Factors controlling planktonic size spectral responses to autumnal circulation in a Mediterranean lake

1. Studies of planktonic size spectra have been common in recent years, but few concerning the effects of autumnal lake processes on those distributions have been reported. We carried out such a study for 93 days during early circulation in a small, mesotrophic, seepage lake with only benthivorous fish. Two distinct mixing periods occurred before full circulation in Las Madres lake (Spain). As a proxy of overall planktonic‐ and phytoplanktonic size distributions, the shape of a Pareto I power function was traced over time. The phytoplanktonic size spectrum was also used to test the hypothesis that phytoplankton might show a trophic cascade during early circulation. 2. Our results demonstrated that the overall size spectrum changed smoothly during the autumnal mixing, with sequential changes controlled by a combination of biotic and abiotic variables, albeit experiencing different temporal delays, always shorter than a week. A first combined, autogenic process, driven both by algal competition and a crustacean trophic effect, and a second physical‐forcing process, driven by the combined effect of convective cooling and decreasing irradiance on mixed layer dynamics, may be related to the overall planktonic spectrum in the first and second periods of mixing, respectively. 3. The phytoplanktonic size spectrum did not appear to be dictated by a trophic cascade in Las Madres lake, their dynamics being mostly controlled by physical forcing, along with some effect of non‐edible primary producers and cladocerans in the first and second periods of mixing, respectively. 4. Our results and others covering early circulation with longer sampling periods suggest that planktonic size spectral dynamics during lake circulation is context‐dependent (i.e. varying from one lake to another), thus preventing generalisation. However, when further studies with finer temporal resolution have been carried out, it is likely that clear‐cut patterns in the planktonic size spectrum will emerge, arising from the interplay of autogenic plankton dynamics, implying some resistance to community change because of external physical forcing, and the velocity of autumnal mixing.     

A phylogenetic reconstruction of the Ichneumonoidea (Hymenoptera) based on the D2 variable region of 28S ribosomal RNA

The D2 variable region of 28S rRNA was sequenced in a wide range of Ichneumonoidea to provide the first comprehensive phylogenetic reconstruction of this superfamily. The two constituent families (Braconidae and Ichneumonidae) were each found to contain a single well-supported clade dominated by the more plesiomorphic life history strategies (idiobiosis, ectoparasitism and attacking endoephytic hosts). In the Braconidae this clade corresponds to the morphologically-defined group called the cyclostomes. In the Ichneumonidae the clade unites for the first time the pimpliformes ( sensu Wahl) with most of the phygadeuontoid subfamilies and several small taxa including Adelognathus and Euceros . Relationships among the remaining, more biologically-derived, subfamilies were less well resolved, but included among the Braconidae a well-supported microgastroid clade and strong evidence for a sister group relationship between the Agathidinae and Sigalphinae.     

Concordance between ecotypes and macroinvertebrate assemblages in Mediterranean streams

1. According to the guidelines of the European Water Framework Directive, assessment of the ecological quality of streams and rivers should be based on ecotype-specific reference conditions. Here, we assess two approaches for establishing a typology for Mediterranean streams: a top-down approach using environmental variables and bottom-up approach using macroinvertebrate assemblages.
2. Classification of 162 sites using environmental variables resulted in five ecotypes: (i) temporary streams; (ii) evaporite calcareous streams at medium altitude; (iii) siliceous headwater streams at high altitude; (iv) calcareous headwater streams at medium to high altitude and (v) large watercourses.
3. Macroinvertebrate communities of minimally disturbed sites ( n  = 105), grouped using UPGMA (unweighted pair-group method using arithmetic averages) on Bray–Curtis similarities, were used to validate four of the five ecotypes obtained using environmental variables; ecotype 5, large watercourses, was not included as this group had no reference sites.
4. Analysis of similarities ( anosim ) showed that macroinvertebrate assemblage composition differed among three of the four ecotypes, resulting in differences between the bottom-up and top-down classification approaches. Siliceous streams were clearly different from the other three ecotypes, evaporite and calcareous ecotypes did not show large differences in macroinvertebrate assemblages and temporary streams formed a very heterogeneous group because of large variability in salinity and hydrology.
5. This study showed that stream classification schemes based on environmental variables need to be validated using biological variables. Furthermore, our findings indicate that special attention should be given to the classification of temporary streams.     

Gametophyte morphology and gametangial ontogeny of Asplenium foreziense and related taxa (Aspleniaceae: Pteridophyta)

Gametophytes of Asplenium foreziense and related taxa have been studied by culture of spores on mineral agar and soil. Those of A. obovatum ssp. obovatum var. protobillotii and var. deltoideum , ssp. numidicum , and of A. macedonicum are described for the first time. Gametophyte development follows the Adiantum type in the A. obovatum group, and the Aspidium type in A. fontanum . Both types of development have been found in A. foreziense , depending on the sporophytic sample. The taxa with hairy gametophytes show significant differences in hair density. As in most of the homosporous ferns, antheridia are formed first and in a high proportion of gametophytes in the A. obovatum group and in A. fontanum , except for one sample; most of these male gametophytes become bisexual. In A. foreziense and A. macedonicum archegonia are formed first or at the same time as antheridia, but the proportion of female gametophytes is higher than in the other taxa; some of the gametophytes become bisexual, most of them differentiated from the female ones. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 139 , 87–98.     

Seed dormancy in relation to seed storage behaviour in Acer

Dormancy in seeds of Acer opalus is shown to be mainly caused by the seed coats, although a slight embryo dormancy exists in fresh seeds. The ability to germinate after drying indicates that seed storage behaviour is orthodox. Recalcitrant seeds were heavier than orthodox seeds not only within section Acer but also within the whole genus after statistical control of phylogeny, through a phylogenetic ANOVA with data from two different Acer phylogenies. An evolutionary change from orthodox to recalcitrant behaviour is postulated for genus Acer , but this change appears not to have been accompanied by a change in seed dormancy, at least in the taxonomic section in which Acer opalus belongs.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 203–208.     

Egg yolk polypeptide variation in acridids (Orthoptera)

The polypeptide composition of egg yolk proteins was analysed in 23 species of grasshoppers by means of SDS-PAGE. Each species has a distinguishable set of polypeptides, varying from three to seven (although most show five or six), which can be classified into two groups of high (H) and low molecular weight (L). The patterns can be interpreted following a two-gene model, each with three domains that codify two H and one L polypeptides. The results suggest strong rearrangements in vitellin during speciation and a later slowing in divergence due to functional constraints. Consequently, the vitellin polypeptide composition may be used for species identification but does not provide phylogenetic information above the genus level. Intraspecific variability was found only in Eyprepocnemis plorans , which appears to be quite recent from an evolutionary point of view, and in Chorthippus parallelus where the subspecies differentiation may be older. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 281–290.