Origin and evolution of the endemic Canary Island shrews (Mammalia: Soricidae)

Until recently the North Atlantic Islands were believed to house only mammals introduced by humans. Recent work has demonstrated that at least the Canary Islands house(d) a native mammal fauna. New data including chromosome numbers, genetic distances and analysis of vocalizations are given for the two extant shrew species, Crocidura canariensis and C. osorio , and their possible sister taxa are evaluated. Evidence is presented for the hypothesis that the two island species originated from two different lineages of the Palaearctic branch of the genus Crocidura. The data support the present status of the Canary Island shrews as local endemics of high conservation priority.     

Recruitment variability of resident brown trout in peripheral populations from southern Europe

1. Population regulation was studied for seven consecutive years (1992–98) in five rivers at the periphery of the distribution of Salmo trutta, where the fish were living under environmental constraints quite different from those of the main distribution area. 2. Recruitment is naturally highly variable and the populations had been earlier classified as overexploited. Thus we expected that densities of young trout in most populations would be too low for density‐dependent mortality to operate. We tested this by fitting the abundance of recruits to egg densities over seven consecutive years (stock–recruitment relationship), and used the results to judge whether exploitation should be restricted in the interests of conserving the populations. 3. The density of 0+ trout in early September, as well as the initial density of eggs and parents, varied greatly among localities and years. The data for all populations fitted the Ricker stock–recruitment model. The proportion of variance explained by the population curves varied between 32% and 51%. However, in most cases the observations were in the density‐independent part of the stock–recruitment curve, where densities of the recruits increased proportionally with egg densities. 4. Our findings suggest that recruitment densities in most rivers and years were below the carrying capacity of the habitats. Although density‐dependent mechanisms seemed to regulate fish abundance in some cases, environmental factors and harvesting appeared generally to preclude populations from reaching densities high enough for negative feedbacks to operate. The findings thus lend support to Haldane’s (1956) second hypothesis that changes in population density are primarily due to density‐independent factors in unfavourable areas and areas with low density due to exploitation. Exploitation should be reduced to allow natural selection to operate more effectively.     

Differential requirement for NO during ABA-induced stomatal closure in turgid and wilted leaves

Abscisic acid (ABA)-induced stomatal closure is mediated by a complex, guard cell signalling network involving nitric oxide (NO) as a key intermediate. However, there is a lack of information concerning the role of NO in the ABA-enhanced stomatal closure seen in dehydrated plants. The data herein demonstrate that, while nitrate reductase (NR)1-mediated NO generation is required for the ABA-induced closure of stomata in turgid leaves, it is not required for ABA-enhanced stomatal closure under conditions leading to rapid dehydration. The results also show that NO signalling in the guard cells of turgid leaves requires the ABA-signalling pathway to be both capable of function and active. The alignment of this NO signalling with guard cell Ca²⁺-dependent/independent ABA signalling is discussed. The data also highlight a physiological role for NO signalling in turgid leaves and show that stomatal closure during the light-to-dark transition requires NR1-mediated NO generation and signalling.     

Variations in the dorso-ventral organization of leaf structure and Kranz anatomy coordinate the control of photosynthesis and associated signalling at the whole leaf level in monocotyledonous species

Photosynthesis and associated signalling are influenced by the dorso-ventral properties of leaves. The degree of adaxial/abaxial symmetry in stomatal numbers, photosynthetic regulation with respect to light orientation and the total section areas of the bundle sheath (BS) cells and the surrounding mesophyll (M) cells on the adaxial and abaxial sides of the vascular bundles were compared in two C₄[ Zea mays (maize) and Paspalum dilatatum ] and one C₃[ Triticum turgidum (Durum wheat)] monocotyledonous species. The C₃ leaves had a higher degree of dorso-ventral symmetry than the C₄ leaves. Photosynthetic regulation was the same on each side of the wheat leaves, as were stomatal numbers and the section area of the BS relative to that of the M cells (BS/M section area ratio). In contrast, photosynthetic regulation in maize and P. dilatatum leaves showed a marked surface-specific response to light orientation. Compared to the adaxial sides of the C₄ monocotyledonous leaves, the abaxial surfaces had more stomata and the BS/M section area ratio was significantly higher. Differences in dorso-ventral structure, particularly in Kranz anatomy, serve not only to maximize photosynthetic capacity with respect light orientation in C₄ monocotyledonous leaves but also allow adaxial and abaxial-specific signalling from the respective M cells.     

