Trophic ecomorphology in eastern Pacific blennioid fishes: character transformation of oral jaws and associated change of their biological roles

Synopsis The ecomorphological relationships between the oral jaws and food spectra were highlighted in 34 species of Gulf of California blennioid fishes (5 Tripterygiidae, 13 Labrisomidae, 11 Chaenopsidae and 5 Blenniidae). Twenty-nine species are microcarnivorous, two are omnivorous browsers, two are algae grazers and one was an ‘ectoparasite’ feeder. The spectrum of oral (as opposed to pharyngeal) jaw (OJA) morphology ranges from plesiomorphic, suction-feeding (relatively large, protrusible jaws, with many coniform-caniniform teeth) to apomorphic, biting (relatively small, non protrusible jaws, with a single row of incisiform teeth). As species with similar morphology may widely differ in food, it is concluded, that morphology is not a reliable predictor for ecology in this case. With the exception of a few specialists, species with apomorphic, biting OJA utilize sessile items in addition to mobile categories and thus show a higher food diversity as compared to species with plesiomorphic OJA. Thus in the present case morphological differentiation goes along with ecological generalization. Only three blenniid species with the most apomorphic OJA may be considered as specialized also with regard to food resource utilization. Transformation of morphological characters and the ecological role of the OJA of blennioids may serve as a model to illustrate the steps required to achieve a biting-browsing and grazing feeding apparatus in many taxa of modern acanthopterygian reef fishes.     

Feeding patterns in eastern tropical Pacific blennioid fishes (Teleostei: Tripterygiidae,Labrisomidae, Chaenopsidae,Blenniidae)

Summary In terms of species number (47) and numerical abundance, blennioids are the most important primary resident rocky reef fishes in the Gulf of California, Mexico. We present the feeding patterns of the 34 most abundant species of blennioid fishes, 8 of which are Gulf endemics. A total of 2,144 specimens were sampled at 51 anaesthetic stations in 9 areas throughout the Gulf. Four feeding guilds were distinguished: 1) The majority (29 of 34 species) are microcarnivores exhibiting a number of different feeding strategies (ambush and stalking predators, active foragers, pickers, etc.). The more important prey categories were mobile invertebrates, and to some extent also sedentary fauna. Algae were of no importance for most of the latter species. 2) Hypsoblennius brevipinnis and H. gentilis are two omnivorous species, browsing mainly on sessile items including 52% and 13% (Vol.) algae in their diets. 3) Entomacrodus chiostictus and Ophioblennius steindachneri are herbivores, grazing on fine algae. 4) Plagiotremus azaleus specializes in cropping mucus and scales from the body surface of other fishes.Crustaceans account for 58.6% of the total volume of prey items in the 34 species investigated. Benthic amphipods were most important and made up 26% of the total volume of all prey items.Cluster analysis of percentage volumetric data using Squared Euclidian Distance and Horn's Index of Overlap produced distinct subgroups which coarsely reflected taxonomic grouping.The species are separated either by their geographic ranges, habitat and microhabitat preferences, feeding, or a combination thereof. Only rarely do sympatric species significantly overlap in diet.Trophic diversity as measured by the Shannon-index provides a tool for distinguishing: 1) specialists (6 species) from 2) low diversity feeders (18 species) and 3) high diversity generalists (10 species). Two different types of specialists can be distinguished: those which feed on the same items as the generalists but utilize only a very restricted prey spectrum (Stathmonotus sinuscalifornici and the chaenopsids Chaenopsis alepidota and Emblemaria hypacanthus). A second group of specialists (Entomacrodus chiostictus and Ophioblennius steindachneri as well as Plagiotremus azaleus) feed on items not utilized by any of the generalists.There is some evidence that high diversity generalists are numerically more abundant than the other trophic groups.In the labrisomids and blenniids a phylogenetic trend from microcarnivory towards feeding on sessile items appears to be expressed.     

