The fauna of athalassic saline waters in Australia and the Altiplano of South America: comparisons and historical perspectives

Similarities and differences between the fauna of inland saline waters in Australia and on the Altiplano are explored and explanations sought.Elements common to both continents include the calanoid copepod genus Boeckella (B. triarticulata in Australia, B. poopoensis and B. meteoris in South America) and the cladoceran genus Daphniopsis. Salinity data for Altiplano lakes are given for six species of Boeckella and for Daphniopsis.Ostracods have adapted to the open water of saline lakes in Australia but not in South America, a difference that may reflect past differences in the degree of predation by birds. In South America, diatoms are grazed by the flamingos Phoenicoparrus andinus and P. jamesi, while in Australia the main diatom grazer is probably the aquatic oniscoid isopod Haloniscus searlei. However, at least four species of flamingos were present in Australia during the late Cenozoic and one or more of these may well have grazed diatoms. The extinction of diatom-grazing or carnivorous flamingos, or both, in Australia may have been factors in the unique colonization of inland saline waters by H. searlei.     

Gregarious aggregative behavior in the marine isopod Cirolana harfordi

Gregarious huddling behavior where animals seek the close company of conspecifics is thought to have facilitated the evolutionary transition from sea to land in some species of isopods, the theory being that closely apposed bodies decrease surface area and reduce desiccation. In this study, specimens of the marine isopod Cirolana harfordi were investigated to determine whether they displayed gregarious aggregative behavior. Animals were placed in a 20‐cm‐diameter acrylic cylinder arena that contained two 5‐cm‐diameter circular acrylic shelters that were tinted red (to reduce light transmittance), one at either end of the arena. Specimens of C. harfordi chose one of the two identical shelters at random, and the majority of animals congregated under this winning shelter. When an arena with one shelter tinted red and one clear shelter was used, the majority of animals congregated under the red shelter. These data indicate that the aggregative behavior displayed by this marine isopod species is driven by gregarious, conspecific attraction as well as reactions to environmental heterogeneity and negative phototaxis. Gregarious behavior in this marine isopod may afford the species advantages other than avoiding desiccation.     

Key stages in the evolution of the Antarctic marine fauna

We are beginning to appreciate that the origin of the modern Antarctic marine fauna is related to a series of key events throughout the Cenozoic era. In the first of these, the mass extinction at the Cretaceous–Palaeogene boundary (66 Ma) reset the evolutionary stage and led to a major radiation of modern taxa in the benthic realm. Although this took place in a greenhouse world, there is evidence to suggest that the radiation was tempered by the seasonality of primary productivity, and this may be a time‐invariant feature of the polar regions. Although there could well have been a single, abrupt extinction event at c. 34 Ma, there is also evidence to suggest a phased extinction of various taxa over a period of millions of years. Important new molecular phylogenetic data are indicating that a wide variety of both benthic and pelagic taxa radiated shortly after a second major phase of cooling at c. 14 Ma. Such a phenomenon is linked to a series of major palaeoceanographic changes, which in turn led to a proliferation of diatom‐based ecosystems. Although the modern benthic marine fauna can be traced back some 45–50 Myr, a substantial component of the modern pelagic one may be less than 14 Myr old. The latter is also characterized by assemblages of high abundance but comparatively low species richness and evenness. A distinctive signature of low diversity but high dominance within Antarctic marine assemblages was maintained by the interplay between temperature and primary productivity throughout the Cenozoic.     

