A 5000-YEAR FOSSIL RECORD OF LARVAL SHELL MORPHOLOGY OF SUBMARINE CAVE MICROSHELLS

A 5000-year fossil series of minute submarine cave bivalves was studied using morphometric and evolutionary analyses. The obtained results indicate that the shapes of larval shells of studied species were labile, whereas the size of the larval shell was stable in each species studied. This result is different than that previously reported in most other studies in which size change is more common than shape change. This unique evolutionary pattern of these bivalves might be attributed to their refugial lifestyle.     

End‐Triassic bivalve extinction: Lombardian Alps,Italy

A major biotic crisis affecting virtually all major marine invertebrate clades occurred at the close of the Triassic. Species‐level data on bivalves from the Lombardian Alps of Italy record the extinction and suggest a possible causal mechanism. A significant decline in species richness is observed during the lower Rhaetian, where 51% of bivalve species, equally distributed among infaunal and epifaunal filter‐feeders, went extinct. The taxonomic loss at the middle Rhaetian was more severe, where 71% of the bivalve species were eliminated, including all infaunal and 50% of the epifaunal species. The data indicate that the extinction selectively eliminated infaunal bivalves.

An initial loss of bivalve species richness during the middle and upper Rhaetian correlates with changes in sedimentary facies related to a fall in relative sea level. This sea level fall is marked by the onset of peritidal micrites and shifting ooid shoals which may have rendered substrates unsuitable for both epifaunal and infaunal bivalves. The possible influences of temperature and salinity fluctuations are difficult to assess, but they may also have had a deleterious effect on the local bivalve fauna. The loss due to peritidal conditions is not consistent with the selective survivorship of epifaunal taxa recurring in overlying Jurassic rocks.

We propose that physiologic differences and selective resistance to physical stress are consistent with the pattern of selective extinction. Facies shifts associated with the marine regression are not sufficient to account for the extremely high magnitude of infaunal extinction. This selection against infaunal bivalves is probably caused by their decreased capacity to filter feed relative to their metabolic demands. A decrease in primary productivity could have selectively eliminated the infauna. Oceanographic processes or atmospheric darkening, perhaps caused by an extraterrestrial impact, could drastically limit food resources (primary productivity) and is consistent with the selective extinction at the end of the Triassic.     

Biology and conservation of freshwater bivalves: past,present and future perspectives

Freshwater bivalves have been highly threatened by human activities, and recently their global decline has been causing conservational and social concern. In this paper, we review the most important research events in freshwater bivalve biology calling attention to the main scientific achievements. A great bias exists in the research effort, with much more information available for bivalve species belonging to the Unionida in comparison to other groups. The same is true for the origin of these studies, since the publishing pattern does not always correspond to the hotspots of biodiversity but is concentrated in the northern hemisphere mainly in North America, Europe and Russia, with regions such as Africa and Southeast Asia being quite understudied. We also summarize information about past, present and future perspectives concerning the most important research topics that include taxonomy, systematics, anatomy, physiology, ecology and conservation of freshwater bivalves. Finally, we introduce the articles published in this Hydrobiologia special issue related with the International Meeting on Biology and Conservation of Freshwater Bivalves held in 2012 in Bragança, Portugal.     

<Emphasis Type="Italic">Arctica islandica:</Emphasis> the longest lived non colonial animal known to science

The ocean quahog, Arctica islandica is not just the longest living bivalve, it is also the longest lived, non-colonial animal known to science. With the maximum life span potential ever increasing and currently standing in excess of 400 years the clam has recently gained interest as a potential model organism for ageing research. This review details what is known about the biology of A. islandica, it discusses observed age-associated changes and reviews previous ageing research undertaken on the species and other long-lived bivalves which may be applicable to future ageing research and discusses future directions for ageing research with A. islandica. Historically much of the research on bivalves has been targeted at their utilization as a food source, environmental sentinels and more recently the use of their shells as archives of environmental change. The result of this has been an abundance of knowledge on bivalve life strategies, and a limited amount of information on the physiological changes in the cells and tissues of bivalves during the ageing process. However, research into the mechanisms of senescence of long-lived bivalves from a biogerontological perspective has advanced only recently. The research undertaken thus far has documented age-related differences in anti-oxidant defences and accumulation of oxidative products but despite the recent attention into ageing of A. islandica it is still to be ascertained if the species experiences senescence. Future directions for ageing research using A. islandica are discussed.     

