Anatomy of the mechanosensory lateral line canal system and electrosensory ampullae of Lorenzini in two species of sawshark (fam. Pristiophoridae)

It has long been assumed that the elongated rostra (the saws) of sawsharks (family: Pristiophoridae) and sawfish (family: Pristidae) serve a similar function. Recent behavioural and anatomical studies have shed light on the dual function of the pristid rostrum in mechanosensory and electrosensory prey detection and prey manipulation. Here, the authors examine the distributions of the mechanosensory lateral line canals and electrosensory ampullae of Lorenzini in the southern sawshark, Pristiophorus nudipinnis and the longnose sawshark, Pristiophorus cirratus. In both species, the receptive fields of the mechano- and electrosensory systems extend the full length of the rostrum indicating that the sawshark rostrum serves a sensory function. Interestingly, despite recent findings suggesting they feed at different trophic levels, minimal interspecific variation between the two species was recorded. Nonetheless, compared to pristids, the pristiophorid rostrum possesses a reduced mechanosensory sampling field but higher electrosensory resolution, which suggests that pristiophorids may not use their rostrums to disable large prey like pristids do.     

First insights into the function of the sawshark rostrum through examination of rostral tooth microwear

Potential roles of the rostrum of sawsharks (Pristiophoridae), including predation and self‐defence, were assessed through a variety of inferential methods. Comparison of microwear on the surface of the rostral teeth of sawsharks and sawfishes (Pristidae) show that microwear patterns are alike and suggest that the elongate rostra in these two elasmobranch families are used for a similar purpose (predation). Raman spectroscopy indicates that the rostral teeth of both sawsharks and sawfishes are composed of hydroxyapatite, but differ in their collagen content. Sawfishes possess collagen throughout their rostral teeth whereas collagen is present only in the centre of the rostral teeth of sawsharks, which may relate to differences in ecological use. The ratio of rostrum length to total length in the common sawshark Pristiophorus cirratus was found to be similar to the largetooth sawfish Pristis pristis but not the knifetooth sawfish Anoxypristis cuspidata. Analysis of the stomach contents of P. cirratus indicates that the diet consists of demersal fishes and crustaceans, with shrimp from the family Pandalidae being the most important dietary component. No prey item showed evidence of wounds inflicted by the rostral teeth. In light of the similarities in microwear patterns, rostral tooth chemistry and diet with sawfishes, it is hypothesised that sawsharks use their rostrum in a similar manner for predation (sensing and capturing prey) and possibly for self‐defence.     

Sex-related variability of rostrum morphometry of Aristeus antennatus (Decapoda: Aristeidae) from the Ionian Sea (Eastern Mediterranean, Greece)

Sex-related rostral variability was studied in the aristeid shrimp Aristeus antennatusfrom the Eastern Ionian Sea (Mediterranean). Shrimps were collected on a monthly basis from December 1996 to November 1997 using a commercial bottom trawl in a depth range of 446–728 m. Female relative growth of rostrum proved to be negative allometric both seasonally and in the pooled annual data set. Males on the other hand, showed no or negative correlation of rostrum length with size. Mature males with short rostra dominated in the male population all year around. The appearance of males with long and intermediate rostra during winter, which disappear thereafter in favour of those with short rostra, indicates that rostrum shortening takes place during the end of winter. The increase of mated females during spring supports the hypothesis already addressed by other authors on the function of the male short rostrum in this species mating behaviour. Nevertheless, the paucity, in comparison to other Mediterranean populations, of males with long or intermediate rostra could indicate that for the bulk of the male population, the process of rostrum shortening in the Eastern Ionian Sea occurs outside the geographical locality or depth range sampled.     