Diversity of Cenozoic marsupiate echinoids as an environmental indicator

McNamara, K.J. 1994 10 15: Diversity of Cenozoic marsupiate echinoids as an environmental indicator. Marsupiate echinoids are today largely confined to the seas around Antarctica. Consequently, it has often been inferred that the presence of marsupiate echinoids in the fossil record is indicative of the former existence of low oceanic temperatures. In this study the distribution of marsupiate echinoids through the Cenozoic succession of southern Australia is compared with palaeo-temperature data to test this assumption. The analysis reveals that there is no positive correlation between high marsupiate echinoid diversity during the Cenozoic and low oceanic temperatures. An alternative hypothesis, based on life-history strategies, is investigated. This reveals that marsupiate echinoids show many characteristics typical of organisms with slow growth, long life spans and production of few, large offspring. It is suggested that the northward migration of Australia during the Cenozoic from an original high-latitude location in the early Cenozoic was accompanied by an increase in environmental instability in the southern Australian region in the late Cenozoic. This led to a consequent decrease in marsupiate echinoid diversity. During the Pliocene these direct brooding echinoids were replaced by non-brooders with pelagic lecithotrophic larvae, which dominate the southern coastal echinoid fauna of Australia today. The environmental stability experienced in southern Australia in the early Cenozoic persisted throughout the Cenozoic in the Antarctic region, particularly with regard to predictability of nutrient supply. The result has been the dominance of marsupiate echinoids in that region today. Temporal changes in the diversity of marsupiate echinoids in southern Australia therefore supports the view that their spatial and temporal distribution may be more closely correlated with aspects of their life-history strategy and environmental stability than with low temperature. Echinoidea, evolution, diversity, life-history strategy, Cenozoic.     

Genotypic and phenotypic variation in diatom silicification under paleo‐oceanographic conditions

Diatoms have co‐evolved with the silicon cycle and are largely responsible for reducing surface concentrations of silicate in the ocean to their present levels. We quantify silicification in marine diatoms at a range of high silicate concentrations representative of environments found over their geological history. The species examined include Stephanopyxis turris, an ancient centric species found throughout the Cenozoic, Thalassiosira pseudonana and Thalassiosira weissflogii, two younger centric species, and two pennate ecotypes of Staurosirella pinnata isolated from different nutrient regimes. Frustule thickness and micromorphological structure are strongly affected by silicate concentration. All species become increasingly silicified with silicate concentrations at concentrations vastly in excess of surface ocean concentrations today. In contrast, the half‐saturation constant for silicate uptake for most modern diatoms is below 2 μm . Based on the results, we hypothesize that silicate uptake is multiphasic in diatoms and that multiple silicate transport systems may have evolved in response to decreases in surface silicate concentration over geological time. The oldest species examined is more heavily silicified than the more modern species, presumably reflecting the conditions under which it originated. Yet diversification in silicification can be rapid, as illustrated by greater silicification in onshore versus the offshore ecotype of the same modern species. This work suggests that silicification of fossil frustules may eventually provide a paleoproxy for surface silicate concentrations over the Cenozoic, although development of species‐specific calibrations will be necessary and the effects of a range of environmental conditions must be investigated.     

Pathogenic effect of entomopathogenic nematode-bacterium complexes on terrestrial isopods

In this study, we evaluated the effect of entomopathogenic nematodes (EPNs) Steinernema carpocapsae, Steinernema feltiae and Heterorhabditis bacteriophora, symbiotically associated with bacteria of the genera Xenorhabdus or Photorhabdus, on the survival of eight terrestrial isopod species. The EPN species S. carpocapsae and H. bacteriophora reduced the survival of six isopod species while S. feltiae reduced survival for two species. Two terrestrial isopod species tested (Armadillidium vulgare and Armadillo officinalis) were found not to be affected by treatment with EPNs while the six other isopod species showed survival reduction with at least one EPN species. By using aposymbiotic S. carpocapsae (i.e. without Xenorhabdus symbionts), we showed that nematodes can be isopod pathogens on their own. Nevertheless, symbiotic nematodes were more pathogenic for isopods than aposymbiotic ones showing that bacteria acted synergistically with their nematodes to kill isopods. By direct injection of entomopathogenic bacteria into isopod hemolymph, we showed that bacteria had a pathogenic effect on terrestrial isopods even if they appeared unable to multiply within isopod hemolymphs. A developmental study of EPNs in isopods showed that two of them (S. carpocapsae and H. bacteriophora) were able to develop while S. feltiae could not. No EPN species were able to produce offspring emerging from isopods. We conclude that EPN and their bacteria can be pathogens for terrestrial isopods but that such hosts represent a reproductive dead-end for them. Thus, terrestrial isopods appear not to be alternative hosts for EPN populations maintained in the absence of insects.     

