Relationship between shape and trophic ecology of selected species of Sparids of the Caprolace coastal lagoon (Central Tyrrhenian sea)

Synopsis The shapes of juveniles of nine species of the family Sparidae (Diplodus annularis, Diplodus puntazzo, Diplodus sargus, Diplodus vulgaris, Lithognathus mormyrus, Pagellus acarne, Sarpa salpa, Sparus aurata, Spondyliosoma cantharus), collected in the tide channel of the Caprolace Lagoon (Central Tyrrhenian Sea—Italy) were studied using geometric morphometry. These species have different ecologies. The trophic ecology of each species, reported as TROPH values, are related to shape. For the first time the relationship between shape and trophic ecology in sparids was studied in a quantitative way giving an ecomorphological meaning to the shape differences. Mean shapes of carnivorous, omnivorous and herbivorous fish were extracted, analyzed and found to be unique. Strict herbivores such as Sarpa salpa have a small mouth gap; omnivores such as the four species of the genus Diplodus have a higher body (discoidal) and a caudal peduncle shorter and higher; carnivorous species such as Lithognathus mormyrus, possess a relatively larger head region, a larger mouth gap, a longer body and a caudal peduncle longer and narrower.     

Tooth reorientation affects tooth function during prey processing and tooth ontogeny in the lesser electric ray, Narcine brasiliensis

The dental anatomy of elasmobranch fishes (sharks, rays and relatives) creates a functional system that is more dynamic than that of mammalian dentition. Continuous dental replacement (where new teeth are moved rostrally to replace older ones) and indirect fibrous attachment of the dentition to the jaw allow teeth to reorient relative to the jaw over both long- and short-term scales, respectively. In this study, we examine the processing behavior and dental anatomy of the lesser electric ray Narcine brasiliensis (Olfers, 1831) to illustrate that the freedom of movement of elasmobranch dentition allows a functional flexibility that can be important for complex prey processing behaviors. From static manipulations of dissected jaws and observations of feeding events in live animals, we show that the teeth rotate during jaw protrusion, resulting in a secondary grasping mechanism that likely serves to hold prey while the buccal cavity is flushed free of sediment. The function of teeth is not always readily apparent from morphology; in addition to short-term reorientation, the long-term dental reorientation during replacement allows a given tooth to serve multiple functions during tooth ontogeny. Unlike teeth inside the mouth, the cusps of external teeth (on the portion of the tooth pad that extends past the occlusal plane) lay flat, such that the labial faces act as a functional battering surface, protecting the jaws during prey excavation.     

The relative congruence of cranial and genetic estimates of hominoid taxon relationships: implications for the reconstruction of hominin phylogeny

Previous analyses of extant catarrhine craniodental morphology have often failed to recover their molecular relationships, casting doubt on the accuracy of hominin phylogenies based on anatomical data. However, on the basis of genetic, morphometric and environmental affinity patterns, a growing body of literature has demonstrated that particular aspects of cranial morphology are remarkably reliable proxies for neutral modern human population history. Hence, it is important to test whether these intra-specific patterns can be extrapolated to a broader primate taxon level such that inference rules for understanding the morphological evolution of the extinct hominins may be devised. Here, we use a matrix of molecular distances between 15 hominoid taxa to test the genetic congruence of 14 craniomandibular regions, defined and morphometrically delineated on the basis of previous modern human analyses. This methodology allowed us to test directly whether the cranial regions found to be reliable indicators of population history were also more reliable proxies for hominoid genetic relationships. Cranial regions were defined on the basis of three criteria: developmental-functional units, individual bones, and regions differentially affected by masticatory stress. The results found that all regions tested were significantly and strongly correlated with the molecular matrix. However, the modern human predictions regarding the relative congruence of particular regions did not hold true, as the face was statistically the most reliable indicator of hominoid genetic distances, as opposed to the vault or basicranium. Moreover, when modern humans were removed from the analysis, all cranial regions improved in their genetic congruence, suggesting that it is the inclusion of morphologically-derived humans that has the largest effect on incongruence between morphological and molecular estimates of hominoid relationships. Therefore, it may be necessary to focus on smaller intra-generic taxonomic levels to more fully understand the effects of neutral and selective evolutionary processes in generating morphological diversity patterns.     