Electric field detection in sawfish and shovelnose rays

In the aquatic environment, living organisms emit weak dipole electric fields, which spread in the surrounding water. Elasmobranchs detect these dipole electric fields with their highly sensitive electroreceptors, the ampullae of Lorenzini. Freshwater sawfish, Pristis microdon, and two species of shovelnose rays, Glaucostegus typus and Aptychotrema rostrata were tested for their reactions towards weak artificial electric dipole fields. The comparison of sawfishes and shovelnose rays sheds light on the evolution and function of the elongated rostrum ('saw') of sawfish, as both groups evolved from a shovelnose ray-like ancestor. Electric stimuli were presented both on the substrate (to mimic benthic prey) and suspended in the water column (to mimic free-swimming prey). Analysis of around 480 behavioural sequences shows that all three species are highly sensitive towards weak electric dipole fields, and initiate behavioural responses at median field strengths between 5.15 and 79.6 nVcm(-1). The response behaviours used by sawfish and shovelnose rays depended on the location of the dipoles. The elongation of the sawfish's rostrum clearly expanded their electroreceptive search area into the water column and enables them to target free-swimming prey.     

The rostral micro-tooth morphology of blue marlin,Makaira nigricans

Billfish rostra potentially have several functions; however, their role in feeding is unequivocal in some species. Recent work linked morphological variation in rostral micro-teeth to differences in feeding behavior in two billfish species, the striped marlin (Kajikia audax) and the sailfish (Istiophorus platypterus). Here, we present the rostral micro-tooth morphology for a third billfish species, the blue marlin (Makaira nigricans), for which the use of the rostrum in feeding behavior is still undocumented from systematic observations in the wild. We measured the micro-teeth on rostrum tips of blue marlin, striped marlin, and sailfish using a micro–computed tomography approach and compared the tooth morphology among the three species. This was done after an analysis of video-recorded hunting behavior of striped marlin and sailfish revealed that both species strike prey predominantly with the first third of the rostrum, which provided the justification to focus our analysis on the rostrum tips. In blue marlin, intact micro-teeth were longer compared to striped marlin but not to sailfish. Blue marlin had a higher fraction of broken teeth than both striped marlin and sailfish, and broken teeth were distributed more evenly on the rostrum. Micro-tooth regrowth was equally low in both marlin species but higher in sailfish. Based on the differences and similarities in the micro-tooth morphology between the billfish species, we discuss potential feeding-related rostrum use in blue marlin. We put forward the hypothesis that blue marlin might use their rostra in high-speed dashes as observed in striped marlin, rather than in the high-precision rostral strikes described for sailfish, possibly focusing on larger prey organisms.     

The biology of extinct and extant sawfish (Batoidea: Sclerorhynchidae and Pristidae)

Sclerorhynchids (extinct sawfishes, Batoidea), pristids (extant sawfish, Batoidea) and pristiophorids (sawsharks, Squalomorphi) are the three elasmobranch families that possess an elongated rostrum with lateral teeth. Sclerorhynchids are the extinct sawfishes of the Cretaceous period, which reached maximum total lengths of 100 cm. The morphology of their rostral teeth is highly variable. Pristid sawfish occur circumtropically and can reach maximum total lengths of around 700 cm. All pristid species are globally endangered due to their restricted habitat inshore. Pristiophorid sawsharks are small sharks of maximum total lengths below 150 cm, which occur in depths of 70–900 m. Close examination of the morphology of pectoral fin basals and the internal structure of the rostrum reveals that sclerorhynchids and pristids evolved independently from rhinobatids, whereas pristiophorids are squalomorph sharks. The elongation of the rostrum may be an adaptation for feeding, as all marine vertebrate taxa that possess this structure are said to use it in the context of feeding.     

