Suckermouth armored catfish resolve the paradox of simultaneous respiration and suction attachment: a kinematic study of Pterygoplichthys disjunctivus

Suckermouth armored catfishes (Loricariidae) use their suckermouth for inspiration, feeding, and attachment to substrates. The sucker consists of a pre-valvular cavity, formed by a modified lip disc, and is separated from the larger post-valvular buccal cavity by a muscular oral valve. The combination of respiration and suction attachment seems paradoxal, as a properly functioning suction device would need a sucker without leakage (yet inspiration must occur via the sucker), and continuous subambient pressure in the sucker cavity (even during expiratory mouth floor elevation). In the loricariid Pterygoplichthys disjunctivus, the anatomy of the suckermouth structures was examined, and a kinematic analysis was performed to acquire insights into how respiration and attachment are combined. High-speed external and X-ray recordings show that suckermouth attachment influences respiratory parameters such as decreasing excursion amplitudes of mouth floor elements, and the way water enters the mouth via furrows in the lip disc. Respiration, however, continues during attachment and is not blocked. Our data show that the muscular oral valve actively separates the post-valvular buccal cavity from the pre-valvular sucker cavity. Volume changes of this pre-valvular cavity are opposite to those of the post-valvular cavity and assure sucker function even during expiration. These volume changes are caused by movements of the lower lip, the lower jaws, and the oral valve. The lateral inflow furrow openings, controlled by the maxillary barbels, can occur unilaterally. Morphological and kinematic data also show that the opercle is anatomically and functionally decoupled from the gill opening.     

Effects of prey density on growth and survival of white sucker,Catostomus commersoni,and pumpkinseed,Lepomis gibbosus,larvae

Synopsis Growth and survival of white sucker and pumpkinseed larvae were examined in the laboratory in relation to prey density. Mortality of both species was greatest during the transition from endogenous to exogenous nutrition. Mortality prior to yolk absorption was substantial for white suckers and was not related to prey density whereas, pumpkinseed mortality during the same period was low. After yolk absorption, however, pumpkinseed suffered considerably higher mortality rates than white sucker larvae and, in both species, mortality and growth were directly related to prey density. The minimum prey density supporting 10% survival of pumpkinseed larvae was estimated at 0.16 plankters ml^-1 whereas, for white suckers it was 0.15 plankters ml^-1. Significant growth of both white sucker and pumpkinseed larvae, however, occurred only at prey densities higher than 0.25 plankters ml^-1. We suggest that since egg size and yolk reserve are greater in sucker larvae, suckers are better adapted to survive short term declines in prey abundance during the transition to exogenous feeding than pumpkinseed larvae. The reproductive strategies of each species seems to reflect this, with suckers spawning over a short time interval, but producing young with large yolk. Pumpkinseed, in contrast, spawn intermittently over an extended period but produce young with relatively small volk reserves.     

Comparative morphology and osteology of pelvic fin‐derived midline suckers in lumpfishes,snailfishes and gobies

Some fishes use modified body structures – including pelvic fins – to produce suction to facilitate stability in turbulent environments. This study compares the morphology and osteology of the pelvic suckers of representative lumpfishes (Cyclopteridae), snailfishes (Liparidae) and gobies (Gobiidae). In all species studied the midline sucker (pelvic suctorial organ [PSO]) is formed from the pelvic girdle and fin rays I and 5 of the pelvic fins, comprised of similar osteological elements to those found in the pelvic girdle and pelvic fin rays although the morphology of the bony elements is species‐specific. Pelvic suctorial organs in those fishes that lack pelvic girdles are therefore homologous to pelvic girdles. The phenotypic diversity seen in so few species indicates that many sucker morphologies have arisen, origination depending on the concerted development of muscular, skeletal, nervous, and skin body tissues. The structure of the soft rays of the pelvic fins in the liparids and cyclopterids is unusual and indicative of unconventional developmental patterning of fin ray halves and of evolution in the underlying mechanisms responsible for the development of midline suckers.     