Testing for adaptive evolution of the female reproductive protein ZPC in mammals,birds and fishes reveals problems with the M7-M8 likelihood ratio test

Background  

Adaptive evolution appears to be a common feature of reproductive proteins across a very wide range of organisms. A promising way of addressing the evolutionary forces responsible for this general phenomenon is to test for adaptive evolution in the same gene but among groups of species, which differ in their reproductive biology. One can then test evolutionary hypotheses by asking whether the variation in adaptive evolution is consistent with the variation in reproductive biology. We have attempted to apply this approach to the study of a female reproductive protein, zona pellucida C (ZPC), which has been previously shown by the use of likelihood ratio tests (LRTs) to be under positive selection in mammals.     

The role of challenging incentives in feedback-assisted heart rate reduction for coronary-prone adult males

Three experiments were performed to study the influence of challenging incentives on feedback-assisted heart rate reduction for coronary-prone (Type A) and non-coronary-prone (Type B) males. In the first experiment, when subjects were given a competitive instructional set, Type As were significantly more successful relative to Type Bs in reducing their heart rate; with a noncompetitive set, Type Bs were significantly more successful than were Type As. In the second experiment, when told that heart rate reduction was a scarce ability, Type As reduced heart rate significantly better than did Type Bs; when told that heart rate reduction was a common ability, Type Bs achieved significantly greater heart rate reduction than did Type As. In the third experiment, when heart rate reduction was described as being instrumental to time-urgency (i.e., getting more done in less time), Type As reduced heart rate significantly bettern than did Type Bs; when heart rate reduction was described as being instrumental to relaxation, Type Bs were significantly better able to reduce heart rate. In all three studies, the incentives had no effect on heart rate when feedback was not provided. The results are discussed as support for the notion that Type A behavioral pattern characteristics can be exploited to reduce Type A symptoms. Implications for how coronary-prone individuals may be challenged to modify symptoms within the clinical setting are discussed.     

Life-history characteristics and sexual strategy of Mytilopsis sallei (Bivalvia: Dreissenacea), introduced into Hong Kong

First recorded from Hong Kong in 1980, Mytilopsis sallei now dominates the intertidal pier community within the Government Dockyard, Victoria Harbour. Analysis of monthly samples of M. sallei has demonstrated aspects of the reproductive strategy and life-history characteristics correlated with seasonal changes in local water quality.
Mytilopsis sallei is dioecious, has a high fecundity, matures early (at 8–10 mm shell length), grows fast and the majority of the population is probably semelparous. These are characteristic traits of opportunistic r -strategists. Comparable characteristics are typical of other introduced bivalves. Maximum life span of M. sallei in the Dockyard is probably less than 20 months with, however, most of the population dying before that. Heavy recruitment, particularly during spring-summer, suffocates older individuals. The shells of dead animals similarly last for little more than one year, dissolution and crushing effecting this. A mat of byssal threads serves to bind the mass and anchor it to the substratum.
Mytilopsis sallei exhibits two periods of reproductive activity and settlement per year. These are possibly two elements of a single recruitment divided into minor (autumn-winter) and major (spring-summer) components by either high summer temperatures or low salinities. Summer and winter recruits of M. sallei , respectively, mature to produce the summer and winter juveniles of the following year. Over-stepping generations plus survival of a few individuals into their second year thus ensure continued success of M. sallei , and account for its spread and dominance in its introduced range. Such a bimodal pattern appears typical of many Hong Kong intertidal, estuarine and freshwater bivalves.     

Population biology patterns of commercially important mollusks in México

The need to propose recommendations for the management of over 80 species of bivalves and gastropod mollusks exploited commercially in Mexico, led to look for trends on the population and reproductive biology in relation to prevailing environmental conditions of the habitats where they are exploited. The reproductive cycle, growth parameters for the von Bertalanffy equation, mortality and recruitment of 18 populations of 14 species from 13 localities are compared and related to ambient temperature, precipitation, evaporation, geomorphology, tides, and water salinity and temperature. Localities were classified as influenced by landmasses or with marine influence, with a desert or tropical humid climate. With restricted or continuous communication to oceanic waters and with or without freshwater runoff. The reproductive cycles were classified in four groups in relation to intensity and duration of the spawning season: 1) limited to one annual spawning, 2) two or more defined spawning periods, 3) two or more extended spawning periods, and 4) continuous low intensity spawning. And three groups in relation to gonad recovery, and duration and intensity of gametogenesis: 1) post spawn and rest stages absent or restricted, 2) fast gametogenesis and a clear mature stage. and 3) extended gametogenesis and limited maturity stages. The population parameters were classified in relation to age structure and number of cohorts, intensity and duration of recruitment, and growth rates as expressed by infinity and K. In relation to their life cycle four types were found: 1) population represented by only one cohort, at least during part of the year, 2) with two or more cohorts at any time, 3) longevity under five years, and 4) longevity over live years. In relation to recruitment: 1) one recruitment period restricted to a short season, 2) two or more recruitment periods, 3) constant recruitment with one or more peaks, and 4) constant recruitment without periods of dominance.     

