Physiological effects of dominance hierarchies: laboratory artefacts or natural phenomena?

Studies of fish behaviour have demonstrated the existence of social interactions that result in dominance hierarchies. In environments in which resources, such as food, shelter and mates, are limited, social competition results in some fish becoming dominant and occupying the most profitable positions. This behaviour has been observed in natural environments and also in many laboratory‐based experiments. When two fish have been confined in a small tank, one of them usually has exhibited behaviour that suggests it is dominant over the other submissive animal. Physiological consequences of social interaction can be seen in both dominants and subordinates but are more extreme in the subordinate. However, this scenario is without doubt an artificial situation. Fewer experiments have been conducted using laboratory experiments that are more socially and physically complex than those experienced by dyads in tanks. In simple fluvial tanks, through which water is recirculated, the physiological responses of fish to social competition have generally been qualitatively similar to those recorded among dyads. However, when environmental disturbances, complex resource distributions, increase in water flushing, presence of predators and competing species of fish have been included in experimen‐tal designs, there have been fewer, diminished or no physiological dierences between dominant and subordinate fish. There have been very few studies of physiology in relation to dominance in natural habitats, and those that have been conducted suggest that under some circumstances hierarchies may cause less intense physiological responses than have been suggested based on results of laboratory studies in simple environments. Possible reasons for these variations are discussed. The need is identified for a well structured experimental approach to the investi‐gation of the causes and consequences of hierarchies if the ecology of wild fish is to be modelled eectively based on physiological processes. It is also suggested that the further development and application of techniques for monitoring physiologies of fish in the wild is important.     

Line Orientation Adaptation: Local or Global?

Prolonged exposure to an oriented line shifts the perceived orientation of a subsequently observed line in the opposite direction, a phenomenon known as the tilt aftereffect (TAE). Here we consider whether the TAE for line stimuli is mediated by a mechanism that integrates the local parts of the line into a single global entity prior to the site of adaptation, or the result of the sum of local TAEs acting separately on the parts of the line. To test between these two alternatives we used the fact the TAE transfers almost completely across luminance contrast polarity [1]. We measured the TAE using adaptor and test lines that (1) either alternated in luminance polarity or were of a single polarity, and (2) either alternated in local orientation or were of a single orientation. We reasoned that if the TAE was agnostic to luminance polarity and was parts-based, we should obtain large TAEs using alternating-polarity adaptors with single-polarity tests. However we found that (i) TAEs using one-alternating-polarity adaptors with all-white tests were relatively small, increased slightly for two-alternating-polarity adaptors, and were largest with all-white or all-black adaptors. (ii) however TAEs were relatively large when the test was one-alternating polarity, irrespective of the adaptor type. (iii) The results with orientation closely mirrored those obtained with polarity with the difference that the TAE transfer across orthogonal orientations was weak. Taken together, our results demonstrate that the TAE for lines is mediated by a global shape mechanism that integrates the parts of lines into whole prior to the site of orientation adaptation. The asymmetry in the magnitude of TAE depending on whether the alternating-polarity lines was the adaptor or test can be explained by an imbalance in the population of neurons sensitive to 1^st-and 2^nd-order lines, with the 2^nd-order lines being encoded by a subset of the mechanisms sensitive to 1^st-order lines.     

Seed development: With or without sex?

In Arabidopsis, mutations in the genes FIE, FIS2 or MEDEA disrupt the normal dependence of seed development on fertilization. The products of these genes are similar to Polycomb group proteins, suggesting possible mechanisms for determining whether seeds can be produced sexually or asexually.     

Amplification and latency in photoreceptors: Integrated or separated phenomena?