Prey handling using whole-body fluid dynamics in batoids

Fluid flow generated by body movements is a foraging tactic that has been exploited by many benthic species. In this study, the kinematics and hydrodynamics of prey handling behavior in little skates, Leucoraja erinacea, and round stingrays, Urobatis halleri, are compared using kinematics and particle image velocimetry. Both species use the body to form a tent to constrain the prey with the pectoral fin edges pressed against the substrate. Stingrays then elevate the head, which increases the volume between the body and the substrate to generate suction, while maintaining pectoral fin contact with the substrate. Meanwhile, the tip of the rostrum is curled upwards to create an opening where fluid is drawn under the body, functionally analogous to suction-feeding fishes. Skates also rotate the rostrum upwards although with the open rostral sides and the smaller fin area weaker fluid flow is generated. However, skates also use a rostral strike behavior in which the rostrum is rapidly rotated downwards pushing fluid towards the substrate to potentially stun or uncover prey. Thus, both species use the anterior portion of the body to direct fluid flow to handle prey albeit in different ways, which may be explained by differences in morphology. Rostral stiffness and pectoral fin insertion onto the rostrum differ between skates and rays and this corresponds to behavioral differences in prey handling resulting in distinct fluid flow patterns. The flexible muscular rostrum and greater fin area of stingrays allow more extensive use of suction to handle prey while the stiff cartilaginous rostrum of skates lacking extensive fin insertion is used as a paddle to strike prey as well as to clear away sand cover.     

Otolith development and daily increment formation in larvae of the Kabyabya,a Malawian cyprinid, <Emphasis Type="Italic">Opsaridium tweddleorum</Emphasis>

Features of the sagitta, asteriscus, and lapillus of laboratory-hatched larvae of the Kabyabya, Opsaridium tweddleorum, were investigated until day 33 after hatching. The sagitta was round until day 17, subsequently becoming arrowhead-shaped with the development of anterior and posterior rostra. Increments in the sagitta increased at the rate of one per day before rostrum formation. However, they were occasionally overestimated in rostrum sections as a result of subdaily increment occurrence. Furthermore, both anterior and posterior rostra were fragile, being thin and platelike, and were often damaged during the extraction and grinding processes. The lapillus was also round until day 17, thereafter becoming fan-shaped. Increments in the lapillus were distinctive from the core to the margin, usually increasing at the rate of one per day after hatching. The asteriscus appeared in fish larger than 9.15 mm in standard length (from day 17), being oval with a somewhat ambiguous core, causing difficulty in discerning the first increment. These features indicated that the lapillus was the most appropriate otolith part for daily increment analysis in this species, although the sagitta was useful before rostrum formation.     

Annual breeding in a captive smalltooth sawfish,Pristis pectinata

The critically endangered smalltooth sawfish Pristis pectinata reproduces biennially in central west Florida, U.S.A. Here we demonstrate that smalltooth sawfish are physiologically capable of reproducing annually in a captive environment. The smalltooth sawfish are held in an open system, with abiotic conditions that vary naturally with the surrounding environment in The Bahamas. This suggests wild smalltooth sawfish may also be capable of annual reproduction provided there are adequate prey resources, limited competition and mate availability.     

Exaggerated Trait Allometry,Compensation and Trade-Offs in the New Zealand Giraffe Weevil (Lasiorhynchus barbicornis)

Sexual selection has driven the evolution of exaggerated traits among diverse animal taxa. The production of exaggerated traits can come at a cost to other traits through trade-offs when resources allocated to trait development are limited. Alternatively some traits can be selected for in parallel to support or compensate for the cost of bearing the exaggerated trait. Male giraffe weevils (Lasiorhynchus barbicornis) display an extremely elongated rostrum used as a weapon during contests for mates. Here we characterise the scaling relationship between rostrum and body size and show that males have a steep positive allometry, but that the slope is non-linear due to a relative reduction in rostrum length for the largest males, suggesting a limitation in resource allocation or a diminishing requirement for large males to invest increasingly into larger rostra. We also measured testes, wings, antennae, fore- and hind-tibia size and found no evidence of a trade-off between these traits and rostrum length when comparing phenotypic correlations. However, the relative length of wings, antennae, fore- and hind-tibia all increased with relative rostrum length suggesting these traits may be under correlational selection. Increased investment in wing and leg length is therefore likely to compensate for the costs of flying with, and wielding the exaggerated rostrum of larger male giraffe weevils. These results provide a first step in identifying the potential for trait compensation and trades-offs, but are phenotypic correlations only and should be interpreted with care in the absence of breeding experiments.     

