Evolutionary modifications of Astyanax larval prey capture (LPC) in a dark environment

Feeding strategies of an organism depend on the multimodal sensory processing that most efficiently integrates available visual,chemosensory,and/or mechanoreceptive cues as part of their environmental adaptation.The blind cavefish morph of Astyanax mexicanus has developed sensory-dependent behaviors to find food more efficiently than their eyed,surface-morph counterparts while in darkness.In the absence of light,adult cavefish have evolved enhanced behaviors,such as vibration attraction behavior(VAB),and changes in feeding angle.Here,we identified evolved differences in cavefish larval prey capture(LPC)behavior.In the dark,LPC is more efficient in cavefish than in surface fish.Furthermore,different cave populations express laterality in their LPC and strike towards prey preferentially located on their left or right sides.This suggests the occurrence,to some extent,of divergent LPC evolution among cave populations.While LPC can be triggered exclusively by a vibration stimulus in both surface and cavefish,we provide evidence that LPC is,at least partially,a multimodal sensory process different from adult VAB.We also found that a lack of food may exacerbate the laterality of LPC.Thus,we proposed a mathematical model for explaining laterality based on a balance between:(1)enlarged range of foraging field(behavioral or perceptive)due to asymmetry,(2)food abundance,and(3)disadvantages caused by laterality(unequal lateral hydrodynamic resistance when swimming,allocation of resources for the brain and receptors,and predator escape).

ACUPOINT-LIKE STRUCTURE AND MERIDIAN-LIKE DISTRIBUTION ON THE BODY SURFACE OF PLATYFISH

Objective To probe into whether an acupoint-like and meridian-like structure was existed in platyfish. Methods Adult platyfish was put in 30 μM 4-Di-2-ASP water solution for 3 h, then, in pipe water for 20min, afterward, the fish was anesthetized in 10% aether water solution, and the fluorescent labeling was observed under fluorescent microscope with B-3A combination filter. Results The labels observed under the microscope were in round bright dot, a majority of dots were distributed separately and a part of them was in cluster （2- 5 dots/cluster） on various parts of the body in regular arrangement. The labels on the head were circularly distributed around the eye and two arches were formed posterior to the eye and in the inferior 3/4 quadrant. These two arches joined one arch in the anterior superior 1/4 quadrant. On the fish trunk, it was observed that the labels were distributed from the back to the abdomen along the longitudinal axis of the trunk, forming 6 lines, located on No. 2, 4, 6, 7, 8 and 9 scale rows successively on the dorsal part of fish. Each line was composed of 7 to 22 label clusters and 1 -5 labels were counted in each cluster. The labels were arranged as 3-4 lines on the tail. Conclusion 1） Acupoint-like and meridian-like structure was existed in platyfish. 2）The skin sensory organs of animal were not distributed evenly all over the body. Instead, a number of sensory organs were put together in cluster and a number of them were in linear distribution regularly along the long axis of the trunk, which was similar to the distribution of traditional meridians and acupoints.

Isolation, characterization and expression analysis of TRPV4 in half-smooth tongue sole Cynoglossus semilaevis

The transient receptor potential vanilloid 4(TRPV4),another Ca^2+entry channel,belongs to the vanilloid subfamily and responds to a number of different physical and chemical stimuli and exists widely in mammals.However,our understanding of the TRPV4 in fish remains poor.Therefore,we studied the TRPV4 gene from Cynoglossus semilaevis,named CsTRPV4 that encodes a putative protein of 870 amino acids common in structure and characteristic of mammalian TRPV4,including the domains of ANK repeats,six TM,TRP domain,and CaMBD.The CsTRPV4 was expressed ubiquitously in examined tissues:higher expression in the heart,spleen,testis,and eye,but lower expression in kidney and liver.Surprisingly,the expression of CsTRPV4 in lateral line was significantly higher than in many other tissues as the CsTRPV4 was expressed significantly in the free neuromasts.In addition,CsTRPV4 in the free neuromast from the larval fish was significantly expressed in the hair cells of the free neuromasts.Therefore,the free neuromasts can act as a mechano-sensor to the mechanical stimulation in molecular level in C.semilaevis,which lays a foundation for further study of the functions of the free neuromasts.

