Induction of Synchronized Fissions in Telotrochidium henneguyi

SYNOPSIS. Cultures of Telotrochidium henneguyi , begun with logarithmic phase cells, were employed in an effort to produce synchronized fission by heat treatment. The cells tolerated a temperature range of 20–50 C; temperatures above 50 were lethal. When cells were exposed to a single shock for 30 min, 30–40 produced 0–50% encystment with total excystment after 10 min exposure to room temperature (heat shock range). No encystment occurred between 20–30 (intershock range). Encystment and excystment time varied directly with temperature between 40–50.
The most effective procedure for inducing synchronized fission consisted of 6 cycle program of 38/28 C (shock temperature/intershock temperature) administered for 15/15 (shock/intershock duration in min). Division indices (DI = cells dividing/total population X 100 =%) ranged from 12–66% with a mean of 37.25%. In control cells, division indices ranged from 2–20% with an average of 12%. Inferences from these independently derived findings are discussed.     

The influence of ice scour on benthic communities at three contrasting sites at Adelaide Island,Antarctica

Abstract Ice scouring is a key structuring force acting on high latitude shallow benthic communities. Despite its importance, detailed studies of scoured communities are still rare. Here we report the ecological effects of 12 iceberg impacts, across three contrasting study sites, at Adelaide Island, West Antarctic Peninsula. Grounded icebergs were marked with GPS and the newly formed scours (at 10–17 m depth) were sampled within 20 days of formation. Comparisons between scoured and adjacent unscoured assemblages were made using measures of abundance, biomass, taxon richness and the relative abundance of secondary consumers. Ice scouring was catastrophic at all sites, despite differences in substratum type, exposure and background community. Compared with undisturbed areas, scour assemblages were 95% lower in mean macrofaunal abundance and 75.9% lower in species richness. There was no general trend across all sites of ice scouring selecting for secondary consumers. The echinoid Sterechinus neumayeri and bivalve mollusc Mysella charcoti were highly abundant in undisturbed areas and were the biggest contributors to the observed differences between scours and undisturbed areas.     

Phylogeography of lions (Panthera leo ssp.) reveals three distinct taxa and a late Pleistocene reduction in genetic diversity

Lions were the most widespread carnivores in the late Pleistocene, ranging from southern Africa to the southern USA, but little is known about the evolutionary relationships among these Pleistocene populations or the dynamics that led to their extinction. Using ancient DNA techniques, we obtained mitochondrial sequences from 52 individuals sampled across the present and former range of lions. Phylogenetic analysis revealed three distinct clusters: (i) modern lions, Panthera leo ; (ii) extinct Pleistocene cave lions, which formed a homogeneous population extending from Europe across Beringia (Siberia, Alaska and western Canada); and (iii) extinct American lions, which formed a separate population south of the Pleistocene ice sheets. The American lion appears to have become genetically isolated around 340 000 years ago, despite the apparent lack of significant barriers to gene flow with Beringian populations through much of the late Pleistocene. We found potential evidence of a severe population bottleneck in the cave lion during the previous interstadial, sometime after 48 000 years, adding to evidence from bison, mammoths, horses and brown bears that megafaunal populations underwent major genetic alterations throughout the last interstadial, potentially presaging the processes involved in the subsequent end-Pleistocene mass extinctions.     

Climate change induced hybridization in flying squirrels

There is now unequivocal evidence for global climate change; however, its potential impacts on evolutionary processes remain unclear. Many species have responded to contemporary climate change through shifts in their geographic range. This could lead to increased sympatry between recently diverged species; likely increasing the potential for hybridization. Recently, following a series of warm winters, southern flying squirrels ( Glaucomys volans ) in Ontario, Canada rapidly expanded their northern range limit resulting in increased sympatry with the closely related northern flying squirrel ( Glaucomys sabrinus ). This provided the opportunity to test the prediction that contemporary climate change can act as a catalyst creating conditions for the formation of hybrid zones. Following extensive sampling and molecular analyses (nuclear and mitochondrial DNA), we identified the occurrence of hybridization between sympatric G. sabrinus and G. volans . There was evidence of backcrossing but not of extensive introgession, consistent with the hypothesis of recent rather than historic hybridization. To our knowledge, this is the first report of hybrid zone formation following a range expansion induced by contemporary climate change. This is also the first report of hybridization between North American flying squirrel species.     