Postnatal ontogenetic size and shape changes in the craniums of plateau pika and woolly hare(Mammalia: Lagomorpha)

In the present study, postnatal ontogenetic size and shape changes in the cranium of two lagomorph species, the plateau pika(Ochotona curzoniae) and woolly hare(Lepus oiostolus), were investigated by geometric morphometrics. The ontogenetic size and shape changes of their cranium exhibited different growth patterns in response to similar environmental pressures on the Qinghai-Tibetan Plateau. The overall size change in the cranium of the plateau pika was slower than that of the woolly hare. The percentage of ontogenetic shape variance explained by size in the woolly hare was greater than that in the plateau pika. The overall shape of the cranium was narrowed in both species, and morphological components in relation to neural maturity showed negative allometry, while those responsible for muscular development showed isometric or positive allometry. The most remarkable shape variations in the plateau pika were associated with food acquisition(temporalis development), though other remarkable shape variations in the incisive and palatal foramen in the ventral view were also observed. The most important shape change in the woolly hare was demonstrated by the elongation of the nasal bones, expansion of the supra-orbital process and shape variation of the neurocranium.     

A comparison of the electrosensory morphology of a euryhaline and a marine stingray

The electrosensory system is found in all chondrichthyan fishes and is used for several biological functions, most notably prey detection. Variation in the physical parameters of a habitat type, i.e. water conductivity, may influence the morphology of the electrosensory system. Thus, the electrosensory systems of freshwater rays are considerably different from those of fully marine species; however, little research has so far examined the morphology and distribution of these systems in euryhaline elasmobranchs. The present study investigates and compares the morphology and distribution of electrosensory organs in two sympatric stingray species: the (euryhaline) estuary stingray, Dasyatis fluviorum, and the (marine) blue-spotted maskray, Neotrygon kuhlii. Both species possess a significantly higher number of ventral electrosensory pores than previously assessed elasmobranchs. This correlates with a diet consisting of benthic infaunal and epifaunal prey, where the electrosensory pore distribution patterns are likely to be a function of both ecology and phylogeny. The gross morphology of the electrosensory system in D. fluviorum is more similar to that of other marine elasmobranch species, rather than that of freshwater species. Both D. fluviorum and N. kuhlii possess ‘macro-ampullae’ with branching canals leading to several alveoli. The size of the pores and the length of the canals in D. fluviorum are smaller than in N. kuhlii, which is likely to be an adaptation to habitats with lower conductivity. This study indicates that the morphology of the electrosensory system in a euryhaline elasmobranch species seems very similar to that of their fully marine counterparts. However, some morphological differences are present between these two sympatric species, which are thought to be linked to their habitat type.     

Geometric morphometrics of the skull of Tinamidae (Aves, Palaeognathae)

The Tinamidae comprise exclusively Neotropical palaegnathous birds, with homogeneous body morphology and no sexual dimorphism. The goal of this work was to explore the variation in skull morphology between taxa and its possible correspondence with features such as diet or gender using geometric morphometric tools. Eleven landmarks were analyzed in 53 skulls of 4 genera that inhabit grasslands: Nothoprocta, Eudromia, Nothura and Rhynchotus. Intrageneric and intergeneric variability was analyzed. The genera studied here can be distinguished based on the geometric shape of their skull, with prenarial region length and neurocranium shape as the most outstanding features. In the genus Eudromia, males and females could be differentiated, while in the genus Nothoprocta, the species differentiated according to their trophic habits. This study allows establishing that genera and, in some cases, the gender of the Tinamidae can be differentiated based on cranial shape.     