It is shown that the models for the transduction process in photoreceptors which treat latency and amplification as integrated phenomena (integrated models) yield time scales for single photon signals (quantum bumps) which distinctly conflict with the experimentally observed ones for the ventral nerve photoreceptor of Limulus: the ratio of bump duration/ latency t _B/t _lat is predicted by integrated models to be 3 in contrast to the experimental result of 0.5. Moreover, integrated models lead to a predicted value of an extinction rate of 50%, i.e., 50% of the absorbed photons should be expected to cause no signal in the dark adapted state of the cell. In this paper it is shown that separation of latency and amplification in such a way that the latency causing process precedes amplification in the transduction process eliminates these discrepancies. In addition, the separate modeling of latency and amplification resolves the rather large ambiguity in determining the exponent n of the initial signal current J(t) ⁿreported in the literature to be between n2 (from noise analysis) up to n17 (from flash experiments). Two alternative models for the latency part of transduction are suggested which give a qualitatively much better agreement with the experimental histograms of latencies.List of Symbols A quantum bump amplitude, maximum of quantum bump signal current - latency criterion as a fraction in terms of J _max - E energy of the stimulating flash - g conductance of a single light-regulated channel - I(t) light intensity of the stimulating flash as a function of time - J(t) response current of photoreceptors to light flashes under voltage clamp - J _max maximum signal current response signal - J _min minimum current above which the signal current becomes distinguishable from the base line noise - k rate constant in models separating latency from amplification - L ligand in ligand binding model - rate constant of exponential bump decay - m number of amplification steps following gainless latency process in models separating latency and amplification - n exponent in the initial behaviour J(t)t ⁿ - Q net charge transfer of quantum bump signal current - (t) first-passage time probability density - t _B duration of quantum bump response - t _lat latency time - t _max time to peak for quantum bumps - t _r rise time for quantum bumps - U U-U _L, U=clamp voltage, U _L=reversal potential of light-regulated channels - v amplification factor - X _k intermediate conformations in transduction models This work was supported by Deutsche Forschungsgemeinschaft (SFB 160)     

Positive relationship between regional distribution and local abundance in stream insects: a consequence of niche breadth or niche position?

A positive relationship between regional distribution and local abundance of species is almost ubiquitous macroecological pattern, yet the mechanisms behind this pattern remain poorly understood. I tested for the relationship between regional distribution and local abundance of stream insect species in a boreal drainage system, with a specific aim to examine if this relationship follows the mechanistic basis of either the niche-based (niche breadth and niche position) or metapopulation models. There was a positive relationship between regional distribution and local abundance of stream insects, and there also were significant relationships between distribution/abundance and niche breadth or niche position. These results thus suggest that widely distributed species tend to be, on average, locally more abundant, have wider niches and lower marginality of niche position with regard to environmental factors than species that have more restricted distributions. However, although significant, there was much unexplained variability around these relationships, suggesting that other mechanisms (e.g. metapopulation dynamics) besides differences in species' niches are likely to affect the distribution and abundance of stream insects, at least within a drainage system. The results thus showed that 1) although niche position was more consistently related to the positive distribution-abundance relationship, ecologists should not abandon niche breadth as a potential mechanism behind this relationship, and 2) that several mechanisms are likely to act in concert in determining the relationship between distribution and abundance of species.     

Awesome or ordinary? Global diversity patterns of oribatid mites

Diversity of most above-ground organisms increases with decreasing latitude, but the biogeographical and macroecological diversity patterns of below-ground animals have been poorly studied. We investigated the latitudinal diversity gradient in a primarily below-ground living soil taxon, oribatid mites. Furthermore, oribatid mite species richness from islands and mainlainds was tested for correlation with the size of the respective area (island or mainland) to evaluate if their species–area relationships are similar to those of above-ground taxa. The results suggest that for oribatid mites 1) diversity increases from the boreal to the warm temperate region but not further to the tropics, and 2) species–area relationships for islands and mainlands are similar to those of above-ground taxa, but this is mainly caused by very small islands, such as Cocos islands, and very large islands, such as Madagascar. When these islands are excluded the species–area relationship strongly differs from those of typical islands. The results support the view that below-ground animal taxa are generalists that inhabit wide niches. Most small islands have relatively rich oribatid mite faunas, supporting the observation that a large number of species can coexist in a small area (high α-diversity).     

Evolution of development type in benthic octopuses: holobenthic or pelago-benthic ancestor?

