Causes and consequences of animal dispersal strategies: relating individual behaviour to spatial dynamics

Knowledge of the ecological and evolutionary causes of dispersal can be crucial in understanding the behaviour of spatially structured populations, and predicting how species respond to environmental change. Despite the focus of much theoretical research, simplistic assumptions regarding the dispersal process are still made. Dispersal is usually regarded as an unconditional process although in many cases fitness gains of dispersal are dependent on environmental factors and individual state. Condition-dependent dispersal strategies will often be superior to unconditional, fixed strategies. In addition, dispersal is often collapsed into a single parameter, despite it being a process composed of three interdependent stages: emigration, inter-patch movement and immigration, each of which may display different condition dependencies. Empirical studies have investigated correlates of these stages, emigration in particular, providing evidence for the prevalence of conditional dispersal strategies. Ill-defined use of the term 'dispersal', for movement across many different spatial scales, further hinders making general conclusions and relating movement correlates to consequences at the population level. Logistical difficulties preclude a detailed study of dispersal for many species, however incorporating unrealistic dispersal assumptions in spatial population models may yield inaccurate and costly predictions. Further studies are necessary to explore the importance of incorporating specific condition-dependent dispersal strategies for evolutionary and population dynamic predictions.     

Communication of stabilizing energy between substructures of a protein

Thermodynamic communication between protein substructures has been investigated by determining the stabilizing effect of mutations at position 52 in the least stable, N-yellow, substructure of cytochrome c on the second least stable, Red, and most stable, Blue, substructures of the protein. A Lys 73 --> His (H73) variant of iso-1-cytochrome c, containing these mutations was used to measure the stability of the Red substructure of cytochrome c through the pH and guanidine hydrochloride (gdnHCl) dependence of the His 73-mediated alkaline conformational transition. The stability of the Blue substructure was measured by global unfolding with gdnHCl and increased by 1 to 3.5 kcal/mol versus the H73 variant. The data demonstrate that the increase in stability of the Red substructure is similar to the increase in global stability, consistent with upward propagation of stabilizing energy from less (N-yellow) to more stable (Red and Blue) protein substructures. The result also supports sequential rather than independent unfolding of the N-yellow and Red substructures of cytochrome c. The data indicate that a leucine at position 52 alters the nature of partial unfolding of the Red substructure, a surprising effect for a single-site mutation. For all variants, the thermodynamics of formation of the Lys 79 alkaline state, which does not unfold the entire Red substructure, shows less stabilization of the portion of the protein unfolded relative to the stabilization of the Blue substructure, indicating that propagation of energy between substructures is somewhat disrupted when unfolding does not correspond to a natural substructure.     

Sea surface temperature gradients, baroclinicity, and vegetation gradients in the sea

We describe the results of an analysis of the 1984 CalCOFI dataset, in which sea surface temperature (SST) gradients were foundto be well correlated to isopycnal slope (baroclinicity) atthe mesoscale. A link was established between the SST gradientsand gradients of integral biomass [mg chlorophyll (Chl) a m^–2]and integral primary production (mg C m^–2day^–1).The water column photosynthetic efficiency, , was calculatedby combining the CalCOFI data base with satellite-based estimatesof the surface irradiance. It was found that was rather stable,but not constant, for a wide range of isopycnal slopes, in whichintegrated nitrate concentrations varied by up to 500x. Variabilityin was most strongly dependent on calendar date, with the highestvalues in winter months and the lowest values in the summer,which was probably due to an effect of day length or irradiance.The relationship between baroclinicity and SST gradients washighly scale dependent; from 0 to 200 km, the data were randomlydistributed, then as the length scales exceeded 400 km, therelationship between baroclinicity and the SST gradient showeda significantly negative slope, with steadily improving correlationcoefficient. Such relationships for individual cruises generallyshowed improved correlation over the generic annual relationship,which highlights the dynamic hydrography of the region. Baroclinicity/SSTgradient relationships also improved in waters of increasingdepth. A technique is described for calculating net integralbiomass or production gradients from SST imagery. The gradientsin biomass and productivity showed increasingly strong tiesto isopycnal slope at larger size scales. Although this topichas long been described by oceanographers, this paper is thefirst to demonstrate a quantitative coupling between baroclinicityand primary production gradients as a function of length scale.Also significant is the observation that the relationships betweenbaroclinicity versus gradients of integral chlorophyll or integralproductivity are consistent over seasons and over an area exceeding1 million km². We conclude that for satellite algorithms toaccount for >50% of the variance in primary production, thenutrient term must be considered. Information on baroclinicityis relevant to estimates of the along-isopycnal nutrient fluxto the euphotic zone. Merging this with the more traditionallight-based estimates of photosynthesis will improve algorithmperformance since the methods utilize entirely independent sourcesof information.     