The Morphology and Adhesion Mechanism of Octopus vulgaris Suckers

The octopus sucker represents a fascinating natural system performing adhesion on different terrains and substrates. Octopuses use suckers to anchor the body to the substrate or to grasp, investigate and manipulate objects, just to mention a few of their functions. Our study focuses on the morphology and adhesion mechanism of suckers in Octopus vulgaris. We use three different techniques (MRI, ultrasonography, and histology) and a 3D reconstruction approach to contribute knowledge on both morphology and functionality of the sucker structure in O. vulgaris. The results of our investigation are two-fold. First, we observe some morphological differences with respect to the octopus species previously studied (i.e., Octopus joubini, Octopus maya, Octopus bimaculoides/bimaculatus and Eledone cirrosa). In particular, in O. vulgaris the acetabular chamber, that is a hollow spherical cavity in other octopuses, shows an ellipsoidal cavity which roof has an important protuberance with surface roughness. Second, based on our findings, we propose a hypothesis on the sucker adhesion mechanism in O. vulgaris. We hypothesize that the process of continuous adhesion is achieved by sealing the orifice between acetabulum and infundibulum portions via the acetabular protuberance. We suggest this to take place while the infundibular part achieves a completely flat shape; and, by sustaining adhesion through preservation of sucker configuration. In vivo ultrasonographic recordings support our proposed adhesion model by showing the sucker in action. Such an underlying physical mechanism offers innovative potential cues for developing bioinspired artificial adhesion systems. Furthermore, we think that it could possibly represent a useful approach in order to investigate any potential difference in the ecology and in the performance of adhesion by different species.     

A scanning electron microscopic investigation of the outer surfaces of Gorgoderina attenuata

The external surface of Gorgoderina attenuata is characterized by ridges that encircle the worm at regular intervals. On the ridges are protuberances that give a beaded appearance to the tegumental surface. Ridges running perpendicular to the encircling bands are apparent close to both suckers. The raised protuberances of the tegumental areas may serve to increase the absorptive surface. A pit-like cavity was observed on the dorsal surface of the oral sucker. In addition numerous raised structures which appear to be of two types were present on the surface of the oral sucker. One type resembles a depression with a small knob barely visible in the center and the second type consists of button-like patches of tissue. From their structure and location these are tentatively identified as sensory organs.     

Abundance,size, and feeding success of larval shortnose suckers and Lost River suckers from different habitats of the littoral zone of Upper Klamath Lake

We examined near-shore habitat use by larval shortnose and Lost River suckers in the lower Williamson River and Upper Klamath Lake of south-central Oregon. Emergent macrophytes Scirpus, Sparganium and Polygonum supported significantly more, larger, and better-fed larvae than submergent macrophytes, woody vegetation, or open water. Abundance, size, and gut fullness were similar for sucker larvae collected from different emergent macropytes. During the larval period, there was no evidence of density dependant effects or habitat shifts. Ranked catch per unit effort data indicated potential predators also were more likely to use emergent macrophytes, but ordination indicated larvae and potential predators were differentially distributed along a vegetation structure-water depth gradient with larvae in shallow vegetated areas. Between-habitat differences appeared to be due to larval sucker selection for, or better survival in, emergent macrophytes, rather than differential access or exclusion from other habitats. The importance of emergent macrophytes appears to be related to increased foraging success and reduced predation. Because larvae in emergent macrophytes have a size and gut fullness advantage, the amount of emergent habitat could affect early survival. However, interannual differences in recruitment to the adult population may or may not be dependent on larval dynamics. Our results suggest larval sucker access to emergent macrophytes may be necessary, but perhaps not sufficient, for promoting good year class formation.     

Computer-generated null models as an approach to detect perceptual range in mark–re-sight studies – an example with grasshoppers

Abstract.  1. Dispersal and habitat detection are key factors for the colonisation of habitat fragments in heterogeneous landscapes. The ability to recognise a habitat from a certain distance should increase the survival chances of a dispersing individual; however, due to methodological problems there is little information on the perceptual range of most species.
2. In a field experiment, 44 individually marked grasshoppers of the species Oedipoda caerulescens (Orthoptera: Acrididae: Locustinae) were released into an unfamiliar, hostile environment at various distances from a patch of preferred habitat.
3. Whether individuals reached the habitat or not was measured, as well as the daily movement distances. The number of individuals that reached the habitat was tested against computer-generated predictions based on different underlying rules for the movement behaviour of individuals but not accounting for the ability to detect habitat from distance.
4. On the first day a significantly higher proportion of grasshoppers arrived in the habitat than predicted by any of the null models.
5. It was concluded that individuals of O. caerulescens are able to detect their preferred habitat from a distance.
6. Edge permeability was very low as none of the individuals left the habitat once they had reached it.
7. Additional analyses showed that individuals changed movement behaviour from a directed walk with great daily distances in unsuitable habitat to a walk with significantly shorter daily distances within the preferred habitat.
8. The problems that arose in the field experiment are discussed and recommendations are given for further studies.     