Octopuses of the family Octopodidae are singular among cephalopods in their reproductive behavior, showing two major reproductive strategies: the first is the production of few and large eggs resulting in well-developed benthic hatchlings (holobenthic life history); the second strategy is the production of numerous small eggs resulting in free-swimming planktonic hatchlings (pelago-benthic life history). Here, we utilize a Bayesian-based phylogenetic comparative method using a robust molecular phylogeny of 59 octopus species to reconstruct the ancestral states of development type in benthic octopuses, through the estimation of the most recent common ancestors and the rate of gain and loss in complexity (i.e., planktonic larvae) during the evolution. We found a high probability that a free-swimming hatchling was the ancestral state in benthic octopuses, and a similar rate of gain and loss of planktonic larvae through evolution. These results suggest that in benthic octopuses the holobenthic strategy has evolved from an ancestral pelago-benthic life history. During evolution, the paralarval stage was reduced to well-developed benthic hatchlings, which supports a “larva-first” hypothesis. We propose that the origin of the holobenthic life history in benthic octopuses is associated with colonization of cold and deep sea waters.     

Neuronal activity during development: permissive or instructive?

Experimental studies over the past year have shown that neural activity has a range of effects on the development of neural pathways. Although activity appears unimportant for establishing many aspects of the gross morphology and topology of the brain, there are many cases where the presence of neural activity is essential for the formation of a mature system of neural connections; in some instances, the pattern of neural activity actually orchestrates the final arrangement of neural connections.     

Limited benefits of non-crop vegetation on spiders in Australian vineyards: regional or crop differences?

In crops, invertebrate natural enemies such as spiders have been documented as responding to non-crop vegetation at the local and landscape scales, particularly in northern Europe. Much of this information is based on data from arable or annual crops and it is possible that spider numbers in more persistent perennial systems including vineyards may be less dependent on non-crop vegetation. To test the relationship between spider abundance and non-crop vegetation within the context of Australian vineyards, we sampled spiders in 54 vineyards with adjacent non-crop vegetation, from three different regions. Landscape composition in the area surrounding each of the 54 sites was characterized at 11 spatial scales from 95?m to 3?km radius and spiders were sampled monthly using canopy sticky traps and ground pitfall traps. There were only weak relationships between pasture or woody vegetation and the abundance of spiders in vineyards at all spatial scales. At the local scale, abundance of most spider families tended to be greater in vineyards with adjacent pasture. At the landscape scale there were inconsistent patterns. We discuss possible reasons for these apparent contrasting patterns between perennial and annual crops and European compared to Australian agroecosystems.     

Dynamics and trophic interactions of small rodents: landscape or regional effects on spatial variation?

Geographically varying rodent dynamics may be due to specific landscape effects or to regional variation. Two common vole species (Clethrionomys glareolus and Microtus agrestis), their main predators and their impact on some important food items were monitored in Sweden on forest clearcuts in two different landscape types, situated in two different regions with different climatic conditions. Censuses, with 10-16 clearcuts in each landscape and both landscapes in the two regions, were designed to permit analyses of variance of the effects of landscape composition and region on dynamics and species interactions. Region had a far greater influence than landscape on vole numbers, on the proportions of generalist and specialist predators and on the winter browsing of bark of indigenous and experimental woody plants as well on seed consumption in experimental supplies. The findings indicated an influence of the depth and quality of the snow cover on the predation rates by generalist and specialist predators. However, there were also clear signs of food limitation in the snow-rich areas. Such areas had fewer generalist predators, which probably meant less directly density-dependent predation. Thus, lack of high-quality food may put a brake on population growth in climatically harsh regions, permitting increasing populations of specialist predators such as small mustelids to subsequently over-utilise their main prey and potentially cause prolonged low densities. Snow conditions may affect numbers and interactions both within habitats, landscapes and regions. Thus, to more fully understand rodent dynamics, small-scale movements and interactions of individuals in relation to the main large-scale factor(s) of various regions need to be examined.