Early Cenozoic Differentiation of Polar Marine Faunas

The widespread assumption that the origin of polar marine faunas is linked to the onset of major global cooling in the Late Eocene – Early Oligocene is being increasingly challenged. The Antarctic fossil record in particular is suggesting that some modern Southern Ocean taxa may have Early Eocene or even Paleocene origins, i.e. well within the Early Cenozoic greenhouse world. A global analysis of one of the largest marine clades at the present day, the Neogastropoda, indicates that not only is there a decrease in the number of species from the tropics to the poles but also a decrease in the evenness of their distribution. A small number of neogastropod families with predominantly generalist trophic strategies at both poles points to the key role of seasonality in structuring the highest latitude marine assemblages. A distinct latitudinal gradient in seasonality is temperature-invariant and would have operated through periods of global warmth such as the Early Cenozoic. To test this concept a second global analysis was undertaken of earliest Cenozoic (Paleocene) neogastropods and this does indeed show a certain degree of faunal differentiation at both poles. The Buccinidae, s.l. is especially well developed at this time, and this is a major generalist taxon at the present day. There is an element of asymmetry associated with this development of Paleocene polar faunas in that those in the south are more strongly differentiated than their northern counterparts; this can in turn be linked to the already substantial isolation of the southern high latitudes. The key role of seasonality in the formation of polar marine faunas has implications for contemporary ecosystem structure and stability.     

Despite marine traits,the endemic Fucus radicans (Phaeophyceae) is restricted to the brackish Baltic Sea

Many of the marine species that were introduced to the Baltic Sea during the Littorina stage (c. 8500–3000 years BP), e.g. Fucus vesiculosus and F. serratus, have adapted to the present low salinity. These marine species have gone from marine conditions into lower salinity environments. In this paper we ask why the recently discovered endemic brown alga Fucus radicans shows the opposite pattern. Fucus radicans is only present in the northern parts of the Baltic Sea, the low salinity Bothnian Sea (4–6 psu). Potentially, the fitness of F. radicans might be reduced in higher salinities if it is better adapted to brackish conditions. We hypothesize, however, that the southern distribution limit of F. radicans is set by biotic factors, e.g. competition with F. vesiculosus and higher grazing pressure by Idotea balthica and not by salinity. Our results show that the reproductive output of F. radicans is limited by low salinity (4 psu) but increases in higher salinities. However, the southern distribution limit, i.e. the northern Baltic Proper, is regulated by biotic factors, where the additive effects from shading by taller F. vesiculosus thalli and grazing on F. radicans by the isopod I. balthica limit the biomass production of F. radicans. We suggest that F. radicans still maintains marine traits due to its ability to propagate clonally and is restricted to the Bothnian Sea by interactions with F. vesiculosus and I. balthica. We also propose that increased precipitation due to climate change might affect the northern range limit and that the distribution of F. radicans could be expected to shift further south into the Baltic Proper.     

A well‐preserved isopod from the Middle Jurassic of southern Germany and implications for the isopod fossil record

A new isopod species, Eonatatolana geisingensis gen. et sp. nov., is described from Middle Jurassic shallow‐water sediments of southern Germany. It shows not only the almost completely preserved dorsal morphology but, in addition, details of the cephalic appendages, the pereiopods, pleopods and uropods. The presence of ambulatory pereiopods I–VII of a wide tridentate mandibular incisor with prominently developed posteriormost tooth and a narrow frontal lamina indicates that the new species belongs to the subfamily Conilerinae of family Cirolanidae within the suborder Cymothoida. It is closer to the species of the modern genus NatatolanaBruce than to any fossil isopod hitherto described. The isopod fossil record as well as current practices of isopod taxonomy in palaeontology are discussed, and the facies distribution and fossilization of isopods is reviewed with examples from the Jurassic.     