Larval trematode infections and spatial distributions of snails

Abstract. The hypothesis that infecting trematodes influence the spatial distribution of the estuarine snail Ilyanassa obsoleta was tested. This work was conducted in the Savages Ditch habitat, Rehoboth Bay, DE, USA, which has an essentially flat, sandy-mud bottom bordered by saltmarsh shorelines and many infected snails. In 1996, two groups of snails were individually marked and released from one location after being screened for trematode infections. One group, transplanted from sites where snails tended not to be infected, consisted of snails that tested as uninfected. The other group consisted of snails native to Savages Ditch. Species of trematode carried by each snail was recorded. Marked snails were found and their positions were recorded until 2001. Snails were in five infection categories: (1) not infected, and infected with (2) Himasthla quissetensis , or (3) Lepocreadium setiferoides or (4) Zoogonus rubellus , or (5) with both H. quissetensis and Z. rubellus . The results show that the spatial distributions of snails depended on whether or not they were infected and, if infected, on which trematode species they carried. To complete life cycles, these parasites must accomplish transmission from the first (the snail) to the second intermediate hosts by short-lived, swimming cercariae. These data do not allow resolution of why snails distributed as they did, but sighting distributions of infected snails can be related to distributions of second hosts and it is proposed that parasites engender host snail distributions that improve chances of transmission.     

Crossing the impassable: genetic connections in 20 reef fishes across the eastern Pacific barrier

The 'impassable' Eastern Pacific Barrier (EPB), ca 5000 km of deep water separating the eastern from the central Pacific, is the World's widest marine biogeographic barrier. Sequencing of mitochondrial DNA in 20 reef fish morphospecies encountered on both sides of the barrier revealed cryptic speciation in two. Among the other 18 species only two showed significant differentiation (as revealed by haplotype networks and FST statistics) between the eastern and the central Pacific. Coalescence analyses indicated that genetic similarity in the 18 truly transpacific species resulted from different combinations of ages of most recent invasion and of levels of recurrent gene flow, with estimated times of initial separation ranging from approximately 30000 to 1 Myr (ago). There is no suggestion of simultaneous interruptions of gene flow among the species. Migration across the EPB was previously thought to be exclusively eastward, but our evidence showed two invasions from east to west and eight cases in which subsequent gene flow possibly proceeded in the same direction. Thus, the EPB is sporadically permeable to propagules originating on either side.     

Distinct patterns of genetic differentiation among annelids of eastern Pacific hydrothermal vents

Population genetic and phylogenetic analyses of mitochondrial COI from five deep-sea hydrothermal vent annelids provided insights into their dispersal modes and barriers to gene flow. These polychaetes inhabit vent fields located along the East Pacific Rise (EPR) and Galapagos Rift (GAR), where hundreds to thousands of kilometers can separate island-like populations. Long-distance dispersal occurs via larval stages, but larval life histories differ among these taxa. Mitochondrial gene flow between populations of Riftia pachyptila, a siboglinid worm with neutrally buoyant lecithothrophic larvae, is diminished across the Easter Microplate region, which lies at the boundary of Indo-Pacific and Antarctic deep-sea provinces. Populations of the siboglinid Tevnia jerichonana are similarly subdivided. Oasisia alvinae is not found on the southern EPR, but northern EPR populations of this siboglinid are subdivided across the Rivera Fracture Zone. Mitochondrial gene flow of Alvinella pompejana, an alvinellid with large negatively buoyant lecithotrophic eggs and arrested embryonic development, is unimpeded across the Easter Microplate region. Gene flow in the polynoid Branchipolynoe symmytilida also is unimpeded across the Easter Microplate region. However, A. pompejana populations are subdivided across the equator, whereas B. symmitilida populations are subdivided between the EPR and GAR axes. The present findings are compared with similar evidence from codistributed species of annelids, molluscs and crustaceans to identify potential dispersal filters in these eastern Pacific ridge systems.     

