Abstract
The sticky viscous capture threads in araneoid orb-webs are responsible for retaining insects that strike these webs. We used features of 16 species' threads and the stickiness that they expressed on contact plates of four widths to model their adhesive delivery systems. Our results confirm that droplets at the edges of thread contact contribute the greatest adhesion, with each successively interior droplet contributing only 0.70 as much adhesion. Thus, regardless of the size and spacing of a thread's large primary droplets, little adhesion accrues beyond a span of 20 droplets. From this pattern we computed effective droplet number (EDN), an index that describes the total droplet equivalents that contribute to the stickiness of thread spans. EDN makes the greatest positive contribution to thread stickiness, followed by an index of the shape and size of primary droplets, and the volume of small secondary droplets. The proportion of water in droplets makes the single greatest negative contribution to thread stickiness, followed by a thread's extensibility, and the area of flattened droplets. Although highly significant, this six-variable model failed to convincingly describe the stickiness of six species, a problem resolved when species were assigned to three groups and a separate model was constructed for each. These models place different weights on the variables and, in some cases, reverse or exclude the contribution of a variable. Differences in threads may adapt them to particular habitats, web architectures or prey types, or they may be shaped by a species' phylogeny or metabolic capabilities.
Highlights
It has been proposed that tissue-specific estrogenic and/or antiestrogenic actions of certain xenoestrogens may be associated with alterations in the tertiary structure of estrogen receptor (ER) ␣ and/or ER following ligand binding; changes which are sensed by cellular factors required for normal gene expression
The primary purpose of 17-estradiol binding to the ER is to induce a conformational change in the tertiary structure of the ER, such that AF-2 is in a position to mediate the assembly of the basal transcription machinery following the recruitment of coactivators or transcription initiation factors [18]
We show that binding of a range of natural and synthetic xenoestrogens to ER␣ and ER alters their abilities to recruit coactivator proteins in vitro, and this may in turn affect their abilities to potentiate the expression of a reporter gene in transiently transfected HeLa cells
Summary
It has been proposed that tissue-specific estrogenic and/or antiestrogenic actions of certain xenoestrogens may be associated with alterations in the tertiary structure of estrogen receptor (ER) ␣ and/or ER following ligand binding; changes which are sensed by cellular factors (coactivators) required for normal gene expression. It is still unclear whether xenoestrogens affect the normal behavior of ER␣ and/or ER subsequent to receptor binding. The recruitment of these proteins to activated receptors is mediated by ␣-helical LXXLL motifs [34] in which L denotes leucine and X denotes any amino acid
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