Seasonal Abundance and Occurrence of the Asian Isopod Synidotea laevidorsalis in Delaware Bay, USA

In 1999 the marine isopod Synidotea laevidorsalis (Miers 1881), indigenous to the northwest Pacific, was first documented in Delaware Bay, USA. We monitored weekly recruitment of this isopod and several other motile species in the Maurice River, a tributary of Delaware Bay. A spatial survey was also conducted. Abundance of S. laevidorsalis varied seasonally but overwhelmingly dominated other co-occurring species by an order of magnitude or more throughout most of the year. Isopod abundance increased through the summer of 2004 and peaked in September, coincident with the passing of Hurricane Ivan. Field observations documented large populations, frequently associated with pilings and buoy lines, throughout Delaware Bay in salinities of 4 through 22 ppt. The dramatic abundance of this isopod indicates that there is considerable potential for altering community structure. This isopod has yet to be observed along the Atlantic Coast of New Jersey or in Chesapeake Bay, but it has been reported near Charleston, SC.     

Driven by the West Wind Drift? A synthesis of southern temperate marine biogeography,with new directions for dispersalism

Aim Twentieth century biogeographers developed intriguing hypotheses involving West Wind Drift dispersal of Southern Hemisphere biota, but such models were largely abandoned in favour of vicariance following the development of plate tectonic theory. Here I present a synthesis of southern temperate marine biogeography, and suggest some new directions for phylogeographic research. Location The southern continents, formerly contiguous components of Gondwana, are now linked only by ocean currents driven by the West Wind Drift. Methods While vicariance theory certainly facilitates the development of testable hypotheses, it does not necessarily follow that vicariance explains much of contemporary southern marine biogeography. To overcome the limitations of narratives that simply assume vicariance or dispersal, it is essential for analyses to test biogeographic hypotheses by incorporating genetic, ecological and geological data. Results Recent molecular studies have provided strong evidence for dispersal, but relatively little evidence for the biogeographic role of plate tectonics in distributing southern marine taxa. Despite confident panbiogeographic claims to the contrary, molecular and ecological studies of buoyant macroalgae, such as Macrocystis, indicate that dispersal predominates. Ironically, some of the better supported evidence for marine vicariance in southern waters has little or nothing to do with plate tectonics. Rather, it involves far more localized and recent vicariant models, such as the isolating effect of the Bassian Isthmus during Pleistocene low sea‐level stands (Nerita). Main conclusions Recent phylogeographic studies of southern marine taxa (e.g. Diloma and Parvulastra) imply that passive rafting cannot be ignored as an important mechanism of long‐distance dispersal. I outline a new direction for southern hemisphere phylogeography, involving genetic analyses of bull‐kelp (Durvillaea) and its associated holdfast invertebrate communities.     

Newly developed PCR primers for polymorphic microsatellite loci from the marine isopod Limnoria sp.

Nine microsatellite loci are isolated and characterized for the marine isopod Limnoria sp., a model invertebrate species for the study of connectivity of marine brooders with high potential of dispersal through rafting. Analysis of 35 individuals of one population revealed a mean number of alleles of 12.66 and mean expected heterozygosity of 0.83, indicating a high level of variability at most loci. These polymorphic microsatellite loci should be useful to the study of the geographical distribution of the genetic diversity of this species of Limnoria.     