The palaeobiology of belemnites – foundation for the interpretation of rostrum geochemistry

Belemnites are an extinct group of Mesozoic coleoid cephalopods with a fossil record ranging from the early Late Triassic [about 240 million years ago (Mya)] to the Cretaceous/Palaeogene boundary (65 Mya). Belemnites were widely distributed, highly abundant and diverse, and an important component of Mesozoic marine food webs. Their internal shells, specifically their low‐Mg calcite rostra, have been used as palaeoenvironmental carbonate archives for the last 70 years. This is primarily due to the assumption that the rostrum calcite formed in equilibrium with the oxygen isotope composition of ambient sea water. Of prime importance for the reliable interpretation of isotope data derived from these biogenic carbonates is a robust reconstruction of the palaeobiology of their producers. Here we provide a critical assessment of published reconstructions of belemnite soft‐body organization and their lifestyle and habitats. Different lines of evidence, including sedimentological, geochemical, morphological, and biomechanical data, point towards an outer shelf habitat of belemnites, for some taxa also including the littoral area. Belemnite habitat temperatures, oxygen content, salinities, and life span are constrained based on observations of the ecology and life history of modern coleoids. Belemnite habitat depth might have been largely controlled by food and temperature, with a temperature optimum between 10°C and 30°C. The distribution of modern coleoids is for most species restricted to well‐oxygenated water masses and a salinity between 27 and 37 psu. The trophic position of belemnites as both predators and prey is documented by unique fossil finds of stomach contents and soft tissue preservation, such as jaws, hooks, and ink sacs. Belemnites were medium‐sized predators in the epipelagic zone (not deeper than ～200 m) hunting for crustaceans, other cephalopods, and fishes. Taxa with elongated rostra probably were fast and highly manoeuvrable swimmers. Forms with conical rostra represent slow but highly manoeuvrable swimmers, and forms with depressed rostra likely had a bottom‐related life habit. Predators of adult belemnites were sharks, bony fishes, and marine reptiles. Belemnites, like most of the modern coleoids, were relatively short lived, most likely living only for 1–2 years. Understanding the biomineralization of belemnite rostra is highly relevant for an improved interpretation of their geochemistry. Here we confirm that belemnite rostra are composed of low Mg‐calcite fibres, but they do not contain distinct types of laminae. These fibres are composed of two distinct calcite phases. One phase is a filigree network of tetrahedral organic‐rich calcite and the second phase is represented by organic‐poor calcite.     

Morphology of the mechanosensory lateral line system in the Atlantic Stingray,Dasyatissabina: The mechanotactile hypothesis

The biological function of anatomical specializations in the mechanosensory lateral line of elasmobranch fishes is essentially unknown. The gross and histological features of the lateral line in the Atlantic stingray, Dasyatis sabina, were examined with special reference to its role in the localization and capture of natural invertebrate prey. Superficial neuromasts are arranged in bilateral rows near the dorsal midline from the spiracle to the posterior body disk and in a lateral position along the entire length of the tail. All dorsal lateral line canals are pored, contain sensory neuromasts, and have accessory lateral tubules that most likely function to increase their receptive field. The pored ventral canal system consists of the lateral hyomandibular canal along the disk margin and the short, separate mandibular canal on the lower jaw. The extensive nonpored and relatively compliant ventral infraorbital, supraorbital, and medial hyomandibular canals form a continuous complex on the snout, around the mouth, and along the abdomen. Vesicles of Savi are small mechanosensory subdermal pouches that occur in bilateral rows only along the ventral midline of the rostrum. Superficial neuromasts are best positioned to detect water movements along the transverse body axis such as those produced by tidal currents, conspecifics, or predators. The pored dorsal canal system is positioned to detect water movements created by conspecifics, predators, or possibly distortions in the flow field during swimming. Based upon the stingray lateral line morphology and feeding behavior, we propose the Mechanotactile Hypothesis, which states that the ventral nonpored canals and vesicles of Savi function as specialized tactile mechanoreceptors that facilitate the detection and capture of small benthic invertebrate prey. J. Morphol. 238:1–22, 1998. © 1998 Wiley-Liss, Inc.     