Morphological structure and peripheral innervation of the lateral line system in the Siberian sturgeon (Acipenser baerii)

Light and scanning electron microscopy(SEM)were used to study the epidermal lateral line system of the Si-berian sturgeon(Acipenser baerii Brandt,1869).This system consists of mechanoreceptive neuromasts,ampul-lae and the electroreceptive organ.The neuromasts are located in 5 pairs of cephalic and 1 pair of trunk canals and superficially in the middle and posterior pit lines that lie dorsomedially along the top of the skull immedi-ately adjacent to the otic ampullae field.Both canal neuromasts and pit organ superficial neuromasts have oppo-site polarized hair cells that are parallel along the axis of the canal and pit line,respectively.However,they dif-fer in both size and shape and in the density and length of the hair bundles.The ampullae are confined on the head,adjacent to the neuromast lines.The morphological structure of the ampullae in the Siberian sturgeon is similar to the ampullae in elasmobranchs and other primitive fish.Nevertheless,it has a relatively large mucus-filled ampulla,and a shorter and narrower canal leading to a small opening to the outer epidermal surface.We also present new information concerning the peripheral innervation of lateral line receptors in sturgeons.The re-ceptors of the lateral line system are innervated by 2 pairs of cranial nerves:anterior and posterior lateral line nerves.The peripheral processes of the anterior lateral line nerve form superficial ophthalmic,buccal,otic and anteroventral rami.The peripheral processes of the posterior lateral line nerve form middle,supratemporal and lateral rami.

Investigation on the Lateral Line Systems of Two Cavefish： Sinocyclocheilus Macrophthalmus and S. Microphthalmus （Cypriniformes： Cyprinidae）

Cavefish, with sensitive lateral lines, can swim freely and locate preys in invisible and complex cave environments, though their eyes are greatly degenerated. Investigations on the morphology and distribution characteristics of their lateral line systems would benefit our understanding of the high-sensitivity mechanism of the fish. In this study, the arrangement and morphology of the lateral lines are described for two species ofSinocyclocheilus： S. macrophthalmus and S. microphthalmus, which live in the karst caves in Guangxi, China. The behavior experiments indicate that the lateral line system of the S. macrophthalmus is more sensitive at a low vibration frequency range from 20 Hz to 70 Hz. The cephalic and trunk lateral line systems both contribute to the efficient object-locating capability. For both of the two species of cavefish, the diameter of the lateral canal nearby the neuromasts is narrower than that nearby the canal pores. This variation can increase the normal pressure to the surface of the cupula, and increase the sensitivity of the canal lateral line system.

TGFβ1a regulates zebrafish posterior lateral line formation via Smad5 mediated pathway

The zebrafish sensory posterior lateral line(pLL)has become an attractive model for studying collective cell migration and cell morphogenesis.Recent studies have indicated that chemokine,Wnt/β-catenin,Fgf,and Delta-Notch signaling pathways participate in regulating pLL development.However,it remains unclear whether TGFβsignaling pathway is involved in pLL development.Here we report a critical role of TGFβ1 in regulating morphogenesis of the pLL primordium(pLLP).The tgfβ1a gene is abundantly expressed in the lateral line primordium.Knockdown or knockout of tgfβ1a leads to a reduction of neuromast number,an increase of inter-neuromast distance,and a reduced number of hair cells.The aberrant morphogenesis in embryos depleted of tgfβ1a correlates with the reduced expression of atoh1a,deltaA,and n-cadherin/cdh2,which are known important regulators of the pLLP morphogenesis.Like tgfβ1a depletion,knockdown of smad5 that expresses in the pLLP,affects pLLP development whereas overexpression of a constitutive active Smad5 isoform rescues the defects in embryos depleted of tgfβ1a,indicating that Smad5 mediates tgfβ1a function in pLLP development.Therefore,TGFβ/Smad5 signaling plays an important role in the zebrafish lateral line formation.

Exquisite structure of the lateral line system in eyeless cavefish Sinocyclocheilus tianlinensis contrast to eyed Sinocyclocheilus macrophthalmus(Cypriniformes:Cyprinidae)

In this study,the lateral line systems in Chinese cavefish eyeless Sinocyclocheilus tianlinensis and eyed Sinocyclocheilus macrophthalmus were investigated to reveal their morphological changes to survive in harsh environments.Compared with the eyed cavefish S.macrophthalmus(atypical),the lateral line system in the eyeless cave-fish S.tianlinensis(typical)has certain features to adapt to the dark cave environments:the superficial lateral line system in the eyeless species possesses a higher number of superficial neuromasts and more hair cells within an individual neuromast,and the trunk lateral line canal system in S.tianlinensis exhibits larger canal pores,higher canal diameter and more pronounced constrictions.Fluid–structure interaction analysis suggested that the trunk lateral line canal system in the eyeless S.tianlinensis should be more sensitive than that in the eyed S.macrophthalmus.These morphological features of the lateral line system in the eyeless S.tianlinensis probably enhance the functioning of the lateral line system and compensate for the lack of eyes.The revelation of the form–function relationship in the cavefish lateral line system provides inspiration for the design of sensitive artificial flow sensors.