Reproductive apparatus and male accessory structures in two batrachoid species (Teleostei, Batrachoididae)

The morphology of the genital apparatus of two batrachoid species, Opsanus tau and Porichthys notatus , was studied. The anatomical organization of the female reproductive apparatus is similar in both species but differences are observed in the rhythm of gametogenesis with individual oocyte production asynchronous in O. tau and group synchronous in P. notatus. The male reproductive apparatus is similarly organized in the two species, with both showing enlongated testes with an efferent duct system, two main testicular ducts, a common sperm duct, and a pair of multi-channel accessory structures. The sperm transport system consisting of the efferent duct system, main testicular ducts, and sperm duct is more developed in P. notatus and only in this species does it secrete sialoglycoproteins. Male accessory organs also secrete sialoglycoprotein in both species, but they appear more developed in O. tau. Intraspecific variability in development of accessory structures and mucin secretion was also observed between the two male morphs of P. notatus. Type I males, which build nests and perform parental care to eggs and fry, have larger accessory organs and more abundant secretion than type II males, which adopt opportunistic spawning tactics. The possible role played by mucins as components of the seminal fluid, in both species, and their inter-and intraspecific variability are discussed in the light of the reproductive biology and the presence of alternative male mating tactics.     

油果樟属和近缘属的网脉结构式样(英文)

对油果樟属(Syndiclis Hook.f.)及其近缘属琼楠属(Beilschmiedia Nees)、孔药楠属(Sinopora J.Li et al.)、国产土楠属(Endiandra R.Br.)和Potameia的网脉结构进行了观察。结果表明,它们的网脉结构可分为3种类型:A型网格小且小脉无游离末端;B型网格小但有不分枝或简单分枝的游离末端;C型网格粗且网脉末端多分枝。琼楠属网脉结构多样,具有全部3种类型,其余4属均仅有1种类型,油果樟属、孔药楠属以及土楠属均为A型,明显不同于Potameia的C型网脉结构。     

Lynx reproduction – Long-lasting life cycle of corpora lutea in a feline species

A review of lynxes’ reproductive biology and comparison between the reproductive cycles of the domestic cat and lynxes is presented. Three of the four lynx species (the bobcat excluded) express quite similar reproductive pattern (age at sexual maturity, estrus and pregnancy length, litter size). Similarly to the domestic cat, the bobcat is polyestric and can have more than one litter per year. Domestic cats and many other felid species are known to express anovulatory, pregnant and pseudo-pregnant reproductive cycles in dependence on ovulation induction and fertilization. The formation of corpora lutea (CLs) occurs after ovulation. In pregnant animals, luteal function ends with parturition, whereas during pseudo-pregnancy a shorter life span and lower hormone secretion are observed. The life cycle of corpora lutea in Eurasian lynxes is different from the pattern described in domestic cats. Lynx CLs produce progestagens in distinctive amounts permanently for at least two years, regardless of their origin (pregnancy or pseudo-pregnancy). It is suggested that long-lasting CLs induce a negative feedback to inactivate folliculogenesis, turning a normally polyestric cycle observed in most felids into a monoestric cycle in lynxes.     

Occurrence,Growth and Food of Longheaded Eagle Ray, <Emphasis Type="Italic">Aetobatus flagellum</Emphasis>, in Ariake Sound,Kyushu, Japan

Synopsis The longheaded eagle ray, Aetobatus flagellum, has recently increased significantly in numbers in Ariake Sound. It is assumed that it feeds on bivalves and so, to prevent predation by eagle rays on bivalves, a ‘predator control program’ aimed at reducing the ray population has been in place since 2001. We examined their occurrence, age, growth and food in Ariake Sound to obtain data on the ecology of the eagle ray and provide basic information on their potential impact on bivalve stocks in Ariake Bay. The eagle ray is a seasonal visitor to Ariake Sound, increasing in numbers from April, and peaking during the summer. None were captured during surveys in December and February. Their movement pattern around the bay differed according to sex. Pregnant females were caught in the estuary during August and September. Females grew to a larger size than males and apparently lived longer. The maximum ages were 19 years for females and 9 years for males. Growth until two years was similar in both sexes, but after 2 years females grew larger. The eagle ray fed only on bivalves, especially Ruditapes philippinarum and Atrina pectinata, very important fishery species farmed in Ariake Bay.     