A catalogue of skulls and jaws of eastern tropical Pacific blennioid fishes (Blennioidei: Teleostei): A proposed evolutionary sequence of morphological change

Skulls and jaws are compared in 35 species of tropical eastern Pacific (mainly Gulf of California) blennioid fishes (5 species of Tripterygiidae, 13 Labrisomidae, 12 Chaenopsidae, 5 Blenniidae). Morphotypes are arranged in a series from relatively large-mouthed fishes (tripterygiids and a few labrisomids) with protrusible jaws and conical teeth to species with small, non-protrusible jaws and a single row of incisiform teeth. This polarity of arrangement probably reflects the direction of phylogenetic development, as suggested by outgroup comparison with other perciform fishes. Distribution patterns of morphotypes in a simple morphospace, obtained by combining dentition, shape of the jaw arch and jaw protrusibility, are discussed within an adaptive context.     

Demographic changes and life-history strategies predict the genetic diversity in crabs

Uncovering what predicts genetic diversity (GD) within species can help us access the status of populations and their evolutionary potential. Traits related to effective population size show a proportional association to GD, but evidence supports life-history strategies and habitat as the drivers of GD variation. Instead of investigating highly divergent taxa, focusing on one group could help to elucidate the factors influencing the GD. Additionally, most empirical data is based on vertebrate taxa; therefore, we might be missing novel patterns of GD found in neglected invertebrate groups. Here, we investigated the predictors of the GD in crabs (Brachyura) by compiling the most comprehensive cytochrome c oxidase subunit I (COI) available. Eight predictor variables were analysed across 150 species (16 992 sequences) using linear models (multiple linear regression) and comparative methods (PGLS). Our results indicate that population size fluctuation represents the most critical trait predicting GD, with species that have undergone bottlenecks followed by population expansion showing lower GD. Egg size, pelagic larval duration and habitat might play a role probably because of their association with how species respond to disturbances. Ultimately, K-strategists that have undergone bottlenecks are the species showing lower GD. Some variables do not show an association with GD as expected, most likely due to the taxon-specific role of some predictors, which should be considered in further investigations and generalizations. This work highlights the complexity underlying the predictors of GD and adds results from a marine invertebrate group to the current understanding of this topic.     

At-sea distributions and abundance of tropicbirds in the eastern Pacific

During spring and autumn 1980–95, we surveyed Red-tailed Phaethon rubricauda , White-tailed P. lepturus and Red-billed Tropicbirds P. aethereus at sea in the Pacific between the coast of the Americas and 176°W. For the Pacific, we had complete coverage of the range of aethereus , but only partial coverage of that of rubricauda and lepturus . Six areas of higher density were indicated: three of rubricauda , two of lepturus and one of aethereus . After pooling data across years, the 'abundance' (total number including subadults and adults) estimate for rubricauda was 81 700 (boreal spring) and 86 500 (boreal autumn) birds. Abundance of each of the three rubricauda subpopulations differed between seasons by about 50% despite seasonal consistency when populations were grouped. Furthermore, high densities of rubricauda occurred at the edge of our study area, indicating that neither of the seasonal estimates for this species could be considered as total numbers. Abundance estimates of lepturus during the non-breeding season (when these birds had dispersed from colonies) were 11 000 and 41 500 birds for northern and southern populations, respectively. Estimated abundance of aethereus during the boreal spring was 26 700 birds, and 33 400 during the boreal autumn. Because tropicbirds are attracted to survey vessels, we also estimated the abundance after excluding those recorded as flying in a steady direction, or having been attracted to the ship. Considering only stationary birds (i.e. those that could not have been attracted), our minimum estimates were 41 000 rubricauda , 15 750 aethereus , 28 000 southern lepturus and 6400 northern lepturus .     

Population differentiation in the life-history characteristics of salt-marsh annuals

Coastal salt marshes are heterogeneous spatially but predictable temporally. Genetic differentiation between populations on different parts of a marsh in response to this combination of circumstances has been well documented in several perennial species; differentiation has been evident in certain features of the life cycle that contribute to overall fitness. Our studies of the annuals in the marshes of the north Norfolk coast of Britain have shown that there are distinct populations, that have particular micro-habitats and different vegetational affinities, within the annual species Suaeda maritima and within the complex of several closely related species of Salicornia. Consequently, three sequential questions about these annuals may be posed: 1. What is the extent of genetic differentiation? 2. What features of the life history show differentiation? 3. Can any of this variation be demonstrated to have adaptive value? This paper reviews evidence for the upper- and lower-marsh populations of (diploid) Salicornia europaea agg. at Stiffkey, U.K. The six main approaches described comprise collateral cultivation, perturbation of the field environment, isozyme analysis and three types of reciprocal transplantation. The value of these complementary methods is discussed, and they are used to demonstrate that there is considerable genetic differentiation between the two populations; it is manifested in the phenology of growth, mortality and density-dependent fecundity. In terms of the ability of individuals to leave descendants, there is a dramatic reduction in fitness of each population when it is grown in the reciprocal environment. This finding indicates that the genetic differentiation has clear adaptive value.     