Changes in fruit shape inproboscidea parviftora ssp.parviflora (martyniaceae) with domestication

Aboriginal cultivators selected a phylogenetically novel fruit shape during the domestication ofProboscidea parviflora ssp.parviflora var.Hohokamiana. The extremely long rostrum of the domesticated var.Hohokamiana is unique for the Martyniaceae. Rostrum length and width are significantly correlated in the wild var.parviflora, but in var.Hohokamiana aboriginal cultivators apparently selected for a weaker correlation between these variables. In both varieties there is an allometric relationship between rostrum and “capsule” lengths, with the former increasing proportionately faster than the latter. The above allometric relationship and the decrease in correlation between rostrum length and width are advantageous to aboriginal cultivators because the proportionately longer and thinner rostra are better for basketmaking. Comparisons of the data presented herein with data from other plants suggest that similar growth factors have been responsible for changes in fruit shape resulting from domestication.     

Behavioral stochastic resonance: how the noise from a Daphnia swarm enhances individual prey capture by juvenile paddlefish.

Zooplankton emit weak electric fields into the surrounding water that originate from their own muscular activities associated with swimming and feeding. Juvenile paddlefish prey upon single zooplankton by detecting and tracking these weak electric signatures. The passive electric sense in this fish is provided by an elaborate array of electroreceptors, Ampullae of Lorenzini, spread over the surface of an elongated rostrum. We have previously shown that the fish use stochastic resonance to enhance prey capture near the detection threshold of their sensory system. However, stochastic resonance requires an external source of electrical noise in order to function. A swarm of plankton, for example Daphnia, can provide the required noise. We hypothesize that juvenile paddlefish can detect and attack single Daphnia as outliers in the vicinity of the swarm by using noise from the swarm itself. From the power spectral density of the noise plus the weak signal from a single Daphnia, we calculate the signal-to-noise ratio, Fisher information and discriminability at the surface of the paddlefish's rostrum. The results predict a specific attack pattern for the paddlefish that appears to be experimentally testable.     

The energetics of feeding strikes in larval carp, Cyprinus carpio

The prey intake of larval carp is described from high-speed (200–1250 frames s⁻¹) films with synchronous lateral and ventral views. Even in first-feeding carp larvae, the operculars are functional in sealing effectively the opercular slit until the moment of prey intake, and the maxillaries close off the corners of the mouth, preventing leak flow. In reducing the distance between larva and prey during attack, the relative importance of sucking the prey towards the mouth and swimming forward is variable; overall they are about equally important. The volume and the velocity of the water sucked into the mouth cavity during prey uptake are calculated. The energy costs of suction, i.e., accelerating the water sucked into the mouth cavity, during prey intake are estimated from these values. The energy costs of suction and swimming are in the same order of magnitude. Together they form only a fraction of 1% of the energetic content of the prey, so considerations about energy expenditure seem unimportant in a strategy to optimize the prey attack. During searching, however, they will be important. Power requirements during attack may also be important.     