The Neanderthal "chignon": variation, integration, and homology

The occipital bun ("chignon") is cited widely as a Neanderthal derived trait. It encompasses the posterior projection/convexity of the occipital squama and is associated with lambdoid flattening on the parietal. A 'hemibun' in some Upper Paleolithic Europeans is thought by some authors to indicate interbreeding between Neanderthals and early modern Europeans. However, 'bunning' is difficult to measure, and the term has been applied to a range of morphological patterns. Furthermore, its usefulness in phylogenetic reconstruction and its homologous status across modern and fossil humans have been disputed. We present a geometric morphometric study that quantitatively evaluates the chignon, assesses its usefulness in separating Neanderthals from modern humans, and its degree of similarity to Upper Paleolithic 'hemibuns.' We measured the three-dimensional coordinates of closely spaced points along the midsagittal plane from bregma to inion and of anatomical landmarks in a large series of recent human crania and several Middle and Late Pleistocene European and African fossils. These coordinate data were processed using the techniques of geometric morphometrics and analyzed with relative warps, canonical variates, and singular warps. Our results show no separation between Neanderthals and modern humans, including early modern Europeans, when the shape of the occipital plane midsagittal-profile is considered alone. On the other hand, Neanderthals are well separated from both recent and fossil modern humans when information about the occipital's relative position and relative size are also included. Furthermore, the occurrence of a highly convex and posteriorly projecting midline occipital profile (interpreted as the occipital bun) is highly correlated (>0.8) with a flat parietal midsagittal profile and with antero-superiorly positioned temporal bones across both our recent and our fossil human samples. We conclude that the shape of the occipital profile alone should not be considered an independent trait, as it is very tightly integrated with braincase shape. Our analysis does not support differences in integration of the posterior midsagittal profile and the cranial base in Pleistocene and recent humans.     

Food resource partitioning among Arctic sublittoral lysianassoid amphipods in summer

Five species of lysianassoid amphipods (Anonyx nugax, Anonyx sarsi, Onisimus caricus, Onisimus edwardsii, Orchomenella minuta) co-occur in the shallow sublittoral of Kongsfjorden (Svalbard, Arctic), share similar functional attributes, and exploit a common food base. All species are known to be necrophagous; however, this study revealed through combination of gut-content analysis with the morphological characteristics of their mandibles and available information on feeding ecology, the complexity of their trophic strategies. Only mature individuals of A. nugax are true scavengers; immature individuals of this species feed on both animal and non-animal food. A. sarsi and O. caricus are scavengers and predators; the former prefers polychaetes, while the latter relies mostly on zooplankton. O. edwardsii is an omnivorous feeder, and the set of its primary food consists of carrion, crustaceans, and algae. O. minuta is a detrivorous–carnivorous species. These results indicate that niche overlap among these closely related species is reduced, not only by spatial segregation, but also by the exploitation of different components of food resources.     

南极磷虾种群生物学研究进展III-摄食

鉴于南极磷虾在南极食物网中所处的关键地位,其摄食活动对南大洋海洋生态系统有着极为重要的影响。南极磷虾食物组成因季节、空间等不同而存在差异,且摄食对象的分类和鉴别也存在着较大困难,选食机制目前尚有不同意见。本文从摄食对象、摄食方式、选食机制及摄食率等方面对近百年来南极磷虾摄食生态学研究进行了总结和归纳,以期为国内外学者开展相关研究提供基础信息,并为进一步开展其摄食生态学研究提供科学思路。     

Cranial movements during suction feeding in teleost fishes: Are they modified to enhance suction production?