Diversity, distribution and larval habitats of North Swedish blackflies (Diptera: Simuliidae)

1. Blackfly species richness and community structure were analysed at fifty-six sites in northern Sweden in two seasons. The sites were situated in a wide range of streams and rivers from small springbrooks, bog streams and lake-outlet streams to medium-sized forest rivers and large rivers draining montane regions.
2. Thirty-nine blackfly species were found, with between two and thirteen species per site. Neither species richness nor abundance could be related to the environmental variables measured.
3. An analysis of labral fan size of blackflies indicated a clear trend for the prevalence of larvae with small fans in large rivers and larvae with larger fan size in small streams. Similarly, fan size related to current velocities so that large fans were associated with slow current velocities and small fans with high velocities.
4. A strong relationship existed between species composition and habitat, as seen in ordination by non-metric multidimensional scaling. The relationship found between fan size and habitat size-related variables, such as channel width, depth, velocity and substratum particle size, along with longitude and altitude, in partial least squares regression analysis offered an explanation of the species composition–habitat relationship.
5. In addition to testing that distributions of blackfly larvae reflect morphological traits, we tested two general hypotheses pertaining to distribution patterns: (a) that blackfly communities show bimodal distributions; and (b) that their distributions are nested. Neither of these two hypotheses was supported by our observations. However, widespread blackfly species were locally more abundant than those found at relatively few sites, thus showing a positive abundance–occupancy relationship.     

胡杨（Populus euphratica）在额济纳绿洲三种生境内的根蘖繁殖特性

以额济纳荒漠绿洲胡杨根蘖幼苗为研究对象,通过对绿洲内胡杨分布的3种主要生境内根蘖幼苗的调查,得出如下结论。近年来绿洲内胡杨种群的更新几乎完全依赖于无性繁殖更新,种子萌发产生的幼苗在调查地内没有发现。河岸沙丘地及胡杨林下地的根蘖幼苗中,3龄幼苗所占比重最大,龄级越小的根蘖苗在群落中的数量越少;在河水漫灌后的林间空地,2龄幼苗的数量最多。水漫灌后的林间空地中根蘖幼苗密度显著大于其余两生境内根蘖幼苗密度,同时该生境内每段胡杨根系萌生出的不定芽也大于另两生境。随着龄级增加,未枯枝根蘖幼苗的比率逐渐减小。根蘖幼苗的萌发点分布于土层30cm以内的根系上,分布深度大于30cm的根系不能萌发出根蘖幼苗。     

Development of Biomimetic Squid-Inspired Suckers

Biomechanical properties of squid suckers were studied to provide inspiration for the development of sucker artefacts for a robotic octopus.Mechanical support of the rings found inside squid suckers was studied by bending tests.Tensile tests were carried out to study the maximum possible sucking force produced by squid suckers based on the strength of sucker stalks,normalized by the sucking areas.The squid suckers were also directly tested to obtain sucking forces by a special testing arrangement.Inspired by the squid suckers,three types of sucker artefacts were developed for the arm skin of an octopus inspired robot.The first sucker artefact made of knitted nylon sheet reinforced silicone rubber has the same shape as the squid suckers.Like real squid suckers,this type of artefact also has a stalk that is connected to the arm skin and a ring to give radial support.The second design is a straight cylindrical structure with uniform wall thickness made of silicone rubber.One end of the cylinder is directly connected to the arm skin and the other end is open.The final design of the sucker has a cylindrical base and a concave meniscus top.The meniscus was formed naturally using the surface tension of silicone gel,which leads to a higher level of the liquid around the edge of a container.The wall thickness decreases towards the tip of the sucker opening.Sucking forces of all three types of sucker artefacts were measured.Advantages and disadvantages of each sucker type were discussed.The final design of suckers has been implemented to the arm skin prototypes.     

Biology of suckers: late-formed shoots in sugarcane

Suckers in sugarcane are tillers that form late in the growing season after the population of main stalks has been established. Their biology has rarely been studied, though unsubstantiated comments relating to their morphology, development and number are abundant. In this paper, the literature is reviewed and new experiments presented. Comparison of suckers, emerging plant and ratoon cane showed that suckers have a different leaf and stem morphology. Suckers have a greater diameter at their stem base and shorter and wider leaves than primary stalks of a similar age. In 1 ‐year‐old crops, suckers have been demonstrated to decrease the net sucrose concentration of harvested material by diluting sucrose in the main stalks. By comparing main stalks without suckers to those that have initiated suckers, evidence is presented that suckers may also be decreasing the sucrose content of the stalks from which they are growing. Genotypic and environmental factors influence sucker number. Several experiments were designed to identify environmental stimuli for suckering. Increased nitrogen, through application late in the growing season, was found to increase the numbers of suckers present. Manipulation of the light environment of main stalks showed that a change in light quality (but not necessarily quantity) stimulated suckering. Further work is underway to define how these environmental stimuli lead to sucker initiation and growth. Major scientific questions that should be addressed are: the identification of other potential environmental stimuli, how the signals are perceived and translated into sucker initiation, and why suckers have different morphology. The practical challenge is to combine the new information about sucker biology and develop from it strategies to alter agronomy and select new cultivars that results in decreased suckering.     