Modeling bivalve diversification: the effect of interaction on a macroevolutionary system

The global diversification of the class Bivalvia has historically received two conflicting interpretations. One is that a major upturn in diversification was associated with, and a consequence of, the Lake Permian mass extinction. The other is that mass extinctions have had little influence and that bivalves have experienced slow but nearly steady exponential diversification through most of their history, unaffected by interactions with other clades. We find that the most likely explanation lies between these two interpretations. Through most of the Phanerozoic, the diversity of bivalves did indeed exhibit slow growth, which was not substantially altered by mass extinctions. However, the presence of "hyperexponential bursts" in diversification during the initial Ordovician radiation and following the Late Permian and Late Cretaceous mass extinctions suggests a more complex history in which a higher characteristic diversification rate was dampened through most of the Phanerozoic. The observed pattern can be accounted for with a two-phase coupled (i.e., interactive) logistic model, where one phase is treated as the "bivalves" and the other phase is treated as a hypothetical group of clades with which the "bivalves" might have interacted. Results of this analysis suggest that interactions with other taxa have substantially affected bivalve global diversity through the Phanerozoic.     

Bivalve ecology in a Silurian shelf environment

The Ludlow Series of the Welsh Borderland represents a gradient from quiet. deep shelf muds to shallow, storm-deposited silts. A fauna of 44 bivalve species shows a pattern of overlapping environmental ranges which span the full extent of the shelf gradient. Bivalve abundance is highest at the extremes of this gradient, where endobyssate forms are common in storm-deposited silts, and nuculoids locally dominate the fauna of the deep shelf muds. Species diversity of bivalves, however, is highest in low-stress. mid-shelf environments, where bivalves of small population sizes comprise a minimal proportion of the benthic fauna. Niche sizes, species diversity. and total environmental range of the bivalves is comparable to that of Ludlow brachiopods, even though the latter group is far more abundant as individuals.     

Mating modifies female life history in a haplodiploid spider mite

Mating usually modifies females' resource allocation pattern, often as a result of conflicts between male and female partners. Can such a switch occur even in the absence of sexual conflicts? We addressed this issue in the haplodiploid spider mite Tetranychus urticae, whose biology and population structure considerably reduce conflicts between males and females over reproductive decisions. Comparing virgin and mated females, we tested the hypothesis that mated females modify their allocation pattern so as to maximize their probability of producing daughters. Mated females produced fewer but larger eggs, resulting in an overall similar reproductive effort but an increased probability of producing daughters, since in this species larger eggs are more likely to be fertilized and thus to become female. Moreover, mated females concentrated their reproduction early in life. Again, this might be a way to produce more daughters, since sperm is more abundant early in life. For virgins, spreading reproductive investment might be a way to save resources to extend life span, thus increasing their probability of encountering a sexual partner. Females with multiple opportunities for mating produced fewer eggs and a less female-biased sex ratio than once-mated females, raising the question of why multiple mating often occurs in this species.     

Different types of circulatory responses to mental tasks

The present study investigated the circulatory responses to two mental tasks. Forty males and females performed a mental subtraction task and a color-word task. During each task, the systolic and diastolic blood pressure, mean arterial pressure, heart rate, stroke volume, cardiac output, and total peripheral resistance were measured as cardiovascular indices for a 5-min baseline, a 5-min task period, and a 10-min recovery period. As for the results, three hemodynamic reactivity patterns were verified: Pattern C, characterized by increased cardiac output and decreased total peripheral resistance; Pattern M, characterized by a moderate increase in both cardiac output and total peripheral resistance; and Pattern V, characterized by increased total peripheral resistance and decreased cardiac output. Also, four response types were found among all subjects: Type 1: cardiovascular responses showed the cardiac pattern for both tasks; Type 2: cardiovascular responses changed between the cardiac pattern and the mixed pattern with a change of tasks; Type 3: cardiovascular responses showed the mixed pattern for both tasks; Type 4: cardiovascular responses changed between the mixed pattern and the vascular pattern with a change of tasks. The comparison between types showed that Type 3 and Type 4 had an elevation in their blood pressure by an increased total peripheral resistance. On the other hand, Type 1 and Type 2 tended to have an increased blood pressure by a rise in their cardiac output. And Type 3 and Type 4 showed higher blood pressure and higher scores on the Type A behavior pattern questionnaire. In conclusion, at least four types of circulation response to the mental tasks existed, with Type 3 and Type 4 having higher blood pressure responses and tending to have an elevated blood pressure by a rise in their total peripheral resistance.     