Changes in temperature tolerance with adult age in Tenebrio molitor

A life table has been constructed, at 25° for male Tenebrio. Their mean life span was found to be 100.4±4.6 days.A dramatic fall in the ability of young beetles to tolerate exposure at 42.5° has been observed. Mean survival times fell from 190 minutes on the day of eclosion to 120 minutes after 5 days of age.It is suggested this decline in physiological performance represents a loss of high pupal tolerance which is carried over into the imago, and that it may be a feature of all holometabolous insects.Some of the factors which may be involved in this phenomenon are discussed as is the possibility that the decline in temperature tolerance merely reflects a general fall in physiological resistance during metamorphosis.

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Zusammenfassung Für Tenebrio-Männchen wurde eine Lebensdauer-Tabelle bei 25° aufgestellt. Ihre mittlere Lebensdauer betrug 100,4±4,6 Tage.Es wurde ein scharfer Abfall in der Fähigkeit junger Käfer festgestellt, eine Temperatur von 42,5° zu ertragen. Die mittlere Überlebensdauer fiel dabei von etwa 190 Minuten in den Tagen nach dem Verlassen der Puppenhülle auf etwa 120 Minuten im Alter von 5 Tagen; und auf diesem niederen Niveau blieb sie sogar bei 70 Tage alten Käfern. Dieser Abfall in der Hitze-Toleranz ähnelt dem, der auch von 3 anderen Insektenarten angegeben wird.Es wird der Schluß gezogen, daß das Absinken der physiologischen Leistung junger Erwachsener einen Verlust der hohen Toleranz der Puppen darstellt, die in die der Adulten übergeleitet wird. Vermutlich ist das eine Eigenschaft aller holometabolen Insekten und eine Folge des Besitzes eines unbeweglichen Puppenstadiums.Einige der Faktoren, die mit diesen Phänomen zusammenhängen könnten, werden erörtert, wie etwa die Möglichkeit, daß das Absinken der Hitze-Verträglichkeit nur einen allgemeinen Rückgang der physiologischen Widerstandsfähigkeit während der Metamorphose widerspiegele.

     

Molecular Epidemiology of Trypanosomatids and <Emphasis Type="Italic">Trypanosoma cruzi</Emphasis> in Primates from Peru

We determined the prevalence rate and risk of infection of Trypanosoma cruzi and other trypanosomatids in Peruvian non-human primates (NHPs) in the wild (n = 126) and in different captive conditions (n = 183). Blood samples were collected on filter paper, FTA cards, or EDTA tubes and tested using a nested PCR protocol targeting the 24Sα rRNA gene. Main risk factors associated with trypanosomatid and T. cruzi infection were genus and the human–animal context (wild vs captive animals). Wild NHPs had higher prevalence of both trypanosomatids (64.3 vs 27.9%, P < 0.001) and T. cruzi (8.7 vs 3.3%, P = 0.057), compared to captive NHPs, suggesting that parasite transmission in NHPs occurs more actively in the sylvatic cycle. In terms of primate family, Pitheciidae had the highest trypanosomatid prevalence (20/22, 90.9%) and Cebidae had the highest T. cruzi prevalence (15/117, 12.8%). T. cruzi and trypanosomatids are common in Peruvian NHPs and could pose a health risk to human and animals that has not been properly studied.     

Evaluation of cooperative interactions between substructures of iso-1-cytochrome c using double mutant cycles

A double mutant cycle has been used to evaluate interaction energies between the global stabilizer mutation asparagine 52 --> isoleucine (N52I) in iso-1-cytochrome c and mutations producing single surface histidines at positions 26, 33, 39, 54, 73, 89, and 100. These histidine mutation sites are distributed through the four cooperative folding units of cytochrome c. The double mutant cycle starts with the iso-1-cytochrome c variant AcTM, a variant with no surface histidines and with asparagine at position 52. Isoleucine is added singly at position 52, AcTMI52 variant, as are the surface histidines, AcHX variants, where X indicates the histidine sequence position. The double mutant variants, AcHXI52, provide the remaining corner of the double mutant cycle. The stabilities of all variants were determined by guanidine hydrochloride denaturation and interaction energies were calculated between position 52 and each histidine site. Six of the seven double mutants show additive (AcH33I52, AcH39I52, AcH54I52, AcH89I52, and AcH100I52) stability effects or weak interaction energies (AcH73I52) of the histidine mutations and the N52I mutation, consistent with cooperative effects on protein folding and stability being sparsely distributed through the protein structure. The AcH26I52 variant shows a strong favorable interaction energy, 2.0 +/- 0.5 kcal/mol, between the N52I mutation in one substructure and the addition of His 26 to an adjacent substructure. The data are consistent with an entropic stabilization of the intersubstructure hydrogen bond between His 26 and Glu 44 by the Ile 52 mutation.