of the matrinxã, Brycon orthotaenia in the São Francisco river, Pirapora Region, Minas Gerais, were studied from December, 1998 to November, 1999. The matrinxã B. orthotaenia is an endemic species in the São Francisco river basin in Brazil and important for commercial fishing. The size of the 1st gonadal maturation, indicated by the total length of the smallest spent males and spawned female, was 32.0 and 40.5 cm respectively. Reproduction occurred from October to January, when high frequencies of females and males at an advanced ripening/mature stage and spawned females were found. The short spawning period and histological characteristics of spawned ovaries containing only oocytes in stages of initial development, along with post-ovulatory and atresic follicles, indicated that Brycon orthotaenia presents total spawning.
The evolution of sexual dimorphism in quantitative characters under natural and sexual selection acting differently on the sexes is analyzed using population genetics models. The effects of genes when in males may be correlated with their effects when in females, producing correlated selective responses between the sexes, so that male and female phenotypes cannot evolve independently But under weak natural selection with constant relative fitnesses, in the absence of sexual selection, the joint evolution of the mean phenotypes of the sexes increases the mean fitness in a population, and if there is genetic variation for sexual dimorphism each sex eventually achieves a locally optimum phenotype. With sexual selection, fitnesses are generally frequency-dependent and evolution of the mean phenotypes does not maximize the mean fitness. Provided individual fitnesses exist, at equilibrium natural and sexual selection balance in each sex. A moderate intensity of sexual selection acting on a character under weak natural selection toward an intermediate optimum phenotype can produce a large deviation of the mean phenotype from the optimum and a substantial decrease of the mean fitness in a population, increasing the probability of extinction. When homologous characters in males and females vary similarly and are highly correlated genetically, the rate of evolution of sexual dimorphism may be one or more orders of magnitude slower than that for the average phenotype in a population. Methods for partitioning sexual dimorphism into contributions from natural and sexual selection are discussed, and genetic experiments are suggested for testing the involvement of non-equilibrium correlated selective responses between the sexes in observed cases of sexual dimorphism.
Sex ratio, gonadal development, breeding season and fecundity of the armoured catfish Loricariichthys castaneus were described to assess its reproductive strategy in a Brazilian tropical reservoir. In total, 226 specimens (199 females and 27 males) were captured from September 2005 to August 2006 and examined in the laboratory. Females outnumbered males and achieved sizes larger than 330 mm TL. Oocyte development, determined by histological analysis, was asynchronous with oocyte size, ranging from pre-spawning (27–270 μm) to spawning (243–3460 μm), followed by a sharp decrease in the mean oocyte diameter postspawning (590–730 μm) as the spawning proceeded. Spawning occurred throughout most of the year, peaking in August–September and reaching a low in April–May, according to variations in GSI and frequencies of stages of gonadal development. Batch fecundity ranged from 242 to 833 vitellogenic oocytes (relative fecundity = 2.27 oocytes g−1), averaging 483 oocytes, and was positively related to gonad weight (P = 0.00003). Oocyte diameters ranged from 0.027 to 5.59 mm, with vitellogenic diameters ranging from 2.08 to 5.59 mm. Continuous development of oocytes throughout the year suggests that L. castaneus presents indeterminate fecundity and is a batch-spawner. These attributes, associated with parental care and a wide reproductive period, correspond to an equilibrium strategy that has proved to be effective in the Lajes reservoir.
Catalog of Fishes. California Academy of Sciences
- W N Eschmeyer
Eschmeyer, W.N. (Ed) (2012) Catalog of Fishes. California Academy of Sciences. Available from: http://
research.calacademy.org/research/ichthyology/catalog/fishcatmain.asp (accessed 19 August 2012).
Nemacheiline loaches from Central Vietnam with descriptions of a new genus and 14 new species (Cypriniformes: Balitoridae)
- D V Serov
- I D Gomes
- F G Araujo
- W Uehara
Fishes of the Nam Theun and Xe Bangfai basins, Laos, with diagnoses of twenty-two new species (Teleostei: Cyprinidae, Balitoridae, Cobitidae, Coiidae and Odontobutidae)
- C L Pelchel
- R Lande
Reproductive roles predict sexual dimorphism in internal and external morphology of lake whitefish
- W E Aguirre
- O Akinpelu
- G W Barlow
- J Bohlen
- V Ŝlechtová
Gametogenesis and reproduction of the matrinxã Brycon orthotaenia (Günther 1864) (Pisces: Characidae) in the São Francisco River
- J Freyhof
- D V Serov
- I D Gomes
- F G Araujo
- W Uehara
- A Sales
- T L Goncalves
- N Bazzonli
- M F G Brito
- S L Hora
- J Kitano
- S Mori
- C L Pelchel
- R Lande
- B A Shinkafi
- J K Ipinjolu
- W A Hassan