头足类腕上吸盘和内壳扫描电镜观察

本文采用扫描电子显微镜对7种头足类腕上的吸盘及乌贼的内壳进行观察。结果表明,蛸科（Octopodidae）的短蛸（Octopus ocellatus）、真蛸（O. vulgaris）和长蛸（O. variabilis）腕的吸盘均无齿,乌贼科（Sepiidae）的日本无针乌贼（Sepia japonica）和金乌贼（S.esculenta）的腕和触腕吸盘上的角质环均有齿,且齿的形状不一样;虎斑乌贼（S. pharoanis）触腕的吸盘角质环光滑无齿,枪乌贼科(Loliginidae)的中国枪乌贼（Uroteuthis chinensis）腕上吸盘的角质环无齿。对３种乌贼的内壳的横切面进行扫描电镜观察,乌贼的内壳的背表面和腹表面的结构均是由文石和铺在上面的球型颗粒构成,但文石的形状和小球的排列存在种间差异,这些差异可以作为头足类的分类辅助特征。     

Feeding and fate of wild larval razorback sucker

The razorback sucker (Xyrauchen texanus) is disappearing throughout its native range in the Colorado River basin of western North America. The largest remaining wild population in Lake Mohave, Arizona-Nevada, has shown no recruitment since the 1950s. Although annual spawning is successful and larvae are seasonally abundant, no juveniles have been collected in recent decades. To evaluate the potential role of food availability in determining fate of larvae, fish and zooplankton samples were taken in 1985 from the reservoir and an adjacent, isolated backwater in which larvae were naturally produced. Food availability and primary dietary constituents were similar in both habitats. Reservoir larvae selectedBosmina spp. (Cladocera) and apparently avoided Copepoda, while larvae from the backwater selectedBosmina, but avoided Rotifera. Larvae from both places showed evidence of selection for certain sizes of zooplankters, but preferred sizes differed between habitats. These differences were neither attributable to larval size nor zooplankton community structure. Nutritional factors such as type, number, or size of available foods do not explain disappearance of larval razorback suckers from Lake Mohave, since larvae survive to far greater ages and size in the backwater. Predation by introduced fishes appears a significant cause of larval mortality.     

The structure and adhesive mechanism of octopus suckers

Octopus suckers consist of a tightly packed three-dimensionalarray of muscle with three major muscle fiber orientations:1) radial muscles that traverse the wall; 2) circular musclesarranged circumferentially around the sucker; and 3) meridionalmuscles oriented perpendicular to the circular and radial muscles.The sucker also includes inner and outer fibrous connectivetissue layers and an array of crossed connective tissue fibersembedded in the musculature. Adhesion results from reducingthe pressure inside the sucker cavity. This can be achievedby the three-dimensional array of muscle functioning as a muscular-hydrostat.Contraction of the radial muscles thins the wall, thereby increasingthe enclosed volume of the sucker. If the sucker is sealed toa surface the cohesiveness of water resists this expansion.Thus, the pressure of the enclosed water decreases instead.The meridional and circular muscles antagonize the radial muscles.The crossed connective tissue fibers may store elastic energy,providing an economical mechanism for maintaining attachmentfor extended periods. Measurements using miniature flush-mountedpressure transducers show that suckers can generate hydrostaticpressures below 0 kPa on wettable surfaces but cannot do soon non-wettable surfaces. Thus, cavitation, the failure of waterin tension, may limit the attachment force of suckers. As depthincreases, however, cavitation will cease to be limiting becauseambient pressure increases with depth while the cavitation thresholdis unchanged. Structural differences between suckers will thendetermine the attachment force.     