The shadow of forgotten ancestors differently constrains the fate of Alligatoroidea and Crocodyloidea

Aim We tested the hypothesis that the evolutionary fates of two sister groups (Alligatoroidea and Crocodyloidea) are differently constrained by phylogenetic and ecological (functional) factors in the face of climatic change. Location Global. Methods We quantified disparity in skull rostrum shape by means of geometric morphometrics. Mechanical performance of the rostrum was analyzed by applying beam theory calculations to morphological data and experimentally measured bite force. The phylogeny was expressed in the form of principal coordinates, the first ones of which were used as a set of explanatory variables. Extents of species occurrence were computed using species distribution maps. Finally, species maximum skull size were measured and considered as a proxy of maximum body size. We performed variation partitioning analyses in order to compare differential contributions of phylogenetic and ecological factors in Alligatoroidea and Crocodyloidea. Results Alligatoroidea show higher ‘pure’ historical components than Crocodyloidea in explaining both rostrum shape and extent of occurrence (after controlling for body size). On the contrary, geometric variation of skull rostra of Crocodyloidea unequivocally shows a higher ‘pure’ functional component (linked to performance on prey capture) and a higher phylogenetically structured environmental variation than those found in Alligatoroidea. Results obtained for body size variation are consistent with these patterns. In Alligatoroidea, body size variation contains a higher phylogenetic signal than in Crocodyloidea. Main Conclusions Our results suggest that Crocodyloidea and Alligatoroidea may react differently when faced with significant environmental changes. We predict that global climatic changes will have a more important effect on Crocodyloidea than in Alligatoroidea by (1) promoting trait shift, adaptation to the new diet and speciation and (2) modifying the geographical range distribution of species (which may track favourable ecological conditions).     

Receptive field organization of electrosensory neurons in the paddlefish (Polyodon spathula)

Paddlefish use their electrosense to locate small water fleas (daphnia), their primary prey, in three-dimensional space. High sensitivity and a representation of object location are essential for this task. High sensitivity can be achieved by convergence of information from a large number of receptors and object location is usually represented in the nervous system by topographic maps. However the first electrosensory center in the brain, the dorsal octavolateral nucleus in the hindbrain, is neither topographically organized nor does it show a higher sensitivity than primary afferent fibers. Here, we investigated the response properties of electrosensory neurons in the dorsal octavolateral nucleus (DON), the lateral mesencephalic nucleus (LMN) and the tectum mesencephali (TM). LMN units are characterized by large receptive fields, which suggest a high degree of convergence. TM units have small receptive fields and are topographically arranged, at least in the rostro-caudal axis, the only dimension we could test. Well-defined receptive fields, however, could only be detected in the TM with a moving DC stimulus. The receptive fields of TM units, as determined by slowly scanning the rostrum and head with a 5 Hz stimulus, were very large and frequently two or more receptive fields were present. The receptive fields for LMN units were located in the anterior half of the rostrum whereas TM units had receptive fields predominantly on the head and at the base of the rostrum. A detailed analysis of the prey catching behavior revealed that it consists of two phases that coincide with the location of the receptive fields in LMN and TM, respectively. This suggests that LMN units are responsible for the initial orienting response that occurs when the prey is alongside the anterior first half of the rostrum. TM units, in contrast, had receptive fields at locations where the prey is located when the fish opens its mouth and attempts the final strike.     

How sailfish use their bills to capture schooling prey

The istiophorid family of billfishes is characterized by an extended rostrum or ‘bill’. While various functions (e.g. foraging and hydrodynamic benefits) have been proposed for this structure, until now no study has directly investigated the mechanisms by which billfishes use their rostrum to feed on prey. Here, we present the first unequivocal evidence of how the bill is used by Atlantic sailfish (Istiophorus albicans) to attack schooling sardines in the open ocean. Using high-speed video-analysis, we show that (i) sailfish manage to insert their bill into sardine schools without eliciting an evasive response and (ii) subsequently use their bill to either tap on individual prey targets or to slash through the school with powerful lateral motions characterized by one of the highest accelerations ever recorded in an aquatic vertebrate. Our results demonstrate that the combination of stealth and rapid motion make the sailfish bill an extremely effective feeding adaptation for capturing schooling prey.     

