Understanding the dynamics of communities in space and time requires reconciling ecological and evolutionary processes, including colonization, adaptation, speciation and extinction. In practice, this has been challenging because empirical data obtained by traditional methods and predictive models typically focus on particular processes driving local community assembly and biogeographical structure. In this issue of Molecular Ecology, by using phylogenomics, population genomics and phenomics approaches, Darwell et al. show that ant community assembly on islands is governed by predictable eco-evolutionary trends of geographical range expansion, adaptive radiation and local population decline. The authors provide one of the most robust lines of evidence that the evolutionary progression of island communities may often be directional and repeatable, as predicted by the concept of taxon cycles.
Macroecologists seek to identify drivers of community turnover (β-diversity) through broad spatial scales. However, the influence of local habitat features in driving broad-scale β-diversity patterns remains largely untested, owing to the objective challenges of associating local-scale variables to continental-framed datasets. We examined the relative contribution of local- versus broad-scale drivers of continental β-diversity patterns, using a uniquely suited dataset of cave-dwelling spider communities across Europe (35-70° latitude). Generalized dissimilarity modelling showed that geographical distance, mean annual temperature and size of the karst area in which caves occurred drove most of β-diversity, with differential contributions of each factor according to the level of subterranean specialization. Highly specialized communities were mostly influenced by geographical distance, while less specialized communities were mostly driven by mean annual temperature. Conversely, local-scale habitat features turned out to be meaningless predictors of community change, which emphasizes the idea of caves as the human accessible fraction of the extended network of fissures that more properly represents the elective habitat of the subterranean fauna. To the extent that the effect of local features turned to be inconspicuous, caves emerge as experimental model systems in which to study broad biological patterns without the confounding effect of local habitat features.
- MeSH
- biodiverzita MeSH
- druhová specificita MeSH
- ekosystém MeSH
- pavouci fyziologie MeSH
- teplota MeSH
- zeměpis MeSH
- životní prostředí * MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Evropa MeSH
Extracellular freezing of insect body water may cause lethal injury either by direct mechanical stress exerted by growing ice crystals on cells and tissues or, indirectly, by deleterious physico-chemical effects linked to freeze-induced cell dehydration. Here we present results showing that the macroscopic damage (cell ruptures, tissue disintegration) to fat body of Drosophila melanogaster is not directly caused by mechanical forces linked to growth of ice crystals but rather represents a secondary consequence of other primary freeze injuries occurring at subcellular or microscopic levels. Larvae of D. melanogaster were acclimated to produce variants ranging from freeze susceptible to freeze tolerant. Then, larvae were exposed to supercooling and freezing stresses at different subzero temperatures. The larval survival and macroscopic damage to fat body tissue was scored in 1632 larvae exposed to cold stress. In most cases, fat body damage was not evident immediately following cold stress but developed later. This suggests that the fat body disintegration is a consequence rather than a cause of cold injury. Analysis of fat body membrane phospholipids revealed that increased freeze tolerance was associated with increased relative proportion of phosphatidylethanolamines (PEs) at the expense of phosphatidylcholines (PCs). The PE/PC ratio increased from 1.08 in freeze-susceptible larvae to 2.10 in freeze-tolerant larvae. The potential effects of changing PE/PC ratio on phospholipid bilayer stability upon supercooling and freezing stress are discussed.
Overwintering insects are categorized either as freeze tolerant or freeze avoiding (supercooling) based on their ability or inability, respectively, to tolerate the formation of ice in their body. The freeze tolerant insects set their supercooling point (SCP) higher for winter to stimulate freezing at higher temperatures, while freeze avoiding insects survive winter in a supercooled state by depressing their SCP. Some supercooling insects, however, were found to survive in frozen state when freezing occurred through inoculation by external ice at mild subzero temperatures. Here, we assessed the potential relevance of inoculative freezing and freeze tolerance strategy in an insect that was so far considered as a classical example of a 'supercooler', the linden bug (Pyrrhocoris apterus). Microclimatic conditions of the overwintering microhabitat of P. apterus (leaf litter layer with buffered temperature fluctuations, mild sub-zero extremes, high humidity, and presence of ice) present a potentially high risk of inoculative freezing. We found that P. apterus is highly susceptible to inoculation by external ice. The temperature at which inoculative freezing occurred (above -3°C) was much higher compared to SCP (-16 °C to -20 °C in winter). The insects were inoculated through body openings and across cuticle and were able to survive after freezing. There was, however, a distinct critical ice fraction, corresponding to 38.7-42.8% of total body water, beyond which survival rapidly decreased to zero. We found that P. apterus adaptively reduces the actual ice fraction below critical ice fraction for winter season. Since many insect species overwinter in habitats similar to that of P. apterus, the ability to tolerate freezing after inoculation by external ice crystals could be much more common among 'supercooling' insects than it is currently appreciated.
