Amphioxus and the Utility of Molecular Genetic Data for Hypothesizing Body Part Homologies between Distantly Related Animals

Expression domains of developmental genes can indicate bodypart homologies between distantly related animals and give insightsinto interesting evolutionary questions. Two of the chief criteriafor recognizing homologies are relative position with respectto surrounding body parts and special quality (for instance,a vertebrate testis, regardless of its location, is recognizableby its seminiferous cysts or tubules). When overall body plansof two animals are relatively similar, as for amphioxus versusvertebrates, body part homologies can be supported by developmentalgene expression domains, which have properties of special qualityand relative position. With expression patterns of AmphiNk2-land AmphiPax2/5/8, we reexamine the proposed homology betweenthe amphioxus endostyle and the vertebrate thyroid gland, anda previously good homology is made better. When body plans ofanimals are disparate, body part homologies supported by moleculargenetic data are less convincing, because the criterion of relativeposition of gene expression domains becomes uncertain. Thus,when expression of amphioxus AmphiBMP2/4 is used to comparethe dorsoventral axis between amphioxus and other animals, acomparison between amphioxus and vertebrates is more convincingthan comparison between amphioxus and other invertebrates withdisparate body plans. In spite of this difficulty, the use ofdevelopmental genetic evidence comparing animals with disparatebody plans is currently putting the big picture of evolutioninto new perspective. For example, some molecular geneticistsare now suggesting that the last common ancestor of all bilateriananimals might have been more annelid-like than flatworm-like.     

Recolonization of forest fragments by a native rodent following experimental ‘extinctions’

The movement of organisms between subdivided populations is considered a key influence on the persistence of species in modified landscapes. In particular, the ability to recolonize ‘empty’ fragments of habitat is directly relevant to conservation management, and to understanding the link between pattern and process in metapopulations. We studied the movement and recolonization ability of the bush rat, Rattus fuscipes, in a highly fragmented agricultural landscape in south‐western Victoria, Australia. Populations were monitored in seven small (<2.5 ha) and two large (>49 ha) forest fragments before removal of all residents from four of the small fragments. Subsequent monitoring (for up to 16 months) allowed the detection of colonizing individuals, and comparisons between ‘experimental’ and ‘control’ fragments. Rattus fuscipes readily moved between fragments and successfully recolonized (i.e. both males and females arrived) two of four fragments in which extinctions were simulated. A single male moved into a third experimental fragment. In one fragment, new animals were detected 1 month after the removal of residents, indicating that recolonization can occur rapidly. Dispersers were not a random sample of the population: although both males and females, and adults and sub‐adults were recorded dispersing, adult males in reproductive condition predominated. Functional connectivity appears to be high for R. fuscipes in the study landscape. Results from this manipulative experiment provide direct empirical evidence that a capacity for movement allows recolonization of fragments of suitable habitat and is a key process responsible for species persistence in fragmented landscapes, as predicted by theory.     

A 5-year comparison of overwintering polyphagous predator densities within a beetle bank and two conventional hedgebanks

Overwintering polyphagous predator density and composition was compared within a mid‐field overwintering refuge (“beetle bank”) and two conventional hedgebanks over a 5‐year period. During the study predator densities in the beetle bank were similar to or greater than those in the conventional hedgebanks. Whilst predator densities remained relatively stable in both of the hedgebanks over time, densities fluctuated significantly within the beetle bank. Many of the species recorded on the beetle bank are considered to be important predators of cereal aphids. The results are discussed in terms of the implications of creating such a habitat for the biological control of cereal aphids.     

The performance of fungal xylan-degrading enzyme preparations in elemental chlorine-free bleaching for Eucalyptus pulp

Cellulase-free xylan-degrading enzyme preparations from Acrophialophora nainiana, Humicola grisea var. thermoidea and two Trichoderma harzianum strains were used as bleaching agents for Eucalyptus kraft pulp, prior to a chlorine dioxide and alkaline bleaching sequence. In comparison to the control sequence (performed without xylanase pretreatment), the sequence incorporating enzyme treatment was more effective. Removal of residual lignin was indicated by a reduction in kappa number. Overall, enzyme preparations from T. harzianum were marginally more effective in reducing pulp viscosity and chlorine chemical consumption and improving the brightness of the kraft pulp. However, the highest reduction in pulp viscosity was mediated by the xylanase preparation from A. nainiana. Xylanase pretreatment compares very favorably with that of chemical pulping. Journal of Industrial Microbiology & Biotechnology (2002) 28, 204–206 DOI: 10.1038/sj/jim/7000227 Received 27 April 2001/ Accepted in revised form 03 November 2001