Some osteological differences between the blennioid fishes Limnichthys polyactis and L. rendahli,with comments on other species of Creediidae

Abstract

The two endemic species of New Zealand Limnichthys differ in several osteological characters. L. polyactis differs from L. rendahli in having a rayed dorsal margin of the opercle (cf. entire), little or no gap between the lower limb of the coracoid and the pelvis (cf. wide gap), one epural (cf. two), and narrow posterior neural and haemal spines (cf. wide spines). Comments are given on some characters in the other 10 recognised named species of Creediidae. Squamicreedia obtusa is removed from the Creediidae, and is provisionally placed in the Percophididae.     

Alternative life-history styles of cartilaginous fishes in time and space

Synopsis Cartilaginous fishes, the sharks, rays and chimaeras (class Chondrichthyes), are a very old and successful group of jawed fishes that currently contains between 900 and 1100 known living species. Chondrichthyians show a high morphological diversity during most of their evolutionary career from the Paleozoic to the present day. They are relatively large predators which have remained a major, competitive element of marine ecosystems despite the varied rivalry of numerous other marine vertebrate groups over at least 400 million years. Although restricted in their ecological roles by morphology, reproduction and other factors, the living cartilaginous fishes are highly diverse and show numerous alternative life-history styles which are multiple answers to exploiting available niches permitted by chondrichthyian limitations. Chondrichthyians living and fossil can be divided into at least eighteen ecomorphotypes, of which the littoral ecomorphotype is perhaps the most primitive and can serve as an evolutionary origin for numerous specialist ecomorphotypes with benthic, high-speed, superpredatory, deep-slope and oceanic components. Reproductive modes in cartilaginous fishes are of six types, ranging from primitive extended oviparity through retained oviparity and yolk-sac viviparity (previously ovoviviparity) to three derived forms of viviparity. Reproductive modes are not strongly correlated with ecomorphotypes and with the phylogeny of living elasmobranchs. The success and importance of cartilaginous fishes is largely underrated by marine biologists and by the public, and requires new and heretical emphasis to overcome the present inadequacies of chondrichthyian research and the problems of overexploitation that cartilaginous fishes face.     

Interethnic genetic differentiation: GM polymorphism in eastern Senegal.

Analysis of GM polymorphism has been performed on 1,806 individuals representing three sympatric ethnic groups--Bedik, Fulani, and Mandenkalu--of eastern Senegal. Haplotype frequencies estimated by maximum likelihood have been used to compute common genetic pools between the three samples and a number of other sub-Saharan African populations. Despite extreme linguistic and sociocultural differentiations and very high levels of endogamy, especially in the Bedik and Niokholo Mandenkalu, the three populations share about 90%-95% of their haplotype frequencies in a system which commonly provides strong genetic differentiations. This supports the view that, despite its importance at a large continental scale level, as it is discussed for a set of populations from many regions of sub-Saharan Africa, sociocultural differentiation usually has little effect on local genetic diversity.     