Suction is produced during prey capture by most teleost fishes. Here, we ask two questions about the functional basis of suction feeding. First, is there variation in the kinematic pattern produced by different species while suction feeding? Second, do species termed 'suction specialists' demonstrate similar modifications to their feeding behavior? We used 10 kinematic variables in a principal component analysis to identify axes of variation among 14 suction feeding teleost species (representing nine families and five orders within the Euteleostei) that demonstrate different feeding habits and habitats. MANOVA and Tukey post hoc tests were used to assess differences among species. Most species clustered together on the principal component axes, suggesting a generalized mechanism that facilitates unidirectional flow. Typically, only one species stood out as 'extreme' on each functional axis, and a species that stood out on one axis did not stand out on others. Only one species, the flatfish Pleuronichthys verticalis, an obligate benthic feeder, demonstrated modifications consistent with enhanced suction production. This species displayed a suite of changes that should enhance suction production, including large hyoid depression, large cranial rotation, and small gape. We suggest that suction performance may be greatest in such obligate benthic feeders because cranial morphology is highly modified and prey are captured from the substrate.     

The functional meaning of “prey size” in water snakes (Nerodia fasciata, Colubridae)

The evolutionary success of macrostomatan (enlarged-gape) snakes has been attributed to their ability to consume large prey, in turn made possible by their highly kinetic skulls. However, prey can be “large” in several ways, and we have little insight into which aspects of prey size and shape affect skull function during feeding. We used X-ray videos of broad-banded water snakes (Nerodia fasciata) feeding on both frogs and fish to quantify movements of the jaw elements during prey transport, and of the anterior vertebral column during post-cranial swallowing. In a sample of additional individuals feeding on both frogs and fish, we measured the time and the number of jaw protractions needed to transport prey through the buccal cavity. Prey type (fish vs. frog) did not influence transport kinematics, but did influence transport performance. Furthermore, wider and taller prey induced greater movements of most cranial elements, but wider prey were transported with significantly less anterior vertebral bending. In the performance trials, heavier, shorter, and wider prey took significantly more time and a greater number of jaw protractions to ingest. Thus, the functional challenges involved in prey transport depend not only upon prey mass, but also prey type (fish vs. frog) and prey shape (relative height, width and length), suggesting that from the perspective of a gape-limited predator, the difficulty of prey ingestion depends upon multiple aspects of prey size.     

Ecological attributes recorded in stable isotope ratios of arboreal prosimian hair

Carbon and nitrogen stable isotope ratios were measured in hair samples from two species of Galago from Gedi Ruins National Monument in eastern Kenya and from Lepilemur leucopus from Beza Mahafaly Special Reserve in southern Madagascar. Forest structure was generally similar in the two areas but average rainfall was lower in Madagascar. Species average ¹³C values varied with feeding height in the forest canopy and with average rainfall level as expected from reported variation in plant ¹³C values. G. garnettii, which feeds higher in the forest canopy, had less negative ¹³C values than G. zanzibaricus, which spends more time below 5 m. L. leucopus, from a drought-afflicted forest, had less negative hair ¹³C values than the two galago species. The values within the Lepilemur sample showed a positive linear relation with percent dependence on a CAM tree species and with xeric conditions within the species reserve. Nitrogen stable isotope ratios varied with trophic level of feeding and with time spent feeding on leguminous plants. The insectivorous galagos had significantly more positive ¹⁵N values than the folivorous L. leucopus. Within the Lepilemur sample, ¹⁵N values varied inversely with the percent of feeding time spent on leguminous plants. The range of ¹⁵N and ¹³C values in each of the prosimian species is larger than reported for animals fed monotonous diets and for New World monkey species. The monkey species feed as groups of individuals whereas the prosimians have solitary feeding habits. The ranges in the prosimian species apparently reflect the greater variation in diet among individual prosimians compared to individual monkeys. The isotope data reported here are equivalent, on average, to those reported for other arboreal species from similar forest habitats and with similar dietary habits. This supports the use of such data for paleoecological reconstruction of forest and woodland systems and diet reconstruction of extinct primate populations and species. Received: 18 April 1997 / Accepted: 11 August 1997