Wing shape variation in the medium ground finch (Geospiza fortis): an ecomorphological approach

Wing design in birds is subject to a suite of interacting selective pressures. As different performance traits are favoured in different ecological settings, a tight link is generally expected between variation in wing morphology and variation in ecological parameters. In the present study, we document aspects of variation in wing morphology in the medium ground finch ( Geospiza fortis ) on Isla Santa Cruz in the Galápagos. We compare variation in body size, simple morphometric traits (body mass, last primary length, wing length, wing chord, and wing area) and functional traits (wing loading, aspect ratio and wing pointedness) across years, among populations, and between sexes. Functional traits are found to covary across years with differences in climatic conditions, and to covary among populations with differences in habitat structure. In dry years and arid locations, wing aspect ratios are highest and wings are more pointed, consistent with a need for a low cost of transport. In wet years and cluttered habitats, wing loading is lowest and wings are more rounded, suggesting enhanced capabilities for manoeuvrability. Sexes differ in wing loading, with males having lower wing loadings than females. Superior manoeverability might be favoured in males for efficient territory maintenance. Lastly, in contrast to functional traits, we found little consistent inter-annual or inter-site variation in simple morphometric traits.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 129–138.     

Effects of host plant architecture on colonization by galling insects

Abstract: To study the abundance and occurrence of herbivore insects on plants it is important to consider plant characteristics that may control the insects. In this study the following hypotheses were tested: (i) an increase of plant architecture increases species richness and abundance of gall‐inducing insects and (ii) plant architecture increases gall survival and decreases parasitism. Two hundred and forty plants of Baccharis pseudomyriocephala Teodoro (Asteraceae) were sampled, estimating the number of shoots, branches and their biomass. Species richness and abundance of galling insects were estimated per module, and mortality of the galls was assessed. Plant architecture influenced positively species richness, abundance and survival of galls. However, mortality of galling insects by parasitoids was low (13.26%) and was not affected by plant architecture, thus suggesting that other plant characteristics (a bottom‐up pressure) might influence gall‐inducing insect communities more than parasitism (a top‐down pressure). The opposite effect of herbivore insects on plant characteristics must also be considered, and such effects may only be assessed through manipulative experiments.     

Drought effect on isoprene production and consumption in Biosphere 2 tropical rainforest

Isoprene is the most abundant of the hydrocarbon compounds emitted from vegetation and plays a major role in tropospheric chemistry. Models predict that future climate change scenarios may lead to an increase in global isoprene emissions as a consequence of higher temperatures and extended drought periods. Tropical rainforests are responsible for more than 80% of global isoprene emissions, so it is important to obtain experimental data on isoprene production and consumption in these ecosystems under control of environmental variables. We explored isoprene emission and consumption in the tropical rainforest model ecosystem of Biosphere 2 laboratory during a mild water stress, and the relationship with light and temperature. Gross isoprene production (GIP) was not significantly affected by mild water stress in this experiment because the isoprene emitters were mainly distributed among the large, canopy layer trees with deep roots in the lower soil profile where water content decreased much less than the top 30 cm. However, as found in previous leaf level and whole canopy studies, the ecosystem gross primary production was reduced by (32%) during drought, and as a consequence the percentage of fixed C lost as isoprene tended to increase during drought, from ca. 1% in wet conditions to ca. 2% when soil water content reached its minimum. GIP correlated very well with both light and temperature. Notably, soil isoprene uptake decreased dramatically during the drought, leading to a large increase in daytime net isoprene fluxes.     

Effects of contrasting demographic histories on selection at major histocompatibility complex loci in two sympatric species of tuco‐tucos (Rodentia: Ctenomyidae)

To explore the impact of history on selection and genetic structure at functional loci, we compared patterns of major histocompatibility complex (MHC) variability in two sympatric species of ctenomyid rodents with different demographic backgrounds. Although Ctenomys talarum has experienced a stable demographic history, Ctenomys australis has undergone a recent demographic expansion. Accordingly, we predicted that MHC allele frequency distributions should be more skewed, differences between coding and noncoding regions should be less pronounced, and evidence of current selection on MHC loci should be reduced in C. australis relative to C. talarum. To test these predictions, we compared variation at the MHC class II DRB and DQA genes with that at multiple neutral markers, including DQA intron 2, the mitochondrial control region, and 8–12 microsatellite loci. These analyses supported the first two of our predictions but indicated that estimates of selection (based on ω‐values) were greater for C. australis. Further exploration of these data, however, revealed differences in the time frames over which selection appears to have acted on each species, with evidence of contemporary selection on MHC loci being limited to C. talarum. Collectively, these findings indicate that demographic history can substantially influence genetic structure at functional loci and that the effects of history on selection may be temporally complex and dynamic. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 260–277.