Ecology and genetics of hybrid zones in the southern African Pycnonotus bulbul species complex

Lloyd, P., Craig, A.J.F.K., Hulley, P.E., Essop, M.F., Bloomer, P. & Crowe, T.M. 1997. Ecology and genetics of hybrid zones in the southern African Pycnonotus bulbul species complex. Ostrich 68 (2–4): 90–96.

The closely related Blackeyed Bulbul Pycnonotus barbatus, Cape Bulbul P. capensis and Redeyed Bulbul P. nigricans have parapatric to locally sympatric distributions within southern Africa. Extensive hybridization along narrow transition zones between each of the three species pairs is described in a region of the Eastern Cape province, South Africa. The transition zones coincide with ecotones between different vegetation types, which in turn follow escarpments or mountain ranges. The lack of population density depressions within the hybrid zones, together with the variability of the hybrids, suggests the hybrids are viable. Sharp step clines in various phenotypic characters are described across the P. barbatus/P. nigricans hybrid zone. A mtDNA analysis found evidence of possible introgression between P. barbatus and P. capensis. All eight P. barbatus x P. nigricans hybrids analysed possessed P. barbatus mtDNA, suggesting the existence of either positive assortative mating or strong directional selection, but our data are unable to distinguish which. Our results do not support the dynamic-equilibrium model, but are compatible with the bounded-hybrid-superiority model. We conclude that the maintenance of the parapatric distributions of the different taxa is due mainly to differences in environmentally-associated fitness between parental phenotypes or among parental and hybrid phenotypes along an ecotone, with the narrowness of the hybrid zones maintained by the steepness of the environmental gradients crossing them.     

Conservation in the community: the Kilum-Ijim Forest Project,Cameroon

Thomas, D.H.L., Anders, S. & Penn, N.J. 2000. Conservation in the community: the Kilum-Ijim Forest Project, Cameroon. Ostrich 71 (1 & 2): 157–161.

BirdLife International has worked for ten years in Cameroon's North-West Province to assist the local people and government of Cameroon in achieving the conservation and sutainable management of the last significant remnant of a unique montane forest ecosystem. The Kilum/Ijim forests are almost certainly the last remaining habitat for the conservation of two endemic and threatened bird species, Bannerman's Turaco Tauraco bannermani and Banded Wattle-eye Platytiera laticincta. The forests have no legal designation as formal protected areas but have been conserved through local concern and knowledge of the multiple values of an intact forest ecosystem, backed up by the enforcement of traditional regulations, and support from the project to finding solutions to peoples' land use and natural resource management needs within and outside the forests. The project is now working under the umbrella of a national Biodiversity Conservation and Management Programme in Cameroon, funded by the Global Environment Facility, to establish the Kilum/Ijirn as the first community-managed forest in the country. A brief history and background to the project is presented, with emphasis on lessons learned by BiraLife and the success of current efforts to achieve the conservation of the forests through community management. The issues are discussed in the general context of an integrated conservation and development programme (ICDP).     

The role of fire in structuring trait variability in Neotropical savannas

Intraspecific trait variability plays a fundamental role in community structure and dynamics; however, few studies have evaluated its relative importance to the overall response of communities to environmental pressures. Since fire is considered a key factor in Neotropical savannas, we investigated to what extent the functional effects of fire in a Brazilian savanna occurs via intra- or interspecific trait variability. We sampled 12 traits in communities subjected to three fire regimes in the last 12 years: annual, biennial, and protected. To evaluate fire’s relative effects, we fitted a general linear mixed models with species as random and fire as fixed factors, using: (1) all species in the communities (i.e., considering intra- and interspecific variabilities); (2) 18 species common to all fire regimes (i.e., intraspecific variability only); and (3) all species with their overall average trait values (i.e., interspecific variability only). We assessed the relative role of intra- or interspecific variability by comparing the significance of each trait in the three analyses. We also compared the within and between fire variabilities with a variance component analysis. Five traits presented larger intraspecific than interspecific variability, and the main effect of fire occurred at the intraspecific level. These results confirm that it is important to consider intraspecific variability to fully understand fire-prone communities. Moreover, trait variability was larger within than among fire regimes. Thus, fire may act more as an external filter, preventing some of the species from the regional pool from colonizing the cerrado, than as an internal factor structuring the already filtered cerrado communities.     

F1-ATPase of Escherichia coli: THE ?-INHIBITED STATE FORMS AFTER ATP HYDROLYSIS,IS DISTINCT FROM THE ADP-INHIBITED STATE,AND RESPONDS DYNAMICALLY TO CATALYTIC SITE LIGANDS*

F₁-ATPase is the catalytic complex of rotary nanomotor ATP synthases. Bacterial ATP synthases can be autoinhibited by the C-terminal domain of subunit ϵ, which partially inserts into the enzyme''s central rotor cavity to block functional subunit rotation. Using a kinetic, optical assay of F₁·ϵ binding and dissociation, we show that formation of the extended, inhibitory conformation of ϵ (ϵ_X) initiates after ATP hydrolysis at the catalytic dwell step. Prehydrolysis conditions prevent formation of the ϵ_X state, and post-hydrolysis conditions stabilize it. We also show that ϵ inhibition and ADP inhibition are distinct, competing processes that can follow the catalytic dwell. We show that the N-terminal domain of ϵ is responsible for initial binding to F₁ and provides most of the binding energy. Without the C-terminal domain, partial inhibition by the ϵ N-terminal domain is due to enhanced ADP inhibition. The rapid effects of catalytic site ligands on conformational changes of F₁-bound ϵ suggest dynamic conformational and rotational mobility in F₁ that is paused near the catalytic dwell position.     

α-Synuclein Senses Lipid Packing Defects and Induces Lateral Expansion of Lipids Leading to Membrane Remodeling

There is increasing evidence for the involvement of lipid membranes in both the functional and pathological properties of α-synuclein (α-Syn). Despite many investigations to characterize the binding of α-Syn to membranes, there is still a lack of understanding of the binding mode linking the properties of lipid membranes to α-Syn insertion into these dynamic structures. Using a combination of an optical biosensing technique and in situ atomic force microscopy, we show that the binding strength of α-Syn is related to the specificity of the lipid environment (the lipid chemistry and steric properties within a bilayer structure) and to the ability of the membranes to accommodate and remodel upon the interaction of α-Syn with lipid membranes. We show that this interaction results in the insertion of α-Syn into the region of the headgroups, inducing a lateral expansion of lipid molecules that can progress to further bilayer remodeling, such as membrane thinning and expansion of lipids out of the membrane plane. We provide new insights into the affinity of α-Syn for lipid packing defects found in vesicles of high curvature and in planar membranes with cone-shaped lipids and suggest a comprehensive model of the interaction between α-Syn and lipid bilayers. The ability of α-Syn to sense lipid packing defects and to remodel membrane structure supports its proposed role in vesicle trafficking.     

The neonate nutrition hypothesis: early feeding affects the body stoichiometry of Daphnia offspring

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