Post-burn reproduction of woody plants in a neotropical savanna: the relative importance of sexual and vegetative reproduction

1. Burning typically occurs at intervals of 1–3-years in the Brazilian cerrado, a rate that exceeds the precolonization fire regime. To determine if woody plants of the cerrado successfully reproduce within the short span of time between burns, experimental burns were used to quantify the effects of fire on sexual and vegetative reproduction of six species of resprouting trees and shrubs.
2. Four of the six species reproduce vegetatively by producing root suckers. For three of these species, Rourea induta , Myrsine guianensis and Roupala montana , sucker production was seven to 15 times greater in burned plots than in unburned controls.
3. Fire had a negative impact on sexual reproduction. Fire caused an immediate reduction in sexual reproductive success by destroying developing reproductive structures and seeds. Additionally, five of the six study species exhibited overall reductions in seed production in the years following fire. Fire had this effect by reducing the individual size of all species and, for three species, by reducing size-specific reproductive output. Only the tree Piptocarpha rotundifolia exhibited increased seed production following burning.
4. Fire caused substantial mortality to both seedlings and suckers. Suckers were larger than seedlings and experienced lower mortality rates for two of three species. Fire-induced mortality of seedlings varied greatly among species, ranging from 33% to 100%.
5. The results indicate that vegetative reproduction is much more successful than sexual reproduction under the high fire frequency typical of current fire regimes. It is concluded that current fire regimes must be causing a shift in species composition, favouring species capable of vegetative reproduction.     

Microsatellite markers for the endangered razorback sucker, Xyrauchen texanus, are widely applicable to genetic studies of other catostomine fishes

We developed 10 polymorphic microsatellite markers for the federally endangered razorback sucker, Xyrauchen texanus. PCR optimization and cross-species amplification experiments indicated that these markers will be useful for analysis of fine-scale population structure in razorback and two other sucker species; the white sucker, Catostomus commersonii and the Rio Grande sucker, C. plebeius. Alleles at locus Xte4 did not overlap when compared between razorback and bluehead (C. discobolus) suckers and permits detection of F1 hybrids. These microsatellite markers appear widely applicable for identifying genetic consequences of population decline, hatchery rearing and release, and hybridization in razorback and other castostomine suckers.     

A bridge between original and novel states: ontogeny and function of "suction discs" in the Branchiura (Crustacea)

The emergence of novel structures in the course of evolution faces an explanatory problem, leaving the gap from the ancestral structures difficult to bridge. This difficulty is caused by the lack of intermediate stages. Branchiurans are ectoparasitic crustaceans which use a pair of "suction discs" to attach to their host. These structures are modified first maxillae. During ontogeny, the first maxillae transform from a normal cephalic appendage to the specialized suction disc. However, supposedly ancestral branchiurans lack the suction discs in the adults and the first maxilla remains a normal appendage throughout. We describe the muscular arrangements in the developing first maxillae in Argulus coregoni. The suction discs originate as a fusion of the first and second podomeres. The sucker muscles of the suction discs are homologous to the muscles that insert in the second podomere at the early larval stages. The developmental process of the suction disc can be seen as a "recapitulation" of the evolutionary process. We thus show how the first maxilla can maintain not just the biological role but also a functional continuity during the evolution of the novel structure. From this example it is obvious that the intermediate stages of the emerging novelty, if present in the ontogeny, can help solve at least some of the enigmatic appearances of novel structures.     

Offspring performance in dynamic habitats: key factors for a riparian carabid beetle

Abstract.  1. Knowledge of the ecology of carabid species is largely restricted to adults, although larval mortality is assumed to be the key factor in overall mortality. As low-mobility larvae are unable to avoid unfavourable conditions, habitat selection of reproducing adults should be clearly affected by the habitat factors which determine offspring performance.
2. The present study examines the key habitat factors governing the distribution patterns of Bembidion velox larvae and adults on the river banks of the River Elbe by means of habitat suitability models. The validity of the determined habitat factors for offspring performance and survival was tested in laboratory experiments.
3. In the field, B. velox adults as well as larvae show a strong association with semi-terrestrial, sandy, open soil habitats.
4. In the laboratory, overall mortality of larvae reared in different substrates was lowest in sand of medium grain size mixed with fine and coarse sand. The first larval instars in particular reacted sensitively to variations in grain size. Furthermore, flood resistance of eggs was demonstrated, as 90% of larvae hatched under permanently flooded conditions.
5. Short development times were recorded, with 4–7 days for hatching of young larvae from eggs after oviposition and approximately 28 days for the development of adults from newly hatched larvae. This probably increases the survival probability for the pre-imaginal stages in dynamic habitats.
6. In conclusion, it can be said that reproductive success is strongly dependent on oviposition site selection by adults as this reflects the ecological demands of the immature stages.