Trade-offs and spatial life-history strategies in classical metapopulations

The metapopulation concept dichotomizes space into the local scale of an ephemeral patch and the broader scale of the persistent multipatch system. Here, we consider how the "best" (i.e., optimal or noninvasible) life history of asexually reproducing organisms might address this dichotomy along environmental gradients via shifts in two key trade-offs. The expansion-survival trade-off expresses the relation between the combined growth and propagule production rate and the mortality rate. The accumulation-export trade-off partitions expansion into a local accumulation of growth plus propagules retained within the patch and the potential-colonist propagules dispersed to other patches, although the dispersal linkages among patches are assumed to be weak (a characteristic of "classical" metapopulations). We identify the best life histories along gradients of productivity, stress, and patch extinction rates for a metapopulation with and without lottery or overgrowth competition, and we compare them with results for an isolated immortal patch. The two trade-offs interact in determining best life histories, but this effect is generally small, supporting the validity of studies addressing the trade-offs separately. The accumulation-export trade-off responds strongly to the three gradients, increasing export with productivity and with patch extinction rate when this rate is high but decreasing export with higher stress; the expansion-survival trade-off increases expansion with productivity but fails to respond to stress and patch extinction rate gradients, except when the other trade-off does not occur. By linking the trade-offs to life-history strategies (i.e., colonization, exploitation, and tolerance), we separate strategies from phenomenology (i.e., from export, accumulation, and survival) along the gradients.     

Patterns of genetic differentiation in Thamnophis and Taricha from the Pacific Northwest

Aim The co‐evolutionary interaction between the common garter snake, Thamnophis sirtalis, and the rough‐skinned newt, Taricha granulosa, takes place throughout much of the Pacific Northwest (North America). The biogeography of the Pacific Northwest has been heavily influenced by the last Pleistocene glaciation, which reached a maximum as late as 14,000 yr bp . We researched: (1) what type of population structure is present for garter snakes and newts, (2) whether the population structure of these species is consistent with a Pleistocene glaciation hypothesis, and (3) how population structure and migration possibly affect co‐evolution between these species. Location The Pacific Northwest of North America, specifically northern California, Oregon and Washington in the USA. Methods We sampled approximately 20 populations for each species from three different transects. Using microsatellite markers and tissue samples from both species, we quantified the population structure for both species. Individual‐based assignment tests were used to estimate contemporary migration rates. Results Both Th. sirtalis and Ta. granulosa exhibited little genetic differentiation among our study sites, even among those separated by large distances. Significant population structure was detected on multiple geographic scales. Differences in population structure were observed among transects and between garter snake and newt transects. Contemporary migration rate estimates indicate high levels of genetic exchange between populations. Main conclusions Prior to this study, little was known about the fine‐scale population structure of either species in this region. Patterns of population structure for garter snakes and newts reflect a shared biogeographical history affected by the Pleistocene glaciation in the Pacific Northwest. Both species apparently migrate frequently between populations, thus potentially retarding the process of adaptive co‐evolution. We find that populations from a northern coastal transect (Washington) are most likely to be locally adapted.     

Evolution of morphological and behavioral ontogenies in females of a highly dimorphic clade of blennioid fishes

Comparison of ontogenetic trajectories with those inferred for ancestors provides a powerful but underused tool for the study of the evolution of different types of phenotypic characters. This approach was used to study morphological and behavioral evolution of the highly dimorphic chaenopsid genus Coralliozetus (Teleostei: Blennioidei). All sexually dimorphic synapomorphies of Coralliozetus involved evolution in females only; one character evolved via terminal addition (peramorphosis), whereas six evolved via terminal deletion (paedomorphosis). Evolution of the ontogeny of two behavioral characters (microhabitat use and feeding rate), as inferred by focal animal observations of eight species of tube blennies, was also confined to females and conformed to terminal deletion. Both sexes of outgroups and males of all species of Coralliozetus exhibit an ontogenetic shift from the open as juveniles to shelters as adults. However, females of all species of Coralliozetus retain the juvenile behavior of residing in the open. Blennies residing in the open take significantly more feeding bites than conspecifics residing in shelters, consequently, female Coralliozetus retain the high feeding rate of juveniles. Several of the paedomorphic morphological features of Coralliozetus females are plausibly associated with their paedomorphosis in microhabitat use. These include their reduced conspicuousness and reduced robustness compared to conspecific males. In groups such as chaenopsids, which undergo significant ontogenetic changes in microhabitat, paedomorphosis provides a mechanism for rapid coevolution of behavior and morphology. This study, the first to document the evolution of sexual dimorphism via both behavioral and morphological paedomorphosis, demonstrates the unique insights to be gained from a multidimensional analysis of phenotypic evolution.     