Reproductive biology of the isopod Excirolana braziliensis at the southern edge of its geographical range

A full analysis of the reproductive biology of the isopod Excirolana braziliensis Richardson 1912 was conducted in a sandy beach of Uruguay, located at the southernmost edge of its distributional range in the Atlantic Ocean. Reproductive and recruitment periods of E. braziliensis were concentrated in austral summer. Females with oostegites appeared in November, whereas total biomass, individual sizes and fecundity of ovigerous females peaked between December and January. These concurrent traits were responsible for the significant peak of juveniles in January. The size at maturity was 9.88 mm. Four embryonic developmental stages were described and identified: mean length linearly increased from stages I to III, whereas dry weight exponentially decreased from stages I to IV. The high reproductive output (0.41–0.58), reported for the first time in this isopod, exceeds the rates documented for other isopods. Reproduction of E. braziliensis at the southern edge of its range is semelparous: females produce one brood during the reproductive season, exhaust their energy reserves during incubation, and probably die at the end of the reproductive season. A macroscale comparison suggests that E. braziliensis at the southern edge of its range counteracts its narrow reproductive period by a short incubation period with larger individual mature female and embryo sizes, higher fecundity and a higher percentage of ovigerous females than in subtropical and tropical populations. These extreme reproductive indicators could be attributed to the internal retention of embryos that assures offspring survival, coupled with a high adaptation capability to environmental variations across its range.     

Social aggregation of the marine isopod Cirolana harfordi does not rely on the availability of light‐reducing shelters

Social aggregation under shelters can afford benefits to animals such as protection from predators. Many isopods and insects are negatively phototactic and this may help them gravitate towards shelter. Previous studies show that, when placed in an arena with two red shelters, specimens of the marine isopod Cirolana harfordi and the terrestrial isopod Porcelio scaber pick one of the two shelters at random and aggregate under it, demonstrating social aggregation under light‐reducing shelters. In the present study, an arena with two clear shelters was used to determine whether group sizes of 4, 8, 12 and 16 C. harfordi specimens display social aggregation when the shelters do not accommodate negative phototaxis. In all group sizes, C. harfordi specimens picked one of the shelters at random and significantly more animals aggregated under this shelter compared with the other. Cirolana harfordi also displayed aggregation in an arena with no shelters. Accordingly, C. harfordi specimens do not require shelters that reduce light to display social aggregation. The ability to locate suitable shelter under which there is no substantial reduction in light could benefit the animal in a natural environment comprising heavily shaded areas, as well as at night.     

The fossil record of Limopsis (Bivalvia: Limopsidae) in Antarctica and the southern high latitudes

Abstract: Limopsis is one of the most speciose and widespread bivalve genera in the Southern Ocean at the present day. However, the fossil record of the genus is poorly known from the southern high latitudes. Here, we review the fossil record in this region to help understand the evolutionary origins of the genus. Limopsis infericola sp. nov. and additional specimens of a previously described species are added to the fossil record of Antarctica. The globally distributed limopsid clade had its earliest occurrences in the Early Cretaceous of Europe and New Zealand, then radiated during the Late Cretaceous (Maastrichtian, 70.6–65.5 Ma). Fossil evidence shows that the genus underwent a second, Cenozoic, radiation related to the isolation of Antarctica and the onset of cooling in the southern hemisphere. The genus has persisted in Antarctica for the last 50 myr, adapting to extreme changes in the environmental conditions, including surviving the last glacial maximum in marine refugia.     

The first record of a terrestrial landhopper (Crustacea: Amphipoda: Talitridae) from Macquarie Island

A terrestrial talitrid crustacean is recorded for the first time from subantarctic Macquarie Island. The species, Puhuruhuru patersoni, is native to the southern part of the South Island of New Zealand. Its distribution on Macquarie Is. is restricted to a single locality near the ANARE station on the Isthmus. All mature females collected in December were carrying eggs; females appeared to be less mobile than males. It seems likely that the species has been transported accidentally from New Zealand, perhaps by the same means that introduced the isopod, Styloniscus otakensis, also from southern New Zealand.     