Faunal evidence for a late quaternary trans‐Antarctic seaway

Collapse of the West Antarctic Ice Sheet (WAIS) would raise global sea level by ～3.3–5 m. Ice‐sheet models and geological data suggest at least one collapse has happened during the last 1.1 Ma, and some scenarios of future climate change predict a collapse within the next two centuries. A complete WAIS collapse would open shallow seaways across West Antarctica, potentially enabling exchange of animals between West Antarctic seas. We investigated biological evidence for past connectivity between different regions of Antarctica by comparing the composition of modern bryozoan assemblages from the continental margin around Antarctica. Surprisingly, we found most similarity between two areas which are not currently connected – the shelves of the Weddell Sea (WS) and Ross Sea (RS). We evaluated three hypotheses to explain this and conclude that bryozoans most likely dispersed through a trans‐Antarctic seaway that opened in response to a WAIS collapse and connected the WS and RS shelves. These bryozoans must have survived glaciations(s) during subsequent ice ages in refuges, whereas they were wiped out in most other regions of the Antarctic shelf. After the last glacial period, bryozoan assemblages could freely disperse between many of the regions we examined (e.g. Antarctic Peninsula and South Shetland Islands), which has allowed recolonization of areas in which bryozoans had been eradicated during the last ice age. For the bryozoans on the WS and RS shelves to be more similar than those which are in close proximity means the trans‐Antarctic seaway may have been as late as the last few interglacials. Current rates of warming are exceptional compared with the near past glacial cycles so our study, the strongest faunal evidence of WAIS collapse during the recent geological past, thus supports predictions of a near future WAIS collapse (with considerable global sea level implications) and resultant future major faunal exchanges.     

Ecological relevance of laboratory determined temperature limits: colonization potential,biogeography and resilience of Antarctic invertebrates to environmental change

The relevance of laboratory experiments in predicting effects of climate change has been questioned, especially in Antarctica where sea temperatures are remarkably stable. Laboratory studies of Southern Ocean marine animal capacities to survive increasing temperature mainly utilize rapid temperature elevations, 100 ×–10 000 × faster than sea temperature is predicted to rise. However, due to small‐scale temperature fluctuations these studies may be crucial for understanding colonization patterns and predicting survival particularly through interactions between thermal tolerance and migration. The colonization of disjunct shelves around Antarctica by larvae or adult drift requires crossing or exposure to, rapid temperature changes of up to 2–4 °C over days to weeks. Analyses of responses to warming at varying rates of temperature change in the laboratory allow better predictions of the potential species have for colonizing disjunct shelf areas (such as the Scotia Arc). Inhabiting greater diversities of localities increases the geographic and thermal range species experience. We suggest a strong link between short‐term temperature tolerance, environmental range and prospects for surviving changing environments.     

Effects of ozone on wild plants

Although there is a great deal of concern about the effects of human activities on biodiversity, until recently there has been very little interest in the effects of ozone on the species that constitute the major part of the flora, the diverse herbaceous and shrubby species of natural and semi-natural communities. However, many wild species have been shown to be at least as sensitive to ozone as crops that show significant yield losses, so there is a pressing need for an evaluation of the risk to wild species posed by ozone. This review attempts to assess progress and highlight problems. It begins with a comment on semantics, discusses the difficulties involved in measuring relative ozone resistance and then proceeds to consider the effects of ozone on growth and resource allocation. The evidence for evolution of resistance is appraised and then the potential effects of several interactions (cutting/grazing, competition, soil water deficit and nutrition) are considered. The review ends with some remarks on observation of oxidant-induced changes in ecosystems.