On bivalve phylogeny: a high-level analysis of the Bivalvia (Mollusca) based on combined morphology and DNA sequence data

Abstract. Bivalve classification has suffered in the past from the crossed-purpose discussions among paleontologists and neontologists, and many have based their proposals on single character systems. More recently, molecular biologists have investigated bivalve relationships by using only gene sequence data, ignoring paleontological and neontological data. In the present study we have compiled morphological and anatomical data with mostly new molecular evidence to provide a more stable and robust phylogenetic estimate for bivalve molluscs. The data here compiled consist of a morphological data set of 183 characters, and a molecular data set from 3 loci: 2 nuclear ribosomal genes (18S rRNA and 28S rRNA), and 1 mitochondrial coding gene (cytochrome c oxidase subunit I), totaling ∼3 Kb of sequence data for 76 molluscs (62 bivalves and 14 outgroup taxa). The data have been analyzed separately and in combination by using the direct optimization method of Wheeler (1996), and they have been evaluated under 12 analytical schemes. The combined analysis supports the monophyly of bivalves, paraphyly of protobranchiate bivalves, and monophyly of Autolamellibranchiata, Pteriomorphia, Heteroconchia, Palaeoheterodonta, and Heterodonta s.l., which includes the monophyletic taxon Anomalodesmata. These analyses strongly support the conclusion that Anomalodesmata should not receive a class status, and that the heterodont orders Myoida and Veneroida are not monophyletic. Among the most stable results of the analysis are the monophyly of Palaeoheterodonta, grouping the extant trigoniids with the freshwater unionids, and the sister-group relationship of the heterodont families Astartidae and Carditidae, which together constitute the sister taxon to the remaining heterodont bivalves. Internal relationships of the main bivalve groups are discussed on the basis of node support and clade stability.     

Abundance – occupancy relationships in macrofauna on exposed sandy beaches: patterns and mechanisms

We studied the relationship between abundance and extent of occupancy of 158 species of macrofauna inhabiting 66 sandy beaches around the coast of Great Britain. We also used these data to test the predictions of two hypotheses proposed to explain positive abundance-occupancy relationships. We found a strong positive relationship between abundance and extent of occupancy; this pattern was apparent in taxonomic subsets of organisms which have contrasting reproductive and dispersal traits such as planktotrophic/lecithotrophic development in the plankton vs brood development under parental care. Moreover, the abundance-occupancy relationships in these taxonomic subsets had statistically indistinguishable slopes, and elevation. We propose that this lends support to the notion that differences in population structure such as the tendency to form metapopulations may not be primary determinants of the abundance-occupancy pattern in these taxa as proposed by the rescue/metapopulation hypothesis. To test the predictions of the niche-breadth hypothesis we derived values describing the range of sediment grain-sizes exploited by members of two taxonomic subgroups: amphipods and bivalves. We found a weak, statistically non-significant relationship between this niche-breadth measure and occupancy in bivalves which have been shown to respond to grain-size in previous studies, however this was negated after correction for possible artefacts of sampling effort. All other relationships between abundance or occupancy and grain-size range were non-significant. The consistency of the demonstrated abundance-occupancy relationship with those demonstrated in other studies of primarily terrestrial fauna indicates some shared mechanistic explanation, but our data fail to provide support for the two mechanistic hypotheses investigated.     

Pan-tropical distribution of the Jurassic ostreid bivalves

Globally, the Jurassic cemented ostreid bivalves from northern Tibet, SW China, have a pan-tropical distribution pattern between palaeolatitudes of 60° South and North. Ostreid bivalves have tiny to large larvae, and nearly all of them have a cemented mode of life during their adult stage. The distribution pattern and the habits of the Jurassic ostreid bivalves revealed that, in the Jurassic time interval, all seas and oceans were interconnected, and ostreid bivalves were very capable of dispersion through their planktonic larval stage or as pseudoplankton during the post-larval stage, and even were able to cross the palaeo-Pacific Ocean from east to west. However, latitudinal temperature variation limited the distribution of these thermophilous bivalves to the lower and middle latitudes.