Size-dependent mating strategies and the risk of cannibalism

The role of sexual selection in determining the nature and direction of sexual size dimorphism may depend upon the timing of sexual selection, and this may also influence the variation in male size. For example, selection through sperm competition favours smaller males in the highly sexually size dimorphic orb-weaving spider Nephila edulis , whereas larger males are better able to exclude their smaller rivals from the central hub of the web where mating takes place. We investigate experimentally the role of body size and hub tenure in determining male fertilization success when males of different sizes compete for a single female over a 24-h period that includes a period of darkness. Our results confirm that small and large males obtain similar paternity share but that, in contrast with previous studies, hub tenure does not translate into greater paternity share. Unexpectedly, smaller males are at greater risk of postmating sexual cannibalism than larger males, suggesting that natural selection through sexual cannibalism may place a lower limit on male size.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 355–363.     

Correlations between genomic GC levels and optimal growth temperatures are not 'robust'

Musto et al. [FEBS Lett. 573 (2004) 73] studied the correlations between GC levels and optimal growth temperatures in 20 prokaryotic families. They reported that positive correlations are generally observed, and many of these are significant. Here, we have shown that these correlations are not "robust," i.e., correlation coefficients and/or significance of correlations can be considerably influenced by exclusion of very few (even as small as one) species from each dataset. The sensitivity of correlations is assumed as a result of high levels of bias in the family datasets. We concluded that solely based on these data, one cannot establish that GC contents of prokaryotic genomes increase as a result of growth temperature increments.     

日光温室栽培对杏花及果实生长发育的影响

对日光温室内与露地栽培的金太阳杏的花期物候、花型及果实生长发育进行了系统观察与分析,结果表明,日光温室栽培比露地栽培的始花期提前33d,花期延长4d,不完全花比例上升33.25%;果枝上花的有效性顺序由露地时的中果枝>长果枝>短果枝>花束状果枝变为温室栽培的短果枝>花束状果枝>中果枝>长果枝;日光温室栽培使杏果实发育的第 、 阶段延长,第 阶段缩短,整个生育期延长15d。统计分析认为:日光温室栽培的第 阶段生长速率显著低于露地,第 阶段的累积生长量显著高于露地。较低的夜间温度是造成温室内杏果实第 阶段较长、生长较慢以及果个变大的原因。     

Genomic affinities in Arachis section Arachis (Fabaceae): molecular and cytogenetic evidence

Section Arachis is the largest of nine sections in the genus Arachis and includes domesticated peanut, A. hypogaea L. Most species are diploids (x=10) with two tetraploids and a few aneuploids. Three genome types have been recognized in this section (A, B and D), but the genomes are not well characterized and relationships of several newly described species are uncertain. To clarify genomic relationships in section Arachis, cytogenetic information and molecular data from amplified fragment length polymorphism (AFLP) and the trnT-F plastid region were used to provide an additional insight into genome composition and species relationships. Cytogenetic information supports earlier observations on genome types of A. cruziana, A. herzogii, A. kempff-mercadoi and A. kuhlmannii but was inconclusive about the genome composition of A. benensis, A. hoehnei, A. ipaensis, A. palustris, A. praecox and A. williamsii. An AFLP dendrogram resolved species into four major clusters and showed A. hypogaea grouping closely with A. ipaensis and A. williamsii. Sequence data of the trnT-F region provided genome-specific information and showed for the first time that the B and D genomes are more closely related to each other than to the A genome. Integration of information from cytogenetics and biparentally and maternally inherited genomic regions show promise in understanding genome types and relationships in Arachis.     

Biased mutations and microsatellite variation

Mutation bias is one of the forces that may constrain the variation at microsatellite loci. Here, we study the dynamics of population statistics and the genetic distance between two populations under multiple stepwise mutations with linear bias and random drift. Expressions are derived for these statistics as functions of time, as well as at mutation-drift equilibrium. Applying these expressions to published data on humans and chimpanzees, the regression coefficient of mutation bias on allele size was estimated to be at least between - 0.0064 and -0.013. The assumption of mutational bias produces larger estimates of divergence times than are obtained in its absence; in particular, the time of split between African and non-African human populations is estimated to be between 183,000 and 222,000 years, assuming one-step mutations and no selection. With multistep mutations, the divergence time is estimated to be lower.      

Three new ground wētā species and a redescription of Hemiandrus maculifrons

Taxonomy lies at the heart of species conservation, yet many large New Zealand orthopterans remain undescribed. Among New Zealand’s anostostomatid wētā, Hemiandrus (ground wētā) is the most speciose genus but also the most poorly characterised and thus most in need of taxonomic and ecological work. Here we redescribe H. maculifrons and describe two new species of ground wētā previously encompassed by the specific name Hemiandrus maculifrons: Hemiandrus luna sp. nov. and H. brucei sp. nov. We also describe a morphologically similar and related species, Hemiandrus nox sp. nov.

http://zoobank.org/urn:lsid:zoobank.org:pub:71EA0879-A2F9-46B2-A105-E97A9AB25061

http://zoobank.org/References/71EA0879-A2F9-46B2-A105-E97A9AB25061     

Benthic insects in Swedish lake-outlet streams: patterns in species richness and assemblage structure

1. We studied how species richness of three hierarchical insect species groups, namely all benthic, lotic and filtering taxa, were related to a number of environmental variables in a data set from fifteen Swedish lake outlets. 2. In partial least-squares analyses, we found that size-related factors (stream width, discharge) and velocity-related factors (current velocity, substratum particle size) were positively associated, and productivity-related factors (chlorophyll a, seston energy, conductivity) negatively associated, with the species richness of the three groups. 3. The weak and negative relationship of richness with productivity largely negated theoretical predictions, whereas the species-environment results corroborated earlier findings from running water systems. 4. The most important factors associated with the species composition of the lake outlets studied included pH, lake area, discharge, channel width and detritus. 5. Of the filter feeders, most species of blackflies (Diptera: Simuliidae) showed a negative relationship with pH. 6. A nested subset analysis demonstrated that species-poor sites did not have a subset of species found at more species-rich sites in any of the three hierarchical groups.