Inbreeding shapes the evolution of marine invertebrates

Inbreeding is a potent evolutionary force shaping the distribution of genetic variation within and among populations of plants and animals. Yet, our understanding of the forces shaping the expression and evolution of nonrandom mating in general, and inbreeding in particular, remains remarkably incomplete. Most research on plant mating systems focuses on self-fertilization and its consequences for automatic selection, inbreeding depression, purging, and reproductive assurance, whereas studies of animal mating systems have often assumed that inbreeding is rare, and that natural selection favors traits that promote outbreeding. Given that many sessile and sedentary marine invertebrates and marine macroalgae share key life history features with seed plants (e.g., low mobility, modular construction, and the release of gametes into the environment), their mating systems may be similar. Here, we show that published estimates of inbreeding coefficients (F_IS) for sessile and sedentary marine organisms are similar and at least as high as noted in terrestrial seed plants. We also found that variation in F_IS within invertebrates is related to the potential to self-fertilize, disperse, and choose mates. The similarity of F_IS for these organismal groups suggests that inbreeding could play a larger role in the evolution of sessile and sedentary marine organisms than is currently recognized. Specifically, associations between traits of marine invertebrates and F_IS suggest that inbreeding could drive evolutionary transitions between hermaphroditism and separate sexes, direct development and multiphasic life cycles, and external and internal fertilization.     

Geographical divergence in host use ability of a marine herbivore in alga–grazer interaction

When the selective environment differs geographically, local herbivore populations may diverge in their host use ability and adapt locally to exploit the sympatric host population. We tested whether populations of the marine generalist herbivore Idotea baltica have diverged in host us ability and whether they locally adapted to exploit the sympatric population of their main host species, the bladderwrack Fucus vesiculosus. We fed isopods from three local populations reciprocally with the sympatric and two allopatric populations of the host. The bladderwrack populations varied in their quality as food for isopods suggesting variation in the selective environment. The ability to exploit the main host showed considerable divergence among the isopod populations. There was no significant interaction between host and isopod origin, indicating that the patterns observed in the reciprocal feeding experiment could be explained by differences in overall suitability of the hosts and differences in overall performance of the isopod populations. Isopod population that was sympatric to a bladderwrack population with low phlorotannin content showed high performance on the algae from the sympatric but low performance on the algae from the two allopatric populations. Performance of isopods, especially in this population, decreased quickly with the increasing phlorotannin content of food algae. We therefore hypothesize that the isopods adapted to a low phlorotannin content were unable to utilize high-phlorotannin algae efficiently. Isopod populations sympatric to the high-phlorotannin bladderwrack populations may be generally better adapted to deal with phlorotannins, being thereby able to utilize a range of bladderwrack populations.     

Chromadorita ceratoserolis sp. n. (Chromadoridae), a free-living marine nematode epibiotically on the isopod Ceratoserolis trilobitoides from Antarctica

Summary Chromadorita ceratoserolis sp. n. is described. Specimens were found amongst eggs in the marsupium of the marine benthic isopod Ceratoserolis trilobitoides from Antarctic sea waters (233–728 m depth).     

Further Studies on Haemogregarina bigemina Laveran & Mesnil,the Marine Fish Blennius pholis L., and the Isopod Gnathia maxillaris Montagu1

Haemogregarina bigemina is redescribed from the blood of the marine fish Blennius pholis, and stages presumed to be those of the haemogregarine are recorded from the hematophagous praniza larva of the isopod Gnathia maxillaris. At College Rocks, Aberystwyth, Wales, the main study area, a high incidence of infection occurred in B. pholis. No exoerythrocytic stages were observed in these fish, nor was sexual dimorphism of the gametocyte evident. As in an earlier study, ecological evidence favored transmission by G. maxillaris rather than by leeches. Gametocytes, syzygy, oocysts, sporoblasts, and sporozoites were identified in the anterior hindgut of the isopod. The stages observed in G. maxillaris are compared with those of other haemogregarines described from the digestive tract of leeches. Mention is made of an intraleucocytic haemogregarine of another fish, Crenilabrus melops.