Genetic polymorphism and trade-offs in the early life-history strategy of the Pacific oyster, Crassostrea gigas (Thunberg, 1795): a quantitative genetic study

We investigated genetic variability and genetic correlations in early life-history traits of Crassostrea gigas. Larval survival, larval development rate, size at settlement and metamorphosis success were found to be substantially heritable, whereas larval growth rate and juvenile traits were not. We identified a strong positive genetic correlation between larval development rate and size at settlement, and argue that selection could optimize both age and size at settlement. However, trade-offs, resulting in costs of metamorphosing early and large, were suggested by negative genetic correlations or covariances between larval development rate/size at settlement and both metamorphosis success and juvenile survival. Moreover, size advantage at settlement disappeared with time during the juvenile stage. Finally, we observed no genetic correlations between larval and juvenile stages, implying genetic independence of life-history traits between life-stages. We suggest two possible scenarios for the maintenance of genetic polymorphism in the early life-history strategy of C. gigas.     

Are distributions of fishes in tropical estuaries influenced by turbidity over small spatial scales?

This study found no evidence that turbidity influenced the distribution of fishes in four tropical estuaries in north-eastern Queensland. When both more turbid and less turbid environments were immediately available to Ambassis vachelli and Leiognathus equulus there was no difference in abundance between the more and less turbid environments and no correlated change in abundance as the difference in turbidity increased. A similar outcome was evident for an additional six species of fish. Furthermore, the distribution of fishes was not correlated with the distribution of an important prey species, juvenile banana prawns Penaeus merguiensis , which exhibited a clear response to differences in turbidity level with higher abundance in the more turbid samples, however, the magnitude of the difference did not alter with changes in the magnitude of the differences in turbidity.     

不同生活史阶段长爪沙鼠尿标记行为的遗传和空间距离效应

气味标记普遍存在于哺乳动物类群中,它能向同类传达领地占有、社会等级及繁殖状态等多种信息。2014年4月至10月,我们在内蒙古锡林郭勒正蓝旗对长爪沙鼠 (Meriones unguiculatus) 野外种群进行了标志重捕,采用中立场的方式测定了不同社群间同性别长爪沙鼠的尿标记行为。通过建立洞群样地坐标后用勾股弦方法计算群间距离,并用微卫星DNA分子标记估算个体间的亲缘系数,以探讨野生动物标记行为是否受个体间空间和遗传距离的影响。广义线性混合效应分析显示,雄鼠间的尿标记强度在繁殖期和贮食期受空间距离或遗传距离的影响均不显著。繁殖期雌鼠间的尿标记强度受空间或遗传距离的影响亦不明显,但在贮食期,遗传距离对雌鼠间标记的强度有显著影响,且遗传距离与空间距离对标记强度有明显的交互作用。本研究结果暗示亲缘关系和空间距离对长爪沙鼠的尿标记行为具有一定影响,这与长爪沙鼠的繁殖或贮食行为相适应。     

Larval budding, metamorphosis, and the evolution of life-history patterns in echinoderms

Abstract. The oral surface and mouth of juvenile asteroids and echinoids with indirect development forms on the lower left side of the larval body, thus establishing a new axis of body symmetry. In contrast, the juvenile mouth of ophiuroids and holothuroids develops from the larval one, and the larval and adult body axes roughly coincide. Explaining how two such disparate modes of development arose in evolution has been a perennial problem for echinoderm biologists, but recent observations on larval budding in asteroids may provide an answer. The juvenile mouth of asteroids forms near the base of the left posterolateral lobe. The posterolateral lobes are also the principal site of bud formation in asteroid larvae that propagate asexually, and buds form mouths. By accelerating the development of oral and ectodermal structures belonging to the bud, and combining these with internal organs derived from the parent larva, a composite individual could be constructed with the same orientation and positioning as the juvenile rudiment in asteroids. Whether this also explains the position of the juvenile rudiment in echinoids is a more complex question, depending in part on whether asexual propagation is derived, and restricted to asteroids and ophiuroids, or is more primitive and hence widespread among stem echinoderms.