The assessment game in sand fiddler crab contests for breeding burrows

The single enlarged claw of male sand fiddler crabs, Uca pugilator, is used in contests for control of breeding burrows. The larger of the two contestants has the larger claw and usually wins. Males use one or more of 10 agonistic elements that vary in intensity from a no-contact extension of the claw to the flip of an opponent. We used the sequence of elements employed and the duration of unstaged, naturally occurring contests in a South Carolina salt marsh to evaluate three models of extended contests: (1) energetic war of attrition, (2) cumulative assessment and (3) sequential assessment. Contests usually began with elements of low action intensity and often proceeded to elements of high intensity. Elements of higher intensity were correlated with both contest duration and the number of contest elements. Contest duration increased as opponents became more evenly matched in size, a result consistent with both cumulative and sequential assessment models. Variation in duration increased as the relative sizes of opponents increased, also in accordance with sequential assessment. The absolute size of the smaller contestant had no effect on contest duration, in contrast to predictions based on cumulative assessment or energetic war of attrition models. Contestants that lost a fight were more likely to engage immediately in another fight without loss of contest intensity, if their previous fight had been long and intense. This result is inconsistent with contests of endurance, such as the energetic war of attrition or the cumulative assessment game, but it is consistent with the ritualized display of strength and fighting skill. Thus, sequential assessment appears to best explain ritualized fiddler crab contests. Cumulative assessment, however, may be the appropriate model for extended, nonritualized, all-out fights. Cumulative assessment may also explain the tenure of individuals on breeding grounds where multiple engagements are likely to test endurance and tolerance to damage over a period of days. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Regulation of voltage-gated Ca channels by lipids

Great skepticism has surrounded the question of whether modulation of voltage-gated Ca²⁺ channels (VGCCs) by the polyunsaturated free fatty acid arachidonic acid (AA) has any physiological basis. Here we synthesize findings from studies of both native and recombinant channels where micromolar concentrations of AA consistently inhibit both native and recombinant activity by stabilizing VGCCs in one or more closed states. Structural requirements for these inhibitory actions include a chain length of at least 18 carbons and multiple double bonds located near the fatty acid's carboxy terminus. Acting at a second site, AA increases the rate of VGCC activation kinetics, and in Ca_V2.2 channels, increases current amplitude. We present evidence that phosphatidylinositol 4,5-bisphosphate (PIP₂), a palmitoylated accessory subunit (β_2a) of VGCCs and AA appear to have overlapping sites of action giving rise to complex channel behavior. Their actions converge in a physiologically relevant manner during muscarinic modulation of VGCCs. We speculate that M₁ muscarinic receptors may stimulate multiple lipases to break down the PIP₂ associated with VGCCs and leave PIP₂'s freed fatty acid tails bound to the channels to confer modulation. This unexpectedly simple scheme gives rise to unanticipated predictions and redirects thinking about lipid regulation of VGCCs.     

Wives and Warriors: Women and the Military in the United States and Canada

Wives and Warriors: Women and the Military in the United States and Canada. Laurie Weinstein and Christie C. White. eds. Westport, CT: Bergin and Garvey, 1997. 252 pp.     

Effects of dexamethasone on carnitine metabolism in liver and extrahepatic tissues

The in vivo effects of dexamethasone administration on liver and extrahepatic tissue carnitine concentrations were assessed in 48-h-starved rats. In heart and kidney, but not in liver, dexamethasone significantly increased total carnitine concentration. Acute (2.5 h) treatment with 2-tetradecylglycidate (TDG), a specific inhibitor of carnitine palmitoyl transferase 1, not only increased total hepatic carnitine concentrations, but also permitted an effect of dexamethasone (a further increase in hepatic carnitine concentration). The results are discussed in terms of acute (substrate-mediated) and chronic (hormonal) control of carnitine turnover.