Morphology of the Mechanosensory Lateral Line System in Elasmobranch Fishes: Ecological and Behavioral Considerations

The relationship between morphology of the mechanosensory lateral line system and behavior is essentially unknown in elasmobranch fishes. Gross anatomy and spatial distribution of different peripheral lateral line components were examined in several batoids (Raja eglanteria, Narcine brasiliensis, Gymnura micrura, and Dasyatis sabina) and a bonnethead shark, Sphyrna tiburo, and are interpreted to infer possible behavioral functions for superficial neuromasts, canals, and vesicles of Savi in these species. Narcine brasiliensis has canals on the dorsal surface with 1 pore per tubule branch, lacks a ventral canal system, and has 8–10 vesicles of Savi in bilateral rows on the dorsal rostrum and numerous vesicles ( = 65 ± 6 SD per side) on the ventral rostrum. Raja eglanteria has superficial neuromasts in bilateral rows along the dorsal body midline and tail, a pair anterior to each endolymphatic pore, and a row of 5–6 between the infraorbital canal and eye. Raja eglanteria also has dorsal canals with 1 pore per tubule branch, pored and non-pored canals on the ventral surface, and lacks a ventral subpleural loop. Gymnura micrura has a pored dorsal canal system with extensive branch patterns, a pored ventral hyomandibular canal, and non-pored canal sections around the mouth. Dasyatis sabina has more canal pores on the dorsal body surface, but more canal neuromasts and greater diameter canals on the ventral surface. Sphyrna tiburo has primarily pored canals on both the dorsal and ventral surfaces of the head, as well as the posterior lateral line canal along the lateral body surface. Based upon these morphological data, pored canals on the dorsal body and tail of elasmobranchs are best positioned to detect water movements across the body surface generated by currents, predators, conspecifics, or distortions in the animal's flow field while swimming. In addition, pored canals on the ventral surface likely also detect water movements generated by prey. Superficial neuromasts are protected from stimulation caused by forward swimming motion by their position at the base of papillar grooves, and may detect water flow produced by currents, prey, predators, or conspecifics. Ventral non-pored canals and vesicles of Savi, which are found in benthic batoids, likely function as tactile or vibration receptors that encode displacements of the skin surface caused by prey, the substrate, or conspecifics. This mechanotactile mechanism is supported by the presence of compliant canal walls, neuromasts that are enclosed in wide diameter canals, and the presence of hair cells in neuromasts that are polarized both parallel to and nearly perpendicular to the canal axis in D. sabina. The mechanotactile, schooling, and mechanosensory parallel processing hypotheses are proposed as future directions to address the relationships between morphology and physiology of the mechanosensory lateral line system and behavior in elasmobranch fishes.     

Sexual dimorphism in head structures of the weevil Rhopalapion longirostre (Olivier 1807) (Coleoptera: Curculionoidea): a response to ecological demands of egg deposition

Extreme sexually dimorphic phenotypes are frequently attributed to strong sexual selection but they can also arise as a consequence of different ecological demands. The evolutionary emergence of elongated rostra was a key event in the adaptive radiation of weevils. Exaggerated female rostra evolved in numerous weevil taxa, enabling females to bore long channels for egg deposition into various parts of host plants. The investigated ecological scenario involves three species of brentid weevils, all associated with the same host plant, Alcea rosea. The present study reveals that: (1) Rhopalapion longirostre bores egg channels into the buds, and the female rostrum is twice as long and its surface is smoother than in the male; (2) Alocentron curvirostre and Aspidapion validum live on the same host plant but use the stems for egg deposition; in these species, female rostra are not exaggerated; (3) the females of all three species possess a stronger mandible musculature than males; (4) the elongated female snout of R. longirostre is a response to the requirements of boring egg channels of maximal depth into the buds of the host plant; and (5) female muscle strength is an adaptation to boring into hard plant tissues, irrespective of rostrum length. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 642–660.